Reversing time = local reversal of thermodynamic arrows?

[Stephen Paul King]

Hi,

   I re-read S. Mitra's paper again and it made more sense than before if I assumed that the reversible measurement idea is to be taken as a local reversal to the "direction of entropy flow" in an area and not the entire universe.

   The trouble is this notion of locality. Are there any favorite definitions of "locality" out there? AFAIK, it does not have a fixed size in space, but may have a fixed size in "space-time" as location information expands at the speed of light if we ignore the effects of local structure that would modulate decoherence. This "decoherence" thing, IMHO, needs to be looked at carefully.

   In deference to Bruno, I should ask a question relevant to the ongoing discussions. Is a finite universe with locally reversible time consistent as a 1p world?

--

Kindest Regards,

Stephen Paul King

[Bruno Marchal]

Hi Stephen,

If the 1p world are described by the []p & p move in arithmetic, then it seems more plausible that they are antisymmetrical, in the finite case, and non cyclical in the infinite case. This match the usual phenomenology, I think. Locally, you can't negate the experience, when you have a pain here and now, you can't negate the immediate memories. Only a bad doctor would do that. It is like when you look up if you are in Moscow or Washington, in the WM duplication. Once you see Washington, that knowledge is not reversible *from* that knowledge pov". At the 3p level, you can reverse locally by inducing an amnesia, but that will not be part of the 1p experience.

Best,

Bruno

http://iridia.ulb.ac.be/~marchal/

[LizR]

I think we have very few measurements of the arrow of time beyond "contingent ones" like - expansion of the universe, entropy increase, radiation etc. All we have that arises from the laws of physics is the famous CPT violation (I think it is?) of certain mesons. So it's problematic to even say what "reversing time" means except for reversing the contingent arrows, which appear to arise from the expansion of the universe, which may itself be contingent (not required to expand in a particular time direction by the laws of physics, assuming a multiverse or string landscape or whatever). Of course eternal inflation puts the arrow of time into the laws of physics, so it may be there, just beyond out ken, so to speak.

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[meekerdb]

I'd say that expansion of the universe is almost necessary, not contingent.  The AoT has to point in the direction of entropy increase and in almost all models that's correlated to the expansion of the universe.  If it is bigger at one time than at another then the AoT will point toward the bigger end.  I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch, at least until the total entropy equals the Bekenstein bound.  Or on the other possibility, L.S. Schulmann has written a nice little book about his investigation of universes in which the AoT reverses so it always points to the biggest phase of the universe.

Brent

[zib...@gmail.com]

At the moment goofy theories abound, typically that divide into infinity structures which derive according to whatever is needed for whatever is the centre piece theory to pass muster. Typically, screen out the infinity section and what's left just isn't becoming of someone given a desk and a job for life entrusted with our most precious incumbent knowledge. The custodians are they who must comprehend value that is there, and through that understand the properties and continuation, levels of applicability, the continuation of the necessary meat and potatoes of a scientific civilization. To compare, to measure, to design, to predict, to solve dynamical, material, fluidphysical stresses and limits, through structures and transports, scales...all the same but now better...some new dimension causing complexity collapses maybe, that new theory explains is because symmetrical equates to a region that is redundant at this scale, that wasn't at the scale above.

You know, something a true scientific breakthrough theory would simply deliver. Something mind boggling before, like emergence, suddenly understood as something very simple and invariant that doesn't explain emergence or talk about levels or scales, because all of that is about to be

[LizR]

On 7 November 2014 09:56, meekerdb <meek...@verizon.net> wrote:

I'd say that expansion of the universe is almost necessary, not contingent.  The AoT has to point in the direction of entropy increase and in almost all models that's correlated to the expansion of the universe.  If it is bigger at one time than at another then the AoT will point toward the bigger end.  I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch, at least until the total entropy equals the Bekenstein bound.  Or on the other possibility, L.S. Schulmann has written a nice little book about his investigation of universes in which the AoT reverses so it always points to the biggest phase of the universe.
     

Yes, that is indeed exactly the position I have long argued for on this very forum.

To summarise my argument, which has at times been vigorously opposed, I think by you amongst others, but not yet actually shot down (kaon decay comes closest, but doesn't appear to be very important in generating the AOT, although it's possible it actually had/has a pivotal role we're unaware of).

a) the universe is expanding for some reason, possibly necessary in the sense of being built into the laws of physics (e.g. as a result of eternal inflation ... perhaps?) - or perhaps contingent, that is to say not mandated by the laws of physics, but maybe the result of some symmetry breaking etc.

b) all the other things regarded as the AOT emerge from (a). I have given details of this at some length on previous occasions, but briefly it's that various bound states (nucleons, galaxies etc) can emerge from the cooling caused by the universal expansion.

[Bruce Kellett]

LizR wrote:
>
> On 7 November 2014 09:56, meekerdb <meek...@verizon.net

I have not seen your arguments for this, being new to the list, but the
expansion of the universe is a universal consequence of general
relativity. So it is built into the laws of physics, and has nothing to
do with whether or not there ever was a period of rapid inflation.

The AoT comes from the third law of thermodynamics and has little to do
with the expansion of the universe. Entropy increases in the same
direction as the expansion solely because the universe 'began' in a
state of very low entropy. (The Past Hypothesis).

Bruce

[meekerdb]

On 11/6/2014 3:15 PM, LizR wrote:

On 7 November 2014 09:56, meekerdb <meek...@verizon.net> wrote:

I'd say that expansion of the universe is almost necessary, not contingent.  The AoT has to point in the direction of entropy increase and in almost all models that's correlated to the expansion of the universe.  If it is bigger at one time than at another then the AoT will point toward the bigger end.  I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch, at least until the total entropy equals the Bekenstein bound.  Or on the other possibility, L.S. Schulmann has written a nice little book about his investigation of universes in which the AoT reverses so it always points to the biggest phase of the universe.
     

Yes, that is indeed exactly the position I have long argued for on this very forum.

To summarise my argument, which has at times been vigorously opposed, I think by you amongst others,

Not me.  I helped edit Vic Stenger's books that presented exactly that view.

but not yet actually shot down (kaon decay comes closest, but doesn't appear to be very important in generating the AOT, although it's possible it actually had/has a pivotal role we're unaware of).

a) the universe is expanding for some reason, possibly necessary in the sense of being built into the laws of physics (e.g. as a result of eternal inflation ... perhaps?) - or perhaps contingent, that is to say not mandated by the laws of physics, but maybe the result of some symmetry breaking etc.

You seem to overlook that the "expansion" is very likely just tautological, i.e. it is nomologically necessary that the AoT points in the direction of bigger. 

b) all the other things regarded as the AOT emerge from (a). I have given details of this at some length on previous occasions, but briefly it's that various bound states (nucleons, galaxies etc) can emerge from the cooling caused by the universal expansion.

Right.  Because the universe expanded very rapidly it is very far from equilibrium.  The actual entropy is at least 22 orders of magnitude smaller than the maximum possible entropy.  Being far from equilibrium leads to complex structures.

Brent

[Bruce Kellett]

meekerdb wrote:
>
> On 11/6/2014 3:15 PM, LizR wrote:
>>
>> On 7 November 2014 09:56, meekerdb <meek...@verizon.net

No, it points in the direction of higher entropy. As I recall it, Vic
later recanted his earlier idea that the AoT reversed if the universe
began to re-contract.

Anyway, that is purely academic. With with known magnitude of dark
energy, the universe will expand for ever, even if it is technically
closed (k = +1).

Bruce

[Richard Ruquist]

Zibbsey, you write amazingly like Hibbsa.

[meekerdb]

Sure, but the physics is such that entropy must increase in the direction of expansion -
the two are linked (that's what I meant by "nomologically necessary").

> As I recall it, Vic later recanted his earlier idea that the AoT reversed if the
> universe began to re-contract.

I don't remember him ever asserting that the AoT would reverse, but he liked the idea of
"the biverse" which "contracted" relative to our time coordinate and also had a reversed
AoT. Schulmann does study the case in which is entropy and the AoT reverse. He ran Monte
Carlo simulations and then selected those that satisfied the reversal.

Brent

[Bruce Kellett]

meekerdb wrote:
> On 11/6/2014 4:08 PM, Bruce Kellett wrote:
>> meekerdb wrote:
>>>
>>> You seem to overlook that the "expansion" is very likely just
>>> tautological, i.e. it is nomologically necessary that the AoT points
>>> in the direction of bigger.
>>
>> No, it points in the direction of higher entropy.
>
> Sure, but the physics is such that entropy must increase in the
> direction of expansion - the two are linked (that's what I meant by
> "nomologically necessary").

I disagree. There is no necessary connection between the expansion and
the increase in entropy. The total possible entropy might increase with
expansion, but if we are always a long way below the total possible for
a given volume, the entropy could increase whether the universe were
actually expanding or contracting. Anything else and you are necessarily
committed to a reversal of the arrow of time if the universe begins to
re-contract at some point.

Bruce

[meekerdb]

I concede it's possible, but I don't know of any model that corresponds to that.

Brent

[LizR]

On 7 November 2014 12:56, meekerdb <meek...@verizon.net> wrote:

On 11/6/2014 3:15 PM, LizR wrote:

On 7 November 2014 09:56, meekerdb <meek...@verizon.net> wrote:

I'd say that expansion of the universe is almost necessary, not contingent.  The AoT has to point in the direction of entropy increase and in almost all models that's correlated to the expansion of the universe.  If it is bigger at one time than at another then the AoT will point toward the bigger end.  I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch, at least until the total entropy equals the Bekenstein bound.  Or on the other possibility, L.S. Schulmann has written a nice little book about his investigation of universes in which the AoT reverses so it always points to the biggest phase of the universe.
     

Yes, that is indeed exactly the position I have long argued for on this very forum.

To summarise my argument, which has at times been vigorously opposed, I think by you amongst others,

Not me.  I helped edit Vic Stenger's books that presented exactly that view.

OK, sorry, maybe it was Bill Taylor on FOR. He tends to sound as though disagreeing when he actually agrees too, so I get you confused sometimes.

   

but not yet actually shot down (kaon decay comes closest, but doesn't appear to be very important in generating the AOT, although it's possible it actually had/has a pivotal role we're unaware of).

a) the universe is expanding for some reason, possibly necessary in the sense of being built into the laws of physics (e.g. as a result of eternal inflation ... perhaps?) - or perhaps contingent, that is to say not mandated by the laws of physics, but maybe the result of some symmetry breaking etc.

You seem to overlook that the "expansion" is very likely just tautological, i.e. it is nomologically necessary that the AoT points in the direction of bigger. 

Yes, sure, not overlooked but maybe glossed over. That's the point, or part of it. I'm at work and don't want to spend TOO long going into all the details (insert innocently whistling smiley here). Anyway I've said it all in past posts - I think it was here, maybe it was FOR or FOAR even....but yes, I can elaborate, and am happy to see other people agreeing considering the huge amount of flak I've taken from presenting this idea in the past (or was it the future? :-)

b) all the other things regarded as the AOT emerge from (a). I have given details of this at some length on previous occasions, but briefly it's that various bound states (nucleons, galaxies etc) can emerge from the cooling caused by the universal expansion.

Right.  Because the universe expanded very rapidly it is very far from equilibrium.  The actual entropy is at least 22 orders of magnitude smaller than the maximum possible entropy.  Being far from equilibrium leads to complex structures.

Yes the fine details may mean a period of inflation was involved etc, but the basic idea is that expansion produces what can be called sources of negative entropy - e.g. bound particles, gravitationally bound objects etc.

There are 2 obvious caveats to this idea

1. kaons

2. black holes

These both appear to violate the idea that the expansion imposes the AOT on otherwise time-symmetric physics. Any thoughts on those?

[LizR]

As I recall it, Vic later recanted his earlier idea that the AoT reversed if the universe began to re-contract.

I think that was Hawking.

I think it was Gold who proposed the idea of a universe where  the AOT reverses in contraction phase. It's a logical outcome of view that AOT derives from expansion, although there may be some symmetry breaking that forces one "pole" of the universe to be the bang and one the crunch. Plus gravitational collapse appears to create a separate AOT that messes with the whole thing (smooth "initial" state and chaotic "final" one - something to do with the Ricci and Weyl tensors or something, Brent will tell me I hope!)

[Stephen Paul King]

Hi Zibbsey,

   A new discovery for you. A computer can be a topological shape! A sector of the structures that are invariant under dilations in Sub-Riemannian manifolds is identical to the Lambda calculus. 

   This can be said to imply that spatial relations can "carry" information just as well as sequences of binary symbols.

On Thu, Nov 6, 2014 at 6:04 PM, <zib...@gmail.com> wrote:

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[LizR]

This may be why the AOT exists, now that we've discovered dark energy. A recontracting universe may not have one, because the two cancel out, so anthropically we find ourselves in a U with Dark Energy. (Just a thought.)

As far as we know the thermodynamic AOT isn't due to fundamental physics. That is, entropy isn't a fundamental feature of physics (despite that famous quote from Arthur Eddington) but an emergent one. Below a certain .level of "coarse graining" it disappears. At the very fine scale (eq particle) all interactions are reversible and it is impossible to define entropy (except for bound states - these emerged at an earlier stage of the universe from a collection of unbound states in which all interactions were time-symmetric - see below).

Hence logically you need to connect the thermodynamic AOT to something that *is* fundamental, or at least more so, to explain why it exists. The expansion is a possible reason and given that it's THE major feature of the entire universe that is time-asymmetric, it looks like an obvious candidate. Plus, even to a bear of little brain like me, the links aren't particularly obscure, although there are some obscure details involved (but that's only because we, or at least I, don't know everything about everything).

Generically, expansion cools aggregates of particles. It does this by separating out particles according to velocity - a particle that is moving faster than average in a region tends to leave it and move to a region where the average speed is nearer to its own velocity. This effectively cools the particle, and hence all the particles cool as expansion proceeds. Also, matter gets less dense, which is also important in generating an AOT since it allows structures like galaxies to form from an almost uniform matter background.

Let's start at the quark soup era. Things are a big vague before that.

Expansion cools the soup, and eventually collision energies drop enough for nucleons to form without being blown apart by subsequent collisions. This is an early (perhaps the earliest) example of how a system that is in equilibrium, and in which all interactions are time-symmetric, can change to one in which there is some structure simply by expanding and hence cooling it.

Expansion cools the nucleons, until nuclei can form...

Expansion cools the nuclei, until ionised atoms can form...

Expansion cools the atoms, until neutral atoms can form...

Expansion now allows a more or less uniform gas to clump into larger scale structures by amplifying any existing inhomogeneities. This allows stars etc to form, and eventually us, without introducing any new physics; all the large scale structure is emergent from time-symmetric physics operating on mass-energy during a non-time-symmetric cosmological expansion.

(Another way to look at this is that the expansion is producing more available states for the universe to move into, effectively raising the entropy ceiling. This means an expanding universe can never reach a state of equilibrium - this is particularly clear during the BB fireball, which I would say is very near to equilibrium for a lot of the time.)

The above sketches how you get the components of the entropy gradient. Each stage is reversible except for black hole formation (which is another topic since it may also violate unitarity, and may generally need more investigation). But if we ignore gravitational collapse, we can definitely get an AOT from expansion + time-symmetric physics.

PS as a side issue, note that in gravitational collapse, you effectively get a mini-big-crunch which illustrates some of the features of time reversal. In particular, note that in normal time, objects are constrained to have certain types of pasts - what we can lower entropy. In gravitational collapse, objects are constrained to have a certain type of future - it is physically impossible to avoid certain outcomes (at least assuming GR is correct "all the way down" - which admittedly violates the BH information paradox...) With the usual caveats, this at least suggests that time would indeed reverse in a collapsing universe.

[LizR]

Yes the boss left early.

[LizR]

On 7 November 2014 12:32, Bruce Kellett <bhke...@optusnet.com.au> wrote:

I have not seen your arguments for this, being new to the list, but the expansion of the universe is a universal consequence of general relativity. So it is built into the laws of physics, and has nothing to do with whether or not there ever was a period of rapid inflation.

Expansion or collapse is a consequence of GR, certainly. However I was thinking on a larger scale with the EI comment, since EI seems to necessitate the existence of expanding universes. Not sure that it can be counted as a TOE though, so it's still in need of ultimate explanation..

The AoT comes from the third law of thermodynamics and has little to do with the expansion of the universe. Entropy increases in the same direction as the expansion solely because the universe 'began' in a state of very low entropy. (The Past Hypothesis).

I didn't realise there was a 3rd law, but anyway - saying the U began in a low entropy state begs the question - why did it? The big bang fireball was more or less in thermodynamic equilibrium as far as I know, and if it had stopped expanding it would have rapidly reached that stage. My point is to explain the

[LizR]

On 7 November 2014 14:27, Stephen Paul King <Step...@provensecure.com> wrote:

Hi Zibbsey,

   A new discovery for you. A computer can be a topological shape! A sector of the structures that are invariant under dilations in Sub-Riemannian manifolds is identical to the Lambda calculus. 

   This can be said to imply that spatial relations can "carry" information just as well as sequences of binary symbols.

How very Platonic. 

[LizR]

Oops I seem to have cut off the end of this. Luckliy I wrote another reply anyway. Damn browser getting me all confused and stuff.

[Bruce Kellett]

LizR wrote:
> On 7 November 2014 12:32, Bruce Kellett <bhke...@optusnet.com.au

Sorry -- typo. I meant the second law, of course.

I agree that the past hypothesis, while it explains the thermodynamic
AoT, itself stands in need of explanation. This is the great unsolved
problem of cosmology -- at least according to many cosmologists. The
initial big bang might be assumed to be in thermodynaic equilibrium, but
that is essentially the same assumption as the assumption of low
entropy. The question remains as to why it was in equilibrium. Generic
creation events might actuallybe expected to produce extremely lumpy
universe down to the smallest scaels. I.e., state with very high entropy.

Bruce

[zib...@gmail.com]

my nick has an ibbsey ring at that

[Bruce Kellett]

LizR wrote:
> On 7 November 2014 13:29, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> meekerdb wrote:
> On 11/6/2014 4:08 PM, Bruce Kellett wrote:
> meekerdb wrote:
>
> You seem to overlook that the "expansion" is very likely
> just tautological, i.e. it is nomologically necessary
> that the AoT points in the direction of bigger.
>
> No, it points in the direction of higher entropy.
>
> Sure, but the physics is such that entropy must increase in the
> direction of expansion - the two are linked (that's what I meant
> by "nomologically necessary").
>
> I disagree. There is no necessary connection between the expansion
> and the increase in entropy. The total possible entropy might
> increase with expansion, but if we are always a long way below the
> total possible for a given volume, the entropy could increase
> whether the universe were actually expanding or contracting.
> Anything else and you are necessarily committed to a reversal of the
> arrow of time if the universe begins to re-contract at some point.
>
> This may be why the AOT exists, now that we've discovered dark energy. A
> recontracting universe may not have one, because the two cancel out, so
> anthropically we find ourselves in a U with Dark Energy. (Just a thought.)

I don't think that makes much sense -- how can arrows-of-time cancel out?

> As far as we know the thermodynamic AOT isn't due to fundamental
> physics. That is, entropy isn't a fundamental feature of physics
> (despite that famous quote from Arthur Eddington) but an emergent
> one. Below a certain .level of "coarse graining" it disappears. At the
> very fine scale (eq particle) all interactions are reversible and it is
> impossible to define entropy (except for bound states - these emerged at
> an earlier stage of the universe from a collection of unbound states in
> which all interactions were time-symmetric - see below).

Just because something is emergent does not mean that it is not
fundamental. Sure, the AoT arises, with entropy, when you coarse-grain
things. But there is very probably a deep connection with QM here -- you
only get definite results for quantum experiment when you coarse-grain.
That is what the partial trace of the density matrix, needed to go from
the initial pure state to the final state mixture, is actually doing. It
amounts to ignoring certain information because it is lost in the
coarse-graining. Entropy arises in the same way -- you ignore certain
microscopic information in the interests of the larger picture. The
second law -- increasing entropy -- then follows as a matter of
statistics. So it is as fundamental as getting a particular result in a
quantum experiment -- and it is hard to get more fundamental than that!

> Hence logically you need to connect the thermodynamic AOT to something
> that *is* fundamental, or at least more so, to explain why it exists.
> The expansion is a possible reason and given that it's THE major feature
> of the entire universe that is time-asymmetric, it looks like an obvious
> candidate. Plus, even to a bear of little brain like me, the links
> aren't particularly obscure, although there are some obscure details
> involved (but that's only because we, or at least I, don't know
> everything about everything).
>
> Generically, expansion cools aggregates of particles. It does this by
> separating out particles according to velocity - a particle that is
> moving faster than average in a region tends to leave it and move to a
> region where the average speed is nearer to its own velocity. This
> effectively cools the particle, and hence all the particles cool as
> expansion proceeds. Also, matter gets less dense, which is also
> important in generating an AOT since it allows structures like galaxies
> to form from an almost uniform matter background.

This is not how it works in cosmology. The expansion is uniform, so it
does not separate particles according to velocity. That would probably
not even work if the expansion were of a hot gas into empty space. And
the cosmological expansion most definitely is not like that!

Cosmological expansion works in different ways depending on whether the
matter in the universe is in the form of radiation, or of particles. If
it is radiation, the expansion stretches the wavelength as well as
decreasing the density, so the energy content falls off like r^{-4}
rather than r^{-3} that we have for particles. The density of particles
decreases because they get spread out, but their relative velocities do
not change.

In the beginning, all matter was very energetic, in the extreme
relativistic domain, so everything was effectively radiation, and cooled
by that law (1/r^4). But since matter and anti-matter annihilated to
produce photons, the number of photons dominated over the number of
particles, so the 1/r^4 cooling continued. Once it reached a temperature
below the ionization energy of Hydrogen atoms, atoms were able to form.
The universe suddenly became transparent. The radiation from this time
is what we now see as the CMB.

> Let's start at the quark soup era. Things are a big vague before that.
>
> Expansion cools the soup, and eventually collision energies drop enough
> for nucleons to form without being blown apart by subsequent collisions.
> This is an early (perhaps the earliest) example of how a system that is
> in equilibrium, and in which all interactions are time-symmetric, can
> change to one in which there is some structure simply by expanding and
> hence cooling it.
>
> Expansion cools the nucleons, until nuclei can form...
> Expansion cools the nuclei, until ionised atoms can form...
> Expansion cools the atoms, until neutral atoms can form...

As outlined above, this is not really correct.

> Expansion now allows a more or less uniform gas to clump into larger
> scale structures by amplifying any existing inhomogeneities. This allows
> stars etc to form, and eventually us, without introducing any new
> physics; all the large scale structure is emergent from time-symmetric
> physics operating on mass-energy during a non-time-symmetric
> cosmological expansion.

Again, the facts are rather different. Gravity comes into the picture,
and gravity can only work on pre-existing inhomogeneities. But the large
scale clumps are gravitationally bound, so they take no more part in the
overall expansion. They do not, therefore, cool further because of
expansion. The only way primeval clouds of gas can clump further is if
they lose energy. Charged particles can lose energy because when they
collide they can radiate. The radiation is not gravitationally bound, so
that energy is lost to the system, which cools - ultimately enough to
coalesce into stars and planets. Electromagnetic interactions producing
radiation are essential for this further cooling and clumping. We see a
dramatic instance of the effect of not having a simple cooling mechanism
in the more-or-less uniform distribution of dark matter throughout
galaxies. Dark matter was part of the initial inhomogeneities that gave
rise to galaxies, but it lacked the possibility of radiating away
energy, so it could not clump further. It does cool very slowly by
evaporative processes, but it is essentially unclumped, even now.

These process are all described by time-reversible dynamics, of course,
but quantum-level coarse graining is still necessary, so statistics and
the thermodynamic arrow are universal in these processes.

> (Another way to look at this is that the expansion is producing more
> available states for the universe to move into, effectively raising the
> entropy ceiling. This means an expanding universe can never reach a
> state of equilibrium - this is particularly clear during the BB
> fireball, which I would say is very near to equilibrium for a lot of the
> time.)

As mentioned above, that homogeneity assumption is as unjustified as the
past hypothesis of low entropy in the initial state.

> The above sketches how you get the components of the entropy gradient.
> Each stage is reversible except for black hole formation (which is
> another topic since it may also violate unitarity, and may generally
> need more investigation). But if we ignore gravitational collapse, we
> can definitely get an AOT from expansion + time-symmetric physics.
>
> PS as a side issue, note that in gravitational collapse, you effectively
> get a mini-big-crunch which illustrates some of the features of time
> reversal. In particular, note that in normal time, objects are
> constrained to have certain types of pasts - what we can lower entropy.
> In gravitational collapse, objects are constrained to have a certain
> type of future - it is physically impossible to avoid certain outcomes
> (at least assuming GR is correct "all the way down" - which admittedly
> violates the BH information paradox...) With the usual caveats, this at
> least suggests that time would indeed reverse in a collapsing universe.

Black hole formation does not lead to reduced entropy. One of the
fundamentals of BH physics is the Bekenstein bound, which states that
the BH is the highest entropy state for an amount of matter equal to the
mass of the BH.

But even this is overturned by Hawking radiation. Hawking radiation also
increases the total entropy of the system, so in the very far distant
future, when everything has collapsed into BHs and evaporated again, the
entropy is even higher than if the total universe were a single black
hole! The final state of the universe is a very high entropy deSitter space.

Cheers,
Bruce

[meekerdb]

What would be the highest possible (and therefore most probable) initial state? A single
black hole? From an information theoretic viewpoint a universe inflating up from a Planck
scale patch would seem most likely - doesn't require any information input.

Brent

[Bruce Kellett]

I know that was Vic's preferred model, but why should one ignore the
possibility of sub-Planckian structure? It is a mere conceit that the
Planck length is some fundamental smallest length. Operationalism is a
sterile philosophy of science.

But it is not really like that. Even if our current observable universe
started out as a Planck-sized sphere before inflation, the
inhomogeneities do not arise pre- or during-inflation. Inhomogeneities
arise at the end of inflation -- the post-inflation reheating is
basically a quantum process so it does not occur at the same time
everywhere. Exiting inflation at different times leads to
inhomogeneities on all scales, and there is no reason to suppose that
these are of bounded magnitude. Inflation models are highly tuned to
give only the degree of inhomogeneity we observe -- which is far from
generic.

Bruce

[LizR]

On 7 November 2014 14:59, Bruce Kellett <bhke...@optusnet.com.au> wrote:

I agree that the past hypothesis, while it explains the thermodynamic AoT, itself stands in need of explanation. This is the great unsolved problem of cosmology -- at least according to many cosmologists. The initial big bang might be assumed to be in thermodynaic equilibrium, but that is essentially the same assumption as the assumption of low entropy.

It's the opposite assumption. A quark-gluon plasma at a few trillion degrees should rapidly tend towards thermodynamic equilibrium, given the chance. Deriving the AOT from the expansion should let the AOT emerge from almost any initial conditions, because it basically says that the universe has no need to start in a low entropy state. It can start in a state near maximum entropy, then chase behind the entropy ceiling, which is continually raised by the expansion. Another way to look at this is that expansion makes more states available for the system to explore. The universe starts with a limited number of available states and wanders amongst them, probably reaching a state of high entropy in the process. In the meantime, the expansion brings more available states into existence - phase space expands, so to speak, as well as real space. The universe continues to explore its options, doing a drunkard's walk through the available states for billions of years, always tending towards higher entropy, while the number of states available to explore continues to increase.

 

The question remains as to why it was in equilibrium. Generic creation events might actuallybe expected to produce extremely lumpy universe down to the smallest scaels. I.e., state with very high entropy.

I don't think anyone is in a position to answer that question, but certainly inflation (eternal or otherwise) naturally produces a very smooth background. But somewhat lumpy backgrounds should work. This is a question of the timescales involved, I imagine - the relaxation time of a volume of matter against the expansion time. I'm not in a position to answer that. Maybe someone else can (Brent?) However the bottom line is that deriving the AOT from the cosmic expansion doesn't require any particular special starting state. It appears that the universe did in fact have a special (smooth) starting state, however, which is why it's a natural assumption that this must be connected to the AOT. But there's no particular reason for this to be a necessary condition that I can see - one can get an expansion derived AOT from many initial conditions, simply because expansion raises the entropy ceiling constantly. So the smooth start is an interesting piece of data that may relate to inflation or whatever, but not necessarily to the AOT. No doubt it affects the way the AOT plays out - similarly all over the universe, presumably, rather than some regions being ahead or behind others.

[LizR]

On 7 November 2014 15:51, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

This may be why the AOT exists, now that we've discovered dark energy. A recontracting universe may not have one, because the two cancel out, so anthropically we find ourselves in a U with Dark Energy. (Just a thought.)

I don't think that makes much sense -- how can arrows-of-time cancel out?

Well, from a GR perspective an AOT is a constraint on the world lines of matter. If you put constraints on the entire contents of the universe at both ends of time, the possible results are (that I can see)

a) the contents of the universe reverse motion at max expansion and you get a mirror image collapse (seen as expansion to its inhabitants)

b) the contents of the universe conspire to arrange themselves in a manner that gives two different expansion histories that still manage to meet in the middle (perhaps all matter decays before the reversal or something)

c) only part of the universe's contents are constrained by each singularity (maybe matter vs antimatter or something from the viewpoint of the inhabitants)

d) there is no well-defined AOT in such a universe

I am open to other ideas. I was suggesting (d) might be the outcome since all the others seem to require some extras.

As far as we know the thermodynamic AOT isn't due to fundamental physics. That is, entropy isn't a fundamental feature of physics (despite that famous quote from Arthur Eddington) but an emergent one. Below a certain .level of "coarse graining" it disappears. At the very fine scale (eq particle) all interactions are reversible and it is impossible to define entropy (except for bound states - these emerged at an earlier stage of the universe from a collection of unbound states in which all interactions were time-symmetric - see below).

Just because something is emergent does not mean that it is not fundamental.

To clarify the vocabulary, I'm assuming there is such a thing as fundamental physics, described by a yet to be discovered TOE. Anything not described by the TOE is called emergent. The second law is a statistical property of large ensembles of particles and hence (ISTM) not likely to be part of this hypothetical TOE - indeed it is likely to emerge in many universes with widely varying fundamental physics - and hence is not "fundamental" under this description.

 

Sure, the AoT arises, with entropy, when you coarse-grain things. But there is very probably a deep connection with QM here -- you only get definite results for quantum experiment when you coarse-grain. That is what the partial trace of the density matrix, needed to go from the initial pure state to the final state mixture, is actually doing. It amounts to ignoring certain information because it is lost in the coarse-graining. Entropy arises in the same way -- you ignore certain microscopic information in the interests of the larger picture. The second law -- increasing entropy -- then follows as a matter of statistics. So it is as fundamental as getting a particular result in a quantum experiment -- and it is hard to get more fundamental than that!

I'm using the description above. This makes the outcome of quantum measurements emergent - they are what is perceived at our level, not what is going on at the hypothetical TOE level (this probably requires an Everettian view of QM, come to think of it).

Hence logically you need to connect the thermodynamic AOT to something that *is* fundamental, or at least more so, to explain why it exists. The expansion is a possible reason and given that it's THE major feature of the entire universe that is time-asymmetric, it looks like an obvious candidate. Plus, even to a bear of little brain like me, the links aren't particularly obscure, although there are some obscure details involved (but that's only because we, or at least I, don't know everything about everything).

Generically, expansion cools aggregates of particles. It does this by separating out particles according to velocity - a particle that is moving faster than average in a region tends to leave it and move to a region where the average speed is nearer to its own velocity. This effectively cools the particle, and hence all the particles cool as expansion proceeds. Also, matter gets less dense, which is also important in generating an AOT since it allows structures like galaxies to form from an almost uniform matter background.

This is not how it works in cosmology. The expansion is uniform, so it does not separate particles according to velocity. That would probably not even work if the expansion were of a hot gas into empty space. And the cosmological expansion most definitely is not like that!

No, it does work. The expansion is uniform but if you assume a normal distribution of particle velocities you can see that only the ones at rest in a given region are going to stay there, the rest will bleed off into adjacent regions, and tend to end up in regions where they are at rest - because they move outwards from their own region, and all volumes in an expanding universe are moving away from where you happen to be. So they will tend to drift into regions where they are more nearly at rest.

Cosmological expansion works in different ways depending on whether the matter in the universe is in the form of radiation, or of particles. If it is radiation, the expansion stretches the wavelength as well as decreasing the density, so the energy content falls off like r^{-4} rather than r^{-3} that we have for particles. The density of particles decreases because they get spread out, but their relative velocities do not change.

I have no argument with that, but I don't see that it affects the basic argument. 

In the beginning, all matter was very energetic, in the extreme relativistic domain, so everything was effectively radiation, and cooled by that law (1/r^4). But since matter and anti-matter annihilated to produce photons, the number of photons dominated over the number of particles, so the 1/r^4 cooling continued. Once it reached a temperature below the ionization energy of Hydrogen atoms, atoms were able to form. The universe suddenly became transparent. The radiation from this time is what we now see as the CMB.

With you so far. Do you think bound states will arise naturally as the temperature falls? If so that's an early example of the AOT being generated by expansion and cooling. 

Let's start at the quark soup era. Things are a big vague before that.

Expansion cools the soup, and eventually collision energies drop enough for nucleons to form without being blown apart by subsequent collisions. This is an early (perhaps the earliest) example of how a system that is in equilibrium, and in which all interactions are time-symmetric, can change to one in which there is some structure simply by expanding and hence cooling it.

Expansion cools the nucleons, until nuclei can form...
Expansion cools the nuclei, until ionised atoms can form...
Expansion cools the atoms, until neutral atoms can form...

As outlined above, this is not really correct.

I don't see from what you've said above why not.

Expansion now allows a more or less uniform gas to clump into larger scale structures by amplifying any existing inhomogeneities. This allows stars etc to form, and eventually us, without introducing any new physics; all the large scale structure is emergent from time-symmetric physics operating on mass-energy during a non-time-symmetric cosmological expansion.

Again, the facts are rather different. Gravity comes into the picture, and gravity can only work on pre-existing inhomogeneities. But the large scale clumps are gravitationally bound, so they take no more part in the overall expansion. They do not, therefore, cool further because of expansion.

No, that's right, but by now they have been arranged into low entropy states by what has happened to them earlier. In particular they contain bound states like nucleons and atoms which are effectively chunks of low entropy (compared to a quark-gluon plasma).

 

The only way primeval clouds of gas can clump further is if they lose energy. Charged particles can lose energy because when they collide they can radiate. The radiation is not gravitationally bound, so that energy is lost to the system, which cools - ultimately enough to coalesce into stars and planets. Electromagnetic interactions producing radiation are essential for this further cooling and clumping. We see a dramatic instance of the effect of not having a simple cooling mechanism in the more-or-less uniform distribution of dark matter throughout galaxies. Dark matter was part of the initial inhomogeneities that gave rise to galaxies, but it lacked the possibility of radiating away energy, so it could not clump further. It does cool very slowly by evaporative processes, but it is essentially unclumped, even now.

Yes. 

These process are all described by time-reversible dynamics, of course, but quantum-level coarse graining is still necessary, so statistics and the thermodynamic arrow are universal in these processes.

But not fundamental, in the sense described above.

I have to stop now. I agree that gravity is the kicker especially in black holes. Of course if you have an alternative theory of the origin of the AOT I would like to hear it.

[Bruce Kellett]

LizR wrote:
> On 7 November 2014 14:59, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> I agree that the past hypothesis, while it explains the
> thermodynamic AoT, itself stands in need of explanation. This is the
> great unsolved problem of cosmology -- at least according to many
> cosmologists. The initial big bang might be assumed to be in
> thermodynaic equilibrium, but that is essentially the same
> assumption as the assumption of low entropy.
>
>
> It's the opposite assumption. A quark-gluon plasma at a few trillion
> degrees should rapidly tend towards thermodynamic equilibrium, given the
> chance. Deriving the AOT from the expansion should let the AOT emerge
> from almost any initial conditions, because it basically says that the
> universe has no need to start in a low entropy state. It can start in a
> state near maximum entropy, then chase behind the entropy ceiling, which
> is continually raised by the expansion. Another way to look at this is
> that expansion makes more states available for the system to explore.
> The universe starts with a limited number of available states and
> wanders amongst them, probably reaching a state of high entropy in the
> process. In the meantime, the expansion brings more available states
> into existence - phase space expands, so to speak, as well as real
> space. The universe continues to explore its options, doing a drunkard's
> walk through the available states for billions of years, always tending
> towards higher entropy, while the number of states available to explore
> continues to increase.

It is a questionable whether the expansion does give rise to more states
that the system can occupy. If position and momentum are continuous
variables, then the number of possible states is infinite, even for
finite volumes. These states might not be quantum mechanically
distinguishable, given the HUP, but the states exist, and eventually
become distinguishable as space-time expands.

There is also the question of Louiville's theorem -- the volume of any
cloud of points moving through phase space remains constant so entropy
cannot increase in this way.

It is rather dubious that the maximum possible entropy increases with
the expansion of spacetime. Entropy is associated with configurations of
matter, and Bekenstein's bound states that the maximum entropy
configuration of any quantity of matter is attained when that matter is
compressed into a BH. The universe in which we live is not a BH, so it
is, and never has been, in a state of maximum entropy. The maximum
entropy remains constant given that the mass-energy remains constant,
regardless of expansion or the lack of it. SO the AoT comes from the
statistics of increasing entropy and is quite disjoint from the
expansion of the universe. Correlation is not causation, after all!

> The question remains as to why it was in equilibrium. Generic
> creation events might actuallybe expected to produce extremely lumpy
> universe down to the smallest scaels. I.e., state with very high
> entropy.
>
> I don't think anyone is in a position to answer that question, but
> certainly inflation (eternal or otherwise) naturally produces a very
> smooth background. But somewhat lumpy backgrounds should work. This is a
> question of the timescales involved, I imagine - the relaxation time
> of a volume of matter against the expansion time. I'm not in a position
> to answer that. Maybe someone else can (Brent?) However the bottom line
> is that deriving the AOT from the cosmic expansion doesn't require any
> particular special starting state. It appears that the universe did in
> fact have a special (smooth) starting state, however, which is why it's
> a natural assumption that this must be connected to the AOT. But there's
> no particular reason for this to be a necessary condition that I can see
> - one can get an expansion derived AOT from many initial conditions,
> simply because expansion raises the entropy ceiling constantly. So the
> smooth start is an interesting piece of data that may relate to
> inflation or whatever, but not necessarily to the AOT. No doubt it
> affects the way the AOT plays out - similarly all over the universe,
> presumably, rather than some regions being ahead or behind others.

The details of the inflation model come into play when one is thinking
about whether the observed smoothness is uniform or not. Actually,
inflation does lead to smoothness, and zero temperature for the universe
at the end of inflation. All the structure we observe comes from the
re-heating phase, when the energy of the inflaton field decayed into
particles and radiation. There is no reason to suppose that this was a
smooth process. Decays proceeding at different rates and at different
times in different places would be expected to produce vast
non-uniformities of temperature. Models have to be extremely fine-tuned
to give results in agreement with observation.

But regardless of this, the AoT cannot be derived from the expansion --
it comes from increasing entropy, and the entropy of the universe was
always a long, long way below the Bekenstein bound.

Bruce

[Bruce Kellett]

LizR wrote:
> On 7 November 2014 15:51, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> LizR wrote:
> This may be why the AOT exists, now that we've discovered dark
> energy. A recontracting universe may not have one, because the
> two cancel out, so anthropically we find ourselves in a U with
> Dark Energy. (Just a thought.)
>
> I don't think that makes much sense -- how can arrows-of-time cancel
> out?
>
>
> Well, from a GR perspective an AOT is a constraint on the world lines of
> matter. If you put constraints on the entire contents of the universe at
> both ends of time, the possible results are (that I can see)

Why would you put constraints on the entire contents of the universe at
both ends of time? That is not how physics normally works. The usual
picture is that if you specify the complete data on some Cauchy surface,
and given time-symmetric dynamics, you can calculate the entire history
of the universe in both time directions.

> a) the contents of the universe reverse motion at max expansion and you
> get a mirror image collapse (seen as expansion to its inhabitants)
> b) the contents of the universe conspire to arrange themselves in a
> manner that gives two different expansion histories that still manage to
> meet in the middle (perhaps all matter decays before the reversal or
> something)
> c) only part of the universe's contents are constrained by each
> singularity (maybe matter vs antimatter or something from the viewpoint
> of the inhabitants)
> d) there is no well-defined AOT in such a universe

Since one does not have a final state constraint in normal physics,
these possibilities are beside the point. The normal expectation is that
entropy increases in normal dynamical evolution for statistical reasons,
and it continues to increase for all time. A re-contraction of the
universe would not change this, but we know from dark energy that the
universe is not going to re-contract anyway.

> I am open to other ideas. I was suggesting (d) might be the outcome
> since all the others seem to require some extras.
>
> As far as we know the thermodynamic AOT isn't due to fundamental
> physics. That is, entropy isn't a fundamental feature of physics
> (despite that famous quote from Arthur Eddington) but an
> emergent one. Below a certain .level of "coarse graining" it
> disappears. At the very fine scale (eq particle) all
> interactions are reversible and it is impossible to define
> entropy (except for bound states - these emerged at an earlier
> stage of the universe from a collection of unbound states in
> which all interactions were time-symmetric - see below).
>
>
> Just because something is emergent does not mean that it is not
> fundamental.
>
>
> To clarify the vocabulary, I'm assuming there is such a thing as
> fundamental physics, described by a yet to be discovered TOE. Anything
> not described by the TOE is called emergent. The second law is a
> statistical property of large ensembles of particles and hence (ISTM)
> not likely to be part of this hypothetical TOE - indeed it is likely to
> emerge in many universes with widely varying fundamental physics - and
> hence is not "fundamental" under this description.

It then depends on whether your TOE assumes mathematics, and hence
statistics. If it does, then statistics is fundamental in your sense.

> Sure, the AoT arises, with entropy, when you coarse-grain things.
> But there is very probably a deep connection with QM here -- you
> only get definite results for quantum experiment when you
> coarse-grain. That is what the partial trace of the density matrix,
> needed to go from the initial pure state to the final state mixture,
> is actually doing. It amounts to ignoring certain information
> because it is lost in the coarse-graining. Entropy arises in the
> same way -- you ignore certain microscopic information in the
> interests of the larger picture. The second law -- increasing
> entropy -- then follows as a matter of statistics. So it is as
> fundamental as getting a particular result in a quantum experiment
> -- and it is hard to get more fundamental than that!
>
>
> I'm using the description above. This makes the outcome of quantum
> measurements emergent - they are what is perceived at our level, not
> what is going on at the hypothetical TOE level (this probably requires
> an Everettian view of QM, come to think of it).

It certainly does! But even the Everettian view (MWI) is not complete.
It requires this pesky thing called the partial trace over environmental
variables in order to explain single outcomes from measurements, and for
decoherence to actually lead to disjoint worlds. This partial trace is
identical to a projection postulate, so even MWI has a quantum AoT built
into it!

That is extremely limited in efficacy because of gravitational binding.
You can't turn gravity off while this happens. So there is essentially
no cooling from this source.

> Cosmological expansion works in different ways depending on whether
> the matter in the universe is in the form of radiation, or of
> particles. If it is radiation, the expansion stretches the
> wavelength as well as decreasing the density, so the energy content
> falls off like r^{-4} rather than r^{-3} that we have for particles.
> The density of particles decreases because they get spread out, but
> their relative velocities do not change.
>
>
> I have no argument with that, but I don't see that it affects the basic
> argument.

It explains the cooling where your argument does not.

> In the beginning, all matter was very energetic, in the extreme
> relativistic domain, so everything was effectively radiation, and
> cooled by that law (1/r^4). But since matter and anti-matter
> annihilated to produce photons, the number of photons dominated over
> the number of particles, so the 1/r^4 cooling continued. Once it
> reached a temperature below the ionization energy of Hydrogen atoms,
> atoms were able to form. The universe suddenly became transparent.
> The radiation from this time is what we now see as the CMB.
>
>
> With you so far. Do you think bound states will arise naturally as the
> temperature falls? If so that's an early example of the AOT being
> generated by expansion and cooling.

Bound states will arise when the local temperature is low enough so that
typical particle energies are below the disassociation energies of the
bound states. But this is true only for particles in low gravitational
fields. Gravitational binding into clumps is independent of the local
temperatures. (The interior of the sun is at a sufficiently high
temperature to form a plasma, but it does not fly apart.)

Bound states of quarks and atoms are not at any particularly low
entropy. As before, entropy is maximized in black holes, not in normal
matter.

> The only way primeval clouds of gas can clump further is if they
> lose energy. Charged particles can lose energy because when they
> collide they can radiate. The radiation is not gravitationally
> bound, so that energy is lost to the system, which cools -
> ultimately enough to coalesce into stars and planets.
> Electromagnetic interactions producing radiation are essential for
> this further cooling and clumping. We see a dramatic instance of the
> effect of not having a simple cooling mechanism in the more-or-less
> uniform distribution of dark matter throughout galaxies. Dark matter
> was part of the initial inhomogeneities that gave rise to galaxies,
> but it lacked the possibility of radiating away energy, so it could
> not clump further. It does cool very slowly by evaporative
> processes, but it is essentially unclumped, even now.
>
>
> Yes.
>
>
> These process are all described by time-reversible dynamics, of
> course, but quantum-level coarse graining is still necessary, so
> statistics and the thermodynamic arrow are universal in these processes.
>
>
> But not fundamental, in the sense described above.
>
> I have to stop now. I agree that gravity is the kicker especially in
> black holes. Of course if you have an alternative theory of the origin
> of the AOT I would like to hear it.

It is gravity, not just black holes that the crunch lies. Most of your
arguments ignore the dominant importance of gravity on the cosmological
scale. The origin of the AoT is simply in the past hypothesis -- the
abnormally low entropy of the initial state of the universe. Everything
else is mathematics.

Bruce

[Dr. John Yates]

> <http://www.google.com/url?q=http%3A%2F%2Farxiv.org%2Fpdf%2F0902.3825v2.pdf&sa=D&sntz=1&usg=AFQjCNFnc0z9SwLW-HfdQv80vaf6sf0heg>

> again and it made more sense than before if I assumed that the
> reversible measurement idea is to be taken as a local reversal
> to the "direction of entropy flow" in an area and not the entire
> universe.
> The trouble is this notion of locality. Are there any
> favorite definitions of "locality" out there? AFAIK, it does not
> have a fixed size in space, but may have a fixed size in
> "space-time" as location information expands at the speed of
> light if we ignore the effects of local structure that would
> modulate decoherence. This "decoherence" thing, IMHO, needs to
> be looked at carefully.
> In deference to Bruno, I should ask a question relevant to
> the ongoing discussions. Is a finite universe with locally
> reversible time consistent as a 1p world?
>
> --
>
> Kindest Regards,
>
> Stephen Paul King
>
>
>
>
>
> --
>
> Kindest Regards,
>
> Stephen Paul King
>
> Senior Researcher
>
> Mobile: (864) 567-3099
>

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>
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You have some interesting material here if anything like all this is
correct. Our current activities are here, http://goo.gl/yNYvSc

[zib...@gmail.com]

On Friday, November 7, 2014 1:27:39 AM UTC, Stephen Paul King wrote:

Hi Zibbsey,

   A new discovery for you. A computer can be a topological shape! A sector of the structures that are invariant under dilations in Sub-Riemannian manifolds is identical to the Lambda calculus. 

   This can be said to imply that spatial relations can "carry" information just as well as sequences of binary symbols.

and I actually love category theory wish I'd done it first.

What follows has its best moments nearer the beginning, but ye should not go too far as it becomes a shaggy dog story of bollocks that terminates in rant about deutsch

The word Carry...that was about disputing gravity is explained by space time in a substantial sense better.

I want your help with this. But I don't think I'm sufficiently clear what my main point was. The gravity thing is said in terms of that.

So the main point is, the equations of special relativity will produce everything the same, if the whole piece about space time is withdrawn from the core theory and in its place a range of visualization tools supporting a preparation process for every kind of calculation, that draws everything toward intuitively friendly forms.

It sounds more complex. But it isn't. Because toolsets and tools, cartoons what not...this would all be outside theory, as a variation on educational courses in some kind of car-crash with a Feynman diagram.

It isn't theoretical complexity. We don't include guides and cartoons and educational feeds when we do Occam.

But we should look at this the other way too: It would add complexity to the formulation and resolution of problems or calculations. This is also a separate domain than theory...in the Applied sector. But for the sake of the point let's lump it with theory. There is new complexity. However proportionate to that, there is new levels of standardization that open up a potential to reinforce around junctures most struggled with, heavy lifting support.

What is the balance, more complex or more simple, is demonstratably intractably convergent to simplification, with other features too. This is because the people it makes life worse for are competent  in current use. But reinforcement of this kind is very much distributed as standard steps find to skip as soon as your god through that part. So those competent don't have to use any of it at all. Or only what they want, and with repetition they'll no longer need any of it.

So its unchanged for them. The truth is they would probably just carry on using the space time piece as if in theory. Who cares. They'd have more time for that, because time taken to teach competency would be slashed right down. Time taken going over getting the direction and relative view....time taken correcting mistakes that had to be traced back through hell. All this what I'm saying would deliver.

The other effect would be a proportionate expansion - numbers but seniority levels ...in the more junior direction too. Expansion of people excited and looking forward to next, using relativity. Cost of Competency would stretch out toward the mean of average ability. Go through it maybe. Change attitudes about what it means to be average. It's feasibly the most complex structure in the universe to nearest approximation. Average is glory. Maybe not dicksize. But other than that.

So that's my replacement notion.

Now it's about why is the space time conception methodologically, Occam, and intuition savvy minded, a serious mistake with damaging ramifications.

- it's first and foremost because it doesn't need to be assumed in theory. As easily it's assumed an enablement metapschor. Basically it's another schema on the replacement notion. I mean, it is in practice and usage, whether we say so or not.

- But as a schema in keeping with my replacement. It isn't very effective. Using requires visualized translations in complex ways. Correct usage requires  competency in the theory, not only equations but conceptions. illegal usage, or most common error points are static over decades. I'd bet how far a given person gets with practical problems, decides how much they try to work with Einstein instead of newton in the future. Two things here I'd bet: Relativity proliferation is dormant and has been so since the end of the beginning.

Actually it's going to be in recession pretty much in line with declining standards in education. And that matters in my view....a hell of a lot.

Einstein should have washed newton away within years. Excuses are made about this like Newton is still fine for most accuracy and precision levels, and newton is a lot easier.

And this is one of distortions that worse the face of science. A stroke is definitely on the radar going by a face like that. Because those are excuses and they are fallacious. They only make sense by collapse the considerations all around to just the points. What about that over the same period 5 generations of scientist and science graduate and engineering career path, in which almost no one...almost no scientist even, has sharpened to engineering competency in use of Einstein. Over that same period virtually no advance on relativity or deepening of knowledge of issues, better defining of the problem with QM, so no methodological supports there. Nothing has progressed and no one has had any good ideas. And given it's the same people that still use newton for everytnking, same teachers that stlll teach newton, and run though Einstein really fast and stick to template problems....because truth is teacher never learned himself.

So there's an independent rationale for supports and reinforsments, around difficult sequences, as standardizations which directions to set it up,and which way to point for solutions. Which isn't easy. I remember in this list, when owen was bombasting his way to the bottle, one of the top competent dudes here, didn't himself understand directions and solutions. He was totally open about that or I wouldn't mention it. He didn't care. I wouldn't either. But we had to ask. And I don't think anyone on the list actually knew the answer before it came.

And this is probably where the top 5% of users most people here are.

So there's already a problem and already major consequences played out and playing out. New level theory needs to wash right through. The process yields discovery. more important, young minds get competent enough to begin thinking about the problems...earlier. A lot of good ideas people have while young and too unimportant and ignorant to taking things that way is stupid and makes them look a fool. But hold on.....one day someone say....show me that way again.

So reasons and levels of reasons just keep on coming. Which indicates these are not trivial matters, and not being attended anywhere by anyone. Nor have ever. I've done a large section of it for reasons of personal self help. It works. One problem takes longer but at 10 its way faster and way higher scoring...and you don't have to do a lot to get that.

And finally the MAIN reason to lose spacetime as an object from theory. Occam simpler to lose it. Occam simpler use it as a knock on. Occam simpler to learn it. So Occam simpler to do the specific translations necessary to replace a newton solution with Einstein for a given sort of problem.

And the bonus, which is enough to be a knock down argument on its own, is that just the fact the spacetime thing is immediately intuitive and everyone agrees realizes the same terrain just by using equations would be too hard. Maybe no one could do that.

And that's getting said as if it's a bad thing if no one did. Which is the assumption spacetime as an object, is objectively true.

But no one will have a single good case for why they think this is a reasonable and necessary assumption to make.

Everything points the other way. It isn't needed. It isn't helpful having once delivered it's boiler insightwhich takes all of itself to deliver. The Occam counting added complexity is the layer itself OF REALITY. A whole fucking layer man. For something just as good as a metaphor, and guess what, What is True doesn't wilt or shrink go to not true. It really doesn't matter if it starts as a metaphor in terms of what's true. There is one step remaining in one direction. Reserved for True.

But if it isn't true, there's a good chance no one ever gets past here to realize that. The metaphor assumed true never discovers that it isn't. How can it...it's just a visual model. An aid. A metaphor. Doesn't matter what you call it, that's definitely what it is. That's the signal. But it might be true as well. Metaphors that are true are just special case metaphors that have a goal of faithfully representing the actual situation. And THAT is still a metaphor however you work it.

Culturally and methodologically and logically and historically, AND IN EVERY OTHER  context you each will encounter the same basic decision. The priority rules run the same way. We do not assume our onception of objective reality is true. We don't estimate it. We can't anyway, but it doesn't add anything. Try to improve the solutitioon process. Try to get independent measure points to gauge if you are going the right way. Try to break down the conception. Or merge it. Or scale it. Or rotate it through to different concepts and scenarios. There's a million ways to example a metaphor. And a million ways examine objective reality. They are the same ways. But translated through some abstractions for metaphor because there's no support for examination there is with the observable world.

Sorry I ranted. For a long time I did that, and worsened it by design by not checking typos or for anything, and by typing too fast for my skill. I did all of that consciously by design because a major item of my own theory unlike anyone elses it seems, is we are much more malleable, and much more impacted by other people and their ideas, esp their ideas about ourselves and our own ideas.

People here there is a culture that tacitly buys popper and deutsch hook line and sinker. the gift of criticism/ Even  though deutsch thinks it's all .bollocks for himself, and he rationalizes routinely and I don't think he even perceives the distinction of that to truth any more. And despite this is actually a typical worsening trait linked to popperianism itself. For example the more versed someone is, the more they do this and do a lot of other things in discussions that actually fall short of the standards most people ignorant of all philosophy and that they even have standards. Even they don't rationalize and use distortive devices on the scale of those two deutsch's lietenants. cHis two wise angels. One for each ear. I think he harmed them. He flattered them with unrealistic but reinforced gestures of parity with himself intellectually and the other ways like communication skills. Determination and drive. competent as necessary in all the other skills necessary to get people listening.

Deutsch was also very clearly insincere in that he regarded their abilities and potential more soberly. As evidenced by the fact over 10 years, for three equals of popperianism. Three faithful musketeer. Criticism loving but never taking sides against the other. Never criticizing at all other than technical. Maybe they were being altruistic. Saving the golden arrow for others needing it more.

OK, but then there's the other stark fact that the logs of FoR and elsewhere are replete with incidents in which they all resort to fallacies or simply just ending the interaction, and it's always when it's pretty clear their position is worsening. Deutsch has actually never acknowledged a problem or even a flaw, let alone that he is refuted. He's never once done it...not that wasn't pretty obvious a throwaway he didn't care one way or another for.

This is now at abnormal levels by any standard person. He's supposed to be one of the leading theorists of our time. He allows this kind of flattery way out of proportion to his real contribution. Why does he allow it, over criticize it? Dawkin

was hailed a genius and credited with gene centric theory, and even evolution itself over Darwin at one point by some. It wasn't true and he was innocent of claiming it. But he would know that what's true is what gets around...a simple strategic choice to be silent when the tides are way too much going his way. The counter-criticism wally.

.But not the other way, Deutsch fields incoming from the criticism direction in exactly the right way to make people sorry they bothered and not bother again. search the list...just search it. Deutsch has an easy history to research hecause he nearly always responds to questions and requests, almost never cuts in or adds a view, or initiates a thread. So he answers.

idivide the questions by answers by threads. Then take the median and mean. You've got the standard deviation from that, so get the curve...there's a spike. So find the spike, the long threads. Filter for threads that start with a question indicating disagreement. Go to the end and see how things develop or end. There are patterns...basically which involve going the wrong way for each scenario, for the direction of all the virtues and worthies which are all the same direction.  and its the other way. If you do get there look for the john clark inductivism debate. Clark wins and the situation is clear. True, it's a technical win, and  nothing is resolved. But equally true popper's refutation and deutsch's depend on technical wheezes, that basically aren't legitimate because they raise issues that don't get addressed in the process. So again it isn't in line with integrity and truth seeking.

Certain people you'd know are a little over their paygrade. Others hace sycophant tendencies or are star struck. I'm starstruck. I'm working class with all the deferential traits and for my superiors and betters. I do...that's the default starting point. But people don't get the relationship...it isn't as abusive or contemptful as people think,either way. Deference is given conditionally and the conditions set a high standard. Typically everything the level above the fella himself. So there's a standard and an easy comparison. That's the condition. And failing it changes the dynamic radically and fast. And the middle and aristocratic classes know it. They know well. And they respect it and don't ask for different.

yeah ok I guess I'm shaggy dogging ya now.

.

[Bruce Kellett]

LizR wrote:
>
> (Another way to look at this is that the expansion is producing more
> available states for the universe to move into, effectively raising the
> entropy ceiling. This means an expanding universe can never reach a
> state of equilibrium - this is particularly clear during the BB
> fireball, which I would say is very near to equilibrium for a lot of the
> time.)

I thought I remembered that someone had written that the idea that the
expansion produces more states so the entropy ceiling increases with the
expansion of the universe is mistaken. I have found the reference, it is
Roger Penrose in 'The Road to Reality' in Section 27.6 (p. 701ff)

He writes:
"There is a common view that the entropy increase in the second law is
somehow just a necessary consequence of the expansion of the universe.
This opinion seems to be based on the misunderstanding that there are
comparatively few degrees of freedom available to the universe when it
is 'small', providing some kind of low 'ceiling' to possible entropy
values, and more available degrees of freedom when the universe gets
larger, giving a higher 'ceiling', thereby allowing higher entropies. ...

"There are many ways to see that this viewpoint cannot be correct....
...The degrees of freedom that are available to the universe are
described by the total phase space. The dynamics of GR (which include
the degree of freedom defining the universe's size) is just as much
described by the motion of our point x in the phase space as are all the
other physical processes involved. This phase space is just 'there', and
it does not in any sense 'grow with time', time not being part of the
phase space. There is no 'ceiling', because all states that are
dynamically accessible to the universe (or family of universes) under
consideration must be represented in this phase space....."

I recommend Penrose's book for a lucid explanation of these things.

Bruce

[meekerdb]

No, but dynamics consist of moving through phase space. Entropy is always relative to
constraints (with no constraints you just have the micro state and entropy is zero). So
relative to a given size I think the number of states does grow with size. Penrose is
right but he's removing the constraint on size.

Brent

[meekerdb]

Unless Bekenstein's bound applies.

> These states might not be quantum mechanically distinguishable, given the HUP, but the
> states exist, and eventually become distinguishable as space-time expands.
>
> There is also the question of Louiville's theorem -- the volume of any cloud of points
> moving through phase space remains constant so entropy cannot increase in this way.

I can because coarse graining is not over fractal grains. Entropy always depends on how
the coarse graining is defined.

>
> It is rather dubious that the maximum possible entropy increases with the expansion of
> spacetime. Entropy is associated with configurations of matter, and Bekenstein's bound
> states that the maximum entropy configuration of any quantity of matter is attained when
> that matter is compressed into a BH. The universe in which we live is not a BH, so it
> is, and never has been, in a state of maximum entropy.

It's not clear that Bekenstein's bound applies *only* to black holes. For example it may
apply to the relative horizon of the Hubble sphere. And it might apply to a white hole as
just the time-reverse of a black hole.

> The maximum entropy remains constant given that the mass-energy remains constant,
> regardless of expansion or the lack of it.

But, as you have pointed out, mass-energy does not stay constant in a universe without a
time-like Killing field.

How can you know that?

Brent

[meekerdb]

But as MWI assumes the projection postulate produces multiple outcomes at the coarse
grained level so will partial traces.

Brent
P.S. Welcome to the everything-list, Bruce. Have you abandoned atvoid-2? :-)

[Bruce Kellett]

The Bekenstein bound applies to information coded in matter. A system
can have more possible states than can be coded in teh amount of
available matter.

>
>> These states might not be quantum mechanically distinguishable, given
>> the HUP, but the states exist, and eventually become distinguishable
>> as space-time expands.
>>
>> There is also the question of Louiville's theorem -- the volume of any
>> cloud of points moving through phase space remains constant so entropy
>> cannot increase in this way.
>
> I can because coarse graining is not over fractal grains. Entropy
> always depends on how the coarse graining is defined.

Of course, which is why arguments over entropy are always rather
pointless. How can you define a maximum when you have not specified a
graining?

>> It is rather dubious that the maximum possible entropy increases with
>> the expansion of spacetime. Entropy is associated with configurations
>> of matter, and Bekenstein's bound states that the maximum entropy
>> configuration of any quantity of matter is attained when that matter
>> is compressed into a BH. The universe in which we live is not a BH, so
>> it is, and never has been, in a state of maximum entropy.
>
> It's not clear that Bekenstein's bound applies *only* to black holes.
> For example it may apply to the relative horizon of the Hubble sphere.
> And it might apply to a white hole as just the time-reverse of a black
> hole.

Regardles sof what BZ says on the avoid list, the Bekenstein bound does
not apply to the Hubble volume. If it did, entropy could not increase
within the volume, and we know that it does.

>> The maximum entropy remains constant given that the mass-energy
>> remains constant, regardless of expansion or the lack of it.
>
> But, as you have pointed out, mass-energy does not stay constant in a
> universe without a time-like Killing field.

True, but that only says that you cannot define the total mass-energy of
the universe, or measure it. It does not say that the mass-energy in any
particular co-moving volume is a meaningless concept.

Because if it were not, it could not increase.

Bruce

[Bruce Kellett]

As I said in my other reply, that simply makes the concept of entropy
otiose in these discussions. In cosmology, by and large, we are talking
classical physics with GR. Liouville's theorem is relevant.

Bruce

[meekerdb]

In your initial response you said the AoT is defined by the direction of increasing
entropy. Now you say the concept of entropy is otiose. ??

Brent

[LizR]

SO the AoT comes from the statistics of increasing entropy and is quite disjoint from the expansion of the universe. 

Bruce, I haven't got time to reply at length but one thing stands out. You have said a few times that the AOT derives from the 2nd law / increasing entropy. That is however just the definition of the (thermodynamic) AOT. They're equivalent - you need something else from which to derive the 2nd law. That is, you have to answer the question - why was the universe in a low entropy state in the past?

(I'll leave aside the radiation arrow and any others that might be around the place. The thermodynamic one is enough to be going on with, and I suspect they're all related anyway.)

I've come up with one suggestion which may or may not be correct (I originally got it from P.C.W. Davies, although admittedly he only applied it to the entropy of large scale systems, IIRC, not the BB fireball) and I can think of at least a couple of others, although I still think cosmic expansion is the most likely simply because it's available everywhere at the start of the universe and certainly generates the bound states which (I contend) act as useful sources of negative entropy, allowing stars to run nuclear fusion and life to exist - which already gives us some features of an entropy gradient.

Do you have a suggestion for an alternative mechanism that creates or drives the entropy gradient? I'm just curious (but if you do, it might enable me to get a better idea of where you're coming from on this).

[Bruce Kellett]

LizR wrote:
> SO the AoT comes from the statistics of increasing entropy and is
> quite disjoint from the expansion of the universe.
>
>
> Bruce, I haven't got time to reply at length but one thing stands out.
> You have said a few times that the AOT derives from the 2nd law /
> increasing entropy. That is however just the definition of the
> (thermodynamic) AOT. They're equivalent - you need something else from

> which to /derive/ the 2nd law. That is, you have to answer the question

> - why was the universe in a low entropy state in the past?

No, I don't have an explanation for the low entropy of the early
universe. One could play with anthropic explanations (if the entropy had
been maximal then there could not have bee an entropy gradient and we
couldn't exist.) This argument has some legs, but I must admit to
generally not being convinced by anthropic arguments. Such arguments can
explain anything, so they really explain nothing.

There are arguments for generation of low entropy starting states from a
pre-existing deSitter universe (Sean Carroll favours such arguments, I
think). But my problem with this is that the real problem arises during
reheating after inflation -- the original birth of the universe from
nothing, or tunnelling from some pre-existing universe, or whatever
becomes irrelevant by the time you get to reheating.

Re-heating is a great mystery in normal inflationary theory, and I do
not actually feel called on to explain absolutely everything. It is more
straightforward to find the flaws in other arguments.

Bruce

[Bruce Kellett]

LizR wrote:
> As I recall it, Vic later recanted his earlier idea that the AoT
> reversed if the universe began to re-contract.
>
> I think that was Hawking.

You are probably right. Although I think several people played with the
idea.

>
> I think it was Gold who proposed the idea of a universe where the AOT
> reverses in contraction phase. It's a logical outcome of view that AOT
> derives from expansion, although there may be some symmetry breaking
> that forces one "pole" of the universe to be the bang and one the
> crunch. Plus gravitational collapse appears to create a separate AOT
> that messes with the whole thing (smooth "initial" state and chaotic
> "final" one - something to do with the Ricci and Weyl tensors or
> something, Brent will tell me I hope!)

Penrose makes a lot of the asymmetry in a closed universe that starts
smooth and becomes very clumpy towards the end as more and more black
holes are formed -- the natural endpoint of relentlessly increasing
entropy. However, as with a lot of things, the discovery of dark energy
has pushed closed, re-contracting universes out of fashion.

No, my main problem with identifying the expansion of the universe as
the origin of the arrow of time is that the expansion of the universe
really has essential zero impact on the everyday physics of our
experience, but we see a consistent AoT associated with increasing
entropy in every phenomenon of our everyday experience. Sure, what
happened in the early universe has had lasting consequences for our
everyday life, but any connection with the expansion is too remote to
provide a plausible explanation of the consistency of our experience of
time. So the increase of entropy itself -- whose universality is easily
understood -- is itself the origin of the AoT.

Bruce

[zib...@gmail.com]

I think the phase space conception is a very good approach. But....on the terms of the phase space there are dynamical histories that correspond to entropy increasing at parity with expansion, that happens to arrange states just about right to get a big pile of sand.

and I rest my case with that. I'd be an impoverished attorney, and not that, being the case

Bruce

[zib...@gmail.com]

about that increasing states entropy thing. It doesn't work there, but I don't see how it would not work for entanglement. when two particles entangle the states of the combined system are fewer than the states 0f the particles isolated.

 

the interest of that is it could be a glimpse of a small part of an energy exchange network that uses entanglement to momentarily reduce entropy to obtain workable energy at the right place and point something gets enough to happen.

I mean...it looks reasonable to me...anything involving workable energy deserves attention

The other thought about entropy is there are several different pairings available. And it makes a large difference which pairing is selected. Like the one above. It was bad pairing to an expanding universe, because it  isn't just about increase of states availability of states to each particular point, including scaling up. entropy makes everything at all scales and so on, pan out at the same boundary or within.f Which is the furthest extents for it and if there's not hing else in reality, reality could be about to go invariant absolutely. Which equilibrium absolutely. Which about no energy available to anything to ever happen again

[LizR]

On 7 November 2014 22:30, Bruce Kellett <bhke...@optusnet.com.au> wrote:

No, my main problem with identifying the expansion of the universe as the origin of the arrow of time is that the expansion of the universe really has essential zero impact on the everyday physics of our experience, but we see a consistent AoT associated with increasing entropy in every phenomenon of our everyday experience. Sure, what happened in the early universe has had lasting consequences for our everyday life, but any connection with the expansion is too remote to provide a plausible explanation of the consistency of our experience of time. So the increase of entropy itself -- whose universality is easily understood -- is itself the origin of the AoT.

So you don't think that the creation of bound states in the BB fireball is a significant contribution to the entropy gradient?

I don't think you can cite the "remoteness of the Hubble flow" (as it were) as a reason to discount expansion as a source of the AOT (I assume you think that because bound systems are effectively separated out from it?). All the matter around us was once in the big bang fireball, and if that's where the conditions that created the entropy gradient originated then we would expect there to be a connection, although it may not be an immediately obvious one.

[Richard Ruquist]

The Big Bang fireball was a quark-gluon plasma which has been recreated in several high energy colliders. That plasma is characterized as a BEC in which all particles share the same wave function, so they say. I would expect that a BEC is very low entropy. Is that true?

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[Bruce Kellett]

No, I said you make the concept otiose by simply redefining the graining
scale at random. My comments, of course, Refer to some coherent and
consistent definition of entropy, given by a coarse-graining that is
relevant to the problem at hand.

You seem determined to play the role of 'spoiler' in this discussion,
regardless of the merit of the arguments. ;-)

Bruce

[LizR]

On 7 November 2014 20:22, Bruce Kellett <bhke...@optusnet.com.au> wrote:

You seem determined to play the role of 'spoiler' in this discussion, regardless of the merit of the arguments. ;-)

Bruce, meet Brent!

 

[Bruce Kellett]

LizR wrote:
> On 7 November 2014 20:22, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> You seem determined to play the role of 'spoiler' in this
> discussion, regardless of the merit of the arguments. ;-)
>
>
> Bruce, meet Brent!

I have known Brent for many years on the avoid list. Surprisingly, we
often agree about things, and it is unusual for Brent's contributions to
the discussion to be other than constructive. The 'spoiler' can lead one
to be more careful about what one says in haste....

Bruce

[LizR]

On 7 November 2014 21:07, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

    SO the AoT comes from the statistics of increasing entropy and is
    quite disjoint from the expansion of the universe.

Bruce, I haven't got time to reply at length but one thing stands out. You have said a few times that the AOT derives from the 2nd law / increasing entropy. That is however just the definition of the (thermodynamic) AOT. They're equivalent - you need something else from which to /derive/ the 2nd law. That is, you have to answer the question - why was the universe in a low entropy state in the past?

No, I don't have an explanation for the low entropy of the early universe.

Well that's the great thing about my explanation, by raising the entropy ceiling with time you don't have to worry about there being a low entropy initial state. In fact the evidence is that there wasn't one, that the BB fireball was more or less isotropic / homogeneous, which implies it was more or less at thermodynamic equilibrium. The definition of entropy as most likely state causes some problems here, because gravitationally a smooth state is a priori unlikely (without some antecedent cause) while for mass-energy it's very likely, given a smooth space-time background.

 

One could play with anthropic explanations (if the entropy had been maximal then there could not have bee an entropy gradient and we couldn't exist.) This argument has some legs, but I must admit to generally not being convinced by anthropic arguments. Such arguments can explain anything, so they really explain nothing.

They should be treated with caution, certainly. 

There are arguments for generation of low entropy starting states from a pre-existing deSitter universe (Sean Carroll favours such arguments, I think). But my problem with this is that the real problem arises during reheating after inflation -- the original birth of the universe from nothing, or tunnelling from some pre-existing universe, or whatever becomes irrelevant by the time you get to reheating.

I think you have reached the limits of my bear's little brain. Could you explain some more what the problem is? I am probably missing something important which will make the "expansion causing bound states" idea fall apart, I realise that. It is fairly simplistic and assumes all sorts of things.

Re-heating is a great mystery in normal inflationary theory, and I do not actually feel called on to explain absolutely everything. It is more straightforward to find the flaws in other arguments.

Of course. I was just curious.

[Alberto G. Corona]

if time is the thermodynamic arrow then then is meaningless the notion of reversal of termodinamic arrow. 

In which time the termodinamic arrow is reversed? Does it mean that the time goes forward while termodinamic arrow goes backward? that contradict the first assumption!!!

2014-10-15 2:14 GMT+02:00 Stephen Paul King <Step...@provensecure.com>:

Hi,

   I re-read S. Mitra's paper again and it made more sense than before if I assumed that the reversible measurement idea is to be taken as a local reversal to the "direction of entropy flow" in an area and not the entire universe.

   The trouble is this notion of locality. Are there any favorite definitions of "locality" out there? AFAIK, it does not have a fixed size in space, but may have a fixed size in "space-time" as location information expands at the speed of light if we ignore the effects of local structure that would modulate decoherence. This "decoherence" thing, IMHO, needs to be looked at carefully.

   In deference to Bruno, I should ask a question relevant to the ongoing discussions. Is a finite universe with locally reversible time consistent as a 1p world?

--

Kindest Regards,

Stephen Paul King

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[Bruce Kellett]

LizR wrote:
> On 7 November 2014 22:30, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> No, my main problem with identifying the expansion of the universe
> as the origin of the arrow of time is that the expansion of the
> universe really has essential zero impact on the everyday physics of
> our experience, but we see a consistent AoT associated with
> increasing entropy in every phenomenon of our everyday experience.
> Sure, what happened in the early universe has had lasting
> consequences for our everyday life, but any connection with the
> expansion is too remote to provide a plausible explanation of the
> consistency of our experience of time. So the increase of entropy
> itself -- whose universality is easily understood -- is itself the
> origin of the AoT.
>
>
> So you don't think that the creation of bound states in the BB fireball
> is a significant contribution to the entropy gradient?

No, and I don't really understand what you are trying to get at with
this. In the early stages of the Big Bang we had a period of
nucleo-synthesis in which the temperature was high enough for protons to
have enough energy to fuse together in collisions, so amounts of
deuterium, helium and lithium were formed. The exact amounts of these is
a significant test of the hot BB theory since we know enough about
nuclear physics to understand these processes. Once the expansion cooled
things further, nucleo-synthesis stopped and could only start again when
collapsing dust created stars which could ignite nuclear reactions --
and ultimately lead to supernovae which cook higher elements.

But all these as standard processes and proceed according to the second
law of thermodynamics just as much as the laws of nuclear physics. I
find it strange that you refer to this as 'creating negative entropy' or
some such.

The entropy gradient can only exist because at any point in time the
actual entropy of matter and radiation is much less than its possible
maximum. This is as true in the early stages of nucleo-synthesis in the
BB as it is now. We can get on entropy gradient only if the initial
entropy was very much lower than might have been expected for a generic
universe.

The entropy gradient between the sun and earth is important, and life of
earth depends on the existence of a cold dark universe into which we can
dump our waste heat.

>
> I don't think you can cite the "remoteness of the Hubble flow" (as it
> were) as a reason to discount expansion as a source of the AOT (I assume
> you think that because bound systems are effectively separated out from
> it?). All the matter around us was once in the big bang fireball, and if
> that's where the conditions that created the entropy gradient originated
> then we would expect there to be a connection, although it may not be an
> immediately obvious one.

The entropy gradient certainly originated at the beginning because it
was a low entropy state. It was not the low entropy was somehow created
by processes at that time. If the hot BB was a quark plasma at
more-or-less thermal equilibrium, that is a relatively high entropy
state for that form of matter, but that does not excite all the
available degrees of freedom. It is only the quarks that are in thermal
equilibrium, they are not in equilibrium with the gravitational and
other degres of freedom, so relative to the maximum possible, that
plasma was a low entropy state.

Bruce

[zib...@gmail.com]

hear hear your comment about Brent. Wish he'd talk to me sometimes. I think I've offended way back somewhere, and have been left on ignore ever since.  

[Richard Ruquist]

Besides the quark-gluon plasma was a BEC

On Fri, Nov 7, 2014 at 5:40 PM, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

Bruce

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[John Clark]

On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <meek...@verizon.net> wrote:

> I'd say that expansion of the universe is almost necessary, not contingent. 

I'd say that by about 1850 when people started to have a understanding of what Entropy was physicists had all they needed to have known that the universe must have started out in a very very low entropy state, that is to say they could have predicted the Big Bang in the early to mid 19th century; and they wouldn't have needed to go near a telescope to do so. But unfortunately they didn't, it's one of the great failures of nerve or imagination in the history of science. 

> The AoT has to point in the direction of entropy increase

But the question is WHY does time point in the direction of entropy increase. The answer is because in the first instant of time the universe was in a extraordinarily low entropy state, probably as low as it could get, and because there are vastly more disordered (high entropy) states than ordered (low entropy) states. So regardless of what the laws of physics were by the second instant of time the chances are overwhelming that entropy will be higher than it was at the first instant.

If instead in the first instant of time the universe was in a very high entropy state then in the second instant Entropy could have been smaller or larger with about equal probability and there would be no second law of thermodynamics and time would have no arrow. 

> I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch

Even if that were true time would still have a arrow, it would just be pointing in the opposite direction we are accustomed to. But why should time have a preferred direction at all? The laws of physics alone can not explain it nor is there any reason to expect that they should. Even if you know all the laws of physics there is to know you still can't predict what a system is going to do tomorrow unless you know what state it is in today; you've got to know the initial conditions. The laws of physics can explain why Entropy will be higher tomorrow than today, but it can't explain why it was lower yesterday than today, for that you need initial conditions. 

  John K Clark

 

[LizR]

On 8 November 2014 11:26, Alberto G. Corona <agoc...@gmail.com> wrote:

if time is the thermodynamic arrow then then is meaningless the notion of reversal of termodinamic arrow. 

In which time the termodinamic arrow is reversed? Does it mean that the time goes forward while termodinamic arrow goes backward? that contradict the first assumption!!!

Exactly. Time doesn't go anywhere, only the entropy gradient does.

[LizR]

On 8 November 2014 11:40, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

On 7 November 2014 22:30, Bruce Kellett <bhke...@optusnet.com.au <mailto:bhkellett@optusnet.com.au>> wrote:

    No, my main problem with identifying the expansion of the universe
    as the origin of the arrow of time is that the expansion of the
    universe really has essential zero impact on the everyday physics of
    our experience, but we see a consistent AoT associated with
    increasing entropy in every phenomenon of our everyday experience.
    Sure, what happened in the early universe has had lasting
    consequences for our everyday life, but any connection with the
    expansion is too remote to provide a plausible explanation of the
    consistency of our experience of time. So the increase of entropy
    itself -- whose universality is easily understood -- is itself the
    origin of the AoT.


So you don't think that the creation of bound states in the BB fireball is a significant contribution to the entropy gradient?

No, and I don't really understand what you are trying to get at with this.

Well, the best thing to do if you don't understand something is to ask for clarification! (I do that a lot...)

The point is that the existence of an AOT is partly derived from the existence of bound states like nuclei. In a quark-gluon plasma at equilibrium at a few trillion degrees, it is safe to say there is no discernible AOT. All interactions occur with equal probability in either time direction. But if you cool and spread out the plasma to the point where nucleons can form, then you have objects which can participate in entropic processes. So you have started to build the components necessary for the existence of an AOT. Similar comments can be applied at lower temperatures.

Several things are needed for an AOT. One is objects like atoms, which can be arranged into low entropy states. Another is objects like nuclei that are able to undergo energy-releasing processes. Nuclei are effectively frozen chunks of negative entropy - a big contribution to the AOT which didn't exist when they were a q-g plasma.

[LizR]

On 8 November 2014 16:53, John Clark <johnk...@gmail.com> wrote:

On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <meek...@verizon.net> wrote:

> I'd say that expansion of the universe is almost necessary, not contingent. 

I'd say that by about 1850 when people started to have a understanding of what Entropy was physicists had all they needed to have known that the universe must have started out in a very very low entropy state, that is to say they could have predicted the Big Bang in the early to mid 19th century; and they wouldn't have needed to go near a telescope to do so. But unfortunately they didn't, it's one of the great failures of nerve or imagination in the history of science. 

Another feature of the big bang / expanding universe is that it continually raises the entropy ceiling (maxium entropy that can exist in a given volume).

> The AoT has to point in the direction of entropy increase

But the question is WHY does time point in the direction of entropy increase. The answer is because in the first instant of time the universe was in a extraordinarily low entropy state, probably as low as it could get, and because there are vastly more disordered (high entropy) states than ordered (low entropy) states. So regardless of what the laws of physics were by the second instant of time the chances are overwhelming that entropy will be higher than it was at the first instant.

The universe could potentially start in a state of maximum entropy (at least in terms of the equilibrium of mass-energy) and still move to states where things can happen (if there are any inhomogeneities). Gravitational entropy is trickier, as it would tend to indicate the universe should start as a black hole (although that would never actually start...) But the rest  of the AOT can be handled by the entropy ceiling being continually raised, almost regardless of initial conditions.

If instead in the first instant of time the universe was in a very high entropy state then in the second instant Entropy could have been smaller or larger with about equal probability and there would be no second law of thermodynamics and time would have no arrow. 

> I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch

Even if that were true time would still have a arrow, it would just be pointing in the opposite direction we are accustomed to. But why should time have a preferred direction at all? The laws of physics alone can not explain it nor is there any reason to expect that they should. Even if you know all the laws of physics there is to know you still can't predict what a system is going to do tomorrow unless you know what state it is in today; you've got to know the initial conditions. The laws of physics can explain why Entropy will be higher tomorrow than today, but it can't explain why it was lower yesterday than today, for that you need initial conditions. 

True, although (see above) I think we can sneak around requiring any "implausibly low entropy starting conditions". 

[John Clark]

On Fri, Nov 7, 2014 at 11:14 PM, LizR <liz...@gmail.com> wrote:

 

> The universe could potentially start in a state of maximum entropy (at least in terms of the equilibrium of mass-energy)

That just means everything is at the same temperature, but that's not the only thing that determines Entropy. 

> and still move to states where things can happen

I don't see how, disordered states outnumber ordered ones by a factor of astronomical to the astronomical power, so however the laws of physics effect things as they are today by tomorrow things will almost certainly be in one of those very numerous more disordered states.  

 

> if there are any inhomogeneities

If there were inhomogeneities in the early universe then it wasn't at maximum entropy

> the AOT can be handled by the entropy ceiling being continually raised,

If that were true things would never run down, but they do. The second law of thermodynamics doesn't say that Entropy must always increase, it says Entropy will increase until it gets as high as it can go, the heat death of the universe. And maximum Entropy means a state of zero order, zero predictability and zero free energy (work); they can't become less than zero because the concepts of negative order, negative predictability and negative work are not well defined.  

> almost regardless of initial conditions.

Initial conditions are every bit as important as the laws of physics.

 John K Clark

[Alberto G. Corona]

>If instead in the first instant of time the universe was in a very high >entropy state then in the second instant Entropy could have been >smaller or larger with about equal probability and there would be no >second law of thermodynamics and time would have no arrow.  

> I say "almost" because there are some ways around it.  If the universe recontracts the AoT will probably continue to point toward the Big Crunch

The arrow of time is defined by the increase of entropy because that is the only direction in which life can operate. 

http://es.slideshare.net/agcorona1/arrow-of-time-determined-by-lthe-easier-direction-of-computation-for-life

Then if there are observers, they live in the direction of entropy increase. and they create the notion of "beginning" as the location in space-time where entropy was the lowest. That notion of beginning that only has meaning for a being living in time.

Then it is redundant to say that the beginning was a state of low entropy. 

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Alberto.

[LizR]

On 9 November 2014 06:36, John Clark <johnk...@gmail.com> wrote:

On Fri, Nov 7, 2014 at 11:14 PM, LizR <liz...@gmail.com> wrote:

 

> The universe could potentially start in a state of maximum entropy (at least in terms of the equilibrium of mass-energy)

That just means everything is at the same temperature, but that's not the only thing that determines Entropy. 

Correct, which is why I've been banging on at length about gravity.

> and still move to states where things can happen

I don't see how, disordered states outnumber ordered ones by a factor of astronomical to the astronomical power, so however the laws of physics effect things as they are today by tomorrow things will almost certainly be in one of those very numerous more disordered states.  

Because expansion raises the entropy ceiling. It's effectively free order. 

 

> if there are any inhomogeneities

If there were inhomogeneities in the early universe then it wasn't at maximum entropy

True. Quantum theory says it can't be. 

> the AOT can be handled by the entropy ceiling being continually raised,

If that were true things would never run down, but they do. The second law of thermodynamics doesn't say that Entropy must always increase, it says Entropy will increase until it gets as high as it can go, the heat death of the universe. And maximum Entropy means a state of zero order, zero predictability and zero free energy (work); they can't become less than zero because the concepts of negative order, negative predictability and negative work are not well defined.  

Expansion raises the ceiling, so entropy can increase indefinitely. But the rate at which the ceiling is raised slows with the scale of the universe, hence the universe gets closer and closer to heat death but never quite reaches it as long as expansion continues. Similar to how the big bang fireball never quite reaches equilibrium at any point because of expansion.

> almost regardless of initial conditions.

Initial conditions are every bit as important as the laws of physics.

Yes initial conditions are "as important", but that misses what I'm saying. Part of the project of science is to either explain how initial conditions got fine tuned or to show that fine tuned initial conditions aren't necessary. The idea I'm suggesting takes the latter approach.

[John Clark]

On Sat, Nov 8, 2014   Alberto G. Corona <agoc...@gmail.com> wrote:

> The arrow of time is defined by the increase of entropy

No, increasing entropy is not sufficient to establish a arrow of time, as I've said it can explain why Entropy will be higher tomorrow but by using the exact same logic Entropy should have been higher yesterday than today too, but clearly that is nonsense.     

To see how that is true consider all the logically possible microstates of Alberto Corona that would produce the macrostate that both you and I would recognize as Alberto Corona,  the vast majority of those microstates must have evolved from high entropy states because they outnumber the low entropy ones by an astronomical (too weak a word but I don't know of a stronger one) number.  But nobody thinks that is really true, and yet it is undeniable that you just can not deduce a asymmetry in time from thermodynamics or from any of the known laws of physics; this dichotomy is sometimes called Loschmidt's Paradox or Loschmidt's Objection. 

 

> because that is the only direction in which life can operate. 

I don't see why that would be true. If the arrow of time were reversed intelligent beings would just discover different laws of thermodynamics. They would remember that in the distant future, that is to say a long way from your "now", perfume molecules "were" (the most difficult part of of reverse time thought experiments is the grammar)  evenly distributed throughout the room, and they would remember that in the more recent future the molecules were only in the lower right part of the room, and they would remember that in the very recent future (very close to your "now") all the molecules were confined inside one small perfume bottle. They would then conclude that entropy always decreases or remains the same.

And as to how the bottle got into that room in the first place.... well, you can make educated guesses but essentially the only way to know for sure what the past was like is to wait and see. .

  

But the deepest question isn't why time points in one direction rather than the opposite direction but why it points in any direction at all. After all the fundamental laws of physics are time reversible, if I show you a film of non-macroscopic things you can't tell if the film is running forward or backwards with the electrical charges reversed and the scene photographed in a mirror. Even the laws of logic are reversible; if I gave you line 9 of a valid proof in pure number theory you could deduce both what line 10 must be and what line 8 must have been. So why do we perceive that time has a preferred direction?

If the arrow of time doesn't come from physical law it must come from the initial conditions and we need to add a past hypothesis, that is in the distant past for some reason entropy was much lower than it is today.  

  John K Clark

[Alberto G. Corona]

Most of the questions are explained in the presentation linked in the text

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Alberto.

[Stephen Paul King]

Hi Alberto,

   Is there really a global thermodynamic arrow of time? We can only infer its existence based on theoretical organizations of data that we collect. AFAIK, all "arrows" in actual physical dynamics are local.

[LizR]

On 9 November 2014 14:25, Stephen Paul King <step...@charter.net> wrote:

Hi Alberto,

   Is there really a global thermodynamic arrow of time? We can only infer its existence based on theoretical organizations of data that we collect. AFAIK, all "arrows" in actual physical dynamics are local.

For one thing it would be very hard to know if there was a reversed AOT in some region of the universe. Stars with a reversed AOT would absorb light, for example (from our perspective) and it would be hard to detect their presence except through gravity...

Hey, did I just come up with a new theory of dark matter? :-)

[Alberto G. Corona]

Hi Stephen:

There must not be a general arrow of time since time in general relativity is local not only in his value but also its direction AFAIK

[Stephen Paul King]

Hi LizR,

  Interesting!

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Stephen Paul King

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[Stephen Paul King]

Hi Alberto,

   you wrote: "There must not be a general arrow of time since time in general relativity is local not only in his value but also its direction AFAIK"

   Exactly! Time can be shown to be local for QM systems as well. So, where does the illusion of a global dimensional time come from? Barbour is right. It doesn't exist. But the illusion persists...

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[Bruno Marchal]

On 08 Nov 2014, at 22:46, John Clark wrote:

On Sat, Nov 8, 2014   Alberto G. Corona <agoc...@gmail.com> wrote:

> The arrow of time is defined by the increase of entropy

No, increasing entropy is not sufficient to establish a arrow of time, as I've said it can explain why Entropy will be higher tomorrow but by using the exact same logic Entropy should have been higher yesterday than today too, but clearly that is nonsense.     

To see how that is true consider all the logically possible microstates of Alberto Corona that would produce the macrostate that both you and I would recognize as Alberto Corona,  the vast majority of those microstates must have evolved from high entropy states because they outnumber the low entropy ones by an astronomical (too weak a word but I don't know of a stronger one) number.  But nobody thinks that is really true, and yet it is undeniable that you just can not deduce a asymmetry in time from thermodynamics or from any of the known laws of physics; this dichotomy is sometimes called Loschmidt's Paradox or Loschmidt's Objection. 

 

> because that is the only direction in which life can operate. 

I don't see why that would be true. If the arrow of time were reversed intelligent beings would just discover different laws of thermodynamics. They would remember that in the distant future, that is to say a long way from your "now", perfume molecules "were" (the most difficult part of of reverse time thought experiments is the grammar)  evenly distributed throughout the room, and they would remember that in the more recent future the molecules were only in the lower right part of the room, and they would remember that in the very recent future (very close to your "now") all the molecules were confined inside one small perfume bottle. They would then conclude that entropy always decreases or remains the same.

And as to how the bottle got into that room in the first place.... well, you can make educated guesses but essentially the only way to know for sure what the past was like is to wait and see. .

  

But the deepest question isn't why time points in one direction rather than the opposite direction but why it points in any direction at all. After all the fundamental laws of physics are time reversible, if I show you a film of non-macroscopic things you can't tell if the film is running forward or backwards with the electrical charges reversed and the scene photographed in a mirror. Even the laws of logic are reversible; if I gave you line 9 of a valid proof in pure number theory you could deduce both what line 10 must be and what line 8 must have been.

Not in general. Proofs are non-deterministic (in the computer science sense). You cannot reverse all classical inferences: from A & B you can deduce B, but from B you cannot come back to A & B, as A can be deduced from A & C too. Now in some linear logic, or in BCI combinators algebra. But with computationalism we can say that the symmetry at the bottom is quickly break down in the asymmetry of the knowledgeable pov. The asymmetry is in the eyes of the duplicated (entangled) observer, as the WM-duplication illustrates: the account in the first person diaries break the symmetries, and record the bit of information.

Bruno

So why do we perceive that time has a preferred direction?

If the arrow of time doesn't come from physical law it must come from the initial conditions and we need to add a past hypothesis, that is in the distant past for some reason entropy was much lower than it is today.  

  John K Clark

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http://iridia.ulb.ac.be/~marchal/

[LizR]

On 10 November 2014 02:30, Stephen Paul King <Step...@provensecure.com> wrote:

Hi Alberto,

   you wrote: "There must not be a general arrow of time since time in general relativity is local not only in his value but also its direction AFAIK"

   Exactly! Time can be shown to be local for QM systems as well. So, where does the illusion of a global dimensional time come from? Barbour is right. It doesn't exist. But the illusion persists...

Perhaps it comes from some large-scale temporal asymmetry imposed on the otherwise time-symmetric laws of physics, such as the universe have a singularity (or something very like one) at one temporal extremity, and timelike infinity at the other. That pushes the question of (apparent?) global time back to the reason why space-time has this large scale structure.

[Bruce Kellett]

LizR wrote:
> On 8 November 2014 11:40, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> LizR wrote:
>
> On 7 November 2014 22:30, Bruce Kellett

> <bhke...@optusnet.com.au <mailto:bhke...@optusnet.com.au>
> <mailto:bhkellett@optusnet.__com.au

I thought that was what you probably meant. I questioned it because it
seemed a bit odd to me. There is no reason to suppose that the initial
quark-gluon plasma the instant after the big bang was in equilibrium.
Even if it were in thermal equilibrium in itself, the gravitational
degrees of freedom were not thermalized, so the total state was very far
from a condition of maximum entropy.

The process is then that this plasma cooled (by the additional 1/r
factor for relativistic particles) during the subsequent expansion. The
formation of protons as bound states was then a process that occurred
according to the standard laws of physics -- the bound state is at lower
energy than the separate constituents, so energy was released at lower
temperature, and this itself increased the total entropy. So this
process itself has the thermodynamic AoT. Similar considerations apply
to all later formation of bound states, such as deuterium, helium and
lithium. All released energy at lower temperatures and led to increases
in the total entropy.

This continues all the way to the formation of stars such as the sun.
Aggregates of elementary constituents, loosely bound together by
gravity, underwent collisions that radiated energy (mainly as photons)
and this also increased the total entropy. The sun was formed and
contracted sufficiently to ignite thermonuclear reactions, burning
hydrogen to form helium. The end result, as you say, was that the sun
appears as a low entropy source in a dark universe. But this all happens
by processes governed by the second law of thermodynamics, so the
formation of this low entropy source itself cost a lot of entropy
increase in the rest of the universe. It could be said that it is only
the fact that thermal photons could escape to the wider universe and
carry off that made any of this possible. Photons are not
gravitationally bound, so could escape, but an essential thermodynamic
precondition was that there was a cooler reservoir to receive them.
Gravitational clumping created this reservoir.

Nothing like this could happpen if the entropy were maximized at the BB.
Expansion does not increase the "entropy ceiling", as has been
previously pointed out.

Bruce

[Bruce Kellett]

LizR wrote:
> On 8 November 2014 16:53, John Clark <johnk...@gmail.com

> <mailto:johnk...@gmail.com>> wrote:
>
> On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <meek...@verizon.net
> <mailto:meek...@verizon.net>> wrote:
>
> > I'd say that expansion of the universe is almost necessary,
> not contingent.
>
> I'd say that by about 1850 when people started to have a
> understanding of what Entropy was physicists had all they needed to
> have known that the universe must have started out in a very very
> low entropy state, that is to say they could have predicted the Big
> Bang in the early to mid 19th century; and they wouldn't have needed
> to go near a telescope to do so. But unfortunately they didn't, it's
> one of the great failures of nerve or imagination in the history of
> science.
>
> Another feature of the big bang / expanding universe is that it
> continually raises the entropy ceiling (maxium entropy that can exist in
> a given volume).

I think you should stop saying this. It is not true. You have not
defined what you mean by "maximum entropy" nor have you specified how
that maximum is calculated. If the maximum is defined as when all
available degrees of freedom are in thermal equilibrium, then the
universe has never been in such a state of maximum entropy, and it
probably will not be until all matter has collapsed into black holes and
these have decayed by Hawking radiation.

At any finite time, one useful concept of maximum entropy is to consider
the state in which all mass energy is in the form of black holes. This
has never happened either.

Neither of these maxima is in any way affected by the expansion of the
universe as a whole.

So you cannot get around the need to postulate a low entropy condition
at the BB.

Bruce

> > The AoT has to point in the direction of entropy increase
>
>
> But the question is WHY does time point in the direction of entropy
> increase. The answer is because in the first instant of time the
> universe was in a extraordinarily low entropy state, probably as low
> as it could get, and because there are vastly more disordered (high
> entropy) states than ordered (low entropy) states. So regardless of
> what the laws of physics were by the second instant of time the
> chances are overwhelming that entropy will be higher than it was at
> the first instant.
>
>
> The universe could potentially start in a state of maximum entropy (at
> least in terms of the equilibrium of mass-energy) and still move to

> states where things can happen (if there are /any/ inhomogeneities).

[meekerdb]

On 11/9/2014 7:01 PM, Bruce Kellett wrote:
> LizR wrote:
>> On 8 November 2014 16:53, John Clark <johnk...@gmail.com
>> <mailto:johnk...@gmail.com>> wrote:
>>
>> On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <meek...@verizon.net
>> <mailto:meek...@verizon.net>> wrote:
>>
>> > I'd say that expansion of the universe is almost necessary,
>> not contingent.
>> I'd say that by about 1850 when people started to have a
>> understanding of what Entropy was physicists had all they needed to
>> have known that the universe must have started out in a very very
>> low entropy state, that is to say they could have predicted the Big
>> Bang in the early to mid 19th century; and they wouldn't have needed
>> to go near a telescope to do so. But unfortunately they didn't, it's
>> one of the great failures of nerve or imagination in the history of
>> science.
>> Another feature of the big bang / expanding universe is that it continually raises the
>> entropy ceiling (maxium entropy that can exist in a given volume).
>
> I think you should stop saying this. It is not true. You have not defined what you mean
> by "maximum entropy" nor have you specified how that maximum is calculated. If the
> maximum is defined as when all available degrees of freedom are in thermal equilibrium,
> then the universe has never been in such a state of maximum entropy,

How about defining the particle maximum as when all mass-energy is in thermal equilibrium
- leaving gravitational modes out. Isn't that how inflation is used to explain the CMB
uniformity?

> and it probably will not be until all matter has collapsed into black holes and these
> have decayed by Hawking radiation.
>
> At any finite time, one useful concept of maximum entropy is to consider the state in
> which all mass energy is in the form of black holes. This has never happened either.

Presumably because inflation was much faster than the time for gravitational collapse.

>
> Neither of these maxima is in any way affected by the expansion of the universe as a whole.
>
> So you cannot get around the need to postulate a low entropy condition at the BB.

I agree that there must have been a low entropy condition, but did it have to be low
relative to various constaints? Of all the ways for the universe to be, being in a
Planck-size volume is a very unlikely one (which is what Penrose points out). But given
that size I don't see why it's conditional entropy could not be high.

Brent

[LizR]

On 10 November 2014 16:01, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

On 8 November 2014 16:53, John Clark <johnk...@gmail.com <mailto:johnk...@gmail.com>> wrote:

    On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <meek...@verizon.net
    <mailto:meek...@verizon.net>> wrote:

        >  I'd say that expansion of the universe is almost necessary,
        not contingent. 
    I'd say that by about 1850 when people started to have a
    understanding of what Entropy was physicists had all they needed to
    have known that the universe must have started out in a very very
    low entropy state, that is to say they could have predicted the Big
    Bang in the early to mid 19th century; and they wouldn't have needed
    to go near a telescope to do so. But unfortunately they didn't, it's
    one of the great failures of nerve or imagination in the history of
    science.
Another feature of the big bang / expanding universe is that it continually raises the entropy ceiling (maxium entropy that can exist in a given volume).

I think you should stop saying this. It is not true. You have not defined what you mean by "maximum entropy" nor have you specified how that maximum is calculated. If the maximum is defined as when all available degrees of freedom are in thermal equilibrium, then the universe has never been in such a state of maximum entropy, and it probably will not be until all matter has collapsed into black holes and these have decayed by Hawking radiation.

I'm dealing with classical thermodynamics, i.e. ignoring gravity and only talking about the arrangements of particles. I don't know how to incorporate gravity into the picture. If that makes what I'm suggesting inadmissible, fair enough.

[Bruce Kellett]

Yes, but that is not the argument Liz is making.

>> and it probably will not be until all matter has collapsed into black
>> holes and these have decayed by Hawking radiation.
>>
>> At any finite time, one useful concept of maximum entropy is to
>> consider the state in which all mass energy is in the form of black
>> holes. This has never happened either.
>
> Presumably because inflation was much faster than the time for
> gravitational collapse.

Of course. The interaction with gravitation is very weak and the
relevant time scales are much loger than those required for a plasma to
thermalize the particle degrees of freedom.

>> Neither of these maxima is in any way affected by the expansion of the
>> universe as a whole.
>>
>> So you cannot get around the need to postulate a low entropy condition
>> at the BB.
>
> I agree that there must have been a low entropy condition, but did it
> have to be low relative to various constaints? Of all the ways for the
> universe to be, being in a Planck-size volume is a very unlikely one
> (which is what Penrose points out). But given that size I don't see why
> it's conditional entropy could not be high.

The hot BB was never a universe of Planck size. The seed for inflation
might have been that small, but remember that at the end of inflation
the universe is at exactly zero degrees absolute -- it is totally
frozen. The hot BB arises with reheating, and that could potentially
been of almost infinite (or at least unbounded) size. It certainly was
not small on any scale.

Bruce

[Bruce Kellett]

LizR wrote:
> On 10 November 2014 16:01, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> LizR wrote:
>
> On 8 November 2014 16:53, John Clark <johnk...@gmail.com

> <mailto:johnk...@gmail.com> <mailto:johnk...@gmail.com

> <mailto:johnk...@gmail.com>>> wrote:
>
> On Thu, Nov 6, 2014 at 3:56 PM, meekerdb
> <meek...@verizon.net <mailto:meek...@verizon.net>

> <mailto:meek...@verizon.net <mailto:meek...@verizon.net>>>

It does. The physics of the BB is set by gravity, so one cannot sensibly
consider conditions then without including gravity. Classical
thermodynamics simple does not cut it.

Bruce

[LizR]

OK, so are you saying that the formation of bound states like nucleons has no bearing on the existence of an AOT?

[Bruce Kellett]

LizR wrote:
> OK, so are you saying that the formation of bound states like nucleons
> has no bearing on the existence of an AOT?

It certainly doesn't play a role in the origin of the AoT. Formation of
bound states is just a routine physical process that follows
conventional dynamical laws, including the second law of thermodynamics.
Since the second law governs these processes, they are subject to an AoT.

Bruce

[LizR]

You appear to be assuming the AOT in order to explain something that emerged from a state in which there was no distinct AOT. The quark soup starts in a high energy, essentially time-reversible state (any nucleons that happen to form sill rapidly fall apart again) - how can the 2nd law apply at that point?

The 2nd law is emergent, as I think we all agree, and we're trying to explain how it might have emerged from time-symmetric physics. The transition from a plasma in which free quarks are interacting in an essentially time symmetric manner to a cloud of nucleons looks like a step on the way to doing that.

[Bruce Kellett]

LizR wrote:
> On 11 November 2014 10:32, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> LizR wrote:
>
> OK, so are you saying that the formation of bound states like
> nucleons has no bearing on the existence of an AOT?
>
> It certainly doesn't play a role in the origin of the AoT. Formation
> of bound states is just a routine physical process that follows
> conventional dynamical laws, including the second law of
> thermodynamics. Since the second law governs these processes, they
> are subject to an AoT.
>
> You appear to be assuming the AOT in order to explain something that
> emerged from a state in which there was no distinct AOT. The quark
> soup starts in a high energy, essentially time-reversible state (any
> nucleons that happen to form sill rapidly fall apart again) - how can
> the 2nd law apply at that point?

I think we have covered this. The quark-gluon plasma is a thermal state
of only those degrees of freedom -- other degrees of freedom,
particularly gravitational, are not thermalized, so it is not a state of
maximum entropy. It is, in fact, a low entropy state compared with what
might be expected -- we could have a soup of black holes for instance,
which would have the same energy density but vastly higher entropy. Why
do we not have such a state? That is the past hypothesis -- things
started in an unusually low entropy state.

If the universe were not expanding, and hence cooling the initial
plasma, then the gravitational degrees of freedom would gradually become
excited, and eventually fully thermalized. The entropy would rise
throughout this process, even though no expansion is hypothesized. The
second law applies because the state has a much lower entropy than other
states which are equally likely. The second law is there in the
statistics of the degrees of freedom -- it does not have to 'emerge'
from anywhere.

Bruce

[LizR]

On 11 November 2014 12:34, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

On 11 November 2014 10:32, Bruce Kellett <bhke...@optusnet.com.au <mailto:bhkellett@optusnet.com.au>> wrote:

    LizR wrote:

        OK, so are you saying that the formation of bound states like
        nucleons has no bearing on the existence of an AOT?

    It certainly doesn't play a role in the origin of the AoT. Formation
    of bound states is just a routine physical process that follows
    conventional dynamical laws, including the second law of
    thermodynamics. Since the second law governs these processes, they
    are subject to an AoT.

You appear to be assuming the AOT in order to explain something that emerged from a state in which there was no distinct AOT. The quark soup starts in a high energy, essentially time-reversible state (any nucleons that happen to form sill rapidly fall apart again) - how can the 2nd law apply at that point?

I think we have covered this. The quark-gluon plasma is a thermal state of only those degrees of freedom -- other degrees of freedom, particularly gravitational, are not thermalized, so it is not a state of maximum entropy. It is, in fact, a low entropy state compared with what might be expected -- we could have a soup of black holes for instance, which would have the same energy density but vastly higher entropy. Why do we not have such a state? That is the past hypothesis -- things started in an unusually low entropy state.

Yes, I have already agreed with this. The flatness of space-time does indeed need explaining (perhaps by inflation?). I'm talking about the (perhaps residual) entropy gradient arising from mainly non-gravitational processes, like the fact that atoms can only exist to the "future" side of a certain point in an expanding universe. The AOT we experience may be many order of magnitude away from the one theoretically attainable by gravitational processes, however I'm assuming the universe got flat somehow, and asking how, given that, the AOT of everyday life might have arisen. Maybe it only arises from flatness, but if so we need a mechanism. My suggestion is that flatness plus cosmological expansion plus our tie-symmetric laws of physics are enough to give the observed AOT.

If the universe were not expanding, and hence cooling the initial plasma, then the gravitational degrees of freedom would gradually become excited, and eventually fully thermalized. The entropy would rise throughout this process, even though no expansion is hypothesized. The second law applies because the state has a much lower entropy than other states which are equally likely. The second law is there in the statistics of the degrees of freedom -- it does not have to 'emerge' from anywhere.

In other words, the gravitational entropy would rise. I agree. And I agree that the second law applies to states in low entropy, as flat space-time clearly is. The flatness of space-time needs to be explained, but that isn't the whole story. I'm discussing whether the expansion turning the q-g plasma into bound states could contribute to the AOT that we experience, given that we're made from those bound states and live off energy generated from them inside stars.

Given that the laws of physics are (almost) time-symmetric, there needs to be some mechanism by which an AOT emerges, and an obvious starting point is the observed boundary conditions on space-time.

.

[Bruce Kellett]

LizR wrote:
> On 11 November 2014 12:34, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> LizR wrote:
>
> On 11 November 2014 10:32, Bruce Kellett

> <bhke...@optusnet.com.au <mailto:bhke...@optusnet.com.au>
> <mailto:bhkellett@optusnet.__com.au

It is not really a question of the flatness of space-time. That arises
from the setting of the parameter k in the Friedmann equations, which is
not a dynamical feature. I think you really mean 'smoothness' -- why is
space-time smooth and not 'lumpy' as it would be in a soup of black
holes. Inflation is supposed to solve this problem, but the solution has
been made opaque by recent developments in inflationary theory --
particularly the reheating problem.

> If the universe were not expanding, and hence cooling the initial
> plasma, then the gravitational degrees of freedom would gradually
> become excited, and eventually fully thermalized. The entropy would
> rise throughout this process, even though no expansion is
> hypothesized. The second law applies because the state has a much
> lower entropy than other states which are equally likely. The second
> law is there in the statistics of the degrees of freedom -- it does
> not have to 'emerge' from anywhere.
>
> In other words, the gravitational entropy would rise. I agree. And I
> agree that the second law applies to states in low entropy, as flat
> space-time clearly is. The flatness of space-time needs to be explained,
> but that isn't the whole story. I'm discussing whether the expansion
> turning the q-g plasma into bound states could contribute to the AOT
> that we experience, given that we're made from those bound states and
> live off energy generated from them inside stars.

These are straightforward physical process that obey the second law. The
AoT exists regardless of such processes.

> Given that the laws of physics are (almost) time-symmetric, there needs
> to be some mechanism by which an AOT emerges, and an obvious starting
> point is the observed boundary conditions on space-time.

Which is what I am pointing to -- the past hypothesis, or the fact that
the entropy was low at the BB. Currently this fact is unexplained. Wrong
explanations do not advance understanding.

Bruce

[LizR]

On 11 November 2014 13:39, Bruce Kellett <bhke...@optusnet.com.au> wrote:

In other words, the gravitational entropy would rise. I agree. And I agree that the second law applies to states in low entropy, as flat space-time clearly is. The flatness of space-time needs to be explained, but that isn't the whole story. I'm discussing whether the expansion turning the q-g plasma into bound states could contribute to the AOT that we experience, given that we're made from those bound states and live off energy generated from them inside stars.

These are straightforward physical process that obey the second law.

Physical processes obey the laws of physics. The 2nd law isn't a law of physics. 

The AoT exists regardless of such processes.

I don't see how. The expansion made a state with no AOT turn into one that had one, by cooling the plasma to the point where a phase transition could occur.

[Bruce Kellett]

LizR wrote:
> On 11 November 2014 13:39, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
>
> In other words, the gravitational entropy would rise. I agree. And I
> agree that the second law applies to states in low entropy, as flat
> space-time clearly is. The flatness of space-time needs to be
> explained, but that isn't the whole story. I'm discussing whether
> the expansion turning the q-g plasma into bound states could
> contribute to the AOT that we experience, given that we're made from
> those bound states and live off energy generated from them inside stars.
>
> These are straightforward physical process that obey the second law.
>
> Physical processes obey the laws of physics. The 2nd law isn't a law of
> physics.

Tell that to the marines!!!!

>
> The AoT exists regardless of such processes.
>
> I don't see how. The expansion made a state with no AOT turn into one
> that had one, by cooling the plasma to the point where a phase
> transition could occur.

No, we have gone as far as we can on this -- and you are wrong.

Bruce

[John Clark]

On Mon, Nov 10, 2014  LizR <liz...@gmail.com> wrote:

> Physical processes obey the laws of physics. The 2nd law isn't a law of physics.

The 2nd law is even more fundamental than a law of  physics, it's more like a law of logic; it's just the result of there being VASTLY more ways to be disorganized (high entropy) than organized (low entropy). So however a physical law changes a system, when it is done with it the system will almost certainly be in a higher entropy state than it was before the changes happened.

In different parts of the multiverse the other laws of physics might be different, but the only universe where the 2nd law would not be true would be a universe already at maximum entropy, a universe that had zero free energy (work), a universe with no structure which contained nothing but white noise. That would be about as dull as it gets, so we can say that in every universe of even the slightest interest the 2nd law must be true

  John K Clark 

[LizR]

On 12 November 2014 15:42, John Clark <johnk...@gmail.com> wrote:

On Mon, Nov 10, 2014  LizR <liz...@gmail.com> wrote:

> Physical processes obey the laws of physics. The 2nd law isn't a law of physics.

The 2nd law is even more fundamental than a law of  physics, it's more like a law of logic; it's just the result of there being VASTLY more ways to be disorganized (high entropy) than organized (low entropy). So however a physical law changes a system, when it is done with it the system will almost certainly be in a higher entropy state than it was before the changes happened.

Correct. The 2nd law is simply the result of statistics - a "law of logic" as you say. It should operate in (hypothetical) universes with all sorts of physical laws - however, for it to do so you need a mechanism that initialises the universe in a low entropy state, or a mechanism that keeps raising the maximum entropy a system can attain (I - and others - have suggested that the expansion of the universe is just such a mechanism).

[LizR]

On 11 November 2014 14:48, Bruce Kellett <bhke...@optusnet.com.au> wrote:

    The AoT exists regardless of such processes.

I don't see how. The expansion made a state with no AOT turn into one that had one, by cooling the plasma to the point where a phase transition could occur.

No, we have gone as far as we can on this  -- and you are wrong.

I would appreciate a short, simple explanation of why.

 

[Bruno Marchal]

On 12 Nov 2014, at 07:58, LizR wrote:

On 12 November 2014 15:42, John Clark <johnk...@gmail.com> wrote:

On Mon, Nov 10, 2014  LizR <liz...@gmail.com> wrote:

> Physical processes obey the laws of physics. The 2nd law isn't a law of physics.

The 2nd law is even more fundamental than a law of  physics, it's more like a law of logic; it's just the result of there being VASTLY more ways to be disorganized (high entropy) than organized (low entropy). So however a physical law changes a system, when it is done with it the system will almost certainly be in a higher entropy state than it was before the changes happened.

Correct. The 2nd law is simply the result of statistics - a "law of logic" as you say.

Well, just a detail, which matters for a logician; Logic is not enough, you need the numbers, and addition + mutiplication, and this entails already the comp multiverse (the UD*). The whole non triviality of reality comes from the Turing universaility that we get when having both + and * laws operating together. 

It should operate in (hypothetical) universes with all sorts of physical laws - however, for it to do so you need a mechanism that initialises the universe in a low entropy state, or a mechanism that keeps raising the maximum entropy a system can attain (I - and others - have suggested that the expansion of the universe is just such a mechanism).

Hmm... For a many-worlder, we need only the 0-information (or near zero) describing the superposition of the vacuum state. It is the opposite in the de Broglie/ Bohm initial state, which needs a priori to be a very-high information state, to enforce (non covariantly) the particles to exist in only one term of the wave, in some chosen base. With computationalism or the MW, the space-time structure is relative to the observers views from inside, like UDA explains it has to be, if computationalism is correct. Now, if computationalism is correct, the wave itself arises phenomenologically, plausibly under the form of a (measure winning) quantum universal dovetailer (which the wave of the vacuum might be). We have already the quantum logic for the sigma_1 "foliation" in the UD, when seen by self-referentially correct machines. Advantage? Consciousness is no more eliminated, (thanks to the Solovay splitting) and corresponds to the first person discourses of the self-aware creatures.

Bruno

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http://iridia.ulb.ac.be/~marchal/

[Bruno Marchal]

Hi Stephen,

On 09 Nov 2014, at 14:30, Stephen Paul King wrote:

Hi Alberto,

   you wrote: "There must not be a general arrow of time since time in general relativity is local not only in his value but also its direction AFAIK"

   Exactly! Time can be shown to be local for QM systems as well. So, where does the illusion of a global dimensional time come from? Barbour is right. It doesn't exist. But the illusion persists...

But the MW explains that illusion in term of personal records in the observing sub-system. Like in the WM-duplication, everything is 100% 3p deterministic, but almost all first person records asserts the contrary, for obvious reason. So the QM theory (without collapse) explains why the illusion persists. In the pure computationalist context, we are less far, and still have to justify the QM wave itself, but we got results in that direction.

Bruno

http://iridia.ulb.ac.be/~marchal/

[Bruce Kellett]

LizR wrote:
> On 11 November 2014 14:48, Bruce Kellett <bhke...@optusnet.com.au

First, the expansion does not increase any entropy limit.

Second, we get the thermodynamic AoT without expansion.

In standard BB cosmology, the expansion cools the initial very hot
state. But it is not necessary to start with a hot BB to get an AoT. We
could image some different mechanism of cosmogenesis whereby the initial
state was a relatively thin cool gruel of hydrogen and a few other bits.
Something like in the current model when the universe is a few million
years old. Imagine it started in that state, but with no further
expansion. We would still get gravitational collapse around local
inhomogeneities, galaxies and stars would form. Planets and occasionally
life would arise. All within a thermodynamic AoT. In other words, we
could get to exactly where we are no without any expansion at all. So
expansion cannot be a necessary prerequisite for an AoT.

You have to beware of making contingent facts into apparent logical
necessities.

Bruce

[LizR]

On 13 November 2014 00:15, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

On 11 November 2014 14:48, Bruce Kellett <bhke...@optusnet.com.au <mailto:bhkellett@optusnet.com.au>> wrote:


            The AoT exists regardless of such processes.

        I don't see how. The expansion made a state with no AOT turn
        into one that had one, by cooling the plasma to the point where
        a phase transition could occur.


    No, we have gone as far as we can on this  -- and you are wrong.

I would appreciate a short, simple explanation of why.

First, the expansion does not increase any entropy limit.

Why not? Informally, from a quantum viewpoint it makes more states available, in a manner similar to Max Tegmartk's calculation of how far away one's duplicate is in a level 1 multiverse. The analogy used by Paul Davies is that if you have a gas at equilibrium inside a container and expand the container, the gas will stop being at equilibrium in the new configuration. It has more states available, and hence its entropy ceiling has been raised. This seems to me a valid argument. Where has Davies (and Tegmark) gone wrnog?

Second, we get the thermodynamic AoT without expansion.

In standard BB cosmology, the expansion cools the initial very hot state. But it is not necessary to start with a hot BB to get an AoT. We could image some different mechanism of cosmogenesis whereby the initial state was a relatively thin cool gruel of hydrogen and a few other bits. Something like in the current model when the universe is a few million years old. Imagine it started in that state, but with no further expansion. We would still get gravitational collapse around local inhomogeneities, galaxies and stars would form. Planets and occasionally life would arise. All within a thermodynamic AoT. In other words, we could get to exactly where we are no without any expansion at all. So expansion cannot be a necessary prerequisite for an AoT.

You're invoking graviation to create the AOT. I am explicitly trying to explain the AOT without invoking gravitation - obviously the universe has to be smooth, this is what else can occur on top of that. Also, the presence of hydrogen in the above is unexplained, but you need something like atoms for the 2nd law to operate. It doesn't operate inside a q-g plasma at equilibrium at several trillion degrees, for example. Hence you need to create those little bundles of negative entropy, so to speak, before you have something on which the statistics of the 2nd law can operate.

You have to beware of making contingent facts into apparent logical necessities.

I will resist making any similarly patronising and irrelevant comments.

 

[LizR]

On 12 November 2014 21:22, Bruno Marchal <mar...@ulb.ac.be> wrote:

On 12 Nov 2014, at 07:58, LizR wrote:

On 12 November 2014 15:42, John Clark <johnk...@gmail.com> wrote:

On Mon, Nov 10, 2014  LizR <liz...@gmail.com> wrote:

> Physical processes obey the laws of physics. The 2nd law isn't a law of physics.

The 2nd law is even more fundamental than a law of  physics, it's more like a law of logic; it's just the result of there being VASTLY more ways to be disorganized (high entropy) than organized (low entropy). So however a physical law changes a system, when it is done with it the system will almost certainly be in a higher entropy state than it was before the changes happened.

Correct. The 2nd law is simply the result of statistics - a "law of logic" as you say.

Well, just a detail, which matters for a logician; Logic is not enough, you need the numbers, and addition + mutiplication, and this entails already the comp multiverse (the UD*). The whole non triviality of reality comes from the Turing universaility that we get when having both + and * laws operating together. 

Thanks Bruno :-)

Yes, of course some arithmetic is also involved in the operation of statistics.

[Bruce Kellett]

LizR wrote:
> On 13 November 2014 00:15, Bruce Kellett <bhke...@optusnet.com.au

> <mailto:bhke...@optusnet.com.au>> wrote:
>
> LizR wrote:
>
> On 11 November 2014 14:48, Bruce Kellett

> <bhke...@optusnet.com.au <mailto:bhke...@optusnet.com.au>
> <mailto:bhkellett@optusnet.__com.au

> <mailto:bhke...@optusnet.com.au>>> wrote:
>
>
> The AoT exists regardless of such processes.
>
> I don't see how. The expansion made a state with no AOT turn
> into one that had one, by cooling the plasma to the
> point where
> a phase transition could occur.
>
> No, we have gone as far as we can on this -- and you are wrong.
>
> I would appreciate a short, simple explanation of why.
>
> First, the expansion does not increase any entropy limit.
>
> Why not? Informally, from a quantum viewpoint it makes more states
> available, in a manner similar to Max Tegmartk's calculation of how far
> away one's duplicate is in a level 1 multiverse. The analogy used by
> Paul Davies is that if you have a gas at equilibrium inside a container
> and expand the container, the gas will stop being at equilibrium in the
> new configuration. It has more states available, and hence its entropy
> ceiling has been raised. This seems to me a valid argument. Where has
> Davies (and Tegmark) gone wrnog?

The problem would seem to be with Davies' analogy. If you expand a
container containing gas at equilibrium, the temperature will drop and
the entropy will rise, but this is because you have extracted heat from
the system. Moving the walls outwards means that molecules that bounce
off the walls will recoil with lower velocity -- transferring energy
from the gas to the outside world. This does not happen in the expanding
universe. The gas cools, but energy is not conserved in the expansion --
it does not go anywhere. There is no reservoir at a lower temperature to
act as a sink, and there is no change in entropy. With no change in
entropy, the gas does not cease to be at equilibrium if it were
initially so, and there is no change in the number of available states.
This is a peculiarity of GR since energy is not globally conserved in an
expanding universe.

> Second, we get the thermodynamic AoT without expansion.
>
> In standard BB cosmology, the expansion cools the initial very hot
> state. But it is not necessary to start with a hot BB to get an AoT.
> We could image some different mechanism of cosmogenesis whereby the
> initial state was a relatively thin cool gruel of hydrogen and a few
> other bits. Something like in the current model when the universe is
> a few million years old. Imagine it started in that state, but with
> no further expansion. We would still get gravitational collapse
> around local inhomogeneities, galaxies and stars would form. Planets
> and occasionally life would arise. All within a thermodynamic AoT.
> In other words, we could get to exactly where we are no without any
> expansion at all. So expansion cannot be a necessary prerequisite
> for an AoT.
>
>
> You're invoking graviation to create the AOT. I am explicitly trying to
> explain the AOT without invoking gravitation - obviously the universe
> has to be smooth, this is what else can occur on top of that.

Gravity is one of the laws of physics. The AoT occurs within physics, so
why not use gravity to explain what happens? The problems arise -- as I
have tried to point out -- when you ignore gravity. Cosmogenesis is,
after all, the quintessential GR/gravitational problem.

> Also, the
> presence of hydrogen in the above is unexplained, but you need something
> like atoms for the 2nd law to operate. It doesn't operate inside a q-g
> plasma at equilibrium at several trillion degrees, for example. Hence
> you need to create those little bundles of negative entropy, so to
> speak, before you have something on which the statistics of the 2nd law
> can operate.
>
>
> You have to beware of making contingent facts into apparent logical
> necessities.
>
> I will resist making any similarly patronising and irrelevant comments.

The comment is apposite. It is neither patronizing nor irrelevant.

Bruce

[LizR]

On 13 November 2014 11:29, Bruce Kellett <bhke...@optusnet.com.au> wrote:

LizR wrote:

Why not? Informally, from a quantum viewpoint it makes more states available, in a manner similar to Max Tegmartk's calculation of how far away one's duplicate is in a level 1 multiverse. The analogy used by Paul Davies is that if you have a gas at equilibrium inside a container and expand the container, the gas will stop being at equilibrium in the new configuration. It has more states available, and hence its entropy ceiling has been raised. This seems to me a valid argument. Where has Davies (and Tegmark) gone wrnog?

The problem would seem to be with Davies' analogy. If you expand a container containing gas at equilibrium, the temperature will drop and the entropy will rise, but this is because you have extracted heat from the system. Moving the walls outwards means that molecules that bounce off the walls will recoil with lower velocity -- transferring energy from the gas to the outside world. This does not happen in the expanding universe. The gas cools, but energy is not conserved in the expansion -- it does not go anywhere. There is no reservoir at a lower temperature to act as a sink, and there is no change in entropy. With no change in entropy, the gas does not cease to be at equilibrium if it were initially so, and there is no change in the number of available states. This is a peculiarity of GR since energy is not globally conserved in an expanding universe.

I think Prof Davies' point is that expansion magnifies any existing inhomogeneities, at least if the expansion is faster than the relaxation time of the medium.

However you haven't addressed Max Tegmark's point, that the number of quantum states available inside a given volume is proportional to the volume, hence expansion allows more quantum states to exist.

    Second, we get the thermodynamic AoT without expansion.

    In standard BB cosmology, the expansion cools the initial very hot
    state. But it is not necessary to start with a hot BB to get an AoT.
    We could image some different mechanism of cosmogenesis whereby the
    initial state was a relatively thin cool gruel of hydrogen and a few
    other bits. Something like in the current model when the universe is
    a few million years old. Imagine it started in that state, but with
    no further expansion. We would still get gravitational collapse
    around local inhomogeneities, galaxies and stars would form. Planets
    and occasionally life would arise. All within a thermodynamic AoT.
    In other words, we could get to exactly where we are no without any
    expansion at all. So expansion cannot be a necessary prerequisite
    for an AoT.


You're invoking graviation to create the AOT. I am explicitly trying to explain the AOT without invoking gravitation - obviously the universe has to be smooth, this is what else can occur on top of that.

Gravity is one of the laws of physics. The AoT occurs within physics, so why not use gravity to explain what happens? The problems arise -- as I have tried to point out -- when you ignore gravity. Cosmogenesis is, after all, the quintessential GR/gravitational problem.

Well, space-time starts out smooth to a very good approximation, so you can look at the behaviour of matter within it to explain at least some features of the AOT. You haven't yet addressed the formation of nuclei and other bound states and why that would make no contribution to the AOT, to the best of my knowledge (I asked for a short simple reply because I don't have time to wade through huge responses - which is why I also trim anything irrelevant from my posts).

Also, the presence of hydrogen in the above is unexplained, but you need something like atoms for the 2nd law to operate. It doesn't operate inside a q-g plasma at equilibrium at several trillion degrees, for example. Hence you need to create those little bundles of negative entropy, so to speak, before you have something on which the statistics of the 2nd law can operate.


    You have to beware of making contingent facts into apparent logical
    necessities.

I will resist making any similarly patronising and irrelevant comments.

The comment is apposite. It is neither patronizing nor irrelevant.

No. You are partonisingly assuming I don't already know about the possibility of making contingent facts into logical connections (not necessities). Even if you have shown that there is no logical connection, which isn't apparent to me (at present, at least), this still reduces to a merely ad hominem remark.

 

[John Clark]

On Wed, Nov 12, 2014 at 6:35 PM, LizR <liz...@gmail.com> wrote:

> the number of quantum states available inside a given volume is proportional to the volume

Although it's counter intuitive the maximum number of quantum states you can put inside a sphere is actually proportional to the sphere's area not its volume. Yet another aspect of the weird quantum world.

  John K Clark

 

[LizR]

Well, yes, I knew someone would mention that when I typed it! And yes, I agree, the Beckenstein bound implies that - although isn't that dealing with information, rather than quantum states (leaving aside any it-from-bitness, at least) ? Or maybe the two are equivalent.

I'm not sure how (or if) Max got around that one when he did his calculation of the distance of the nearest duplicate, but given that the answer came out as something like 10 ^ 10 ^ 28 metres, that makes the surface area to volume ratio awfully low for any sphere enclosing both...

 

Max also calculates the distance to the nearest identical 100-lightyear sphere and nearest identical Hubble volume, and it looks to me as though he's assuming 3D space operates as Euclidean geometry would predict. To be exact, he says that  

These are extremely conservative estimates, derived simply by counting all possible quantum states that a Hubble volume can have if it is no hotter than 10^8 kelvins. One way to do the calculation is to ask how many protons could be packed into a Hubble volume at that temperature. The answer is 10^118 protons. Each of those particles may or may not, in fact, be present, which makes for 2^10^118 possible arrangements of protons. A box containing that many Hubble volumes exhausts all the possibilities. 

FYI the article is here

 

http://space.mit.edu/home/tegmark/PDF/multiverse_sciam.pdf

[LizR]

I've emailed Max to ask him how he gets out of this one (though not in exactly those words) so I am hoping to be elucidated.

[Bruce Kellett]

Whatever the merits of that argument, it has little to do with the
maximum possible entropy. Rember, that occurs when all of the
mass/energy is in the form of black holes.

Bruce

[LizR]

On 13 November 2014 17:42, Bruce Kellett <bhke...@optusnet.com.au> wrote:

Whatever the merits of that argument, it has little to do with the maximum possible entropy. Rember, that occurs when all of the mass/energy is in the form of black holes.

We're a long way from that situation. In order to explain the AOT as it applies to the matter and energy that make up most of the universe, we need to explain how it comes to be arranged as it does, in arrangements that we are far from thermodynamic equilibrium. (And any situation that raises the maximum entropy available for matter and energy in terms of possible configurations is therefore relevant, regardless of whether it affects the theoretical maximum involving black holes.)

[Bruce Kellett]

LizR wrote:
> On 13 November 2014 11:29, Bruce Kellett <bhke...@optusnet.com.au

The expansion would make existing inhomogeneities extend further,
certainly. I doubt that it does much more

> However you haven't addressed Max Tegmark's point, that the number of
> quantum states available inside a given volume is proportional to the
> volume, hence expansion allows more quantum states to exist.

Entropy is given by the number of states in phase space. Phase space
does not expand -- I refer you again to Penrose's argument.

However, all this is somewhat beside the point since any entropy bound,
whether it increases or not, is very far from saturation. Until you
thermalize the gravitational degrees of freedom, entropy will always be
almost infinitely below any supposed maximum.

> Gravity is one of the laws of physics. The AoT occurs within
> physics, so why not use gravity to explain what happens? The
> problems arise -- as I have tried to point out -- when you ignore
> gravity. Cosmogenesis is, after all, the quintessential
> GR/gravitational problem.
>
> Well, space-time starts out smooth to a very good approximation, so you
> can look at the behaviour of matter within it to explain at least some
> features of the AOT. You haven't yet addressed the formation of nuclei
> and other bound states and why that would make no contribution to the
> AOT, to the best of my knowledge (I asked for a short simple reply
> because I don't have time to wade through huge responses - which is why
> I also trim anything irrelevant from my posts).

I did answer your question earlier. I am sorry if my answer was too long
and complicated for you to be bothered reading it.

> The comment is apposite. It is neither patronizing nor irrelevant.
>
> No. You are partonisingly assuming I don't already know about the
> possibility of making contingent facts into logical connections (not
> necessities). Even if you have shown that there is no logical
> connection, which isn't apparent to me (at present, at least), this

> still reduces to a merely /ad hominem/ remark.

I was merely pointing out a logical error. That is neither patronizing
nor ad hominem.

Bruce