As any mother will attest, young children are very inquisitive. At some point they are bound to pose the question to their parents: 'How was the universe created?' Almost everybody has heard of the Big Bang theory, but if the mother replies, 'It was created because of a big bang', the child is sure to ask 'What caused the big bang?' It ends there, because nobody has yet proved what actually caused the Big Bang to happen.

This article will explore all of the current scientific theories that attempt to explain how the Universe came into being. Firstly there are two theories that are direct interpretations of other theories, all of which have not yet been proved; then there are theories proposed independently by theoretical physicists.

Without further ado, let us explore our ultimate origins, and at the end, you can decide for yourself the most plausible way that the Universe was born.

Theory One: There Was No Beginning

If the Universe has always existed, then the question of its beginning is meaningless. However, physicists agree almost unanimously that the Big Bang theory is correct, so an explanation for it is still necessary.

One theory for this was proposed quite recently by Martin Bojowald of the Max Planck Institute for Gravitational Physics in Golm, Germany. He has constructed his theory by using another idea called loop quantum gravity (LQG). Loop quantum gravity is an attempt to unify the two most celebrated theories of the twentieth century: Einstein's theory of relativity and the revolution of quantum mechanics. The two theories are fundamentally incompatible, yet both have been proved experimentally. Loop quantum gravity attempts to explain this by starting with relativity and attempting to add in the quantum mechanical nature of things. It turned out that this meant describing space-time as a mass of tiny loops that were far too small to see, and perhaps even too small ever to detect. What Martin Bojowald has done is to see how the Universe would have been created if this theory is correct.

One thing that most theories about unifying relativity with quantum mechanics agree on is that there is a smallest possible measurement of space and time. This means that at the time of the Big Bang, it could not possibly have been infinitesimally small because there is a limit. Bojowald exploits this concept and discovered from it the very notion that the Universe did not have a beginning.

He gives an analogy to explain it. Imagine blowing up a balloon that is a perfect sphere, and then afterwards you deflate it. If it keeps on deflating even after it gets very small, the sphere will turn itself inside out and the balloon will effectively re-inflate, with all points that were originally on the inside now being on the outside. In other words, objects inside it are reversed left to right.

He says that the same is true of the universe. It had no beginning, and was infinitely large. It got smaller and smaller and smaller until, after an infinite length of time, there was a 'big crunch', just as with the balloon. Left and right were reversed and there was a big bang, after which everything expanded again to produce the Universe we know today. The geometry of this universe is called 'de Sitter space-time', after the Dutch astronomer Willem de Sitter. The universe would look somewhat like an hourglass that has fallen over onto its side.

Now you might be thinking, does the left-right inversion actually make any difference? And the answer is that largely, it doesn't. But there are a few exceptions, and this is because of something known as 'violations of CP symmetry'. This involves certain properties of neutrinos and kaons. Thus, the Big Bang would have marked the event when these properties were reversed.

An advantage of this theory of the origin of the universe is that it neatly explains the theory of inflation, proposed first by physicist Alan Guth. This theory states that after the big bang, the universe underwent a period of extremely rapid expansion. Bojowald's theory explains this because of the nature of space that loop quantum gravity predicts. In the LQG model, space is grainy and loopy. This would prevent the universe from expanding smoothly, so it would expand in short sharp bursts instead, just as inflation says.

The same theory of Bojowald's can also explain what happens at the heart of black holes. Black holes also have a 'singularity' – the point at which it is conventionally believed that matter is infinitely small and dense, the same as has already been described for the Big Bang. If you use the same model with black holes, you find that they too 're-inflate' on the other side, emerging into what can only be described as another universe. If you could navigate through one, you would probably come out of a black hole in this alternate reality. These structures are popularly called 'white holes' or 'cosmic gushers'.

Evidence for this Theory?

At the moment there isn't any, but NASA is planning to launch a new telescope in 2006 called the Gamma Ray Large Area Space Telescope (GLAST). This telescope will track gamma-ray photons of light from very long distances. If loop quantum gravity is correct, then these particles will have accumulated a precise 'spread' as they have been travelling through space because of the loopy nature of space-time. The GLAST should be able to detect this effect.

Other evidence could come from observations of white holes. If Bojowald's theory is right, we could expect to be able to see matter being spewed out of cosmic structures looking like black holes – ie, the other ends of black holes from other universes. As yet, no such entity has been observed in this universe, but obviously that does not mean that the theory is wrong. White holes may be just beyond the range of our telescopes.

Theory Two: The Ekpyrotic Theory

Recall that loop quantum gravity was a theory that started with relativity and tried to incorporate quantum mechanics. Well, there is also another theory that attempts to unify relativity with quantum theory, and this one does it the other way around. It starts with quantum mechanics and then adds relativistic effects to the equations. This theory is called M-Theory, better known as super-gravitational string theory, or just simply string theory.

The string theory suggests that every fundamental particle of the Universe is not actually a very tiny point-particle, as conventional quantum theory dictates. String theory describes particles as... strings. The theory says that all of these strings, made simply of pure energy and too small to detect, vibrate, just like the strings on a violin. And in the same way that the different vibrations of violin strings defines the musical note produced, the different ways that a fundamental string can vibrate defines the nature of the sub-atomic particle. This musical link to physics has led many scientists to refer to string theory as 'elegant'. This elegance is what makes string theory such a popular subject to study. It is estimated that string theorists outnumber researchers in loop quantum gravity ten to one.

String theory has been around for nearly half a century, and one of its major revolutions occurred in 1995. String theorist Edward Witten, of Princeton University, was the man to spark this revolution. He proposed that fundamental particles don't just have to be one-dimensional strings, they can also be two-dimensional planes. Furthermore, they might also be three-dimensional polyhedra. You are probably thinking that he would stop at three dimensions, but you would be wrong. Witten said that the fundamental strings could have not three, not four, not even five, but eleven dimensions.

In fact, string theorists already held the notion that the universe has at least ten dimensions (or twenty-six, according to some interpretations), so it wasn't such a shock to them. Witten simply proposed that it wasn't just the universe that was multi-dimensional, it was everything. His idea was heralded as the greatest discovery string theory has ever had.

So, naturally the theory could not be called string theory any more, since it wasn't just a theory about strings. Many string theorists recognised that these multi-dimensional entities could be called 'membranes', so they wanted to call it membrane theory. However, others liked to think that it was such a revolutionary idea it should be called the 'magic' theory or the 'mother' of all theories. There was also talk of calling it the 'matrix' theory or even 'mystery' theory because nobody could quite explain it. Anyway, the name doesn't really matter because conveniently everybody wanted to call it something beginning with the letter 'm' and so in the end they simply christened it 'M-theory'.

Then, Neil Turok of Cambridge University, UK, working with Paul Steinhardt of Princeton University in New Jersey, USA, realised something else that was just as astounding as Witten's work. Witten had come to the conclusion that if the universe could have so many dimensions, why couldn't the strings? Turok came to the conclusion that if the strings could be membranes, why couldn't the universe?

So a model of the origin of the universe was built from M-theory in which the universe is considered to be a membrane. Turok, who could well have become tired of all the 'm' words floating about his research area, shortened the word membrane to 'brane'. The theory is, in essence, that a universe – taking the form of a brane – exists within a multi-dimensional hyperspace, and that there are other branes existing alongside it – 'parallel' universes, in other words. When two of these branes collide there is a big bang. What could be simpler?

This idea is termed the ekpyrotic model, after a belief of the Greek Stoic philosophers who thought that the universe was occasionally reborn in a ball of fire, a process that they called 'ekpyrosis'.

The trouble with the idea, say critics, is that it does not explain the theory of inflation; the loop quantum gravity idea does. However, the ekpyrotic model replaces the inflationary theory with its own solutions to the problems that inflation originally set out to resolve.

Firstly, there was the problem that cosmologists found the universe to be largely very repetitive over large distances, for no apparent reason. This is called the horizon problem. Inflation solves this because in the early universe, all parts of space were very close to each other, before they quickly got further apart, and thus did not have time to evolve into anything hugely different from anything else they were close to. The ekpyrotic theory solves this because the big bang does not occur at one point, it occurs at every point across the brane, providing they collide face on. Therefore every part of the brane has been subjected to the same treatment and there is no reason for different places to look wildly different.

Secondly, there is the issue that the universe looks flat, serving no specific purpose. The word 'flat' in this sense does not mean two-dimensional and smooth. It means that the universe contains no drastically noticeable curves or ripples in it, neither is it curved around upon itself. The fact that it looks flat, of course, is not evidence that it is; some theories do indeed predict that 'ripples' in the fabric of space and time ought to exist, but are not very conspicuous. If the universe is in fact spherical, it can't be flat, and it could therefore have magnetic poles, just like the Earth. The fact that no such 'monopoles', as they are called, have been observed, is also not explained. Inflation allows for both instances very neatly because enormous expansions will iron out any large curved spaces, whilst the vastness of space predicted by inflation ensures that if the universe has monopoles, they are not likely to be anywhere near us. Again, the ekpyrotic theory has arguments to explain these problems too. Since the colliding branes are both flat, the resulting universe is not likely to be any different, and because there is no singularity of infinite temperature and density, the universe would be too cool (a mere hundred billion degrees) for a magnetic field of its own.

You might want to ask, but where did these branes come from? The theory states that they have always existed and that these collisions that cause big bangs are going on all the time. Due to this cycle of collisions, the theory is sometimes referred to as a 'cyclic' theory.

Evidence for this Theory?

If this cyclic version of the cause for the Big Bang is correct, then inflation is surplus to requirements, and so all of the theories that are spawned from inflation are also unnecessary. This includes the concept of 'gravitational waves', which are basically ripples in space-time that are the footprints of the force of gravity. In another variation of the theory, however, the brane does not collide with another brane, but one brane actually sheds a child brane that then collides with another. In this version, gravitational waves would exist.

Either way, detecting gravitational waves would enable us to prove one of the variations. The Laser Interferometer Space Antenna (LISA), to be launched some time between 2010 and 2015, should be able to do this, according to physicist Kip Thorne's predictions. However, as with theory one, there is no concrete evidence as yet.

Theory Three: The Universe Split in Two

This theory has also derived from M-theory, but it is strangely very different. The idea is that the universe was once ten-dimensional, but that this ten-dimensional universe was very unstable because it had a kind of tension similar to that exhibited by stretched springs or elastic sheets. Thus, it split itself into two universes: one with six dimensions and one with four. The four-dimensional universe is our own (three dimensions of space; one of time), and so the Big Bang was in fact the breaking down of a higher-dimensional universe.

This process was said to happen in a matter of 10^-43 seconds. Our six-dimensional 'sister' universe, meanwhile, collapsed to about 10^-32 centimetres in size. This theory was formulated by a number of individuals, including L. Dixon, J. Harvey, Edward Witten and Cumrun Vafa. According to the Vafa, a Harvard University professor, the six-dimensional universe is in the shape of an orbifold. The simplest example of an orbifold is a cone, but in this case the universe is a 'twisted torus' – a doughnut shape.

The reason that this idea uses a ten-dimensional universe that splits is because in this many dimensions, the four fundamental forces of physics unify themselves naturally. This means that the forces of electricity and magnetism (which are the same force anyway: electromagnetism), gravity and the strong and weak nuclear forces all become different ways of looking at the same force. When the ten-dimensional universe splits, and the four-dimensional universe expands, gravity quickly splits off from the unified force. After 10^-35 seconds, the strong nuclear force becomes independent of the electromagnetism-weak force unification. This is a break-down of the 'GUT', or Grand Unified Theory, and occurs because the universe is getting cooler (a mere 10³² degrees Kelvin). The last forces become independent when the temperature is just 10¹⁵ degrees Kelvin. Then, our conventional picture of the evolution of the universe from the Big Bang comes into play.

Evidence for this Theory?

Most things in the M-theory get away without having any evidence to support them at all, other than the fact that it 'sounds right'. If string theorists can come up with ideas that seem to fit observational data well, as well as explaining sought-after concepts, then it would surely be too coincidental to be wrong?

Short of building devices that need gargantuan quantities of energy, there are few ways to observe or detect the existence of the membranes that M-theory predicts. However, the recent (year 2003) data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP) may be explained by the universe having a shape that could correspond to the shape suggested by this theory. The WMAP data is a chart of hot and cold spots in the universe as it was 380,000 years after the big bang.

Frank Steiner at the University of Ulm, in Germany, pointed out that if the universe is in the shape of a medieval horn – similar in many ways to the orbifold concept – then the WMAP data is explained neatly. The WMAP chart has two interesting properties: areas of very hot or very cold space are never more than sixty degrees across; secondly, the areas of equal temperature all appear to be roughly elliptical – not perfectly round. If the universe were flat, the areas ought to be circular. A horn-shaped universe perfectly fits these criteria.

Theory Four: The Universe Was Free

This is the view of the universe that comes entirely from quantum mechanical theories. Proponents of this theory point to the observation that sub-atomic fundamental particles have the ability to create themselves from nothing. In other words, you could create a vacuum and particles could spontaneously create themselves. However, there is a cost to their abrupt emergence. They must appear in pairs: one of matter; the other of anti-matter. Then, after a strikingly brief period of time, they must come together, at which point they annihilate themselves, usually in a flash of gamma radiation. They are called virtual particles, and the energy created in their annihilation may have been enough after a period of time to cause the inflation of the universe as we know it.

This spontaneous particle creation happens because of the Heisenberg Uncertainty Principle: the quantum mechanical principle that you can never know the exact position and velocity of any particle at the same time. This is the principle that guides the notion of mutually exclusive answers to fundamental questions: in the same way you can't know the velocity of the particle if you know the position, so might Douglas Adams's picture that you can't know the question to the universe and everything if you already have the answer.

This theory of the origin of the universe is a general possibility that many quantum physicists believe, since it can be explained entirely with knowledge we already have, and needs no further work or proof. However, it is widely criticised. J Richard Gott, professor of astrophysics at Princeton, as well as a colleague, Li-Xin Li, have argued that, in this theory, the concept of nothing does not actually exist. There is a quantum state of superposition involved that contradicts the idea that the Universe began with nothing and evolved from the energy from two annihilated virtual particles.

Think of it like a bank. If you don't have enough money, the bank can give you a loan, so long as you pay it back within a pre-set period of time. Fundamental particles can do the same. If they don't have any energy (which means they don't exist), they can borrow it, so long as they repay it very swiftly. The question is, where did the bank come from? This criticism provokes further research into alternative explanations for the origin of the Universe.

Evidence for this Theory?

The evidence for this particular theory is the same evidence that proves the Heisenberg Uncertainty Principle and the existence of virtual particles. For a long time, the effects of virtual particles have been measured and frequently have to be taken into account so that errors are not built into physics experiments. The equations used to calculate the nature of the virtual particles and other quantum mechanical phenomena are often so precise that they rarely fail to explain observations.

Theory Five: The Universe Created Itself

Vacuums are spaces free of matter, which means they can still have an energy content. However, hypothetical spaces that are totally empty can also obtain energy contents. The energy of the empty space is often referred to as a number called 'lambda' (a Greek letter that looks like this: Λ), sometimes called the 'cosmological constant'. So, to explain this theory, let us begin at the beginning with a totally empty space.

The Russian physicist Andrei Linde proposed that quantum fluctuations (just like those in the above theory) can cause the energy state of space to become larger, or in other words, for Λ to increase. Note that the energy state does not decrease. This is due to the laws of thermodynamics, one of which states that a little energy in every process is always wasted. To explain why this happens, we shall take thermal energy (ie, heat) as an example. Heat is simply the random vibrations of particles. You can see this visually when you boil water; it is plain that the particles in the water are moving more vigorously by the bubbles writhing through the liquid. This randomness in movement is clearly 'disordered', and the technical term for this is 'entropy'.

Thermodynamics holds that the universe has a built in 'thermodynamic arrow of time'. This is analogous to the arrow of time that we are used to: we are forever compelled to travel into the future, and never into the past. The same is true of the thermodynamic arrow of time: the universe is forever compelled to move into a higher state of entropy (a more disordered state), and never to get more ordered. This can be demonstrated quite easily with a jigsaw puzzle analogy. When the puzzle is not completed and all the pieces are in a heap together in the box, you do not expect to shake the box and open it to reveal the completed puzzle. You may wonder why it is possible for you to be able to tidy your desk, because that action, after all, would put part of the universe in a state of less entropy. Well, desk-tidying is made possible by the fact that you exert so much energy in doing it (sorry to ruin your excuse for not tidying it).

So, to return to the theory, we have an area of empty space. Imagine that the space is a tennis ball and that its energy content (lambda) is a landscape of hills, mountains and valleys. The tennis ball begins in the lowest valley, with zero energy. However, due to random fluctuations made possible by Linde's theory (called chaotic or eternal inflation), the tennis ball suddenly 'jumps' up to a hill. This is called quantum tunnelling.

When our empty universe suddenly acquires this energy, it is forced to undergo a rapid expansion. Does that sound familiar? It should as it is the theory of inflation that we met a few theories ago. So the universe inflates, and our usual picture of the evolution of the universe takes over.

However, in this theory, it doesn't stop there. This quantum tunnelling effect does not abruptly become obsolete when the universe comes into existence. It carries on. The 'tennis ball' jumps up to a mountain, which causes a part of the universe to inflate much faster than the rest. After a short period of hyper-inflation, it bursts off from the universe and becomes independent. The universe has effectively given birth, hence Stephen Hawking's name for them: 'baby universes', although some physicists prefer the term 'bubble universes'. The process repeats itself, and we eventually have a multiverse of baby universes, who in turn give birth to their own mini-universes, and so on.

J Richard Gott, and his colleague Li-Xin Li, saw problems in the quantum tunnelling idea, which was generally accepted as the reason for inflation. Again, the universe does not begin as empty because it has a quantum superposition state; and additionally, the quantum tunnelling only has one 'end' to it: the result. When quantum tunnelling usually occurs, a particle starts somewhere and ends up somewhere else. Here, it supposedly starts with 'nothing', which is still as awkward as the original 'something-from-nothing' issue.

The two physicists found a possible solution: time travel. Time travel is a very popular concept for science-fiction books and television programs, so it makes sense to use such an example for explaining what Gott and Li-Xin Li are proposing. In the movie Back to the Future, the protagonist goes back in time and meets his own mother before he was born, which jeopardises his own existence. Similarly, in an episode of Red Dwarf¹, one character discovers that the reason he was an orphan (found in a box beneath a pool table) was because he was his own father, and he had gone back in time and left himself in the box.

In both of these examples we find characters that have the potential of being their own fathers. Gott and Li-Xin Li proposed that this could happen in reality. In the same way that the universe can give birth to another universe, why can't it give birth to itself? And that is their theory: the universe went back in time and was its own mother.

You would be forgiven for thinking this sounds odd. So let us picture it in a more physical sense. Imagine the universe is the shape of a trumpet, expanding to infinity at the 'bell' end. At some point along the trumpet's tube, the 'tennis ball' quantum tunnels (Λ suddenly increases), and a new tube on the instrument sprouts from it. The same thing happens with this tube, only this time the tube curls around upon itself and joins the 'mouth-piece' end of the original trumpet. In reality, this tube is extremely small, small enough for quantum effects to prevail. It also represents a repeating space-time. Again, the film industry is ahead of us. The film Groundhog Day depicts a man who inexplicably experiences the same day over and over again. Well, he could have been existing in the loop at the beginning of the Universe.

Evidence for this Theory?

Quantum tunnelling has plenty of evidence. The decay of uranium is one example, calculated by George Gamow in 1928. When it decays, it produces a nucleus of helium. The energy with which the nucleus is emitted is measurable, and we find that it is fairly low. This means that the helium nucleus could not have come from the nucleus of the original uranium atom; it must have come from quite a distance away from it. In other words, it tunnelled spontaneously from the uranium nucleus to the space some distance away.

Quantum tunnelling is so frequently observed, in fact, that few physics experiments today are not conducted without taking into account the effects of tunnelling particles. Superstring theory fits in well with this model too.

Theory Six: The Universe was Constructed in an Alien Laboratory

Don't shy away from the seemingly absurd title. Like some of the other arguably 'crazy' theories, this one has also been proposed by a respectable scientist - Ed Harrison, formerly of the University of Massachusetts at Amherst.

This theory uses a bubble universe, like the ones described in the theory above, where some super-intelligent species has evolved. Having harvested enough energy, they decide to conduct the ultimate laboratory experiment: creating their own baby universe. They do it in such a way that the resulting universe has the specifications suitable for other life-forms to grow.

That solves the problem of why the universe appears so perfect for life: because it was designed that way. The Astronomer Royal, Sir Martin Rees, has long been ruminating over six universal factors that he considers crucial for a universe like ours to evolve, including the density of the universe and the cosmological constant (a.k.a lambda; see above). The question is, why do these factors have such fine-tuned values? Well, if aliens wanted their baby universe to have them, that would be a very fitting theory. Harrison calls this 'self-directed selection'.

The reason that Harrison likes the idea that the universe was made by aliens is because he dislikes the conventional multiverse theory, which would have countless universes void of life and interesting structures. So, he put a twist on it. As soon as the first life-forms emerge, they develop their own baby universes, which are designed specifically for life. Since they are designed specifically for life to evolve, these universes will too grow life-forms that make their own universes, and so the process repeats itself until the multiverse is dominated by life-bearing universes. Thus, there is no waste. In the same way that sons can inherit the business of their fathers, the life-forms in the baby universes inherit the universe-manufacturing ability of their universes creators.

You might wonder how the super-intelligent beings manage to fine-tune the properties to create new life. Well, Harrison has a back-up plan. Somehow, he reckons that baby universes might naturally inherit the qualities of their parents, just like in our everyday theory of genetics in humans. This would mean that all baby universes that came from super-intelligent aliens would also have the properties perfect for life. The baby universes would not be entirely identical, however, because genetics will always allow for 'variation'. Harrison calls this idea the 'natural selection of universes'.

You may be pondering the question of how these intelligent beings go about constructing a universe from within a universe in the first place. Good question, but unlike so many good questions, we actually know the answer to this one. Remember Alan Guth and his inflationary universe? In this picture of the evolution of the universe, space started out with a density of 10⁹⁴ grams per cubic centimetre. If any piece of matter could be squashed to a similar density, it would form a black hole. Guth predicts that when black holes form, they also undergo hyper-inflation, but not within the universe. They inflate on the other side, and thus form a baby universe. However, because of the instability of the space-time in black holes, the tube by which the baby universe is connected to ours snaps, and so the universe is free to expand and cool independently, just like our universe did. And according to our old friend Linde, you would only need about a thousandth of a gram of matter to produce this effect, which is how we know that the experiment can be done in a laboratory.

There is a catch, of course. To shrink something to the critical density needed for a black hole to form, you need a vast amount of energy. We even know how much energy is required: 10¹⁹ billion electron volts, or, with each electron volt being worth 1.602*10^-19 joules, this is equivalent to 1.602*10¹⁰J, enough energy for about 3.5 years worth of balanced meals. At present, the human race obviously does not have the liberty of such vast quantities of energy.

The question is probably on the tip of your tongue now: how was the first universe created? Well, we cannot pretend to have an answer. Suffice to say, pick a theory from elsewhere in this article.

Evidence for this Theory?

The only evidence that can possibly be given for this idea is the fact that we exist in such a 'fine-tuned' environment. Other than that, the only way we might provide some evidence is to try to create a universe for ourselves, or to try to get back to our parent universe, and meet our makers. The latter of these ideas is probably the more difficult and would require a wormhole at the very least.

Theory Seven: The Varying Speed of Light Theory

Assuming your brain still exists after reading all of these mind-blowing theories, we can move on to an idea that is far more abstract, comprehensible and mathematical. This theory has been proposed by João Magueijo of the Imperial College, London, working with Andreas Albrecht of the University of California, Davis.

The origin of this theory is quite simple. Magueijo did not like the theory of inflation because it meant that a new type of particle had to exist before the big bang: anti-gravitational particles. The fact that we have no experimental evidence for these particles today is a worrying thing for inflation. How can an entire family of particles exist to cause a rapid expansion in the universe and then conveniently disappear?

Recall that Guth's theory of inflation set out to solve some crucial issues in observations of the universe: the horizon, flatness and monopole problems. Magueijo had to come up with a rival theory that would also solve them. He proposed that the horizon problem could be solved if light could travel across large distances very quickly and thereby carry 'information' of it to places that are now separated by vast distances (physicists usually refer to information as synonymous with light). For this to happen, the speed of light would have to be quicker in the early universe than it is today.

Cue gasps of shock and horror in the physics community. Albert Einstein's theory of relativity categorically states that the speed of light in a vacuum is a constant: about 299 792.458km/s, nothing more and nothing less. Magueijo claims that he does not seek to contradict everything relativity tells us (and has been proven experimentally), but to expand on the theory.

He goes on to show that the Varying Speed of Light (VSL) idea can solve the flatness problem. This is because of a unique relationship Magueijo managed to find (using mathematics) between the speed of light and...the cosmological constant²! This was a very elegant relationship: if the speed of light gets slower, Λ decreases too. In mathematical terminology, we say that the speed of light is directly proportional to the energy content of empty space.

So, the speed of light was fastest at the beginning of the universe, and Λ (according to the theory) was not zero. When the speed of light got slower, the energy of the vacuum defined by Λ got smaller; ie, energy was lost. However, if you remember your physics lessons, you will recall a principle called the Conservation of Energy/Mass, which states that energy can neither be created nor destroyed; it can only change from one form to another. So when energy is lost from Λ, it can't just get destroyed, it has to convert itself into another form. So it converted itself into radiation, matter, heat, light and all of the other forms of energy we know about. In such concentration, this explosion of energy would undoubtedly cause a rather large bang: in this case, the Big Bang itself.

Due to the speed of light controlling the energy in the universe, Magueijo claims that it can keep the universe generally 'flat', by evening out discrepancies in the energy of the vacuum at any time. Thus, this solves the flatness problem, and flat universes cannot produce monopoles either.

Evidence for this Theory?

For something that seems to contradict a key point in Einstein's theory, a universally celebrated moment for physics, the VSL theory has a surprising amount of evidence to support it. Light coming from the most distant parts of the universe is very old, and so it can tell us something about what the light was like in the early universe. When the light from objects called quasars some ten billion light years away passes through gas clouds in space, it collides with electrons, and hence forms a measurable pattern. It has been found that this pattern is different with older light than light from sources closer to us. This is considered fairly conclusive evidence that the properties of light were very different in the past.

Theory Eight: Providence

When all else fails, one cannot rule out the possibility that the universe has been created by the superior being predicted thousands of years ago in the Bible and other holy scriptures: God. Of course, from a scientific standpoint, theory six is very similar to this, so there is no need to spend so long discussing it.

God needs no scientific explanation. If He exists, He is beyond time and space, existing in a higher universe that is incomprehensible to humans before they get there. The only way to prove the theory would be to ascend to this higher plane of existence.

Statistically, four and-a-half billion people out of the Earth's six billion population are religious, and hence, believe in some kind of God. This is not unanimous, but it is a majority nonetheless, not to mention a traditional belief, and so should be taken as realistically as any other theory of the origin of the Universe. It does not contradict anything that has been said in the previous theories so God is not out of the equation entirely.

Conclusion

There are more theories, but the main contenders are most certainly the eight described above. So here we weigh up the evidence, the pros and the cons of each theory. Which one will you tell your children?

Further Reading

Theory One: There Was No Beginning

• New Scientist, March 20^th 2004.
• Three Roads to Quantum Gravity by Lee Smolin.

Theory Two: The Ekpyrotic Theory

• Astronomy Now, September 2001.
• The Elegant Universe by Brian Greene.

Theory Three: The Universe Split in Two

• Hyperspace by Michio Kaku.

Theory Five: The Universe Created Itself

• Time Travel in Einstein's Universe by J. Richard Gott.

Theory Six: The Universe Was Constructed in an Alien Laboratory

• The Universe Next Door by Marcus Chown.

Theory Seven: The Universe was the Result of Mathematical Proportionality

• Faster than the Speed of Light by João Magueijo.