Fashion, Faith and Fantasy in the New Physics of the Universe
by Roger Penrose
Princeton University Press (2016)
Theoretical physicists are an idealistic lot. Theirs is the noble struggle to understand the nature of the universe: to know, as Stephen Hawking put it, “the mind of God”. Yet physicists are human too. They are as flawed as the rest of us – subject to the whims of fashion, dogmas of unquestioning faith and flights of unadulterated fantasy.
These human flaws have led to the present impasse in physics, warns Sir Roger Penrose. His penetrating new book is the long anticipated follow-up to three eponymous lectures he gave at Princeton in 2003. In those talks, he called out the problems, both sociological and technical, in the way physics is done today. In particular, he calls string theory a “fashion”, quantum mechanics “faith”, and cosmic inflation a “fantasy”.
Penrose is well placed to make such sweeping judgements. He has been a giant of physics and mathematics for five decades, making many deep, original insights into topics ranging from black hole physics and the origin of the universe to art and fundamental geometry. For example, his exploration of “impossible“ objects, such as the Penrose Stairs, inspired the artist M.C. Escher to create some of his most famous woodcuts, including Ascending and Descending and Waterfall. In the estimation of the Perimeter Institute’s Lee Smolin, “there is no one who has contributed more to our understanding of the general theory of relativity, save Einstein himself, than Roger Penrose.”
Penrose is also renowned as a fiercely independent thinker, even a maverick, and it’s in this role as iconoclastic outsider that Penrose tackles the big problems facing physics today.
Fashion, according to Penrose, has long played a role in science. To remind us of how easy it can be for spurious ideas to achieve a status of dogma, he describes several fashionable junk theories of history. For example, Ptolemy’s theory of epicycles (the idea that the orbits of the planets could be described by circles upon circles) was kept alive through 14 centuries of mental gymnastics on the part of proponents whose worldview placed Earth at the centre of the universe and everything else in orbit around it.
Today’s modern equivalent, perhaps, is string theory, the idea that all of physics is based on fundamental vibrating strings, far tinier than any quark or electron. The idea, so tantalising in its simplicity and scope, has dominated theoretical physics for two decades despite making no testable predictions. Joseph Polchinski, a leading string theorist has said “there are no alternatives … all good ideas are part of string theory”.
For Penrose, on the other hand, string theory’s “stranglehold on developments in fundamental physics has been stultifying”. He exposes a series of technical holes in the theory, questioning, in the tone of a bemused schoolmaster, why they have not been seriously addressed. The implication is that string theorists are too caught up in following their field’s latest fashions to be worried about the foundational problems of the theory.
His next target is an even larger one: quantum mechanics, simultaneously the most well-tested theory in all physics, and its most perplexing. For Penrose, quantum mechanics is “faith” because its mathematics uses assumptions that could never really be logically justified – and nobody really understands the theory anyway. For example, we don’t know why the laws of physics seem to have two regimes, one for the very small and another for the very large. For Penrose, this disconnect is a sign that quantum physics is incomplete, and that we must search for something deeper.
Fantasy is how Penrose refers to the wild notions describing the universe at the largest scales. Here we run through some of the strangest ideas in physics (concerning, for example, what is inside a black hole, or what happened before the Big Bang). Penrose’s true quarry is the theory of inflation, a description of the universe’s faster-than light expansion in the first moments after the Big Bang, which he argues has as many serious flaws as its competitors.
When Penrose describes a theory as fantastical he is not necessarily being disparaging. As he emphasises, the universe is full of apparently fantastic notions that are demonstrably valid – the Big Bang origin of the universe, for example, or the existence of black holes. Sometimes wild ideas are appropriate; but only when they describe our observations of the universe better than rival theories.
In the final chapter, Penrose indulges to lay out two wild theories of his own. The first, conformal cyclical cosmology, is his self-described “crazy” theory that the universe has no beginning or end; rather it iterates through infinite cycles. The heat death of one universe becomes the Big Bang of the next. Meanwhile “twistor theory” is Penrose’s stab at linking general relativity and quantum mechanics. The “twist” comes from the idea that quantum spin is tied up in spacetime. Though Penrose first suggested the theory in the 1960s, it has seen a surge in interest in recent years.
For technically minded readers keen to achieve a deep appreciation of the problems facing physics, this is an enlightening book. Just don’t expect the typical spoon-feeding of popular science; there are certainly more equations than metaphors. (For a more digestible account, Lee Smolin’s 2006 book The Trouble with Physics covers much of the same ground.)