What Insights on Time in Physics and Cosmology Emerged from the Pi Conference?

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Discussion Overview

The discussion revolves around insights on the concept of time in physics and cosmology, particularly in relation to Loop Quantum Cosmology (LQC) and its classification as a cyclic model. Participants reference a recent conference that featured prominent cosmologists and express varying interpretations of LQC's implications for the nature of time and cosmological models.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses surprise at the differing views on LQC among experts, suggesting a potential compartmentalization in scientific understanding.
  • Another participant questions the assertion that LQC is not a cyclic model, prompting a discussion on the definitions and implications of cyclic models in cosmology.
  • A participant explains that LQC modifies general relativity at high curvature, replacing the big bang singularity with a bounce, and argues that it does not predict a recollapse due to dark energy, thus not qualifying as a cyclic model.
  • Another participant counters that a universe experiencing a bounce could still be considered "cyclic," even without an infinite series of cycles.
  • A further reply challenges the classification of a non-repeating universe as cyclic, arguing that a cyclic model should involve a repeating process.
  • Some participants reference academic papers to support their claims about the nature of cyclic models and LQC, indicating a distinction between mainstream LQC and other cyclic models discussed in the literature.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the classification of LQC as a cyclic model, with some asserting it is not cyclic due to the absence of repeated cycles, while others argue that a bounce can still warrant the term "cyclic." The discussion remains unresolved with multiple competing views presented.

Contextual Notes

There are limitations in the definitions of cyclic models and the assumptions underlying the interpretations of LQC. The discussion also reflects varying levels of familiarity with the technical aspects of the theories involved.

windy miller
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The Pi just posted a bunch of videos from their conference on time
http://pirsa.org
A lot of the big names in cosmology were there: Sean Carroll, Lee Smolin, Abhay Ashtekar , Andy Albrecht, George Ellis etc
I have to say though I'm a little surprised at some of the questions. How is it i ( layman in this field ) knows that LQC isn't a cyclic model but Andy Albrecht one of the world experts ,doesn't? It makes me think there is far too much compartmentalisation in science, but maybe that's inevitable . Anyway this conference seemed to bring people together form different research programmes and is very interesting if you have the time.
 
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Why do you think LQC isn't a cyclic model?
 
As I understand it , it gives corrections to the Gr at high curvature, replacing the big bang singularity with a bounce. it doesn't make predictions about dark energy turning around and causing a recollapse and hence it is not a cyclic model.
 
windy miller said:
As I understand it , it gives corrections to the Gr at high curvature, replacing the big bang singularity with a bounce. it doesn't make predictions about dark energy turning around and causing a recollapse and hence it is not a cyclic model.
https://arxiv.org/abs/1507.00226
https://arxiv.org/abs/hep-th/0407115

I believe a universe with a bounce is frequently called "cyclic" even if there isn't an infinite chain of cycles.
 
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I have no idea how it can possibly be appropriate to call a universe that contracts and then expands but never repeats this process a cyclic one. One that repeats the process sure, but one that doesn't? i don't see how that makes sense.
 

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