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Brian Gaff
Feb 13, 2013, 10:32:26 AM2/13/13
to
Now if this stuff actually exists in such abundance how does it not muck up
all the calculations of trajectories of the many spacecraft sent out into
the suburbs of our solar system. One would have thought that if it was
there, it would in effect change the laws of gravity to some extent even
relatively locally.
So maybe these are artefacts of what other forces are out there, or maybe
part of gravity that only shows up when you are in a relatively weak field.
Brian
--
>From the Bed of Brian Gaff.
The email is valid as bri...@blueyonder.co.uk
Blind user.
all the calculations of trajectories of the many spacecraft sent out into
the suburbs of our solar system. One would have thought that if it was
there, it would in effect change the laws of gravity to some extent even
relatively locally.
So maybe these are artefacts of what other forces are out there, or maybe
part of gravity that only shows up when you are in a relatively weak field.
Brian
--
>From the Bed of Brian Gaff.
The email is valid as bri...@blueyonder.co.uk
Blind user.
David Spain
Feb 13, 2013, 7:23:13 PM2/13/13
to
On 2/13/2013 10:32 AM, Brian Gaff wrote:
> Now if this stuff actually exists in such abundance how does it not muck up
> all the calculations of trajectories of the many spacecraft sent out into
> the suburbs of our solar system. One would have thought that if it was
> there, it would in effect change the laws of gravity to some extent even
> relatively locally.
> So maybe these are artefacts of what other forces are out there, or maybe
> part of gravity that only shows up when you are in a relatively weak field.
> Brian
>
Well simple. Because 'Dark Matter' doesn't exist!
> Now if this stuff actually exists in such abundance how does it not muck up
> all the calculations of trajectories of the many spacecraft sent out into
> the suburbs of our solar system. One would have thought that if it was
> there, it would in effect change the laws of gravity to some extent even
> relatively locally.
> So maybe these are artefacts of what other forces are out there, or maybe
> part of gravity that only shows up when you are in a relatively weak field.
> Brian
>
:-) IMHO. Dark Matter is like the 'Luminiferous Aether' of two centuries
back. A crutch we are currently leaning on because we don't really
understand Gravity. Much like Classical Newtonian theory had issues
explaining phenom. being discovered by the late 19th century:
> http://en.wikipedia.org/wiki/Luminiferous_aether
'Dark Energy' IMHO ought to by synonymous with non-zero ground state
vacuum energy. Just we can't prove it yet nor do we know how. But we do
know the Universe is expanding at an accelerating rate. Something has to
be driving that expansion. In lieu of a quantum explanation we slap the
label 'Dark Energy' on it.
But to your point, both of these phenomena at local distances are
extremely weak forces. Much much much weaker than even the weakest
'practical' force, gravity. They will not be seen 'relatively locally'
and can be safely ignored when calculating things like spacecraft
trajectories, as we have seen now for over 5 decades.
Dave
David Spain
Feb 14, 2013, 6:08:28 PM2/14/13
to
On 2/13/2013 7:23 PM, David Spain wrote:
> On 2/13/2013 10:32 AM, Brian Gaff wrote:
>> Now if this stuff actually exists in such abundance how does it not
>> muck up
>> all the calculations of trajectories of the many spacecraft sent out into
>> the suburbs of our solar system. One would have thought that if it was
>> there, it would in effect change the laws of gravity to some extent even
>> relatively locally.
[snip]
> On 2/13/2013 10:32 AM, Brian Gaff wrote:
>> Now if this stuff actually exists in such abundance how does it not
>> muck up
>> all the calculations of trajectories of the many spacecraft sent out into
>> the suburbs of our solar system. One would have thought that if it was
>> there, it would in effect change the laws of gravity to some extent even
>> relatively locally.
>
> Well simple. Because 'Dark Matter' doesn't exist!
>
> :-) IMHO. Dark Matter is like the 'Luminiferous Aether' of two centuries
> back. A crutch we are currently leaning on because we don't really
> understand Gravity. Much like Classical Newtonian theory had issues
> explaining phenom. being discovered by the late 19th century:
>
>> http://en.wikipedia.org/wiki/Luminiferous_aether
>
And now, just today, the similarities have becoming blatant and
> Well simple. Because 'Dark Matter' doesn't exist!
>
> :-) IMHO. Dark Matter is like the 'Luminiferous Aether' of two centuries
> back. A crutch we are currently leaning on because we don't really
> understand Gravity. Much like Classical Newtonian theory had issues
> explaining phenom. being discovered by the late 19th century:
>
>> http://en.wikipedia.org/wiki/Luminiferous_aether
>
ludicrously striking! C'mon folks am I the only one that sees the irony
of it all?
> http://www.sciencenews.org/view/feature/id/347258/description/Light_in_the_Dark
Put these two article links up in two windows of your browser,
side-by-side, to maximize hilarity...
Dave
Steve Willner
Feb 15, 2013, 4:31:51 PM2/15/13
to
In article <8rOdnWYIANmHK4bM...@giganews.com>,
matter, in chronological order, is 1) galaxy cluster velocity
dispersions, 2) spiral galaxy rotation curves, 3) cosmic microwave
background fluctuations, and 4) gravitational lensing. I won't swear
this list is complete.
Of course it's conceivable that there's something wholly different
going on that explains all of these, but if so, no one has thought of
it yet.
> But we do know the Universe is expanding at an accelerating
> rate. Something has to be driving that expansion. In lieu of a
> quantum explanation we slap the label 'Dark Energy' on it.
Exactly right except that "know" ought to be qualified by the
standard disclaimer that everything in science is tentative and can
change if new evidence is found. Also 'quantum' should deleted.
There's no reason dark energy can't have a quantum explanation.
> 'Dark Energy' IMHO ought to by synonymous with non-zero ground state
> vacuum energy.
That's perhaps the leading explanation for a cosmological constant,
which is perhaps the leading candidate for dark energy. The trouble
is that a simple estimate for how big this effect should be gives a
value that is >100 orders of magnitude (!) too large. One view is
that there is some cancellation that is almost but not quite
complete, and the cosmological constant is the tiny leftover bit.
Another view is that the whole idea of cosmological constant being
vacuum energy is wrong. The only thing clear at the moment is that
there is not enough evidence.
--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA
David Spain <nos...@127.0.0.1> writes:
> Dark Matter is like the 'Luminiferous Aether' of two centuries
> back.
Are you confusing Dark Matter with Dark Energy? Evidence for dark
> Dark Matter is like the 'Luminiferous Aether' of two centuries
> back.
matter, in chronological order, is 1) galaxy cluster velocity
dispersions, 2) spiral galaxy rotation curves, 3) cosmic microwave
background fluctuations, and 4) gravitational lensing. I won't swear
this list is complete.
Of course it's conceivable that there's something wholly different
going on that explains all of these, but if so, no one has thought of
it yet.
> But we do know the Universe is expanding at an accelerating
> rate. Something has to be driving that expansion. In lieu of a
> quantum explanation we slap the label 'Dark Energy' on it.
standard disclaimer that everything in science is tentative and can
change if new evidence is found. Also 'quantum' should deleted.
There's no reason dark energy can't have a quantum explanation.
> 'Dark Energy' IMHO ought to by synonymous with non-zero ground state
> vacuum energy.
which is perhaps the leading candidate for dark energy. The trouble
is that a simple estimate for how big this effect should be gives a
value that is >100 orders of magnitude (!) too large. One view is
that there is some cancellation that is almost but not quite
complete, and the cosmological constant is the tiny leftover bit.
Another view is that the whole idea of cosmological constant being
vacuum energy is wrong. The only thing clear at the moment is that
there is not enough evidence.
--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA
David Spain
Feb 19, 2013, 12:59:17 PM2/19/13
to
On 2/15/2013 4:31 PM, Steve Willner wrote:
> In article <8rOdnWYIANmHK4bM...@giganews.com>,
> David Spain <nos...@127.0.0.1> writes:
>> Dark Matter is like the 'Luminiferous Aether' of two centuries
>> back.
>
> Are you confusing Dark Matter with Dark Energy?
No I believe the theoretical underpinning for Dark Energy is much
> In article <8rOdnWYIANmHK4bM...@giganews.com>,
> David Spain <nos...@127.0.0.1> writes:
>> Dark Matter is like the 'Luminiferous Aether' of two centuries
>> back.
>
> Are you confusing Dark Matter with Dark Energy?
stronger than that for Dark Matter. The two are combined here because
that was the topic of the OP. In fact in much of the media the two are
often discussed interchangeably, as if somehow the concept of 'dark'
unites the two. But in fact, 'dark' only implies our lack of
understanding. The two are describing very different phenomena.
> Evidence for dark
> matter, in chronological order, is 1) galaxy cluster velocity
> dispersions, 2) spiral galaxy rotation curves, 3) cosmic microwave
> background fluctuations, and 4) gravitational lensing. I won't swear
> this list is complete.
>
Gravitation, not necessarily evidence for the existence of "Dark Matter"
at least as currently envisioned through WIMPs.
My biggest problem with WIMPs is how does this theory jibe with Black
Hole formation? Or the theory that determines the size of an Event
Horizon? When Black Hole theory was devised there was no concept of Dark
Matter (I'll abbrev. as DM from here on). Hence it is not taken into
account in the theory. But if something like 23-24% of all mass in the
universe is DM why hasn't this led to Black Hole inflation? Why doesn't
the current theory have to be revised to take WIMPs into account? Surely
WIMPs don't escape the notice of a Black Hole?
> Of course it's conceivable that there's something wholly different
> going on that explains all of these, but if so, no one has thought of
> it yet.
>
this work will gain momentum as the newer round of experiments trying to
pull DM out into the open... fail.... Steve, how's that for risk taking?
I'm trying to figure out a criteria for establishing a bet with you that
involves Dim Sum at Mary Chung's...
>> But we do know the Universe is expanding at an accelerating
>> rate. Something has to be driving that expansion. In lieu of a
>> quantum explanation we slap the label 'Dark Energy' on it.
>
> Exactly right except that "know" ought to be qualified by the
> standard disclaimer that everything in science is tentative and can
> change if new evidence is found. Also 'quantum' should deleted.
> There's no reason dark energy can't have a quantum explanation.
>
quantum explanation...
>> 'Dark Energy' IMHO ought to by synonymous with non-zero ground state
>> vacuum energy.
>
> That's perhaps the leading explanation for a cosmological constant,
> which is perhaps the leading candidate for dark energy. The trouble
> is that a simple estimate for how big this effect should be gives a
> value that is >100 orders of magnitude (!) too large. One view is
> that there is some cancellation that is almost but not quite
> complete, and the cosmological constant is the tiny leftover bit.
> Another view is that the whole idea of cosmological constant being
> vacuum energy is wrong. The only thing clear at the moment is that
> there is not enough evidence.
>
And now, naturally, I discover the AAAS just finished up their annual
meeting in Boston this weekend, which I totally missed. Steve were you
able to attend any of the sessions? And if you did, did you note
anything remarkable in this area?
For example, I just read this today:
> http://www.bbc.co.uk/news/science-environment-21499765
Dave
Steve Willner
Feb 20, 2013, 4:10:49 PM2/20/13
to
SW> Evidence for dark matter
In article <rb2dnZjzuMcmIb7M...@giganews.com>,
(MOND) alternatives to GR. The idea seems to be to insert a scale
length and have gravity behave differently above and below that
length. Aside from having no theoretical motivation, the problem
seems to be that no single scale length explains all the phenomena
attributed to dark matter. That is to say, the idea is in principle
workable, but so far no specific formulation that fits the data in
one regime even comes close in other regimes. I think there's likely
to be the most severe problem with gravitational lensing; see the
Bullet Cluster for a dramatic example.
> at least as currently envisioned through WIMPs.
No one says dark matter has to be WIMPs. Those (at least in the
sense that the W refers to the weak interaction) are largely
motivated by particle physics. Specific examples can be searched for
(as is being done), but particles that interact _only_ by gravity
satisfy all the astronomical constraints.
> My biggest problem with WIMPs is how does this theory jibe with Black
> Hole formation?
What's the problem? The dark matter density is low, and the
accretion rate of dark matter onto black holes is tiny.
In article <rb2dnZjzuMcmIb7M...@giganews.com>,
David Spain <nos...@127.0.0.1> writes:
> I contend that this is evidence of our incomplete understanding of
> Gravitation, not necessarily evidence for the existence of "Dark Matter"
Possibly. People work on "Modifications of Newtonian Dynamics"
> I contend that this is evidence of our incomplete understanding of
> Gravitation, not necessarily evidence for the existence of "Dark Matter"
(MOND) alternatives to GR. The idea seems to be to insert a scale
length and have gravity behave differently above and below that
length. Aside from having no theoretical motivation, the problem
seems to be that no single scale length explains all the phenomena
attributed to dark matter. That is to say, the idea is in principle
workable, but so far no specific formulation that fits the data in
one regime even comes close in other regimes. I think there's likely
to be the most severe problem with gravitational lensing; see the
Bullet Cluster for a dramatic example.
> at least as currently envisioned through WIMPs.
sense that the W refers to the weak interaction) are largely
motivated by particle physics. Specific examples can be searched for
(as is being done), but particles that interact _only_ by gravity
satisfy all the astronomical constraints.
> My biggest problem with WIMPs is how does this theory jibe with Black
> Hole formation?
accretion rate of dark matter onto black holes is tiny.
Brian Gaff
Mar 3, 2013, 9:14:07 PM3/3/13
to
Hmm, itys a kind of placeholder then till we see what is really going on.
I wonder if these same forces are observable at the very small level, or
will be.
"David Spain" <nos...@127.0.0.1> wrote in message
news:8rOdnWYIANmHK4bM...@giganews.com...
I wonder if these same forces are observable at the very small level, or
will be.
"David Spain" <nos...@127.0.0.1> wrote in message
news:8rOdnWYIANmHK4bM...@giganews.com...
Brian Gaff
Mar 3, 2013, 9:14:26 PM3/3/13
to
Hmm, well, in a way we are inside the experiment and attempting to find out
if there is anything outside it that is affecting what goes on.
"Steve Willner" <wil...@cfa.harvard.edu> wrote in message
news:kfm96s$7it$1...@dont-email.me...
if there is anything outside it that is affecting what goes on.
"Steve Willner" <wil...@cfa.harvard.edu> wrote in message
news:kfm96s$7it$1...@dont-email.me...
cfl...@hotmail.com
May 2, 2013, 8:48:15 PM5/2/13
to
I haven't heard of Anyone addressing this: Is it possible that 'Dark Matter' and 'Dark Energy' are the same thing? In other words, both phenomenia have the same cause?
Bill Burton
May 5, 2013, 9:47:11 AM5/5/13
to
"> I haven't heard of Anyone addressing this: Is it possible that 'Dark
"> Matter' and 'Dark Energy' are the same thing? In other words, both
"> phenomenia have the same cause?
I would not think so. Take a look at what we do know about matter. as an example wood is matter it contains energy but to release that energy a chemical reaction has to take place. If we burn wood it releases heat energy and in doing so changes in to othe--
"> Matter' and 'Dark Energy' are the same thing? In other words, both
"> phenomenia have the same cause?
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David Spain
May 6, 2013, 11:57:17 AM5/6/13
to
On 5/2/2013 8:48 PM, cfl...@hotmail.com wrote:
> I haven't heard of Anyone addressing this: Is it possible that 'Dark Matter' and 'Dark Energy'
> are the same thing? In other words, both [phenomena] have the same cause?
> I haven't heard of Anyone addressing this: Is it possible that 'Dark Matter' and 'Dark Energy'
I haven't read or seen anything addressing this specifically.
It would be fascinating to discover that this were true. But it would
have to be some type of meta-theory, something akin to string theory,
that would try to explain them as different aspects of some other
fundamental process.
But for now, the only commonality between the two are the use of the
word "dark" as a substitute for the phrases "not well understood" & "not
easily observed".
As you may be aware, the two describe very different phenomena.
Dark Matter is an attempt to explain within conventional Gravitational
theory why Galaxy's hold together when there isn't enough "visible"
matter present to gravitationally bind the stars within them together.
Without the "Dark Matter" postulate galaxies should be unstable and
should spin apart.
Dark Energy is an attempt to explain why the Universe is expanding and
doing so at an increasing rate.
Another *very* simplistic way to look at it:
Dark Matter: pro-Gravity
Dark Energy: anti-Gravity
Personally I have grave reservations about the Dark Matter hypothesis.
There are some very peculiar properties about having a Universe full of
(25% thereof give or take) non-baryonic matter. Having it available as a
crutch to aid conventional theories of Gravitation holds our model of
Gravitation together (there's a pun in there somewhere) but it's a weak
crutch for a crumbling theory that hasn't been given much serious
conceptual consideration since the days of Newton. That's starting to
change. Google Roger Babson.
Dark Energy I don't have a problem with. I think it's fundamental to why
the 2nd Law of Thermodynamics is the way it is.
Dave
Steve Willner
May 7, 2013, 5:35:33 AM5/7/13
to
In article <q-qdnTOYI7xuTBrM...@giganews.com>,
> Without the "Dark Matter" postulate galaxies should be unstable and
> should spin apart.
Also galaxy clusters. And the power spectrum of microwave background
fluctuations would be different from what's observed. And there's
direct evidence of dark matter from gravitational lensing.
> Dark Energy is an attempt to explain why the Universe is expanding and
> doing so at an increasing rate.
Right: primarily the supernova distances but also CMB fluctuations
and baryon acoustic oscillations.
> ... a weak crutch for a crumbling theory that hasn't been given
attention if you look for it. There has been no lack of alternative
theories, by the way, but so far nothing but GR fits the data.
David Spain <nos...@127.0.0.1> writes:
> But for now, the only commonality between the two are the use of the
> word "dark" as a substitute for the phrases "not well understood" & "not
> easily observed".
>
> As you may be aware, the two describe very different phenomena.
Looks right to me.
> But for now, the only commonality between the two are the use of the
> word "dark" as a substitute for the phrases "not well understood" & "not
> easily observed".
>
> As you may be aware, the two describe very different phenomena.
> Without the "Dark Matter" postulate galaxies should be unstable and
> should spin apart.
fluctuations would be different from what's observed. And there's
direct evidence of dark matter from gravitational lensing.
> Dark Energy is an attempt to explain why the Universe is expanding and
> doing so at an increasing rate.
and baryon acoustic oscillations.
> ... a weak crutch for a crumbling theory that hasn't been given
> much serious conceptual consideration since the days of Newton.
General relativity? I think you will find ample experimental
attention if you look for it. There has been no lack of alternative
theories, by the way, but so far nothing but GR fits the data.
Bill Dugan
May 7, 2013, 5:35:55 AM5/7/13
to
post-Newton.
David Spain
May 28, 2013, 10:30:40 AM5/28/13
to
On 5/7/2013 5:35 AM, Steve Willner wrote:
>> ... a weak crutch for a crumbling theory that hasn't been given
>> much serious conceptual consideration since the days of Newton.
>
> General relativity? I think you will find ample experimental
> attention if you look for it. There has been no lack of alternative
> theories, by the way, but so far nothing but GR fits the data.
>
Sorry for the long delay in response. The day job has kept me pretty busy lately.
>> ... a weak crutch for a crumbling theory that hasn't been given
>> much serious conceptual consideration since the days of Newton.
>
> General relativity? I think you will find ample experimental
> attention if you look for it. There has been no lack of alternative
> theories, by the way, but so far nothing but GR fits the data.
>
I figured my posting would bring in a comment or two about Einstein.
I have no qualms with GR, but I prefer to think of it as more a theory dealing with effect rather than cause. It's of course the
accepted theory for the effects of gravity at the macroscopic scale. But has little to nothing to say about gravitation at the
microscopic (quantum) scale. Which is where we get to causation. Right now we have even a struggle to bring gravitation into the
Standard Model, which could do almost by itself w/o gravitation. But of course not a situation anyone really wants to accept. We
have a notion of "exchange" of "gravitons" from what I have read. But where are the "Gravity Waves" we should have discovered by now?
The need for CDM theory to explain why galaxy's hold together should be cause for concern. I think we have a whole lot of learning
ahead of us. We have the same reasons not to get complacent about our knowledge of Physics today as we did at the end of the
nineteenth century, when, after the discovery of Maxwell's equations (which I read recently are actually Oliver Heavisides'
restatement of Maxwell's work) physicist generally assumed that between Newton and Maxwell we pretty much understood all the
phenomenon of nature with just a little janitorial work remaining. Some clean-up effort since...
Dave
Steve Willner
May 30, 2013, 5:47:48 AM5/30/13
to
In article <d9idnbo5Yr9eHD7M...@giganews.com>,
ask are whether the theory fits the data (and how much data and how
well) and how many free parameters there are.
> [GR] has little to nothing to say about gravitation at the
> microscopic (quantum) scale.
Yes, there is no quantum theory of gravity, and GR is incorrect in
that sense. I think that's in the relativity FAQ; anyway it's no
surprise. But that's not relevant at cosmological scales.
> But where are the "Gravity Waves" we should have discovered by now?
Did you mean "gravitational waves?" Why do you say "should have
discovered by now?" What amplitude waves do you expect from what
sources, and how does that compare to detection sensitivity?
Gravitational waves have been detected indirectly via binary pulsar
timing, but you probably knew that.
> The need for CDM theory to explain why galaxy's hold together
> should be cause for concern.
I'm not sure what "cause for concern" means. People are working on
alternative theories, but so far none fits the data (at least not
without a lot of free parameters). Remember, galaxy rotation curves
are not the only phenomenon explained by dark matter. Either one
needs separate theories for all these, or one needs a theory that
explains them all in some way other than dark matter. So far, no
success.
David Spain <nos...@127.0.0.1> writes:
> I have no qualms with GR, but I prefer to think of it as more a
> theory dealing with effect rather than cause.
How does that differ from any other theory? The questions scientists
> I have no qualms with GR, but I prefer to think of it as more a
> theory dealing with effect rather than cause.
ask are whether the theory fits the data (and how much data and how
well) and how many free parameters there are.
> [GR] has little to nothing to say about gravitation at the
> microscopic (quantum) scale.
Yes, there is no quantum theory of gravity, and GR is incorrect in
that sense. I think that's in the relativity FAQ; anyway it's no
surprise. But that's not relevant at cosmological scales.
> But where are the "Gravity Waves" we should have discovered by now?
discovered by now?" What amplitude waves do you expect from what
sources, and how does that compare to detection sensitivity?
Gravitational waves have been detected indirectly via binary pulsar
timing, but you probably knew that.
> The need for CDM theory to explain why galaxy's hold together
> should be cause for concern.
alternative theories, but so far none fits the data (at least not
without a lot of free parameters). Remember, galaxy rotation curves
are not the only phenomenon explained by dark matter. Either one
needs separate theories for all these, or one needs a theory that
explains them all in some way other than dark matter. So far, no
success.
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