Thirty orders of magnitude in a fraction of second? Contrary to what we sometimes read, that’s only a hypothesis:
In the popular science media, inflation is sometimes presented as if it was established fact. It isn’t. Its status is similar to that of particle dark matter. They are both unconfirmed hypotheses. But while most physicists agree that particle dark matter has yet to be empirically confirmed, opinions about inflation are extremely polarized.
On the one hand you have people like Alan Guth, one of the inventors of inflation theory, arguing that the theory has made many correct predictions and that evidence speaks for it. On the other hand, you have people like Paul Steinhardt, interestingly enough also one of the inventors of inflation, who argue that inflation doesn’t make any predictions and isn’t even science. In an essay some years ago, Steinhardt together with Anna Ijjas and Avi Loeb wrote “inflationary cosmology, as we currently understand it, cannot be evaluated using the scientific method.”Sabine Hossenfelder, “Did the early universe inflate?” at BackRe(Action) (March 5, 2022)
So to summarize. Guth is right in saying that inflation is good science. But he is wrong with the reason for why that’s the case. Steinhardt is right with pointing out that Guth’s argument doesn’t hold up. But his conclusion is wrong because there are other reasons for why inflation is good science.
However, that doesn’t mean inflation is right. Physicists have proposed many other theories for the early universe, for example cyclic cosmology, and those can also explain observations. And maybe in the end one of those other theories will be the better explanation.Sabine Hossenfelder, “Did the early universe inflate?” at BackRe(Action) (March 5, 2022)
It’s the part in between that’s the most fun.
You may also wish to read:
Sabine Hossenfelder asks: Will the Big Bang repeat? Hossenfelder: I am not sure that CCC actually solves the problem it was supposed to solve. Remember we are trying to explain the past hypothesis. But a scientific explanation shouldn’t be more difficult than the thing you’re trying to explain. And CCC requires some assumptions, about the conformal invariance and the erebons, that at least to me don’t seem any better than the past hypothesis.
At Mind Matters News: Theoretical physicist: Quantum theory must be replaced
Sabine Hossenfelder can live with the neutrinos that are inconsistent with the Standard Model of physics but quantum uncertainties are beyond the pale. We might conclude that the universe is a stranger place than we have sometimes been led to suspect and that the amount and type of strangeness each of us can tolerate depends, to some extent, on prior commitments. But it is what it is anyway.