# Photon frequency loss over time?

1. May 30, 2006

### rcgldr

I remember reading an article many years ago that there was a theory that part of the red-shift we observe from far away galaxy's could be do to a time (or distance) related reduction in frequency of light, in addition to the "doppler" effect. Has this theory ever re-surfaced again (it may have been 10 or more years ago that I read this article)?

2. May 30, 2006

### neutrino

http://curious.astro.cornell.edu/question.php?number=278 [Broken]

Last edited by a moderator: May 2, 2017
3. May 30, 2006

### Chronos

Jeff, what do you imagine those photons give up their energy to? Eventually they must glow, don't you think?

4. May 30, 2006

### rcgldr

Possibly, but I'm pretty sure that there was an inference that it was more than just space stretching or speed that contributed to red shift. Maybe it was related to dark matter or something similar between an observered galaxy and the earth.

It wasn't clear, but I assume the strecthing of the space in universe is due to the decrease in graviational fields as objects move away from each other?

5. May 30, 2006

### ratfink

Do you mean the tired light theory as first proposed by fritz Zwicky (1927?).
Photons lose energy as they travel and since E = hf the frequency reduces and wavelength increasesd. They are redshifted.
He put it down to gravitational effects.

6. May 30, 2006

### rcgldr

That's probably what I read, athough I'm not quite old enough to have remembered it went first published. Has this theory been abandonded now?

7. May 30, 2006

### ratfink

Last edited by a moderator: Apr 22, 2017
8. May 30, 2006

### SpaceTiger

Staff Emeritus
Tired light theory hasn't been taken seriously by the mainstream for quite some time. It was a viable alternative for several decades after it was proposed (20s), but the CMB and other cosmological tests have since put it very firmly to sleep.

9. Jun 1, 2006

### ratfink

Let me put this another way! Instead of just quoting ‘cosmological tests’ it would help if you stated what they are.
As far as I know, we have the Tolman surface brightness test and supernovae time dilation. Any more?
The Tolman surface brightness test was always 'iffy' as it relied on models on how galaxies aged. On nearby galaxies it showed that expanding models were probably nearer the truth than static models. But this was on nearby galaxies (three in the same cluster?)
However the HUDF came along and now the tolman test comes out very firmly in favour of a static universe.
That leaves us with ‘time dilation.’ Supernovae light curves’ are stretched which agrees with the expanding theory whilst quasar light curves are not stretched – which agrees with the static universe. Since this is the same phenomenon, until such time as anyone can come with a theory that unifies these effects then the jury must remain out.
CMB? Didn’t you tell me that the axis of evil is still there on the latest data?
If the clumps are aligned about our solar system and galactic plane then even that has a problem. Furthermore, the horizon problem in the CMB is only solved by inflation and that has no experimental verification whatsoever!
So we can neglect cosmological tests and the CMB to rule out a static universe – unless you know of any other?

10. Jun 1, 2006

### SpaceTiger

Staff Emeritus
The abundances of light elements, the cosmic microwave background, the formation of large scale structure, star formation rate vs. redshift, the Soltan argument, evolution of morphology with redshift, supernova time dilation, GRB time dilation, and much more, I'm sure. The CMB, abundances, and large scale structure all constitute multiple tests of BB predictions.

Eric Lerner is a well-known crank. Those results come about from one of the effects I mentioned above -- the evolution of star formation with redshift. High-z galaxies are nothing like low-z ones, so as you've suggested, the test is not very useful. It may have some value at low redshifts and where galaxies haven't evolved much, but it's still not a very strong test.

The "axis of evil" is a sign of possible contamination in the data at low multipoles. The vast majority of the information in the CMB lies at high multipoles, where the standard model fits the data to very high precision. The CMB is a very dramatic test of mainstream theory -- it comes as no surprise to me that most of the laymen advocating steady state models don't understand the WMAP results.

Wrong again. Inflation is actually doing quite well lately. The universe has continued to be consistent with flat, now to a precision of a few percent. Furthermore, the fluctuations in both the CMB and large scale structure (see the "genus" test) have been shown to be gaussian, another prediction of inflation. Finally, the WMAP measurements indicate a spectral slope just slightly deviant from unity, just as predicted by inflation.

11. Jun 2, 2006

### Nereid

Staff Emeritus
I suspect this is not well known among PF readers; could anyone provide both a succinct summary of what it is? Also, when was it first published? And how widely has it been used (in cosmology)?

12. Jun 2, 2006

### setAI

it would be nice if an actual physicist or student would have metioned that the question is scientifically invalid- since photons have no tau- thus they can't do anything 'over time' to begin with-

13. Jun 2, 2006

### Garth

A good point.

Observed cosmological red shift is to do with the way the photon is being observed, compared with how it was emitted.

A photon is emitted by one atom and absorbed by another much later in the universe's history. Cosmological curvature results in a time dilation between the two, but should not that time dilation affect the mass of the atom as well as the frequency of the photon? i.e. if there is a de Broglie frequency associated with the atom's rest mass.

Just a thought.

Garth

14. Jun 2, 2006

### SpaceTiger

Staff Emeritus
They can certainly change as a function of coordinate time, which is usually what people mean by "time" in cosmology.

15. Jun 2, 2006

### ratfink

Eh Up!
Space tiger tells us that
Garth says
Which means that neither knows what they are talking about?

16. Jun 2, 2006

### Garth

Not at all.

Cosmological curvatue is space-time curvature, the present mainstream model is concordant with a spatially flat, or near flat universe.

The isotropic and homogeneous space-like foliations appear to have a flat geometry even though they are embedded in a 4D space-time that has curvature.

This curvature is represented by the scale function R(t) as well as the (space) curvature constant k.

I hope this helps.

You might well be right - "cosmologists are often in error but never in doubt"

But I will let SpaceTiger speak for himself.

Garth

Last edited: Jun 2, 2006
17. Jun 2, 2006

### SpaceTiger

Staff Emeritus
The Soltan argument basically compares the present day mass density of black holes to the integrated luminosity density of quasars. The idea is that supermassive black holes are expected to grow by mass accretion -- a process that radiates energy that we see in the form of active galactic nuclei. If we add up the total radiated energy from AGN over the history of the universe, we can infer how much mass was accreted. If our ideas about AGNe and cosmology are correct, this inferred accreted mass density ought to be comparable to the mass density of black holes. In general, the luminosity and mass accretion rate are related by

$$L=\epsilon \dot{M}c^2$$

The efficiency, $\epsilon$, is not known in general, but has characteristic values of order 0.1 in most black hole accretion theories. The Soltan argument can be used in several ways -- for example, to infer the efficiency of accretion. In the present context, it can be used to support the expansion paradigm. Using a reasonable value for the efficiency, the present-day mass density of black holes is comparable (to within an OOM) to the inferred accreted mass density:

http://www.arxiv.org/abs/astro-ph/0203082" [Broken]

Last edited by a moderator: May 2, 2017
18. Jun 2, 2006

### SpaceTiger

Staff Emeritus
To the contrary, Garth knows quite a bit about GR. I won't insult you and suggest that you didn't know that the universe had been measured to be flat, but when two ideas seem to contradict one another, it's always wise to consider the possibility that you might yourself be misunderstanding something about them.

19. Jun 2, 2006

### ratfink

So, is it flat or is it curved?

20. Jun 3, 2006

### Garth

The consensus of opinion is the WMAP data is consistent with spatially flat universe. Such a spatially flat 3D hyper-surface would be embedded in a 4D curved space-time.

The curvature of space-time is revealed by working out all the components of the Riemannian tensor with the Robertson-Walker metric in which k = 0, they are not all zero. It is this 4D space-time curvature that describes the gravitational field.

The peculiar thing about the GR cosmological solution is when all the Riemannian components are zero, in the empty universe case, then the 3D space hyper-surface is not flat but hyperbolic and expanding linearly.

My caveat on that consensus opinion is, as the WMAP data is angular in nature and conformal transformations preserve angles, it is also consistent with a spatially conformally flat universe.

Garth

Last edited: Jun 3, 2006
21. Jun 3, 2006

### ratfink

Thanks garth,
Sorry for the delay, been stargazing - the alignment of the planets is brill at present!
So, what you are saying is that it has taken nearly one hundred years and several COBE type satellite results to show that in X,Y,Z coordinates space is flat - which is what they thought it looked like at the beginning?
Out of interest, what evidence is there that space is curved in 4D space time?
Thanks.

22. Jun 4, 2006

### Garth

At the beginning they also thought space was static.
Gravitation.
It particular, the finer details of the orbits of planets such as Mercury and the trajectories of light rays passing close to the Sun follow the geodesics ('straight -lines') through a curved 4D space-time as predicted by GR.

Garth

23. Jun 4, 2006

### ratfink

Well no, These are local perturbations and I am sure we are all happy with that. In this thread we are looking at the universe in total. When we look at the Universe as a whole, in 3d it is flat and in 4d it is supposedly curved? I was just wondering which way it curves in 4D space (do we know?) and what evidence do we have?
Ta

24. Jun 4, 2006

### Garth

Astrophysics, and scientific cosmology, is the application of the physics 'down here' in the laboratory to observations of the universe 'out there'.

The 'down here' bit in GR are the solar system experiments that verify the predictions of the theory. These verify the understanding that "space is curved in 4D space time".

Once GR is accepted as an accurate description of gravitational fields the GR field equation is solved for the cosmological case, with a maximally symmetric space, which is homogeneous and isotropic.

This yielded the Friedmann models that are then verified by:
1. Hubble red shift.
2. BB nucleosynthesis predicting a 3/4 H and 1/4 He composition by mass of the primordial gas exiting the BB. This is concordant with the present day element relative abundance mix taking 10 Gyrs. worth of stellar nucleosynthesis into account.
3. The CMB.
4. The relative abundance of some rare isotopes that were produced in the BB, although these are often model dependent and do not constitute a hard prediction.

The standard model also requires, Inflation, non-baryonic DM and DE which have been able to be combined into a self consistent model. Although I have an issue with this as they have not been discovered in laboratory physics.

However, the veracity of the first three predictions are grounds for confidence in the basic GR understanding that ""space is curved in 4D space time".

Garth

Last edited: Jun 4, 2006
25. Jun 4, 2006

### Garth

Also there is large scale gravitational lensing of distant quasars by nearer galaxies. Although this is not quite on the cosmological scale.

As far as this question is concerned the curvature of space-time around the Sun has a definite direction, light rays are bent towards the Sun as they pass close by. However cosmological curvature has no such direction in space. Instead it is revealed as a time dilation.

The expression "space-time curvature" is a mathematical one that may be confusing. It may have a spacial component as well as a temporal one. The temporal 'curvature' though manifests itself as a time dilation - you cannot 'bend' time in the normal sense (http://www.tauworkshop.com/DaliWatch.JPG [Broken] not withstanding!)

Garth

Last edited by a moderator: May 2, 2017