What a Wonderful World (30 page)

The picture of the big bang as one among perhaps an infinite number of other bangs going off in an ever-expanding sea of vacuum is a remarkable one. But it is far from being bedded in firm theoretical ground. Inflation is an add-on, bolted onto the basic big-bang picture. It is not part of a single seamless theory of the Universe. And, worse, it is not the only thing bolted on.

The basic big-bang model not only predicts that the temperature of the cosmic background radiation should vary over the sky when it does not – something fixed by inflation – it predicts two other things that conflict with observations. For instance, it
predicts
that the expansion of the Universe should be slowing down. The galaxies, after all, are pulling on each other with their mutual gravity. It is as if they are connected by a vast web of elastic, dragging on them and hindering their headlong flight from each other. However, in 1998, physicists discovered that the expansion of the Universe, contrary to all expectations, is not slowing down. It is
speeding up.

On the largest scales, another force must be operating in the Universe, overwhelming the force of gravity and driving apart the galaxies. This mysterious force appears to have switched on about 10 billion years ago and has been calling the cosmic shots ever since. The gaze of physicists has settled on the vacuum between the galaxies. They claim it is filled with dark energy. It is invisible. It fills all of space. And it has repulsive gravity. It is this repulsive gravity that is speeding up the expansion of the Universe.

Dark energy accounts for a 68.3 per cent of the mass energy of the Universe. Imagine how embarrassing it is to have
overlooked the single biggest mass component of the Universe until 1998.

Dark energy could be an intrinsic energy of space predicted by Einstein’s theory of gravity or it could have some other origin. Nobody knows. Physicists are pretty much at sea in explaining it. When quantum theory is used to predict the energy density of the cosmic vacuum – the dark energy – it comes up with an energy density of 1 followed by 120 zeros bigger than what is observed.
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This is the biggest discrepancy between a prediction and an observation in the history of science. It does not take a genius to realise that some big idea is missing.

The dark energy, with its repulsive gravity, is reminiscent of the inflationary vacuum that speeded up the expansion of the Universe in its first split second of existence. The difference is that it was hugely more puny and nowhere near as short-lived. Nobody knows whether there is a connection between the dark energy and the inflationary vacuum.

Dark energy and inflation, however, are not the only two things that must be bolted on to the basic big-bang model to make it agree with what we observe. There is a third thing predicted by the big-bang model that is at odds with reality. In fact, it is quite a serious thing. The big bang predicts that
we should not exist.

Recall that the galaxies, such as our own Milky Way, congealed out of the cooling debris of the big-bang fireball.
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This was possible because the fireball was not completely uniform. The temperature of the cosmic background radiation is remarkably even all over the sky but it is
not totally even
. There are places
where the temperature departs by a few parts in 100,000 from the average. The temperature undulations are believed to reflect the fact that some parts of the big-bang fireball were ever so slightly denser than their surroundings.

The small unevenness in the matter of the big-bang fireball is believed to have been caused by microscopic convulsions, or quantum fluctuations, of the inflationary vacuum in the first spilt second of the Universe. These were then magnified by the tremendous expansion of inflation. By about 379,000 years after the birth of the Universe, they had created slight bumps in the distribution of matter in the big-bang fireball. With slightly stronger gravity, these gathered matter about them faster, which boosted their gravity yet more. In a process akin to the rich
getting
ever richer, they grew remorselessly, eventually becoming the galaxies we see around us today.

It is a detailed and compelling picture. Only there is a problem. The 13.8 billion years since the big bang has not been enough time to assemble galaxies as big as the Milky Way. Not nearly enough. In short, we should not be here.

Undeterred, astronomers fix this problem by postulating that the Universe contains a vast quantity of invisible, or dark, matter, whose extra gravity speeded up the process of galaxy formation so it was completed within 13.8 billion years.
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In fact, the dark matter in the Universe amounts to about 26.8 per cent of the mass of the Universe.
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It outweighs the visible stars by a factor of more than five.

Nobody knows the identity of the dark matter. It could be in the form of fridge-sized black holes formed in the first split second of the Universe ’s existence.
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Or it could be in the form of hitherto undetected subatomic particles. Certainly, theories of
particle physics are not short of possible candidates. But the bottom line is that
nobody knows.

To summarise, then, the basic big-bang picture must be supplemented by three bolt-ons: inflation, dark energy and dark matter. A figure of 68.3 per cent of the mass of the Universe is mysterious dark energy. Another 26.8 per cent is mysterious dark matter. That leaves a mere 4.9 per cent of the Universe made of ordinary matter – the stuff that you and I and the stars and galaxies are made of.
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And, actually, we have only ever seen about half of that with our telescopes. The rest is ultra-hot hot gas floating around the galaxies that gives out little visible light.

To say that this is an embarrassing situation is an
understatement
. We have based the great edifice of our cosmological model on a mere 4.9 per cent of the Universe we have seen directly, whereas 95.1 per cent is made of invisible stuff whose identity eludes us. Imagine if Charles Darwin had tried to concoct a theory of biology knowing only of frogs but nothing of fish or birds or elephants.

Actually, it is not quite as bad as this. Dark matter and dark energy, to steal a phrase from Donald Rumsfeld, are ‘known
unknowns
’. Astronomers, though hazy on the details, are confident that their overall picture is correct. Nevertheless, few would deny that there must be a deeper theory of the Universe out there, which unites inflation, dark matter and dark energy into a
seamless
whole.

Such a deeper theory might have to acknowledge one rather basic thing. Our Universe is not all there is. There might be other universes.

The key thing to remember is that the Universe was born 13.8 billion years ago. This means that we can see only those galaxies whose light has taken less than 13.8 billion years to reach us. Those whose light would take more than 13.8 billion years, well, their light is still on its way. Consequently, the Universe is bounded by a horizon – the light horizon. Think of it as the surface of a bubble. The bubble, centred on the Earth, contains about 100 billion galaxies, and is commonly known as the observable Universe.

But, just as we know there is more of the ocean over the horizon at sea, we know there is more of the Universe over the cosmic horizon. In fact, according to the theory of inflation, there is effectively an
infinite amount
. In other words, beyond the soap bubble of our observable Universe, are an infinite number of other soap bubbles. What is it like in them? Well, each had its own big bang – or, to look at it another way, a
portion
of our big bang. And, out of the cooling debris, congealed galaxies and stars –
different
galaxies and stars.
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In other words, each bubble had a different history. ‘Many and strange are the universes that drift like bubbles in the foam of the river of time,’ said English science-fiction writer Arthur C. Clarke.
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There is a twist. Because the Universe is quantum, or grainy, there are only a finite number of possible histories for each bubble. Here is the reasoning …

According to quantum theory, the world at a microsocopic level is grainy, like a newspaper photograph. Ultimately,
everything
comes in indivisible chunks, or quanta. Energy comes in chunks. Matter does. Time does. And so does
space
. So, if we
were able to look at space closely with some kind of
super-microscope
, we would see space resolve itself into indivisible grains. Think of it as a chessboard with squares of space. Now, if we run the expansion of the Universe all the way back to the beginning of inflation, we find that there were a mere 1,000 squares of space. The number is not relevant – although it is amazingly small. It is the fact that there is only a finite number of squares.

The seeds of galaxies turn out to be stuff on those squares. If a square contains energy that energy is the seed for a galaxy. But, just as there are only a finite number of ways to arrange the chess pieces on a chessboard, there is only a finite number of ways to fill the squares, some with energy, some empty of energy. In other words, the inflationary chessboard can create only a finite number of possible arrangements of galaxies, only a
finite
number of possible cosmic histories.

So we have a finite number of possible histories and an infinite number of locations for them to be played out. Consequently, every history occurs an infinite number of times. So there is an infinite number of copies of you whose lives until this moment have been exactly like yours. In fact, it is possible to calculate how far you would have to go to meet your nearest doppelgänger. The answer is roughly 10^10^28 metres.

In scientific notation, the number 10^28 is 1 followed by 28 zeros, which is 10 billion billion billion. Consequently, 10^10^28 is 1 followed by 10 billion billion billion zeros. It is a
tremendously
big number. It corresponds to a distance enormously
further
than furthest limits probed by the world’s biggest, most powerful telescopes. But do not get hung up on the size of this number. The point is not that your nearest double is at a
mind-bogglingly
great distance from the Earth. The point is that you have a double at all.

Don’t believe this? Unfortunately, it is an unavoidable
consequence
of two things: a fundamental theory of the Universe and our fundamental theory of physics – quantum theory. If it is wrong, one or both of these must be wrong. This would not be an unusual state of affairs. ‘Cosmologists are often wrong,’ said the great Russian physicist Lev Landau, ‘but they are never in doubt.’

Black holes are regions of space–time where gravity is so
enormously
strong that nothing, not even light, can escape. Probably, you think these celestial objects are esoteric and have no bearing on your everyday life. Nothing could be further from the truth. The birth of the Milky Way Galaxy, without which you would not be reading these words, might have been triggered by a black hole. Not only that but black holes reveal something about everyday reality that is so startling it is scarcely believable. Our Universe might be a giant hologram.
You
might be a hologram.

A black hole is a testament to the irresistible force of gravity, which, like the German football team, can be halted temporarily but always wins in the end. It triumphs because it is an attractive force between
every
piece of matter in the Universe and
every
other
piece and nothing can nullify it. By contrast, the
electromagnetic
force – which holds together the atoms in your body – can be both attractive and repulsive and, on the large-scale at least, it is pretty much always cancelled out.

A black hole is a prediction of Einstein’s theory of gravity, the general theory of relativity. It is cloaked by an event horizon, an imaginary membrane that marks the point of no return for in-falling matter and light. If an astronaut were able to hover just outside the event horizon, his time would slow down so much, as a consequence of Einstein’s theory, that, in principle, it would be possible for him to look outwards and watch the entire
future history of the Universe flash past his eyes like a movie in fast-forward.
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Inside the horizon, the distortion of time is so great that time and space actually swap places. This is why the singularity, the point at which in-falling matter is crushed out of existence at the centre of the hole, is unavoidable. It is exists not across space but across
time
so can no more be avoided than you can avoid tomorrow.

At the singularity, all physical quantities such as density
sky-rocket
to infinity. ‘Black holes are where God divided by zero,’ said the American comedian Stephen Wright. The singularity is an indication that Einstein’s theory of gravity has been stretched beyond its limits and no longer has anything sensible to say. Almost certainly, a better theory – a quantum theory of gravity – will show that the singularity is not a singularity but instead just a super-high-density knot of mass energy.

‘The black hole teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be
extinguished
like a blown-out flame, and that the laws of physics that we regard as “sacred”, as immutable, are anything but,’
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said John Wheeler, the American physicist who popularised the term black hole.
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Although the general theory of relativity predicted black holes, Einstein never believed in their existence. This is not
uncommon
in physics. Theorists often have difficulty overcoming their sheer disbelief that nature really dances to the tune of the arcane symbols they scrawl across a whiteboard. ‘Our mistake is not that we take our theories too seriously,’ as Nobel
Prize-winning
physicist Steven Weinberg observed, ‘but that we do not take them seriously enough.’

Stellar black holes – which form from the catastrophic shrinkage of massive stars at the end of their lives – are, by their very nature, hard to spot. After all, they are very small and, well, very black. However, if a black hole is in a binary star system, we may see the telltale X-rays emitted by matter ripped from a companion star and heated to incandescence as it is sucked down into the hole. The first stellar-mass black hole, Cygnus X-1, was discovered by the Uhuru satellite in 1971. But, actually,
something
that would turn out to be far more significant in the
black-hole
story – and, crucially, more significant for
us
- was found eight years earlier.

Quasars, discovered by Dutch-American astronomer Maarten Schmidt in 1963, are the super-bright cores of galaxies, blazing like beacons at the edge of the Universe. Because their light has taken most of the age of the Universe to reach us, they also blaze at the beginning of time. Typically, a quasar pumps out the energy of 100 normal galaxies such as the Milky Way but from a region smaller even than our Solar System. Nuclear energy – the power source of the stars – is woefully inadequate. The only process that can explain the prodigious energy output of quasars is matter heated to incandescence as it swirls down into a black hole. But not a mere stellar-mass black hole – a black hole with a mass of
billions of suns.

For a long time after Schmidt’s discovery, astronomers thought that such supermassive black holes were cosmic anomalies. They believed that such monsters powered only the badly behaved 1 per cent of galaxies of which the most extreme
examples were quasars. But, over the past few decades, it has become clear that there is a supermassive black hole not only in the heart of these active galaxies but in the heart of pretty much
every
galaxy, including our own Milky Way. Most are quiescent, having gorged on and utterly exhausted their feedstuff of
interstellar
gas and ripped-apart stars.

The origin of supermassive black holes – unlike their stellar-mass cousins – is a mystery. Perhaps they are born when stellar-mass black holes collide and coalesce in the crowded heart of a galaxy. Or perhaps they form directly from the shrinkage of a giant pre-stellar cloud of gas. One thing is for sure: they grow extremely big extremely quickly. By the time the Universe was 500 million years old – a mere 5 per cent of its current age – there were supermassive black holes in existence that had already reached billions of solar masses.

But, although supermassive black holes are impressive on a human scale, they are minuscule on a cosmic scale. Not only are they tiny compared with their parent galaxies – even the biggest would fit easily within our Solar System – but they also have very small masses compared with the mass of the stars in their galaxies.

Despite this, they appear to control the stellar content and structure of their parent galaxies. For instance, the mass of the stars in the core of a galaxy is invariably about 1,000 times the mass of the central black hole, hinting that there is an intimate connection between a supermassive black hole and its parent galaxy. Consider for a moment how surprising this is. It is as if the growth of a mega-city such as Los Angeles were controlled by something as small as a single mosquito.

The means by which tiny supermassive black holes project their power over vast reaches of space are jets. Propelled by twisted magnetic fields in the gas swirling down to oblivion, these channels of super-fast matter stab outwards from the poles of the spinning black hole. They punch their way through the galaxy’s stars and out into intergalactic space, where they puff up titanic balloons of hot gas – some of the largest structures in the known Universe.

In fact, such balloons of gas were the first hint that science got of the existence of supermassive black holes. In the 1950s, radio astronomers, using equipment adapted from war-time radar,
discovered
that the radio emission observed from some galaxies came not, as expected, from the central knot of stars but, mysteriously, from giant, radio-emitting lobe, on either side of the galaxy.

In the early 1980s, the thread-thin jets that are feeding the lobes were imaged for the first time by the 27 radio dishes of the Very Large Array in New Mexico. They mock our puny attempts at accelerating matter. Whereas the Large Hadron Collider near Geneva can whip a nanogram or so of matter to within a whisker of the speed of light, nature can boost many times the mass of the Sun each year to similar speeds along cosmic jets.

The jets control the structure of their parent galaxies because, in the inner regions where the jets are still fast and powerful, they drive out all the gaseous raw material of stars, snuffing out star formation. In the outer regions of galaxies, however, where the jets are slower, the jets have the opposite effect. As they slam into gas clouds, the concussion may trigger them to collapse under gravity to give birth to new clutches of stars.

But supermassive black holes, by starting and stopping star formation, do not merely sculpt galaxies. They might also
determine
the very
character
of the stars that form in them. Galaxies that contain the biggest supermassive black holes – so-called giant elliptical galaxies – appear to contain a much greater proportion of cool, red, long-lived stars, and there is evidence that the black hole might be responsible. Such red dwarfs spawn planets with few heavy elements such as carbon and magnesium and iron. Crucially, these are essential for life.

This has implications for our own Galaxy because, 27,000 light years away in the dark heart of our Milky Way, lurks a
supermassive
black hole 4.3 million times the mass of the Sun. Sagittarius A* might sound impressive but, actually, it is an insignificant tiddler compared with its 30-billion-solar-mass cousins in the cores of some quasars. Until recently, it was believed to be a mere coincidence that our Galaxy contains only a relatively small supermassive black hole. But is it? The giant elliptical galaxies that litter the cosmos might be chock-a-block full of planets but every last one of them might be a desert world, sterile and lifeless. The benign black hole in the heart of our Milky Way might be a large part of why we find ourselves here and not somewhere else. It might be a large part of why you are at this moment reading these words.

Actually, we might be even more beholden to supermassive black holes than this. Most astronomers believe that galaxies give birth to supermassive black holes. But there is a contrary view and that is that supermassive black holes
give birth to galaxies.

In this view, a giant gas cloud out in space shrinks
catastrophically
under its own gravity and, without forming any stars first, spawns a supermassive black hole. When its jets switch on, they stab outwards across space. If they happen to slam into an inert gas cloud floating in the void, the concussion causes the cloud to collapse, fragmenting into stars. In other words, it makes a galaxy.

This is no idle theoretical speculation. Astronomers know of a supermassive black hole floating in the void without a
discernible
galaxy of stars surrounding it. Extending from this naked quasar are two oppositely directed jets. And, at the end of one, is a newborn galaxy about the size of our Milky Way. It appears to have been triggered to form about 200 million years ago when the jet stabbed like a laser beam into a sleeping gas cloud. In the future, the supermassive black hole will fall into the heart of the galaxy it created and the galaxy birth process will be complete.
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If the idea that supermassive black holes zap galaxies into being is right, it is an extraordinary story how these objects have come in from the cold. Once they were thought to power only a tiny minority of anomalous active galaxies. Then it was
discovered
they exist in the heart of pretty much every galaxy. Now it appears they may actually
create
galaxies. You and I might owe our very existence to a supermassive black hole.

But black holes, in addition to being essential to our existence, might also have something extraordinary to tell us about the Universe we live in – and indeed the nature of everyday reality. The Universe might be a hologram – a 3D representation of an
underlying 2D reality.
You
, without knowing it, might be a hologram.

Recall that a black hole is born when a massive star reaches the end of its life and shrinks catastrophically, crushing the star to a point-like singularity. The vanishing of a star in such a dramatic way was not a problem for physics until, in 1974, Stephen Hawking showed that, paradoxically, black holes are not completely black. They radiate into space so-called Hawking radiation.

Hawking imagined quantum processes going on just outside the event horizon. All the time, in the vacuum around us,
subatomic
particles and their antiparticles are popping into existence along with their antiparticles and then popping out of existence again. The energy to create such virtual particles is paid back quickly and so nature turns a blind eye. However, sometimes one particle of a pair falls into the black hole. The remaining partner, with no twin with which to annihilate, cannot pop back out of existence. No longer a fleetingly real particle, it now has a
permanent
existence. The energy to create it has to come from
somewhere
. And it comes from the gravitational energy of the black hole. Bit by bit, as the energy of countless particles of Hawking radiation has to be paid for, the hole loses its mass energy until, eventually, it vanishes, or evaporates.

The trouble with Hawking’s discovery is that it implies that, when a black hole evaporates, all information about the star that initially shrunk to create the black hole – the type and location of all its atoms, for instance – will disappear too. This contradicts a fundamental edict of physics that information can never be created or destroyed.
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A clue to the resolution of the black-hole information paradox came from Israeli physicist Jacob Bekenstein. He discovered
something profound about the event horizon: its surface area is related to the entropy of the black hole. In physics, a body’s entropy is synonymous with its microscopic disorder.
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But you do not need to know this. The crucial thing to know is that entropy is intimately related to information. A billion-digit number in which each digit is unrelated to the next has a high degree of disorder, or entropy; simultaneously, it contains a lot of information since the only way to convey it to someone is to tell them all billion digits.