Critique of Mainstream Cosmology


by Garth
Tags: cosmology, critique, mainstream
turbo
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#37
Oct17-07, 07:57 AM
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Redshift is fundamental, and perhaps is in need of epistemological treatment. Hubble never bought into the notion that redshift had to arise from recessional velocity, despite the often-repeated statements that he "discovered" universal expansion. That view was promoted by physicists (Eddington, Le Maitre, De Sitter, etc) as opposed to observational astronomers. Fritz Zwicky's view of redshift was that of "tired light" - light that has lost energy while on its journey to our detectors. This idea has been out of favor for a long time, although it may make a resurgence. Several years ago, Fotini Markopoulou of the Perimeter Institute posited that light must lose energy through its interaction with the space through which it propagates. She reasoned that light of short wavelength must interact more frequently with space than light of longer wavelengths, and its arrival time would therefor be delayed. She speculated that GLAST would demonstrate this by observing a gap between the arrival times of gamma rays and longer-wavelength EM. As it stands presently, the MAGIC consortium may have trumped GLAST by recording a delay of about 4 minutes in the arrival times of high-energy EM. This result needs to be confirmed and duplicated with other observations. If indeed similar delays are observed in high-energy bursts from other sources, and the delays prove to be proportional to the redshifts of the sources, "tired light" may once again join the lexicon.
Garth
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#38
Oct17-07, 08:40 AM
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The general observation of cosmological red-shift serves to confirm the expanding universe model and is therefore not a candidate for discussion in this Thread.

If there are any specific red-shift observations that question the standard [itex]\Lambda[/itex]CDM model, such as high red-shift objects that appear older than the universe at that red-shift, then they would be appropriate to discuss here.

Opinions of how the observed red shift may be interpreted will make a valid discussion in another thread. Unless there is a published theory that makes such an interpretation, and the Jordan Frame of Self Creation Cosmology would be one example of such, claims for alternative interpretations will have to continue on the Independent Research Forum, of course after observing their Rules for Submission.

It is not up to me, but I would think it all right to pose intelligently framed questions about the standard model in this Forum, but in another thread please.

BTW turbo-1 I have already given one explanation for the 4-minute delay in post #6 of this thread.

Garth
turbo
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#39
Oct17-07, 09:19 AM
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So noted, Garth. Additional observations are required, as I said, and as you said it may turn out that there is a mundane explanation for the observed delay. There are some rather stringent requirements that must be met for the MAGIC result to stand, including the correlation of frequency-dependent delay and the redshift of the source.

As for high-redshift objects that appear too old to be viable at their redshifts, one only need refer to the papers of Fan, Strauss, et al of the SDSS consortium. They have discovered quasars at redshifts up to ~6.5, and if the quasars are truly at the distances implied by a standard interpretation of their redshifts, they would have to be comprised of BHs of perhaps 10 billion solar masses, residing in host galaxies of about a trillion solar masses. In addition, these quasars show no evolution in their absolute metallicities or relative metallicities, despite the fact that the various metals comprising them are thought to arise through processes that are currently believed to be time-dependent. As Strauss notes, theorists have not been able to explain how such massive, highly-metallized objects could have formed only a few hundred million years after the BB. His presentation to the STSCI is the 6th on this page. It is very informative, and I highly recommend watching it if you have the bandwidth to stream it, or can download it overnight.

http://www.stsci.edu/institute/itsd/...oquiaFall2005/
Garth
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#40
Oct17-07, 11:18 AM
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Indeed, unambiguous observations of high red-shift SMBH's could bring into question the expansion history of the standard model.

One of Michael Strauss (Princeton) conclusions from the SDSS survey: Active Galaxies at Low and High Redshift: Type II Quasars, Reionization, and Other Insights from the Sloan Digital Sky Survey
The highest red-shift quasars have luminosities in excess of 1013 solar luminosities.
These are around z > 6 when the universe was less than 1Gyr old.

Theorists of the standard model have their work cut out to explain the formation of the large BHs required to power such quasars at those early times. For example: SDSS J1148+5251: a hyperluminous high metallicity galaxy, in the early universe
SDSS J1148+5251 is a distant quasar at z=6.42. It is a nearly solar metallicity
hyper-luminous IR galaxy, in the early universe. It challenges our understanding of dust
formation in extreme environments ⇒ how could such a high mass of dust have formed in
only a few 100 Myr ?

Garth
Chronos
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Oct18-07, 12:45 AM
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More data, less theory is suggested. While existing data is not irrefutable, the odds increasingly disfavor Arpian interpretations.
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Oct18-07, 01:20 AM
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I wasn't suggesting Aarp, just a modification to R(t) at high z.

Is it possible the standard model equation of state for (DE + matter) is incorrect?

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jonmtkisco
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#43
Oct18-07, 07:55 PM
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Hi folks,

The best critique of mainstream cosmology I've read is "Endless Universe: Beyond the Big Bang" by Paul J. Steinhardt and Neil Turok. It was published at the end of May this year. Steinhardt was one of the pioneers who helped shape current inflation theory.

The authors of this book rip current inflation theory into many tiny pieces. They think it is full of inconsistencies and unjustified assumptions. Their alternative theory involving the "M Theory" and branes leaves me cold, because I have no basis to know whether it makes any sense at all. It sounds a bit goofy to me. They say that further analysis of the WMAP CMB data may clearly identify whether their theory is more likely than inflation. With the WMAP data released so far (including the May installment) they consider it to be a temporary tie. In any event, it is thrilling to see mainstream inflation theory demolished in a very logical manner by insiders.

Can there be any such thing as "accepted mainstream cosmology" when the best minds in the discipline disagree with each other so strenuously? If inflation ultimately is invalidated as a theory, cosmology will have a lot of backpedaling to do. But of course it's too early to tell, and a great many cosmologists undoubtedly think these authors are barking up the wrong tree.

Jon
SpaceTiger
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#44
Oct18-07, 09:50 PM
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Quote Quote by jonmtkisco View Post
Can there be any such thing as "accepted mainstream cosmology" when the best minds in the discipline disagree with each other so strenuously? If inflation ultimately is invalidated as a theory, cosmology will have a lot of backpedaling to do.
Not really. The reason inflation is still so controversial is that it's so hard to test experimentally -- inflationary models can explain almost anything. If it turned out that Steinhardt's theory was right, it would would be of little consequence to most cosmologists because both theories predict the same thing in the regimes they're concerned with. LCDM itself doesn't actually rely on inflation.
Garth
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Oct19-07, 01:22 AM
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Quote Quote by SpaceTiger View Post
LCDM itself doesn't actually rely on inflation.
S.T. I am mystified by this statement.

Is not Inflation necessary to resolve the density, smoothness and horizon problems of the decelerating universe in that early stage of the [itex]\Lambda[/itex]CDM model?

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oldman
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Oct19-07, 02:09 AM
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Quote Quote by SpaceTiger View Post
Not really......LCDM itself doesn't actually rely on
inflation.
Quote Quote by Garth
This thread is not the place to discuss a multitude of speculative ideas, rather it is intended as a discussion of observations that may raise questions about the consensus
If the LCDM consensus is so limited as to not necessarily include infation, as Space Tiger seems to imply in the above quote, then the observation that opposite sides of the sky are similar falls back into the category of observations to be discussed here. Perhaps you should clarify the intended purpose of this thread, Garth, before it runs away.
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Oct19-07, 02:23 AM
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As I have said this thread is to discuss observations that may call the standard [itex]\Lambda[/itex]CDM model into question.

As far as the horizon problem is concerned, arising from the observation that "opposite sides of the sky are similar", I await S.T.'s answer to my question about his statement.

To my way of thinking you are right, if Inflation is not part of the standard [itex]\Lambda[/itex]CDM model then that observation would question that model.

The horizon problem arises because in a decelerating universe, disparate parts of the present sky would have been beyond their mutual casual horizons in the earliest stages of the BB. The standard [itex]\Lambda[/itex]CDM is decelerating for most of its expansion history, DE acceleration only 'kicking' in since z ~ 1 or so.

Garth
SpaceTiger
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#48
Oct19-07, 03:02 AM
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Quote Quote by Garth View Post
Is not Inflation necessary to resolve the density, smoothness and horizon problems of the decelerating universe in that early stage of the [itex]\Lambda[/itex]CDM model?
Yes and no. Yes, these are conceptual problems with the mainstream cosmological model that are not resolved without inflation. However, inflation is primarily a tack-on. What I normally understand to be [itex]\Lambda CDM[/itex] (and this is merely a matter of convention) is the general relativistic model of the expansion that occurs after the end of the inflationary period. This is the part that most observational projects rely on and this is the part that has been tested to the most precision. All we need for the majority of cosmological studies is to know that the universe is flat and that the initial power spectrum of perturbations is nearly scale-invariant. The theory that explains these facts is irrelevant for most purposes.

I'm not sure to what extent the community separates inflation and LCDM, but my point is that it's an easy separation to make. Disproving inflation does not invalidate the work of people working outside of inflationary theory. By contrast, if it were found, for example, that the interpretation of redshift as expansion were incorrect, then there would have to be major revision of almost everything cosmological from the last 30 or 40 years.
SpaceTiger
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#49
Oct19-07, 03:07 AM
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Quote Quote by Garth View Post
As far as the horizon problem is concerned, arising from the observation that "opposite sides of the sky are similar", I await S.T.'s answer to my question about his statement.

To my way of thinking you are right, if Inflation is not part of the standard [itex]\Lambda[/itex]CDM model then that observation would question that model.
It's not clear to me why. If LCDM is not claiming to explain the origin of fluctuations, why would a problem concerning the initial distribution of those fluctuations bring it into question?
SpaceTiger
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Oct19-07, 03:16 AM
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Quote Quote by oldman View Post
If the LCDM consensus is so limited as to not necessarily include infation, as Space Tiger seems to imply in the above quote, then the observation that opposite sides of the sky are similar falls back into the category of observations to be discussed here. Perhaps you should clarify the intended purpose of this thread, Garth, before it runs away.
Actually, I think questioning inflation is an excellent choice of topic for this thread, as the theory seems to have settled into the mainstream without being rigorously tested. It certainly isn't inconsistent with the observations so far, but things like the flatness problem, the horizon problem, the monopole problem, etc. should not be considered evidence (IMO) because the theory was designed to solve those problems.
Garth
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Oct19-07, 12:27 PM
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Quote Quote by SpaceTiger View Post
It's not clear to me why. If LCDM is not claiming to explain the origin of fluctuations, why would a problem concerning the initial distribution of those fluctuations bring it into question?
In GR, a decelerating universe raises a series of questions: the horizon problem (why are opposite sides of the sky similar when they are casually unconnected?), the smoothness problem (Why are the fluctuations ~ 10-5 just right to produce a universe with large scale structure and galaxies etc. yet not too great so all matter clumps together in a few hyper-massive BHs?), the density problem (Why is [itex]\Omega_{total}[/itex] ~ 1?), which can only be answered by special pleading - i.e. by setting specific initial conditions that can perhaps only be explained by Anthropic reasoning.

Another answer is of course that the universe may not have been decelerating over most of its history. [Apart from the Inflation era: 10-35 sec to 10-33 sec, according to the mainstream model the universe has been decelerating from the Planck era t = 10-43 sec to t > 10+17 sec, when DE acceleration kicked in. The present age t ~ 4 x10+17 sec.]

The monopole problem is different in that it arises from the GUT, which predicts magnetic monopoles should be plentiful and detectable. A lack of their detection therefore requires an explanation, such as Inflation, which would have diluted their density to undetectable levels.

Another explanation is of course that the GUT is wrong and they never existed in the first place.

Inflation resolves these problems by injecting massive expansion at that early yet post-Planck era stage, which more than counteracts the effects of the subsequent deceleration. Without it the standard model has some explaining to do.

One resolution would be to have an unorthodox equation of state for DE in order to have an extended era of acceleration, i.e. a kind of 'smeared out' inflation, or indeed a strictly linear expansion , but that is definitely 'non-standard'!

Garth
jonmtkisco
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#52
Oct19-07, 05:13 PM
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Garth,

Your concerns are valid if you take Steinhardt & Turok's critique of inflation alone. But of course the authors go beyond that and propose a replacement theory. They are very confident that their replacement theory has an answer for the issues that inflation was supposed to solve. Their concept is that the universe is cyclical -- it repeats a cycle every few trillion years where it expands, contracts, and then expands again. During the lengthy expansion phase, they say that flatness and homogeneity are achieved to a high degree, and are preserved through the subsequent collapse phase. They don't need to solve the magnetic monopole problem because their contraction phase never gets hot enough to go through the GUT phase transition. They don't have a horizon problem because the universe is already at thermal equilibrium when it starts expanding. They also claim to almost exactly match the perturbations in the CMB.

But I don't see why their critique of inflation can't be considered separately from their replacement theory. They clearly do not believe that inflation is a solid theory. So even if their replacement theory is disproved, that doesn't necessarily mean that they would put inflation back on its former pedestal.
Garth
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Oct19-07, 05:44 PM
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One advantage of the inflation theory is that is has been derived within a GR 'environment, and GR has definitely been tested locally (but note the caveats I have raised earlier in this thread).

When extrapolated to cosmological regimes problems may arise with GR but the standard model seems to fit so far. It has of course the disadvantage of relying on physics undiscovered so far in the laboratory: Inflation, DM and DE.

Replacement theories also tend to be speculative, so, for example, how do we test that the Steinhardt & Turok theory actually does preserve homogeneity and flatness through the recycling process?

If there are problems with Inflation then maybe we should we not look for a testable theory that does not suffer from the horizon, smoothness and flatness/density problems in the first place? i.e. One that does not decelerate.

That has been my approach. The task in this thread is to look for observations that may indicate which way to go!

Garth
SpaceTiger
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Oct19-07, 06:53 PM
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Quote Quote by Garth View Post
Inflation resolves these problems by injecting massive expansion at that early yet post-Planck era stage, which more than counteracts the effects of the subsequent deceleration. Without it the standard model has some explaining to do.
But you're just repeating what I already said. Your reasoning would suggest that you should question that the earth revolves around the sun just because we don't fully understand how the solar system formed.

We have a large body of solid observational evidence (e.g. element abundances, CMB, large-scale structure) to support the late-period deceleration of the universe and it appears to be well-fit by the LCDM model in the regimes we can measure. You haven't really demonstrated to me why these observations should be brought into question by an overturning of our early universe model. Certainly Paul Steinhardt (from whom I took a cosmology class) doesn't take issue with our post-inflation model of the universe, despite his misgivings about inflation. Why should you?


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