Before the Big Bang. Emmanuel Lim Duke University [email protected] Abstract The inflationary model of the universe postulates that the universe began with a Big Bang (a singularity in spacetime) at which space and time began. This was followed by a period of rapid exponential expansion, which resulted in the matter, light and forces we observe and experience today. However, this inflationary model fails to provide an answer to the question of what occurred before the Big Bang itself. At the exact point of the Bang, Einstein’s General Relativity predicts a singularity, which to modern physicists implies failure of the model. Consequently, today’s scientists have looked for other models - eternal inflation (a multiverse of small bubble universes that arise from quantum disturbances within a greater universe that is constantly inflating), a cyclic universe that oscillates between Bang-Crunch states, universes based on loop quantum gravity that Bounce rather than Bang (which eliminates that singularity), but which are either dissimilar or virtually identical throughout time, or universes based on string and M theory that propose that our universe was born in a black hole, or that it arose from the collision of two branes in multidimensional space. There are many other theories, but we will just focus on these ones here. 1 2 Despite the plethora of ideas about what happened before our Big Bang, none of them have yet been confirmed by experiment. As with any scientific theory, empirical evidence would provide one (or possibly none) of these theories the support to be accepted by the scientific community. However, while experiments such as LIGO (the Laser Interferometer Gravitational Wave Observatory) and WMAP (the Wilkinson Microwave Anisotropy Probe) are hard at work trying to find evidence for these cosmological models, the only real conclusion that has been drawn is that some kind of Bang occurred several billion years ago. If further conclusions are drawn from the current evidence, and if future experiments yield successful results regardless of what theory is supported, the current cosmological dilemma (which at times can be more philosophical than scientific) may eventually be resolved. Before the Big Bang? Before we grapple with the question of what happened before the Big Bang, we must look at why the Big Bang itself has become such a popular idea. It began with Edwin Hubble in 1929, who observed that galaxies move away from us at increasing rates with distance. His findings suggested that at some point in the past, all matter began at an infinitesimally compact point: a singularity, and somehow, our universe sprung out of nothing. This idea gained speed with the discovery of the cosmic microwave background (CMB) in 1965 by physicists Arno Penzias and Robert Wilson at Bell Tele- phone Laboratories. Penzias and Wilson were performing experiments with a sensitive microwave detector and were bothered by a low-frequency and omnipresent hiss [11]. Regardless of where they pointed their detector and at what time of the year they mea- sured, the background noise persisted. As the story goes, Penzias and Wilson believed that pigeon droppings were interfering with the incoming signals, but even after the dishes were cleaned and the birds eliminated, the hiss still remained. On a stroke of coincidence, two Princeton physicists (Robert Dicke and Jim Peebles) were interested in these very same signals. Dicke and Peebles postulated that if the early universe 3 were incredibly hot and energetic we would still be able to detect it, though only as a minor “echo”. Its signal would be so far redshifted that it would appear to us only in the microwave spectrum. Upon hearing of this search, the two Bell Lab scientists realized that they had already discovered what would come to be known as the cosmic microwave background, and were eventually awarded the Nobel Prize in 1978. This radiation moved scientists closer to confirming the existence of a Bang, though the kind and size of Bang, and whether it was the Big Bang or a Big Bang are yet to be determined. In fact, a handful of theories currently exist that are all vying to answer the fundamental questions about the cosmos, not least the question of what happened before the most recent Bang. Big Bang + Inflation In one model of the universe, the idea of before the Big Bang simply doesn’t exist. Time commenced at the Big Bang, and hence there was simply no before it. By Einstein and Minkowski’s four-dimensional view of the universe, with the three spatial dimensions and the one of time, the universe had a definitive starting point at the Big Bang. Einstein’s equations of general relativity predict a singularity at the very beginning when all of matter and energy were compressed into a n infinitesimally small point, and where the curvature of spacetime and the temperature and density of matter were infinite. Therefore, by some unexplained reason, when the universe first began to expand from this singularity, space and time themselves emerged. This view of the cosmos is held by some physicists such as Sir Stephen Hawking of the University of Cambridge. According to him, because Einstein’s equations fail at the point of the Big Bang, there is no reason to think about what happened before it since it would have no theoretical bearing on what would happen after. Since the equations fail at this point, there is no mathematical link between the “before” and the “after”. To Hawking and the 4 supporters of his theory, “the Big Bang was the beginning of the time” [11]. This is the conventional and well-accepted Big Bang theory. There is one gaping problem about this Big Bang + Inflation model, and one that may seen to be scientifically irresponsible. It doesn’t seem to have an explanation for why the Big bang even occurred at all. If the Big Bang was the beginning of everything, what had given rise to this beginning in the first place? The authors don’t provide a cause and effect mechanism at the very beginning. Eternal Inflation Hawking’s version of the cosmos included in it a period of inflation after the Big Bang. First described by Alan Guth of the Massachusetts Institute of Technology in the early 1980s, inflation posited that the universe underwent a period of immense and rapid expansion that caused it to become about 1030 times larger than it was originally. It had hoped to explain our universe’s homogeneity (in addition to other observable features we see today) but it was error-ridden and led to huge postinflation inhomogeneity [5]. Andrei Linde of Stanford University soon proposed a different kind of inflation that followed the Big Bang. By instead considering the scalar field in an inflationary universe, Linde proposed a form of self-reproducing inflation. The parts of the universe that could accrue enough quantum fluctuations in the scalar field to cause it to increase would eventually experience sudden expansion - in other words, Big Bangs [5]. These Bangs would number infinitely and would “keep going as a chain reaction, producing a fractallike pattern of universes” [5]. The greater universe in which these mini-verses would appear - quite like bubbles - would expand forever. 5 Fig. 1: An illustration from Linde’s 1994 Scientific American article of bubble universes in his model of eternal inflation (p. 55 [5]) His inflationary model overcame the problems surrounding Guth’s. Since he predicted 12 that the universe expanded to 1010 centimeters after inflation, it would become so large and hence “stretch” out any previous inhomogeneity [5]. Furthermore, its sheer size meant that we would only be able to observe a small fraction of it, and hence it would appear flat to us (in the same way that we observe earth to have a flat surface since the area that we live in is so much smaller compared to the rest of it). More importantly though, Linde did away with a unique and originative Big Bang in his model altogether. He proposed that inflation was eternal, a “pre-existing condition” [1], and therefore our universe emerged from it; we would probably have appeared out of another bang and did not need our own. In fact, Linde has calculated that as a result 107 of this inflation there are an estimated 1010 (essentially, infinitely many) universes 6 out there [1]. Without us, other universes would simply pop into existence while others would fizzle away. For ever and ever ... the Cyclic model In the cyclic model of the universe, before the Big Bang, there was yet another universe. The Big Bang that spawned our universe is only one out of an infinity of interchanging Bangs and Crunches. After a new universe is create from a Bang, it expands at an increasing rate. Eventually though, it would lose steam by the diminishing effects of dark energy and would begin to contract until eventually it became a singularity again. Another Bang occurs, and the universe pops in and out of existence in this infinitely repetitive manner. As Brian Clegg describes, “with enough repeats, in principle every possible life could unfold as time after time a universe would come into being, pass through its many billion years of life, and be destroyed” [6]. Such a theory would avoid all the problems associated with the uniformity and flatness of the universe that constantly trouble researchers. Indeed, if the universe that preceded ours had the familiar properties of uniformity and flatness and contained stars and galaxies, we would have no trouble explaining the properties of our own universe. Unfortunately, this cyclic model doesn’t explain how, if a previous universe contained all or most of the elements (especially the heavy ones that we understand today to have originated from stars and supernovae), a crunch could cause them to disappear, the lightest elements to disperse, and for the heavier elements to be created again in stars and supernovae [6].