Knocking On Heaven's Door

by Lisa Randall

Science is all about extending the boundaries of our knowledge, and when it comes to physics those frontiers are all a matter of scale. Just how far can we probe the vastness of the universe, or look into the mysteries of minute subatomic particles? It's amazing what we do know, but it's also never enough. Knocking On Heaven's Door is an update on the state of this search, and it includes details of the methods and extraordinary lengths physicists will go to in order to increase our knowledge.

This is a wide-ranging book, and it does tend to wander from its central theme rather a lot. Earlier chapters deal with the history of scientific enquiry, such as Galileo's contributions to the development of early instruments that made further discoveries possible. This leads to a discussion on religion, and why it is incompatible with scientific thinking. At this point I wondered whether the well-worn faith versus science issue was going to make up the bulk of this book, given its title. Fortunately that's not the case, and religion is little more than an aside before we move on to more heavyweight topics.

Quite a lot of the book is given over to CERN and the Large Hadron Collider, with an emphasis on how impressive this project is. There are pictures and diagrams to drive the point home. The figures are pretty terrifying: the LHC is vast, expensive, colder than space and precision-engineered, and it could yield important clues about the structure of particles that are too small to be detected by any other method. Lisa Randall does a good job of communicating her excitement about this project, making clear what it means to the physics community and ultimately to the rest of us. The book left me wanting to know all the latest news on the LHC, right now.

The author is also on something of a PR exercise for this machine, and she goes to some lengths to explain why it's not likely to engulf us with Earth-swallowing black holes once it's switched on. That would be more reassuring if she hadn't also mentioned the large amount of radiation the LHC will produce, which is one of the reasons it's underground. How much radiation, of what kind, and for how long? Frustratingly the book doesn't say, and I thought this missing detail was important.

Instead there's a chapter on risk and its role in scientific predictions, and how scientists use models to try to forecast the results they expect to find. Again the author is on a PR mission. She compares the approach of physicists with that of banks and financiers playing the markets, in the light of the risks of economic bubbles and financial disasters. "The currency in science is reputation. There are no golden parachutes," she writes in chapter 11. Of course this makes scientists look good, but only in the same way as they might look good if you compared them with people who drive over cats for fun. Enough with the propaganda!

However there is a fair amount of nitty-gritty physics, even though this is aimed at general readers so there are few equations and notes. The author explains several theories that attempt to solve the hierarchy problem, which is to do with the masses of elementary particles. There are various outlandish ideas, such as extra dimensions or supersymmetry where every particle has its opposite, and so on. Hopefully the LHC will provide insights in the near future that render some or all of these ideas obsolete since they can't all be right. It seems unnecessary to try to understand these concepts when most of them will turn out to be wrong, but this part illuminates the process of theorising solutions that will get modified or discarded when more and better data comes in, so it's not redundant. Some of these concepts are tough for a non-physicist to understand, and I found I had to re-read quite a few sections. Sometimes this is because information was missing, for instance in chapter 21 there's a graph showing data from the PAMELA detector, but no explanation of what the "position fraction" on the Y axis actually stands for.

Knocking On Heaven's Door takes us from the Big Bang and questions of the age of the universe, right down to the tiny scale of particles smaller than the wavelength of light. It's a fascinating book, although it can be a little patchy. In-depth physics is interspersed with conversational anecdotes and pro-science propaganda, so that most of the book is easy to understand but once in a while something completely baffling comes along. It's a worthwhile overview of the state of modern physics, but quite variable in readability.