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I'm happy that the universe is expanding, because we have good scientific evidence in the form of galactic redshift. The Wikipedia Hubble's law article gives what I think is a fair explanation of that. It redirects from cosmological redshift and maybe gives too much emphasis to Doppler shift, but no matter. Because like I said I'm happy that the universe is expanding. Even if there was no evidence, my understanding of general relativity would be telling me that the universe just has to expand. For the life of me, I still don't know why Einstein didn't predict it.

But what I'm not happy about is inflation. I take note of articles like Physicist Slams Cosmic Theory He Helped Conceive where Paul Steinhardt is critical of inflation. He says things like this:

"The whole point of inflation was to get rid of fine-tuning – to explain features of the original big bang model that must be fine-tuned to match observations. The fact that we had to introduce one fine-tuning to remove another was worrisome. This problem has never been resolved".

I empathize. I don't empathize with his cyclic universe, but I share his view that we have not explained any feature of the universe by introducing inflation. In fact, I would dispute the claims that inflation explains why the universe is isotropic, homogeneous, flat, and bereft of magnetic monopoles. I'd even say that I think inflation is a solution to a problem that doesn't exist. But as the Wikipedia article says:

"The basic inflationary paradigm is accepted by most scientists, who believe a number of predictions have been confirmed by observation;

I don't. I'm just some IT guy, but I'm like "the substantial minority of scientists who dissent from this position". Steinhardt is mentioned, as are John Earman and Jesus Mosterin. I can read their paper on SciHub. But what I'm struggling to find is any big-bang cosmological model or models that don't feature inflation. It seems to be included in all big bang literature and images, including this "wine flute" public domain image courtesy of NASA:

enter image description here

Can anybody point some out to me? In other words my question is this:

Are there expanding-universe cosmological models that do not feature inflation?

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    $\begingroup$ Hard to begin to give an answer given that you don't think inflation solves any of the well-known problems of the big bang theory. But you don't say why. $\endgroup$
    – ProfRob
    Mar 28, 2017 at 17:40
  • $\begingroup$ @Rob Jeffries : inflation is said to be the reason why the universe is homogeneous. See for example this answer where jdmcbr x says "Creating a universe where the temperature everywhere was essentially the same requires exceptional fine tuning". It doesn't. It simply needs a different initial situation. $\endgroup$
    – John Duffield
    Mar 28, 2017 at 18:27
  • $\begingroup$ And I misspoke. The Big Bang is most definitely a model, not a theory. $\endgroup$
    – ProfRob
    Mar 28, 2017 at 22:31
  • $\begingroup$ I found this: An Alternative to Inflation by Stefan Hollands and Robert M. Wald. $\endgroup$
    – John Duffield
    Mar 30, 2017 at 22:02
  • $\begingroup$ ^ Seems to be a pretty direct response to inflationary hypothesis $\endgroup$
    – Daddy Kropotkin
    Apr 29, 2021 at 17:38

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Variable speed of light (VSL) theories (for instance Petit (1988) and Moffat (1993)) have been introduced in the past to solve the horizon problem you mentioned, i.e. that the observable universe appears to be isotorpic and homogeneous. If certain universal "constants" (including $c$, the speed of light) are allowed to change, then it is possible for interactions between extremely distant sections of the universe to occur, solving the horizon problem. These modifications still fit in with general relativity and the idea of an expanding universe.

VSL theories, though, have not gained much traction, and inflation is still the prevailing theory in the scientific community today. It solves the horizon problem, the flatness problem (dealing with how fine-tuned the initial density of the universe appears to have been), and the magnetic monopole problem (i.e. why we don't see magnetic monopoles). Inflation isn't the only possible solution to these problems, but it works quite well.

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  • $\begingroup$ Thanks for the answer. I have to say though that I've previously discounted the Moffat/Albrecht/Magueijo VSL idea for reasons of my own. It hasn't gained much traction with me either. $\endgroup$
    – John Duffield
    Mar 28, 2017 at 18:34
  • $\begingroup$ @JohnDuffield I think you'll find there's a reason that non-inflationary theories haven't gained much traction. Mainly because they tend to introduce more problems than they solve. You may not agree with inflation, but it is the best answer anyone has come up with so far. Any non-inflation theories which may exist are likely harder to accept given that they do things like assuming physics isn't constant and usually can't explain everything inflation can. $\endgroup$
    – zephyr
    Mar 29, 2017 at 15:28
  • $\begingroup$ @zephyr : the bottom line is that I don't think it really explains anything at all. HDE talks about the flatness problem, but "the parameter which appears fine-tuned is the density of matter and energy in the universe". Only conservation of energy tells you it surely has to be reducing. As for the magnetic monopole problem, IMHO that comes from a misunderstanding of electromagnetism. The electron has an electromagnetic field, not an electric field. So electric charge is a misnomer. So magnetic charge is misguided. $\endgroup$
    – John Duffield
    Mar 29, 2017 at 17:15
  • $\begingroup$ @JohnDuffield I don't want to turn into an off-topic debate, but I wonder if you really have a firm understanding of these concepts. It seems you're claiming the source of the magnetic monopole problem is a misunderstanding of electromagnetism by every physicist on Earth. You then claim (lone) electrons have magnetic fields which is patently false. They may be able to generate magnetic fields, but they do not have a magnetic pole as part of their constituency. If the solution were as simple as clearing up a misunderstanding, don't you think physicists would have figured that out by now? $\endgroup$
    – zephyr
    Mar 29, 2017 at 17:33
  • $\begingroup$ @zephyr : I have a firm understanding of electromagnetism, perhaps you misread something somewhere? A lone electron doesn't have an electric field or a magnetic field, it has an electromagnetic field. And a magnetic moment. I can't explain why anybody thinks inflation explains the monopole problem. IMHO when you understand electromagnetism you understand why magnetic monopoles do not exist: the electron has an electromagnetic field, not an electric field, so electric charge is a misnomer, so magnetic charge is misguided. $\endgroup$
    – John Duffield
    Mar 30, 2017 at 16:13

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