Landmark talk by Steinhardt (28 minute video online)

[marcus]

Seriously excellent talk given Monday 23 June at the Princeton Strings 2014 conference by Paul Steinhardt:
http://physics.princeton.edu/strings2014/videos/talk1h.mp4 [Broken]

You may have to pause it and wait for buffering. I found that after the video had played through I could drag the button back to portions I wanted to hear again.

The Monday afternoon plenary session was chaired by Witten and had the theme "what have we learned from BICEP2?" and more generally state of inflationary cosmology from standpoint of normal empirical science. Steinhardt's was the second talk, right after John Kovac (Harvard, BICEP collaboration).

At the end of Steinhardt's talk there was just time for one question, an interesting one posed by Raphael Bousso (UCBerkeley), which got an interesting answer from Steinhardt, so it is worth going through to the end.

In first 15 minutes Steinhardt discussed the inflation paradigm and eternal inflation (à la Guth and Linde) in particular. At minute 15 he concluded that cosmology must be rethought. At minute 17 he introduced the bounce paradigm in a form that achieves homogeneity and flatness without inflation. At minute 21 he made a prediction of NO observable tensor mode in CMB--a prediction which, in his cosmic model, cannot be avoided. So he declared his model readily falsifiable (all they have to do is observe polarization swirls in the background and his particular style of bounce model is dead.)

He had a lot of interesting things to say woven in and around the main points. One side remark was that he and collaborators (e.g. Turok) have a paper coming out soon where they present a version of string theory which can survive their model's bounce. He already claims that they have shown there can be matter degrees of freedom which pass through his style of bounce, so this is just making that more specific, to strings. He invited researchers at the conference to join in the effort to study what happens at the bounce.

 

[marcus]

References:
http://arxiv.org/abs/1312.0739
Sailing through the big crunch-big bang transition
Itzhak Bars, Paul Steinhardt, Neil Turok

http://arxiv.org/abs/1402.6980
Inflationary schism after Planck2013
Anna Ijjas, Paul J. Steinhardt, Abraham Loeb

http://arxiv.org/abs/1404.1265
A general mechanism for producing scale-invariant perturbations and small non-Gaussianity in ekpyrotic models
Anna Ijjas, Jean-Luc Lehners, Paul J. Steinhardt

http://arxiv.org/abs/1407.0992
Dynamical String Tension in String Theory with Spacetime Weyl Invariance
Itzhak Bars, Paul Steinhardt, Neil Turok

The last listed here would seem to be the paper he mentioned towards the end of his talk as soon to appear, and which I referred to above at the end of the previous post. Watching the 28 minute video will, I think, put these four recent papers clearly in context, motivate them, and make them easier to understand.

 

[marcus]

David Gross' "vision" talk partially responds to crit raised by Steinhardt (or implied by Steinhardt's discussion of inflation cosmology as too vague or too flexible)
http://physics.princeton.edu/strings2014/videos/visiontalk5gross.mp4 [Broken]