Fine structure constant probably doesn't vary with direction in space!


by bcrowell
Tags: constant, direction, fine, space, structure, vary
VelocideX
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#109
Sep15-10, 07:44 PM
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Quote Quote by Jonathan Scott View Post
Consider for example the suggestion that gravitational collapse doesn't actually occur (for which there is some recent evidence) for some unknown reason. In that case, quasars could for example be huge star-like objects with an extremely intense magnetic field, rapid spin and an intrinsically redshifted luminous surface, as in the "MECO" model. That would mean that much of the redshift range, and hence most of the absorbing clouds, would be close to the quasar, and hence potentially affected by its intense magnetic field in a way which would increase with proximity to the quasar and hence with redshift.

Can we rule that out, or at least find some observational constraints on that possibility?
How do you explain the fact that the host galaxies of the quasar absorbers can be identified in many cases?
e.g. http://adsabs.harvard.edu/abs/2008A%26A...487..583B

Also, this does also does nothing to explain the Lyman-alpha forest -- the dense series of Lyman alpha transitions along the line of sight to the quasar which all occur below the Lyman alpha emission peak. High column density Lyman alpha absorbers have been identified with host galaxies at cosmological redshifts. Hydrodynamic Lambda-CDM simulations reproduce the observed statistical properties of the forest as far as I know. No-one takes the gravitational redshift explaination for quasar sources seriously anymore.
twofish-quant
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#110
Sep15-10, 07:47 PM
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Quote Quote by turbo-1 View Post
Don't say that too loudly. Intrinsic redshifts in quasars are the third rail of astronomy/cosmology. Any hint that two physically-associated astronomical bodies might have widely discordant redshifts will get you marginalized in short order.
That's funny because I don't recall anyone asking me to turn in my astrophysics card when we talk about this sort of stuff at lunch.

Suggesting that associated astronomical bodies *might* have discordant redshifts won't get you looked at funny. It's when you telling that the person you are talking to that they are an idiot and part of an evil conspiracy that will get you problems.
twofish-quant
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#111
Sep15-10, 07:50 PM
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Quote Quote by VelocideX View Post
No-one takes the gravitational redshift explaination for quasar sources seriously anymore.
Yup.

And one point that I'm trying to make here is that while "quasars are caused by gravitational redshift" is considered a nutty idea by people in the field, the idea that "the fine structure constant may be varying in space and time" isn't, and there are theoretical reasons why you are getting telescope time to look at this whereas as the gravitational redshift people aren't.
turbo
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Sep15-10, 07:52 PM
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Quote Quote by twofish-quant View Post
That's funny because I don't recall anyone asking me to turn in my astrophysics card when we talk about this sort of stuff at lunch.

Suggesting that associated astronomical bodies *might* have discordant redshifts won't get you looked at funny. It's when you telling that the person you are talking to that they are an idiot and part of an evil conspiracy that will get you problems.
What do you think of NGC 7603? Cosmic coincidence, chance projection, or a real viable example of 4 interacting astronomical bodies (excluding the bridge as an entity) having a wide range of redshifts.

My co-conspirators and I are taking baby-steps, studying redshift differentials in M-51 type galaxy associations. Getting published is easy. Getting people to think about the implications is a bit more problematic.
twofish-quant
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#113
Sep15-10, 08:04 PM
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Quote Quote by VelocideX View Post
Large scale electric fields cannot build up in the plasma; the electric field gradient would rapidly cause mixing of charges.

Magnetic fields in galaxy clusters typically have strength of ~ microGauss, which is roughly 9 orders of magnitude below the strength required to cause significant effects.
One other question. Have you tested your code to see what happens if you do have stray electric and magnetic fields? The general electric and magnetic field in the IGM might be microGauss, but if you have a large number of black holes and neutron stars in the cloud, you can easily get tesla level magnetic fields within the cloud.

Not to say this is a bad thing. Discovering that clouds are highly magnetized is as interesting as finding a varying alpha.
VelocideX
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#114
Sep15-10, 08:55 PM
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Quote Quote by twofish-quant View Post
One other question. Have you tested your code to see what happens if you do have stray electric and magnetic fields? The general electric and magnetic field in the IGM might be microGauss, but if you have a large number of black holes and neutron stars in the cloud, you can easily get tesla level magnetic fields within the cloud.
What would be the origin of large numbers of neutron stars and black holes in the IGM?
Old Smuggler
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#115
Sep15-10, 09:29 PM
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Quote Quote by twofish-quant View Post
But you can already. Look at the doppler shift with respect to CMB. If the difference in alpha is due to some big-bang field that is weakening over time, then I don't see any problems that are worse than the fact that the CMB creates a preferred reference frame.
It seems that I did not express myself clearly enough. What I had in mind, was a theory of varying
alpha in flat space-time. How do you construct such a theory compatible with SR? Even if you
could declare a preferred inertial frame in flat space-time, it would be arbitrary.
Quote Quote by twofish-quant View Post
Sure. The preferred reference frame of the CMB.
That is not a preferred frame in the sense we are discussing here.

A preferred frame could be part of the gravitational physics of some metric theory of gravity without
violating the EEP (but the SEP would be violated). In that case, the preferred frame cannot be
detected by doing local non-gravitational experiments. If it can, the the preferred frame must be part
of some flat space-time theory to fulfil the EEP.

Of course, according to GR, the frame of the CMB is preferred in neither way, it is just a frame where
a lot of stuff is at rest, on average.
Quote Quote by twofish-quant View Post
I'm still not seeing out a time shifting alpha is worse than dark energy. You could in principle measure the space time curvature that is caused by dark energy, and that is going to change over time.
That's part of the gravitational physics, and is consistent with GR with an exotic energy field as
source. A time-shifting alpha raises more fundamental problems.
Quote Quote by twofish-quant View Post
I still don't see how a time varying alpha field is worse than dark energy or anything else that is already in the standard model, and none of those is considered to break GR. One thing that should be pointed out is that in the 1960's these sorts of arguments were taken pretty seriously as reasons why the BB could not be correct. The BB creates a preferred reference frame.
A preferred frame that can be detected locally, by gravitational or non-gravitational experiments,
does indeed break GR.
Quote Quote by twofish-quant View Post
For example, you can come up with a theory in which dark energy creates some sort of shielding effect on electric charge and as the universe expands, changes in dark energy causes observable effects in alpha.
This seems too speculative for my taste. Anyway, the problem is also how alpha varies in vacuum.
Old Smuggler
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#116
Sep15-10, 10:14 PM
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Quote Quote by twofish-quant View Post
And if you attribute the change in time of alpha over time is due to the X-field, which you can set differently for different parts or space by increasing or decreasing the strength of the X-field.
But what does the variation of the X-field depend on? Is there a theory of the X-field in flat
space-time? It seems that all you have done, is to transfer the problems of varying alpha to the
X-field.
Quote Quote by twofish-quant View Post
If you view alpha as some fundamental property of the universe then I can see the issue, but most high energy physicists don't.
I am inclined to believe that the universe has some fundamental properties. The reason why alpha
does/does not vary might well be one of them. And I cannot really see that you have answered my
specific concerns regarding varying alpha. Note that I do not say that the idea of varying alpha is
"nutty" or something like that, I just claim that it is radical, and with no particular theoretical motivation
how to change the mainstream framework to implement it. To me, this seems to signify another dead end.
Quote Quote by twofish-quant View Post
Yes this sounds a lot like the return of ether, but so what? Among the theoretical cosmological community there isn't this idolatry of mathematical principles that you seem to think exists.
We seem to have very different philosophies how to do science. I prefer parsimonity combined
with a careful assessment of observational results. That is, any extra assumptions specifically made
to make observational results fit theory, is regarded with strong suspicion. Besides, I am well aware
that what is presented as observational "facts" may well depend crucially on theoretical assumptions
made when analyzing the data. Therefore it is important to analyze data within different frameworks.

Since our views do not seem to converge, I think it's just as well to stop here, and just agree to
disagree.
twofish-quant
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#117
Sep15-10, 10:39 PM
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Quote Quote by VelocideX View Post
What would be the origin of large numbers of neutron stars and black holes in the IGM?
You said yourself that the clouds were likely to be in the halo of galaxies. You have a self-gravitating cloud of hydrogen. It's likely that you will have massive star formation. In any case you know that there has had to have been some star formation in the clouds. Otherwise how did the Mg and Fe get there?

So what I'm proposing is that you have these clouds of Mg and Fe because they were undergoing massive star formation, and if that's the situation then you should have large numbers of black holes and neutron stars in the clouds.

I think it's going to be rather difficult for you to come up with a scenario in which you have strong Mg and Fe lines in which you don't have some neutron stars or black holes floating around somewhere from the supernova that produced those elements.

Also should I infer from the line of questioning that you haven't done an experiment to see if stray magnetic or electric fields will cause some effects mimicking a change in the fine structure constant? If you haven't or if you have and it turns out it does, then I think you should mention in the paper that you are assuming that the clouds don't have strong magnetic or electric fields in them.
twofish-quant
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#118
Sep15-10, 10:45 PM
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Quote Quote by Old Smuggler View Post
But what does the variation of the X-field depend on? Is there a theory of the X-field in flat
space-time? It seems that all you have done, is to transfer the problems of varying alpha to the X-field.
At that point we are in the world of string theory, and supersymmetry in which you can make up a dozen fields, and no one will mind.

We seem to have very different philosophies how to do science. I prefer parsimonity combined with a careful assessment of observational results. That is, any extra assumptions specifically made to make observational results fit theory, is regarded with strong suspicion.
Maybe it's because we are in different fields. The problem is that in my field (supernova research) parsimonity just doesn't work. There are about twenty different things happening and they all interact with each other.

When you are in the world of GR, you can get away with parsimonity, but that comes at the cost of ignoring much of the rest of the universe. Once you get out of the nice clean world of GR into the messy real work, then parsimonity just doesn't work.
VelocideX
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#119
Sep15-10, 11:50 PM
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Quote Quote by twofish-quant View Post
Also should I infer from the line of questioning that you haven't done an experiment to see if stray magnetic or electric fields will cause some effects mimicking a change in the fine structure constant? If you haven't or if you have and it turns out it does, then I think you should mention in the paper that you are assuming that the clouds don't have strong magnetic or electric fields in them.
Large scale electric fields have never been observed in astrophysics AFAIK. The issue of magnetic fields was dealt with in a 2001 paper on systematic effects and the statements made were uncontroversial then. The magnetic field strength in the strong absorbers has been inferred from Faraday rotation and is just too small.

As I noted earlier, our paper only has 4 pages. Even the long forthcoming paper doesn't describe everything in detail. All our current papers refer to the 2003 paper on systematics, which itself refers to the 2001 paper on systematics.
twofish-quant
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#120
Sep16-10, 01:58 AM
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Just for some more of the theory of what is going on....

There are not only papers on varying constants, there are also textbooks and conferences

http://www.amazon.com/Cosmology-Dime.../dp/1402011385

http://www.springerlink.com/content/e5ukm4rty3k93c28/

Also some papers

http://arxiv.org/PS_cache/hep-ph/pdf/0204/0204142v2.pdf

* Indeed, it is well known that in string theory any coupling constant is promoted to a vacuum expectation value (vev) of a scalar field such as the dilaton or some other modulus. If this scalar field is extremely light, m  10−33 eV, its expectation value could be still evolving in the recent past (or even today.)

Here is a very interesting paper "Questioning the Equivalence Principle"

http://arxiv.org/PS_cache/gr-qc/pdf/0109/0109063v1.pdf

* The Equivalence Principle (EP) is not one of the “universal” principles
of physics (like the Action Principle). It is a heuristic hypothesis
which was introduced by Einstein in 1907, and used by him to construct
his theory of General Relativity.

* An experimental “violation” of the EP would not at all shake the foundations of physics
(nor would it mean that Einstein’s theory is basically “wrong”). Such a violation
might simply mean that the gravitational interaction is more complex
than previously assumed, and contains, in addition to the basic Einsteinian
spin-2 interaction, the effect of another long-range field.

• String theory suggests the existence of new gravitational-strength
fields, notably scalar ones (“dilaton” or “moduli”), whose couplings
to matter violate the equivalence principle. These fields can induce a
spacetime variability of the coupling constants of physics (such as the
fine-structure constant).
Haelfix
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#121
Sep16-10, 02:16 AM
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Quote Quote by Old Smuggler View Post
But what does the variation of the X-field depend on? Is there a theory of the X-field in flat
space-time? It seems that all you have done, is to transfer the problems of varying alpha to the X-field.
The problem isn't introducing this field, indeed such things show up in HEP theories all the time, as Quant explained. The problem is explaining why it's natural.

If the field is massive and cosmological in origin, you expect that the physics that originated it occured sometime in the very early universe. The typical mass scale would be, say grand unification or Planck scales. The problem is that such a field would give totally negligable contributions in experimental searches in ordinary galactic physics, so that probably isnt what is responsible.

Really, what you need is a field that is massless or almost massless, and you want it to be very slowly varying (so that it doesn't produce completely ridiculous physics). Now if the field was massless or almost massless, you do run the risk of introducing new (real or apparent) long range forces that would *likely* start running afoul of solar system equivalence principle tests.

http://arxiv.org/abs/hep-ph/0111282

However there is a bit of a tightrope that you can walk in this sort of game, but typically it comes with steep phenomenological baggage and or arbitrary tweaking. All this is general, the additional problem faced with changing alpha, is to explain why the physics only targets this coupling constant and not the others. Prima facie, it requires a terribly adhoc and explicit symmetry breaking term but anyway I digress.

The point is, if the result is true (and I am skeptical of course given the dirty business and complications in measuring quasar spectral line's and controlling the possible systematics), it's goign to be rather unlovely to explain theoretically.
Jonathan Scott
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#122
Sep16-10, 03:00 AM
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Quote Quote by VelocideX View Post
How do you explain the fact that the host galaxies of the quasar absorbers can be identified in many cases?
e.g. http://adsabs.harvard.edu/abs/2008A%26A...487..583B

Also, this does also does nothing to explain the Lyman-alpha forest -- the dense series of Lyman alpha transitions along the line of sight to the quasar which all occur below the Lyman alpha emission peak. High column density Lyman alpha absorbers have been identified with host galaxies at cosmological redshifts. Hydrodynamic Lambda-CDM simulations reproduce the observed statistical properties of the forest as far as I know. No-one takes the gravitational redshift explaination for quasar sources seriously anymore.
Thanks for the reference. I think the suggestion is only that part of the redshift is intrinsic, by no means all of it, so identification of intervening host galaxies provides limits on the amount of intrinsic redshift, but does not rule it out.

Also, Arp's controversial observations have always indicated that quasars which appear to be closer to their "parent galaxy" have higher redshifts, which suggests that quasars lose their intrinsic redshift as they age and "mature" into new galactic cores.

From what I've heard (although I admit I don't have any references to hand), the Lyman-alpha forest is not actually uniform with redshift, so any explanation involves some sort of evolution, usually expressed as a power law, and I've heard that although the number density towards different objects of similar redshift is often statistically similar, there is a surprising amount of variation, and it is difficult to match up the varying densities consistently with different redshifts.
twofish-quant
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#123
Sep16-10, 03:24 AM
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Quote Quote by Jonathan Scott View Post
Thanks for the reference. I think the suggestion is only that part of the redshift is intrinsic, by no means all of it, so identification of intervening host galaxies provides limits on the amount of intrinsic redshift, but does not rule it out.
It's not inconceivable that quasars have some intrinsic redshift, but no one has suggested a mechanism that gives you redshifts that have anything close to the Hubble flow.

Also, Arp's controversial observations have always indicated that quasars which appear to be closer to their "parent galaxy" have higher redshifts, which suggests that quasars lose their intrinsic redshift as they age and "mature" into new galactic cores.
No one takes Arp's observations seriously now. As we've gotten better and better observations of quasars, Arp's ideas are taken less and less seriously.

From what I've heard (although I admit I don't have any references to hand), the Lyman-alpha forest is not actually uniform with redshift, so any explanation involves some sort of evolution, usually expressed as a power law
That's correct, but the problem for people that assert that quasars are not cosmological need to explain why there is a lyman alpha forest at all.
twofish-quant
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#124
Sep16-10, 03:32 AM
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One thing to remember is that I'm a theorist, so my job involves coming up with explanations. If you start seeing independent confirmations of varying alpha over the next year or two none of this matters, and you can collect your Nobel prize without worrying about any of this. (That's not sarcastic, if this observation holds, then someone will be in line for a Nobel.)

What I'm interested right now is imagining what the possibilities are if people continue to get null results.

Quote Quote by VelocideX View Post
Large scale electric fields have never been observed in astrophysics AFAIK.
Neither have time varying alphas until now. :-) :-)

The issue of magnetic fields was dealt with in a 2001 paper on systematic effects and the statements made were uncontroversial then. The magnetic field strength in the strong absorbers has been inferred from Faraday rotation and is just too small.
I'll look at the 2001 paper, but something to realize is that people in doing Faraday studies have been looking at microgauss strengths, and if the light goes through a reason of tens of gauss oriented in random directions, the likely outcome is that any preexisting polarization is going to get lost, and so what you'll see is something unpolarized.
cristo
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#125
Sep16-10, 04:48 AM
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This thread has strayed too far from the PF rules of allowing discussion on only published, peer-reviewed articles. Thus, I'm locking this thread now. This topic can be reopened when the paper is published.


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