杏吧原创

STRANGE as the idea of other universes is, it has become almost commonplace in physics. Parallel worlds are central to one interpretation of quantum mechanics. Inflation versions of the cosmological theory also imply that there is an infinite tree of branching universes. Cosmologists have even suggested that there could be parallel universes a millimetre away along some higher dimension.

In Parallel Worlds, Michio Kaku explores this conjectured multiverse with a particular end in mind. Our own universe is likely to become inhospitable to life one day, and Kaku believes that a sufficiently advanced civilisation might be able to escape this universe and find a home in a parallel world.

It is an appealing idea, but Kaku鈥檚 book is slightly frustrating. There are fine, lucid passages and some nicely told personal stories, but also explanations that are thoroughly confusing or irrelevant. We do not need the detailed historical development of string theory (Kaku is a physicist working on string theory), and I could have done without a last chapter that approaches the moral and theological implications of the multiverse without reaching much of a conclusion. Few would disagree that 鈥渨e should try to leave the world a better place than when we entered it鈥�, but who buys this kind of book for that kind of sentiment?

We do eventually reach Kaku鈥檚 plans for escaping the universe through a wormhole. Much of his later stuff is entertaining. For example, he makes the intriguing suggestion that to be able to gain enough computing power to control a wormhole, a civilisation might have to expand right across the galaxy and harness the power of its stars.

He lists steps such as 鈥渃reate and test a theory of everything鈥�, 鈥渟end probes through a black hole鈥�, 鈥渃reate a baby universe鈥�, 鈥渦se negative energy from squeezed states鈥�, though some are alternatives rather than necessary links in the chain. One step 鈥� developing a warp drive 鈥� is not central to any of the plans for escaping. In the end, I am not as convinced by Kaku鈥檚 provocative claim as I had hoped to be.