IN EVERY time and in every culture, there have been stories of creation 鈥� how the universe began. In our time the story is that of the big bang, the incredibly hot, dense state from which the universe expanded. But this is not the whole story.
鈥淭o believe that the big bang is the first moment of time is more religious mysticism than science,鈥� says Lee Smolin of the Perimeter Institute in Waterloo, Ontario, Canada. Smolin is not suggesting that the big bang never happened: astronomical observations and Einstein鈥檚 general theory of relativity leave little doubt that it did. But they don鈥檛 explain why it happened or what may have come before.
To do that, we need a more complete theory of how the universe works, a theory that unites the theories of quantum mechanics and relativity. So far, we don鈥檛 have one, but there are strong contenders. And these ideas may tell us where the universe really came from.
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One idea comes from a theory called loop quantum gravity, first proposed by Smolin, which ascribes a complex quantum architecture to space. Martin Bojowald of the Max Planck Institute for Gravitational Physics in Golm, Germany, was the first to use it to peer into the core of creation. What he found there was not a beginning at all, but rather a portal to a universe that came before, a universe that, as it turned out, was completely inside out.
In this looking-glass world, expansion is replaced by contraction 鈥� and a big crunch reflects our big bang. 鈥淲hen we follow the universe beyond the classical singularity, we can do so forever, until we reach negative infinity,鈥� Bojowald explains. 鈥淭herefore, the universe does not have a beginning. It has always existed.鈥�
It鈥檚 quite a claim, but can we believe it? That depends on whether you can believe in loop quantum gravity. Smolin developed the theory, working with a small group of physicists including Ted Jacobson, Abhay Ashtekar and Carlo Rovelli, by rewriting the equations of general relativity in a quantum framework. The new framework described space as if it were made up of tiny loops a mere 10-35 metres in diameter. These loops, the team suggested, are the very building blocks of space. Understanding the structure of the universe became a matter of understanding how the loops link together. The web-like networks of the theory, called spin networks, encode on a two-dimensional map all the information needed to construct a three-dimensional quantum space. So, for example, each vertex on the web is taken to represent a volume in space, while each line represents an area. According to the theory, both the volumes and areas can only increase in discrete steps.
But how can this web-like pattern tell us anything about the origin of the universe? The key is that the passage of time can be represented as a function of the volume of the loop universe, something that is possible in other theories that attempt to construct space-time from individual quanta (New Scientist, 4 October 2003, p 36). Since volume is made up of individual loops, time also hops along in discrete jumps. As Bojowald followed cosmic evolution backwards, the volume grew smaller and smaller until it reached the big bang itself. And that was where things got really interesting.
In the quantum network, areas and volumes are finite and indivisible. There cannot be a singularity, because space just cannot get that small. And since the theory no longer broke down, Bojowald could continue following time back beyond what had previously been viewed as the beginning.
The looking-glass universe he found there would have looked very similar to the one we know, with all the same laws of physics. Except, that is, for the bizarre fact that it was inside out. Because Bojowald measured time in volume, he found that as he ventured into negative time, the orientation of space flipped so that its volume and other spatial quantities became negative.
Bojowald likens the spatial flip to a balloon. If we idealise a balloon as a perfect sphere, and then deflate it, it will collapse to a single point. If we then imagine it continuing to collapse even further, all the points will pass through one another until the balloon reinflates, with the inside of the sphere now on the outside. Any object in the balloon would be reversed left to right, and that is just what happens in the universe before the big bang.
So would this make a difference? 鈥淭his would be mostly imperceptible,鈥� says Smolin, 鈥渁s most properties of the universe and most of the fundamental laws are symmetric under the exchange of left for right.鈥� But there are a few exceptions. Some reactions involving neutrinos and kaons are asymmetrical, because the reactions鈥� products are preferentially spinning in one direction rather than the other. In the universe on the other side of the big bang looking glass, those directions are reversed. So although in Bojowald鈥檚 model the big bang no longer marks a beginning of time, it remains a vitally significant event in cosmic history: the time when space flipped over, and left and right reversed. The universe has an eternal past, but all the details of the big bang evolution that have been worked out by cosmologists on this side of the big bang still apply.
Of course, loop quantum gravity is not the only idea in town. String theorists, who suggest that elementary particles have a structure that resembles tiny loops of string, have their own ideas about what came before the big bang. Gabriele Veneziano of CERN, the European Laboratory for Particle Physics near Geneva, for example, has attempted to use the finite size of strings to avoid a singularity, leading him to a universe that has existed forever (New Scientist, 3 June 2000, p 24).
And physicists Paul Steinhardt of Princeton University and Neil Turok of the University of Cambridge, UK, proposed a model in which the extra dimensions of string theory are put to cosmological use (New Scientist, 16 March 2002, p 26). According to their 鈥渆kpyrotic鈥� model, the three dimensions of space we experience actually live on the surface of a brane (short for 鈥渕embrane鈥�) that is floating in an additional dimension. Another brane hovers a microscopic distance from ours, and every few trillion years the two branes collide. What we perceive as the big bang, the model says, is just one of these collisions.
鈥淭he idea that underlies the cyclic model,鈥� explains Steinhardt, 鈥渋s that what appears to be a classical singularity in the usual 3-space plus one time dimension corresponds to a collision between branes in an extra dimension. There is a singularity in the sense that an extra dimension is disappearing, but it鈥檚 not our three dimensions that are disappearing.鈥�
This cycle, in which the branes move toward one another, collide, and then move apart again, can repeat over and over again eternally, which means that this idea, too, says the universe may never have had a beginning. So, if the best ideas in physics are to be believed, our search for the start of everything may go on for ever 鈥� in vain.
