The Ascent of Man (24 page)

That is the core of the Principle of Relativity. But the obvious question is ‘Well, what holds his box and mine together?’ The passage of light: light is the carrier of information that binds us. And that is why the crucial experimental fact
is the one that puzzled people since 1881: that when we exchange signals, then we discover that information passes between us always at the same pace. We always get the same value for the speed of light. And then naturally time and space and mass must be different for each of us, because they have to give the same laws for me here in the tram and for the man outside, consistently – yet the same value
for the speed of light.

Light and the other radiations are signals that spread out from an event like ripples through the universe, and there is no way in which news of the event can move outwards faster than they do. The light or the radio wave or the X-ray is the ultimate carrier of news or messages, and forms a basic network of information which links the material universe together. Even if
the message that we want to send is simply the time, we cannot get it from one place to another faster than the light or the radio wave that carries it. There is no universal time for the world, no signal from Greenwich by which we can set our watches without getting the speed of light inextricably tied up in it.

In this dichotomy, something has to give. For the path of a ray of light (like the
path of a bullet) does not look the same to a casual bystander as to the man who fired it on the move. The path looks longer to the bystander; and therefore the time that the light takes on its path must seem longer to him, if he is to get the same value for its speed.

Is that real? Yes. We know enough now about cosmic and atomic processes to see that at high speeds that is true. If I were really
travelling at, say, half the speed of light, then what I have been making three minutes and a little on my watch, Einstein’s tram-ride, would be half a minute longer for the man on the pavement.

We will take the tram up towards the speed of light to see what the appearances look like. The relativity effect is that things change shape. (There are also changes in colour, but they are not due to
relativity.) The tops of the buildings seem to bend inwards and forwards. The buildings also seem crowded together. I am travelling horizontally, so horizontal distances seem shorter; but the heights remain the same. Cars and people are distorted in the same way: thin and tall. And what is true for me looking out is true for the man outside looking in. The
Alice in Wonderland
world of relativity
is symmetrical. The observer sees the tram crushed together: thin and tall.

Evidently this is an altogether different picture of the world from that which Newton had. For Newton, time and space formed an absolute framework, within which the material events of the world ran their course in imperturbable order. His is a God’s eye view of the world: it looks the same to every observer, wherever
he is and however he travels. By contrast, Einstein’s is a man’s eye view, in which what you see and what I see is relative to each of us, that is, to our place and speed. And this relativity cannot be removed. We cannot know what the world is like in itself, we can only compare what it looks like to each of us, by the practical procedure of exchanging messages. I in my tram and you in your chair
can share no divine and instant view of events – we can only communicate our own views to one another. And communication is not instant; we cannot remove from it the basic time-lag of all signals, which is set by the speed of light.

The tram did not reach the speed of light. It stopped, very decently, near the Patent Office. Einstein got off, did a day’s work, and often of an evening stopped
at the Café Bollwerk. The work at the Patent Office was not very taxing. To tell the truth, most of the applications now look pretty idiotic: an application for an improved form of pop gun; an application for the control of alternating current, of which Einstein wrote succinctly, ‘It is incorrect, inaccurate, and unclear’.

In the evenings at the Café Bollwerk he would talk a little physics with
his colleagues. He would smoke cigars and drink coffee. But he was a man who thought for himself. He went to the heart of the question, which is ‘How in fact do, not physicists but human beings, communicate with one another? What signals do we send from one to another? How do we reach knowledge?’

And that is the crux of all his papers, this unfolding of the heart of knowledge, almost petal by
petal.

So the great paper of 1905 is not just about light or, as its title says,
The Electrodynamics of Moving Bodies
. It goes on in the same year to a postscript saying energy and mass are equivalent, E=mc
²
. To us, it is remarkable
that the first account of relativity should instantly entail a practical and devastating prediction for atomic physics. To Einstein, it is simply a part of drawing
the world together; like Newton and all scientific thinkers, he was in a deep sense a unitarian. That comes from a profound insight into the processes of nature herself, but particularly into the relations between man, knowledge, nature. Physics is not events but observations. Relativity is the understanding of the world not as events but as relations.

Einstein looked back to those years with
pleasure. He said to my friend Leo Szilard many years after, ‘They were the happiest years of my life. Nobody expected me to lay golden eggs’. Of course, he did go on laying golden eggs: quantum effects, general relativity, field theory. With them came the confirmation of Einstein’s early work, and the harvest of his predictions. In 1915 he predicted, in the General Theory of Relativity, that the
gravitational field near the sun would cause a glancing ray of light to bend inwards – like a distortion of space. Two expeditions sent by the Royal Society to Brazil and the west coast of Africa tested the prediction during the eclipse on 29 May 1919. To Arthur Eddington, who was in charge of the African expedition, his first measurement of the photographs taken there always stayed in his memory
as the greatest moment in his life. Fellows of the Royal Society rushed the news to one another; Eddington by telegram to the mathematician Littlewood, and Littlewood in a hasty note to Bertrand Russell,

Dear Russell:

Einstein’s theory is completely confirmed. The predicted

displacement was 1"·72 and the observed 1"·75 ± ·o6.

Yours, J.E.L.

Relativity was a fact, in the special theory and
the general. E=mc
²
was confirmed in time, of course. Even the point about clocks running slow was singled out at last by an inexorable fate. In 1905 Einstein had written a slightly comic prescription for an ideal experiment to test it.

If there are two synchronised clocks at
A
and if one of these is moved along a closed curve with constant velocity
v
until it returns to
A
, which we suppose to
take
t
seconds, then the latter clock on arriving at
A
will have lost ½t (
v/c
)
²
seconds by comparison with the clock which has remained stationary. We conclude from this that a clock fixed at the Earth’s equator will run slower by a very small amount than an identical clock fixed at one of the Earth’s poles.

Einstein died in 1955, fifty years after the great 1905 paper. But by then one could
measure time to a thousand millionth of a second. And therefore it was possible to look at that odd proposal to ‘think of two men on earth, one at the North Pole and one at the Equator. The one at the Equator is going round faster than the one at the North Pole; therefore his watch will lose’. And that is just how it turned out.

The experiment was done by a young man called H. J. Hay at Harwell.
He imagined the earth squashed flat into a plate, so that the North Pole is at the centre and the equator runs round the rim. He put a radio-active clock
on the rim and another at the centre of the plate and let it turn. The clocks measure time statistically by counting the number of radio-active atoms that decay. And sure enough, the clock at the rim of Hay’s plate keeps time more slowly than
the clock at the centre. That goes on in every spinning plate, on every turntable. At this moment, in every revolving gramophone disc, the centre is ageing faster than the rim with every turn.

Einstein was the creator of a philosophical more than a mathematical system. He had a genius for finding philosophical ideas that gave a new view of practical experience. He did not look at nature like
a God but like a pathfinder, that is, a man inside the chaos of her phenomena who believed that there is a common pattern visible in them all if we look with fresh eyes. He wrote in
The World as I See It
:

We have forgotten what features in the world of experience caused us to frame (pre-scientific) concepts, and we have great difficulty in representing the world of experience to ourselves without
the spectacles of the old-established conceptual interpretation. There is the further difficulty that our language is compelled to work with words which are inseparably connected with those primitive concepts. These are the obstacles which confront us when we try to describe the essential nature of the pre-scientific concept of space.

So in a lifetime Einstein joined light to time, and time to
space; energy to matter, matter to space, and space to gravitation. At the end of his life, he was still working to seek a unity between gravitation and the forces of electricity and magnetism. That is how I remember him, lecturing in the Senate House at Cambridge in an old sweater and carpet slippers with no socks, to tell us what kind of a link he was trying to find there, and what difficulties
he was running his head against.

The sweater, the carpet slippers, the dislike of braces and socks, were not affectations. Einstein seemed to express, when one saw him, an article of faith from William Blake: ‘Damn braces: Bless relaxes’. He was quite unconcerned about worldly success, or respectability, or conformity; most of the time he had no notion of what was expected of a man of his eminence.
He hated war, and cruelty, and hypocrisy, and above all he hated dogma – except that hate is not the right word for the sense of sad revulsion that he felt; he thought hate itself a kind of dogma. He refused to become president of the state of Israel because (he explained) he had no head for human problems. It was a modest criterion, which other presidents might adopt; there would not be many
survivors.

It is almost impertinent to talk of the ascent of man in the presence of two men, Newton and Einstein, who stride like gods. Of the two, Newton is the Old Testament god; it is Einstein who is the New Testament figure. He was full of humanity, pity, a sense of enormous sympathy. His vision of nature herself was that of a human being in the presence of something god-like, and that is
what he always said about nature. He was fond of talking about God: ‘God does not play at dice’, ‘God is not malicious’. Finally Niels Bohr one day said to him, ‘Stop telling God what to do’. But that is not quite fair. Einstein was a man who could ask immensely simple questions. And what his life showed, and his work, is that when the answers are simple too, then you hear God thinking.

Revolutions are not made by fate but by men. Sometimes they are solitary men of genius. But the great revolutions in the eighteenth century were made by many lesser men banded together. What drove them was the conviction that every man is master of his own salvation.

We take it for granted now that science has a social responsibility. That idea would not have
occurred to Newton or to Galileo. They thought of science as an account of the world as it is, and the only responsibility that they acknowledged was to tell the truth. The idea that science is a social enterprise is modern, and it begins at the Industrial Revolution. We are surprised that we cannot trace a social sense further back, because we nurse the illusion that the Industrial Revolution ended
a golden age.

The Industrial Revolution is a long train of changes starting about 1760. It is not alone: it forms one of a triad of revolutions, of which the other two were the American Revolution that started in 1775, and the French Revolution that started in 1789. It may seem strange to put into the same packet an industrial revolution and two political revolutions. But the fact is that they
were all social revolutions. The Industrial Revolution is simply the English way of making those social changes. I think of it as the English Revolution.

What makes it especially English? Obviously, it began in England. England was already the leading manufacturing nation. But the manufacture was cottage industry, and the Industrial Revolution begins in the villages. The men who make it are craftsmen:
the millwright, the watchmaker, the canal builder, the blacksmith. What makes the Industrial Revolution so peculiarly English is that it is rooted in the countryside.

During the first half of the eighteenth century, in the old age of Newton and the decline of the Royal Society, England basked in a last Indian summer of village industry and the overseas trade of merchant adventurers. The summer
faded. Trade grew more competitive. By the end of the century the needs of industry were harsher and more pressing. The organisation of work in the cottage was no longer productive enough. Within two generations, roughly between 1760 and 1820, the customary way of running industry changed. Before 1760, it was standard to take work to villagers in their own homes. By 1820, it was standard to bring
workers into a factory and have them overseen.

We dream that the country was idyllic in the eighteenth century, a lost paradise like
The Deserted Village
that Oliver Goldsmith described in 1770.

Sweet Auburn, loveliest village of the plain,

Where health and plenty cheated the labouring swain.

How blest is he who crowns in shades like these,

A youth of labour with an age of ease.

That is
a fable, and George Crabbe, who was a country parson and knew the villager’s life at first hand, was so enraged by it that he wrote an acid, realistic poem in reply.