Cosmological Observations Conundrum

[wstrohm]

Is this animation from a priori calculations, or actual data from the spacecraft ?

 

[marcus]

I read recently that the Pioneer anomalous acceleration had finally been explained in satisfactory manner as due to heat radiation from its power supply.

EDIT: The Wikipedia article on "Pioneer anomaly" agrees"
==quote==

Both Pioneer spacecraft are escaping the Solar System, but are slowing under the influence of the Sun's gravity. Upon very close examination of navigational data, the spacecraft were found to be slowing slightly more than expected. The effect is an extremely small acceleration towards the Sun, of 8.74±1.33×10−10 m/s2. The two spacecraft were launched in 1972 and 1973 and the anomalous acceleration was first noticed as early as 1980, but not seriously investigated until 1994.[1] The last communication with either spacecraft was in 2003, but analysis of recorded data continues.
Various theories, both of spacecraft behavior and of gravitation itself, were proposed to explain the anomaly. Over the period 1998-2012, one particular explanation became accepted. The spacecraft , since it is in a vacuum, can only get rid of its heat by radiation. If due to the design of the spacecraft , more heat is emitted in the direction opposite the sun, then the spacecraft would slow down due to the radiation pressure of the emitted radiation. Since this force is due to the recoil of the thermal photons, it is also called the thermal recoil force.
By 2012 several papers by different groups, all reanalyzing the thermal radiation pressure forces inherent in the spacecraft , showed that a careful accounting of this could account for the entire anomaly, and thus the cause was mundane and did not point to any new phenomena or need for a different physical paradigm.[2][3] The most detailed analysis to date, by some of the original investigators, explicitly looks at two methods of estimating thermal forces, then states "We find no statistically significant difference between the two estimates and conclude that once the thermal recoil force is properly accounted for, no anomalous acceleration remains."[4]
==endquote==
http://en.wikipedia.org/wiki/Pioneer_anomaly

 

[ConformalGrpOp]

I was thinking about my reference to Richard Feynman in this thread, and recalling the occasion when we were in Mexico City, sitting in a taxi cab and J.A. Wheeler got in. After some amount of conversation back and forth, my mother asked him, Dr. Wheeler, what do you believe your greatest contribution to science has been? He smiled, and with a slightly mischieveous smirk said, "Richard Feynman! and then he laughed.

Feynman is notable for several quotes. Another one is "I have great suspicion that [mathematicians] don't know that this stuff is wrong and that they're intimidating people." The thing I liked about him was that, he was both a genius and a skeptic. You just can tell that some where at some time when he was growing up, he took to heart the fairy tale by Hans Christian Anderson, about the perils of pride and intellectual vanity. He was the sort of guy that if you asked him, what do we really know about quantum gravity, he'd say...not very much, and be serious about it, and then give you a thumbnail sketch of the research that had been done in the field to date and explain why none of it amounted to a hill of beans.

But more to the point of this thread, the way this field has been proceeding, non baryonic matter and its corollary dark energy which together dominate the universe is enough of a stretch to require a rather searching approach to the fundamental science underlying the entire field.

I mean, let's see how this has worked. Non baryonic DM is required to explain several characteristic features of celestial dynamics which our observations say are taking place. Originally, the impetus for conjuring up such an idea was the discovery that the observed rotations of spiral galactic systems violated the virial theorem. There wasnt enough visible mass to account for the observed rotations, so Zwicky coined the term dunkle Materie to describe what he postulated might be able to account for the phenomenon he and others had observed. So, we embarked upon a search to find something with mass that we can't seem to observe to provide the necessary gravitational impetus to explain the peculiar motions.

Except, we come to discover that, well, there is a problem insofar that if this postulated "matter" is baryonic, we would be able to detect it by various means, but when we try to use those means, we can't detect it at all. Well, the stuff has got to be there because otherwise, we cannot explain the dynamic behavior of these galactic systems, and the only thing we can think of to fit the bill is non-baryonic dark matter.

Now, if non baryonic dark matter constitutes a substantial percentage of all the matter contained in the universe, it was thought that well, its high time we went about using the observable gravitational effects of this stuff to calculate where it actually is. And once we do that, we should be able to then confirm its existence there because it will result in the gravitational lensing of EM radiation from sources emitting light with a path through this material. In fact, we should be seeing such lensing just about everywhere we look in the sky. But, as it turns out, "its a very difficult thing to observe and our attempts have all but failed to successfully confirm the existence of non baryonic DM", except, most notably it seems, with respect to some "filaments" of DM between galactic complex that are postulated to evidence the "scaffolding" that connects the entire universe. And now, using this methodology, we are trying to build a 3D contour map of all the DM in the universe, which we are having such problems trying to detect despite the fact that it is the dominant for of matter in the universe.

No doubt this sort of thing is comforting to many, and reaffirms in the minds of others that we are discovering new facts about the universe which show that we are on the right track in the way we are approaching confirming our theories with observations.

However, in perusing the literature, it seems that the Slipher/Zwicky keplerian internal galactic rotation problem has not been adequately addressed by the proposed DM theory sufficiently to provide a general solution to the observed peculiar motions. That is to say, where there should be large concentrations of DM in these galactic systems, to explain the non keplerian motions, we are having a very difficult time detecting the lensing effects that should everywhere be observable from the presence of this nonbaryonic material in these systems.

It seems, then, that there are fundamental questions which are not receiving adequate attention. Too much effort is given over to polemical defenses of various models of the universe, and not enough energy focused on basic scientific inquiries into the fundamental assumptions that lie at the foundation of these theories.

For example, in perusing the literature, I do not find any reports which demonstrate that we can rely on the assumption that light travels across vast distances in a metric which is Minkowskian. If light is traveling across cosmological distances in a metric that is not Minkowskian, what does it mean for our interpretation of celestial events?

In fact, in the 21st Century, it is somewhat fantastic that this is an open subject of multiple rounds of debate and controversy, decade in and decade out. If I were on a board of scientific advisors directing research grant money, (which no doubt, I will never be--I do have other interests!), I would be urging NASA, JPL and other agencies in the international scientific community with capable scientists working in the field to focus on the problem of the behavior of light, and to produce some substantial scientific evidence that we know everything we can possibly within out means know about how light behaves out to distances where Hubble's relation becomes measurable. (If there is scientific data on this subject which I have failed to come across, I would like to be directed to it). At this time in the history of science, as near as I can determine, it has never been systematically tested.

Because of the essential role that EM radiation plays in our models, until such data is available, it would seem that the appropriate mindset is to be skeptical of the interpretation of any celestial events as confirming any particular model of the universe.

 

[Bobbywhy]

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

 

[Chronos]

Conformal, if you are suggesting variable c casts doubt on all current cosmological models, you are in the good company of notable crackpots - like Thomas Van Flandern. That is not newsworthy. If you presume c is invariant, like the vast majority of mainstream scientists, you get something that resembles the LCDM model. If you know of any generally accepted observational evidence that c is not invariant, please cite your sources instead of rambling on with this nonsense.

 

[ConformalGrpOp]

Conformal, if you are suggesting variable c casts doubt on all current cosmological models, you are in the good company of notable crackpots - like Thomas Van Flandern. That is not newsworthy. If you presume c is invariant, like the vast majority of mainstream scientists, you get something that resembles the LCDM model. If you know of any generally accepted observational evidence that c is not invariant, please cite your sources instead of rambling on with this nonsense.

Chronos, your post made me chuckle. If by c you refer to the velocity of light in an unobstructed field free space, Maxwell's equations clearly establish the invariance of c and define its velocity. (Ok, so I had to google Thomas Van Flandern. It does seem he was able to make a living being interested in things which would not hold my attention)

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.

If one looks at the assumptions incorporated into just about every scientifically credible model, if the Michelson-Morley experiment was hypothetically scaled up to say, 120 AU, it would still give a null result. That is, there would be no fringe shift due to wave interference of the recombined beams. (Even that "crack pot" colleague of Peebles, Prof. Hogg acknowledges that we really have never investigated what happens to light beyond the point where the Hubble relation is observable or words to that effect).

But, if, in fact, the light signals traveling across cosmologically relevant distances propagate in a metric that is not Minkowskian, say, for argument's sake, one with a metric that is equivalent (but not necessarily so) and isomorphic to Hubble's relation, the observer is going to interpret the received signals as a red shift. Such a metric would, not be Poincare invariant, but it would be conformal, in the sense that angles are preserved within the metric. If this were the case, then, taking the hypothetical example of the scaled up M-M experiment, the result would not be null and a wave shift would be observed by the interferometer.

Can we preform an analog of such an experiment? Of course we can. It can be done with just one space craft, but I would prefer it to be done with two. So, why don't we perform the experiment and find out about the behavior of light at such distances? Its one thing for Robertson, Eddington, et als. to say, well, we don't have a way to test this, and so, we have to go with what we know, and our lab results suggest that there isn't any observable ether and beyond that, they show that at least at small scales, light doesn't change its behavior as it propagates, ergo, we are left with the Hubble relation, and an expanding universe. But, such a position, in this day in age, is untenable when we clearly have the means to conduct the experiment to resolve the question.

Of course, if you know of some such experiment whereby the data confirms that light propagates across such distances in a metric that is Minkowskian (though it is presumed to be traveling across a universe governed by a metric which is expanding), I would be very grateful if you could direct me to those results, so I could move on to other topics of interest that have absolutely nothing to do with the structure and conformal geometry of the universe. But, I can'd find anything in the literature on the subject at all.

 

[ConformalGrpOp]

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]

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]

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]

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]

...after further review...

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]

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]

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]

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?