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Relativity and Cosmology

This is a Blog on relativity and cosmology for engineers and the like. My website "Relativity-4-Engineers" has more in-depth stuff.

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Roger Penrose and Conformal Cyclic Cosmology

Posted July 23, 2020 6:00 PM by Jorrie

I have mentioned cosmological work from Sir Roger Penrose, a British mathematical physicist, in-passing a few times in the past, but have never zoomed in a bit. Despite the fact that his work in general relativity is more highly regarded than his cosmology work, the latter has recently evoked some renewed interest among the Cosmo-community. He came up with an interesting variant of his earlier (discredited?) cyclic cosmological model proposals, now called Conformal Cyclic Cosmology (CCC).

So what has changed to evoke the new interest? CCC is technically tough to follow, but in a nutshell, he performs a conformal rescaling at time > 10100 yr (one Googol year) that equates the then cold empty space to the hot Big-bang, without the inflationary period. It does two neat tricks: Firstly, it resets the universe's entropy to a low value again without needing inflation; Secondly, it allows signals from our cycle (aeon) through to the next aeon. Likewise, signals from the preceding aeon have been allowed through to our aeon. He claims that their signatures have already been observed in the CMB radiation - by both the WMAP and Planck missions. Interesting!

There are many talks and interviews with sir Roger recorded in the last few years. Instead of doing an injustice to his work, I recommend this particular talk of mid-2019 at the Paris Astrophysics Institute: "Are we Seeing Hawking Points in the Microwave Sky?". Penrose's 'Hawking points' are Hawking radiation from evaporation of mega-massive black holes near the end of the previous aeon, that are posited to have left a defined imprint on the CMB.

The video sports clear hand-drawn graphics with the typical Penrose clarity of explanation, which is amazing for a (then) 88 year old. It is a tad long (1h10m), but well worth the time. After the initial introductions, he starts talking about 5 minutes into the YouTube video. But be aware: once the talk starts, it is difficult to stop watching - so pick your time.

I noticed that he has lately been invited by many science popularizers to their podcasts and public discussions. I get the feeling that some inflation- and string-threorists are trying to get him off their backs. I can imagine that their students are asking difficult questions about sir Roger's ideas, so they can't ignore him anymore...

I did a wee-bit of self-study into CCC, so you are welcome to ask my opinion, once you have watched the video (I can't compete!).

J-

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#1

Re: Roger Penrose and Conformal Cyclic Cosmology

07/24/2020 9:38 PM

Cosmic reincarnation... I thought it sounded crazy at first, but not any crazier than the universe inflating from smaller than a proton. Maybe he's on the right track.

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Re: Roger Penrose and Conformal Cyclic Cosmology

07/25/2020 4:54 AM

Yes, maybe. I liked his stacked expanding visual, but not the stacked funnel part, because while matter is the dominating energy in the universe, one cannot conformally rescale space without having some weird form of conformal time. I adapted my Relativity-4-Engineers Fig. 15.4 to the following log-log Plank scale depiction:

This shows more vividly that the singularity and inflation are eliminated, without any weird scaling.

It also made me realize that the actual size of the universe could stay infinite throughout all the cycles - it is only the observable universe that scales up and down. And that conformal down-scaling resets the particle horizon and entropy - and hence time...

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Re: Roger Penrose and Conformal Cyclic Cosmology

07/25/2020 11:23 AM

Since we are allowed to choose any consistent coordinate system in physics, another interesting way of looking at it is through the "telescope" of stacked conformal time against comoving distance. It "portrays" the Penrose infinities beautifully, because the right-hand vertical scale shows the cosmic scale factor from essentially zero to infinity (equivalence of zero and infinity in this scheme).