Shadowlands by Robert Foot, Universal Publishers, $25.95, ISBN 158112645X Reviewed by Marcus Chown
GALAXIES, stars and planets are all very well, but most of the matter in the Universe is entirely invisible. There are dozens of candidates for this dark matter, but one has recently elbowed its way to the front. It鈥檚 called 鈥渕irror matter鈥�, and its chief proponent, Australian physicist Robert Foot, sets out the case in highly entertaining style in Shadowlands.
Nature, for reasons nobody understands, has chosen fundamental laws that exhibit the maximum possible symmetry. The laws of physics are the same today as yesterday, the same in New York as in London, and they respect a myriad other, more abstract symmetries besides. But in one respect nature is not symmetrical. The laws are not the same when reflected in a hypothetical mirror. 鈥淓lectrons and other elementary particles are, in a sense, left-handed,鈥� says Foot. 鈥淎lthough most scientists have come to accept that God is left-handed, somehow it has always bothered me.鈥�
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Foot鈥檚 unease has led him to embrace a radical idea: nature鈥檚 left-right symmetry isn鈥檛 really flawed, it only looks that way. For every known particle, there is a 鈥渕irror particle鈥� that interacts in a right-handed way. We haven鈥檛 noticed these mirror particles because they don鈥檛 interact with normal particles, and vice versa. It鈥檚 as if they鈥檙e ignoring each other. If Foot is right, there is an invisible mirror universe occupying the same space as our Universe, complete with mirror galaxies, perhaps even mirror life. Hey presto, an explanation for dark matter just like that.
All this would be science fiction if it wasn鈥檛 for baffling experiments with orthopositronium at CERN, the European centre for particle physics. This intriguingly named stuff consists of an electron and a positron 鈥� the antimatter counterpart of an electron 鈥� orbiting each other and each spinning in the same direction. Puzzlingly, it decays 0.1 per cent faster than predicted. What鈥檚 speeding up the loss? Foot claims that the orthopositronium is changing, or 鈥渙scillating鈥�, into mirror orthopositronium and then decaying in the mirror world before it oscillates back.
Foot believes there is evidence of mirror stars, mirror planets, mirror meteorites and mirror neutrinos. However, he reins in his enthusiasm towards the end of this intriguing book, admitting the possibility that mirror matter might not exist at all. Quoting Bertrand Russell, he says: 鈥淚t鈥檚 good to have an open mind, but not so open that your brains fall out.鈥�