The concept of cyclic time is embedded in Hindu philosophy; the universe is created (not necessarily through an agent), destroyed, and recreated, over and over again. This book explores a similar radical theory of cosmology. Readers who intuitively grasp the above will probably find it more emotionally accessible.
The “Standard Model” offers the Big Bang Theory as the accepted scientific consensus on the universe’s origin. Everything starts with the Big Bang. A singularity explodes and expands over time in a process that continues. Big Bang is accepted because among other things, cosmic microwave background radiation (CMBR) was predicted by the theory some two decades before it was, accidentally, discovered to exist.
However, despite the consensus on origins, the ultimate fate of the universe remains a matter of speculation. Known physical properties, equations governing Big Bang, and so on, can be solved in many internally consistent ways to derive possible means of “death”. What is more, there is nothing “before” the Big Bang in standard theory. The laws of physics break down at that instant and most cosmologists consider it literally nonsense to refer to “before Big Bang”.
Each “death theory” has consequent assumptions, as with Big Bang and CMBR. So, some route to experimental verification may be available. Penrose espouses what is called the Big Crunch Theory. Under some conditions, the universe may reverse expansion and contract in the far future, eventually collapsing into a singularity. A Big Crunch could trigger another Big Bang, followed by another Big Crunch, Big Bang, and so on.
This oscillating universe theory stands or falls on breakthroughs in understanding several cutting-edge areas in physics. Penrose builds his case for what he terms Conformal Cyclic Cosmology (CCC), by a series of linked essays that present the consequent assumptions and lay down the pre-conditions for CCC to occur.
At the stage of defining proofs and pre-conditions (Chapter 1), the book becomes exceedingly mathematical. The publisher’s classification as “Popular Science” is a total misnomer. Though the really hard maths is in the appendices, the main narrative is mathematically challenging.
I’d guess the reader would need at least a graduation-level background in physics or maths to grasp the basic arguments. He would need to be gifted, and probably possess a PhD, to critique those meaningfully.
If you can follow it, the approach is absolutely delightful. Penrose introduces a series of new concepts, and offers a multitude of superbly-conceptualised diagrams to walk readers through speculations about the nature of time, physical dimensions, entropy, black and white holes and other arcana.
Each of the three sections is a gem in itself. They are dexterously meshed together in a narrative, which presents the same sense of harmony as a great symphony with several movements. Penrose has never been condescending, and by not eschewing maths here, where it is vitally necessary, he avoids over-simplifying difficult ideas. This does, however, narrow the audience. While practitioners and maths buffs will be entertained and enlightened, this is unlikely to percolate immediately to a wider audience.
The unidirectional flow of time, calculations of current entropy, of entropy immediately post-Big Bang and the ways in which these can be projected forward, the retention and loss of information within a system and the implications, are all grist to the CCC mill.
The first core area is the nature of entropy, which is dealt within a six-chapter section that introduces the concepts. The Second Law of Thermodynamics mandates time flows forward and its passage is marked by things being more “messy”, as entropy increases.
To explain entropy, we need to use the concept of phase space. Most physical laws (Newton, Einstein) work equally well if time runs in both directions. But the path taken by physical processes through phase space is time-asymmetrical.
For example, we can record a video of a glass that breaks when it’s dropped. Running the video backwards shows broken pieces of glass rising off the floor and reforming. The Second Law makes this trick photography very unlikely (but not absolutely impossible) to occur. The paradox is, entropy must have hit maximal value at Big Bang — so how did it decline before rising again?
This leads to the “oddly special nature of the Big Bang”, which is the theme of the second section. In this six-chapter introduction of the universe’s origins, Penrose also displays his mastery of black and white hole theory, which is where he, and his collaborator Hawking, carved out reputations.
The third section is CCC, given Big Bang and entropy. Some implications are counter-intuitive. In particular, CCC would mean reviewing accepted quantum theory about the invariability of rest-masses of fundamental particles. This is useful, since experiments using equipment like the Large Hadron Collider may be able to gather relevant data for experimental verification.
Penrose’s previous book The Road to Reality discussed our current understanding of physics. That 1,000-page tour de force is actually easier to grasp since it is in textbook format. Reading it before Cycles of Time could help lay readers.
If you can make the effort, and it will be an effort, Cycles of Time is among the most rewarding and entertaining books of the decade. CCC may be right or wrong. Either way, your understanding of entropy, the universe and how a great scientist thinks about these things, will be much enhanced.
CYCLES OF TIME
Roger Penrose
Bodley Head
288 pages; £25
