Assume that there could be a property of light that it gets very gradually steadily red-shifted by traveling large astronomical distances, in exactly the same way that Doppler shift from receding velocity would. Perhaps there is a period of 1000 years or more from emission before there is any observable red-shift, so we would not be able to measure this effect in laboratory for quite a while. Could this be an alternate explanation for why other galaxies appear red-shifted in proportion to distance from us, as opposed to the proportional redshift being from Doppler effects?

Also assume that there could be a property of light that after an enormous distance, it stops traveling as observable light. Something unknown happens that may conserve mass and energy or whatever, but practically speaking, we can't observe light after it has traveled the radius of the observable universe. Could this be an alternate explanation of why there seem to be a finite number of observable galaxies in the visible universe? Could this not also be a possible explanation for what cosmic background radiation is (i.e. perhaps light at superlong range degrades in stages, first producing the noise of cosmic background radiation which is what we can detect of galaxies beyond what we see as galaxies, and it's not infinitely bright because a certain range beyond that, it doesn't even reach us as cosmic background radiation)?

In other words, is it possible that the observed galaxies are not generally all expanding away from each other, but that light simply redshifts over extreme distance? What evidence besides redshift and a finite number of observed galaxies suggests that galaxies are all expanding away from each other? Is there a non-redshift-based distribution of observed galaxies in relation to each other that points to a specific location other than our own from which everything seems to expand? Is there some evidence that contradicts the hypothesis that light has a maximum range after which it can't be observed? Do we seem to be on one particular side of the universe of known galaxies? (I have read a bit about the Tolman surface brightness test - is there a reason this could not just be a property of light at great distance? Is it just that there is a convincing correspondence of galaxy redshift data to independent calculations of expected frequencies from expanding/receding sources?)

Furthermore, even if we have multiple forms of evidence that there seems to be one cloud of galaxies expanding from one point, what if there is a limited range of light propagation that could be even greater than the width of the cloud of visible galaxies? Could there not then be other galaxies (or whatever) even further than what we can see? Or is there some evidence that contradicts that possibility? Does the universe seem to be a non-Cartesian bubble in some sense?

Post-script: I have read about the history of "tired light" theories and how they have been discounted since the 1990's and (as I mentioned) about the Tolman surface brightness test (about which I am just interested why it might not be that light just behaves that way at range - is it because of congruence of distant galaxy data with a previous finite expansion theory's formulae which would have no other reason to match some arbitrary behavior of light over distance?). I am not proposing that my assumptions be treated as competing theories - I am asking about the nature of the evidence and reasoning there is that has people discount such theories.

Also I am not asking "what else could explain cosmological redshift?", as the people who marked this as duplicate suggest. I am asking "what evidence contradicts the possibility that some unknown long-range properties of light are leading to an expanding finite cosmological model?"

Post post-script: Again this has been marked as a duplicate, and SE generated a message asking if the answers there answer my question. There is overlap in the questions, but I prefer my more detailed wording to the suggested one, and I prefer the answers and comments found here.

And no, the answers there don't entirely answer my question, or at least I don't understand the detail of them. It seems to me that the downvoted answer here leaves an aspect that I still don't really understand the answer to - that is, could it not be that the "time dilation" could also be the result of some long-distance effect, and would we not expect to be able to see more large-scale effects of this time dilation on the movements of objects? The suggestion was galaxy rotation statistics, though I wonder if anything else is distant-yet-distinguishable enough to test this.


marked as duplicate by knzhou, ZeroTheHero, Jon Custer, user191954, A.V.S. Mar 2 at 8:43

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  • $\begingroup$ I'm sure someone can answer this more thoroughly, but I'd say two things: (1) Why would light not exhibit any signs of frequency drop until 1000 ly? Travelling a distance does nothing inherently to light, so how would these light waves "store" the information of how long they've travelled? (2) If this universe was not expanding, we would experience a "big crunch" $\endgroup$ – Señor O Oct 31 '14 at 19:53
  • $\begingroup$ @Dronz, your hypothesis is the long-considered Tired Light Theory. See en.wikipedia.org/wiki/Tired_light. $\endgroup$ – DavePhD Oct 31 '14 at 20:04
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    $\begingroup$ This strikes me as a combination of already well known physics (limits on size of observable universe) and gibberish (alternate red shifting) $\endgroup$ – Sean Oct 31 '14 at 20:19
  • $\begingroup$ @SeñorO (1) Because of some unknown detail of the unknown property of the inner mechanics of a photon. A machine or algorithm can easily have some threshold where one aspect reduces only after some other aspect reduces. I'm just trying to suppose that possibility in order to see what the counter-evidence is, apart from Occam's Razor. (2) That's a good point, though if light has some extreme range limit, why not gravity? $\endgroup$ – Dronz Oct 31 '14 at 20:52
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    $\begingroup$ @Dronz Read the wikipedia article on tired light. I think a straightforward piece of counterevidence it mentions is the time dilation of distance events consistent with the expanding universe/redshift models. $\endgroup$ – Señor O Oct 31 '14 at 23:05

The light curve peaks of Type Ia supernova become broader at higher redshifts. The amount of broadening is in proportion to the amount of redshift $(1+z)$. i.e the cosmological time dilation works exactly as expected for an expanding universe, see for example Blondin et al. (2008). A "gradual redshifting" of light as it travelled a distance does not explain this time dilation.

The plot below shows how the measured "de-dilation factor" from supernova light curves depends on their redshift (from Blondin et al. 2008). It goes as $1/(1+z)$, exactly as expected. The horizontal dashed line is what would be expected from "tired light".

This method was proposed by Wilson (1939) as a test of the expanding universe theory rather than the "gradual dissipation of photonic energy" (aka "tired light"). The test has been passed with flying colours.

"Stretching of light curve width in Type 1a supernovae from Blondin et al. (2008)

  • $\begingroup$ Super! So to paraphrase, supernova explosions appear to happen in slow motion at a rate exactly predicted by relativistic time dilation formula. Thank you and congratulations for being the first person in ten weeks to seem to answer my question! What then of the claim in Bill Wesley's answer that galactic rotation speeds do not seem to show this effect? $\endgroup$ – Dronz Jan 13 '15 at 23:12

If all galaxies in the universe have always rotated at roughly the same speed and if more distant galaxies are receding more rapidly than we should observe slower rotation rates for more distant galaxies. This is simple classical physics, if an ice cream truck drives away from the observer the song is not just lower in pitch, it is also slower in tempo so the tempo of galactic rotation should appear to be slower with distance.

This is NOT what has been observed however, the speed of galactic rotation is observed to show a consistent average with distance which means that over the presumed life of the universe galactic speeds must have been decreasing if inflation/expansion is the explanation for the red shift which seems very unlikely.

To presume an unknown process by which light is downshifted in frequency, possibly by transferring its energy with downshifting into increasing the strength of the gravitational fields it is passing through is far less of a leap than presuming dark matter and energy.

The real reason the tired light hypothesis is anathema is that it would falsify the big bang which any such attempt is career suicide,anyone who tries must be discredited Dark mater and energy are terms used to imply evidence will be found in the future that will prove the big bang hypothesis, current observations falsify the big bang hypothesis however, there is no explanation for why galaxies are able to hold together given the current calculated rate of rotation assuming a Doppler shift explanation for the red shift, and the Doppler shift explanation requires an infinite acceleration of expansion which can not be explained in terms of energy, so falsifying evidence against the big bang is instead touted as future evidence that will prove the big bang, the scientific equivalent of a knowledge pyramid scheme

scientists are people, falsifying the popular big bang theory is career suicide if one works as a scientist hence all the hysterical derogatory name calling. Its very unfashionable to attempt to extend Newtonian physics to account for current observations

this book will answer your questions in a rational manner


and this is a general data base that will provide a complete picture from the late Physicist James Paul Wesley


  • $\begingroup$ Tired light fails because it doesn't match observables. $\endgroup$ – Kyle Kanos Jan 13 '15 at 21:55
  • $\begingroup$ Thanks! I find it odd that no one seems to be able to present an actual explanation, but they are willing to downvote this answer and call my question gibberish. This seems like evidence for the "career suicide" theory showing a louder signal here than the unexplained "time dilation" handwave. As I asked in comment reply to "time dilation", would we not expect distant galaxies to seem to rotate more slowly, if that is the case? Or not? $\endgroup$ – Dronz Jan 13 '15 at 22:19
  • $\begingroup$ @KyleKanos Your link refers to a gravitational cause, but what if light simply redshifts over extreme distances? $\endgroup$ – Dronz Jan 13 '15 at 22:21
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    $\begingroup$ @Dronz: Here is a better link, then. As stated, tired light fails because it doesn't match the observables. $\endgroup$ – Kyle Kanos Jan 14 '15 at 2:42
  • $\begingroup$ @KyleKanos Thanks! That is a very good link and right on topic. Do you happen to know of anything discussing the galactic rotation idea Bill mentioned on this answer? $\endgroup$ – Dronz Jan 14 '15 at 4:17

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