Marcus Chown on Cosmology

Your first book, by Richard Feynman, is just called QED. Presumably to demonstrate that it’s a science book.

Well you know who Richard Feynman is, don’t you? Probably the greatest American postwar physicist. He worked on the atomic bomb in his 20s and he got the Nobel Prize. But he was also famous for writing his papers in topless bars. His wife died of tuberculosis when they were at Los Alamos building the bomb and he decided you could go one of two ways. You could either say, “I’m going to be totally depressed for the rest of my life,” or, “I’m going to enjoy myself.” I was a student of Feynman’s at Cal Tech [the California Institute of Technology] and I remember he used to sunbathe nude on top of the physics building and hug all the secretaries every day.

He got the Nobel Prize for quantum electrodynamics, which is essentially the Mona Lisa or Sistine Chapel of physics. It’s the most successful physical theory humans have ever devised. It describes the interaction between light and matter, between photons and electrons. That interaction governs absolutely everything around you: the forces that hold together the molecules in your body, that burn the petrol in a car, that make the ground beneath your feet solid. It governs everything except gravity and the nuclear forces – the things that go on inside a nucleus like radioactivity. Apart from that quantum electrodynamics explains the world around us and predicts what we see to an obscene degree of accuracy.

So Feynman writes about this in a way that makes you want to read about it?

Yes, and that’s the point. When Feynman was at Cal Tech, this wealthy couple who’d grown up in the same New York neighbourhood as he had said, “Look, you’ve won this Nobel Prize, now explain to ordinary people what for.” And Feynman said, “No, it’s too complicated.” But eventually he did this series of public lectures, and that was the book. It’s a tiny book and in it he describes the whole of quantum electrodynamics without a single equation. It’s the most fantastic achievement: the most successful theory in physics described by the guy who invented it in 150 pages.

Tell me about Darkness at Night, because, frankly, it doesn’t surprise me that nights are dark. What’s the point of the title?

Well, when people think about darkness at night they take it as obvious that it’s because the sun isn’t shining on that side of the earth. But actually it’s a lot more mysterious – in fact it’s a 400-year mystery first noticed by Johannes Kepler, the German astronomer. Exactly 400 years ago, Galileo looked through his telescope and wrote The Starry Messenger, and one of the things he saw was lots of faint stars that were not visible to the naked eye. Kepler read about that and wrote a reply, Conversation with the Starry Messenger, and pointed out something. He pointed out that if the universe goes on for ever, there would be stars behind the faint stars, and behind those stars other, still fainter stars. In fact, between every two bright stars there would be two fainter stars and between those another pair. So the whole sky should be papered with stars and as bright as the surface of the sun from horizon to horizon.

So why is it not?

Well, people have been wondering about it ever since, and oddly enough the first person who had an inkling of an answer was Edgar Allan Poe. Between 1840 and 1850 – some time around then – he conjectured that the light from the most distant objects might not have actually got here yet. And of course that was the explanation that everybody embraced in the late 20th century when we discovered the Big Bang. If the universe was born 14 billion years ago, it turns out that we can only see objects whose light takes less than 14 billion years to get here. So the answer to the mystery of darkness at night seems to be that the universe is not eternal: that it was born.

Amazing.

Except that’s not the answer. That’s what most professional astronomers think, but they’re wrong. And that’s why Harrison wrote Darkness at Night. There’s a flaw in Kepler’s logic, and the flaw is that he assumes stars burn for ever. In Kepler’s time, of course, they didn’t realise that the fuel stars burned would eventually run out. Conservation of energy was only discovered in around 1850. So the question is really, how long would it take the stars to flood the whole universe with light? Think of the universe as a bath and light as the water. How long would it take the stars to fill it? You can actually calculate that, and the fact is that stars don’t live that long. Kepler’s paradox is really no paradox at all, which is a bit of an anticlimax, but finding out why takes you on an amazing history of astronomy, as well as giving you the right answer to a question that 99 per cent of professional astronomers get wrong. It includes loads of historical and literary asides and really brings the subject to life.

Let’s look at The Strangest Man by Graham Farmelo.