From: The Cyclic Universe

Does it make sense to use the vehicle of a popular science book to put forward one’s own detailed theory of modern cosmology?

Obviously not.

After all, cosmology is a highly technical, deeply abstract field of study that represents the culmination of much of modern physics. In order to fully comprehend its subtleties, one must have a thorough mastery of general relativity, differential geometry, thermodynamics, quantum field theory, and a good deal else besides.

Frankly put, it is virtually inconceivable that a non-specialist could somehow navigate his way through the rigorous arguments to have a genuinely clear idea of what is actually being proposed. In order to reach a broad audience, many highly technical issues will have to be glossed over, which will clearly trivialize the ideas beyond recognition, eviscerating them of any scientific content whatsoever.

And then there’s the fact that a well-defined, international community of scientific experts already exists for precisely the purpose of evaluating new ideas: there is a welter of well-respected journals in which to publish original work, and no shortage of scientific conferences to attend to speak to one’s professional colleagues. Any attempt to somehow circumvent this process and publish one’s pet theory in a popular book is hardly destined to be enthusiastically endorsed by the scientific establishment.

For most of us, then, the idea of producing a popular book about our iconoclastic cosmological views is little short of a terribly bad idea. The general public won’t be the slightest bit interested, and the scientific community will have you for lunch.

But then, most of us aren’t Roger Penrose.

Penrose’s scientific credentials are, of course, unimpeachable. One of the world’s most accomplished mathematical physicists and a specialist in general relativity and cosmology, his litany of intellectual achievements is nothing less than outstanding. He is the originator of the singularity theorem in general relativity — later extended to cosmological scales in his collaboration with Stephen Hawking — twistor theory, the cosmic censorship hypothesis, Penrose-Terrell rotations, Penrose tilings, spin networks, and much more. His work on black holes that began with his singularity theorem was recognized in him being a co-recipient of the 2020 Nobel Prize. He is, quite simply, beyond whatever slings and arrows the scientific establishment might care to hurl at him.

He has also, surprisingly, become a fantastically successful popular writer. Why surprisingly? Because he has long eschewed the common dictum that the public can’t handle mathematical details. His 2005 opus The Road to Reality was firmly ensconced on the bestseller list for months on end, despite both its daunting size and equally daunting number of equations.

So Roger Penrose, clearly, is different. But what has he got to say this time? His popular book, Cycles of Time, explains his theory of Conformal Cyclic Cosmology — CCC — to a broad, general audience. Well, what’s that all about?

In essence, it proposes that cosmology should properly be regarded as an infinitely repeating series of “aeons,” with the far distant future of one aeon mapping on to the Big Bang of another one, thereby producing endlessly repeating cycles.

Given the seemingly endless proliferation of bizarre-sounding theories of fundamental physics out there, you might well think that this is just another in a long line of provocatively speculative ideas cooked up by a restless physicist anxious to distinguish himself by the sheer power of his creative, science-fiction-like energies.

But you’d be dead wrong.

Because what’s essential to understand is that Roger’s latest ideas hardly represent a departure from a fundamental cosmological paradox that has long haunted him: Why is the beginning of the universe in such a remarkably smooth state?

Howard Burton in conversation with Roger Penrose, University of Oxford

“It’s often claimed that there are these big mysteries about the universe — What is dark matter? What is dark energy? Where do they come from? What are they doing? — together with the values of all sorts of other parameters that seem completely mysterious. But they never mention the Second Law of Thermodynamics. For some reason, when people enunciate the various problems of cosmology they don’t even ask, Why was the Big Bang not only such a state of low entropy, but a state of such low entropy in a very strange way — that it singles out gravity as the one thing that is not taking part in this thermal state?

“Gravitation is aloof from everything else going on, and only gradually does it get brought in and produce the concentrations of stars and thermonuclear reactions and all sorts of things. But the key reason why the entropy was low was due to gravity, because it’s taking advantage of this reservoir of low entropy since the gravitational field was not taking part.”

For those who claim that the theory of cosmic inflation solves this deep puzzle, Roger is swift to disabuse them. He admits to not liking inflationary cosmology on “aesthetic” grounds, feeling that it is too ad hoc. But that’s not his main issue with the theory.

“My principal concern is that it didn’t actually explain what it was supposed to explain. And the reason for that is that, in my view, the bigger problem is the Second Law of Thermodynamics. The spatial uniformity that inflation is designed to address is part of this problem: How is it that the gravitational degrees of freedom were not activated? Putting inflation in doesn’t solve it.

“In fact, I can show you why it doesn’t solve it. It’s so remarkably simple I can’t see why others haven’t been copying this idea endlessly. I’m going to turn the universe upside down. Why? Well, because I’m now going to think of time as going in reverse back towards the Big Bang.

“Entropy will increase through gravitational clumping. There will be irregularities as the universe collapses, and these will increase and form black holes: a huge, horrendous mess.

“That is, almost certainly — with fantastically likely probabilities — what our universe would do. And if we had been in this unbelievable messy situation to begin with, then inflation wouldn’t do anything for us at all. The ‘unbelievable mess’ would have been a state of enormously high entropy (in terms of the gravitational degrees of freedom), and inflation, being a time-reversible dynamical process acting in accordance with the Second Law of Thermodynamics, wouldn’t be any use at all: it would just spread out the clumps. So it’s really no explanation to the question of why our universe is so uniform.”

Roger has long been preoccupied with this issue, and believes that a key piece of the puzzle can be properly addressed by closely examining aspects of a particular type of geometry — so called conformal geometry.

In fact, a careful examination of Roger’s research orientation, from Penrose diagrams to twistor theory to the Weyl curvature hypothesis, demonstrates a consistent belief in the importance of conformal geometry.

CCC then, is hardly some new, fantastic theory that comes straight out of left field, but rather a logical culmination of many of Roger’s remarkably fruitful scientific beliefs, intriguingly extending these to incorporate fascinating ideas about dark energy, dark matter and information loss in black holes.

Unfortunately, however, many contemporary physicists summarily dismiss these ideas, looking askance at CCC on experimental grounds. Because one of the main predictions of the theory is a specific ring-shaped pattern in today’s cosmic microwave background (CMB) caused by giant black-hole collisions from the previous aeon.

Some believe that such ring-shaped patterns are nowhere to be found, while others admit that they are there, but are not at all particular to CCC. Of course, time will tell.

But as important as experimental confirmation is to any scientific theory, even more important is a recognition of the need to address fundamental, underlying issues.

Because even if CCC is only somehow half-right, or not right at all, that hardly means that Roger’s long-standing cosmological concerns are misplaced.

“You have this amazing piece of evidence of a thermal state, which means a state with maximum entropy. To me, that doesn’t make any sense. Why aren’t people saying, ‘WHAT? You go back to the state of smallest entropy and get this thermal equilibrium state, which is a sign of maximum entropy?’ Why aren’t they scratching their heads and saying, ‘This is madness!

“I don’t understand why they don’t worry.”

Which brings us, in a roundabout sort of way, to the subject of why Roger wrote Cycles of Time to begin with.

“When I wrote The Emperor’s New Mind, I went into this business of the low entropy state of the Big Bang and the fact that gravitational degrees of freedom had to be suppressed. I’d been lecturing about this for several years before that, and nobody paid the slightest bit of attention to it. But after I’d done it in The Emperor’s New Mind, a lot of my scientific colleagues wrote to me and said, ‘Oh, that’s interesting. Now I see what you’re saying’. It did actually get across to people in a way which writing articles in journals and so on didn’t.”

Might that just explain the Penrose publishing phenomenon? Could it be that, through the guise of writing for the layperson, Roger is really addressing the global community of theoretical physicists? And might it also be that, despite their official professional disdain for popular science books, a significant fraction are going out and buying his?

This is the introduction written by Howard Burton of the book, The Cyclic Universe, which is based on an in-depth, filmed conversation between Howard and Roger Penrose, Emeritus Rouse Ball Professor of mathematics at the University of Oxford and co-recipient of the 2020 Nobel Prize in Physics.

The book is broken into chapters and includes questions for discussion at the end of each chapter. The book is also available as part of the 5-part Ideas Roadshow Collection called Conversations About Astrophysics & Cosmology.

Visit the dedicated page for our conversation with Roger Penrose on Ideas On Film: On our Ideas On Film YouTube channel you can watch a clip from the filmed conversation:

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