What a Wonderful World (27 page)

Emergence might seem like magic but, really, it is not. Nothing is being added. It is more that information is being thrown away. Although it might be perfectly possible to predict the motion of a single molecule of gas flying through space, it is impossible to keep track of the countless quadrillions of gas atoms that make up the entire gas. So physicists ignore a vast amount of
information
. They approximate. They clear out some of those irrelevant details so that they can zoom out and see the big picture. This involves them inventing quantities such as pressure and
temperature
, which are averages of the behaviour of vast numbers of microscopic constituents. It is only when they zoom out intelligently in this way that they are able to spot correlations between the averaged-out parameters – new laws that govern their behaviour.

‘The world of the quark has everything to do with a jaguar circling in the night,’ wrote the Chinese-American poet Arthur Sze. But, in practice, connecting the two in a single explanatory framework is way beyond our twenty-first-century capabilities. We approximate because we do not have the mathematical ability to explain everything in terms of the behaviour of the most fundamental building blocks.

And we pile approximation upon approximation. And out of this process there emerge new laws. Ever more approximate laws. This is how we
understand
the Universe. This is how we make sense of a world that is far too complicated to be perceived in its entirety by the 3-pound lump of jelly and water that constitutes our puny ape brain. As Thomas Carlyle said, ‘I don’t pretend to
understand the Universe – it’s a great deal bigger than I am … People ought to be modester.’

What all this means is that a Theory of Everything, if it is ever discovered, will not supplant all of science. Though it will explain the interaction the fundamental building blocks of the world, it will have nothing to say about flowers or sonnets or the chuckle of a newborn baby.

Imagine you look out of your window and see Normans, and, behind them, Romans, and, behind them, Egyptians. Crazy? No crazier than it is for astronomers looking out across the Universe with their telescopes. The further away a celestial object the
further back in time it is.

Light travels at about 300,000 kilometres a second in a vacuum. But if, instead, it travelled at a mere
100 metres a century,
about a kilometre away you would indeed see William the
Conqueror
still
invading England; about 2.2 kilometres away, Publius Scipio
still
battling Hannibal and his elephants; and not far from the horizon, about 4.5 kilometres away, the Pharaoh Khufu
still
making his weekly inspection of the building site of the Great Pyramid of Giza.

The reason all these events would still be visible is because, at 100 metres a century, the light bringing you news of them would
crawl snail-like
across the intervening distance. The point? Douglas Adams memorably observed, ‘
Space
is big. Really big. You just won’t believe how vastly hugely mind-bogglingly big it is.’
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What this means is that light, despite travelling
10 million billion
times faster than 100 metres a century, nevertheless
crawls
snail-like
across the enormous expanses of the Universe.

Standing outside on a crystal-clear night, you see the Moon as it was 1¼ seconds in the past; the nearest star system, Alpha
Centauri
– and you need to live in the southern hemisphere to see
this – as it was 4.3 years ago; and the Andromeda Galaxy – the most distant object visible to the naked eye – as it was when our
Homo erectus
ancestors were first venturing out onto the African savannah 2.5 million years ago.

With the aid of powerful telescopes, astronomers can drill back yet farther through cosmic time, revealing galaxies that lived and died long before the Sun and Earth were born. And, out at the very edge of the observable Universe, they can see the shimmering veil of the ‘surface of last scattering’,
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13.8 billion years back in time and the furthest it is possible to see with light.

What all this demonstrates is that time is not what we think it is. Because of the finite speed of light, time is inextricably bound up with distance. Or, as Einstein said, ‘There is an inseparable connection between time and the signal velocity.’ As we look
outwards
from the Earth, we might think we see the Universe as it is ‘now’. But, actually, what we see are ‘shells’ of space at
successively
earlier times.

Telescopes drill through the onion-skin layers of cosmic time just as archaeologists dig through the dirt layers of terrestrial time. Astronomers, however, have the great advantage that they can actually
see
the past. Although they cannot know what the Universe looks like ‘now’, their compensation is that they can see the entire history of the Universe played out before their
telescopic
eyes.
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In our Universe, then, the concept of ‘now’ is meaningless. It is impossible know what it is like on Alpha Centauri at this moment since the light, carrying news of the star system, permits us to know only what it was like
a minimum of 4.3 years ago.

The connection between time, space and the speed of light is as true on Earth as it is in the Universe. The crucial difference,
however, is that terrestrial distances are far shorter. The light carrying an impression of the face of a friend you are talking with reaches your eyes in less than a billionth of a second. This is about 10 million times shorter than the briefest interval of time that can be perceived by your brain. Consequently, you notice no delay. The concept of ‘now’, which does not exist at all in the large-scale Universe, is on Earth in most circumstances a very good approximation. We can all safely assume that we are living in the same
present
.

Or can we?

According to Einstein, the finite speed of light does more than simply
delay
news of events. Light is the cosmic speed limit and everyone, no matter what their speed relative to a source of light, measures exactly the same speed for a beam of light.
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This can happen, as Einstein realised in 1905, only if the space of someone moving relative to you shrinks in the direction of their motion while their time slows down.

Einstein later generalised special relativity. According to his general theory of relativity of 1915, if someone is accelerating with respect to you – which is equivalent to
experiencing stronger gravity
– their time appears to slow down.
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For instance, when astronomers look out across the Universe to a shell of space at an earlier epoch, the matter of the Universe at that time occupied a smaller volume than today – simply because space has been expanding since the big bang. With matter more concentrated, the Universe ’s overall gravity was stronger, and time flowed more slowly.

With time flowing at different rates for people moving relative to each other
or
who are experiencing different gravity, it is
impossible
for people to agree on what is past, present and future. In fact, the concept of a
common
past, present and future simply does not appear in Einstein’s theory of relativity, our
fundamental
description of reality. The question then is: why do we have such a strong impression that it exists?

The answer is that the effects of relativity on time are
appreciable
only if two people are experiencing markedly different gravity or are moving relative to each other at an appreciable fraction of the speed of light. And, on Earth, all 7 billion of us are experiencing pretty much the
same
gravity and, even when flying in jet planes, moving relative to each other at less than a millionth the speed of light.

This is not true, by the way, for the Global Positioning Satellites, with respect to which electronic devices such as mobile phones calculate our location on the planet. In their elongated orbits, they swoop down towards the Earth before swinging back out into deep space. This means that not only do they speed up and slow down during each orbit but they also experience strong gravity close to the Earth and weaker gravity further away. As a consequence, the satellites do not experience a common past, present and future. And this must be taken into account by the program that computes our position relative to the GPS satellites. Relativity, it turns out, is not such an esoteric theory. It is an essential part of our everyday lives in the
twenty-first
century.

Still, we ourselves live our lives in the ultra-slow lane and in ultra-weak gravity where relativity would appear to have few consequences. Appearances, however, can be deceptive.
Relativity
,
it turns out, still has a trick up its sleeve. And it has
devastating
consequences for our concept of time.

Einstein showed not only that one person’s interval of time is different from another person’s interval of time. He showed that one person’s interval of time is another person’s interval of time
and space
. And that one person’s interval of space is another person’s interval of space
and time
. ‘From now on, space of itself and time of itself will sink into mere shadows and only a kind of union between them will survive,’ said Hermann Minkowski, Einstein’s one-time mathematics professor.

Minkowski’s union is space–time. ‘The most important single lesson of relativity theory’, says British physicist Roger Penrose, ‘is that space and time are not concepts that can be considered independently of one another; they must be combined together to give a 4-dimensional picture of phenomena: the description in terms of
space–time
.’
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As lowly 3D creatures, we are incapable of experiencing 4D space–time in its full glory. All we can experience are
shadows
of 4D space–time, as Minkowski put it. And those shadows – space and time – change their magnitude depending on how fast we are moving relative to someone else. We might think we live in a
universe
with three dimensions of space and one of time but,
actually
, we live in a universe with four dimensions of space–time.

And herein lies the devastating problem for our concept of time.

Each of the four space–time dimensions has the
character of space.
Which means that space–time has the character of a
map
– a 4D map, granted, but a map none the less. And, just as New York,
Los Angeles and the Grand Canyon are locations on a terrestrial map, the big bang, the birth of the Earth and the end of the
Universe
are locations on the 4D map of space–time. Along with all the events of your life. What this means, according to Einstein, is that the past, present and future all exist
simultaneously
.

Disconcerting as this is to most people, it gave comfort to Einstein when, in 1955, his long-time friend, Michele Besso, died. In a letter to Besso’s bereaved family (which they might not have entirely appreciated), Einstein wrote, ‘Now he has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.’

But, if the past, present and future are only a stubborn illusion and in no sense do we actually
move through time
, why do we have such a strong sense that we do? In fact, why do we have such a strong sense that we are not only moving through time but moving through it in a
particular direction
? Why do we experience the past as L. P. Hartley’s ‘foreign country’?

For a long while – even before the advent of Einstein, who threw things into sharp focus – this was a complete mystery to physicists. The fundamental laws of physics do not prefer any direction of time. The law of gravity, for instance, could equally well allow the Earth to orbit the Sun in a backward direction. Despite this time reversibility, we emphatically cannot live our lives backwards, going from grave to cradle, growing younger with each passing year. Yet, incredibly, there is no explanation of why we feel we are moving through time – and in a particular direction – in fundamental physics. But there is such an
explanation
somewhere else – in thermodynamics.
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If you were to show a picture of a castle and the same castle as a crumbled, vine-covered ruin, you would
know
that the derelict castle came later. Castles crumble. They do not uncrumble. The direction in which things decay, or become disordered, is the
direction
we associate with the direction of time. And it is the second law of thermodynamics that provides this ‘arrow of time’.

There is a simple way of seeing this. Throw the fragments of a broken cup into the air. It is possible that the pieces come down to reassemble into an intact cup. However there is only
one
way this can happen, only one way a cup can be intact. Contrast this with the countless ways that the cup can come down in
even more
broken pieces
. It is because there are overwhelmingly more ways that the cup can come down broken than intact – overwhelmingly more disordered states than ordered states – that cups break and do not unbreak. This is why time flows forwards but not
backwards
. It is why castles crumble but do not uncrumble, why coffee left in a cup grows cold rather than hot, and why people grow old rather than young.

And this is the way that the nineteenth-century Austrian
physicist
Ludwig Boltzmann formulated the second law of
thermodynamics
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– in terms of the number of possible ways in which the components of a body can be arranged and still be the body.
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There is only one way for an intact cup. But trillions upon
trillions
for a broken cup. If all outcomes are equally likely, therefore, it is overwhemingly likely that a cup will stay broken, not leap back together as an intact cup. It is not utterly impossible – the second law of thermodynamics is different from fundamental laws of physics in not being cast iron but
statistical
– but the
likelihood is you would have to wait many times the current age of the Universe to see such a bizarre thing happen.

So, even though our basic picture of reality – relativity –
predicts
that all of space–time is laid out like a map, and nothing actually moves through time, the thermodynamic arrow of time explains why we experience time flowing remorselessly in one direction only.

So, what is the ultimate origin of the arrow of time? Well, clearly, the Universe can get more disordered only if in the past it was
more ordered
. If it was already maximally disordered, it would have nowhere to go. So, the ultimate reason there is an arrow of time is that the Universe in big bang was in a highly ordered state.
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So maybe at last we are getting somewhere in understanding time. Although the concept of a common past, present and future appears nowhere in our fundamental description of reality – relativity – we nevertheless experience them because we live out our lives in the cosmic slow lane and in weak gravity. And, although relativity sets no direction for time, we grow old rather than young because the big bang was an unusual, highly ordered state.