Relative Values

by Andrew Crumey

Review of Einstein's Greatest Mistake, by David Bodanis. Literary Review, October 2016.

It took me a while to figure out what this book was about. Einstein famously said (or is said to have said) that his biggest mistake was the inclusion in general relativity of a "cosmological constant" that he came to regard as spurious. But he also made other great mistakes, arguably greater, such as declaring that God doesn't play dice when quantum mechanics suggested the contrary. The subtitle of this book, "The life of a flawed genius", meanwhile suggests a biography highlighting Einstein's less than saintly behaviour in regard to those closest to him, particularly the two wives he cheated on. In fact Bodanis touches on all of these, with a breeziness that will please anyone not too concerned with scientific detail, psychological insight or historical accuracy.

Einstein, we are told, had a "Victorian childhood", when the scientific universe consisted of "two great realms", energy and matter, that he would come to unify. Bismarck would have had something to say about the first assertion, while the second is a less obvious abuse of language. What Einstein showed with his famous equation, E=mc2 , is the equivalence of energy and mass. Confusing matter and mass, as Bodanis does repeatedly, is like mixing potatoes with kilograms.

Einstein's early years are summarised in a few pages that soon quell any suspicion this book might be called a biography. The immediate destination is 1905, the annus mirabilis when Einstein not only published his first papers on relativity theory, but also showed that light could be considered as being made of particles (later called photons), and that the existence of atoms could be proved by the dance of pollen grains sprinkled on water. What we are offered is a heavily cut-down version with a level of simplification suggestive of a Hollywood screenplay. Scientists are of two types: visionary revolutionaries (Einstein) or obstructive old fools (his teachers and university professors). Einstein's single significant breakthrough in 1905 is E=mc2 , the rest is incidental background. The equation itself is portrayed as a "tunnel" between the "domed cities" of matter and energy.

We get rather more on Mileva, Einstein's fellow-student who fell pregnant by him. Their daughter Lieserl was given up for adoption - her existence only came to public notice after Einstein's death, and it's not known what became of her. After marrying in 1903 the couple had two sons, but the relationship cooled and Einstein struck up with a distant relative, Elsa, who became his wife in 1919. In the same year Einstein became world famous after measurements during a solar eclipse showed the gravitational bending of starlight in accordance with his general theory of relativity. Bodanis' abbreviation for that theory, fair enough given its complexity, is G=T . Really it stands for ten equations, with G expressing the geometry of four-dimensional spacetime, and T encoding the sources of gravitation, which Einstein showed included pressure as well as mass/energy. Bodanis explains it with the analogy of objects moving on a bendy surface, familiar to anyone who's ever watched a Brian Cox documentary or rolled a ping-pong ball into a "black hole" in a science museum.

Like most popularisers, Bodanis emphasises the novelty and strangeness of general relativity in comparison with Newtonian gravitation. This is good for dramatic effect but disguises a fundamental similarity. Newton's theory is still accurate enough for most situations, so Einstein had to come up with something almost identical, differing in only the most extreme scenarios. So when Einstein applied general relativity to cosmology he found exactly the same problem Newton had: if all the stars are pretty much stationary in space, as was thought to be the case, then gravity will make them fall together in a lump. Newton solved it with the hand of God, Einstein did it by supposing empty space to have pressure and therefore gravitation. That's the cosmological constant, though Bodanis doesn't explain it that way, staying instead with curved space and rolling boulders.

There are unexpected detours from Einstein's life and work, into those of Edward Abbott (author of the famous fantasy Flatland ) and Henrietta Leavitt, who discovered how certain stars could be used as "standard candles" revealing the true extent of astronomical distances. Other players appear: Lemaître, Hubble. In Bodanis' version, the unknown Lemaître approaches Einstein, shows him data from unknown astronomers, and argues that the universe is expanding. Einstein rejects the idea, only being persuaded when he later visits the famous Hubble. In fact the data that Lemaître showed Einstein was Hubble's, and the demise of the cosmological constant was a complicated story involving theoretical as well as observational work. But subtle details are not Bodanis' concern, and his sketchy account gives the gist well enough.

Einstein's other big mistakes are left for the latter part of the narrative; a sensible arrangement that, if it had been signalled in the opening chapter, would have made the overall shape and scope of the book much clearer from the outset. Heisenberg and Bohr appear on the scene, and Einstein enters the famous debate on quantum theory which he was ultimately to lose. His last years were spent in Princeton, working on a futile attempt to unify gravitation and electromagnetism. Technical details are, as ever, kept to the barest minimum, reliance instead being placed on metaphors and analogies that Bodanis clearly relishes. Imagine, for instance watching actors in an operetta in a Berlin theatre, and note the costume changes that occur between each scene. Do this over several nights, and notice how the same singer might be a princess or a peasant. After a paragraph of this picturesque reverie it dawned on me that it was meant to be an explanation of Heisenberg's matrix mechanics. An appendix is supplied for readers wanting a bit more scientific detail, and there we get an extended story about ordering items in a Zurich restaurant, which is supposed to explain tensors, but may well leave the reader with mental indigestion.

There are hundreds of books about Einstein's life and work, not to mention countless websites that explain relativity at any level of sophistication one might desire. Bodanis' offering is no better or worse than most. Like the cosmological constant it has no obvious reason for existing; it just does.