His optimism about the future of the human race knows no bounds. And as he leads the way to the planetarium in the basement of the physics department of New York's City University, he hums to himself and rattles a large set of keys. He likes to give lectures down here. He also likes to come here on his own, to gaze at the cosmos and think. He is a deep, deep thinker. You could say he casts miles below the surface of normal thought. He has to. His ambition is to crack the elusive 'theory of everything', the one that defeated even Einstein, his mentor of sorts.
Today the planetarium does not lend itself to deep thinking because there is construction work going on directly above it: a raspy drilling sound, metal on metal, that vibrates the walls for minute-long bursts. We try to ignore it as we talk about his work. Although he is known as a populariser of science - he writes bestselling books with titles such as Hyperspace and Parallel Worlds, and presents programmes for BBC4 with equally imposing titles: Time and Visions of the Future - he is very much a practising theoretical physicist. He co-founded field string theory, after all.
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We'll come to that in a minute. For now it is enough to say that Stephen Hawking believes string theory may hold the key to the theory of everything: that is, to the single equation that unifies the very big (the theories of general relativity and gravity) with the very small (quantum mechanics). This is what the CERN experiment in Switzerland is all about, where physicists are recreating the conditions of the Big Bang in a Super Collider, or atom-smasher, that is 27 kilometres in circumference.
Although Prof Kaku is awaiting the results with eagerness, he does wish the experiment had taken place in America, as had originally been the plan. 'In the world of theoretical physics there is a certain amount of snobbery aimed at those of us who try to engage the public,' he says in a soft Californian accent. 'In 1994, we were going to build one near Dallas that would have been several times bigger than the one in Switzerland, and therefore several times more useful. But we needed to win Congress over to get 20 billion dollars' worth of funding for it. On the last day of the hearings, a Congressman asked one of the physicists if we would find God with our machine. The physicist answered that we would discover the Higgs Boson [the sub-atomic particle]. Our machine was duly cancelled.'
How would Michio Kaku have answered the question? 'I would have said this machine will take us as close as is humanly possible to the creation of the universe. This is a genesis machine. And yes, it may even let us read the mind of God... I think they would have opened their cheque books.'
That answer would have been true to form. Prof Kaku has a gift for communicating complex scientific ideas in a way that lay people can understand. He argues, moreover, that good physics should be simple, so simple that it can be understood as an image. I'll let him explain. 'A good physicist is driven by a childlike fascination and imagination. If we find ourselves getting jaded or bored we have to try to recapture that childishness. Einstein used to do that. He could be quite childish. He wanted to get access to that feeling of wonderment.
'He also believed that if a theory couldn't be broadly explained to a child it wasn't working. He believed that there should be a picture behind the theory. So his special relativity, for example, can be understood as a 16-year-old boy out-racing a light beam. Out of this arose the image of space and time being curved like the surface of an egg, warped by the presence of stars and planets, and finally Einstein's general theory of relativity, a mathematical description of the structure of the universe only one inch long on the page.' He smiles gently and looks up at the ceiling of the planetarium. 'But for the last 30 years of his life Einstein lost his picture. There was no picture guiding him; he said as much in his memoirs. That is why he wandered into various mathematical fields and got lost.'
Continued
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