Why gravity makes macroscopic Schroedinger's cat impossible (was:
Jon J Thaler
>
>Two other answers:
>
>(1) The whole graviton idea is way off base, as is shown by minor
>inconsistencies like this. Gravity's not a field. It look nothing like a
>field, it acts nothing like it. There are no gravitons. It's warped
>spacetime
>and that's all it is!
If gravity is not subject to the rules of QM, then QM is wrong. It is
easy to show (via a Heisenberg microscope tpye argument) that the
uncertainty principle will be violated by the existence of *ANY* non-QM
phenomenon. This has nothing to do with the possible breakdown of QM
at the Planck length; it is strictly a long distance (ie, d >> planck)
argument, and it applies equally well to variations in the geometry
of spacetime.
>(2) Particles under the Planck mass do not gravitate (!) because their
>gravitational radii are lie under their Planck wavelength. Gravitation
>is a statistical property of ensembles much like temperature is. The
>spacetime
>continuum is likewise a 'statistical' approximation of an underlying
>discrete structure. Points don't exist. [...more stuff deleted...]
It's fun to speculate, but there is neither evidence nor need for any
new theory to explain how the graviton gets out of a black hole, any more
than a new theory is required to explain how the photon gets out of an
electrically charged black hole. Any force which is mediated by a massless
particle will be observable outside.
Samuel Joseph Pullara
DOCTORJ> In article <11...@uwm.edu>, ma...@csd4.csd.uwm.edu (Mark William Hopkins) says:
>(2) Particles under the Planck mass do not gravitate (!) because
>their gravitational radii are lie under their Planck wavelength.
>Gravitation is a statistical property of ensembles much like
>temperature is. The spacetime continuum is likewise a 'statistical'
>approximation of an underlying discrete structure. Points don't
>exist. [...more stuff deleted...]
DOCTORJ> It's fun to speculate, but there is neither evidence nor need for any
DOCTORJ> new theory to explain how the graviton gets out of a black hole, any more
DOCTORJ> than a new theory is required to explain how the photon gets out of an
DOCTORJ> electrically charged black hole. Any force which is mediated by a massless
DOCTORJ> particle will be observable outside.
This is the way I view the problem of gravitons actually exiting a
black hole. It seams rather obvious to me, gravitons that transmit
forces are virtual just like the photons that transmit the
electromagnetic force and the mesons that transmit the weak force and
the gluons that trasmit the strong force. They cannot be observed
because they are using virtual energy to propagate, and they are not
affected by other virtual gravitons because they are just that,
virtual. Therefore, gravitons should be able to exit a black hole.
This is just my opinion and I can't back it up with any tool other
than logic, so if there is a flaw in that please point it out.
--
/------------------------------------------------------------------------\
| Sam Pullara, Undergraduate Physics Worcester Polytechnic Institute |
| ave...@wpi.wpi.edu (c) 1990 Avenger Publications |
|______________-All my opinions were expressed or implied.-______________|
Christopher Neufeld
>This is the way I view the problem of gravitons actually exiting a
>black hole. It seams rather obvious to me, gravitons that transmit
>forces are virtual just like the photons that transmit the
>electromagnetic force and the mesons that transmit the weak force and
>the gluons that trasmit the strong force.
>
bosons, which are not mesons.
A pre-QCD theory of strong interactions used pions (pi mesons) as the
dominant force-mediating particle between nucleons, and that model is
still useful in some situations, though the gluon model is probably the
more "correct" representation of reality.
>| Sam Pullara, Undergraduate Physics Worcester Polytechnic Institute |
>| ave...@wpi.wpi.edu (c) 1990 Avenger Publications |
--
Christopher Neufeld....Just a graduate student | Flash: morning star seen
neu...@aurora.physics.utoronto.ca Ad astra! | in evening! Baffled
cneufeld@{pnet91,pro-cco}.cts.com | astronomers: "could mean
"Don't edit reality for the sake of simplicity" | second coming of Elvis!"
John Price
> A pre-QCD theory of strong interactions used pions (pi mesons) as the
>dominant force-mediating particle between nucleons, and that model is
>still useful in some situations, though the gluon model is probably the
>more "correct" representation of reality.
Well, yes, but...
Actually, they aren't just using pions anymore. Rhos, omegas, and
etas are also being used these days to describe interactions in
intermediate-energy physics.
Also, many observations in nuclei are incompatible with gluon
transfer - a nucleus looks like several colorless balls (i.e. nucleons)
interacting via meson exchange.
---------------------------------------------------------------------------
John Price | Internet: pr...@uclapp.physics.ucla.edu
5-145 Knudsen Hall | BITNET: price@uclaph
UCLA Dept. of Physics | SPAN: uclapp::price
Los Angeles, CA 90024-1547 | YellNet: 213-825-2259
---------------------------------------------------------------------------
Where there is no solution, there is no problem.
Kevin Dooley
pr...@uclapp.physics.ucla.edu (John Price) writes:
> Also, many observations in nuclei are incompatible with gluon
> transfer - a nucleus looks like several colorless balls (i.e. nucleons)
> interacting via meson exchange.
>
This is not true. The nucleus DOES look like several colorless blobs
which are weakly bound, but this fact says nothing about the mediating
particles of the force. While it is also true that there is meson
exchange among the nucleons, it has been shown in quark model calculations
that one can get a fairly good deuteron from Born order gluon exchange
(followed by quark rearrangement to restore color singlet nucleons) plus
pi exchange. I believe that the reason that people so fervently believe
in meson exchange as the sole source of the nuclear potential is the
choice to expand that potential in Yukawa terms rather than, say Gaussians.
It is, of course, possible to expand in any basis you like, but just
because you choose to do so in a basis which has dimensionful quantities
such as masses doesn't mean that there is anything physical about these
masses. In short, the nuclear potential looks like it is the result
of meson exchange, but that is because of how it has been written and
not necessarily because that is the underlying physics.
Kevin Dooley
Dept. of Physics, Univ. of Tennessee, Univ. of Toronto (don't ask)
doo...@utkux1.utk.edu
John Price
>In article <00947250...@uclapp.physics.ucla.edu>,
>pr...@uclapp.physics.ucla.edu (John Price) writes:
>> Also, many observations in nuclei are incompatible with gluon
>> transfer - a nucleus looks like several colorless balls (i.e. nucleons)
>> interacting via meson exchange.
>This is not true. The nucleus DOES look like several colorless blobs
>which are weakly bound, but this fact says nothing about the mediating
>particles of the force.
Well, yes, it does. If the blobs are colorless, then the particles
that mediate the forces must be colorless as well. At least, the *net*
color transfer must be zero.
>While it is also true that there is meson
>exchange among the nucleons, it has been shown in quark model calculations
>that one can get a fairly good deuteron from Born order gluon exchange
>(followed by quark rearrangement to restore color singlet nucleons) plus
>pi exchange. I believe that the reason that people so fervently believe
>in meson exchange as the sole source of the nuclear potential is the
>choice to expand that potential in Yukawa terms rather than, say Gaussians.
I always thought that the reason we still used meson exchange was
that it still seemed to work better than gluon exchange (in this energy
regime). Once the theories advance to the point where we understand the
quark model well enough to predict things better than (or at least as well
as) meson exchange theories, people will start using them more.
>In short, the nuclear potential looks like it is the result
>of meson exchange, but that is because of how it has been written and
>not necessarily because that is the underlying physics.
Fair enough. However, until we *do* understand the underlying
physics, we still need to be able to predict things. Although there are at
least aesthetic problems with meson exchange theory, it still works better
than gluon exchange (again, in this energy regime).
Kevin Dooley
|> In article <1991Apr15....@cs.utk.edu>, doo...@utkux1.utk.edu (Kevin Dooley) writes:
|> > The nucleus DOES look like several colorless blobs
|> >which are weakly bound, but this fact says nothing about the mediating
|> >particles of the force.
|>
|> Well, yes, it does. If the blobs are colorless, then the particles
|> that mediate the forces must be colorless as well. At least, the *net*
|> color transfer must be zero.
The situation is similar to the way uncharged atoms attract in a molecule
via electromagnetic Van der Waals interactions. The VdW force is a dipole-
dipole interaction so it isn't exactly the same, but you get the idea. In
the nuclear case a color octet gluon is exchanged between two quarks of
different nucleons which renders both nucleons color octets themselves.
They can quickly be returned to color singlets by both giving each other
a quark. So net color transfer is zero, but it happens in two steps.
|> > I believe that the reason that people so fervently believe
|> >in meson exchange as the sole source of the nuclear potential is the
|> >choice to expand that potential in Yukawa terms rather than, say Gaussians.
|>
|> I always thought that the reason we still used meson exchange was
|> that it still seemed to work better than gluon exchange (in this energy
|> regime). Once the theories advance to the point where we understand the
|> quark model well enough to predict things better than (or at least as well
|> as) meson exchange theories, people will start using them more.
This is an important distinction. People have spent a great deal of time
and effort adjusting the parameters of the well known nuclear potential
models so that they fit the data very well. It is only in the past few
years that quark modellers have even attempted to rough out a deuteron
from more fundamental principles. (The 'interface' between nuclear and
particle physics is a pretty hot topic these days.) If you want accuracy,
use the model which fits the data better. This doesn't mean that it is more
correct, just more accurate.
|>
|> >In short, the nuclear potential looks like it is the result
|> >of meson exchange, but that is because of how it has been written and
|> >not necessarily because that is the underlying physics.
|>
|> Fair enough. However, until we *do* understand the underlying
|> physics, we still need to be able to predict things. Although there are at
|> least aesthetic problems with meson exchange theory, it still works better
|> than gluon exchange (again, in this energy regime).
|>
Agreed. By the way, it has been nice to see somebody talking seriously
about actual physics on this net instead of Schrodinger's cat and relativity
misunderstandings. Keep up the good work!
|> ---------------------------------------------------------------------------
|> John Price | Internet: pr...@uclapp.physics.ucla.edu
|> 5-145 Knudsen Hall | BITNET: price@uclaph
|> UCLA Dept. of Physics | SPAN: uclapp::price
|> Los Angeles, CA 90024-1547 | YellNet: 213-825-2259
|> ---------------------------------------------------------------------------
|> Where there is no solution, there is no problem.
--
Sverker Johansson
>
>>(2) Particles under the Planck mass do not gravitate (!) because their
>>gravitational radii are lie under their Planck wavelength. Gravitation
>>is a statistical property of ensembles much like temperature is. The
>>spacetime
>>continuum is likewise a 'statistical' approximation of an underlying
Elementary particle DO gravitate. The gravitational force on electrons
was measured by Witteborn and Fairbank some years ago (I don't have
the reference handy.) There is an experiment in progress at CERN,
Switzerland, to measure the gravitation of _anti_matter, and check
if it really has the same sign as matter gravitation. (Oakley et al,
exp. LEAR/GRAV PS200).
All the particles involved in these experiments have masses several
orders of magnitude below the Planck mass. Nevertheless they gravitate
just like everything else. Even if you talk about ensembles, it wouldn't
surprise me if the _total_ mass of particles in the detector
at any one time is smaller than the Planck mass. (The measurement could
in principle be done with a single antiproton at a time.)
Sverker Johansson
l...@quark.lu.se ql...@selund.BITNET l...@cernvm.cern.ch l...@cernvm.BITNET
Mark William Hopkins
>Elementary particle DO gravitate. The gravitational force on electrons
>was measured by Witteborn and Fairbank some years ago ...
To prove electrons gravitatate, you have to prove there's a gravitational
force FROM electrons.
The word gravitate meant "originates a gravitational force/field" in the quoted
reference where it says "particles under the Planck mass do not gravitate".
Is "from" what you meant?
Van Snyder
be a black hole?
--
vsn...@jato.Jpl.Nasa.Gov
ames!elroy!jato!vsnyder
vsn...@jato.uucp
Troy E Daniels
with other particles. This is not true. If the virtual particle (VP) doesn't
interact with something, it will exist forever! The VP MUST interact with
the particle that created it, or with another particle that it transmits a
force to. Along the way, it can interact with other particles, real or virtual, also. Such an example would be
| |
| /\ |
| / \ |
|~~~~~\ /~~~~|
| \/ |
| ~ |
| ~ |
| ~ |
| /\ |
| / \ |
|~~~~~\ /~~~~|
| \/ |
where the solid lines represent charged (anti-)fermions, and the ~'s are
virtual photons. I will admit that this is a very high-order process,
but virtual particles do interact with each other.
Troy Daniels +--------------------------------------------------+
| H H AA V V EEEE AA DDD AA Y Y o o |
dan...@mitlns.mit.edu | HHH AAAA V V EE AAAA D DD AAAA Y . |
tdan...@athena.mit.edu | H H A A V EEEE A A DDD A A Y --- |
------------------------+--------------------------------------------------+
Sverker Johansson
I thought gravitate could equally well mean "to be affected by gravitation".
But then, English is not my native language, so I'll check my dictionary:
"TO gravitate: 1) to move under the influence of gravity, 2) to be influenced
or drawn 3) to sink or settle" ( Collins English Dictionary ) Anyway, if
I misunderstood the original poster's special use of it, I apologize.
But see also below.
>
>Is "from" what you meant?
If Newton's third law holds, then it doesn't make a difference.
The force with which the Earth pulls an electron has to be equal
to the force with which the electron pulls the Earth.
And Newton's third law (or conservation of momentum in general)
has been verified to high precision for other interactions of
elementary particles, so there's no reason to expect it doesn't
hold for gravity. Anyway, if momentum is _not_ conserved, then
the current physics paradigm as a whole is in serious trouble.
If I recall undergrad quantum mechanics correctly, then
spatial invariance of physical laws ==> momentum conservation.
But of course, in one sense you are right. What has actually been
_measured_ is how elementary particles are affected
by the gravitational field of the Earth. (I.e. verifying that
antiprotons fall downwards like everything else.) To measure the
gravitational field of a single proton is a bit tricky...
Mark William Hopkins
>Is "from" what you meant?
In article <1991Apr22.1...@lth.se> l...@quark.lu.se (Sverker Johansson) writes:
(All kinds of diversions)
>To measure the gravitational field of a single proton is a bit tricky...
Next time, just answer the question...
To read this, you're saying no. Nobody's ever seen a gravitational field for
a proton or any other elementary particle.
Matt Crawford
) >Elementary particle DO gravitate. The gravitational force on electrons
) ^^
) >was measured by Witteborn and Fairbank some years ago ...
Mark William Hopkins:
) To prove electrons gravitatate, you have to prove there's a gravitational
) force FROM electrons.
Maybe Hopkins doesn't realize what he's suggesting.
If the earth's gravity pulls the electrons, but the electrons exert
no graviational force on the earth, we can all kiss conservation of
momentum goodbye.
________________________________________________________
Matt Crawford ma...@oddjob.uchicago.edu
Charles Poirier
>) Sverker Johansson:
>) >Elementary particle DO gravitate. The gravitational force on electrons
>) ^^
>) >was measured by Witteborn and Fairbank some years ago ...
>
>Mark William Hopkins:
>) To prove electrons gravitatate, you have to prove there's a gravitational
>) force FROM electrons.
>
>Maybe Hopkins doesn't realize what he's suggesting.
Maybe Crawford doesn't realize what Mr. Hopkins is asking. One instance of
the question might be "Do electrons affect each other via gravity?"
>If the earth's gravity pulls the electrons, but the electrons exert
>no graviational force on the earth, we can all kiss conservation of
>momentum goodbye.
If a magnet and a non-magnetized ferromagnetic object attract each other,
then all non-magnetized ferromagnetic objects have to attract each other?
Think again. Something can be *affected* by a force which it does not
itself generate. Conservation of momentum is irrelevant to the question.
Perhaps gravitational force (of electrons on the earth) is induced into
electrons *by* the earth, much as magnetic attraction is induced into
otherwise inert iron. Perhaps gravitation isn't strictly a force. I sure
don't know the answer, but I don't care much for Crawford's argument.
Cheers,
Charles Poirier poi...@dg-rtp.dg.com
Warren G. Anderson
>In article <1991Apr24.1...@midway.uchicago.edu> ma...@group-w.uchicago.edu (Matt Crawford) writes:
>>
>>Maybe Hopkins doesn't realize what he's suggesting.
>
>Maybe Crawford doesn't realize what Mr. Hopkins is asking. One instance of
>the question might be "Do electrons affect each other via gravity?"
>
>>If the earth's gravity pulls the electrons, but the electrons exert
>>no graviational force on the earth, we can all kiss conservation of
>>momentum goodbye.
>
>If a magnet and a non-magnetized ferromagnetic object attract each other,
>then all non-magnetized ferromagnetic objects have to attract each other?
Maybe Matt didn't understand it in this context, but I doubt he would
have considered it any more likely, at least, I don't. Magnets induce
a magnetic moment in ferromagnetic materials. That is because magnetic
dipoles are possible (in fact, possibly th only form of magnetic
"charge"). Gravity, as we have come to understand it, couples to mass,
specifically, if relativity is true, to inertial mass (thus the relation
to conservation of momentum). If the earth is inducing a mass dipole in
an otherwise "neutral" mass electron, then one can safely conclude that
there must be some sort of "negative" mass, an antigravitating type of
mass, if you will.
Perhaps negative mass does not bother you. But if it exists, we can
chuck most of our modern theories. Conservation of energy would also
be violated (I believe), as would conservation of momentum, and we
would have very little to start over with.
Grant R. Davis
have the same gravitational pull as a live one? :-)
Charles Poirier
>In article <1991Apr25....@dg-rtp.dg.com> poi...@ellerbe.rtp.dg.com (Charles Poirier) writes:
>>In article <1991Apr24.1...@midway.uchicago.edu> ma...@group-w.uchicago.edu (Matt Crawford) writes:
>>
>>>If the earth's gravity pulls the electrons, but the electrons exert
>>>no graviational force on the earth, we can all kiss conservation of
>>>momentum goodbye.
>>
>>If a magnet and a non-magnetized ferromagnetic object attract each other,
>>then all non-magnetized ferromagnetic objects have to attract each other?
>
>a magnetic moment in ferromagnetic materials. That is because magnetic
>dipoles are possible (in fact, possibly th only form of magnetic
>"charge").
I meant to make an analogy bearing on the form of the argument. I was
certainly not implying that a hypothetical induced gravitational attraction
would have to use the same mechanism for the "induction" as do magnets.
>Gravity, as we have come to understand it,
This is exactly the problem though. We have not come to understand it.
>couples to mass,
My question was not "what does gravity couple to", but "what generates the
coupling" in the first place. Aren't they different questions?
>specifically, if relativity is true, to inertial mass (thus the relation
>to conservation of momentum). If the earth is inducing a mass dipole in
>an otherwise "neutral" mass electron, then one can safely conclude that
>there must be some sort of "negative" mass, an antigravitating type of
>mass, if you will.
I'm glad someone feels safe. None of the physicists on the net can tell me
anything about the structure of the electron. I asked about the status of
electron spin, and got authoritative but diametrically opposed answers as to
whether it represents physical spin or just acts that way in certain
measurements.
Some years ago, I asked the net a similar question about whether photons
"generate" gravity, as distinct from just being affected by it. No one could
say for certain. To this day there is no concensus as to whether gravity
travels at light speed or some other speed. If gravity propagates no faster
than light, how could two photons passing by each other have a gravitational
interaction? Sorry, but I don't feel at all safe about any of this.
Anyway, I'm sorry to be so uncool as to raise questions without having a
pat answer all the time.
Cheers,
Charles Poirier poi...@dg-rtp.dg.com
Warren G. Anderson
>In article <1991Apr28.1...@watdragon.waterloo.edu> wgand...@violet.waterloo.edu (Warren G. Anderson) writes:
>>In article <1991Apr25....@dg-rtp.dg.com> poi...@ellerbe.rtp.dg.com (Charles Poirier) writes:
>>>
>>>If a magnet and a non-magnetized ferromagnetic object attract each other,
>>>then all non-magnetized ferromagnetic objects have to attract each other?
>>
>>Magnets induce
>>a magnetic moment in ferromagnetic materials. That is because magnetic
>>dipoles are possible (in fact, possibly th only form of magnetic
>>"charge").
>
>I meant to make an analogy bearing on the form of the argument. I was
>certainly not implying that a hypothetical induced gravitational attraction
>would have to use the same mechanism for the "induction" as do magnets.
Then what mechanism do you suppose it has? It doesn't matter.
Given that the equivalence principle holds, which we have observed to be
pretty much the case, then gravitational mass corresponds to inertial
mass. If an electron has no observed graviational mass, it would have
no observed inertial mass. Yet, put it in an electric field, and we
can see the field's energy and momentum decrease. Where is the energy
going? We could give up our conservation laws, but they are fairly
well extablished too. So, we have a choice. No equivalence principle,
no energy conservation, or electron gravitates. The last seems to
be the most experimentally viable, don't you think?
>>Gravity, as we have come to understand it,
>
>This is exactly the problem though. We have not come to understand it.
Why do you say that? We don't have perfect understanding, but we do know
some of the underlying principles.
>>couples to mass,
>
>My question was not "what does gravity couple to", but "what generates the
>coupling" in the first place. Aren't they different questions?
Your question was "why can't the earth induce gravitation in an electron
that produces no gravitational field of it's own". How is someone supposed
to answer that without bringing mass? If I had just said "gravity couples
to mass", I would understand your criticism. But that was just one step
in my answer, so why does it upset you?
>>specifically, if relativity is true, to inertial mass (thus the relation
>>to conservation of momentum). If the earth is inducing a mass dipole in
>>an otherwise "neutral" mass electron, then one can safely conclude that
>>there must be some sort of "negative" mass, an antigravitating type of
>>mass, if you will.
>
>I'm glad someone feels safe. None of the physicists on the net can tell me
>anything about the structure of the electron. I asked about the status of
>electron spin, and got authoritative but diametrically opposed answers as to
>whether it represents physical spin or just acts that way in certain
>measurements.
I'm not telling you anything about the structure of an electron. I am
simply saying that you can't have a dipole without positive and negative
charges, in this case, gravitating and "antigravitating" masses. As for
spin, I believe that it is generally accepted that the particle does
not produce it by simply rotating.
>Some years ago, I asked the net a similar question about whether photons
>"generate" gravity, as distinct from just being affected by it. No one could
>say for certain.
Then let me tell you that according to general relativity all energy
produces graviational effects, but I doubt this could be tested directly
for a single photon.
>To this day there is no concensus as to whether gravity
>travels at light speed or some other speed. If gravity propagates no faster
>than light, how could two photons passing by each other have a gravitational
>interaction? Sorry, but I don't feel at all safe about any of this.
It depends what you mean by gravity. The field (ie. curvature)? Gravitational
waves?
>Anyway, I'm sorry to be so uncool as to raise questions without having a
>pat answer all the time.
Actually, I find that an admirable quality. What I don't find admirable
is your not bothering to listen to and try to understand the answers.
Are you asking because you want to know, or because you enjoy challenging
people? If you want to know, then why don't you try to understand?
--
########################### _`|'_ #############################################
## Warren G. Anderson |o o| "It consists in noticing that he who can ##
## Dept. of Applied Math ( ^ ) do more can do less." J. Hadamard ##
## University of Waterloo /\-/\ (wgand...@violet.uwaterloo.ca) ##
Graeme Williams
>passing by each other have a gravitational interaction?
Hey! I like this little thought experiment. Here's another question:
Is there a soln. of Einstein's fld. eqns. which describes essentially
a single photon?? - or at least some massless light-like particle?
Graeme Williams
gcwi...@daisy.waterloo.edu
ecs...@lure.latrobe.edu.au
Schrodinger's cat has lots of high-valued quantum numbers.
These make for lots of "information" to be exchanged.
Electromagnetism (and maybe even gravity) has plenty of opportunity
to interact with the cat. I don't believe we can ever come close
to completely sealing the cat off from the "outside universe".
(Heat flow is a good example of something that we cannot cease
completely. That cat is going to be colder than it used to be,
if it dies.)
What's that box made of, any way?
How much interaction constitutes "measurement"?
If only machines measure an event, but we humans have not arrived
to check the dials, then has the measurement occurred?
(I say it has: it's WE who have not occurred. :-)
An electron has how much "state-information"? If it interacts via
a spin-1 field (eg, scatters a photon), then its angular momentum
"information" is grossly altered.
Yes, this is a low quantum number vs high quantum number argument.
And I think it makes sense. Not only a measurement, but any
interaction, makes a big difference to an electron. Why do we
allow our physical theories to be as anthropocentric as we are?
(I think the question answers itself.)
Now, let's look at classical Special Relativity for isolation arguments.
If two events are separated by a spacelike interval, then they cannot
know anything of each other. (This assumes the universe is not totally
deterministic, in which case there is no information anywhere, anytime;
and time as progress is an illusion. But noone acts on that belief,
do they? If that's not convincing, then compare the life expectancies
of fatalists who act on their convictions with those of the rest of the
population.)
So in SR, does either event exist? At either event, can it be said that
the other event exists? Yes, I know that if there is an event that is
later than both of them, then this event knows (something) of them both.
I know also that it is consistent to assume that unobserved parts of
space-time exist, and that to assume otherwise is to make a perhaps
messy model. Still, what does "exist" mean for events that have not
yet occurred?
Is this silly? Philosophically a side-issue? No. As scientists, most
of us accept that what we do changes the future. That's why we take
our role as theorists, designers, experimenters, and observers seriously.
We have therefore implicitly assumed that the future is indeterminate.
To put it boldly, the future is unreal. We ascribe reality to our
past and current measurements, however. So some events in space-time
are unreal; some are real; and which events are in which set depends
on the vantage point.
This is the common sense view. It adds something that's not in the laws
of motion, viz that the arrow of time is intrinsic. But it is simple,
we practise it, and it always works.
I hope I've been provocative enough.
Yours sincerely,
Geoffrey Tobin
ecs...@lure.latrobe.edu.au
ecs...@lure.latrobe.edu.au writes:
> To put it boldly, the future is unreal. We ascribe reality to our
> past and current measurements, however. So some events in space-time
> are unreal; some are real; and which events are in which set depends
> on the vantage point.
>
> This is the common sense view. It adds something that's not in the laws
> of motion, viz that the arrow of time is intrinsic.
Moreover, it's the preceding view that we are defending when we propose
that causality is obeyed.
Oh, I just noticed! By the above argument, causality => nonreality.
Geoffrey