Can life survive for ever in the Universe? Yes! – as long as it steers the Universe along a very special path.
They will have time enough, in those endless aeons, to attempt all things, and to gather all knowledge … no gods imagined by our minds have ever possessed the powers they will command … But for all that, they may envy us, basking in the bright afterglow of creation; for we knew the Universe when it was young.
Arthur C. Clarke, Profiles of the Future, 1962
‘We are alive,’ said Lucinda and at that moment she felt herself to be what she said. ‘We are alive and on the very brink of eternity.’ Peter Carey, Oscar and Lucinda, 1988
You’ve had a long life but, finally, your time has come. If you were a wit like Oscar Wilde, you would say something amusing like: ‘Either these curtains go or I do.’ But you are suffused by such an awful tiredness that you can barely think, let alone speak. You no longer have the strength to fight on. This is it. As your eyelids begin to fall, coming down like metal shutters on your life, the hubbub of the world fades to a distant murmur. You draw one last breath …
… and it is summer and you are young again. Your favourite dog – the one you loved so much as a child and thought you would never see again – has knocked you to the ground and is licking your face furiously. Through tears of joy, you see your father and mother – long dead – standing over you. They are young – just as they were when you were ten years old – and they are laughing and stretching out their hands to you.
What is happening? Have you died and gone to Heaven? Not exactly. You’ve been resurrected as a simulation on a computer at the end of time!
Surely, such a scenario is pure fantasy? You would be forgiven for thinking so. But, according to a prominent American physicist, an extraordinary fate like this awaits each and every one of us after we die. His name is Frank Tipler and he has come to this outrageous conclusion not for any theological reasons but after applying the formidable armoury of modern physics to a single, profound question – Can life survive for ever in the Universe?
The first scientist to seriously address this question was the Anglo-American physicist Freeman Dyson in 1979.* His immediate problem was to define ‘life’, a thorny and controversial issue which is to this day hotly debated. Dyson settled on the idea that a living thing is a ‘processor of information’.
The advantage of this definition is that it is general. For all we know, life in the far future may be implemented not in the wetware of biology but in the software of computers – or, more likely, in some form beyond anything we can currently imagine. But regardless of how life is implemented, argued Dyson, it will still have to process information. The question of whether life can go on for ever in the Universe can therefore be turned into another, more tractable, question. Can information processing go on for ever? The answer, realised Dyson, depends crucially on the long-term fate of the Universe.
‘Prediction is always difficult, especially of the future,’ warned the Danish physicist Neils Bohr. However, in the case of cosmology – the science of the Universe – there are grounds for optimism. Currently, the Universe is expanding, its constituent ‘galaxies’ flying apart from each other like pieces of cosmic shrapnel in the aftermath of the Big Bang. In the ultra-long-term future there are two possibilities.
One possibility is that the expansion of the Universe will eventually run out of steam and the Universe will then embark on a phase of runaway contraction. If we live in such a ‘closed’ universe, we can expect it to shrink all the way back down to a Big Crunch, a sort of mirror image of the Big Bang in which all the galaxies are piled up on top of each other in a great cosmic smash-up. The other possibility is that the Universe will continue to expand for ever, its constituent galaxies perpetually receding from each other into the empty cosmic night. In such an ‘open’ universe, the fate of everything, to coin a phrase from
T. S. Eliot, will be to end ‘not with bang but with a whimper’. The thing that determines whether the Universe is open or closed is the amount of matter it contains. If there is more than a critical threshold of matter, its combined gravity will be enough to brake and eventually reverse the expansion. If there is less than the threshold, nothing will ever stop the expansion. In 1979, when Dyson considered the question of whether life could survive for ever in the Universe, it looked very much to astronomers as if there was insufficient matter tied up in stars and galaxies and clouds of gas drifting out in space to close the Universe. It was therefore in the context of an open universe that he posed his question: Can information processing go on for ever?
The processing of information involves what physicists refer to as ‘work’. In the case of an everyday PC, for instance, work must be done to flip a transistor on a microchip from a state representing the binary digit ‘0’to a state representing a ‘1’, and vice versa. Work is possible, however, only if there exists an energy difference. For instance, a difference in electrical energy – characterised by a voltage difference – drives the electrical current that flips the state of a transistor. Similarly, a difference in heat energy between the Earth’s equator and the poles – characterised by a temperature difference – drives the planet’s weather systems.
In the Universe as a whole, the ultimate driving force behind all activity is the temperature difference between different regions – specifically, between the stars like the Sun, which are tremendously hot, and interstellar space, which is tremendously cold.
If the Universe is eternally expanding, however, the stars will eventually burn out and even the feeble heat that criss-crosses space will be diluted by being smeared throughout greater and greater volumes of emptiness.* The overall effect will be to iron out any differences in temperature that exist between different parts of the Universe so that, eventually, no further work will be possible and all cosmic activity will die away. Ever since the nineteenth century, when this miserable cosmic end-state was first recognised as a distinct possibility, physicists have referred to it as the ‘heat death’ of the Universe.
On the face of it, an ever-expanding universe, heading for inevitable heat death, would appear a very unfavourable arena for the processing of information – and therefore life – to continue for ever. Appearances, however, can be deceptive. Surprisingly, Dyson’s calculations showed that, even in such an unpromising universe, life can survive indefinitely. Mind you, its survival is at a considerable cost. Life must continually slow itself down, even entering a state of hibernation for extended periods of time.
If life gets ever slower, constantly scaling down its energy needs, even the meagre temperature differences between different regions of the Universe can be enough to keep it ticking over. For a creature condemned to live in the far future of such a universe a single thought might take a million years, a billion years, or even more. It would not matter, however, how long it took. After all, if there is one resource that is available in inexhaustible abundance in an eternally expanding universe it is time.
But, as Dyson discovered, slowing down may not be enough on its own to ensure the perpetual survival of an organism. At times there may be insufficient energy for even a single thought. This is where hibernation comes in. By entering a period of suspended animation, a being can wait patiently until enough of a temperature difference has built up in the external universe to drive its next thought.
By a clever combination of slowing down interspersed by periods of hibernation, life can survive into the infinitely far future. The active word here is of course ‘survive’. By no stretch of the imagination can life be said to flourish. It merely clings desperately to existence. ‘And who would want to live that way?’ says Tipler.
Another difficulty with Dyson’s survival strategy is connected with the ‘red shift’. As the Universe expands, light – the only means by which an entity can transmit its thoughts from one part of itself to another – becomes stretched out, or red-shifted.* When light is stretched in this way, it loses energy. To compensate for this an organism therefore needs even more energy for its internal signalling. In a universe already severely strapped for energy, the red shift makes things worse, pushing up still further the energy requirements for the processing of information.
The red-shift problem – not to mention the general unattractiveness of Dyson’s scenario – set Tipler wondering whether there was any other kind of universe in which life could survive for ever. Since Dyson had considered an open universe, Tipler considered the only other possibility: a closed universe.
At first sight, it seems patently obvious that life cannot go on for ever in a closed, shrinking, universe. A closed universe, after all, eventually comes to an end. However, it is important to make a distinction between the external time in such a universe – which undeniably is in limited supply – and the internal, or ‘subjective’, time which is experienced by a creature living in the universe. The two may be quite different.
That subjective time is an elastic concept is common human experience. For an eighty-year-old, a year appears to fly by, while for an eight-year-old a summer’s day seems to stretch for ever. A child lives its life perpetually on the brink of eternity, blissfully unaware that it will one day die. However, it is not necessary to be unaware of death to experience time in an altered manner. A similar effect might be achieved if it were possible to change the speed at which thoughts are processed. In Dyson’s heat-death universe, for instance, a creature ensures its perpetual survival by drastically slowing down its thought processes. In the time it takes it to yawn and slip back into hibernation, trillions of years may have marched on by in the external universe. Of course, this slowing down of information processing is the complete opposite of what is necessary to extend subjective time in a closed universe. Here, external time is severely limited by the looming Big Crunch and a creature must speed up rather than slow down its thought processes in order to squeeze as much as possible out of every second remaining before the cosmic curtain call.
Whether or not this is possible depends crucially on the temperature difference between different parts of the Universe since this is the driving force behind all cosmic activity. In the case of a heat-death universe, the temperature difference dwindles to next to nothing, causing cosmic activity, including information processing, to all but cease. If, however, information processing is to speed up, the temperature differences throughout the Universe must grow bigger.
At first sight, a closed Universe heading for the inevitable Big Crunch seems promising. After all, things get hot when they are compressed into a small volume, as anyone who has squeezed the air in a bicycle pump knows. So, as the universe shrinks, more and more heat energy will become available. In fact, if the universe shrinks all the way to zero size, an infinite amount of energy should become available.* It would seem that in a closed Universe there is an embarrassment of energy for information processing.
The problem is that it is not energy that is required to do work, including process information – it is an energy difference. And, in a shrinking universe, everywhere heats up at the same rate. So, no matter how hot it gets, it gets hot everywhere pretty much equally and no appreciable temperature difference develops. Consequently, there is no scope for the speeding up of the processing of information – and no scope for a creature to live an enormously long subjective time in the limited time before the Big Crunch.
It would appear that, despite its abundance of energy, a closed universe is an even worse place for life to cling to existence than an open, heat-death universe. Perhaps this is obvious. A closed universe, with the Big Crunch presiding over the end of time like a black widow spider, never seemed very promising. But it is possible to be too hasty. What exactly is it about a closed Universe that is the real problem?
The real problem, according to Tipler, is that such a universe shrinks at the same rate in all directions. This is the reason why no appreciable temperature differences ever arise. And this is the reason why information processing cannot speed up. But does it have to be this way? What would happen if the Universe did not shrink at the same rate in all directions? This is the remarkable possibility considered by Tipler.
In Tipler’s universe, space shrinks faster along two directions than along the third. Imagine a terrestrial globe that tightens its belt – shrinking in on itself at the equator far faster than it shrinks between the poles. In a universe behaving in this way, the stuff that shrinks fastest – the material in the plane of the equator – gets hotter than the stuff that does not – the material out by the poles. And this difference in temperature just keeps on growing.
The bigger and bigger temperature difference drives ever more cosmic activity, enabling information to be processed faster and faster. Eventually, if the Universe dwindles down to a dimensionless point, the temperature difference will become infinite, which means it will be possible to process information infinitely fast!
Surely, this is too good to be true? Certainly, there are possible problems with this scenario (not least how such a peculiar universe could come about!). For one thing, as the temperature goes up, more energy is needed to store each single ‘bit’ of information. After all, by definition, information can exist only if it is noticeable. And that requires it to have a temperature above the Universe’s average temperature, which is of course sky-rocketing.
Another problem with Tipler’s universe is that the processing of information inevitably generates waste heat, which must somehow be got rid of. In the case of a PC, the waste heat is commonly expelled into the air by a cooling fan. This warms up the surroundings, reducing the temperature difference between the computer and its environment. Such an evening-out of the temperature is small for a PC. However, for a searing-hot universe in which enormous quantities of heat must be dissipated, it might seriously slow down the processing of information.
At first sight, the problems of getting rid of waste heat and finding enough energy to store the information being processed appear serious. However, as the Universe shrinks, the temperature difference which drives information processing continually goes up. The key question is therefore: does it go up fast enough to compensate for these problems? Tipler has done the calculations, and the remarkable answer is, yes!
Incredibly, the laws of physics permit a future universe in which the energy for information processing goes up without limit. In such a universe, the amount of energy available grows at a faster rate than the time left in the universe shrinks. So, although any creature that adapts to think faster and faster will have less and less time left to do their thinking, this will be entirely compensated for by the fact that they can do more and more in that time. From their subjective point of view, the imminent end of the universe will appear to recede until it is an infinite distance away in their future. There will literally be time enough for an eternity of living before the curtain comes down at the end of the universe. ‘Time yet for a hundred indecisions. And for a hundred visions and revisions. Before the taking of toast and tea’, in the words of T. S. Eliot.*
If our world was to end in a day but someone were to find a way of speeding up our lives so we could fit a whole lifetime of experiences in a single hour, in a single minute, what would the end of the world matter to us?† Similarly, of what consequence would the end of the Universe be to creatures who can squeeze an infinite number of lifetimes in the remaining seconds, remaining nanoseconds – creatures who, in the ever-shrinking time that is left, can live for a subjective eternity?
The fact that the laws of physics permit a future universe in which life can potentially survive for ever is a miraculous thing to behold. In fact, Tipler believes it is so remarkable that it can be no accident. It must mean that life has a crucial, though mysterious, role to play in the Universe. Tipler has coined a name for the extraordinary processing frenzy in which such an eternal universe ends. He calls it the ‘Omega Point’.‡
The Omega Point universe could never come about naturally. The only way to create a universe that shrinks at different speeds in different directions is artificially. It must be ‘engineered’. Life must grab the Universe by the scruff of the neck and steer it in the desired direction. It must exert a controlling influence over the long-term fate of the Universe.
To say this is a staggering challenge is a bit of an understatement. Before even asking how it might be done, there is another, more basic question: Why do it?
The answer, according to Tipler, is self-evident: ‘Because life can do nothing else.’ Ever since the emergence in the primeval slime of the first self-replicating molecule – the ancestor of all terrestrial organisms – life on Earth has been driven by one overriding impulse: the need to perpetuate itself. And the only way life can perpetuate itself indefinitely in our Universe is if it finds a way of driving things along the path that leads to the Omega Point.
As Dyson has observed: ‘It is impossible to calculate in detail the long-range future of the Universe without including the effects of life and intelligence. It is impossible to calculate the capabilities of life and intelligence without touching, at least peripherally, on philosophical questions. If we are to examine how intelligent life may be able to guide the physical development of the Universe for its own purposes, we cannot altogether avoid considering what the values and purposes of intelligent life may be. But, as soon as we mention the words value and purpose, we run into one of the most firmly entrenched taboos of twentieth-century science.’
Tipler, like Dyson, is unafraid to confront the taboos. He believes that life, driven by its unwavering instinct for survival, will spread to fill the entire Universe, at which point it will inevitably contemplate the ultimate engineering project – the steering of the Universe down to the promised land of the Omega Point.
If this sounds like madness, think again. According to Tipler, the first step on the long road to the Omega Point is pre-ordained. It is an inescapable consequence of the survival impulse. ‘Provided that humans do not wipe themselves out in some global catastrophe’, he says, ‘our descendants will one day leave for ever the cradle of the Earth and spread among the stars.’
This abandonment of Earth will not be a matter of choice, says Tipler. It will be forced on our descendants. In about five billion years, the Sun will have exhausted the hydrogen fuel deep in its core. By then, it will have puffed up into a monstrous, super-luminous ‘red giant’, pumping out more than 10,000 times the heat it does today. If this bloated star does not completely swallow our planet – and it will definitely envelop the close-in worlds of Mercury and Venus – it will certainly reduce the Earth to a burnt and blackened lump of slag.*†
The death of the Sun sets a critical deadline for our far-future descendants. Long before a blood-red orb swells to fill half the terrestrial sky, they must have vacated their home planet for the stars.
The crossing of interstellar space presents an immense and daunting challenge. The environment between the stars is unimaginably harsh. Creatures made of flesh and blood can survive it only if they are shielded from the hard vacuum, from the shattering cold and from the lethal sleet of cosmic ray particles which permeate space and can blast apart the fragile strands of DNA.
Tipler thinks the necessary degree of shielding is unattainable. He is therefore pessimistic that humans can tough it out in the abyss between the stars. ‘Flesh-and-blood is simply too fragile for the rigours of interstellar space,’ he maintains. ‘And, by the time our descendants are ready to leave the Solar System, they will have long realised this.’
According to Tipler, there is only one way our descendants can possibly cross interstellar space – in the guise of machines. ‘First they will have to “download” their minds into computers,’ he says. ‘Minds implemented in machinery will be much easier to harden against the conditions of interstellar space than minds implemented in jelly and water.’
If Tipler is right, the ships that will one day stream outwards from the dying Earth, like so many dandelion seeds scattered to the wind, will contain steel and plastic not flesh and blood.
The aim of this diaspora will be to seek out and colonise inhabitable worlds around other suns. However, the new worlds – other Earths – can never provide much more than a temporary respite from the exigencies of survival. Other suns will grow old and die, just like our own. Faced with this inescapable fact of cosmic life, our far-future descendants will have no choice but to keep on moving, for ever discarding used-up planets before they can be scorched and blackened by their dying suns. In this way they will spread inexorably from one end of the Galaxy to the other.
Our Milky Way is a great, ponderously turning, pinwheel of stars, crammed with a few hundred billion suns and spanning about 150,000 light years. This is almost 40,000 times the separation between Sun and its nearest stellar neighbour, Alpha Centauri, so the challenge of spreading throughout the Galaxy is of an altogether more formidable character than merely reaching nearby stars. Tipler, typically, is unfazed. He believes there is a sure-fire way of colonising the Milky Way – and relatively quickly. It involves exploiting a device first envisaged by the Hungarian-American mathematician John von Neumann.
A ‘self-reproducing von Neumann probe’ is a cross between a starship and a robotic factory. As the first step in the colonisation of the Galaxy, a large number of such probes would be despatched to nearby stars. On arrival at their target planetary systems, they would land on planets or moons or asteroids and set about using the available resources to build copies of themselves. Once completed, the copies would depart for nearby stars, where the whole process would repeat itself. In this way, von Neumann probes would multiply and spread throughout the Milky Way, infecting billions upon billions of planetary systems like some unstoppable galactic virus.
How long it will take these robot descendants of the human race to reach every last nook and cranny of the Milky Way will clearly depend on how fast they travel. According to Tipler, a speed close to the cosmic speed limit itself – the speed of light – is possible. Boosting a probe close to such a tremendous speed will of course not be easy. However, Tipler believes it is possible by exploiting the ultimate fuel – antimatter.*
Antimatter’s key characteristic is that, when it meets matter, 100 per cent of its mass-energy is instantly converted into other forms of energy such a heat. An H-bomb, by contrast, turns less than 1 per cent of its mass-energy into heat energy. It is antimatter’s ability to pack the biggest punch possible for a given weight that makes it the fuel of choice for interstellar travel. The only problem is obtaining enough of the stuff. Despite the best efforts of physicists, they have so far managed to accumulate no more than a billionth of a gram of antimatter. Tipler, however, thinks this is merely a technological problem, and that almost certainly it will be solved in the fullness of time.
Tipler envisages antimatter-powered von Neumann probes travelling at about 90 per cent of the speed of light. These will take about twenty million years to colonise the Galaxy. Though admittedly a very long time in human terms, this is a mere blink of the eye in the life of the Galaxy – less than a tenth the time it takes the great flywheel of stars to turn once on its axis.†
With the Milky Way colonised, the next obvious target for the von Neumann probes will be the ‘Local Group’, the sparse cluster of galaxies dominated by the great spirals of the Milky Way and the Andromeda Galaxy. According to Tipler, this could be overrun in a mere billion years. And, with the Local Group conquered, our robot descendants will stand at the very brink of known space, contemplating the great black gulf beyond and the galaxy clusters marching away into misty invisibility. Their next challenge – pre-ordained by the survival imperative – will be nothing less than the colonisation of the entire observable Universe.
It goes without saying that visiting every star in every galaxy in the entire observable Universe is a long-term project! Tipler estimates that it will take about twenty billion years, which is slightly longer than the Universe has currently been in existence.
Of course, the tacit assumption in all this discussion is that our spacefaring descendants have things totally their way and encounter no serious opposition among the teeming stars and galaxies. But what if other intelligent races are abroad in the Universe? Surely, these too will spread among the stars, impelled by exactly the same survival imperative as the human race? Colonising the Universe might not be an option – it may already be occupied.
Tipler, however, is confident that this is not the case. He believes that we are the first intelligent to race to appear on the scene, certainly in our Galaxy, and he bases this claim on a straightforward observation. The Earth does not appear to have been visited by extraterrestrials.
Tipler’s logic is simple. Any civilisation that gains a space-faring capability can clearly build their own von Neumann probes. In twenty million years or so, they can spread to all the stars in the Galaxy – including our Sun. But they are emphatically not here! ‘Where is everybody?’ as the Italian-American physicist, Enrico Fermi asked.*
The only way to resolve the ‘Fermi paradox’, according to Tipler, is to accept that intelligence has arisen on Earth before it has arisen elsewhere. Incredible as it seems, we are the first. ‘Sometimes I think we are alone, sometimes I think we are not,’ said Buckminster Fuller. ‘Either way, the thought is staggering.’
Not only is it a staggering thought that we might be totally alone in the vast Universe, it is a deeply sad one too. The human race, like the last person alive after a global catastrophe, is destined never to find anyone else to talk to, never to find anyone else with whom to share a single one of its experiences. But cosmic loneliness is not the only curse of being the first intelligence to emerge. A huge burden of responsibility comes with it. ‘It will be up to us, and us alone, to ensure the survival of life into the eternal future,’ says Tipler.
By the time our descendants have spread to fill all the stars and galaxies in the Universe, the Universe will be more than twice as old as it is today. With so many more stars burnt out, it will be a darker, colder place. The dying of the light will serve only to underline the awful dwindling of options open to our far-future descendants. They will die out, along with the stars all around them – unless they can rise to the ultimate challenge. That challenge will be to gain control of the Universe and force it, kicking and screaming, towards the Omega Point, with its seductive promise of survival for subjective eternity.
But how can such an engineering project – the most ambitious conceivable – ever be carried out? Remarkably, there is a way.
Almost certainly, it will be necessary to shunt large amounts of matter around the Universe, boosting the density in some places and lowering it in others. Think of great clusters of galaxies being moved from place to place like chess pieces on a gargantuan chess board. This will be astroengineering on an unimaginably heroic scale. But it will be needed to ensure that the Universe collapses in on itself in the necessary way, shrinking faster in one direction than in the others.
For a while, as the Universe shrinks, everything in the cosmological garden will be rosy. The ever-growing temperature differences will drive ever-more information processing. Nothing will appear to stand in the way of the attainment of the Omega Point. All, however, is not quite as straightforward as it seems.
Matter today is not smeared completely smoothly throughout the Universe and nor will it be in the far future. Inevitably, there will be slightly more material in one place than another. The trouble with this is that, as the Universe shrinks ever close to zero volume, even tiny irregularities in the matter distribution will become grossly magnified. And this is not all. According to Einstein, matter warps space. So the gross irregularities in the matter distribution will cause gross distortions in the fabric of space-time as well. Those distortions will change from instant to instant. Like a piece of toffee, the Universe will be stretched one way one moment and another the next.
But this is not the worst of it. As John Barrow of Cambridge University has shown, the distortions in space-time in the far future of the Universe are ‘chaotic’.
It is characteristic of chaotic systems that their long-term behaviour is unpredictable. A good example is the Earth’s weather system. It is impossible to forecast with any reliability what it will be like at a given location on the planet more than a week or so in advance. In the same way, as the Omega Point is approached, it will be impossible to predict the chaotic fluctuations in the distortion of space-time. With every instant they will become more unstable, more violent.
All is not lost, however. Although the long-term evolution of the Universe is chaotic and unpredictable, paradoxically it presents life with an opportunity.
The source of the unpredictability of the weather is the fact that chaotic systems are fantastically sensitive to initial conditions. Even a tiny difference in the state of the atmosphere on one day will lead to a dramatically different state a month later. As chaos researchers often point out, the beat of a butterfly’s wings in one part of the world can eventually spawn a hurricane in another part of the world, a feature known as the ‘butterfly effect’.
If something as insignificant and trifling as the fluttering of a butterfly’s wings can in the fullness of time spawn something as tremendous and awe-inspiring as a hurricane, it opens up a remarkable possibility. It might be possible to change the weather in a major way merely by modifying the atmosphere in a minor manner – for instance, by tweaking the temperature of a small patch of sea, covering perhaps a few hundred square kilometres. With the aid of such ‘weather control’, we might one day be able to deflect a hurricane from its deadly path and spare a major city.
As with the weather, so with the Universe. Far from being a curse, its hypersensitivity to ‘initial conditions’ can turn out to be a blessing. By ruthlessly exploiting this property, our far-future descendants can steer the Universe along any evolutionary route they desire. All that will be necessary will be a small nudge here, a small nudge there.
Exactly what will have to be nudged where in order to make the Universe shrink down towards the Omega Point, is not clear. Figuring it out, according to Tipler, will require complex and detailed calculations.
The point is that a single, one-off redistribution of the matter of the cosmos will not be sufficient to achieve the desired Omega Point. Like a snake trying to squirm out of a jar, the chaotically fluctuating Universe will perpetually try to evolve away from the state that leads to the Omega Point – unless it is pushed back, again and again. Consequently, the occupants of this far-future universe will continually have to calculate how to correct matters. They will continually have to step in and tweak things. It will be impossible for them to relax for an instant. The price of attaining the elusive Omega Point will not only be engineering on a scarcely believable scale. It will be eternal vigilance, eternal intervention.
But steering the Universe towards the Omega Point will be only one of the problems faced by our descendants. As the Universe shrinks ever smaller, and the temperature sky-rockets towards infinity, atoms will split asunder, then the constituents of atoms, then the constituents of the constituents of atoms … The Universe will become a raging inferno of subatomic particles the like of which we cannot imagine with our rudimentary twenty-first-century theories of physics. It will be in the midst of this firestorm of exotic matter that our descendants will have to find a way to store the essence of their being and carry out the information processing which is synonymous with thinking.
Eventually, however, life will have to deal not with matter but the wildly fluctuating distortions of space-time. Though these will provide a tremendous source of energy, they will also create a new and unprecedented challenge. Somehow, some way, life must find a way to transfer its very essence from fiery matter into tortured space-time.
In short, if life is to survive the tumultuous journey down towards the Omega Point it will have to perpetually reinvent itself. The task will be immense but the price of failure will be oblivion. As Groucho Marx said: ‘I plan to live for ever, or die trying.’ That just about sums up the situation our descendants will face.
There is, however, a big spanner in the works. We do not appear to live in a Universe that will one day re-collapse – one whose runaway shrinkage can be corralled along the eccentric evolutionary path that leads to the Omega Point. Quite the reverse.
As pointed out before, physicists and astronomers in California and Australia discovered in 1998 that, contrary to all expectations, the expansion of the Universe appears to be speeding up. This is hard to understand because the gravity between every galaxy and every other galaxy should be acting to pull them back together again like some great cosmic web of elastic. Far from speeding up the expansion of the Universe, it ought to be braking it.
The inescapable conclusion is that gravity is not the only force orchestrating the fate of the large-scale Universe, as everyone had believed. Another, hitherto unsuspected, force must be at play. Since the Universe contains only galaxies, which dance to the tune of gravity, and the empty space between the galaxies, the mysterious force must be a property of empty space. It cannot therefore be as empty as it looks. Instead, it must contain some kind of invisible stuff which is counteracting gravity – dark energy.
Because space contains dark energy, it is springy. The more space there is the more springiness there is. Doubling the volume of space doubles the total quantity of dark energy and doubles its repulsive effect. What this means for the Universe is that, in the beginning, when the Universe was small and there was very little space, dark energy had only a minuscule effect and gravity dominated the Universe. However, as the Universe expanded and space grew, more and more dark energy was created. Today, there is enough around that it has overwhelmed gravity.
There are two outstanding questions concerning the dark energy. The first and obvious one is – What is it? Here, physicists are utterly at sea. As already mentioned before, their best theory – quantum theory – predicts an energy for empty space which is 1 followed by 123 zeroes bigger than what is in fact observed. The second dark energy question is – Why is it gaining control of the Universe now? In the distant past, when there was very little space, dark energy had an entirely negligible effect. However, over the past 13.7 billion years, as space has expanded, its repulsive effect has been steadily building. Only now is it beginning to overwhelm gravity. The question is – How come we are alive at this special moment? Nobody knows the answer. But the coincidence is definitely very, very odd.
In the future, as the Universe continues to swell and dark energy grows remorselessly in importance, it will begin to drive a runaway cosmic expansion of space. Eventually, the galaxies will become infinitely isolated islands in an unimaginably vast and empty ocean of space. This is hardly what the doctor ordered if life, as Tipler believes, is to gain control of the Universe and force it down to the Omega Point. The obvious problem faced by intelligence in a universe which is growing ever faster is colonising the place. Spreading to fill every last nook and cranny of Creation is akin to completing a 100-metre race when the finishing line is receding faster and faster. But this, it turns out, is not the most serious problem posed by an accelerated universe. There is another, even more fundamental one. It has to do with the Universe’s ‘horizon’.
Because the Universe has been in existence for just 13.7 billion years, the only galaxies we can see are those whose light has taken less than 13.7 billion years to reach the Earth. Objects which are so far away that their light would take more than 13.7 billion years to reach us we cannot currently see. Their light is still on its way. Because of this, we can see only a limited portion of the Universe, commonly called the ‘observable’ Universe.*
Every year we can in principle see objects whose light has taken an extra year to travel to us. Consequently, every year, the observable Universe grows – by a light year a year – the horizon expanding outwards into the greater Universe like the surface of a swelling bubble.
A deep question is – How did so much of the Universe get to be beyond the horizon in the first place? The answer has to do with inflation, the phase of super-fast cosmic expansion that was over and done with in the first split-second of the Universe’s existence. During inflation, space expanded faster than light, something which is permitted for space – the backdrop of the cosmos – but not for any material object in the Universe. Consequently, most of the Universe was stretched far from the Earth’s present location – so far away that its light, though it has been travelling since the dawn of time, still has not managed to get here. The tremendous ballooning of space in effect caused the horizon of the observable Universe to shrink so that it enclosed an ever smaller portion of the greater Universe. Only when inflation had run out of steam did the horizon begin expanding again – at roughly a light year a year – gradually bringing back into the view parts of the Universe which had been driven out of sight.
The accelerated expansion of inflation fizzled out long ago and so would seem to have little relevance to the present and future Universe. Nevertheless, it does. The reason is that the Universe, after a multi-billion-year hiatus, appears once again to be embarked on a period of accelerated expansion – driven by the repulsive force of dark energy. What this means is that the horizon of the Universe will one day start shrinking again, just as it did during inflation, and the observable Universe will become an ever smaller part of the total Universe. The trouble is that a shrinking horizon has profound consequences for life in the far future and its chances of steering the Universe towards the Omega Point. It makes it difficult for life across the cosmos to coordinate its actions.
Coordination is essential in order to push the Universe towards the Omega Point. After all, matter will have to be shifted from place to place across the entire cosmos. However, our far-future descendants – or, if we are not alone, the far-future descendants of intelligent races from all the galaxies – will here face a severe difficulty. The horizon around every observer will be shrinking as the expansion of the Universe speeds up. And this means it will be impossible to see or know about a greater and greater portion of the Universe. In such circumstances, how can intelligence in different parts of the Universe possibly communicate with each other so as to coordinate their actions?
The answer is, they cannot. In a universe containing dark energy, the Omega Point option can never be engineered. Not only is it impossible in practice, it is impossible even in principle. Unless, of course, there is some way that the dark energy can be ‘switched off’.
Switching off the dark energy, and with it the runaway expansion of the Universe, may seem a tall order. However, the fact that it wrested control of the fate of the Universe from gravity relatively recently in cosmic history may mean it ‘switched on’ recently. And, if it switched on, whatever switched it on might one day be used to switch it off. This is the belief Tipler subscribes to.
Not only does Tipler think that the dark energy can be neutralised, he actually thinks that this is inevitable. It will be an unavoidable by-product, he says, of information processing – the very characteristic that defines living things.
Tipler believes that to process more and more information life will have to use energy as efficiently as possible. The most concentrated form of energy is mass-energy. Life will therefore have to convert mass-energy into other forms of energy such as light and heat. In short, it will have to destroy mass.
No one knows for sure the origin of mass.* However, many physicists suspect that it arises from an invisible ‘field’ which fills all of space. As mentioned earlier, it is known as the Higgs field after the Scottish physicist Peter Higgs who proposed its existence, and it acts like treacle, impeding the motion of matter and thereby making matter difficult to budge – the property we associate with mass.
As Newton discovered, action and reaction are equal and opposite. Push against a wall and it pushes back. In the same way, Tipler believes that the destruction of mass will have a kind of ‘back reaction’ on the Higgs field, robbing it of its strength.
Why has this any bearing on the dark energy? Well, nobody knows what the dark energy is. Your guess is as good as mine. But Tipler identifies it with the ‘cosmic repulsion which has to exist in order to cancel out the cosmic attraction of the Higgs field’. Admittedly, this is an opaque statement! But, to go into any more detail here would be to obscure things yet more. Suffice to say that Tipler believes the cosmic repulsion and the cosmic attraction of the Higgs field are not in balance today – there is a small uncancelled surplus which manifests itself as the dark energy. Furthermore, he believes that the back reaction caused, as mass is destroyed across the cosmos, will gradually bring things back into balance, bit by bit depleting the dark energy. It will nullify it, gradually robbing it of its central ability – the ability to accelerate the expansion of the Universe.
How then does this solve the coordination problem? Well, the destruction of mass is simply a by-product of the information processing that creatures will be doing naturally all over the Universe. There will be no need for them to coordinate their actions. There will be no need for them to know about each other’s existence. The destruction of mass will inevitably occur everywhere across the Universe. And, with it, the dark energy will be neutralised.
Of course, once the dark energy is neutralised the horizon around each observer will cease to shrink and begin to expand. Eventually, everyone in the Universe will be able to see everyone else. There will be no barrier to cosmic coordination. There will be no obstacle to a universe-wide engineering project. The minor hiccup of the dark energy having been dealt with, it will be possible to steer the Universe all the way down towards the elusive Omega Point.
As the Universe shrinks closer and closer to the Omega Point, the amount of information processing that can be done will of course skyrocket without limit. To perpetually keep on top of things our descendants will have to adapt to ever more extreme conditions of density and temperature, which will involve them transferring their minds – their essential software – into hardware composed of ever more exotic subatomic particles. Provided that our descendants can find a way to keep on doing this, however, stretching before them like a never-ending road, will be a future of infinite promise, infinite subjective time.
Speculating on what super-intelligent life might do with all this time on its hands is a risky business, to say the least. Nevertheless, as Dyson has pointed out, if we wish to contemplate the long-term fate of the Universe, we have no choice but to grapple with the question of the values and purposes of intelligent life. And, on this subject, Tipler believes his guesses are as good as anyone else’s.
One thing a super-intelligence might want to do, says Tipler, is harness the phenomenal information-processing power close to the Omega Point universe to create simulations of real life. With so much computing power available, such simulations could be rendered with such extraordinary fidelity that they would be indistinguishable from the real thing.* And this, according to Tipler, opens up a fascinating possibility. It all hinges on another remarkable property of the Omega Point universe.
The Omega Point is not simply a point in space and time with the capacity to carry out an infinite amount of information processing. It is a point in space and time onto which converge light rays from the entire past history of the Universe. This is an extraordinary and significant fact. Just think. Before converging on the Omega Point, those light rays will have bounced off stars and galaxies and planets throughout the length and breadth of the past Universe. Consequently, they will carry with them information about the location and arrangement not only of every chunk of inert matter but also of every living creature that ever existed. With such information, it will be possible to create the ultimate computer simulation – a simulation of everything that has ever existed in the Universe. ‘What we’re talking about, in effect, is “resurrecting” each and every one of us – in fact, every creature who has ever lived,’ says Tipler.
Once again, we come up against the sticky problem of anticipating the motivations of a super-intelligence – a super-intelligence moreover whose thought processes will likely be as far beyond ours as ours are beyond those of the lowliest bacterium. Tipler, however, is undaunted. ‘The reason our far-future descendants will want to run the ultimate simulation will be simply to find out all they can about their past,’ he says. ‘Just like us, they will have burning desire to know exactly where they came from.’
The ultimate simulation is not, however, without its problems – even for an intelligence that possesses near-infinite computing resources. The reason has to do with the all-important light rays funnelling down to the Omega Point. Although the information they carry about the past history of the Universe is available in principle, extracting it will in practice be exceedingly difficult. The torrent of light raining down onto the Omega Point will be tremendous. Disentangling anything useful from it will be like picking out the individual voices from the roar of a football crowd stadium – only hugely, hugely harder.
All is not lost, though. Even if the past cannot be deduced in its entirety from the light rays converging on the Omega Point, Tipler sees another, ingenious, way to resurrect every creature that has ever lived. It all depends on a quantum theory – our description of the microscopic world of atoms and their constituents – and one ‘interpretation’ of quantum theory in particular.
As pointed out before, quantum theory predicts something bizarre about the world: an atom can be in many places at once. This is not some weird theoretical prediction. In experiments, it is in fact possible to observe an atom being in two places at once – or, more accurately, the consequences of an atom being in many places at once. But if an atom can be in many places at once, how is it that, when atoms come together to make big things like chairs, tables and people, these big things cannot be in many places at once? According to the standard explanation, some process intervenes between the scale of atoms and scale of tables to force them to behave themselves and stop being in many places at once. But there is another, arguably simpler, explanation, which is increasingly favoured by physicists. And that is that nothing intervenes. In other words, the small-scale world is exactly the same as the large-scale world. And, just as an atom can be in many places at once, so too can a table, a chair and a person.
Why then do we never see a person in two places at once – for instance, going through two adjacent doors at the same time? The answer is because the two possibilities happen in separate, or parallel, realities. This is the Many Worlds idea that there are an infinity of parallel realities in which all possible histories are played out.* In some realities there are versions of you living similar lives; in other realities versions living very different lives; in yet other realities there are no versions of you at all because you were never born.
Tipler – no prizes for guessing – is a strong proponent of the Many Worlds idea. Consequently, he believes that, even if the creatures at the end of time cannot extract the information necessary to re-create the past Universe from the light funnelling down towards the Omega Point, there will be another option open to them. They can simulate all the possible realities of the Many Worlds that lead up to the Omega Point. Among this uncountable profusion of past histories of the Universe, inevitably they will find the history followed by their ancestors.
Of course, simulating all possible histories of the Universe requires mind-bogglingly more computer resources than simulating a solitary history. But this is no problem, according to Tipler. If, at any time, our descendants have insufficient computing resources to carry out the necessary mega-simulation, they will merely have to wait a little longer. With the Universe’s ability to process information sky-rocketing so rapidly, pretty soon they will find themselves in possession of the necessary computing resources, no matter how great those resources might be.
Inevitably, among all the possible realities leading up to the Omega Point, will be the reality that contains you and me. ‘One way or another, we are going to find ourselves resurrected in a computer simulation at the end of time,’ says Tipler.
Wait. How do we know that we are not in a computer simulation at this very moment? How do we know, as is remarked in the film Breathless, that we are not ‘the dead on vacation’? Outrageous as it seems, some people think it is a serious possibility that we are currently in a giant computer simulation, though not necessarily the Omega Point simulation envisaged by Tipler.
The argument is based on a simple premise: at some time in the future, if technological progress continues unabated, it will be possible to build computers powerful enough to mimic human consciousness. If this premise is accepted, says the philosopher Nick Bostrom of Oxford University, there are only three possible future scenarios.*
In the first scenario, some kind of global catastrophe wipes out the human race before it can build the necessary super-computers. If this is to be our fate, we can at least console ourselves with the thought that the reality we are currently experiencing is definitely real. In the second future scenario, we develop the necessary super-computers but have no interest whatsoever in running simulations. Though not impossible to believe, this may not be too likely given our proven habit of doing things, such as trigger nuclear chain reactions or clone human beings, ‘just to see what happens’. That just leaves the third scenario.
In this final future, we will not only simulate conscious beings but also the universes in which they will live. If this scenario is the true one, then the likelihood is that the simulations have already been done and we are at this moment living in an artificial reality!
It is always possible, of course, that we are living in the pre-simulation, ‘real’ world. However, Bostrom points out that the future stretching before us is vast – time enough to run a large number of simulations. With the overwhelming majority of simulations being artificial, what is the chance that we should find ourselves in the only simulation that is truly real? Bostrom thinks the answer is clear. No chance. We are living in someone’s computer simulation with 100 per cent certainty.
But, if we are in a computer simulation, how can we ever tell? Clearly, if the rendering of reality is near-perfect – as Tipler believes is possible arbitrarily close to the Omega Point – it will be extremely difficult to distinguish pseudo-reality from reality. Nevertheless, even the best computer simulations have their flaws.
In any simulation, it is not possible to record to an unlimited degree of accuracy the position, speed, and so on, of every particle of matter. In practice, such numbers have to be truncated to a finite number of digits. Inevitably, this leads to tiny errors creeping into the simulation. And, with each new round of number-crunching, which is necessary to maintain the simulation, such tiny errors will get magnified. Eventually, like the butterfly whose flapping wings spawn a hurricane, they will have a significant and noticeable effect.
Putting an error-ridden simulation back on track requires reaching into the computer on which the simulation is running and resetting the numbers. If we are indeed living in simulation then, from time to time, such computational course corrections are unavoidable. How would they manifest themselves? Well, the most likely way is as sudden changes in the laws of physics – an abrupt jump in the strength of gravity, perhaps, or in the electrical charge carried by the electron.
Remarkably, just such a change appears to have happened in our Universe many billions of years ago. The change has revealed itself in the light of distant quasars, the super-bright cores of newborn galaxies.* Their prodigious brightness means that they can be seen at enormous distances. And, since their light has taken so long to travel across space to us, we see quasars as they were when the Universe was in its youth, many billions of years ago.
From the light coming from quasars astronomers can deduce the elements they contain. This is because the atoms of a particular element emit light at wavelengths which are as unique to that element as a fingerprint is to an individual person. If astronomers detect the light at the wavelength’s characteristic of calcium, for instance, they know for sure that the quasar contains calcium.
In 1998, a team of astronomers from the University of New South Wales in Australia and the University of Sussex in Britain reported that it had found subtle differences between the fingerprint of atoms of a particular element on Earth today and atoms of the very same element in quasars about ten billion years in the past.
If correct – and no one has yet managed to show that the observation is in error – this is an extraordinary discovery. The light given out by atoms is determined by a number known as the ‘fine-structure constant’. This orchestrates the delicate interplay between light and matter. In doing so, it determines how tightly normal matter, including the matter in our bodies, is glued together. If ten billion years ago the light given out by atoms was different, it can only mean that the fine-structure constant must also have been different. In fact, the observations show it was several parts in 100,000 smaller than today.
So, did the simulation we live in go awry at some time in the past ten billion years and have to be corrected by whoever or whatever is running it? And, if it did, can we expect other corrections? Will the speed of light suddenly jump one day? Or the strength of the gravity pinning our feet to the ground? Or will we look up one day and see the kind of sight described by Arthur C. Clarke in his 1953 short story, ‘The Nine Billion Names of God’?*
‘Look,’ whispered Chuck, and George lifted his eyes to heaven.
(There is a last time for everything.) Overhead, without any fuss, the stars were going out.
Tipler has no particular view on whether or not we are currently living in such a generic computer simulation. However, he has a strong view on whether or not we are living in the ultimate simulation – the one near the Omega Point at the end of time. ‘It is extremely unlikely,’ he says.
Tipler’s reasoning is interesting. ‘Our world is so imperfect,’ he says. ‘Why would an intelligence with pretty much unlimited computing power go to the trouble of simulating such a flawed reality?’
Of course, Tipler is once again in the position of guessing the motivations of an intelligence vastly in advance of our own. Though many would say this is impossible, Tipler believes he can anticipate at least some of the things such a super-intelligence might want to do with its superpowers. To support his belief, he points to some remarkable features of the Omega Point – features which give any intelligence in its vicinity extraordinary, and deeply suggestive, abilities.
As discussed earlier, a super-intelligence close to the Omega Point will be able to carry out an unlimited amount of information processing. It will be able to resurrect everyone who has ever lived and give them eternal life. ‘With this kind of power to create and manipulate reality, it will be omnipotent,’ says Tipler.
But this is not all.
As also mentioned earlier, all the myriad light rays from the entire past of the Universe converge on the Omega Point. Since these light rays carry with them knowledge about everything and everyone that ever existed, any super-intelligence near the Omega Point will be all-seeing. ‘They will be omniscient,’ says Tipler.
See where this is going? Tipler – controversially – identifies the Omega Point with God! ‘People talk of God as the creator of life,’ he says. ‘But maybe the purpose of life is to create God.’
Tipler, by making this outrageous claim, is stretching physics way beyond its widely accepted boundaries and striking deep into the territory of theology. It goes without saying that the majority of physicists think he has stretched physics far beyond its breaking point. They think it is important to draw a line in the sand between what is science – the possibility of life surviving for ever at the Omega Point – and what is theological speculation.
Tipler, however, makes no apology for his claim. He points out that the stated aim of physics is to describe the Universe in its entirety. ‘If it is to succeed in this task, clearly it must also describe any Supreme Being living in the Universe,’ he says. ‘It therefore follows that theology must eventually be shown to be a branch of physics.’
If Tipler’s identification of the Omega Point with God is taken seriously, then, bizarrely, there is a connection between God and the matter content of the Universe. After all, the only way the Universe can shrink – either down to a standard Big Crunch or to a non-standard Omega Point – is if it contains sufficient gravitating mass to slow, then slam into reverse, its headlong expansion. Having the right mass is the key. ‘The existence of God depends on the amount of matter in the Universe,’ says Tipler.
Of course, there is a subtle difference between God, in the widely accepted sense of the word, and a location in space-time with many of the attributes of God, which is Tipler’s Omega Point. Nevertheless, any intelligence inhabiting the tortured space-time close to the Omega Point will, by virtue of its omniscience and omnipotence, have God-like powers. It will, in effect, be God.
So now we come back to Tipler’s conviction that, although we will all be resurrected in a computer simulation at the end of time, we are not actually living in that simulation at present. What makes him so sure of this is his belief that any God-like entity which is both omnipotent and omniscient would likely be infinitely benevolent as well. In other words, they would be highly unlikely to simulate a reality which contained poverty, unhappiness, war and misery – one, that is, that closely corresponds to the world we find ourselves in.
According to Tipler, bad things simply will not happen in the simulation at the end of time. Unhappiness will not exist. Once again, Tipler cannot resist using a highly emotive word to describe what it will be like. ‘It’ll be Heaven,’ he says.
Your destiny, he claims, is to die, then wake up in a computer simulation that is indistinguishable from the Judaeo-Christian Heaven. What will it feel like? Well, dead people, by definition, perceive nothing. So, although trillions upon trillions of years will separate your death on Earth from your rebirth near the Omega Point, you will be totally unaware of this yawning chasm of time. One moment you will close your eyes and the next you will open them at the end of time. From your point of view, your resurrection will be instantaneous.
It is impossible not to marvel at the temerity of Tipler. In the Omega Point theory, he has taken science and stretched it to within a hair’s breadth of breaking point. If Tipler is right, none of us will die. We all meet up with our family and friends at the great party at the end of time. ‘If anyone has lost a loved one, or is afraid of death,’ writes Tipler, ‘modern physics says: “Be comforted, you and they shall live again”.’ Whether or not you believe him, there is no doubt that Tipler has journeyed to the far shores of modern physics.
* Reviews of Modern Physics (vol. 51, p. 447, 1979).
* The feeble heat that fills space is mostly the left-over heat of the Big Bang, cooled to a chilly -270 degrees Celsius by the expansion of the Universe in the past 13.7 billion years.
* The red-shift effect can be pictured by drawing a wave on a balloon. If the balloon is inflated, the wave is stretched. This is exactly what happens to a light wave as the fabric of space expands. Physicists characterise light by its ‘wavelength’, which is a measure of the distance between successive crests of the wave. And, since red light has the longest wavelength of any visible light, stretching the wavelength of light shifts it towards the red end of the ‘spectrum’, red-shifting it.
* Actually, physicists expect quantum theory to prevent a Big Crunch universe from shrinking all the way to a single point, or ‘singularity’. Unfortunately, because they do not yet possess a quantum theory of gravity, they do not quite know how this fate is to be avoided.
* ‘The Love Song of J. Alfred Prufrock’.
† Arthur C. Clarke explores a scenario like this in his story ‘All the Time in the World’ (The Other Side of the Sky, VGSF, 1987). A petty criminal is approached by a mysterious man who gives him a bracelet which speeds up his personal time so that the outside world appears to creep by in ultra-slow motion. All the criminal has to do – for a ridiculous payment of millions of dollars – is to use the bracelet to steal a list of major world treasures. Only too late does he learn that the mysterious man is an alien who knows that the Sun is about to go nova and has come to loot the Earth before the planet is incinerated.
‡ The term is actually borrowed from the French theologian Pierre Teilhard de Chardin.
* The Earth will actually become uninhabitable in much less than five billion years. This is because the Sun is slowly getting hotter as it burns through its hydrogen fuel (since its birth 4.56 billion years ago, it has brightened by about a third). As the Sun continues to get hotter, it will drive out the ‘greenhouse gas’ carbon dioxide from chalk cliffs, which will lead to yet more global warming, which will in turn cause the oceans to gradually boil away. The Earth’s water vapour will be destroyed by solar ultraviolet light when it rises to the top of the atmosphere. This, according to Juliana Sackmann of the California Institute of Technology in Pasadena and Arnold Boothroyd of the University of Toronto, will, within a mere billion years, leave the planet an uninhabitable desert.
† 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, Juliana Sackmann’s team has pointed out that, although the Sun will certainly get to the Earth’s orbit, when it does the Earth will not be there! It is all down to the fact that red giants lose material at a terrific rate via their ‘stellar winds’. A less massive Sun will also 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 farther 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 with it 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.
* Every subatomic particle has an associated antiparticle with opposite properties such as electrical charge. For instance, the negatively charged electron is twinned with a positively charged antiparticle known as the positron. When a particle and its antiparticle meet, they self-destruct, or ‘annihilate’, in a flash of high-energy light, or gamma rays. Antimatter is the term for a large accumulation of antiparticles.
† Actually, the pinwheel of our Galaxy does not rotate like a solid body. The speed at which stars at a particular distance from the centre of the Galaxy orbit the centre depends on how much material there is inside their orbit pulling on them with its gravity. For this reason, the orbital speed of stars is different at different distances. At the Sun’s distance from the centre – about 27,000 light years – the stars go round on the galactic merry-go-round about once every 230 million years.
* Fermi, the creator of the first nuclear reactor in 1942, asked the question at the Los Alamos Laboratory in New Mexico in the summer of 1950. At the time, he was having lunch with a handful of physicist friends including Edward Teller, the ‘father of the H-bomb’. Knowing Fermi’s genius, Teller and the rest immediately realised he had asked a profound and troubling question. See If the Universe is Teeming with Aliens – Where is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life by Stephen Webb (Copernicus, New York, 2002).
* See Chapter 1, ‘Elvis Lives’.
* See Chapter 8, ‘Mass Medium’.
* The perfect simulation of reality is a possibility because of the ability of a computer – otherwise known as a Universal Turing Machine – to mimic the operation of any conceivable machine (see Chapter 6, ‘God’s Number’). One such machine is the world around us.
* See Chapters 1 and 4, ‘Elvis Lives’ and ‘Keeping It Real’.
* Bostrom’s paper ‘The Simulation Argument’ from the journal Philosophical Quarterly (vol. 53, no. 211, pp. 243–255, 2003) is at: http://www.simulationargument.com/
* A quasar typically pumps out the light energy of 100 normal galaxies – that is ten million million suns – from a tiny region smaller than our Solar System. Such objects are believed to be powered by rapidly spinning black holes, up to ten billion times the mass of the Sun. In a quasar, matter swirls down through an ‘accretion disc’ onto a ‘supermassive’ black hole. As it does so, it is heated to millions of degrees by internal friction. It is the light from this super-hot accretion disc that we see as the burning beacon of the quasar.
* Collected in The Other Side of the Sky by Arthur C. Clarke (VGSF, London, 1987).