The subject says it all.

Blondin et al. (2008), recently accepted to ApJ, and posted to the astro-ph preprint server this past Friday finds unambiguously confirms time dilation in 13 supernova spectra up to z~0.62. This has been observed before in relatively nearby supernova, but this paper goes to much higher redshift and is much more robust. They also make the point that this unambiguously rules out Zwicky's tired light hypothesis...

The paper is fairly short, quite thorough and is a good read. Can we check this one off the list now?

Also, while looking at the references, I found Davis & Lineweaver (2004) discussing common misconceptions about the standard cosmology, including "misleading ... statements in the literature." Might be a good one to keep in mind for all the times such things come up in ATM threads.

No we can't and we should not: Once again, supernova researchers have presented us with a new data reduction exercise and a new set of assumptions, not the least of which is:

If the proper interpretation of the spectrum includes a power law reduction of the spectrum that is consistent with aging in the supernova population, what does this tell us about prior studies? In 2001, Goldhaber and Perlmutter assumed that there was no aging bias and determined there was no Malmquist bias in crop of supernovae up to much redshifts higher that 0.62. They published curves in which their residuals fell evenly upon both sides of their mean at all redshifts.

In their introduction, Blondin says:

There are several lines of evidence that suggest Malmquist bias in a major factor: We find much brighter supernova events with longer lightcurves in the local sample that in the high redshift time-dilation corrected sample. That is a red flag. There are fewer supernova being found at high redshift than a simple extrapolation from the local population would predict. Fewer observed events at high redshift is consistent with the local population, if cosmic attenuation factors are severely underestimated. In this case, the punitive sample of high redshift events observed is consistent with the small population of overluminous events observed locally. Finally, their is the observation of a few supernova at high redshift that have the spectra of type Ia, but their light curves are much too short (after time dilation correction) to consider them 'normal' type Ia. If space is more greatly attenuated that currently believed, this small sample of understudied events may actually be more representitive of the nominal local population.

I don't think you will see a hard verdict on supernova light curves and time dilation until the scopes are both powerful enough to more clearly identify 'underluminous' supernova at great distances and compare the 'underluminous' distributions at high and low redshifts. In any case, The distant sample should include events featuring extremely long light curves (after time dilation corrections) - lightcurves that are much longer than the longest light curves found in the local space. These extremely long lightcurves have not been observed.

__________________
jwj

The Reluctant Cosmologist

It is a misconception to say that the time dilation here rules out tired light hypotheses (whether Zwicky's or others). I have often pointed out that time dilation has been found wherever redshifts occur, whether in SR, GR or even the classical Doppler shift (the latter being used to predict time dilation in SNe in the first place). Can anyone think of a case of a redshift which has not been so connected? We can reasonably expect to find time dilation when the tired light mechanism is finally pinned down.

ExpErdMann: do you have any evidence whatsoever that any tired light scenario actually predicts time dilation? The reason that an expanding universe and classical doppler shift predict time dilation is because the sources are moving and thus have different relative velocities. Tired light claims that the sources are not moving, and thus there should be no time dilation.

Do you have any evidence to the contrary? Zwicky's tired light certainly does not predict time dilation.

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Think of a train of em waves travelling through space. Now suppose that something redshifts the whole train. In that case, the length and duration of the wave train must increase by the (1 + z) factor. It doesn't matter what's doing the redshifting.

What? Do you actually have a citation for a tired light model that predicts time dilation? It certainly is not mentioned in Zwicky's 1929 paper. I'm also pretty sure that compton scattering (which produces a frequency shift) does not produce time dilation, though I'd be happy to be proved wrong on that point.

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

The problem with most alternative suggestions to relativistic time dilation is that they would also result in time-incoherence and bad spectral blurring.

Ordinary Doppler shifting would result in similar light cones to relativity, but not time dilation as calculated in relativistic models. When distant supernova light curves are studied, the number of days the event occurs over is assumed to have expanded by the 'z factor', correlating with redshift of the spectral lines. Simple 'tired light' models generally assume energy has been depleted from the spectrum; and any time element lost during radiation transfer and such is assumed to be trivial (yes? No?). ExpErd man has a point, but it would help to elaborate a little.

__________________
jwj

The Reluctant Cosmologist

First off, I would point out that the mainstream story has changed over time. The current view is not that it's a Doppler shift that's causing the redshift (and time dilation). Instead they call it a "cosmological redshift" and attribute it to a "stretching" of space time. Now does the spacetime stretching idea imply that there should be time dilation? I don't know. But let's say it does. Then it may not be too hard to connect that with a tired light mechanism too. The waves in a wave train need not be stretched as a result of expansion, just stretched through a loss of energy. Incidentally, the fate of the lost photon energy in the mainstream view is considered problematic in mainstream discussions.

You're focusing on the fact that no one has come up with a tired light mechanism yet that is free of problems. I would agree we don't have the mechanism yet (but would add that my own mechanism, not fully worked out, could avoid most of those problems. See my recent paper in Apeiron). The common error people make (including the authors of the paper you mention) is to equate the tired light concept with a specific mechanism (eg, Zwicky, Compton) and then conclude that the SN data prove the expansion case. Tired light can still be used without a well-defined mechanism to get a better handle on cosmology. The precise mechanism can come later. We can be sure the actual tired light mechanism, once it is found, will show time dilation too. Time dilation actually helps the tired light case with respect to the Tolman surface brightness test.

So, if I might summarize what you are saying:

This as-yet-unspecified tired light theory, which has neither specifics nor mechanism nor coherent mathematical formulation, is certain to predict time dilation of distant sources, even though no tired light model yet proposed does so, nor are there any specific reasons why we should believe that a new one would.

Is that about right?

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Not quite. Let's try again. I'll go to the paper you cited. Here's what they have on p. 7.
There are two things to take note of here. First, Zwicky proposed a specific tired light hypothesis, which was based on a gravitational drag mechanism. Basically, light loses energy due to gravitational drag by the matter it passes in space. The second thing to note is their lumping together of all tired light hypotheses as "Zwicky's". Many tired light hypotheses have been proposed and will continue to be proposed and so the statement that "this hypothesis does not predict a time-dilation effect" is simply invalid. You would have to examine each mechanism on an individual basis to see if time dilation is predicted or not. Maybe one will come along that does. So their blanket statement in the abstract that tired light is unambiguously ruled out is simply false. Expansion is not proved.

Again I ask you: can you provide me with any tired light model that does predict time dilation? Saying "maybe one will come along that does" is irrelevant. Maybe a version of "turtles all the way down" will predict our motion around the Milkyway, but until such a model is put forward there is no reason to think that it will appear, since none of the "turtle" class of models has been even remotely successful so far. The same for tired light.

And the paper explicitly states that they were comparing it with Zwicky's model. So my question at the top of this post (and my summary of the state of things in my previous post) still stands.

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

No, I think they are referring to tired light hypotheses generically and excluding them all. They just use Zwicky's as a convenient handle. Check the wording "interact with matter and other photons in a static universe". That's pretty vague, not what Zwicky said. All you have to concede is that it is possible that a tired light mechanism can possibly arise which predicts time dilation too. Is this so hard? It seems it was hard for the authors of the article, but you too?

Well, as they say: "Anything's possible!" But if all such proposals to date don't work, and we have a perfectly valid theory that does explain the observations, I'm not going to hold my breath waiting for the latest version of "tired light" which may or may not predict time dilation.

__________________
"What do you care what other people think?" -- Richard Feynman
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Feynman, at the conclusion of his Challenger report

Fair enough!

And let's also not forget that this as yet unspecified mechanism for tired light would have to predict, somewhat peculiarly, the same time dilation mechanism as a FLRW expanding universe model....

Even that aside, tired light is dead for other reasons.

I don't see much point in trying to rule out Zwicky's tired light hypothesis anyway. To me that's similar as if I would try to rule out some 1930's version of Big Bang hypothesis, which would be rather pointless exercise. Zwicky's tired light hypothesis didn't even try to explain the supernova time dilation because that body of evidence didn't exist back then.

__________________
"Stupidity gets denser in the crowd" - Old Finnish saying. [My website] [Nimblebrain forums]

So maybe you'd like to suggest another, which also doesn't fail in this way (as noted in the link I gave, above):

It seems to me that what ExpErdMann is proposing is NOT tired light, but rather some other unelaborated idea that would somehow both take away photon energy over distance, and increase the distance between photons as they travel, but NOT cause an expanding universe... It strikes me this can only happen if we are loose with the idea about what constitutes an expanding universe, verses simple inserting more space into a non expanding universe and changing the scale.

__________________
Forming opinions as we speak

I wonder if this simple analogy can help. Suppose we have a pool of water and drop a stone into the middle. The waves move out with initially small wavelength. As they travel, the wavelength will increase. Someone measuring the time between wave crests will see a 'dilation' effect. Mathematically, is there a difference between this stretching and the spacetime stretching of the BBT? In the paper by Blondin et al. in the OP, Appendix A gives the time dilation derivation for the latter. I'm thinking I can work these equations for the effect I'm describing. I emphasize that this is just an analogy. I have a more detailed model for what's happening, which I linked to above.