[Bradley_A_Pliam]

After seeing more results and news coming from the JWST, it felt like time to pull the trigger on this article. I probably should've dug into Professor Sean Carol's list of evidence for the prevailing interpretation of redshift coming from distant objects. I may be eating crow for this neglect. Wouldn't be the first time.

[pfdietz]

Various alternatives to the Big Bang have fatal problems. If you tell me your alternative, I'll explain where it goes wrong.

[Bradley_A_Pliam]

That would be much appreciated. I'm interested in learning even if it takes me away from things that seem intuitive. So as I've mentioned in my article, light from more distant objects could be shifted red, not by a dopplar effect, but by its interaction with space debris or just propagation itself over extremely long distances. Where the expanding universe theory seems to "go wrong" is by violating the cosmic speed limit.

[pfdietz]

Ok, that's a "tired light" theory. It fails because that process just changes the frequency of photons, but not their density in space. The background radiation is (to extreme accuracy) blackbody radiation. Blackbody radiation has a spectrum, and an intensity, dictated by physics. The expansion of space preserves both aspects of "black bodiness"; tired light does not.

Tired light also doesn't explain the observed stretching in time of supernova light curves with distance.

Ned Wright explains this at his web site:

https://www.astro.ucla.edu/~wright/tiredlit.htm

[Bradley_A_Pliam]

> that process just changes the frequency of photons, but not their density in space.

Frequency is precisely the necessary thing that needs to be considered as an observed phenomenon that can have alternative explanations, since frequency relates to shifting toward red.

Are you saying that density/luminosity is an independent way of corroborating universal expansion? I don't believe that's the case.

Neither luminosity nor redshift seem, IMHO, to be strong enough evidence to uphold a "preposterous" (to use Sean Carroll's favorite descriptive term for the world) theory that massive things are not just traveling but accelerating away from oneanother.

[pfdietz]

I'm saying that tired light makes an incorrect prediction: that (absent some incredible coincidence) the CMBR will not have the density of blackbody radiation at the same spectral temperature.

It also falsely predicts that SN light curves are not stretched out at higher red shift.

Theories that make incorrect predictions are dead theories. We know for sure they are wrong.

This has nothing to do with the Big Bang, btw. Science works by killing theories, and tired light has been slain. It would be ruled out even if there wasn't an alternative theory available.

[Bradley_A_Pliam]

I don't doubt that the "tired light" theory has been slain. I can update my orientation from your informed response without hesitation. However, I don't think I'm truly talking about the "tired light" theory in a way that plugs into your understanding of it. Although I mention debris in the article, and then kind of took it off the table, what I still have left to posit is that light propagation looses energy over billions of light years, not some short distances that can be tested in a lab or verified via other corroborating observations that relate to shorter distances or parallax geometry. I've completely placed my theory and conjecture out of reach of the lab! Or have I? If I have it might not be worth much in the community of experts, but it still means something to me because I feel like, and nobody seems to be responding to this in any detail, cosmic speed limits are being broken all over the place, as my article states.

[Bradley_A_Pliam]

Thank you for the link. I will be checking that out.

[tadfisher]

The expansion of space is entirely consistent with special relativity (the source of the "cosmic speed limit"). What relativity says is that the speed of light is consistent in all reference frames, which leads to all the phenomena you've heard about, such as time dilation, redshifting, and the upper bound on velocity. However, you have to understand that space and time are the same substance called "spacetime", and adding new space changes the basis of your velocity measurement (v = dx/dt). It's entirely possible that adding space between two regions can cause those regions to separate at a velocity faster than light in either reference frame, because space is the `dx` in the formula.

Another apparent violation of the speed limit occurs beyond the event horizon of a black hole. Space itself is drawn to the singularity faster than light.

[Bradley_A_Pliam]

I worded my reply poorly. I mean to say, Your notion or model of the universe is all downstream of assumptions that redshift can only be related to the Doppler effect (apparently there are a couple types of Doppler effect as the article mentions and links to info relating to "a normal Doppler redshift"). If everything rests on that assumption, it would be something to scrutinize if more and more observed astronomical data continues to pour in contradicting the big bang or expanding universe.

Separating "space itself" from the objects that are governed by universal laws is like saying there could be a north pole without a planet such as Earth. Take away Earth, you have no north pole. Take away objects in motion, you have no basis for talking about spacetime. That's just my intuition, but it seems to point to a gap in explanations, at least from science popularizers.

[Bradley_A_Pliam]

This is all downstream of assumptions that redshift is a certain kind of doppler effect. Redshift could actually be something other than that, and space from outta nowhere feels like just wishful thinking to me. And why is that space getting introduced without also bring with it its own time component? This seems to contradict your point that we don't just deal with space, but spacetime!