|Jun29-04, 03:06 PM||#1|
Are these guys high?
hey, i was reading about "variable light speed" theories by Joćo Magueijo and John Moffat
Is there any meat to these theories? that light goes through various "phase changes" as the universe expands? They claim that their theories do away with all the inflation, dark matter, etc. needed to explain the flatness and horizon problems and all that.
I realize that these guys have been around for many years, so what's wrong with their theories?
|Jun29-04, 03:28 PM||#2|
Looks like just another shot in the dark. Recent studies [see link] have further confirmed Lorentizian invariance; which puts the constancy of c [and Einstein] on pretty solid footing.
|Jun29-04, 03:50 PM||#3|
from what i understood of their premise: light has one speed now
it also had one speed back when, but that speed was higher
it's changed through various phase changes over the lifetime of the universe
other things have to give in order for this to happen
i guess i just don't know if that still "breaks Lorentzian invariance"
it says: "The evidence is currently slim -- redshift dependence in the atomic fine structure, anomalies with ultra high energy cosmic rays, and (to a much lesser extent) the acceleration of the universe and the WMAP data."
This sounds like they are trying to squeeze the VSL theory into current theory, but it looks like the originators were attempting to provide alternatives to inflation (acc. of the U) and used their theory to explain things like the CMB. I just don't know enough about it, i guess.
says: "Scientists have hoped to find Lorentz invariance violations by studying gamma-rays coming from the farthest reaches of the visible universe, where the quantum foam of space may act to slow light traveling to us for billions of years.
Stecker looked much closer to home to find that Lorentz invariance is not being violated. He analyzed gamma-rays from two relatively nearby galaxies about half a billion light-years away with supermassive black holes at their centers, named Mkn 421 and Mkn 501."
He didn't look far enough back in time. He was supposed to look at quasars. From what I read, it was weird data from quasars that started the whole VSL thing. The light wasn't being absorbed at the right wavelength or something light that, and one of thwo things had to be the cause. Either there was once a difference charge on the electron or that there was a different speed of light.
As a side: What happened to the "anthropic principle" where all these physical constants (mass of p, charge of e, speed of light) must be perfectly tuned or the whole universe is unstable.
|Jun29-04, 04:09 PM||#4|
Are these guys high?
Blinne cites as authority a paper of Stecker (astro-ph/0308214) which is based on a paper of Lee Smolin (stecker's reference )
stecker does not support what either you say or what Blinne says
Stecker says "for a more extensive discussion" of various quantum gravity theories some of which have LIV and others not, see  which is Smolin's 2003 paper "How far are we from the quantum theory of gravity".
Stecker just confirms what smolin says which is that earlier theories that had one type of Lorenz violation with a preferred frame are pretty much ruled out. Smolin pointed to the evidence and said that explicitly.
Stecker is saying SOME theories, which Smolin already ruled out, are ruled out. Not much new but he adds more certainty. The more current and prevalent theories with VSL are not excluded.
Some of Stecker's language is a bit broad and sweeping, you just have to look at whose analysis he depends on and look at what Smolin actually said.
We had a thread here at PF earlier about the relevant portion of the Smolin 2003 article. Other people had the same impression and referred to the same Stecker 2003 paper.
since 2003 there has been a fair amount of new stuff
It does not violate LI in the sense of having a preferred frame but it
refines or tweaks it---the sym. group is modified.
Stecker's paper and suchlike is not relevant to this
Shrumeo may be referring to this recent work---I dont know what his links refer to but if they are recent they probably do.
Personally I dont know what to think about theories with variable speed of light. I am beginning to suspect it would be unwise to rule them out even if they seem bizarre and incomprehensible to me now.
|Jun29-04, 04:32 PM||#5|
there are two VSL topics going
one, i guess Shrumeo is talking about, is the historical change in c
and every time I see something about that it is being ruled out more and more stringently
I am not up on this but my sense is that the amount of change in c over time has been observationally restricted down to almost nothing
I dont like to give advice but I would be inclined to just forget about
the talk (which has been dying down) about historical change in c'
or in the fine structure constant for that matter
But there is more excitement about the variability of the speed of light that appears in certain newer theories that is not historical
but depends on energy
all the light we are familiar with is low energy light and it goes c or indististinguishable from c
but in these new theories some extremely high energy light, gamma rays, could go slightly faster----but you could not detect it until the light had traveled several billion LY.
You have to give the faster photons a long long time before their slight additional speed allows them to move noticeably ahead of the others
Nereid knows about this. It is why we were talking in earlier PF threads about the GLAST satellite due to go up around 2007. It will detect gamma ray bursts and has some chance of detecting this energy-dependence in the speed photons travel which has been proposed.
It sounds bizarre and I must say I dont like the sound of it, but more and more people are getting involved with this or with related hypothetical modifications of the basic theories----things observable only over astronomical distances at astronomical (gammaray) energies.
|Jun29-04, 06:22 PM||#6|
There are some things that may effect the invariance of the speed of light and/or the frequency of light. Some of them are pretty basic.
For instance: we reference the speed of light to its speed in a vacuum, not in other media. We know, however, that "the vacuum" is a sea of virtual particles, and that if space has expanded so greatly since the Big Bang, "the vacuum" was once a lot more dense than it is today. What was the speed of light in that denser medium, and did the speed of light increase as the medium became more diffuse (as the universe expanded)?
|Jun29-04, 06:28 PM||#7|
yeah, i never understood the expansion of space conceptually.
plainly speaking does MORE vacuum get put in between 2 points, or
does the vacuum become "stretched" and is now "more diffuse"
( i know it's weird to talk about vacuum as if it were a gas or something)
i guess this would come out of the geometry of it all (?)
I don't know if i can find it again, but i'll try to find the webpage that discussed the observations that lead Moffet to think about the variable speed of light.
|Jun29-04, 06:47 PM||#8|
well, i couldn't find the exact page where I first saw it, but here is something else:
Monthly Notices of the Royal Astronomical Society
Volume 327 Issue 4 Page 1208 - November 2001
Possible evidence for a variable fine-structure constant from QSO absorption lines: motivations, analysis and results
M.T. Murphy1 J.K. Webb1 V.V. Flambaum1 V.A. Dzuba1 C.W. Churchill2 J.X. Prochaska3 J.D. Barrow4 A.M. Wolfe5
An experimental search for variation in the fundamental coupling constants is strongly motivated by modern high-energy physics theories. Comparison of quasar (QSO) absorption-line spectra with laboratory spectra provides a sensitive probe for variability of the fine-structure constant, a, over cosmological time-scales. We have previously developed and applied a new method providing an order-of-magnitude gain in precision over previous optical astrophysical constraints. Here we extend that work by including new quasar spectra of damped Lyman-a absorption systems. We also reanalyse our previous lower-redshift data and confirm our initial results. The constraints on come from simultaneous fitting of absorption lines of subsets of the following species: Mg i, Mg ii, Al ii, Al iii, Si ii, Cr ii, Fe ii, Ni ii and Zn ii. We present a detailed description of our methods and results based on an analysis of 49 quasar absorption systems (towards 28 QSOs) covering the redshift range 0.5 < z < 3.5. There is statistical evidence for a smaller a at earlier epochs: [delta] a/ a = (-0.72 ± 0.18) x 10^-5.
The new and original samples are independent but separately yield consistent and significant non-zero values of [delta] a/ a. We summarize the results of a thorough investigation of systematic effects published in a companion paper. The value we quote above is the raw value, not corrected for any of these systematic effects. The only significant systematic effects so far identified, if removed from our data, would lead to a more significant deviation of
Ok, so it's not c it's a (which depends on both e and c). I'll keep digging for that other webpage.
|Jun29-04, 06:47 PM||#9|
One of the reasons for a VSL came about via longstanding cosmological data which did not match any of our ,then 'current' observations, a good example is the fine-structure-constant. The consensus of opinion by some of the field leaders across most disciplines was that:
1) The accepted viewpoint of how the Universe came to be was totally inaccurate, therefore most of physics understanding was really nothing more than a stab in the dark?
2)Either the Speed of Light in the distant past was different, or the Electron was Different.
I believe Webb .J is one of the founder Cosmologists who through observational data asked the awkward questions around mid-nineties.
|Jun29-04, 07:36 PM||#10|
Here is a nice layman's description of various VSL theories:
I was forbidden to download the pdf, but Google could give it to me in html.
I like the part that says that despite the various approaches taken to VSL, the value of the earlier light speed comes out to about the same (really fast).
Then it talks about some guy using some aether theory to derive Planck's black body spectrum from Maxwell's eqs. and bases the speed of light on the background temperature. (Well, if it works, it works.)
But about page 12-13, it starts talking about the "evidence" from quasar absorption spectra.
I'm not quite sure what to make of the "Doubly Special Relativity" section.
|Jun29-04, 07:58 PM||#11|
if it is, click on PDF and you should be able to get it
|Jun29-04, 08:20 PM||#12|
it is not an up-to-date exposition of DSR and is also too brief and not very clear
but DSR is IMHO the only part of it worth following up on
the rest of the paper is about mid-1990s speculation that you could dispense with inflation scenarios by jiggling c
but inflation scenarios are now pretty well entrenched and that attempt to replace them with VSL----historical variation in c----never caught on.
however DSR is the energy-dependent variation in photon speed I was talking about
it has changed from what Giov. AmelinoCamelia proposed (and that paper talks about) so probably better not read that paper but something more representative of current work----the idea is
that c is the constant low energy limit of photon speed
and almost all the light we can detect is lowenough energy so it goes at a speed that is c or indistinguishable from it
but very high energy gamma rays from some major catastrophe like a star collapse or "hypernova" socalled might exhibit enough extra speed to be detectable after traveling a very long ways
it is a prediction that comes out of several models of quantum gravity
there is a current bunch of papers about it and a growing interest in it
and it gives the experimenters, or observational astronomy people, something to look for---they like to have theories to test and either shoot down or confirm
so DSR (and a new one called TSR, for "triply special") bears watching
one of the TSR things may have a potential for explaining the dark energy business, but it is still very preliminary and iffy, dont believe but stay alert
|Jun29-04, 09:22 PM||#13|
Energy dependent variation in light speed is predicted by quantum loop gravity theory. Smolin and Markopoulou Kalamara have published a couple articles regarding this in Scientific American
|Jun30-04, 01:07 AM||#14|
thanks for the link to the pdf!
I also liked te column on LQG, pretty cool.
|Jun30-04, 01:18 AM||#15|
Amazing stuff comes out of quantum loop theory. I admit being drawn by the concept. String theory is still very much alive and produces similar predictions, but, not having to submit to all those annoying extra dimensions holds a lot more appeal to me.
|Jun30-04, 01:39 AM||#16|
Blog Entries: 4
Magueijo even pokes fun at himself pondering if perhaps he should not yet give up his day job.
|Jun30-04, 02:14 AM||#17|
Quantum fluctuations in the physical constants [c, g, e] must be incorporated into any TOE i can imagine. Is 'c' invariant over time? I doubt that. I also doubt that any physical constants, fine structure or otherwise, are invariant by any measure. This is the same as saying that 'c' is no more a constant than any other 'yardstick' you care to apply. Problem is, we have no better measure to date. The other problem is referential. If c' cannot be trusted, what can? Every other measure in current theory rests upon the concept that 'c' is the ultimate authority. If you change the 'coupling constant' implied by 'c', you unravel the fabric of reality. Preferred reference frames [i.e., Lorentzian relativity] solve some of the problems, but, create others that do not match observation. Perhaps we have only defined our observational limits. Perhaps the universe is only confined by our perceptional limitations.
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