Reviews Physics World  August 2017
(Detlev van Ravenswaay / Science Photo Library)

Building baby universes

Peter Coles reviews A Big Bang in a Little Room: the Quest to Create New Universes by Zeeya Merali

The thought of a scientist trying to design a laboratory experiment in which to create a whole new universe probably sounds like it belongs in the plot of a science-fiction B-movie. But as author Zeeya Merali explains in her new book A Big Bang in a Little Room, there are more than a few eminent physicists who think that this is theoretically possible – although there’s a long way to go before it can be achieved in practice. There are many variations on the general idea of how this apparently outrageous plan might be turned into reality, and while they are all speculative, the basic idea underpinning them is part of the cosmological mainstream.

Many – indeed, probably most – modern cosmologists think that, shortly after the Big Bang that brought our universe into existence, everything we can observe was compressed into a region much smaller than an atom. This tiny seed then grew to the immense scale of the current cosmos because it underwent a period of accelerated expansion known as inflation. Such an inflationary epoch could have occurred in a number of ways, but one particularly attractive conjecture is that matter underwent some form of phase transition as it cooled, and ended up trapped in a metastable state known as a “false vacuum”. Einstein’s general theory of relativity dictates that a universe configured in this way should cause space to expand at an accelerating rate, pumping up a tiny subatomic bubble into an entire cosmos that eventually provides a home to stars, galaxies and, eventually, to you and me.

If this line of reasoning is correct, then there is no reason, in principle, why humans could not reproduce what nature managed 14 billion years ago, by manufacturing a tiny patch of false vacuum in a laboratory. You might think this sounds a rather dangerous experiment, but it wouldn’t be – a small piece of space–time would merely “pinch off” and form an entirely separate mini-universe, causally disconnected from the space–time left behind. This would then inflate to form another cosmos, perhaps even one as big as ours, but we would never be able to observe it as it would be completely detached from our own piece of space–time.

In some ways, the possible creation of baby universes is a bit like the possible creation of mini black holes in high-energy particle collisions at the Large Hadron Collider (LHC). For one thing, both sound a bit scary and potentially dangerous to attempt. However, what would be left behind in the experiment by either of these events would just be a slight energy anomaly and (perhaps) a flash of radiation. Neither would cause the end of the world, as was claimed when the LHC was switched on but which clearly was not the case. On the other hand, no evidence has yet been found of mini black holes actually being created at the LHC, which suggests that creating a mini universe might require more advanced technology than we currently have available.

One specific way of creating a baby universe along these lines involves making a monopole: a hypothetical point-like topological defect that might well be formed in a phase transition in the early universe and could perhaps be reproduced in a laboratory. Nobody yet knows how to make monopoles in practice, or even whether they exist at all, but the idea is reasonably well motivated from a physical point of view. There are other ideas besides this one, and though it is worth repeating that none are close to being realized in practice, they are not silly – at least, not as far as we know based on current theoretical understanding.

Some would argue that, because it doesn’t yet lead to predictions that can be tested in a real experiment, this kind of work is not really “science”. I disagree. Many ideas that were not testable when first presented subsequently proved to be so. Moreover, the approach exemplified here, of taking a theoretical notion and asking “what if?”, is one that has served science extremely well in the past, even if it led to discoveries far away from what might have been initially anticipated. This can be a very creative activity, and though it must ultimately bow to the rigour of experimental test, it is a vital part of our science works.

As well as taking the reader through the basic aspects of modern cosmology needed to understand this somewhat controversial topic, Merali draws on a series of interviews with leading physicists to present as balanced a discussion as possible of the many differences of opinion. This approach also gives her an opportunity to include enjoyable little thumbnail sketches of some of the personalities involved – such as Alexander Vilenkin, Don Page and Andrei Linde – which will ring true to anyone who has actually met them. These tales also help to bring the human side of story more vividly to life by emphasizing the creative personalities of some of the protagonists.

A Big Bang in a Little Room doesn’t just discuss the science behind the quest to create new universes; it also touches on moral and even theological matters. As an atheist I do not feel particularly well qualified to act as a guide to theological territory, but I can certainly understand that those of a religious disposition might feel uncomfortable at the thought of creating a new universe because (presumably) that is supposed to be a job for God. If we could create a universe in a laboratory, would that threaten your belief in a divine creator? And if we could make a universe, how can we be sure that ours wasn’t created by other beings just like us, rather than a deity of some sort?

One philosophical (if not particularly religious) question Merali raises is: if we did create a baby universe, would we have moral responsibility for what happens in it? Every action we take in this universe affects its future, though the effects are often hard to predict. Surely the argument that one should not try to make a mini universe, on the grounds that something evil might happen in it, is an argument for not doing anything at all for fear of an unintended consequence? Whether you are interested in philosophy, or physics, or both, this is an enjoyable and thought-provoking book. I don’t agree with everything in it, but found it an immensely stimulating read.