A long time ago, my mother bought me a poster with my astrological sign at the top. The text read "Capricorn: You are a lazy, practically worthless individual who has to be forced to undertake any activity more strenuous than sleeping. You must avoid standing still for too long or a dog might mistake you a for a tree and..." You get the drift. But before waves of sympathetic readers start commiserating with me about a cruel parent, let me explain.

My mother was giving me something that emphasised her feelings about astrology. She didn't like it and she passed that dislike on to me. It drives me crazy when I'm told, "You're a typical Capricorn/Leo/Gemini, whatever". My response was to point to the poster. What astrologer, with his thoughts on the wad of cash he was about to be paid for his predictions, would tell me that I was a lazy sod, and that it was because of the stars? No one has ever been able to explain to me how celestial objects billions if not trillions of kilometres away influence hairless mammals on an insignificant watery planet near the edge of the Milky Way?

A friend with an astrological bent once suggested to me that gravity was somehow behind the phenomenon. I think not. If gravity shaped our personalities, our own Earth must surely be the biggest influence on us. The moon, the sun and the other planets of solar system would make us happy, sad and indifferent by turns. We'd each have multiple personalities that chopped and changed as Venus passed by, and the moon was in the seventh house (what does that mean? Are there "houses" in space?). When Jupiter and Mars are lined up, we'd all crave cheeseburgers or go to war with a nearby country. Think of the great excuses we'd have. "I'd love to come and see you but, Neptune is pulling me towards the pub." "Honest officer, I only drove my car into the road sign because of the influence of Mercury and seven large asteroids."

I know, I know. That's more or less what happens. I can hear the astrologers telling me that as I write. But it isn't true. Gravity doesn't influence personality, destiny or politics. Nor do the other forces that physicists believe shape the universe-all measurable and pondered over by men and women of immense intellect. There is a certain haunting mysticism to theoretical physics. The late great Carl Sagan used to talk about the fundamental harmony of the universe and its component parts-matter and energy. Sagan was demonised by the religious right in the United States for appearing to question the existence of God, but what he was actually saying was that the universe was perfect. It could not have come about in any other form, and that was something to marvel at.

Such lofty science can seem cold, distant and irrelevant to daily life. But theoretical physics is almost like religion. It tries to explain why things are the way they are. And it is necessarily democratic, open to constant debate, revision and change. There is no dogma. Physicists admit that they are simply human beings with theories that could be wildly off base. Astrologers, by contrast, predict events and give personality profiles that depend on what they perceive to be position of stars and planets. Some are so far away that they may have blown up millions of years ago and the light from the explosion has yet to reach the Earth. The astrologer still gets paid, whether or not the star exists. It's all the same to him.

Yes, yes, it is just a (largely) harmless pastime that most people don't take particularly seriously. But don't expect me to take an interest in my fate as ordained by the stars. I'm just too lazy to care. And watching out for dogs.