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ExpErdMann
2009-Jan-12, 10:59 PM
Tired light models hold that the redshifts seen in distant galaxies arise from loss of the photon energy as it travels towards us, rather than universal expansion. As such, they are considered ATM here. But my question is not itself ATM. As shown in Ned Wright's page on tired light models (http://www.astro.ucla.edu/~wright/tiredlit.htm), the discovery of time dilation in supernovae was seen as almost conclusive proof that the tired light theory, advanced by Zwicky and others, is wrong. This is because a tired light redshift mechanism is not generally thought to impart time dilation. Redshift mechanisms involving the Compton effect do appear problematic, as Ned Wright argues, because of blurring and also because all frequencies are shifted uniformly in the cosmological shift. The SR and GR redshifts are both associated with time dilation and affect all frequencies uniformly. Does it not then follow that some other non-Compton type of redshift mechanism which affects all frequencies equally would also be associated with time dilation? One example here would be Zwicky's original gravity drag idea. To help out, I repeat a little thought experiment which I used in a recent ATM thread.

Consider a distant supernova at redshift distance z. At a certain instant, suppose the supernova emits an x-ray and at the same instant starts emitting a continuous train of longer wavelength em radiation. After a time interval t, a second x-ray is emitted and at this same instant the star stops emitting the continuous em wavetrain. This will be our 'event'. What is the time interval for the event as seen on Earth? The continuous wavetrain of em waves will be lengthened by a factor (1 + z) due to the 'whatever' redshift. Now ask yourself when does the receiver see the first x-ray. It has to be at the same instant as the first wave of the longer wavelength radiation, right? Otherwise, one of the waves was travelling at a different speed than c. Ditto for the second x-ray. So the time t of the whole event must be lengthened by a factor of (1 + z).

If people think this is wrong, then why? I won't debate tired light per se here, as per the forum rules. I'd just like to hear what people think.

G O R T
2009-Jan-12, 11:21 PM
Now ask yourself when does the receiver see the first x-ray. It has to be at the same instant as the first wave of the longer wavelength radiation, right? Otherwise, one of the waves was travelling at a different speed than c.


Light frequencies from a distant source event often do not arrive here simultaneously. This is due to frequency dependent refraction during travel.

Arneb
2009-Jan-12, 11:43 PM
You might have a look here, within Ned Wrights cosmology turorial:

http://www.astro.ucla.edu/~wright/tiredlit.htm
http://arxiv.org/abs/0804.3595
http://www.astro.ucla.edu/~wright/sne_cosmology.html

The second and third link appear on the main page of the turoial.

If you speak German, the excellent series Alpha Centauri (http://www.br-online.de/br-alpha/alpha-centauri/index.xml), featuring a Munich astronomy professor, has an episode (http://www.br-online.de/br-alpha/alpha-centauri/alpha-centauri-licht-2002-ID1208358841371.xml) where tired light is quite efficiently debunked in layman's terms (in the 2002 collection).

Ari Jokimaki
2009-Jan-13, 05:52 AM
Consider a distant supernova at redshift distance z. At a certain instant, suppose the supernova emits an x-ray and at the same instant starts emitting a continuous train of longer wavelength em radiation. After a time interval t, a second x-ray is emitted and at this same instant the star stops emitting the continuous em wavetrain. This will be our 'event'. What is the time interval for the event as seen on Earth? The continuous wavetrain of em waves will be lengthened by a factor (1 + z) due to the 'whatever' redshift. Now ask yourself when does the receiver see the first x-ray. It has to be at the same instant as the first wave of the longer wavelength radiation, right? Otherwise, one of the waves was travelling at a different speed than c. Ditto for the second x-ray. So the time t of the whole event must be lengthened by a factor of (1 + z).

If people think this is wrong, then why? I won't debate tired light per se here, as per the forum rules. I'd just like to hear what people think.
Think about two photons being emitted instead of wavetrain. Photon's energy is E = hf, where h is Planck constant and f is the frequency of the electromagnetic wave associated to the photon. In order to get a photon redshifted, i.e. change it's frequency, you have to change photon's energy. Tired light mechanisms do just that; they reduce photon's energy.

Now, two photons are being emitted in different times with certain time interval. During their voyage, the photons start to lose energy due to the hypothetical tired light processes, so they are experiencing redshifting. But photons still have the same time interval between them because there is no process that would shift the t also.

I understand why you think the time dilation would arise when looking things at wavetrain point of view, but you need to redshift individual photons too, and from that point of view the time dilation doesn't seem to arise.

ExpErdMann
2009-Jan-13, 01:57 PM
Light frequencies from a distant source event often do not arrive here simultaneously. This is due to frequency dependent refraction during travel.
This may be so, but would it not apply just as easily to the BBT redshift mechanism as to tired light mechanisms?

ExpErdMann
2009-Jan-13, 02:06 PM
You might have a look here, within Ned Wrights cosmology turorial:

http://www.astro.ucla.edu/~wright/tiredlit.htm
http://arxiv.org/abs/0804.3595
http://www.astro.ucla.edu/~wright/sne_cosmology.html

The second and third link appear on the main page of the turoial.
Yes, I've looked at this before. The first link mentions not just the time dilation issue, but also the evidence of higher temperature CMBR in the past and the Tolman surface brightness test. I have put forward ATM explanations for both of these. For the Tolman test, it turns out that the problem disappears if time dilation is assumed to apply in a postulated tired light mechanism. In fact, TL then fits the data better than BBT. However, could we remain focused on the time dilation point here? The second link is another study of time dilation in distant supernovae. In the abstract they make the assertion, being questioned here, that Zwicky's tired light mechanism, for example, does not predict time dilation. The last link appears to be related to the Tolman test already discussed.


If you speak German, the excellent series Alpha Centauri (http://www.br-online.de/br-alpha/alpha-centauri/index.xml), featuring a Munich astronomy professor, has an episode (http://www.br-online.de/br-alpha/alpha-centauri/alpha-centauri-licht-2002-ID1208358841371.xml) where tired light is quite efficiently debunked in layman's terms (in the 2002 collection).I'll see what my high school German can do here. Thanks!

ExpErdMann
2009-Jan-13, 02:16 PM
Think about two photons being emitted instead of wavetrain. Photon's energy is E = hf, where h is Planck constant and f is the frequency of the electromagnetic wave associated to the photon. In order to get a photon redshifted, i.e. change it's frequency, you have to change photon's energy. Tired light mechanisms do just that; they reduce photon's energy.

Now, two photons are being emitted in different times with certain time interval. During their voyage, the photons start to lose energy due to the hypothetical tired light processes, so they are experiencing redshifting. But photons still have the same time interval between them because there is no process that would shift the t also.

I understand why you think the time dilation would arise when looking things at wavetrain point of view, but you need to redshift individual photons too, and from that point of view the time dilation doesn't seem to arise.
Of course you're right, Ari, but what are you implying exactly? You must agree that em wavetrains are also redshifted in the BBT, not just photons, right? And so the whole em wave train would be time dilated too. This could apply to some non-Compton effect TL mechanism too. What is your answer to my thought experiment then? Do the start and end of the wave train become separated from the two x-rays?

Nereid
2009-Jan-13, 06:01 PM
Tired light models hold that the redshifts seen in distant galaxies arise from loss of the photon energy as it travels towards us, rather than universal expansion. As such, they are considered ATM here. But my question is not itself ATM. As shown in Ned Wright's page on tired light models (http://www.astro.ucla.edu/~wright/tiredlit.htm), the discovery of time dilation in supernovae was seen as almost conclusive proof that the tired light theory, advanced by Zwicky and others, is wrong. This is because a tired light redshift mechanism is not generally thought to impart time dilation. Redshift mechanisms involving the Compton effect do appear problematic, as Ned Wright argues, because of blurring and also because all frequencies are shifted uniformly in the cosmological shift. The SR and GR redshifts are both associated with time dilation and affect all frequencies uniformly. Does it not then follow that some other non-Compton type of redshift mechanism which affects all frequencies equally would also be associated with time dilation? One example here would be Zwicky's original gravity drag idea. To help out, I repeat a little thought experiment which I used in a recent ATM thread.

Consider a distant supernova at redshift distance z. At a certain instant, suppose the supernova emits an x-ray and at the same instant starts emitting a continuous train of longer wavelength em radiation. After a time interval t, a second x-ray is emitted and at this same instant the star stops emitting the continuous em wavetrain. This will be our 'event'. What is the time interval for the event as seen on Earth? The continuous wavetrain of em waves will be lengthened by a factor (1 + z) due to the 'whatever' redshift. Now ask yourself when does the receiver see the first x-ray. It has to be at the same instant as the first wave of the longer wavelength radiation, right? Otherwise, one of the waves was travelling at a different speed than c. Ditto for the second x-ray. So the time t of the whole event must be lengthened by a factor of (1 + z).

If people think this is wrong, then why? I won't debate tired light per se here, as per the forum rules. I'd just like to hear what people think.
How about this?

Forget distant supernovae, your thought experiment should work the same whether z is 1 or 0.000000001. By recasting it as a 'local' experiment, you may find (thought) tests you'd not otherwise have thought of.

Start with the classical Doppler experiment, your 'distant supernova' is merely a spaceship somewhere between here and Alpha Cen (say), travelling at a relative (line of sight) speed of v (to you). The transmitter on the spaceship does its x-ray and (radio?) em thing, as above.

What, then, are the answers to your questions? How do they vary, as a function of v?

With this understanding in hand, maybe we could then ask how 'expanding space' and 'tired light' variations would work ...

ExpErdMann
2009-Jan-13, 07:20 PM
Not sure how changing the venue helps. Can you enlighten? BTW, the original prediction of time dilation in supernovae in 1939 used just the classical formula, so not sure how going classical helps us either.

Nereid
2009-Jan-13, 07:26 PM
Not sure how changing the venue helps. Can you enlighten? BTW, the original prediction of time dilation in supernovae in 1939 used just the classical formula, so not sure how going classical helps us either.
Sorry, I meant the straight-forward SR 'classical', not the pre-20th century 'classical'.

There are subtleties enough in understanding the Doppler effect in Special Relativity, but at least the (SR) thought experiments are easy enough to do.

Use an SR thought experiment, with two x-ray pulses and a continuous em wavetrain, as the baseline to your more bracing GR/tired light thought experiment ...

Ari Jokimaki
2009-Jan-14, 06:50 AM
You must agree that em wavetrains are also redshifted in the BBT, not just photons, right?
Think what happens when we measure the redshift. Let's use simple prism that changes the direction of light, and there are light detectors in different directions receiving the deflected light. In this setup, the energy of incoming photons determines the direction of deflection, so redshifted photon (of some element) is deflected to different direction than non-redshifted photon (of same element). If we think about this using photons, only way I can think of making a wavetrain is to have successive photons creating a wave pattern. When that wavetrain made of photons arrives to the prism, first photon is deflected to the direction determined by it's energy, same with second photon, third photon, and so on. The wave pattern doesn't change (if we ignore frequency dependent travel times for argument's sake), so the wavetrain did not experience time dilation.

To me it seems that you are thinking the frequency of light differently than I am. In a wavetrain of successive photons every photon will have it's own frequency, and all those frequencies are redshifted by same cosmological redshift, but the time between the photons doesn't change due to the tired light redshift mechanism. Well, that's my opinion anyway. I hope this helped at least in explaining my point of view.

ExpErdMann
2009-Jan-14, 04:00 PM
Think what happens when we measure the redshift. Let's use simple prism that changes the direction of light, and there are light detectors in different directions receiving the deflected light. In this setup, the energy of incoming photons determines the direction of deflection, so redshifted photon (of some element) is deflected to different direction than non-redshifted photon (of same element). If we think about this using photons, only way I can think of making a wavetrain is to have successive photons creating a wave pattern. When that wavetrain made of photons arrives to the prism, first photon is deflected to the direction determined by it's energy, same with second photon, third photon, and so on. The wave pattern doesn't change (if we ignore frequency dependent travel times for argument's sake), so the wavetrain did not experience time dilation.
I think it will be confusing to bring reflection or refraction into this. Okay, let's say a wave of blue light is redshifted by whatever mechanism to a wave of red light. The wavetrain of blue light is initially comprised of countless photons of blue light. Due to the redshift mechanism, each blue photon is redshifted to a red one. But the whole train of light waves is also shifted from blue to red. That means the time for a wavelength of light to pass a specific point will increase and the time for the whole train to pass would also.


To me it seems that you are thinking the frequency of light differently than I am. In a wavetrain of successive photons every photon will have it's own frequency, and all those frequencies are redshifted by same cosmological redshift, but the time between the photons doesn't change due to the tired light redshift mechanism. Well, that's my opinion anyway. I hope this helped at least in explaining my point of view.
I would say that whatever the redshift mechanism, the spacing between the photons comprising the wave train would increase. Time dilation would thus arise whether TL, SR, GR or whatever.

Ari Jokimaki
2009-Jan-14, 04:12 PM
Hmm... let's make a simpler example. Assume there's two photons emitted from a source with one second interval. The photons fly through a tired light mechanism. After the mechanism both photons are redshifted, but I think the time interval between them is still one second. Apparently you think it is more than one second?

Cougar
2009-Jan-14, 04:33 PM
Due to the redshift mechanism, each blue photon is redshifted to a red one. But the whole train of light waves is also shifted from blue to red. That means the time for a wavelength of light to pass a specific point will increase and the time for the whole train to pass would also.

Ah, this explains your position. But an overall "increase in time" doesn't seem right because light always travels at c, a constant.

But never mind that. Your alternative redshift mechanism, whatever it is, does not and cannot explain why distant Ia supernova reach their peak brightness more slowly and then fade more slowly than more nearby Sne Ia. This phenomenon has little to do with redshift and everything to do with relativistic time dilation.

ExpErdMann
2009-Jan-14, 05:11 PM
Hmm... let's make a simpler example. Assume there's two photons emitted from a source with one second interval. The photons fly through a tired light mechanism. After the mechanism both photons are redshifted, but I think the time interval between them is still one second. Apparently you think it is more than one second?
My answer is ... yes! Now this is the same answer you would expect for an SR or GR or cosmological (BBT) redshift. Your example is just the same as my original thought experiment, but just not having the long em wave. You would still expect time dilation in the SN due to the BBT redshift. Why should time dilation occur in the tired light case? That would depend on your specific TL mechanism of course. Here I am only supposing that the TL redshift affects all frequencies as in the BBT redshift. In your example you took out the middle of the wave train and left just a photon at either end. But the middle part of wave train could have been there, right? And so would have been entirely redshifted (and thus time dilated).

(My answer may seem counter-intuitive, but here's an analogy that could help. In the BBT, it is the supposed stretching of spacetime that causes the redshift. Looking at light from the wave side, we can say that it must be a wave travelling in something else. It could be an 'ether' or it could be a more fundamental em carrier wave. It would be this carrier for the light wave which could actually be degrading in a TL mechanism. The light wave is just secondarily redshifted.)

ExpErdMann
2009-Jan-14, 05:36 PM
Ah, this explains your position. But an overall "increase in time" doesn't seem right because light always travels at c, a constant.
In a tired light model the waves are being stretched out just as in BBT. So I think it would take longer for the stretched wave to pass a point, whether in BBT or TL.


But never mind that. Your alternative redshift mechanism, whatever it is, does not and cannot explain why distant Ia supernova reach their peak brightness more slowly and then fade more slowly than more nearby Sne Ia. This phenomenon has little to do with redshift and everything to do with relativistic time dilation.
Well, if the whole supernova event originally takes a time t, then the BBT redshift increases the time to t(1 + z). Since I am supposing that the stretching of light waves in a TL model occurs in the same frequency-independent way as in BBT, then it too should produce observed time dilation in the supernova.

ExpErdMann
2009-Jan-14, 05:40 PM
Sorry, I meant the straight-forward SR 'classical', not the pre-20th century 'classical'.

There are subtleties enough in understanding the Doppler effect in Special Relativity, but at least the (SR) thought experiments are easy enough to do.

Use an SR thought experiment, with two x-ray pulses and a continuous em wavetrain, as the baseline to your more bracing GR/tired light thought experiment ...
I've been slow to follow you up here, because I'm not sure where you want me to go. If your approach has not already been covered in the posts subsequent to yours, perhaps you could lead out a bit more.

Nereid
2009-Jan-14, 05:45 PM
I'm quite confused, EEM.

If the source has a non-zero line of sight relative speed (wrt the receiver/detector), in a standard (non-GR/cosmology) SR part of the universe, the two photons in Ari's example will be detected as having a different energy (frequency) than that which the observer at rest wrt the source measures (redshifted or blueshifted, depending) AND the time interval measured on the receiver's clock between the arrival of the two photons will be different than the time interval between the emission, as measured on the source's clock.

Is that your understanding too?

Switching to the continuous em wavetrain: how about we start with a precise description of the detector? We will, in our thought experiment, install identical 'continuous em wavetrain detectors' in both the source's and receiver's spaceships* ...

And back to my earlier post: let's see if we can arrive at mutual agreement of how this thought experiment works in a situation where there should be no room for misunderstanding, before exploring the same setup under different (physical) circumstances.

* note that a precise description of 'photon detector' is not needed here, I hope.

speedfreek
2009-Jan-14, 07:54 PM
Does it not then follow that some other non-Compton type of redshift mechanism which affects all frequencies equally would also be associated with time dilation? One example here would be Zwicky's original gravity drag idea.

I am no expert, so here is my strictly amateur analysis.

There is no known mechanism where a stream of photons that is emitted over a given duration at source can be detected/received/absorbed/re-emitted somewhere else over a different duration, except for the various forms of time-dilation accepted by the mainstream.

Light does not "slow down" as it bends around stars or travels through galaxies or is absorbed/re-emitted by dust. No stream of photons enters any system with the stream being a given length and leaves that system with the stream having a different length, unless that system has changed the definition of distance or time whilst the photons were travelling through it.

With absorption/re-emission by something (gas clouds, dust etc) in between emission at source and final detection, even if that intervening medium introduces some sort of lag in between absorption and emission, the overall stream will leave over the same duration it arrived, as each photon would be affected equally at any given time. If our "one second clip" of photons enters the dust, gets delayed and then exits the dust, it is still a "one second clip", although the energy of the photons might have been changed. If the amount of dust were changing as the light made its journey, the amount of lag between absorption and emission might change over time, but this still does not change the length of our "one second clip" in the end, it just affects the time it takes that clip to reach us.

With gravitational time-dilation the energy of the photons is not even changed if it enters and exits a system. If our photons enter an area of a certain gravitational potential they would be blueshifted on their way in and redshifted on their way out by the same amount. If our "one second clip" of photons enters an area of lower gravitational potential than the area around its original source and is detected in that area, it would show an overall redshift and the clip would be time-dilated relative to observers in that area, as they live in a place where light is less blueshifted on the way in than it was redshifted on the way out at source.

But if the light continues out of that area of lower gravity, it would be redshifted by the potiential in that area on its way out by the same amount that it was blueshifted on the way in. Our "one second clip" enters and leaves a galaxy as a "one second clip". Gravitational time-dilation only occurs between the source and the receiver, but not in between.

One might argue that the gravitational potential of the universe the light would be travelling through when it was emitted was a lot higher than it is today as we detect that light, but you have to provide a mechanism for that change in the gravitational potential. Perhaps everything was a lot closer together in those days, eh? ;)

So, until someone can come up with a tired-light mechanism where you can locally aim a "one second stream" of photons at something and that photon stream exits that something over a period of more than one second, where each photon is progressively delayed by an increasing amount of time, you cannot apply that mechanism in any global sense.

Any valid mechanism needs to vary either the speed of light, the size of the universe or the size of the things in the universe in order to be consistent with our observations. For the universe not to be expanding relative to the speed of light, either the speed of light needs to be decreasing relative to a static universe (the photons arrive over a longer duration than they were emitted), or everything in a static universe needs to be contracting relative to the speed of light (the gaps in between the photons are now larger).

If things were the same distance away in the past as they are now, either everything is a lot smaller than it was and the speed of light remained constant, or for some reason the speed of light is decreasing in a static universe.

One has to ask though, if the universe is not expanding from a definite beginning point, did it have a beginning point if it is static? I have always assumed that a static universe implies it has been here forever? Does this universe contain some sort of aether that progressively slows down light and stops you seeing more than certain distance away? Surely that would mean that light emitted at further distances would be moving at a different speed from light emitted at closer distances?

But if the speed of light is changing everywhere at the same time in a static universe, presumably there will come a time when no light can move anymore. Presumably there was a time when light moved really fast, crossing the gaps between galaxies in a fraction of the time it takes today. In that case we are very lucky indeed to live in these times. Just how long has this static universe been around then? When did light travel at its fastest?

Ari Jokimaki
2009-Jan-15, 07:36 AM
My answer is ... yes! Now this is the same answer you would expect for an SR or GR or cosmological (BBT) redshift. Your example is just the same as my original thought experiment, but just not having the long em wave. You would still expect time dilation in the SN due to the BBT redshift. Why should time dilation occur in the tired light case? That would depend on your specific TL mechanism of course. Here I am only supposing that the TL redshift affects all frequencies as in the BBT redshift. In your example you took out the middle of the wave train and left just a photon at either end. But the middle part of wave train could have been there, right? And so would have been entirely redshifted (and thus time dilated).
I took the wavetrain out because it was just confusing the situation.

When the second photon flies through the tired light mechanism, how does the mechanism know that the first photon already went through, so that it knows to delay the second photon? Why the first photon did not experience the same delay?

G O R T
2009-Jan-15, 01:34 PM
Now ask yourself when does the receiver see the first x-ray. It has to be at the same instant as the first wave of the longer wavelength radiation, right? Otherwise, one of the waves was travelling at a different speed than c.


Light frequencies from a distant source event often do not arrive here simultaneously. This is due to frequency dependent refraction during travel.


This may be so, but would it not apply just as easily to the BBT redshift mechanism as to tired light mechanisms?

You mentioned differing frequencies ....


So the time t of the whole event must be lengthened by a factor of (1 + z).

This "event", if one second long, would stay one second long. You seem to be imagining a stretch instead of degredation. For the same number of cycles to stay in the event (without expansion) the event must be stretched so that c changes.

ParaDoctor
2009-Jan-16, 09:56 AM
I took the wavetrain out because it was just confusing the situation.That's the problem, the "wavetrain" is essential to ExpErdMann's argument. I agree it can be confusing, looking like a metaphor stretched too far, pardon the pun. ;) That's the reason I failed to understand it the first time I encountered it.

ExpErdMann's argument:


A distant light source emits a continuous signal of coherent light, a wavetrain.
A wavelength-proportional redshift (1+z) acts on the wavetrain.
Assuming the number of crests and troughs is conserved, the time for a given number of oscillations to be counted at the receiver increases by a factor (1+z), introducing time dilation in the signal.
No assumptions have been made about the redshift mechanism
Hence, any redshift mechanism will introduce time dilation.


So there.

The problem is with statement 4. ExpErdMann, you implicitly assumed that the redshift mechanism keeps the photons coherent. There may be mechanisms that do, but you'd have to provide a separate argument for the specific mechanisms used. In general, there is no reason why a redshift mechanism should keep the photons constituting a wavetrain coherent. Scattering mechanisms would be expected to destroy any coherence in the signal due to thermal fluctuations in the scattering medium. This means that statement 4 fails in at least some cases, rendering statement 2 meaningless, as the wavetrain quickly distintegrates into a stream of uncorrelated photon.

So there. ;)

ExpErdMann
2009-Jan-16, 03:51 PM
That's the problem, the "wavetrain" is essential to ExpErdMann's argument. I agree it can be confusing, looking like a metaphor stretched too far, pardon the pun. ;) That's the reason I failed to understand it the first time I encountered it.
Thanks for making a house call, ParaDoctor. The patient was starting to go under! But let's see:


ExpErdMann's argument:


A distant light source emits a continuous signal of coherent light, a wavetrain.
A wavelength-proportional redshift (1+z) acts on the wavetrain.
Assuming the number of crests and troughs is conserved, the time for a given number of oscillations to be counted at the receiver increases by a factor (1+z), introducing time dilation in the signal.
No assumptions have been made about the redshift mechanism
Hence, any redshift mechanism will introduce time dilation.


So there.
Nice, you stated this probably more clearly than I did.


The problem is with statement 4. ExpErdMann, you implicitly assumed that the redshift mechanism keeps the photons coherent. There may be mechanisms that do, but you'd have to provide a separate argument for the specific mechanisms used. In general, there is no reason why a redshift mechanism should keep the photons constituting a wavetrain coherent. Scattering mechanisms would be expected to destroy any coherence in the signal due to thermal fluctuations in the scattering medium. This means that statement 4 fails in at least some cases, rendering statement 2 meaningless, as the wavetrain quickly distintegrates into a stream of uncorrelated photon.

So there. ;)
But wait! I did specify that whatever was causing the redshift, it had to act uniformly on each frequency. Scattering mechanisms were excluded. We have at least three examples of redshifts uniformly affecting frequencies and causing time dilation: SR, GR and the BBT spacetime-stretching redshift. I'm just saying there's room for more at this table, including tired light ones.

PD, the other posters have given me second thoughts. I'm thinking that the only tired light redshift which could work is the one I mentioned to Ari, namely that the spacetime in which photons travel does not expand but rather is recycled over time. This might most easily be imagined if "spacetime" is comprised of some more fundamental wave (eg, QM matter wave). The segment of spacetime in which a particular photon is moving slowly decomposes, but elsewhere new segments are being made. Like a wave moving down a wire, the thinning wire would lead to longer wavelengths (and hence time dilation).

What do you think about Zwicky's gravity drag mechanism? Suppose it can make time dilation?

speedfreek
2009-Jan-16, 04:20 PM
We have at least three examples of redshifts uniformly affecting frequencies and causing time dilation: SR, GR and the BBT spacetime-stretching redshift.

And all of them can be attributed to the difference in the frame of reference of the source when compared to the receiver. With SR it is a difference in relative speed, with GR it is a difference in gravitational potential and with BBT spacetime-stretching redshift it is the difference between the scale factor of the background metric, the metric that defines distance.


What do you think about Zwicky's gravity drag mechanism? Suppose it can make time dilation?

It seems (http://en.wikipedia.org/wiki/Dynamical_friction#Photons) that Zwicky made a mistake in his original analysis (which was pointed out to him by Eddington), and he accepted that the actual magnitude of the effect of dynamical friction on photons should have been zero.

Nereid
2009-Jan-16, 04:45 PM
[...]

But wait! I did specify that whatever was causing the redshift, it had to act uniformly on each frequency. Scattering mechanisms were excluded. We have at least three examples of redshifts uniformly affecting frequencies and causing time dilation: SR, GR and the BBT spacetime-stretching redshift. I'm just saying there's room for more at this table, including tired light ones.

Yes, but ...

As has already been pointed out, these three have an essential common element, and an implication is that any other mechanisms will need to also include that common element, or replace/reproduce GR.

Of course, absent any specific other(s), one cannot say the implication is binding, but it's surely quite a challenge.


PD, the other posters have given me second thoughts. I'm thinking that the only tired light redshift which could work is the one I mentioned to Ari, namely that the spacetime in which photons travel does not expand but rather is recycled over time. This might most easily be imagined if "spacetime" is comprised of some more fundamental wave (eg, QM matter wave). The segment of spacetime in which a particular photon is moving slowly decomposes, but elsewhere new segments are being made. Like a wave moving down a wire, the thinning wire would lead to longer wavelengths (and hence time dilation).

[...]

In some respect, this looks a little like LQG ... and to the extent that it does, LQG may give some pointers to what's possible, and the nature of the constraints the great experimental successes of SR and GR impose ...

ExpErdMann
2009-Jan-16, 04:48 PM
I took the wavetrain out because it was just confusing the situation.

When the second photon flies through the tired light mechanism, how does the mechanism know that the first photon already went through, so that it knows to delay the second photon? Why the first photon did not experience the same delay?

I agree when you take the middle long wave out it's hard to see why the two x-rays would get further apart. But when you put it back in, do you suppose it stretches out further in space than the two x-rays or what? I think the answer lies along the lines I suggested earlier, ie., that a transformation in the light medium (or 'spacetime') is needed, but I would just like to exclude the other possibility first, that it's a general effect of all redshifts.

ExpErdMann
2009-Jan-16, 05:59 PM
And all of them can be attributed to the difference in the frame of reference of the source when compared to the receiver. With SR it is a difference in relative speed, with GR it is a difference in gravitational potential and with BBT spacetime-stretching redshift it is the difference between the scale factor of the background metric, the metric that defines distance.
Yes, I can see that the difference in reference frame is behind the time dilation in SR and GR, but does this also apply to the BBT scale factor shift? I guess I'm so used to hearing the cosmic redshift as being due to spacetime stretching that I've come to think of the reddening as occurring en route to us. How wrong is it to think of it that way and is there any evidence that supports the frame-dependent versus travel-dependent redshift? Does this question make sense?

And thanks for your earlier post!


It seems (http://en.wikipedia.org/wiki/Dynamical_friction#Photons) that Zwicky made a mistake in his original analysis (which was pointed out to him by Eddington), and he accepted that the actual magnitude of the effect of dynamical friction on photons should have been zero.

This is quite remarkable. I once checked out all the refs to Zwicky's first paper to see who had refuted him, yet somehow missed this one, possibly because it was written by Zwicky himself! Thanks! From this new paper it seems Zwicky got private correspondence from Eddington which suggested he was wrong, but I would disagree with you that he concurs with Eddington. The arguments are complicated and beyond me, I'm afraid.

ExpErdMann
2009-Jan-16, 06:08 PM
In some respect, this looks a little like LQG ... and to the extent that it does, LQG may give some pointers to what's possible, and the nature of the constraints the great experimental successes of SR and GR impose ...

Thanks for the suggestion and it is surely worth checking out, but somehow I hope the winning cosmology ends up being less complicated than loop quantum gravity!

speedfreek
2009-Jan-16, 09:02 PM
Yes, I can see that the difference in reference frame is behind the time dilation in SR and GR, but does this also apply to the BBT scale factor shift? I guess I'm so used to hearing the cosmic redshift as being due to spacetime stretching that I've come to think of the reddening as occurring en route to us. How wrong is it to think of it that way and is there any evidence that supports the frame-dependent versus travel-dependent redshift? Does this question make sense?

Yes it does make sense, and the question seems to be a current issue in cosmology, although some think the difference is essentially irrelevant. Here are some links to articles and papers that I think are relevant to the question, in chronological order:

Inflation and the Cosmic Microwave Background (http://arxiv.org/abs/astro-ph/0305179)

Misconceptions about the Big-Bang (http://www.mso.anu.edu.au/%7Echarley/papers/LineweaverDavisSciAm.pdf)

Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe (http://arxiv.org/abs/astro-ph/0310808)

Is space really expanding? A counterexample (http://arxiv.org/abs/astro-ph/0601171)

A direct consequence of the expansion of space? (http://arxiv.org/abs/astro-ph/0610590)

Eppur si espande (http://arxiv.org/abs/astro-ph/0612155)

Expanding Space: the Root of all Evil? (http://arxiv.org/abs/0707.0380)

Coordinate Confusion in Conformal Cosmology (http://arxiv.org/abs/0707.2106)

Cosmological Radar Ranging in an Expanding Universe (http://arxiv.org/abs/0805.2197)

A short answer to critics of our article "Eppur si espande" (http://arxiv.org/abs/0812.3266)

Eppur si muove (http://arxiv.org/abs/0812.3972)

ParaDoctor
2009-Jan-16, 11:33 PM
Thanks for making a house call, ParaDoctor. The patient was starting to go under!That's my hypercritic oath: I never leave the table before the patient is dead. :D


But wait! I did specify that whatever was causing the redshift, it had to act uniformly on each frequency.If you mean by that the relative redshift is independent of the photon's frequency, then that is exactly what I stated in step 2. of the argument. Otherwise, I need an explanation of what you mean by "act uniformly on each frequency".


Scattering mechanisms were excluded.Yep, I intended that only as an example.

Basically, your argument merely establishes that a coherence-preserving tired light redshift mechanism will introduce an apparent time dilatation. The problem is, without global knowledge about the signal, how can a patch of space introduce just the right delay for photons arriving later? For successive photons, the delay becomes larger and larger, which implies that more and more photons back up in that patch, until we reach the point where the photons pile up so high that the whole shebang collapses. Unless you find a way of solving this paradox, the conclusion is that there can be no coherence-preserving tired light redshift mechanism.


What do you think about Zwicky's gravity drag mechanism?Years ago, I did a back-of-the-envelope calculations which indicated, even under extremely mild assumptions, that gravitational interaction is too small by many orders of magnitude.


Suppose it can make time dilation?Since Zwicky's drag is a form of gravitational scattering (http://www.bautforum.com/against-mainstream/82267-case-against-tired-light-2.html#post1389625), and since scattering destroys coherence, it's obvious that zwicky's mechanism can't produce time dilatation.

Ari Jokimaki
2009-Jan-17, 07:11 AM
I agree when you take the middle long wave out it's hard to see why the two x-rays would get further apart. But when you put it back in, do you suppose it stretches out further in space than the two x-rays or what?
I think that the middle wavetrain would also be constructed from individual photons, so it would be hard to see why any of them would get further apart from each other. If you still think of just two photons, it makes no difference if they are one second apart, one day apart, or one nanosecond apart; the mechanism would still treat them as individual photons (at least that's what I think). It would not be enough just to have redshift mechanism working equally in all frequencies, because I don't think individual photons would combine to make a "frequency". It would just be a train of photons each with their own frequency, and the mechanism would treat them as individuals. So, in addition to redshifting, your mechanism should be capable of introducing delay to photon's processing time.


The problem is, without global knowledge about the signal, how can a patch of space introduce just the right delay for photons arriving later?
There is a way to do that in principle. The "patch of space", or whatever we would call this tired light mechanism, could have a property of delaying the photons going through it. The amount of delay would slowly change with time. That would naturally cause an effect that would look like time dilation.

sounddoctorin
2009-Jan-17, 09:44 AM
If people think this is wrong, then why? I won't debate tired light per se here, as per the forum rules. I'd just like to hear what people think.

Hehe...I got kicked out of the 'Physics forum' for even asking for blue shift data. What is it with people saying 'well show us a peer reviewed article' when you can't even TALK about it without some nazi hacking your head off?

Good grief. I saw an article that made me think maybe this forum was open to reasonable discussion.

Hoping for the best:

1) The dilation of Supernovae data I call to question. Most of the data seems to indicate that there is dilation relating to the perceived speed away from us from red shift. However SOME of the data (and for very far out objects at that as I recall!) is RIGHT on the flat line, not on the curve with the rest of the data!!! This makes me wonder if the same people collected the data that is on the curve. I mean...you only get one shot at recording event like this. You can't go back and check the data! So if a bunch of people wanted to FINALLY have some seeming proof that tired light is not the theory of the day, this would be one way to accomplish it.

2) CMB is laughable. Historically the estimates for the temperature of space had gradually RISEN until the big bang hit. Then suddenly the estimate dropped from about 30 to 50K down to 2.7k to accomidate the CMB observation IN the model of a black body radiator which the universe is *not*. :)

So I just don't see a lot of hard evidence and I'd love to know how each point in 1) was collected. We have what was it 60 data points or something.

My real issue is the movement of M31 past M33. The thought that there is some large imbalanced dark matter out there is not substantiated at all. So the acceleration on M31 right now from our galaxy and the ones surrounding us would only be max about 6km/sec/billion years. So plainly the age of the universe can't even account remotely for the speed of either of these galaxies towards us. Not to mention HOW M31 would have passed M33 on it's path towards us 1.8Billion years ago! :-)

I hope people understand that everything didn't come from a common point. There is a complex distribution of velocities of these systems of starts...and a complex yet overall organized pattern of velocities in each of them. Quite something to contemplate for people who understand something about celestial mechanics. -Bob

antoniseb
2009-Jan-17, 11:40 AM
The dilation of Supernovae data I call to question...

Hi sounddoctorin,

Please read the rules of this forum. We DO have a section called Against The Mainstream where you can present and discuss specific ideas about how modern astronomy and cosmology have got things wrong. It is against the rules to post this sort of thing in any other section. Please take some time to read the rules. You might find yourself more welcome here than in the physics forum you got banned from. Just play by the rules.

tusenfem
2009-Jan-17, 01:30 PM
sounddoctorin, welcome to the board.
Like antoniseb already told you, please read the rules of the board.
I will put a few links here that you can find your way around.
Looking forward to see your input.




1) The dilation of Supernovae data I call to question.


As does e.g. Jerry, and there is a thread about it in the astronomy section (http://www.bautforum.com/astronomy/73365-supernova-time-dilation-confirmed-again.html), where the techniques and interpretation of the data is discussed.



2) CMB is laughable.


There is a thread in Questions and Answers (http://www.bautforum.com/questions-answers/82618-cmbr-not-affiliated-big-bang.html) about the relationship between CMB and the BB. However, there are no open thread about the CMB in the "against the mainstream" section at the moment.



My real issue is the movement of M31 past M33. The thought that there is some large imbalanced dark matter out there is not substantiated at all.

I could not find a thread on this in BAUT, but maybe I did not look correctly. At the top of the page there is a search function in the blue bar. Use it and see if there are any threads to your liking.

Naturally, you are welcome to open your own threads about things you want to discuss. Please choose your section carefully, but if it appears in a completely wrong section one of the moderators will move it, with a redirect in the old section.

ToSeek
2009-Jan-17, 03:31 PM
2) CMB is laughable. Historically the estimates for the temperature of space had gradually RISEN until the big bang hit. Then suddenly the estimate dropped from about 30 to 50K down to 2.7k to accomidate the CMB observation IN the model of a black body radiator which the universe is *not*. :)


I wanted to address these for the benefit of those who might not be familiar with the issues: the important thing about the CMB is not its predicted or measured temperature (which depends on assorted factors like the age of the universe and just how fast it's expanding), but on the fact that it's a perfect blackbody spectrum to within 1 part in 100,000. There is currently no steady-state hypothesis that can account for this, while it falls out naturally from big-bang models.

Spaceman Spiff
2009-Jan-17, 03:51 PM
2) CMB is laughable. Historically the estimates for the temperature of space had gradually RISEN until the big bang hit. Then suddenly the estimate dropped from about 30 to 50K down to 2.7k to accomidate the CMB observation IN the model of a black body radiator which the universe is *not*. :)
:rolleyes:
Uggh. For those of you who are actually interested in the CMB and its history (various early predictions and measurements), try here (http://www.astro.ucla.edu/%7Ewright/CMB.html) (go about half way down the page), here (http://en.wikipedia.org/wiki/CMB#History) and here (http://en.wikipedia.org/wiki/Discovery_of_cosmic_microwave_background_radiation ) for starters.

Nereid
2009-Jan-17, 03:55 PM
Maybe the recent items in this thread that are not directly relevant to the "tired light" of the OP could be split out into a new thread?

I for one would like to keep this thread clean and focussed on "tired light" topic introduced in the OP.

ExpErdMann
2009-Jan-17, 08:07 PM
Yes it does make sense, and the question seems to be a current issue in cosmology, although some think the difference is essentially irrelevant. Here are some links to articles and papers that I think are relevant to the question, in chronological order:

Inflation and the Cosmic Microwave Background (http://arxiv.org/abs/astro-ph/0305179)

Misconceptions about the Big-Bang (http://www.mso.anu.edu.au/%7Echarley/papers/LineweaverDavisSciAm.pdf)

Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe (http://arxiv.org/abs/astro-ph/0310808)

Is space really expanding? A counterexample (http://arxiv.org/abs/astro-ph/0601171)

A direct consequence of the expansion of space? (http://arxiv.org/abs/astro-ph/0610590)

Eppur si espande (http://arxiv.org/abs/astro-ph/0612155)

Expanding Space: the Root of all Evil? (http://arxiv.org/abs/0707.0380)

Coordinate Confusion in Conformal Cosmology (http://arxiv.org/abs/0707.2106)

Cosmological Radar Ranging in an Expanding Universe (http://arxiv.org/abs/0805.2197)

A short answer to critics of our article "Eppur si espande" (http://arxiv.org/abs/0812.3266)

Eppur si muove (http://arxiv.org/abs/0812.3972)

I've only had a chance to look at these briefly, but I can see already that they are interesting and to the point. Thanks again! As you suggest, there seems to be disagreement on whether spacetime stretching is indeed the cause of the BBT redshift. I'll try to get back to these later.

speedfreek
2009-Jan-17, 08:40 PM
I've only had a chance to look at these briefly, but I can see already that they are interesting and to the point. Thanks again! As you suggest, there seems to be disagreement on whether spacetime stretching is indeed the cause of the BBT redshift. I'll try to get back to these later.

Well just to be clear (in case anyone else misunderstood) the disagreement is about what is the true cause of cosmological redshift in an expanding universe. All the articles refute tired-light as they all accept that the universe is expanding and that the expansion causes cosmological redshift, they are simply arguing about the concept of "expanding space" and whether it is correct to attribute the redshift to a "gradual stretching" of the light or to a difference in reference frames where the background metric that defines distance has changed.

From Expanding Space: the Root of all evil?:


The key is to make it clear that cosmological redshift is not, as is often implied, a gradual process caused by the stretching of the space a photon is travelling through. Rather cosmological redshift is caused by the photon being observed in a different frame to that which it is emitted. In this way it is not as dissimilar to a Doppler shift as is often implied. The difference between frames relates to a changing background metric rather than a differing velocity. Page 367 of Hobson, Efstathiou, & Lasenby (2005) as well as innumerable other texts shows how redshift can be derived very simply by considering the change in the orthonormal basis of observers with different scale factors in their background metrics. This process is discreet, occurring at the point of reception of the photon, rather than being continuous, which would require an integral. If we consider a series of comoving observers, then they effectively see the wave as being stretched with the scale factor.

So what they are saying is that the end result is the same, a series of observers that are co-moving with the expansion of the universe would see the light as being stretched with the scale factor, which looks the same as if the light were being stretched as it moved. The unanswerable question is what someone that was co-moving with the light would see.

ParaDoctor
2009-Jan-17, 09:38 PM
There is a way to do that in principle. The "patch of space", or whatever we would call this tired light mechanism, could have a property of delaying the photons going through it. The amount of delay would slowly change with time. That would naturally cause an effect that would look like time dilation.Sorry, no sale. If you do the numbers, you'll find that the delay depends not just on time, but also on the distance between the signal source and the receiver. As this information is not encoded in the photons passing through, there is no way to impart the proper time delay.

The No-Dilatation Theorem
Assume a static, flat, open universe.
Assume there is a delay effect operating on a class of particles in a time-independent, homogenous, isotropic manner. Such a delay effect cannot simulate time dilatation, because such an effect would have to introduce a delay that depends on the distance between source and receiver, an information not available until after the particle has arrived at the receiver.

Please note that this is a very general theorem, applying not just to photons. If neutrino astronomy should ever become good enough to produce timecurves, the theorem would apply to them as well. Even charged particles might be used in a hypothetical UHECR (http://en.wikipedia.org/wiki/UHECR) astronomy. But whatever the instruments, under the stated assumptions any delay introduced by any tired light effect will sooner or later become observably inconsistent with source time dilatation.

Nereid
2009-Jan-17, 10:10 PM
It's worth quoting Ken G (http://www.bautforum.com/1412777-post53.html) in another Q&A thread (http://www.bautforum.com/questions-answers/83475-other-way-look-universes-expansion.html) on a related topic, in full:

I agree with publius-- if two models are purely 100% indistinguishable by any physical experiment, so make all the same predictions, then they are exactly the same model (until such a time as they can be distinguished). In the absence of any demonstrable distinction, the only difference between them could be termed pedagogical-- i.e., differences in how you explain or picture the model. Indeed, physics is positively rife with pedagogical differences in its models. The best way to handle them is to know them all, and select whichever pedagogy serves the need at hand. You never know which way of picturing something will stimulate the next useful idea.

In regard to "shrinking dots", that pedagogy is particularly useful in answering the common questions: "what is the universe expanding into?" and "where is the center of the expansion?" Framed as a shrinking, it becomes more obvious why these could actually be nonsensical questions.

As I understand it, any and all 'tired light' ideas implicit in the OP would be capable of being distinguished from the GR-based models that are the current consensus among cosmologists, by experiments and/or observations (if only in principle).

So, in Ken G's words, 'tired light' models are not, and cannot be, merely pedagogically different versions of BBT models*.

* at least, as I understand 'tired light' as it has been presented so far in this thread

Ari Jokimaki
2009-Jan-18, 07:39 AM
Sorry, no sale. If you do the numbers, you'll find that the delay depends not just on time, but also on the distance between the signal source and the receiver.
Yes, of course, but I meant that single "tired light mechanism unit" would introduce a delay, and amount of that delay would change with time. When a photon would travel in space filled with these single units, it would go through many of the units, so the introduced delay would then be a function of distance.

ExpErdMann
2009-Jan-19, 02:00 PM
That's my hypercritic oath: I never leave the table before the patient is dead. :D
That explains your bedside manner!
<>


Basically, your argument merely establishes that a coherence-preserving tired light redshift mechanism will introduce an apparent time dilatation. The problem is, without global knowledge about the signal, how can a patch of space introduce just the right delay for photons arriving later? For successive photons, the delay becomes larger and larger, which implies that more and more photons back up in that patch, until we reach the point where the photons pile up so high that the whole shebang collapses. Unless you find a way of solving this paradox, the conclusion is that there can be no coherence-preserving tired light redshift mechanism.
If you look at my OP I was not specifying how the tired light redshift occurs. I just specified that if one existed which acted proportionately on each frequency, as in the SR and GR redshifts, it would also produce time dilation. I have given no proof that such a tired light mechanism exists, but you have not proved the contrary.


Years ago, I did a back-of-the-envelope calculations which indicated, even under extremely mild assumptions, that gravitational interaction is too small by many orders of magnitude.
Must have been a big envelope!


Since Zwicky's drag is a form of gravitational scattering (http://www.bautforum.com/against-mainstream/82267-case-against-tired-light-2.html#post1389625), and since scattering destroys coherence, it's obvious that zwicky's mechanism can't produce time dilatation.
It does appear from reading Zwicky's second 1929 paper (http://prola.aps.org/abstract/PR/v34/i12/p1623_2) that you are right.

ExpErdMann
2009-Jan-19, 02:17 PM
I think that the middle wavetrain would also be constructed from individual photons, so it would be hard to see why any of them would get further apart from each other. If you still think of just two photons, it makes no difference if they are one second apart, one day apart, or one nanosecond apart; the mechanism would still treat them as individual photons (at least that's what I think). It would not be enough just to have redshift mechanism working equally in all frequencies, because I don't think individual photons would combine to make a "frequency". It would just be a train of photons each with their own frequency, and the mechanism would treat them as individuals. So, in addition to redshifting, your mechanism should be capable of introducing delay to photon's processing time.
I can see what you're saying, but here's a problem with it. You're saying that the light coming from a distant star is composed of photons which are not physically connected to each other. If you now apply the BBT scale factor shift to each one of these photons individually, you would find that each separate photon is redshifted and time dilated (since a longer wavelegth photon takes longer to pass a point), but that the whole ensemble of photons emitted during a time interval t would not be. A population of blue photons would be converted, say, to red photons, but the time interval t at our end would be the same.


There is a way to do that in principle. The "patch of space", or whatever we would call this tired light mechanism, could have a property of delaying the photons going through it. The amount of delay would slowly change with time. That would naturally cause an effect that would look like time dilation.
I'm not sure that a time delay would work. Would this not compress the waves into a smaller space than a larger. An increase in c might work.

ExpErdMann
2009-Jan-19, 02:23 PM
Hehe...I got kicked out of the 'Physics forum' for even asking for blue shift data. What is it with people saying 'well show us a peer reviewed article' when you can't even TALK about it without some nazi hacking your head off? sounddoctorin, your medicine might be more palatable than ParaDoctor's, but you prescribed for the wrong ailment. Come back when you find any tired light resuscitation pills in your bag!

ExpErdMann
2009-Jan-19, 02:32 PM
Well just to be clear (in case anyone else misunderstood) the disagreement is about what is the true cause of cosmological redshift in an expanding universe.
Hey, I understood you!

All the articles refute tired-light as they all accept that the universe is expanding and that the expansion causes cosmological redshift, they are simply arguing about the concept of "expanding space" and whether it is correct to attribute the redshift to a "gradual stretching" of the light or to a difference in reference frames where the background metric that defines distance has changed.

From Expanding Space: the Root of all evil?:


So what they are saying is that the end result is the same, a series of observers that are co-moving with the expansion of the universe would see the light as being stretched with the scale factor, which looks the same as if the light were being stretched as it moved. The unanswerable question is what someone that was co-moving with the light would see.
It seems to me that the faction who are just saying it's a frame of reference thing are being a little too cute. By saying this they can sort of wave off some of the conceptual difficulties. For instance, one unanswered question in BBT is where does the energy from the redshifted photons go? If it's spacetime stretching that causes redshift, then the problem is clear. If it's just frame of reference switching (what you originally stated), then the problem seems to go away. The BBT shift then seems not so different than the SR or GR shifts.

ExpErdMann
2009-Jan-19, 02:53 PM
As I understand it, any and all 'tired light' ideas implicit in the OP would be capable of being distinguished from the GR-based models that are the current consensus among cosmologists, by experiments and/or observations (if only in principle).

So, in Ken G's words, 'tired light' models are not, and cannot be, merely pedagogically different versions of BBT models*.

* at least, as I understand 'tired light' as it has been presented so far in this thread
I would agree that we can't try to sneak in tired light as just another member of the BBT family. I don't think TL would be accepted as such! However, let us focus on just the piece of evidence against TL, considered so convincing by many, that it can't support time dilation. For BBT we seem to have at least two schools of thought about the redshift, one that it is due to an actual stretching of spacetime, the other that it is due to a change in reference frames. I don't think anyone is saying the cosmic shift is an SR or GR redshift. From my (limited) reading, most BBT proponents seem to be in the spacetime stretching camp. Spacetime stretching creates an opening for tired light, since, as discussed above, we can also think of the spacetime occupied by a photon as being slowly degraded or recycled. This could give that particular patch of spacetime the characteristic of apparent expansion (think again of a transverse wave running down a wire that is getting thinner as you go along), but elsewhere new patches of new, compact spacetime are being formed.

Nereid
2009-Jan-19, 03:14 PM
I would agree that we can't try to sneak in tired light as just another member of the BBT family. I don't think TL would be accepted as such!
Why not?

If there were no experiments or observations which could distinguish between some GR-based cosmological model and some TL model, then they are equivalent ... by definition!


However, let us focus on just the piece of evidence against TL, considered so convincing by many, that it can't support time dilation. For BBT we seem to have at least two schools of thought about the redshift, one that it is due to an actual stretching of spacetime, the other that it is due to a change in reference frames. I don't think anyone is saying the cosmic shift is an SR or GR redshift. From my (limited) reading, most BBT proponents seem to be in the spacetime stretching camp.
Again, it is irrelevant what some BBT proponents are saying, or how many ways a GR-based cosmological model can be sliced and diced ... as long as there is no inconsistency with the relevant observational and experimental results, nor with any in-principle experiment, they are all equivalent*.

End of discussion.


Spacetime stretching creates an opening for tired light, since, as discussed above, we can also think of the spacetime occupied by a photon as being slowly degraded or recycled. This could give that particular patch of spacetime the characteristic of apparent expansion (think again of a transverse wave running down a wire that is getting thinner as you go along), but elsewhere new patches of new, compact spacetime are being formed.
Well, unless and until it can be shown that any such TL idea would predict a different result for any experiment or observation - even any in-principle one - then it might be a fascinating discussion, it might lead to some new insights, and so on ... but there would be no new physics.

Surely it's a more productive use of time to develop a TL idea to the point where it can actually be tested? Assuming, of course, that it's not equivalent to something already found in textbooks.

* of course, tomorrow someone may come along and propose an experiment which breaks the 'pedagogical degeneracy' (so to speak), but until that day ...

Ari Jokimaki
2009-Jan-20, 07:21 AM
You're saying that the light coming from a distant star is composed of photons which are not physically connected to each other. If you now apply the BBT scale factor shift to each one of these photons individually, you would find that each separate photon is redshifted and time dilated (since a longer wavelegth photon takes longer to pass a point), but that the whole ensemble of photons emitted during a time interval t would not be. A population of blue photons would be converted, say, to red photons, but the time interval t at our end would be the same.
No, the time dilation applies to the train of photons by introducing a delay between the photons because in BBT the expanding space increases the distance between the photons.


I'm not sure that a time delay would work. Would this not compress the waves into a smaller space than a larger.
Increasing the time delay between the photons stretches the lightcurve of supernovae, and I think that is what we are trying to do. I don't understand why it would compress the waves.

ExpErdMann
2009-Jan-20, 03:30 PM
No, the time dilation applies to the train of photons by introducing a delay between the photons because in BBT the expanding space increases the distance between the photons.
It seems to me that if we interpret light as a wave phenomenon, then my position as stated in the OP has to be right, ie, every (non-Compton) redshift will cause time dilation. However, if we take light as a particle (photon) phenomenon, then you might well be right. Since we know light can be taken as either a particle or wave, then clearly one of us has to be right! :)

To get closer to the right answer would seem to require more background info on how photons are bunched together to make em waves (loosely, tightly, coherent, etc.) I'm not able to easily access that info, so I will have to have to leave it at this for now.

Nereid
2009-Jan-20, 03:44 PM
It seems to me that if we interpret light as a wave phenomenon, then my position as stated in the OP has to be right, ie, every (non-Compton) redshift will cause time dilation. However, if we take light as a particle (photon) phenomenon, then you might well be right. Since we know light can be taken as either a particle or wave, then clearly one of us has to be right! :)

To get closer to the right answer would seem to require more background info on how photons are bunched together to make em waves (loosely, tightly, coherent, etc.) I'm not able to easily access that info, so I will have to have to leave it at this for now.
Digging deeper into physical models of electromagnetic radiation/photons will certainly be A Good Thing.

However, the real test comes when you do (thought) experiments ... what do you expect real (thought) detectors to record?

There's agreement (I think) on the 'photon' picture ... no matter where you put your photon detectors, from source to Earth (and everywhere in between, in principle), we seem to agree on what they will record.

However, for the 'wave' picture, we don't even have an in-principle detector yet, let alone ideas on what any such thing might record ...

ExpErdMann
2009-Jan-20, 03:55 PM
Well, unless and until it can be shown that any such TL idea would predict a different result for any experiment or observation - even any in-principle one - then it might be a fascinating discussion, it might lead to some new insights, and so on ... but there would be no new physics.
Well, there is still the Tolman surface brightness test. I pointed out in the PD thread (http://www.bautforum.com/against-mainstream/82267-case-against-tired-light-2.html#post1388871) that tired light actually fits the Sandage et al data better once you include time dilation in TL.


Surely it's a more productive use of time to develop a TL idea to the point where it can actually be tested? Assuming, of course, that it's not equivalent to something already found in textbooks.
We're trying!

Nereid
2009-Jan-20, 04:16 PM
Well, there is still the Tolman surface brightness test. I pointed out in the PD thread (http://www.bautforum.com/against-mainstream/82267-case-against-tired-light-2.html#post1388871) that tired light actually fits the Sandage et al data better once you include time dilation in TL.

[...]

Maybe ...

One of the difficulties, both here and there, is that the various generic TL ideas are, apparently, so imprecise as to preclude generic tests.

So, for example, some generic TLs that include 'time dilation' may be equivalent to GR-based models, while others may be distinguishable in terms of real experimental or observational tests (if only in-principle).

Ari Jokimaki
2009-Jan-21, 06:18 AM
It seems to me that if we interpret light as a wave phenomenon, then my position as stated in the OP has to be right, ie, every (non-Compton) redshift will cause time dilation.
I'm not very knowledgeable in particle physics, but I think that your wave interpretation is different than traditional interpretation, at least I haven't heard it interpreted as wave made of combination of successive photons. I think each photon individually can act as a wave or a particle, but perhaps someone with particly physics knowledge would be kind enough to correct me, or you, or us both.


Since we know light can be taken as either a particle or wave, then clearly one of us has to be right! :)
Or both half right - half wrong. ;)