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Discussion Overview

The discussion revolves around recent videos from the Perimeter Institute (PI) regarding cosmological concepts, particularly focusing on Roger Penrose's Conformal Cyclic Cosmology (CCC), bubble collisions in the early universe, and the measure problem in cosmology. Participants explore observational evidence, theoretical implications, and the challenges associated with these ideas.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that Penrose presented new observational evidence for CCC, specifically regarding concentric circles in the Cosmic Microwave Background (CMB), though there is uncertainty about the validity of this interpretation.
  • Others argue that Penrose's interpretation of the CMB data reflects a misunderstanding of the statistical correlations inherent in CMB science.
  • Hiranya Peiris suggested that if bubble collisions occurred in the early universe, they would be detectable by the Planck satellite, with some participants expressing interest in this claim.
  • Alan Guth posited that the measure problem is not exclusive to inflationary models but also applies to cyclic cosmology, indicating a broader issue in infinite cosmological models.
  • Neil Turok faced challenges regarding the plausibility of inflation based on loop quantum gravity calculations, with some participants expressing skepticism about his dismissal of these results.
  • There is a discussion about finite universe models and their implications, with references to degrees of freedom on the horizon potentially explaining phenomena typically attributed to conditions outside the horizon.
  • Participants shared references to relevant papers and blog posts that explore these concepts further.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement, particularly regarding the interpretations of Penrose's findings and the implications of the measure problem. There is no clear consensus on the validity of the claims made by different participants.

Contextual Notes

Some claims rely on specific interpretations of observational data and statistical methods, which may not be universally accepted. The discussion also highlights the complexity of cosmological models and the challenges in understanding their implications.

Who May Find This Useful

This discussion may be of interest to those studying cosmology, particularly in the areas of cyclic models, the Cosmic Microwave Background, and the implications of infinite cosmological theories.

skydivephil
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I watched a few of the videos on line at the PI
http://pirsa.org/C11008
Some thoughts: it seems to me Penrose did show some new material on observational evidence of CCC, in particular he argued that families of 3 or 4 concentric circles were observed more frequently than a Gausian analysis. I don't think the comparison he had in the talk was what was in his arxiv paper so I think its new, but I am going off memory so might be wrong.

Hiranya Peiris said that if there were bubble collisions in the ealry universe, PLanck will find them.

Alan Guth argued the measure problem is not specific to inflation but is true for cyclic comsology.

This was echoed in Turoks talk, a lot of the the audience agreed with him in what he outlined as the challenges but disagreed that these problems were specific to inflaiton.

Neil Turok was challeneged by the audience on the unlikely nature of inflation given calculation using loop quanutm gravity. I presune they were referring to the Ashkebar/Sloan paper . He simply said he didn't believe it, they must have made a mistake. I would be intrgued if he could fill this out rather than argue from personal incredulity. There seemed to be little loop stuff browsing through the video descriptions, I have no idea why this is.
 
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skydivephil said:
I watched a few of the videos on line at the PI
http://pirsa.org/C11008
Some thoughts: it seems to me Penrose did show some new material on observational evidence of CCC, in particular he argued that families of 3 or 4 concentric circles were observed more frequently than a Gausian analysis. I don't think the comparison he had in the talk was what was in his arxiv paper so I think its new, but I am going off memory so might be wrong.
These supposed concentric circles were just a complete failure to understand the statistics of the CMB. Basically, he took random to mean uncorrelated. But the whole thrust of CMB science is about understanding the correlations in the CMB: fluctuations on the CMB tend to have a certain characteristic angular size on the sky. That characteristic angular size is important, and relates directly to the physics of what happened before the emission of the CMB.

All that Penrose saw in that paper were effects of this characteristic size scale.

skydivephil said:
Hiranya Peiris said that if there were bubble collisions in the ealry universe, PLanck will find them.
Perhaps you're thinking of this result? http://arxiv.org/abs/1012.3667

This is much better science than Penrose's case. It will be interesting to see what Planck has to say.

skydivephil said:
Alan Guth argued the measure problem is not specific to inflation but is true for cyclic comsology.
The measure problem is a hallmark of any infinite cosmology.
 
yes that is the paper. Hiranya Peiris is the lead authors PHd supervisor.
Guth had an interesting analalogy quoting Arthur Eddington who refused to accept black holes as we could never understand them. Similairly I think he was arguing the universe doesn't owe us a finite easier to understand reality.
 
skydivephil said:
yes that is the paper. Hiranya Peiris is the lead authors PHd supervisor.
Guth had an interesting analalogy quoting Arthur Eddington who refused to accept black holes as we could never understand them. Similairly I think he was arguing the universe doesn't owe us a finite easier to understand reality.
Well, I've become very interested in the recent finite universe models, where the degrees of freedom of the horizon are sufficient to explain anything that we would otherwise consider going on "outside" the horizon. This is analogous to recent work in understanding black holes where degrees of freedom on the event horizon of the black hole can be used to represent everything that happens inside it.
 
any refernces to such models?
 

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