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By Root 951 0

sun fuses with another proton to make a deuteron, thereby triggering the release of energy. Actually, the process would never even occur if it weren’t for the fact that the quantum theory reigns supreme at such small distances: In the pre-quantum worldview, the sun is simply not hot enough to push the protons close enough together for fusion to take place—it would have to be around 1,000 times hotter than its current core temperature of 10 million degrees. When the British physicist Sir Arthur Eddington first proposed that fusion might be the power source of the sun in 1920, he was quickly made aware of this potential problem with his theory. Eddington was quite sure that hydrogen fusion into helium was the power source, however, and that an answer to the conundrum of the low temperature would soon be found. “The helium which we handle must have been put together at some time and some place,” he said. “We do not argue with the critic who urges that the stars are not hot enough for this process; we tell him to go and find a hotter place.”

So ponderous is the conversion of protons into neutrons that, “kilogram for kilogram,” the sun is several thousand times less efficient than the human body at converting mass to energy. One kilogram of the sun generates only 1/5,000 of a watt of power on average, whereas the human body typically generates somewhat more than 1 watt per kilogram. The sun is of course very big, which more than makes up for its relative i nefficiency.

As we have been so keen to emphasize in this book, nature works according to laws. So it will not do to get too excited about an equation that tells us, as E = mc2 does, about what might possibly happen. There is a world of a difference between our imagination and what actually happens, and although E = mc2 excites us with its possibilities, we must still understand just how it is that the laws of physics allow mass to be destroyed and energy released. Certainly the equation itself does not logically imply that we have a right to convert mass to energy at will.

One of the wonderful developments in physics over the past hundred years or so has been the realization that we appear to need only a handful of laws to explain pretty much all of physics—at least in principle. Newton seemed to have achieved that goal when he wrote down his laws of motion way back in the late seventeenth century, and for the next two hundred years there was little scientific evidence to the contrary. On that matter, Newton was rather more modest. He once said, “I was like a boy playing on the sea-shore, and diverting myself now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me,” which beautifully captures the modest wonder that time spent doing physics can generate. Faced with the beauty of nature, it seems hardly necessary, not to mention foolhardy, to lay claim to having found the ultimate theory. Notwithstanding this appropriate philosophical modesty about the scientific enterprise, the post-Newton worldview held that everything might be made up of little parts that dutifully obeyed the laws of physics as articulated by Newton. There were admittedly some apparently minor unanswered questions: How do things actually stick together? What are the tiny little parts actually made of? But few people doubted that Newton’s theory sat at the heart of everything—the rest was presumed to be a matter of filling in the details. As the nineteenth century progressed, however, there came to be observed new phenomena whose description defied Newton and eventually opened the doors to Einstein’s relativity and the quantum theory. Newton was duly overturned or, more accurately, shown to be an approximation to a more accurate view of nature, and one hundred years later we sit here again, perhaps ignoring the lessons of the past and claiming that we (almost) have a theory of all natural phenomena. We may well be wrong again, and that would be no bad thing. It is worth remembering not only that scientific hubris has