Guth, Kaiser and Nomura versus Ijjas,Steinhardt and Loeb

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In summary, the conversation discusses a recent paper defending the concept of inflation and eternal inflation from criticism following the Planck results. The authors argue that under a multiverse scenario, such criticism can easily be refuted as anything that can happen must happen. The conversation also touches on the fallacy of using probabilistic sifting in this scenario and compares the multiverse theory to theological discussions, as both require a leap of faith.
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skydivephil
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Happy new year, an interesting paper just posted on arxiv :
http://arxiv.org/pdf/1312.7619.pdf
defending inflation and eternal inflation from recent criticism re Planck results.
 
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I believe the authors have mainly succeeded in pointing out that such criticism is easily refuted under a multiverse scenario. Anything that can happen, must happen, therefore probabilistic sifting [which I view as what ISL was attempting] is an exercise in futility. The fallacy of such thinking is evident in this quote:

"For a start, how is the existence of the other universes to be tested? To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there are an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions. Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith."

— Paul Davies, A Brief History of the Multiverse
 

FAQ: Guth, Kaiser and Nomura versus Ijjas,Steinhardt and Loeb

What is the main difference between the two theories?

The main difference between Guth, Kaiser and Nomura's theory and Ijjas, Steinhardt and Loeb's theory is the concept of inflation. Guth, Kaiser and Nomura's theory proposes that the universe underwent a rapid period of expansion, known as inflation, in the early stages of its existence. On the other hand, Ijjas, Steinhardt and Loeb's theory suggests that the universe did not experience inflation, but instead underwent a phase transition where it rapidly changed from a contracting state to an expanding state.

Which theory is currently more widely accepted among scientists?

Currently, Guth, Kaiser and Nomura's theory of inflation is more widely accepted among scientists. This is due to the fact that it has been supported by a large amount of observational evidence, such as the cosmic microwave background radiation, and has been able to successfully explain many of the observed features of our universe.

How do these theories explain the origin of the universe?

Both theories attempt to explain the origin of the universe, but in different ways. Guth, Kaiser and Nomura's theory proposes that the universe began with a rapid period of expansion due to the presence of a hypothetical field called the inflaton field. Ijjas, Steinhardt and Loeb's theory, on the other hand, suggests that the universe originated from a phase transition in a pre-existing contracting universe.

Are there any ongoing experiments or observations that could potentially support one theory over the other?

There are several ongoing experiments and observations that could potentially provide evidence for one theory over the other. For example, the upcoming James Webb Space Telescope will be able to observe the cosmic microwave background radiation in more detail, which could provide more insight into the early stages of the universe and potentially support one theory over the other.

Can these theories be reconciled or combined?

Some scientists have attempted to reconcile or combine these two theories, but so far, there has been no widely accepted unified theory. However, as more evidence is gathered and new theories are proposed, it is possible that a unified theory may emerge in the future.

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