I Interesting controversy about inflation models of the universe

[kodama]

I'm opening this thread for discussion on the latest debate over inflationary cosmology as outlined over at scientific american

the original article on inflation was

Scientific American published an article by Ijjas, Steinhardt and Loeb

https://www.cfa.harvard.edu/~loeb/sciam3.pdf

then a rebuttal signed by 33 physicists, A Cosmic Controversy,

https://blogs.scientificamerican.com/observations/a-cosmic-controversy/

followed up by a rebuttal again

http://physics.princeton.edu/~cosmo/sciam/index.html#faq

followed by a counter

https://undark.org/2017/05/09/a-deb...d-editing-at-scientific-american-gets-heated/

any thoughts comments

any prospects of large hadron collider finding evidence of the inflaton ?

 

[mitchell porter]

any prospects of large hadron collider finding evidence of the inflaton ?

Some people think the inflaton was found in 2012...

 

[kodama]

Some people think the inflaton was found in 2012...

I assume you are referring to the Higgs - higgs inflation model is not favored.

 

[fresh_42]

<moved and merged from another thread>

I just found this interesting controversy about inflation models of the universe.
As it is often a subject here, I thought, it might be interesting to our members.

https://blogs.scientificamerican.com/observations/a-cosmic-controversy/

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.

This is a response on

http://physics.princeton.edu/~cosmo/sciam/assets/pdfs/SciAm.pdf

The principal message of the press conference was that the Planck data perfectly fit the predictions of the simplest inflationary models, reinforcing the impression that the theory is firmly established. The book on cosmology seemed to be closed, the team suggested. ...
If anything, the Planck data disfavored the simplest inflation models and exacerbated long-standing foundational problems with the theory, providing new reasons to consider competing ideas about the origin and evolution of the universe

which led to the controversy.

As a rare instance of scientific disputes to become public, I think it sheds some light on different views within the community of renowned cosmologists and how the emergence of opinions often evolves.

 

[websterling]

higgs inflation model is not favored.

What exactly causes Higgs inflation to be disfavored?

 

[kimbyd]

Sean Carroll also responded to this statement (and cosigned the above statement):
http://www.preposterousuniverse.com/blog/2017/05/10/is-inflationary-cosmology-science/

 

[durant35]

The most interesting thing in this is how Steinhardt once was one of the three kings of inflation/multiverse hypothesis and now he is the leader of criticism. It will be nice to see if anybody else will jump on his bandwagon. I hope so, because I think that eternal inflation specifically is BS.

 

[kodama]

The most interesting thing in this is how Steinhardt once was one of the three kings of inflation/multiverse hypothesis and now he is the leader of criticism. It will be nice to see if anybody else will jump on his bandwagon. I hope so, because I think that eternal inflation specifically is BS.

could our universe expansion due to dark energy be evidence of eternal inflation

 

[windy miller]

I am curious as to how Paul Steinhart squares his comments on inflation today with what we said when he brought his Ekpyrotic model when he said it was a myth that inflation makes no firm predictions
http://wwwphy.princeton.edu/~steinh/dense8.pdf

 

[kimbyd]

could our universe expansion due to dark energy be evidence of eternal inflation

No, not really. The magnitude of the expansion is vastly different. There have been a number of theorists who have considered that the inflaton and dark energy might potentially be the same thing (lookup "quintessence"), but so far nothing really compelling has come forward.

 

[kodama]

No, not really. The magnitude of the expansion is vastly different. There have been a number of theorists who have considered that the inflaton and dark energy might potentially be the same thing (lookup "quintessence"), but so far nothing really compelling has come forward.

ok.
how about multiple bounces followed by a slow expansion The magnitude of the expansion is same as dark energy

 

[kimbyd]

ok.
how about multiple bounces followed by a slow expansion The magnitude of the expansion is same as dark energy

During the rebound from the bounce, the rate of expansion would have been many orders of magnitude faster than the current expansion rate. I'm not aware of any models which connect the current expansion to the LQC bounce. I could certainly have missed those models, however.

 

[Thomas Moore]

For those that are interested, there are two papers I found also intrigued by this recent "controversy" that specifically show eternal inflation models have many issues:
1. https://arxiv.org/abs/1408.2249 - Published in CQG
2. https://arxiv.org/abs/1508.02670 - Published in PRD

Thomas

 

[durant35]

Are there any plausible models in which inflation is NOT eternal, and the multiverse is avoided?

This seems one of the things that bothers Steinhart. I wonder if he feels the same way about MWI.

 

[windy miller]

There may be models of inflation that are not eternal but Planck data seems to favour models of inflation that are eternal according to Steinhardt.

 

[kodama]

There may be models of inflation that are not eternal but Planck data seems to favour models of inflation that are eternal according to Steinhardt.

could we be in an eternally inflating universe with dark energy expansion as a part of it?

 

[durant35]

There may be models of inflation that are not eternal but Planck data seems to favour models of inflation that are eternal according to Steinhardt.

I lost you here.

Isn't Steinhardt saying that the Planck data experiments disfavour eternal inflation (and inflation all together)?

 

[windy miller]

That

I lost you here.

Isn't Steinhardt saying that the Planck data experiments disfavour eternal inflation (and inflation all together)?

Thats not my understanding. in the paper they are very clear Planck favours models of inflation that are plateau like and these models are eternal. They then claim that there other conceptual problems with these plateau models.
So the debate between these parties is no whether the Planck data favours multiverse models, it does. Rather the debate is whether the problems that arise in a multiverse such as the measure problem can be overcome or are they are so serious that an alternative like a cyclic model should be considered instead.