Is the Universe alive? John Gribbin New Scientist Jan 94
NOBODY would argue that human beings appeared out of nothing. We are complex creatures, and could not have arisen "just by chance" out of a brew of chemicals, even in some warm little pond of the kind envisaged by Charles Darwin. Simpler kinds of living organisms came first, and it took hundreds of millions of years of evolution on Earth to progress from single-celled life forms to complex organisms like ourselves. Could something similar have happened with the Universe? It is a large complex system which, some cosmologists argue, cannot have appeared by chance. Simpler universes came first, they say, and it may have taken hundreds of millions of universal generations to progress to a universe as complex as our own. Lee Smolin, professor of physics at the Center for Gravitational Physics and Geometry at the Pennsylvania State University, is a leading proponent of this idea, which also takes on board notions about baby universes developed by Andrei Linde of the Lebedev Physics Institute in Moscow and Stephen Hawking of the University of Cambridge. One of the jumping off points for such speculation is that the Universe we see around us seems to be in a very peculiar state, not "typical" of the way a universe might be expected to emerge from a big bang. According to the basic laws of physics, universes should be much smaller and shorter-lived.
The puzzle has become more pressing as evidence has mounted that the Universe really did emerge from a big bang some 15 billion years ago. The evidence suggests that the Universe was bom out of a singularity-a point of infinite density occupying zero volume-and thit in the first split second the tiny seed containing all the mass and energy in the observable Universe werit through a period of exponential expansion, known as inflation.
The key feature of inflation is that it stretches space-time-the three dimensions of space together with time-by a very large amount, smoothing out any irregularities that are present. Think of the difference between the wrinlded skin of a dry prune and the smooth surface of the same prune when it has absorbed its fill of water, then picture how smooth the skin of the prune would be if it were inflated to the size of the Earth, and you get some idea of how the process works. But cosmic inflation happened on a much smaller scale, and had ended by the time the Universe reached the size of a grapefruit. Around this time, matter was distributed evenly-but not perfectly evenly. There were small irregularities, or clumps of matter. Once inflation slowed, these clumps had enough gravity to gather other matter around them. Since then, more leisurely inflation has taken 15 billion years to expand the grapefruit to its present size, with the clumps of matter yielding galaxies, stars-and people. At first sight, therc is no obvious reason why the inflation process should have gone on for just long enough and at just the right rate to produce a Universe in which stars and galaxies could form. A shorter, less intense burst of inflation would have left the matter too jumbled up, and the proto-universe in danger of quickly recollapsing back into a singularity. A longer, stronger burst of inflation would have spread the stuff of the proto-universe so thin that no stars and galaxies could ever form.
This problem of fine-tuning is generally regarded as the biggest difficulty with inflation. It is essentially an example of the Goldilocks effect: why is inflation, like so many other properties of the Universe, "just right" to allow our Universe to exist. But the fine-tuning problem can be resolved by taking on board the idea that the Universe itself is alive and has evolved. A key feature of the argument is that the birth of the Universe-an outburst from a singularity-is essentially a mirror image of the collapse of a massive object into a black hole, which is an iniplosion towards a singularity. it is 30 years since Roger Pentose, now at the University of Oxford, and Hawking established that the equations describing the big bang expansion of the Universe are precisely the time-reverse of the equations describing the collapse of a black hole. But it was only in the 1980s that cosmologists realised that our Universe may contain so much material, most of it in the form of invisible, dark matter, that one day die enormous gravitational force would first halt the present expansion and then reverse it, making the Universe collapse back into a singularity that is a mirror image of the one that gave it birth. At about the same time, relativists reatised that there is nothing to stop the material that falls into a singularirv in our three dimensions of space and one of time from being shunted through a kind of space-time warp and emerging as an expanding singularity in another set of dimensions-another space-time. Mathematically, this "new" space-time is represented by a set of four dimensions, just like our own, but with all the dimensions at right angles to all the familiar dimensions of our own space-time. Every singularity, on this picture, has its own set of spacetime dimensions, forming a bubble universe within the framework of some "super" space-time, which we can refer to simply as "superspace". One way to picture what this involves is to use the analogy between the threc dimensions of expanding space around us and the two-dimensional expanding surface of a balloon steadily filling with air. The analogy is not with the volume of air inside the balloon, but with the expanding skin of the balloon ' stretching uniformly in two dimensions but curved around upon itself in a closed surface. Imagine a tiny pimple forming on the surface of the balloon, a small piece of the stretching rubber that gets pinched off and starts to expand in its own right. It develops into a bubble, attached to the original balloon by a tiny, narrow throat-the black hole. And this new bubble can expand away happily in its own right to become as big as the original balloon, or even bigger, without the skin of the original balloon (the original universe) being affected. There can be many bubbles growing out of the skin (the space-time) of the original universe in this way at the same time, all interconnected by a system of black hole "throats' referred to as wormholes or tunnels. And new bubbles can grow out of each new universe, ad infinitum, Instead of the collapse of a black hole representing a one-way journey to nowhere, Hawking, Linde and Smolin and others suggest that it is a one-way journey to somewhere-to a new expanding universe in its own set of dimensions. The dramatic implication is that many, perhaps all the black holes that form in our Universe may be the seeds of new universes. And, of course, our own Universe may have been born in this way out of a black hole in another universe. Whaes more, it tums out that the fact that the Universe seems to be so efficient at the job of making stars and fuming them into black holes means that it is also efficient at making more universes. This is a spectacular shift of viewpoint, and most cosmologists are still struggling to come to grips with it. If 6ne Universe exists, then it seems that there must be many-very many, perhaps even an infinite number of universes. Our Universe has to be seen as just one component of a vast array of universes, a self-reproducing system connected only by the tunnels through space-time, which in this view are perhaps better regarded as cosmic umbilical cords that join a baby universe to its parent. But there is still a puzzle of why inflation should have just the right strength to lead to a universe like our own. The "natural" size for a universe is down in the subatomic region, on the scale of the Planck length, IO^-35 of a metre, the smallest "distance" that can exist. This is where evolution comes in. The key element that Smolin has introduced is the idea that every time a black hole collapses into a singularity and a new baby universe is formed with a new space-time, the laws of physics that are bom with it are slightly different. The force of gravity, for example, may be a little stronger -or weaker-in the baby universes than in the parent. The process, he argues, resembles the way mutations provide the variability among organic life forms on which natural selection can operate.
Each baby universe, says Smolin, is not a perfect replica of its parent but a slightly mutated form. The original, natural state of a baby universe may indeed be to expand out to a few times the Planck length, before collapsing once again. But if the random changes in the workings of the I ' aws of physicsthe mutations-happen to allow a little bit more inflation, a baby universe will grow a little larger. If it becomes big enough, it may separate into two or more different regions that each collapse to make a new singularity and thereby trigger the birth of another generation of universes. Those new universes will also be slightly different from their parents. Some may lose the ability to grow much larger than the Planck length, and will fade back into the quantum realm. But some may have a little more inflation still than their parents, growing even larger, producing more black holes and giving birth to more baby universes in their turn. The number of new universes that are produced in each generation will be roughly proportional to the volume of the parent universe. "The essential point," says Smolin, "is that the universes that reproduce the most successfully by leaving the largest number of progeny dominate the ensemble after many generations."
The Universe within
The end product should be not one but many universes, an about as big as it is possible to get while still being inside a black hole and in which the parameters of physics are such that the formation of stars and black holes is favoured. Our Universe exactly matches that description. This explains the otherwise baffling mystery of why the Universe we live in should be "set up" in what seems, at first sight, such an unusual way. Just as you would not expect a random collection of chemicals suddenly to organise themselves into a human being, so you would not expect a random collection of physical laws emerging from a singularity to give rise to a Universe like the one we live in. Smolin has stopped short of suggesting that the Universe is alive. But heredity is one of the defining attributes of life, and Smolin suggests that universes pass on their characteristics to their offspring with only minor changes, just as people pass on their characteristics to their children with only minor changes. Universes that are successful in evolutionary terms are the ones that leave the most offspring. Provided that the random mutations are indeed small, there will be a genuinely evolutionary process favouring larger and larger universes. Smolin's ideas are far from being accepted. One criticism is his assumption that the physical laws a universe is bom with will be only slightly different from those of its parent; they could equally be very different or the same. "I don't go along with all the details of Smolin's argument," says Paul Davies of the University of Adelaide, "but it's a welcome new way of looking at the old problem of why the Universe is as it is." Before Charles Darwin and Alfred Wallace came up with the idea of evolution, many people believed that the only way to explain the existence of so unlikely an organism as a human being was by supematural intervention. The apparent unlikelihood of the Universe has similarly led some people to suggest that the big bang may have resulted from supematural intervention. Even respectable cosmologists such as Davies and Frank Tippler of the University of New Orleans talk of the new cosmology as revealing "the mind of God" at work. But if Smolin is right, there is no longer any basis for invoking the supematural. We live in a Universe which is exactly the most likely kind of universe to exist if there are many living universes that have evolved in the same way that living things on Earth have evolved.
In the Beginning 24 Jan 98 New Scientist
COULD the Universe have been its own mother? Two physicists in New Jersey say that this may be a more satisfying way of explaining the origin of the Universe than any alternatives dreamt up so far. Physicists have huge problems trying to work out how the Universe got going ("The day time began", New Scientist, 29 April 1996, p 30). Some say the question of what happened before the beginning of time, space and matter is like asking what is south of the South Pole. Others argue that the Universe has existed forever, or somehow popped into existence out of nothing. "We suggest that the Universe emerged from something rather than nothing-and that that something was itself," says Richard Gott III of Princeton University in New Jersey. This strange suggestion is a spin-off from the theory of inflation which purports to describe what happened immediately before the big bang. In inflation an unusual state of the vacuum grows rapidly and exponentially One version is "chaotic inflation", suggested by Andrei Linde of Stanford University in California, in which inflating regions spawn others of their kind. "These are baby universes which bud off from the Universe like the branches of a tree," says Gott. Gott and his colleague Li-Xin Li say it's possible that a branch of spacetime could loop backwards to rejoin the tree trunk. "Such a thing is possible because Einstein's general theory of relativity permits closed time-like currents - loops of time", says Gott. Gott and Li found that a time loop could have existed before the big bang without violating any laws of physics. Space would have been in a loop of time, perpetually recreating itself. If so, the Universe could be viewed as having given birth to itself. Gott says that asking what the first event in the Universe was becomes meaningless. "Every event in the Universe could have an event preceding it," he says. One consequence of the idea is a natural explanation for the so-called arrow of time. Theories of general relativity and electromagnetism do not rule out the idea that waves can affect events that occurred in the past. For instance, they do not forbid light from travelling back in time. Yet in our Universe light always travels with us into the future. The reason, say Gott and Li, has to do with what would happen to waves that regressed in time in the kind of universe they envisage. "They would travel back to the epoch of the time loop and circle forever, constantly reinforcing each other," says Gott. Such a universe could not exist, Gott concludes, because the time loop would quickly become unstable. "This whole area of cosmology is incredibly speculative," comments Astronomer Royal Martin Rees at the University of Cambridge. "But I think this is a fascinating contribution." Gott and Li say that they have only begun to explore their idea and much more work needs to be done. Their results have been submitted to the J Phys Rev D. Marcus Chown N
In the Beginning/2 NS 25 April 1998
A discrepancy in the size of primordial fluctuations has been found in the extrapoliation of galaxy clusters back to the primordial distribution of matter. An apparent preponderance of clusters 300 million light years across was found by Subir Sarkar, suggesting there may be an imprint of the complex phase transition accompanying inflation.
Whoops apocalypse NS 9 May 1998
A certain class of supersymmetric theories suggests further Higgs fields could turn on at arbitrary times, causing abrupt changes in physics like those which accompanied symmetry-breaking and cosmic inflation. Fortunately the probability of this happening in the universes lifetime is slight or negligible.
The Day Time Began
Paul Davies New Scientist 27 Apr 96
Can science explain how the universe began? Such questions have provoked an angry and passionate response from many quarters. Religious people tend to see the claim as a move to finally abolish God the Creator. Atheists are equally alarmed, because the notion of the Universe coming into being froin nothing looks suspiciotisly like the creation, ex nihilo of Christianity. The general sense of indignation was well expressed by writer Fay Weldon. "Who cares about half a second after the big bang," she railed in 1991 in a scathing newspaper attack on scientific cosmology. "What about the half a second before?" What indeed. The simple answer is that, in tile standard picture of the cosmic origin, there was no such thing as the half-second before.
To see why, we need to examine this standard picture in more detail. The first point to address is why anyone believe, the Universe began at a finite time. How do we know it hasn't been around forever? Most cosmologists reject this alternative because of the severe problem of the second law of thermodynamics. Applied to the universe as a whole, this law satates that the cosmos is in a one-way slide towards disorder, or entropy. Irreversible changes, such as the gradual consumption of fuel by the Sun and stars, ensure that the Universe must eventually "run down" and exhaust its supplies of useful energy. lt follows that the Universe cannot have been drawing on this finite stock of useful energy for all eternity.
Body of evidence
Direct evidence for a cosmic origin in a big bang comes from three observations. The first, and most direct, is that the Universe is still expanding today. The second is the existence of a pervasive heat radiation that is neatly explained as the fading afterglow that accompanied the big bang. The third strand of evidence is the relative abundances of the chemical elements, which can be correctly accounted for in terms of nuclear processes in the hot dense phase that followed the big bang. But what caused the big bang to happen? Where is the centre of the expiosion? Where is the edge of the Universe? Why didn't the big bang turn into a black hole?
Though they seem pertinent, they are in fact based on an entirely false picture of the big bang. To understand the correct picture, it is first necessary to have a clear idea of what the expansion of the Universe entails. Contrary to popular belief, it is not the explosive dispersal of galaxies from a common centre into the depths of a limitless void. The best way of viewing it is to imagine the space between the galaxies expanding or swelling. The idea that space can stretch, or be warped, is a central prediction of Einstein's general theory of relativity, and has been well enough tested by observation for all professional cosmologists to accept it. According to general relativity, space-time is not a static arena, but an aspect of the gravitational field. This field manifests itself as a warping, or curvature, of space-time geometry, atid when it comes to the large scale structure of the Universe, such a warping occurs in the form of space being stretched with time. A helpful, albeit two-dimensional, analogy for the expanding Universe is a balloon with paper spots stuck to the surface. As the balloon is inflated so the spots, which play the role of galaxies, move apart from each other. Note that it is the surface of the balloon, not the volume within, that represents the three-dimensional Universe. Now, imagine playing the cosmic movie backwards, so that the balloon shrinks rather than expands. If the balloon were perfectly spherical (and the rubber sheet infinitely thin), at a certain time in the past the entire balloon would shrivel to a speck. This is the beginning. Translated into statements at)out the real Universe, I am describing an origin in which space itself comes into existence at the big bang and expands from nothing to form a larger and larger volume. The matter and energy content of the Universe likewise originates at or near the beginning, and populates the Universe everywhere at all times. Again, I must stress that the speck from which space emerges Is not located in anything. lt is not an object surrounded by emptiness. It is the origin of space itself, infinitely compressed. Note that the speck does not sit there for an infinite duration. It appears instantaneously from nothing and immediately expands. This is why the question of why it does not collapse to a black hole is irrelevant. Indeed, according to tile theory of relativity, there is no possibility of the speck existing through time because time itself begins at this point. This becomes the most difficult and most critical aspect of the big bang theory. The notion that ihe physical universe came into existence with time and not in time has a long history, dating back to St. Augustine in the fifth century. But it took Einstein's theory of relativity to give the idea scientific respectability. The key feature of the theory of relativity is that splice and time are part of the physical Universe, and not merely an unexplained background arena in which the Universe happens. Hence the origin of the physical Universe must involve the origin of space and time too. But where could we look for such an origin? Well, the theory of relativity periis space and time to possess di variety or edges, technically known as singularities. One type of singularity exists in the centre of a black hole. Another corresponds to a past boundary of space and time at the big bang. The idea is that, as you move backwards in time, the Universe becomes more and more compressed and the curvature or warping of space-time escalates without limit, until it becomes infinite at a singularity. Very roughly, it resembles the apex of a cone, where the fabric of the cone tapers to an infinitely sharp point and ceases. lt is here that space and time begin. Once this idea is accepted, it is iinmediately obvious that the question "What happened before the big bang?" is meaningless. There was no such epoch as "before the big bang". Because time began with the big bang. Unfortunately, the question is often answered with the bald statement "There was nothing before the big bang", and this has caused yet more misunderstandings. Many people interpret "nothing" in this context to niean empty space, but as I have been at pains to point out, space did not exist either prior to tile big bang.
Perhaps "nothing" here means something more subtle, like pre-space, or some abstract state from which space emerges? But again, this is not what is intended by the word. As Stephen Hawking has remarked, the question 'What lies north Of the North Pole?" can also be answered by "nothing". not beccause there is some mysterious land of nothing there but simply because the region referred to does not exist. It is not merely physically, but also logically, non-existent. So too with the epoch before the big bang, In my experience, people get very upset when told this. They think they have been tricked, verbally or logically. They suspect that scientists can't explain the ultimate origin of the Universe and are resorting to obscure and dubious concepts like the origin of time merely to befuddle their detractors. The mind-set behind stich outraged objection is understiindable: our brains are hard wired for us to think in terms of cause and effect. Because normal physical causation takes place ewithin time with effect following cause, there is a natural tendency to think of a chain of causation stretching back in time, either without any beginning, or else terminating in a metaphysical First Cause, or Uncaused Caused, or Prime Mover. But cosmolo gists now invite us to contemplate the origin of the Universe as having no prior cause in the normal sense, not because it has an abnormal or supernatural prior cause but because there is simply no prior epoch in which a preceding causative agency-natural or supernatural-can operate. Nevertheless cosmologists have not explained the origin of the Universe by the simple expedient of abolishing any preceding epoch. After all, why should time and space have suddenly "switched on"? The latest thinking is that this spontaneous origination of time and space is a natural consequence of quantum mechanics. Quantum mechanics is the branch of physics that applies to atoms and subatomic particles, and it is characterised by Heisenberg's uncertainty principle, according to which sudden and unpredictable fluctuations occur in all observable quantities. Quantum fluctuations are not caused by allytilingthey are genuinely spontaneous and intrinsic to nature at its deepest level.
For example, take a collection of uranium atoms suffering radioactive decay due to quantum processes in their nuclei. There will be a definite time period, the half-life, after which half of the nuclei present should have decayed. But according to Heisenberg it is not possible, even in principle, to predict when a given nucleus will decay. If you ask, having seen a particular nucleus decay, why the decay event happened at that moment rather than some other, there is no deeper reason, no underlying set of causes, that explains it. It just happens. The key step for cosmogenesis is to apply this same idea not just to matter, but to space and time as well. Because space-time is an aspect of gravitation, this entails applying quantum theory to the gravitational field of the Universe. The application of quantum mechanics to a field is fairly routine for physicists, though it has to be said that there are special technical problems associated with the gravitational case that have yet to be satisfactorily resolved ("Can gravity take a quantum leap?', 10 September 1994, p 28). The quantum theory of the origin of the Universe therefore rests on shaky ground. In spite of these technical obstacles, one may say quite generally that once space and time are made subject to quantum principles, the possibility immediately arises of space and time "switching on", or popping into existence, without the need for prior causation, entirely in accordance with the laws of quantum physics. The details of this process remain both subtle and contentious, and depend to some extent on the interrelationship between space and time. Einstein showed that space and time are closely interwoven, btit in the theory of relativity they are still distinct. Quantum physics introduces the new feature that the separate identities of space and time can be "smeared" or "blurred" on an ultramicroscopic scale. in a theory proposed in 1982 by Hawking and American physicist Jim Hartle, this smearing implies that, closer and closer to the origin, time is more and more likely to adopt the properties of a space dimension, and less and less likely to have the properties of time. This transition is not sudden, but blurred by the uncertainty of quantum physics. Thus time does not switch on abruptly in Hartle and Hawking's theory, but it emerges continuously from space. There is no specific first moment in which time starts, but neither does time extend backwards for all eternity (see Diagram p 34). Unfortunately, the topic of the quantum origin of the Universe is fraught with confusion because of the publicity given to a preliminary, and in my view wholly unsatisfactory theory of the big bang based on an instability of the quantum vacuum. According to this alternative theory, first niooted by Edward Tryon in 1973, space and time are eternal, but matter is not. lt suddenly appears in a pre-existing and unexplained void due to quantum vacuum fluctuations. In such a theory, it would indeed involve a serious misnomer to claim that the Universe originated from iiotliing: a quantum vacuum in a background space-time is certainly not nothing.
Law unto itself
However, if there is a finite probability of an explosive appearance of matter, it should have occurred an infinite time ago. In effect, Tryon's theory and others like it run into the same problem of the second law of thermodynamics as most models of an infinitely old Universe. it will be obvious from what I have said that the attempt to explain the origin of the Universe is based on an application of the laws of physics. This is normal in science: one takes the underlying laws of the Universe as given. But when tangling with ultimate questions, it is only natural that we should also ask about the status of these laws. One must resist the temptation to imagine that the laws of physics, and the quantum state that represents the Universe, somehow exist before the Universe. They don't any more than they exist north of the North Pole. In fact, the laws of physics don't exist in space and time at all. They describe the world, they are not "in" it. However, this does not nican that the laws of physics came into existence with the Universe. If ihey did-if the entire package of physical Universe plus laws just popped into being from nothingthen we cannot appeal to the laws to explain the origin of the Universe. So to have any chance of understanding scientifically how the Universe came into existence, we have to assume that the lqaws have an abstract eternal character. The alternative is to shroud the origin in mystery and give up. It might be objected that we haven't finished the job by baldly taking the laws of physics as given. Where did those laws come from? And why those laws rather than some other set? This is a valid objection. I have argued that we must eschew the traditional causal chain and focus instead on an explanatory chain, but inevitably we now confront the logical equivalent of the First Cause-the beginning of the chain of explanation. In my view it is the job of physics to explain the world based oii lawlike 1)rijiciples. Scientists adopt differing attitudes to the metaphysical problem of how to explain the principles themselves. Some simply shrug and say we must just accept the laws as a brtite fact. Others suggest that the laws must be what they are froni log. iciii necessity. Yet ()Ilieis 1)i,ol)ose tlliii there exist iiiajiy wotids, each with differing laws, and that only a small subset of these universes possess the rather special laws needed if life and reflective beings like ourselves are to emerge. Some sceptics rubbish the entire discus. sion by claiming that the laws of physics have no real existence anyway-they are merely human inventions designed to help us make sense of the physical world. It is hard to see how the origin of the Universe could ever be explained with a view like this.
In my experience, almost all physicists who work on fundamental problems accept that the laws of physics have some kind of independent reality. With that view, it is possible to argue that the laws of physics are logically prior to the Universe they describe. That is, the laws of physics stand at the base of a rational explanatory chain in the same way that the axioms of Euclid stand at the base of the logical scheme we call geometry. Of course, one cannot prove that the laws of physics have to be the starting point of an explanatory scheme, but any attempt to explain the world rationally has to have some starting point, and for most scientists the laws of physics seem a very satisfactory one. in the same way, one need not accept Euclid's axioms as the starting point of geometry; a set oftheorems like Pythagoras's would do equally well. But the purpose of science (and mathematics) is to explain the world in as simple and economic a fashion as possible, and Euclid's axioms and the laws of physics are attempts to do just that. in fact, it is possible to quantify the degree of compactness and utility of these explanatory schemes using a branch of mathematics called algorithmic information theory. Obviously, a law of physics is a more compact description of the world than the phenomena that it describes. For example, compare the succinctness of Newton's laws with the complexity of a set of astronomical tables for the positions of the planets. Although as a consequence of Godel's famous incompleteness theorem of logic, one cannot prove a given set of laws, or mathematical axioms, to be the most compact set possible, one can investigafte mathematically whether other logically self-consistent sets of laws exist. One can also determine whether there is anything unusual or special about the set that characterises the observed Universe as opposed to other possible universes. Perhaps the observed laws are in some sense an optimal set, producing maximal richness and diversity of physical forms. It may even be that the existence of life or mind relates in some way to this specialness. These are open questions, but I believe they forin a more fruitful meeting ground for science and theology thani dwelling on the discredited notion of what happened before the big bang.
World Without End New Scientist 27 Apr 96 Gabrielle Walker
TRY asking a bunch of cosmologists about the origin of the Universe, and it's hard to get a clear answer. "The Universe didn't start. It's infinite." says British cosmologist Fred Hoyle. "It's an open question." says Steven Weinberg, Nobel prize-winning particle physicist from the University of Texas. "It's up in the air." says Paul Steinhardt from Pennsylvania State University. co-developer in the 1980s of a key theory about the early Universe. "It must have had a beginning," says cosmologist Alexander Vilenkin of Cruft, University in Massachusetts. The standard big-bang model is agreed say Roger Penrose and everything else is embellishments and flights of fancy. So what gives? Well, Hoyle is convinced that the big bang is a myth, and that the Universe is eternal, with matter continuously created at the centres of galaxies. But virtually everyone else is happy with the big bang model. at least as far back as the early stages of the Universe. Says Weinberg, "We are in an expanding Universe which at one time, before any of the stars or galaxies formed was very hot and dense. I don't think there', any serious argument that in that sense there was a big bang, and the part of the Universe that we live in had a start. gut beyond that we really don't know." To try to trace the history of the Universe back to its origin, cosmologists picture the expansion running backwards to a point where the Universe was almost unimaginably small and dense. The first problem they meet. when they do this. is that the concept of time comes apart in their hands. The reason is that at the so-called Planck scale (a mere IO^-35 metres), Two theories begin to clash. Einstein's smooth, large-scale, classical theory of gravity makes no provision for the fuzzy, indeterminate quantum theory of tiny particles. and all bets are off. "Questions about what happened before what begin to lose meaning says Steinhardt "Before only makes sense if there is a sensible time ordering to things, and that notion breaks down at the Planck scale." Weinberg agrees: "Any description that tries to go to earlier times has to give up the idea of time. It's no longer a maeningful concept." Glimmers of hope for reconciling relativity and quantum theory come from an idea called superstrings-in which all matter is made up of tiny 10-dimensional strings. Although we appear to live in a Universe with just four dimensions, three for space and one for time, the theory goes that the other dimensions present are curled up so tightly that we can't detect them directly. But this cause, even greater problems, because at the Planck Scale the tightly curled extra dimension, become significant. "You go back in time and it looks like you're heading towards a singularity and all of a s.d. den-wham-physics changes because all those extra dimensions that you weren't aware of suddenly come into Play." says Steinhardt. It is usually easy to tell time and space apart. But, says Steinhardt, "When you unwrap the extra dimensions. you don't know what they'll be like lt may be that you even have two time-like: coordinates, or more." The idea of before and after would then be been shakier. How the Universe could appear from nothing in the first place? In 1982, Vilenkin came up with the idea that the universe literally tunnelled its way into existence, something allowed by quantum theory but impossible on an everyday large scale. In the classical world, it you have a heavy object lying in a dip it will need a push to climb over hie edge and roll down the other side. But in the quantum world, there is a small, but non-zero probability that the object can simply tunnel to the other side of the dip without any outside help. The only condition is that it does not gain any energy in the process. So how does this relate to the Universe? Well, say you start with nothing at all-not even space or time. Presumably the total energy of this system would be zero. Is it possible to make a Universe of space, time and matter whose total energy is still zero? The answer is yes. "You can't create something out of nothing," says Vilenkin. "But the Universe is an exception. Gravitational energy is negative and matter energy is positive. In a closed Universe, one where if you keep going in one direction you come back to the same point-the negative energy of gravity exactly cancels the positive energy of matter, so the total energy is zero." In the classical picture, the Universe cannot appear out of nothing because it is forbidden to adopt a certain range of sizes. But in quantum theory, the Universe can tunnel through this size barrier, and appear spontaneously with a size greater than the critical value.
Can we ever know if the universe began at a single point or has simply been going on forever. There is yet another complication which may make the whole question academic. lt stems from an idea called inflation, first developed in the early 1980s to solve some vexing problems with the standard big bang model. In its earliest versions. inflation theory stipulated that. immediately after the big bang, the Universe suddenly ballooned, increasing its diameter by more than a trillion trillion times in just a tiny fraction of a second. After this, the Universe switched to a noninflationary phase, and expanded at a more sedate rate. But in the mid 1980s. cosmologist Andrei Linde at Stanford University realised that such a system would be self-replicating. Once you kicked it off with a big bang, it would go on forever. Even when most of the Universe had moved out of the inflationary phase, Linde reasoned, tiny fluctuating regions would still be capable of undergoing inflition. These would then go from being infinitesimal regions to sizeable chunks of Universe in a split second, and would themselves go on to spawn new patches of Universe and so on. In each case, once inflation was over, the patch would evolve according to standard big bang theory. If this is true, the whole Universe could be made up of a huge number of expanding patcheswhich could be quite different from our own. The problem is that we can never know. "We are removed be a tremendous distance from regions that underwent a different history." says Steinhardt. "Inflation casts a pall on things because it makes the part of the Universe we see so infinitesimal compared to the entire Universe, and perhaps not even representative. We will never be able to see the edge of the patch we live in, and this puts us beyond the ability to be able to probe things through observations." What's more, an eternal. self-replicating Universe may not even need a big bang. Vilenkin says he has proved in a theorem that the inflationary Universe must have had an origin, but Linde is skeptical. He thinks it likely but unproved that there was an initial big bang from which all of the "pretty big bangs" came. However, he adds that the question is so far removed from our experience that it is irrelevant: "Say you have an infinite number of bubbles, all producing new ones. You live in one of these bubbles and you look at the point the bubble -as formed. For all practical purposes that's the beginning of your Universe." Because there are infinitely many such bubbles, we have no reason to believe that ours is the first, or even the hundredth. It's more likely, says Linde, that our own personal big bang is actually a pretty insignificant one. way down the list from the one that set the Universe going.