Cosmology: Inflation theory under attack (Introduction)

by David Turell , Wednesday, August 02, 2017, 00:54 (2460 days ago) @ BBella

There are problems with the theory:

https://evolutionnews.org/2017/08/cosmic-inflation-theory-loses-hangups-about-scientifi...

"Two features of our universe puzzle cosmologists: One is the horizon problem: The universe looks the same in all directions and the cosmic microwave background radiation is about the same temperature everywhere. As String Theory for Dummies puts it, “This really shouldn’t be the case, if you think about it more carefully.” Assuming that current measurements are correct, the radiation must have exceeded the speed of light if it really communicated in this way, but that is forbidden by the standard Big Bang model of the universe.

"Then there is the “flatness problem”: “The matter density and expansion rate of the universe appear to be nearly perfectly balanced, even 14 billion years later when minor variations should have grown drastically” (Dummies). Inconveniently, the apparent 1:10^66 fine-tuning of the Big Bang, of which horizon and flatness are features, is frequently used as an argument for the existence of God.

"Cosmic inflation theory, first proposed by Alan Guth in 1981, modified the Big Bang theory (the Standard Model) by proposing that the universe, instead of unfolding at a steady pace, expanded rapidly shortly after it was created, which could account for apparent fine-tuning.

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"The “bouncing cosmology” was initially proposed by Steinhardt and others in 2001, and fleshed out in 2014. When BICEPS II failed to find evidence of inflation in 2014, Michael Slezak crowed at New Scientist “Inflation is dead, long live inflation! The very results hailed this year as demonstrating a consequence of inflationary models of the universe — and therefore pointing to the existence of multiverses – now seem to do the exact opposite. If the results can be trusted at all, they now suggest inflation is wrong, raising the possibility of cyclic universes that existed before the big bang.” Some were willing to trade the shadowy multiverse for (at least) one other (past) universe, however modest.

"An exchange of letters followed, between the three authors (IS&L) and 33 cosmologists who defended early rapid inflation, among whom readers may recall Alan H. Guth, Sean Carroll, Andrei D. Linde, Stephen Hawking, Lawrence Krauss, Martin Rees, George F. Smoot III, Leonard Susskind, Alexander Vilenkin, and Steven Weinberg.

"The 33 signatories pointed to the fact that 14,000 papers that use the word “inflation” or “inflationary” in their titles or abstracts have been written by 9,000 scientists. They were stung by the accusation that inflationary cosmology “cannot be evaluated using the scientific method” and that some proponents have proposed discarding a defining property of science: “empirical testability.” They retort that “it has been subjected to a significant number of tests and so far has passed every one.” That would settle the matter except that, as they admit, “Inflation is not a unique theory but rather a class of models based on similar principles.” Empirical science, they concluded with a flourish, “is alive and well!”

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"IS&L replied that “The claim that inflation has been confirmed refers to the outdated theory before we understood its fundamental problems,” including the fact that generic inflation leads to eternal inflation and, in consequence, a multiverse: “And if inflation produces a multiverse in which, to quote a previous statement from one of the responding authors (Guth), ‘anything that can happen will happen’—it makes no sense whatsoever to talk about predictions. Unlike the Standard Model, even after fixing all the parameters, any inflationary model gives an infinite diversity of outcomes with none preferred over any other. This makes inflation immune from any observational test.”

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"All parties to the dispute assume, as a metaphysical stance, that science cannot address the possibility that the universe shows evidence of design. Even if design turns out to be the best explanation and the most fruitful for progress, it cannot be accepted, as a matter of first principles."

Comment: Inflation explains much of why the universe looks as it does, but not without problems. A cyclic universe gets rid of the origin problem but keeps the Big Bang. It also gets rid of the multiverse. A cyclic universe doesn't get rid of a first cause.