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Please NOTE: "For example, a question that proposes a new concept or paradigm, but asks for evaluation of that concept within the framework of current (mainstream) physics is OK."

And: "Similarly, a wrong answer that makes false statements but claims to work within the bounds of a mainstream theory is also allowed."

See: Is non-mainstream physics appropriate for this site?

The question is indeed in the realm of mainstream science: It's asking about the existence and/or evaluation of a model that explains mainstream observations, such as expanding space and the big bang--but in a slightly different way. Please actually read the question...

I thought of a hypothetical explanation of cosmological redshift. Namely, the light's reference frame (space) is expanding but the distance between objects, galaxies, for instance, is not.

It's just a thought I had. I'd like to know if anyone has explored or refuted the idea. I've never heard it mentioned before.

To re-summarize the idea: Space is expanding but the universe is not, i.e., space expands without changing the distance between objects.

EDIT. To avoid causing confusion, I thought I'd point out, it might seem strange to have expanding space that does not cause objects to move apart, there are, however, at least two ways that this might happen:

  1. As space expands, all objects move towards one another in just such a way that expansion does not cause an increase in distance. Inward motion/contraction cancels out the increase in distance.

  2. Matter and light have two distinct reference frames.

NOTE. Also please note, I'm not talking about the past expansion of the universe from extreme density after the big bang. This is about the macroscopic recession of large objects long, long after the big bang. In other words, the cosmological redshift we see today.

Remember, this is just a fun thought exercise.

SR999
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    Since distance measures the separation of objects in space, how exactly can space expand without affecting the distance between between objects ? – gandalf61 Mar 04 '22 at 18:24
  • @gandalf61 Great question, I updated the post to clarify. Remember this would be in the context of Relativity, also. Thanks. – SR999 Mar 04 '22 at 18:26
  • Option 1 seems very coincidental. I'm also having trouble making that work with cosmology, but maybe it's just me. By option 2, do you mean some kind of bimetric theory? https://en.wikipedia.org/wiki/Bimetric_gravity – Dan Mar 04 '22 at 18:39
  • @Dan Yes, it would be a form of biometric gravity 'theory,' of sorts. For 1., remember, this is all just a hypothetical idea.... If any of this were true, there would presumably be something to explain the coincidence that it presents. Thanks for the comment. – SR999 Mar 04 '22 at 18:45
  • Your distinction between how space and matter transform sounds like covectors and contravectors, Your coordinate axis (space?) are covectors $x_a$ and your matter coordinates are contravectors $x^a$. Then for a linear transformation matrix $M$, $d'^2= x'_a x'^a= x_b(M^{-1})^b_a M^a_c x^c= x_b I^b_c x^c= x_bx^b=d^2 $. The nonorthogonal part of $M$ includes your expansion and contraction, and the distance d of the mass from the origin doesn't change when the expansion/contraction is done. I don't see what this has to do with redshift though? – Gary Godfrey Mar 04 '22 at 23:46
  • (continued} This is somehow different from how theorists+GR explain the expansion of the universe. They would say the distance d between galaxies is NOT invariant and is increasing as the universe evolves (expands). – Gary Godfrey Mar 04 '22 at 23:58
  • spacetime expansion and universe expansion?, Why does space expansion not expand matter? – mmesser314 Mar 05 '22 at 00:05
  • @GaryGodfrey Thanks for the great answer!

    1. Yes, that's what I'm referring to. The reason this relates to redshift is that this expansion is applied to light--but obviously by definition, not to matter.

    2. Well, that's what I'm wondering: wouldn't invariant distance with the above expansion and contraction provide a model of redshift without a (presently!) expanding universe?

    So, in essence, I'm asking has anyone explored this idea? Is there anything wrong with it?

    Thanks!

     – SR999 Mar 05 '22 at 00:55
  • @mmesser314 Thanks for the comment, but those questions relate to different sorts of ideas. – SR999 Mar 05 '22 at 00:56
  • To all, please also note: "Firstly, be certain that it is indeed off topic by the above rules. Note that if a post is simply wrong, leave a constructive comment explaining why, and downvote."

    https://physics.meta.stackexchange.com/questions/4538/is-non-mainstream-physics-appropriate-for-this-site/4539#4539

     – SR999 Mar 05 '22 at 16:32
  • @SR999 If your post is closed, simply editing it to include the rules other users already know will hardly get it reopened. Instead, consider asking on Meta why the question was closed in first place. While the Help Center provides useful guidelines, Meta also discusses many cases that are not covered in the Help Center. This is one of the features of the site being moderated by the users themselves: it adapts and improves itself. – Níckolas Alves Mar 06 '22 at 07:09
  • I'm voting to keep this question closed because the way it is currently formulated is of the form "What do you think of my theory?", which tends a lot to the non-mainstream side and is not particularly useful for the community. It is formulated in a way that challenges mainstream physics without a good reason to do so. I believe it would be better welcomed if you rewrote it in the form "Why do physicists usually dismiss this possibility?" – Níckolas Alves Mar 06 '22 at 07:11
  • @NíckolasAlves Thank you for the feedback. I will rephrase it. However, this is really a matter of semantics in the most extreme sense, as that's literally what I asked, accept, I don't know if they do usually dismiss it or not, or if it's been considered yet, or if there's inherently something wrong with my understanding of the ideas surrounding the subject as a whole... – SR999 Mar 06 '22 at 15:33
  • @NíckolasAlves Also, it's not a theory, a theory is verified, e.g., relativity.

    The goal of science is to 'challenge' mainstream explanations in the sense of asking why it's true instead of something else.

    This sort of approach that you seem to be espousing doesn't seem to encourage actual understanding.

     – SR999 Mar 06 '22 at 15:40

1 Answers1

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The universe is measurably much colder and less dense than it was in the very early universe. Things have to have gotten farther apart at some point - that is, diffused and cooled by adiabatic expansion against the gravitational field, because we can infer without recourse to cosmic expansion that the early universe must have been filled with an incandescent plasma. There's not enough mass in our own comparatively ultra-dense solar system to fill it with gas dense enough to ignite; and there's not enough energy in our own comparatively ultra-hot solar system to ignite the gas into incandescent plasma. Forget about the unimaginable emptiness that is our comparatively dense galaxy, or the brain-smashingly huge nothingness that is intergalactic space.

Matter is conserved, matter density is much smaller, therefore space is much bigger. Energy is conserved, energy density is much smaller, therefore space is much bigger.

g s
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  • Great answer. (I'd like it if I could, sorry not enough rep.) However, my question wasn't really about the past density of the universe per see. Rather, it was about the hypothetical explanation of redshift that I recently thought of. My explanation is compatible with the universe having once been dense. What it addresses is whether or not the objects in the universe are still moving away from each other at cosmological distances. – SR999 Mar 04 '22 at 20:17
  • In other words, whether, the distance between objects is still increasing.... – SR999 Mar 04 '22 at 20:19
  • I misunderstood your intent to be asking why we think that one particular weird idea (the universe can expand) is better over other hypothetical weird ideas, to which I think the redshift-independent inference that the universe has expanded is pretty conclusive. If the question is about evaluating your particular personal theory specifically, I think it is off topic for Physics SE, which tries to stay narrowly focused on questions concerning the current state of mainstream physics. – g s Mar 04 '22 at 21:34
  • I wouldn't say it's off topic: Asking about a hypothetical interpretation of mainstream observations lends insight and is 'mainstream science.' In biology, for instance, it is perfectly reasonable to ask if humans would have been likely to evolve if the whole process were run again with different parameters. Even though no one can really answer this, and even though any ideas are mostly just speculation...This is where all science starts--thinking about how things might work. – SR999 Mar 04 '22 at 21:40
  • Also worth noting, I'm not asking about 'my' hypothetical idea (which isn't a scientific theory, BTW), I'm more asking if anyone in the scientific community has engaged with this kind of idea or if such ideas haven't been explored yet. – SR999 Mar 04 '22 at 21:46