Will the Big Bang repeat?

Does the universe cycle through eons, in which an infinite sequence of big bangs happen? How does Roger Penrose's conformal rescaling work and what does it have to do with entropy increase? I go through this in today's video.

The paper I talk about at 7 mins 3 seconds about rings in the CMB is this:

The paper about Hawking Points that I mention at 7 mins 28 seconds is this:

The re-evaluation of Hawking Points in the CMB that I talk about at 7 mins 55 seconds is here:

The paper about the past incompleteness of Steinhardt's cyclic cosmology which I refer to at 11 mins 20 seconds is here:

0:00 Introduction
0:51 What is Conformal Cyclic Cosmology?
3:01 What is CCC good for?
5:00 What's with the physics?
9:25 What do I think about it?
12:20 Sponsor message

[Lagrange_Point_]

Excellent. I enjoyed that talk. Have to say, I rather like Penrose's CCC idea. It's a brave effort. He himself admits it is quite speculative and I am sure he'd have no problem with it being discussed in this informed and fairly detailed way.

[alisaiterkan]

I had been waiting for this episode! Penrose's contributions for the geometrification of the puzzle we have been trying to solve has been spectacular; and he seems to be such a gentleman that one can't help but root for him. Still, I don't see this video as a negative thing at all. When one gets on the podium and says "I claim X", the audience is supposed to ask how/why? Sabine is doing just that. I now hope for a response from Penrose.

[geraldvaughn]

I think Penrose has a point. Rescaling can be done when all matter has decayed. No matter means no time which means no distance.

[johnholly]

I love getting notifications on Saturday morning letting me know that Sabine has dropped a new episode. I hope your back is doing better!

[TheoriesofEverything]

Yes. Looking forward to watching your comments on Penrose's ideas.

[painless]

Without being able to imagine a 'beginning', Penrose's idea seems to be the most intuitive, which is why im drawn to it. I recognize that the universe is not always intuitive.

[RandyLunn]

Sabine, after every one of your videos, I have more appreciation for you and your ability to capture the essence of a topic in a concise and understandable manner. Thank you.

[cagrulucyildirimoglu]

Even though there are many holes in this idea, it is incredibly creative. Thank you for the video!

[MeppyMan]

My brain was in a superposition while watching this video. It both made complete sense and was simultaneously unintelligible.

[dewiz]

It seems to me that we have to deal with a lot of complications because of the “fact” that the expansion of the universe is accelerating. This acceleration, is, of course, based on our current “best efforts” at measuring cosmological distance. To me, distances beyond what are directly measurable by parallax methods are suspect. Given that the strong nuclear force is an (extremely) local phenomenon, why are we convinced that gravity and/or electromagnetism not also local, with a redefinition of what “local” means on these scales. . .

As for inflation. . . I’m reminded of a cartoon, where a white-coated researcher standing in front of a blackboard full of equations says “and then a miracle happens”.

Thanks, Sabine, as always, for making me think.

[aquacruisedb]

So in layman's terms, CCC is the equivalent of "Turtles all the way down"?

[ollywright]

Thank you for covering my favourite crazy theory. It's fun trying to explain the conformal boundary to people, and the idea that the universe could become conformally invariant (and why).

[dj_laundry_list]

10:40 The fluctuations feed into each other recursively, but what is to say the gain is greater than 1 if they in fact amplify? Or what if there is some kind of destructive interference?

[TwentyNineJP]

If this cycle exists, could previous hyper-advanced civilizations hypothetically leave a message in the CMB?

[orri]

In R. Penrose favor I have heard him call CCC "outrageous" so he knows that it is a wild speculation. But if I remember correctly, he originally studied mathematics and they can do wild speculations and crazy generalizations.
Also I have heard him explain that at the end of each cycle every particle would need to decay to photons. If only a single massive particle is left the whole thing doesn't work.
Anyway thanks 💕 for a good video.

[gefginn]

I appreciate the education I receive here on this channel. Much love and care and blessings to you Sabine.

[hughcaldwell]

I really like this idea from an aesthetic point of view. Though, as my father-in-law observed after I gave him a (very rough and ready) explanation of what CCC was,
"Only a mathematician could think it worked that way."
I.e. same as Sabine's question of what the conformal rescaling actually means in practice. Which is a fair objection, and one I leave to the actual physicists. The idea that reality might be so pure in its adherence to mathematical elegance is too good to be true - but this platonist lives in hope.

[IncompleteTheory]

At last, thanks for this Episode. I missed some more details about the fact, that CCC does not need an inflation part, because what we need for the inflation part of our past is naturally the expansion of the previous eon. I always found this an interesting part because the current inflation theory always seem a bit like a hat trick to me. Anyway, thanks for the episode and the much more polite than usual way to discuss/criticize a very decent man's theory indeed.

[henrikrolfsen]

We no longer live in "Biblical Times". This is the 21st Century: Science has the benefit of so much investigation, assisted by amazing technologies. Fact: Everything in Nature, (in the Universe), is part of a cycle. All matter is bundled energy. Matter/Energy can neither be created, nor destroyed. Time/Space curves back on itself. There is no such thing as a perfectly straight line: Every line is part of a great curve. So let us please stop asking: "How was the Universe created". "THERE WAS NO DAY OF CREATION"! Furthermore: No "God" in his right mind, would want to take the blame for such a flawed world where humans have to fight against hundreds of dreadful diseases in a highly flawed biosphere. Science heals millions every day!

"Big Bang" is Big BS! If there ever was a time when nothing existed, nothing would exist now! Asking "How and when was Universe created?", is like asking a man who has never been married: "When did you stop beating your wife?". The fabric of Space/Time is a giant circle. Look at a circle: It has neither a beginning nor an end! Light which has travelled billions of lightyears, has been subjected to reflection, absorption, deflection, and refraction as it travels across vast space littered with matter and energy of every kind. Your "Red-Shift" is NOT "Doppler", it is the same red-shift you see at every sunset!

[michaelsommers]

Penrose gave a talk at my university when I was an undergrad. In the Q&A I asked him about cyclic cosmologies. He said that they were only possible in perfectly uniform universes (at least that's how I remember his answer). I guess he's changed his mind.