In this book, Lawrence Krauss addresses the problem of how the complex universe we observe arose out of `nothing'. In the Preface he briefly discusses the different meanings ascribed to this word by scientists, philosophers and theologians. Not surprisingly, there is little progress to be made here. Better to leave the philosophers and theologians to their word games and concentrate on the job of exploring its consequences in nature. That is what is done in this book.
Krauss starts with the standard history of the Big Bang: the evidence that supports it, and the need to introduce `dark matter' to reconcile measurements of galactic dynamics with the observed mass of their constituents. Dark matter is about 30% of the energy of the universe. Its nature is still unknown and is a very active field of research in particle physics. Then came the speculation that quantum fluctuations result indirectly in `empty space' being the source of an even greater energy, the so-called `dark energy', which would be about 70% of the total energy of the universe. The amount of mass/energy in the universe determines its geometry, and experiments in 1998 confirmed a `flat' universe (the meaning of this term is carefully explained) so the existence of dark energy is now inescapable. It implies a resulting force that causes the expansion of the universe to increase, rather than to decrease, as had been assumed. The origin and nature of dark energy is the greatest unsolved puzzle in physics today.
Krauss then considers how quantum fluctuations could have produced the conditions for a flat universe, since even a minute deviation from flatness at the time of the Big Bang would not produce the flat universe we see today. The answer is `inflation', the idea that the universe could have experienced a super-rapid expansion for a very short time after the Big Bang, the only viable explanation of the observed flatness and extreme homogeneity of the universe. He also explains how inflation `freezes' these fluctuations, which later emerge as the minute matter inhomogeneity that has been observed by experiments like WMAP and which later, under the influence of gravity, led to the formation of galaxies, stars and eventually us. Hence the title of the book.
The most startling consequence of living in a flat universe is that as it continues to expand, galaxies will eventually have velocities that exceed the velocity of light (the velocity is that of the expansion of space, not particles travelling through space, so no problems with special relativity) and will no longer be visible from any other galaxy. Paradoxically, this means that any future astronomers will not longer have the evidence to deduce that they are part of an expanding universe and so `starting from scratch' they could well come to an entirely different conclusion. Krauss gives a very interesting discussion of the extraordinary fact that we live in a relatively short time window (in terms of cosmological time) where it is possible to make the deductions we have about the universe, because `now' is the only time when the energy in empty space is comparable to the energy density in matter. Had the dark energy been even only 50 times bigger than at present, galaxies would not have formed and we would not exist. This leads on the ideas of multiple universes and the anthropic principle, which is the cause of so much controversy in physics today. Along the way he cannot resist gently prodding string theories and `theories of everything' (or `theories of anything' as he calls them).
The known scientific story essentially ends here, but the book continues with three more chapters. The first returns to the `something from nothing' question and essentially re-emphasizes how our knowledge of the universe has been obtained purely from the laws of physics and without the need for divine intervention. The second explores how a quantum theory of gravity might, via quantum fluctuations, produce a stable universe, with matter and radiation, from a `nothing' that did not include even space itself, and that such a universe would necessarily be flat, just as our own universe. This is highly speculative and the matter-antimatter asymmetry problem is far from solved. The last chapter tackles head-on the argument that there still needs to be a deity to determine the laws of physics - a First Cause. Here he discusses even more speculative ideas that imply universes can arise without the necessity of the laws of physics, the latter being random. His conclusion is that theology and philosophy are incapable of answering fundamental questions and that only by using the scientific method can we let nature tell us its secrets: `God is either unnecessary, or at best redundant'.
This book gives a very clear discussion of some of the most exciting ideas in cosmology today, and gives a real feeling for what enormous strides have been made in understanding the origins of the universe, as well as the unanswered questions. But the discussion is necessarily sometimes quite technical, with terms and concepts introduced without much explanation. This could mean a steep learning curve for someone without at least some previous acquaintance with the material, although there is an excellent index to enable one to navigate around the book. The poor quality of the illustrations does not help. Some of these would have been more impressive and easier to understand had they been in colour. Given the high price of £17.99 for a book of less than 190 pages (published by the ironically named Free Press), surely this could have been possible. Despite these minor reservations, this is a superb book.