A Cosmic Controversy

In the February 2017 issue of Scientific American an article, Pop Goes the Universe argues against the idea of cosmic inflation in the early Universe. The authors, Anna Ijjas, Paul J. Steinhardt and Abraham Loeb argue instead for a "bouncing cosmology." Cosmic Inflation Theory Faces Challenges

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The latest astrophysical measurements, combined with theoretical problems, cast doubt on the long-cherished inflationary theory of the early cosmos and suggest we need new ideas

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Now there has been a response by 33 physicists and a response to the response.
A Cosmic Controversy

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In "Pop Goes the Universe," by Anna Ijjas, Paul J. Steinhardt and Abraham Loeb, the authors (hereafter "IS&L") make the case for a bouncing cosmology, as was proposed by Steinhardt and others in 2001. They close by making the extraordinary claim that inflationary cosmology "cannot be evaluated using the scientific method" and go on to assert that some scientists who accept inflation have proposed "discarding one of [science's] defining properties: empirical testability," thereby "promoting the idea of some kind of nonempirical science." We have no idea what scientists they are referring to. We disagree with a number of statements in their article, but in this letter, we will focus on our categorical disagreement with these statements about the testability of inflation.

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There is no disputing the fact that inflation has become the dominant paradigm in cosmology. Many scientists from around the world have been hard at work for years investigating models of cosmic inflation and comparing these predictions with empirical observations. According to the high-energy physics database INSPIRE, there are now more than 14,000 papers in the scientific literature, written by over 9,000 distinct scientists, that use the word "inflation" or "inflationary" in their titles or abstracts. By claiming that inflationary cosmology lies outside the scientific method, IS&L are dismissing the research of not only all the authors of this letter but also that of a substantial contingent of the scientific community. Moreover, as the work of several major, international collaborations has made clear, inflation is not only testable, but it has been subjected to a significant number of tests and so far has passed every one.

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This sort of discussion in science is one of the best things about science. This is a form of peer review that all too often the public is unaware of.Edited by Admin, : Fix character issue.

Thread copied here from the A Cosmic Controversy thread in the Links and Information forum.

Inflation is the name for several models of the very evolution of the universe. It's sort of an "add-on" to the Big Bang Model. The main problems with the early universe are:(a) It is very flat
(b) There are very little gravitational waves
(c) The universe looks roughly the same in each direction
(d) There are no magnetic monopoles
(e) Galaxies look like they formed from fluctuations in the homogenous soup of the early universe.Both (a) (b) (c) are quite non-generic. The universe from current understanding could have been more curved, look different in different directions and should have plenty of gravitational radiation.Inflation attempts to solves all of these. However it does quite poorly at (b), for (c) it doesn't seem to match precisely how the galaxies formed and (d) seems like less of an issue today as it was a problem suggested by theories popular in the 80s.Certainly some of the extreme models of inflation get into very ambiguous territory where it is hard to know if you could every disprove them because the parameters can be adjusted to stay consistent with observations.For the decent models of inflation they seem to explain some things but not all.It's very hard to know how the science of the early universe is going to continue since we've learned a lot about quantum mechanics in the last decade that suggests parts of the world are not amenable to mathematical description and this is probably very relevant in the early universe. Probably plenty of work ahead of us.Edited by Son Goku, : Don't write posts on the phone when you're in a rush