And This Is The Epilogue

‘An evil fate wills it that men will from time to time revert to darkness out of boredom with light. Ours is such a time, with great opportunities to learn the right things being spurned, and a wealth of the most lucid truths being disregarded in favour of obscure trivialities.’

That was how Gottfried Leibniz, mathematician and philosopher, expressed his frustrations at the beginning of the eighteenth century. You might think he was complaining about people rejecting the rational lines of enquiry that were born in the Enlightenment — people persisting with astrology, perhaps, in an age when astronomy was in the ascendant. In fact, the jibe was aimed squarely at Newton, and his weird and occult idea of ‘forces’. The complaint comes in a treatise Leibniz called ‘Against Barbaric Physics’ directed at those who ‘speak of attracting and repelling, adjusting, expanding and contracting forces’. Leibniz admits that the idea of the planets ‘gravitating and striving toward each other’ has been confirmed as correct. But he rejects the new idea that ‘matter is supposedly able to perceive and covet even things which are remote’. Physics stripped of all mysticism is ‘too clear and simple for these people,’ Leibniz complained. ‘Instead they revert to fanciful ideas.’

Leibniz compares Newton to those who suggest a foetus is formed by intelligent spirits that attend to it in the womb. ‘How can any reasonable person today subscribe to a belief in fantastic qualities that is tantamount to a betrayal of all natural principles? … all this is bound to lead us completely into the realm of the obscure …’ Everything, Leibniz says, should ultimately be reduced to mechanisms, for mechanics.

Leibniz would be horrified at where we have got to today. David Bohm suggested that quantum mechanics is a misnomer: it should be called quantum non-mechanics because everything we have learned says there is no physical mechanism to be found within the theory. There is certainly no mechanism that explains entanglement. There is no physical conception of what happens when the photon approaches the double slit. And as for Newton’s gravity, a proper mechanical explanation still eludes us.

Einstein reworked Newton’s gravity as a set of contours in space and time: we can predict the trajectories of the planets if we consider them as traversing a landscape of hills and valleys created by the mass and energy contained within the universe. But we sometimes confuse our success in explaining what happens with an explanation for why or how it happens. Einstein’s work has proved an extraordinary success, with myriad successful predictions and explanations of physical phenomena under its belt. But it is not an explanation of why and how mass and energy should give shape to the cosmic landscape — or even that the shape is really there in the way we say it is. After all, a deformation in a two dimensional rubber sheet requires a third dimension. If we are distorting the four dimensions of space and time, into what dimension are they distorting? Don’t misunderstand me — Einstein’s explanation is wonderful. But that doesn’t mean the explanation is actually how it is. Where gravity is concerned, we haven’t progressed much beyond ‘red sky at night, shepherd’s delight’.

The truth is that quantum mechanics and relativity remain our best theories, yet also provide our most frustrating impasse. We present them as useful schema for explaining observed phenomena, but only to a point. We cannot actually account for the details of either. ‘Nobody knows how it can be like that,’ Richard Feynman said of quantum theory. And relativity, most agree, is a theory already in need of an overhaul, for it simply doesn’t give us meaningful answers to all the questions we ask of it. Hundreds of years after Jerome’s investigations of the universe, the job is still only half done.

If that. Roger Penrose’s ‘gravitational collapse’ interpretation of quantum theory is an attempt to sketch out what a theory that unites relativity with quantum mechanics might achieve, but it is barely even a sketch. It is impossible to know how far along the path to such a ‘final theory’ we have travelled. In Jerome’s time, astronomers had made major steps forward since the times of the ancients, but to us their tiny, Earth-centred universe still looks like a primitive and wholly inadequate attempt at understanding the nature of the cosmos. Unless we live in a special time in the history of humanity — and it is unscientific to think that we do — there is no reason to believe that the humans of the twenty-fifth century will look at us any differently from how we look at our scientific predecessors. But what will they make of our inability to parse the meaning of quantum theory? Will our take on entanglement and superposition look to them as Jerome’s astrological inference looks to us?

If they were to visit us in the prison cells of our ignorance, what secrets might they convey? Part of me hopes they would tell us that the astrologers were onto something. Something deep within me, deep within all humans that have ever lived, yearns to be connected to the cosmos, to be a cog, however tiny and infinitesimally unimportant, that turns because of a distant rotation elsewhere in time and space. I suppose that is part of the appeal of Gerard ‘t Hooft’s superdeterminism interpretation of quantum mechanics: it feeds the desire to be part of something bigger. It absolves us of the duty to explain, and allows us to just be, to let Fate direct our path through the cosmos.

Not that most physicists would subscribe to superdeterminism. But neither are they comfortable with what is currently considered the best hope for understanding how the universe works: string theory.

Remember how Einstein and Schrödinger were reduced to dust by the attempt to unite quantum theory with relativity? There were times when they refused to talk to one another, so intense was the competition between them to crack this puzzle. They even spoke of lawsuits to prevent the other from stealing ideas. String theory, our current best candidate for a quantum theory of gravity is very different from anything that pair suggested, but it is proving equally divisive.

To its critics, it is so far off the mark that it is ‘not even wrong’ and a ‘new version of medieval theology’. Those who think it worth pursuing, on the other hand, are often puzzled by others’ inability to appreciate its ‘beauty’.

What is string theory? A true understanding of this attempt to unite quantum theory and Einstein’s relativity is only possible for those who deal in mathematics more easily than in language. So I can only tell you an approximation of its claims: string theory says that all the familiar particles arise from the different vibrational modes of strings and loops of pure energy. The energy vibrates one way and it creates a photon. Another kind of vibration gives us an electron. And so on.

The idea has arisen from work carried out in the 1920s, when even quantum theory was young. Two mathematical physicists, Theodor Kaluza and Oskar Klein, independently worked out that Einstein’s relativity can give birth to the electromagnetic theory governing the behaviour of photons and electrons if the universe is allowed to have four spatial dimensions instead of the usual three. Kaluza and Klein’s extra dimension had to be curled up into a tiny circle for the maths to work, but it was an interesting result that mathematicians played with for decades, slowly expanding its sphere of influence. By the 1980s, the idea had become a theory that accounted for the existence of all the fundamental particles. There was only one problem. The mathematics only worked if the string theorists invoke even more spatial dimensions. According to string theory, there are ten dimensions of space, with seven of them lying, curled up, beyond our perception. What’s more the theory doesn’t describe our universe specifically. It describes a plethora of universes, each with slightly different physical properties. We inhabit — hopefully — one of 10500 universes described by string theory.

It is a situation that some have described as nonsensical. It is, after all, a theory that doesn’t make any testable predictions and so can never be tested. ‘I have been brought up to believe that systems of belief which cannot be falsified are not in the realm of science,’ is how Nobel laureate Sheldon Glashow has dismissed string theory. Hence his contention that it is no different to medieval theology.

Glashow probably doesn’t appreciate that it is closer to medieval — or at least Renaissance — science. In some sense, Jerome’s aevum is still with us. String theory even has a contemporary version of Jerome’s centre that ‘corresponds to every point on the circumference’. It is known as the ‘holographic principle’, and was conceived by an Argentinian string theorist called Juan Maldacena. His idea is that all of what we term physical reality results from information held on the edge of our cosmos — a cosmos that has many more dimensions of space than the three we experience. Our physical universe, in other words, is just a small manifestation of something that exists in the great beyond, something that is unreachable, and beyond our understanding.

Though many of today’s physics luminaries, Stephen Hawking among them, enthusiastically subscribe to the holographic principle, there is no experimental test that can tell us whether it is right. It is simply our best stab at a final theory. We are still very much on the road towards understanding, still travelling in the dark, with still only the faintest hope of arriving at our destination. And we are almost certainly only a few steps ahead of the man who showed us the path that we should follow, my friend Jerome.