We’ve come a long way. But there is still a long way to go. In the late nineteenth century, physicists confidently claimed they had discovered pretty much all there was to be discovered. That was before the twin bombshells of quantum theory and relativity blew the edifice of nineteenth-century, ‘classical’ physics sky high. A hundred years later, physicists such as Stephen Hawking – not overly quick to learn their lesson – were predicting we would have a ‘theory of everything’ within a decade or so. That was before the unexpected discovery in 1998 that you, me, the stars and the galaxies account for a mere 4 per cent of the mass of the Universe. The cosmos instead is dominated by mysterious invisible stuff with repulsive gravity – dark energy – not to mention invisible stuff with ordinary gravity – dark matter. And, if any further proof is needed that the theory of everything might be farther away than the optimists think, there is the small matter that quantum theory – our very best physical theory – overestimates the energy density of dark matter by a factor of 1 followed by 123 zeroes!
Perhaps some novel idea like string theory will tie together quantum theory and general relativity in a neat ten-dimensional package. In some quarters there is great hope that this will happen – though perhaps not soon. In other quarters there is scepticism about a ‘bandwagon’ theory which makes few, if any, predictions that are testable in the short-term. They point out that the theory is undoubtedly beautiful but that there are many equally beautiful ideas which the Creator in his wisdom has chosen not to implement.
Maybe string theory will be the saviour of modern physics. Then again, perhaps it won’t. One thing is in no doubt, however. Scientifically, we live in extremely interesting times. We can ask questions our forebears couldn’t even formulate and expect to get answers well within a lifetime. Some of the questions we can ask I have addressed in this book. But of course many are left:
* What is dark energy?
* What is dark matter?
* What is space?
* What will be the ultimate fate of the Universe?
* Why is the speed of light the ultimate cosmic speed limit?
* What is consciousness?
* Does life have any special role to play in the Universe?
Then, of course, there is that most puzzling question of all: Why has the Universe given rise to matter that contemplates its surroundings and asks ‘why?’ Now that is a question and a half. I think I can feel another book coming on …