The immediate aftermath of the Big Bang was an incredible time. For extremely brief periods the rapidly expanding universe went through a series of different states that saw subatomic particles crashing into each other at massive speeds. Periods known as the Quark-Gluon Plasma era and the Grand Unified era followed in quick succession, followed by longer periods (of minutes) which saw the formation of the first protons and neutrons, followed by the creation of nuclei in the 50,000 years that followed. It is a complex time during which, as Hooper points out, "almost everything... remains a mystery to us". It is a time when the laws of physics we know today probably behaved very very differently, and when the universe expanded faster than the speed of light.
It is this inflationary period to which Hooper devotes much of his discussion - because it is in this period that the large scale structures of the contemporary universe have their origin. It, as he says, ends after a brief moment and "in a sense one can think of the end of inflation as the true beginning of the universe we live in". When Weinberg wrote his book, the idea of the Big Bang had only just been accepted by most cosmologists. Hooper explains that many of them probably expected that 50 years later we would know much of what there is to know, but that isn't true. In fact some of this book is tinged with disappointment as he points out that he, and many of his colleagues, expected the Large Hadron Collider to answer most of their questions about what took place in the very early universe.
The book is easy to understand, though readers without some physics and astronomy background might find some of it hard going. I was challenged by some of it - one realises that ones physics degree from the early 1990s is going out of date quite quickly when reading Hooper or Chanda Prescod-Weinstein). But at times I wasn't sure my incomprehension was simply lack of clarity on physics. For instance, I thought that Hooper confused the many universes theory by simply explaining how the existing universe is broken up into sections that are unobservable due to them being beyond a cosmic horizon where they are receding from the observer faster than light. This is important because, as Hooper points out, we cannot really explain how the temperatures in those distant areas are so similar. But it is not, in my opinion, quite the same as the many universes idea that speculates about multiple universes with (perhaps) different physical laws.
The book is at its best when Hooper is linking these complex ideas to his day to day work. In fact there is rather a nice part when he explains what he actually does! I think this sort of communication is important because it helps to ground science in reality, as well as making it clear that scientists are ordinary workers too.
For those fascinated by astronomy and the early universe, Dan Hooper's book is excellent. Let us hope that his firm belief that many of the unknowns he highlights will be explained soon.
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