Cosmological Observations Conundrum


by wstrohm
Tags: conundrum, cosmological, observations
ConformalGrpOp
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#37
Feb6-13, 08:52 AM
P: 40
Quote Quote by Bobbywhy View Post
ConformalGrpOp,

Non-baryonic dark matter does help explain some astrophysical observations. But it remains an enigma; it is unobservable. This is one reason why I agree with maintaining a skeptical attitude regarding “standard” cosmological models.

Would this paper fit your definition of “scientific data about how light behaves out to distances where Hubble's relation becomes measurable”? Does it cast any light (pun intended) on the subject?

“Cosmological Redshift in FRW Metrics with Constant Spacetime Curvature”
By: Fulvio Melia
ABSTRACT

Cosmological redshift z grows as the Universe expands and is conventionally viewed as a third form of redshift, beyond the more traditional Doppler and gravitational effects seen in other applications of general relativity. In this paper, we examine the origin of redshift in the Friedmann-Robertson-Walker metrics with constant spacetime curvature, and show that—at least for the static spacetimes—the interpretation of z as due to the “stretching” of space is coordinate dependent. Namely, we prove that redshift may also be calculated solely from the effects of kinematics and gravitational acceleration. This suggests that its dependence on the expansion factor is simply a manifestation of the high degree of symmetry in FRW, and ought not be viewed as evidence in support of the idea that space itself is expanding.

See: arXiv:1202.0775v1

Cheers,
Bobbywhy

Bobby, thanks for the reference to the Melia paper. I had read some of his work, but don't recall seeing that particular paper. It's terrific because, as I understand the analysis, it clearly and methodically demonstrates that the nature of the Hubble red shift is either kinematic or gravitational (or a combination of both). The analytical approach in the paper is elegant for its power to effectively elucidate the aphysical character of this ill-conceived notion of a "cosmological" red shift of the sort that is popularly bandied about...that of the "stretching of light" as space expands as if space was a medium with the physical characteristic of being capable of "expanding" (and, in that sense transporting the inertial frame of) the light wave along its path, (like an dot on the surface of an inflating balloon.

But, it is a theoretical paper in the sense that there is no discussion of any observational data about the behavior of light itself. That is, the paper is concerned with the analysis of the models it is investigating, not anything to do with the physical properties of light per se. But what it does mean, is that we can focus on the physical characteristics of the red shift from the standpoint of kinematics and then add in gravitational effects once we have an effective model for explaining the behavior of light based on experimental data. (see my reply to Chrono's post).
Chalnoth
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#38
Feb6-13, 09:18 AM
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Quote Quote by Bobbywhy View Post
Non-baryonic dark matter does help explain some astrophysical observations. But it remains an enigma; it is unobservable.
Unobserved != unobservable.

And it is possible we are nearing the answer on what dark matter is:
http://arxiv.org/abs/1301.6243

There remains some skepticism as to whether the particles detected by DAMA/LIBRA are dark matter, but it is clear they are detecting something.
ConformalGrpOp
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#39
Feb7-13, 01:14 AM
P: 40
Chalnoth,

Interesting paper. Well worth reading. The paper certainly sets forth a case which attempts to establish that they have been collecting evidence of something (which they provide a methodology for falsifying whether they are detecting evidence of dark matter) for quite sometime. Thanks for the post. I look forward to studying it further.
ConformalGrpOp
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#40
Feb7-13, 01:18 AM
P: 40
Chalnoth,

Interesting paper. Well worth reading. The paper certainly sets forth a case which attempts to establish that they have been collecting evidence of something (which they provide a methodology for falsifying whether it is evidence of dark matter) for quite sometime. Thanks for the post. I look forward to studying it further.
ConformalGrpOp
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#41
Apr12-13, 10:22 PM
P: 40
Quote Quote by Chalnoth View Post
Unobserved != unobservable.

And it is possible we are nearing the answer on what dark matter is:
http://arxiv.org/abs/1301.6243

There remains some skepticism as to whether the particles detected by DAMA/LIBRA are dark matter, but it is clear they are detecting something.
Chalnoth, I have had some opportunity to investigate the "hot off" the press paper by the researchers administering the DAMA/LIBRA experiment. I have not assembled all the background material nor completed my review of all the relevant articles (which date back to the 1970s), that predicted the phenomena DAMA/LIBRA was designed to detect. (I have also been reviewing the work recently released by the researchers associated with the Planck project....which is also, truly remarkable and fascinating).

Before making my comment about the paper, let me first state that all of the work that has been done on this particular question...(speculating on, hypothesize about, predicting the effects of, and detecting evidence of an hypothetical "dark matter halo" as a dominant component of the total mass of the Milky Way), is of the first rank within the field of cosmology as it is presently explored.

Without taking anything away from the investigations that have been conducted for the past 4 decades on this subject as it particularly relates to the Milky Way, the impression that one comes to when reviewing the literature is that the component of speculation involved in the development of the entire hypothetical superstructure upon which current predictions and efforts to detect local dark matter are based does not inspire confidence that the analysis or data have a meaningful explanatory value of very much at all, including, what aspect of what phenomena they might, in fact, be detecting.

The level of speculation involved at the most fundamental level of the hypothesis is for me, the first cause for substantial reserve regarding the significance of the data reported in the cited paper, based as it is, on a model of DM associated with the Milky Way.

A review of the papers published on the rotational dynamics of the Milky Way yields a clear sense that a unequivocal model of the rotation curve for the entire system does not presently exist, though the endeavor to build it up (populate the data), is worthy and admirable. The best "fit" is based on a statistical model of discrete rotation velocities of a relatively minute sample of galactic objects. And, it appears that the level of uncertainty involved in determining each object's relative velocity is itself a cause for doubt, such that, taking all the difficult challenges these researchers have before them in trying to develop sufficient data to establish a meaningful rotation curve for our spiral galaxy, the ability to predict how much dark matter might exist and what effect it is having on the dynamics of the system, and so on and so forth......well, it does not inspire much confidence at this stage of the investigation that we know very much on anything or that we can reach any particular conclusions about what phenomenon these detectors are evidencing.

From my point of view, the model used to develop the data on the rotational dynamics of the Milky Way is unduly speculative, unnecessarily analytically complex, and otherwise frought with uncertaintly. That is, it is my view that a lot of this could readily be resolved, and the results of these researchers work taken with a much higher degree of confidence than anyone but themselves at the present time believes their work deserves.

Fundamentally, I maintain that until they obtain empirical data from an experiment sufficient to demonstrate how light behaves across cosmologically relevant distances, these researchers have little hope of developing a sufficient interpretation of the rotational dynamics of the Milky Way, (or any other galactic system in the universe that apparently exhibits rotational dynamics that violate the virial theorem), to warrant a meaningful degree of confidence in their results.

The only measuring apparatus we have available is light. In an unobstructed, field free, static vacuum, we presume that the metric governing the propagation of light is Minkowskian. I think we need to verify whether or not that is true. With that accomplished, we can go forward with a much greater degree of confidence that the data and the hypothesis are really telling us something reliable about the universe we live in...so that we do not have to proceed with the nagging feeling that every new phenomena we encounter will be creatively explained by a heretofore unthought of and unpredicted "ad hoc" solve.

It is interesting that until the latter part of the 20th century, physicists, astronomers and cosmologists published their discoveries with a degree of reserve about the meaning of their results which I find refreshing, admirable and ultimately, inspiring of confidence. Now, everyone writes up their speculations as if they have fully, unequivocally, and indisputably explained the subject matter at hand, without a hint of reference to the level of uncertainty that lies at the foundation of their hypotheses.

Nothwithstanding these remarks, it is clear that the DAMA/LIBRA project has yielded data which means something, and Bernabei, et al, make a compelling argument that data related to what their detector has detected is different and more definitive than the results obtained by 20+ other research teams seeking by various methods and at various latitudes to detect the same thing.....
Bobbywhy
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#42
Apr12-13, 10:54 PM
PF Gold
P: 1,854
We are doomed to ignorance unless we settle this matter
And eschew alternate explanations that do matter
Faith in unobservables is what’s the matter
As we eliminate our need for dark matter
Faith in Bandwagon Beliefs will certainly shatter

Bobbywhy
TrickyDicky
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#43
Apr13-13, 11:07 AM
P: 2,892
Quote Quote by ConformalGrpOp View Post
What Maxwell's equations do permit, however, is that EM radiation itself may propagate in a metric that is not Minkowskian. To all observers, the velocity of the propagated EM waves will remain invariant, but the wavelengths will not. This means that we cannot, a priori, assume that light propagates within a Minkowskian metric.

What is generally known is that for all observers, the metric of spacetime is locally Minkowskian.
[...]
HI ConformalGrpOp, I also miss the rigour of authors from the first half of the 20th century, but I think there could be some either conceptual or terminological errors here. Or maybe I'm just misunderstanding you.
You are aware that locally the metric is Minkowskian, but what do you mean we cannot assume that light propagates within a Minkowskian metric? If by minkowskian you mean flat , nobody assumes that, GR is precisely based on assuming that the metric is not Minkowskian like is the case in SR, but curved.

I also find hard to understand what you mean by "What Maxwell's equations do permit, however, is that EM radiation itself may propagate in a metric that is not Minkowskian". Maxwell equations in the covariant special relativistic formulation are dependent on the Minkowskian background, so I'd say radiation according to Maxwell equations must propagate in a Minkowskian metric or at most in one that linearly approximates it.
Chalnoth
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#44
Apr13-13, 05:32 PM
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Quote Quote by ConformalGrpOp View Post
I agree, the idea of invisible pink elephants, (especially undergoing inversion and transformations which cause them to rotate back into themselves), are without question, beyond absurd. Furthermore, while it is true that petty nitpickers can be off-putting, that is not the case for sticklers.
So, somehow theories which have predictive power, and then those predictions are upheld by subsequent experiment, that is the equivalent of "pink elephants" that nobody should believe in? Why?


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