Enough ideas to fill a Tardis

When Doctor Who first burst onto British television in 1963, it was purely a children's programme. Gradually it invaded the adult field and the latest series, starring David Tennant as the tenth Doctor, found many adults glued to the screen. Daleks, Autons, Cybermen... aliens, time travel, parallel universes... great fun.

But is there any real science behind it or is it pure fancy? Could the Tardis, looking outwardly like an ordinary police box, ever expand inwardly into a spacious headquarters? Paul Parsons, editor of Focus magazine, has written a very clever book. While realising that the Doctor's science is far beyond our present capabilities, he points out that some of it, at least, does have a credible basis, and science fiction has a knack of turning eventually into science fact. After all, compare the technology of 2006 with that of, say, 1806, a mere two centuries ago. What would Napoleon have thought about computers, television or rockets to the Moon? He would have scorned any such ideas, and it is therefore unwise for us to scorn the ideas of Doctor Who . Two centuries hence, the science of 2006 will no doubt seem very antiquated.

Quite apart from this, Parsons gives excellent descriptions of techniques that already exist but about which many people (perhaps most) will be blissfully ignorant. Within the first 20 pages he launches into an account of the Casimir effect, which involves quantum theory and what is termed negative pressure - have you ever heard of it? The explanation given here is much clearer than that given in many textbooks.

Aliens, naturally, feature in many of the episodes, but this is reasonable enough, because many eminent scientists consider that life is likely to be widespread in the universe. Our galaxy contains a hundred thousand million stars, and we can see at least a thousand million galaxies, so there is no reason why other habitable planets should not be common, and there is already an enthusiastic Seti programme - Search for Extraterrestrial Intelligence. Some aliens may resemble us, but others will be very different, and the Doctor has had plenty of experience.

For example, he has met the repulsive Slitheens, "flatulent aliens with a taste for human flesh, who plot to sell off the Earth as radioactive fuel", according to the ninth Doctor. The Slitheens are bulky and 8ft tall; they aim to take over the Earth by impersonating world leaders. For this they don "compression field generators" that shrink them down to human size. This could be said to be a form of miniaturisation, which today does not sound outlandish.

Of course, science has changed since the time of the first Doctor, William Hartnell, more than 30 years ago. In some ways, so has the series, and this was brought home to me recently when I watched a old episode with Jon Pertwee, the third (and in my view incomparably the best) Doctor facing his arch-enemy, The Master. Yet some of the concepts that were utterly incredible then seem rather less so now. In some ways the Doctor's science may always be too much for us - but one never knows.

Frankly, I picked up this book expecting to dislike it. In fact, I enjoyed it immensely. It is as instructive as it is entertaining. I suggest that you buy a copy.

Sir Patrick Moore is a fellow of the Royal Society and the author of more than 60 books, mainly on astronomy.