The Ascent of Gravity

by Marcus Chown

  ‘Albert, what are you thinking?’

  Even before he answers, she knows it will be something she would never, ever have guessed. Although he is just sixteen, already he sees the world differently from other people, thinks different thoughts from everyone else. The textbooks she has seen him studying in his room until the early hours might as well be written in hieroglyphics. She knows she cannot go where he goes, that she cannot enter his world. She has a sudden premonition that she will soon begin to bore him and that he will leave her, and a tear forms in her eye.

  ‘What am I thinking?’ he says, as if waking from a dream.

  ‘Yes.’ She wipes her tear on the sleeve of her coat, but he does not notice.

  ‘I was thinking: what would it be like to catch up a light beam?’3

  Rolling her eyes, she takes his hand and pulls him towards home.

  Albert, you are so strange.’

  Of course, this is fantasy. But it is fun to imagine! When the sixteen-year-old Einstein formulated his critical question, light was known to be a wave like a wave rippling over the surface of a pond. This is not an obvious fact because the distance between successive crests of a light wave is very small — much less than the width of a human hair. But an ingenious experiment carried out by an English physician called Thomas Young in 1801 had confirmed the wave nature of light.4 Still, nobody had the slightest idea what light was.

  Everything changed in 1863. In a theoretical tour de force, the Scottish physicist James Clerk Maxwell succeeded in summarising all electric and magnetic phenomena in one neat set of formulae. ‘Maxwell’s equations’ describe how a changing electric force ‘field’ creates a magnetic field, and how a changing magnetic field creates an electric field. The knitting together of electricity and magnetism into a seamless garment ranks as science’s third great ‘unification’ after Newton’s unification of Heaven and Earth, and Charles Darwin’s unification of the human and animal worlds.5

  Maxwell, on inspecting his elegant equations, noticed something very unexpected. They permitted a wave to ripple through the electric and magnetic fields that permeated empty space. And that was not all. The wave had a remarkable property: it propagated at the speed of light in a vacuum. The implication was as obvious to Maxwell as it was astonishing. Light must be an ‘electromagnetic wave’. Not only had Maxwell found a link between electricity and magnetism, he had discovered a link between electricity, magnetism and light.6

  Within two decades, Maxwell’s theory had scored a remarkable technological success. The German physicist Heinrich Hertz, following the Scottish physicist’s recipe, actually created artificial electromagnetic waves. In November 1886, using an electric spark as a ‘transmitter’, he broadcast invisible ‘radio waves’.7 They induced an electric current in a coil of wire, acting as a ‘receiver’, on the other side of his laboratory.

  Our ultra-connected world, in which the invisible chatter of a billion voices courses through the air around us, was born on that day in 1886. ‘From a long view of the history of mankind -seen from, say 10,000 years from now,’ said the twentieth-century American physicist Richard Feynman, ‘there can be little doubt that the most significant event of the nineteenth century will be judged as Maxwell’s discovery of the laws of electrodynamics.’8

  But, for all its triumphs, Maxwell’s theory posed a very serious problem for physics. It was incompatible with the laws of motion of Galileo and Newton.

  All waves ripple through something — water waves through water, sound waves through air. The hypothetical medium through which light rippled was christened the ‘aether’.9 An unavoidable consequence of the existence of this aether was that the speed anyone measured for a beam of light must depend on how fast they were travelling through the medium. Say you are standing on the deck of a sailing boat. The speed of the wind hitting your face depends on whether the boat is heading into the wind or whether it has the wind at its back. But the odd thing about Maxwell’s equations was that they made no reference whatsoever to any light-carrying medium. Instead, they contained one, and only one, speed for a beam of light in a vacuum. It was immutable, constant, utterly impervious to the world in which it was embedded.

  The obvious conclusion to draw from this was that Maxwell’s equations were in error and required modification. They were, after all, the new kid on the scientific block. Newton’s laws of motion, on the other hand, had been established almost two centuries earlier and, since that time, nobody had found a single instance in which reality departed from their predictions. Enter Einstein. He was mesmerised not only by Hertz’s dramatic confirmation of Maxwell’s equations but by their beauty, a quality he considered a strong indication of their rightness.

  Newton had written in his notebook: ‘Plato is my friend -Aristotle is my friend – but my greatest friend is truth.’ Ironically, it was because Einstein concurred 100 per cent with this sentiment of his predecessor that he had the temerity to doubt him. And that was why, aged sixteen, he had asked himself the critical question: what would it be like to catch up a light beam?

  Seeing the impossible

  A light wave, according to Maxwell, is a complex beast consisting of an electric field and a magnetic field oscillating at right angles to each other and at right angles to the wave’s direction of travel. The electric field grows as the magnetic field decays and vice versa. In fact, the decay of one field generates the other so that the two fields alternate to create a self-sustaining electromagnetic wave.

  The details are not important here. It is sufficient to think of a light wave as like a water wave rippling across a lake. If you were to catch it up, it would appear stationary, a long train of undulations frozen as if in a photograph. But – and here is the problem that occurred to the teenage Einstein in Aarau, Switzerland -Maxwell’s equations do not permit the existence of a stationary electromagnetic wave. Put simply, if you were to catch up a light beam, you would see something impossible – something that, according to the laws of physics, simply cannot exist.

  How is it possible to resolve this paradox? If Maxwell’s theory is correct, there is only one way, realised Einstein. Since travelling at the speed of light means seeing something impossible, travelling at the speed of light must itself be impossible. It is as simple as that. The trouble is that Newton’s laws of motion permit a body to travel at any speed whatsoever. They say nothing about an ultimate cosmic speed limit.

  Consequently, the price of saying that nothing material can travel at the speed of light is very high. It means overthrowing the worldview of Newton, the greatest scientist who ever lived. No one would do this lightly. Not without an awful lot of supporting evidence. And this is why Einstein spent nine years wrestling with the problem of squaring the theory of electromagnetism with the laws of motion. Everything finally came to a head in the spring of 1905.

  Patent paradise

  By now, Einstein, aged twenty-six, was a Technical Expert, Class III, at the Swiss Federal Patent Office in Bern, a post he had held since 1902. He was living in a two-room, third-floor apartment at Kramgasse 49 with his Serbian wife, Mileva Marić, and their one-year-old son, Hans Albert. Marić, four years his senior, had been the only woman in his class at the Swiss Federal Polytechnic in Zurich. Their romance had scandalised both their families, especially when a baby was born out of wedlock in 1902. Lieserl, the only reference to whom is in letters to and from Novi Sad, where Mileva returned to give birth, either died eighteen months later or was given up for adoption by Mileva’s family. Einstein and Mileva, who hid Lieserl’s existence from their friends in Switzerland, were the only ones who knew the truth of her fate.

  The Patent Office saved Einstein’s life, something he would remain grateful for until the day he died. After failing to obtain either a teaching or a university post, and, by his own admission, half-starving, it also provided him with the income and respectability to marry Mileva in 1903. Although grief for the loss of Lieserl must have hung over their union, playing a part in dooming it
from the start, Einstein’s time at the Patent Office proved to be one of the happiest periods of his life.10

  Not only did his job as a Technical Expert, Class III, pay the bills, it placed him right at the high-tech frontier of the new electrical age. His knowledge of electrical devices had been gained -sadly – at his father’s failed electrical lighting company in Milan. But he put it to good use in his office on the top floor of the new Postal and Telegraph Administration building, near Bern’s central train station, on Genfergass. Much to the approval of his boss, Friedrich Haller, Einstein was able to spot the subtlest flaws in the designs submitted each month to the Patent Office for dynamos, motors, transformers, and the like. But the best thing about his 48 hours a week as a Technical Expert, Class III, was that it did not overly tax his brain – as a teaching or university post might have done – and it left him time for creative thinking. And, boy, did he create.

  The year 1905 is generally known in the annals of science as Einstein’s ‘miraculous year’. ‘No one before or since has widened the horizons of physics in so short a time as Einstein did in 1905,’ said physicist Abraham Pais.11 No one, perhaps, except Isaac Newton. But, whereas Newton’s ‘miraculous year’ lasted about eighteen months, Einstein’s spanned barely more than three months. At least, that was the period – between 17 March and 30 June – when Einstein finished four scientific papers of such seismic importance that they would utterly remake the landscape of physics.

  The first paper, which Einstein called ‘very revolutionary’ and which would earn him the 1921 Nobel Prize for Physics, questioned the very idea of light as a wave, and suggested that atoms instead spit out or gobble up light in tiny chunks, or ‘quanta’.12 The second paper, which would earn Einstein a doctorate at the University of Zurich, determined the true size of atoms – whose existence at the turn of the twentieth century was still far from universally accepted – from the way in which they diffused through a liquid.13 The third paper pointed out that the curious dance of pollen grains suspended in water – so-called Brownian motion, first seen through a microscope by the botanist Robert Brown in 1827 – was the result of their jittery bombardment by water molecules.14 Finally, the fourth in this remarkable series addressed the problem of the uncatchability of light.15

  The catalyst was Michele Besso, whom Einstein visited in mid-May 1905. Besso, six years Einstein’s senior, had been a close friend since 1896 when Einstein was studying for a teaching qualification at the Swiss Federal Polytechnic in Zurich and Besso was working as a mechanical engineer in nearby Winterthur. Both loved music – Einstein being a competent violin player – and they had met through a Zurich woman called Selina Caprotti who gave over her home on Saturday afternoons to people wanting to play music together.16

  Besso not only recommended books for Einstein to read but entered into endless philosophical discussions with his friend about the foundations of physics. Most importantly, Besso was a critical sounding board for Einstein’s ideas. Recalling his visit in mid-May to Besso to discuss the problem of the uncatchability of light, Einstein said: ‘It was a beautiful day. We discussed every aspect of the problem. . .’17 He did not say how long he and Besso talked, where they talked or whether the discussion was heated. But the outcome, according to Einstein, was like a light coming on in a dark room and in an instant revealing everything. ‘Suddenly, I understood where the problem lay!’

  Perhaps that evening Einstein discussed it with his wife, Mileva. Or perhaps he lay sleepless in bed, turning the problem over and over in his mind, examining it from every possible side in the manner of Newton. Or perhaps he worked at the kitchen table until the early hours, furiously filling page after page of his notebook with scribbled notes. There is no record. Mileva, preoccupied and worn down by her domestic chores, kept no diary, wrote nothing about these times, and was never at any later time interviewed by any journalist.

  But, when Einstein saw Besso the next day, such was his state of excitement that he did not even say ‘hello’. ‘Thank you,’ he said. ‘Eve completely solved the problem. An analysis of the concept of time was my solution. Time cannot be absolutely defined, and there is an inseparable relation between time and signal velocity.’18

  Light plays the role of infinite speed

  If a light beam is uncatchable, Einstein asked, what does that say about the speed of light? An analogy may help. Infinity is a number in mathematics that is bigger than any other number. If something were to travel at infinite speed, it would be impossible to catch. The fact that light is uncatchable must mean that, in our Universe, for some unknown reason, the speed of light plays the role of infinite speed. ‘Nothing travels faster than the speed of light, with the possible exception of bad news, which obeys its own special laws,’ said Douglas Adams.19

  The analogy with infinite speed is useful. If something were moving at infinite speed, it would not matter what your own speed was or whether you were travelling towards it or away from it. Your speed would be so negligible by comparison that you would measure its speed to be infinite. Similarly, if the something moving at infinite speed were launched from a body travelling towards you or away from you, the body’s speed would be so negligible by comparison, that once again the infinite-speed thing would always appear to be travelling at infinite speed. It follows that, if the speed of light plays the role of infinite speed, it always appears the same, irrespective of the speed of its source or of the speed of an observer. The speed of light is constant, doggedly unvarying for everyone no matter what their state of motion, exactly as Maxwell’s theory suggests.

  So much for generalities, what about the details? How, in practice, is it possible for everyone, no matter how fast they are moving, to measure exactly the same speed for a beam of light?

  Well, speed is simply the distance a body travels in a given time — think of a car speeding along a motorway at 100 kilometres in an hour. If everyone is to agree on the same speed of light, something must therefore happen to each person’s measurements of distance and time.

  What actually happens, Einstein discovered, is that someone moving past you appears to shrink in the direction of their motion and, simultaneously, their time as shown by their watch appears to slow. Think of them flattening like a pancake and at the same time moving in slow motion.20

  And all of this shrinking of space and slowing of time works in such a way that each person, no matter what their state of motion, estimates the distance that a light beam travels in a given time to be exactly the same. It is a huge cosmic conspiracy to ensure the constancy of the speed of light.

  Of course, nobody ever sees space and time distort when someone walks by in a park or drives past in the street. This is because these strange effects would become apparent only if someone could fly past you at an appreciable fraction of the speed of light. But the speed of light is about a million times faster than a Boeing 747 and nothing in the everyday world even remotely approaches it.

  Time dilation

  Nevertheless, time dilation is detectable in the everyday world. Just. In 1971, super-accurate ‘atomic clocks’ were synchronised then separated, one being flown round the world on an airliner while the other stayed at home. When the clocks were reunited, the experimenters found that the round-the-world clock had registered the passage of marginally less time than its stay-at-home counterpart. The shorter time measured by the moving clock was precisely what is predicted by Einstein.

  The slowing of time affects astronauts too. As the Russian physicist Igor Novikov points out: ‘When the crew of the Soviet Salyut space station returned to Earth in 1988 after orbiting for a year at 8 kilometres a second, they stepped into the future by one hundredth of a second.’21

  The time dilation effect is far greater for cosmic ray ‘muons’, subatomic particles created when cosmic rays – super-fast atomic nuclei from space – slam into air molecules at the top of the Earth’s atmosphere. In fact, the evidence that time slows and space contracts at close to the speed of light is actually
coursing through your body at this very instant.

  Muons are created about 12.5 kilometres up in the atmosphere. They shower down through the air like subatomic rain. But here’s the thing. A muon disintegrates after a characteristic interval of time. The interval is very short —a mere 1.5 millionths of a second. By rights, none should travel more than about 500 metres down through the atmosphere before disintegrating. Certainly, none should reach the ground, 12.5 kilometres below.

  But they do.

  The reason is that muons are travelling at 99.92 per cent of the speed of light. From your point of view, they live their lives in slow motion. In fact, time passes 25 times slower for them than for you, which means they take 25 times as long as expected to realise it is time to disintegrate. When they do, they have already reached the Earth’s surface.

  But, of course, there is another point of view – that of the muon. From its angle, time is passing at its normal rate – after all, a muon is stationary with respect to itself, as are you. Instead, it sees you shrink in the direction of its motion – or, rather, our motion, since, from the point of view of a muon, it is the ground that is approaching at 99.92 per cent of the speed of light. But not only do you shrink, so too does the atmosphere. It shrinks to a mere 1/25th of its normal thickness. Which means the muons have time to get to the surface before they disintegrate.

  Whatever way you look at it – from your point of view, where the muon’s time slows down; or from the muon’s point of view, where the atmosphere shrinks – the muon gets to the ground. This is the magic of Einstein’s theory.