Read What a Wonderful World Online
Authors: Marcus Chown
The key thing to know is that the fireball radiation broke free of matter –
was created
, in essence – a mere 379,000 years after the big bang. Consequently, the Universe, for most of its
existence
, has, in relative terms, been close to Heat Death. Despite this, there is still plenty of scope for cosmic entropy to increase. There are a few tens of trillions years to go until the stars have all gone out and the Universe is plunged into a night without an end.
Take heart from the German physicist Arnold Sommerfeld. Discussing thermodynamics, he wrote, ‘The first time you go
through it, you don’t understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don’t understand it, but by that time you are so used to it, so it doesn’t bother you any more!’
1
Carl Sagan, ‘Wonder and Skepticism’,
Skeptical Enquirer,
vol. 19 no. 1, January–February 1995.
2
The scars of the Late Heavy Bombardment are evident on the face of the Moon. The impacting bodies were big enough to puncture the lunar crust, causing lava from deep inside to well up onto the surface, creating the lunar seas, or
Mare
basins. The LHB is believed to have been caused when large numbers of ice bodies from the outer Solar System were flung sunwards. The sequence of events is not completely clear. But, in one plausible scenario, Jupiter’s
interaction
with the Kuiper Belt, a band of icy rubble left over from the formation of the Solar System and orbiting beyond the outermost planet, Neptune, caused Jupiter to migrate outwards from the Sun. When the time taken for it to circle the Sun was exactly
half
that of Saturn, the two planets lined up regularly on the same side of the Sun, which meant that gravity of the two planets
pulled together
on other bodies in the Solar System. This caused Uranus and Neptune to change their orbits. As they moved, they stirred up the Kuiper Belt, sending large numbers of icy bodies into the inner Solar
System
, where they slammed into planets and their satellites, including the Earth and the Moon.
3
The best evidence that the oceans have an extraterrestrial origin
comes from observations of the water ice on Comet Hartley 2 in 2011. Hydrogen in water, H
2
O, comes in two forms – the normal form, H, and a much rarer, heavier form, or isotope, known as deuterium, D. D
2
O is popularly known as heavy water. The
evidence
from Hartley 2 is that the ratio of heavy water to water in its ice is exactly the same as in the water of Earth’s oceans (Nancy Atkinson, ‘Best Evidence Yet That Comets Delivered Water for Earth’s Oceans’,
Universe Today
, 5 October 2011, http://tinyurl. com/6zazxwj).
4
See Chapter 2, ‘The rocket-fuelled baby: Respiration’.
5
The main reason the Sun heats the equatorial regions more than the polar regions is that the Sun is almost immediately above the ground at the equator while, from near the pole, it appears very low on the horizon. (At some times in the year the Sun is even
below
the horizon and out of sight.) This means that near the poles a given amount of heat is spread over a much larger area of the ground than at the equator, diluting its heating effect.
6
John Tyndall,
In Forms of Water in Clouds and Rivers, Ice and Glaciers.
7
Venus rotates on its axis every 243 Earth days with respect to the fixed stars. Since it also orbits the Sun every 225 days, it would appear that its day is
longer
than its year. However, Venus actually rotates
backwards
compared with all other planets – except Uranus. The combination of this retrograde rotation and the planet’s orbit around the Sun means that the duration of a Venusian day – from sunrise to sunset – is 117 Earth days. In other words, there are 1.92 Venusian days in a Venusian year.
8
Naively, it might be expected that heat could simply be conducted from the equator to the poles, with hot air heating the cooler air standing next to it, and that air, in turn, heating the even cooler air next to it, and so on. However, air is a bad
conductor
of heat and the atmosphere cannot conduct the necessary heat from the equator to the poles fast enough. This can happen only if there is bulk
movement
, or convection, of the air.
9
We do not realise that we are on a rapidly spinning planet for the
same reason we do not realise we are travelling at 900 kilometres per hour inside an airliner. Motion at constant velocity, as Galileo recognised four centuries ago, is undetectable. This is in marked contrast with
changes in our velocity
, which are very obvious. When a plane accelerates down a runway, for instance, the passengers are pinned in their seats.
10
Our common (but illusory) experience is that the ground is
not moving
. Consequently, physicists have invented a force to explain the deflection of air as it moves from the equator to the poles,
assuming that the Earth is not turning
. This Coriolis force is fictitious force but it is convenient for calculations.
11
Latitude is defined as the angular distance of any place on the surface of the globe from the equator, measured in degrees. By convention, the equator has a latitude of 0° and the poles 90°. To distinguish between places above and below the equator, a location may be said to be 34°
North
or 52°
South
.
12
The reason the deflection of north–south-moving air by the Earth’s rotation is the most severe in mid-latitudes is that the deflection depends on two things: how fast the Earth’s surface is rotating at the particular latitude and how fast the rotation is changing. Take the region near the poles. Although the Earth’s rotation velocity is changing fast, the velocity itself is small, so the
deflection is small.
Contrast this with the tropics. Although the Earth’s rotation velocity is large, it is changing only slowly, so the
deflection is again small.
But, in mid-latitudes, the Earth’s rotation velocity
and
the rate at which it is changing are large. Consequently, the deflection of air as seen from the ground is significant. This is why the circulation band at mid-latitudes is the most unstable and turbulent. And why the polar and tropical bands behave like relatively well-behaved mini Hadley cells.
13
The pressure of a gas is a consequence of it being made of
innumerable
atoms flying about randomly. If they drum on any obstacle, they impart on it a jittery force. This, averaged out, is the pressure. The denser the gas, the more atoms there are drumming and the greater the pressure; the hotter the gas, the faster are the
drumming atoms and, again, the higher the pressure. Because the atmosphere is unevenly heated and sloshes about, it is unavoidable that in some regions there is lower than average pressure and in others higher than average pressure.
14
Robert T. Ryan,
The Atmosphere.
15
Edward Lorenz, ‘Does the flap of a butterfly’s wings in Brazil set off a tornado in Texas?’, paper presented at the 139th Annual Meeting of the American Association for the Advancement of Science on 29 December 1979 (
The Essence of Chaos
, appendix 1), p. 181.
16
It might be imagined that, because the southern hemisphere receives more heat from the Sun in its summer than the northern hemisphere does in its summer, summer in the south is
hotter
than in the north. Surprisingly, it is not. The extra solar energy during the
southern-hemisphere
summer principally heats the top of the atmosphere but this is not translated to the surface below. The temperature at any place on the surface depends not only on solar heating but on a complex mix of factors, including the amount of cloud cover, and the speed at which the air and ocean currents transport heat to and from the location.
17
It is a characteristic of a spinning body such as the Earth that it doggedly maintains its spin direction in space (this is why we get
regular
seasons). However, over long periods of time, the combined gravitational pulls of the Sun, Moon and planets tug on the Earth and make it wobble like a top. This precession causes the planet’s spin axis – still maintained at 23.5° to the vertical – to rotate about the vertical
once every 26,000 years.
Currently, the star roughly above the North Pole – that is, in the direction of the Earth’s spin axis if it were extended into space – is Polaris. Because of the effect of
precession
, however, Polaris was not the Pole Star when the Pyramids were built 5,000 years ago. And it will not be the Pole Star 5,000 years hence. Only in 26,000 years’ time will it return to where it is today.
18
The magnetic field of the Sun, like that of the Earth, is generated by electrically charged material circulating deep inside. Because the
Sun rotates faster at the equator than at its poles, the magnetic field emerging from the Sun becomes twisted up, eventually releasing its pent-up energy in flares. For some reason, which is not clear, the cycle of build-up and release of energy takes about twenty-two years. This is the solar cycle. During the active part of this solar cycle, the surface of the Sun is covered by many sunspots and violent flares.
19
Ultraviolet is a type of light emitted by matter at extremely high temperature. On the Sun, it is produced by flares – fountains of matter hurled into space by pent-up magnetic energy. These can easily attain temperatures of 10 to 20 million °C.
20
See Chapter 12, ‘No vestige of a beginning: Geology’.
21
The Sun shines by fusing the cores, or nuclei, of the lightest element, hydrogen, into the nuclei of the second lightest, helium. The
by-product
of this nuclear reaction is sunlight. Helium, being heavier than hydrogen, sinks to the core of the Sun, where gravity squeezes it tightly. As anyone who has squeezed the air in a bicycle pump knows, when a gas is squeezed it gets hotter. Consequently, as the Sun turns hydrogen into helium, its core – and consequently the whole Sun – gets hotter.
22
A big puzzle is why did the Earth not freeze solid if the Sun was 30 per cent less luminous at the planet’s birth? One possible
solution
to the faint young sun paradox is that the newborn Earth was shrouded in a thick enough atmosphere of greenhouse gases and that their warming effect prevented the planet plunging into an interminable ice age.
23
Many astronomy books say the Earth will be swallowed by the Sun which, as a red giant, will balloon out almost to the orbit of Mars. However, a team led by Juliana Sackmann of the California Institute of Technology in Pasadena has pointed out that, although the Sun will get to the Earth’s orbit, when it does, the Earth
will not be there.
The reason is that red giants lose material at a terrific rate via their stellar winds. A less massive Sun will have weaker gravity with which to hold onto the Earth, so the Earth will gradually move away. By the time the Sun reaches the Earth’s current orbit, it will have
only 60 per cent of its present mass and the Earth will be 70 per cent further away, so the planet will probably escape being gobbled. A team led by Mario Livio of the Space Telescope Science Institute in Baltimore, however, points out there is a competing effect. The Earth raises a tidal bulge in the Sun, which it will try to drag around as it orbits. As a consequence, the Earth will spin up the envelope of the Sun while it slows and moves inward. The rate at which the Earth is sapped of orbital energy depends crucially on how viscous is the stuff of the Sun’s envelope, which nobody knows well.
Currently
, therefore, it is not possible to tell which of the two effects will win and whether or not the Earth will be gobbled.
God does not play dice with the Universe.
ALBERT EINSTEIN
Stop telling God what to do with his dice.
NIELS BOHR
Quantum theory is our very best description of the microscopic world of atoms – the building blocks of ordinary matter – and their constituents. It is a fantastically successful theory. Not only has it given us lasers and computers and nuclear reactors but it has provided an explanation of how the Sun shines and why the ground beneath our feet is solid.
But, in addition to being a fantastic recipe for making things and understanding things, quantum theory provides a unique window on the weird, counter-intuitive,
Alice-in-Wonderland
world that underpins everyday reality. It is a place where a single atom can be in two places at once; where things happen for absolutely no reason at all, and where two atoms can influence each other
instantaneously
even if they are on opposite sides of the Universe.
Quantum theory was born out of a conflict between two great theories of physics – the theory of matter and the theory of light. The theory of matter holds that, ultimately, everything is made of tiny indivisible grains, or atoms.
1
The theory of light says that light is a wave, spreading outwards from its source like a ripple on a pond.
Both theories are very successful. For instance, the theory of atoms explains the behaviour of gases such as steam. If a gas is
squeezed into half its volume, it pushes back with twice the force, or pressure, an observation encapsulated in Boyle’s law. This can be explained if the pressure is caused by countless tiny atoms drumming on the walls of the container like rain on a tin roof. When the volume is halved, the atoms have only half as far to fly between striking and restriking the walls and so drum twice as often on the walls, doubling the pressure.
The theory of light is also very successful. However, the phenomena it explains generally involve light waves that overlap each other and reinforce or cancel each other out. And, since the distance between successive crests of a light wave is far less than the width of a human hair, such interference or diffraction phenomena are hard to spot and take scientific ingenuity to make visible to the naked eye.
The clash between the theory of light, which says light is a wave, and the theory of matter, which maintains matter is made of atoms, occurs not surprisingly in the place where
light meets matter
. Specifically, when an atom spits out light – for instance, in a light bulb – or when an atom gobbles up light – for example, in your eye.
The problem is not hard to appreciate. A light wave is
fundamentally
a spread-out thing whereas an atom is fundamentally a localised thing – it would take 10 million laid side by side to span the full stop at the end of this sentence. In fact, a wave of visible light is about 5,000 times bigger than an atom. Imagine you have a matchbox and you open it and out drives a 40-tonne lorry. Or, alternatively, a 40-tonne lorry approaches, you open a matchbox, and the lorry slips inside. That’s the way it is when light meets matter. Somehow an atom must swallow or cough out something 5,000 times bigger than itself.
Logically, the only way something can be emitted and absorbed by something as small and localised as an atom is if it too is small and localised. ‘Nothing fits inside a snake like another snake,’ observed TV survival expert Ray Mears. The trouble is there are countless experiments that show unequivocally that light is indeed a spread-out wave.
Resolving the paradox was mental torture for the physicists of the 1920s. ‘I remember discussions … which went through many hours until very late at night and ended almost in despair,’ wrote the German physicist Werner Heisenberg. ‘And when, at the end of the discussion, I went alone for a walk in the
neighbouring
park I repeated to myself again and again the question: Can nature possibly be so absurd as it seemed to us in these atomic experiments?’
2
In the end physicists were forced to accept something scarcely believable: that light is both a spread-out wave
and
a localised
particle
. Or, rather, light is neither a wave nor a particle. It is
something
else
for which we have no word in our language and nothing with which to compare it in the everyday world. It is as fundamentally ungraspable as the colour blue is to a person blind from birth. ‘We must content ourselves with two incomplete analogies – the wave picture and the corpuscular picture,’ said Heisenberg.
3
In retrospect, perhaps physicists should not have been
surprised
to find the submicroscopic world
weird
. Why should the world of the atom – which is 10 billion times smaller than a human being – contain objects that behave in any way like those in the everyday world? Why should they dance to the same tune, the same laws of physics?
Light is an ungraspable thing and all we can ever do is observe the facets of it. When light is absorbed or spat out by an atom,
we see its particle-like face, known as a photon. When light bends around a corner, we see its wave-like face.
4
‘On Mondays, Wednesdays and Fridays, we teach the wave theory and on Tuesday, Thursdays and Saturdays the particle theory,’ joked the English physicist William Bragg in 1921.
But, it turns out, things are much worse than this. In 1923, the French physicist Louis de Broglie, writing in his doctoral thesis, proposed that not only can light waves behave as localised
particles
, particles such as electrons can behave as spread-out waves. According to de Broglie, all the microscopic building blocks of matter have two faces. All share a peculiar wave–particle duality. In fact, if there is one thing you need to know in order to
understand
quantum theory – one thing from which pretty much everything else logically follows – it is this:
Waves can behave as particles and particles can behave as waves.
Take the first half of the sentence first: waves can behave as particles. Imagine you are looking though a window at the street outside. Maybe you see a car going past, a woman walking her dog past a tree. If you look closely, however, you will also see a faint reflection of your own face staring out. This is because glass is not perfectly transmitting. Most of the light – say, 95 per cent – goes right through but the remainder – 5 per cent – is reflected back. The question is: how is this possible if light behaves as particles – a stream of identical photons like so many miniature machine-gun bullets?
Surely, if the photons are all identical, they should all be affected
identically
by the window pane? Either they should
all
be transmitted or
all
reflected. There appears to be no way to explain how
some
can be transmitted and
some
reflected. Unless – and here physicists were forced to accept a diminished, cut-down version of what it means to be
identical
in the microscopic world – photons have an identical
chance
of being transmitted, an
identical
chance
of being reflected.
But this, as Einstein first realised, is catastrophic for physics. Physics is a recipe for predicting the future with 100 per cent certainty. The Moon is over here today and Newton’s theory of gravity predicts where it will be tomorrow with
absolute
confidence
. But, if photons merely have a particular chance of being transmitted, then it is impossible to predict what an individual photon will do when its strikes the window pane. Whether it goes through or bounces back is entirely down to chance.
And we are not talking about the kind of chance with which we are familiar in the everyday world. We may think a roulette ball ends up where it ends up by chance. But, actually, if we knew the initial motion of the ball, the friction between the wheel and the ball, the play of air currents in the casino, and so on, Newton’s laws would predict
exactly
where the ball would end up. The fact we cannot do this is merely down to not being able to measure all these things accurately enough and do the required calculation to enough decimal places. Though we could do it in principle, we could not do it in practice. However, when we come to a photon impinging on a window, what it does – whether it is
transmitted
or reflected – is not even predictable
in principle
. Quantum unpredictability is
truly
something new under the Sun.
And it turns out that it is not just photons that are
fundamentally
unpredictable. So too are
all
the denizens of the
submicroscopic
world, from neutrons to neutrinos, electrons to atoms.
Einstein was so appalled by this that he famously declared: ‘God does not play dice with the Universe.’ But Einstein was wrong.
5
An obvious question arises: if the Universe at its fundamental level is unpredictable, how come we know the Sun will rise tomorrow, that a ball will go roughly where we throw it? The answer is that what nature takes away with one hand it
grudgingly
gives back with the other. Yes, the Universe is
unpredictable
. But, crucially, the
unpredictability is predictable
. In fact, this is what quantum theory
is
: a recipe for predicting the unpredictable – the probability of this event, the probability of that event. And this, it turns out, is enough to create the largely predictable world we find ourselves in.
The fact that, ultimately, things happen randomly, for no reason at all – the consequence of waves behaving as particles – is arguably the most shocking discovery in the history of science. But, recall, there is a second half to that crucial sentence: particles can behave as waves. The consequence of this turns out to be equally stunning.
Clearly, if particles can behave as waves, they can do
all
the things waves can. And one thing in particular waves can do is mundane in the everyday world but has truly earth-shattering consequences in quantum world.
Imagine there is a storm out at sea and huge waves are rolling in to a beach. Imagine that the next day the storm has passed and the surface of the sea is ruffled into small ripples by a gentle breeze. Now, anyone who has watched the sea knows that it is possible to have a wave that is both big and rolling
and
that also
has small ripples on its surface. This is a general property of all waves. If two waves can occur individually, it is always possible to have a combination, or superposition of the two.
Now consider a quantum wave associated with, say, an atom. Actually, this is a slightly peculiar wave because it is a
mathematical
thing. Nevertheless, it can be imagined extending through out space. The important thing is that where it is big there is a high probability of finding the atom and where it is small there is a low probability.
6
So far, nothing untoward.
Now imagine two quantum waves. One is a quantum wave for an oxygen atom that is highly peaked 10 metres to your left, so there is a very high probability of finding it there. And the other is a quantum wave for the same oxygen atom that is highly peaked 10 metres to your right, so there is a very high probability of finding it there. But, recall, it is a general property of waves that, if two waves are possible, so too is a superposition of the two. But, in this case, such a combination will correspond to an oxygen atom that is simultaneously 10 metres to your left and 10 metres to your right – in other words, in
two places at once
. That is the equivalent of you being in London and New York at the same time.
Actually, nature is set up in such a way that it is impossible to observe something being in two places at once. That is because, if we try to locate something, we are implicitly looking for its particle-like property, which precludes seeing a wave-like property such as superposition. So who cares? Well, although it is impossible to observe something being in two places at once, it is nevertheless possible to observe the
consequences
of
something
being in two places at once. The wave phenomenon that
makes this possible and spawns all kinds of quantum weirdness is called interference.
If you have ever seen raindrops falling in a pond, you will have seen concentric ripples spreading out from each impact and
overlapping
with each other. Where the crests of two waves coincide, they reinforce each other, making a bigger wave; where the crest of one wave coincides with the trough of another, they cancel each other, creating dead calm. This is interference. Now,
imagine
inserting a piece of card in the region of overlap of the waves spreading from two raindrops. There will be places on the card where big waves strike and there will be places on the card where no waves hit.
Actually, this experiment was done with light by the English physician and polymath Thomas Young in 1801. With
considerable
ingenuity, he managed to engineer a situation in which there was an overlap between the light spreading from two point sources of illumination. When he inserted a screen in the
overlapping
region, there appeared a pattern of alternating light and dark stripes, not unlike a modern-day barcode. It was undeniable proof that light exhibits the characteristic wave phenomenon of interference. Young had proved that light ripples through space like an undulation on the surface of a pond. Nobody had noticed it before because the waves of light are simply far too small to be seen with the naked eye.