10 December 2005
From New Scientist Print Edition.
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THE 21st century, so pundits keep telling us, will be the century of biology. There is no doubt that biology is advancing rapidly on many fronts, from molecular biology to evolutionary theory. On the other hand, the opposition is not making much of a race for it. Physics' greatest endeavour has ground to a halt.
We are in "a period of utter confusion", said Nobel laureate David Gross, summing up last week's prestigious Solvay conference on the quantum structure of space and time (see "Baffled in Brussels"). That is worrying because the topic is central to finding a "theory of everything" that will describe every force and particle in nature.
Einstein's relativity, which reigned supreme for a century, is a flawed basis for such a theory. Although it deals with gravity, it tells us nothing else about the nature and interactions of matter. Crucially, general relativity is incompatible with quantum theory. Since the 1960s, theorists have struggled to solve this problem, so far to no avail. And the trouble is we have nothing to put in relativity's place.
The great hope, string theory, which views particles as emanating from minuscule strings, has generated myriad mathematical descriptions linked to the dance of particles. But these equations tell us nothing about where space and time come from and describe nothing we would recognise. At best, string theory depicts the way particles might interact in a collection of hypothetical universes.
For decades, string theorists have been excused from testing their ideas against experimental results. When astronomers discovered the accelerating expansion of the universe, which string theory fails to account for, many string theorists took shelter in a remarkable excuse: that their equations describe all possible universes and should not be tied to matching data in just one of them.
But when the theory does not match the one data set we have, is it science? There is a joke circulating on physics blogs: that we can, after all, call our universe unique. Why? Because it is the only one that string theory cannot describe. Should we laugh or cry?
There is a growing feeling that string theory has run into the sand. Gross thinks we are missing something fundamental. We need a leap in understanding, though where it will come from is not clear. Many of the greatest minds in physics were there at last week's conference, and none had an answer.
We are approaching the end of Einstein's centennial year - a celebration of physics. While some lesser-known areas of the subject are flourishing, the search for a theory of everything is in a sorry state. Unless string theory gets a radical shake-up, gifted but frustrated minds will begin to drift into other areas of science. And if that is what makes biology the subject of the century, it will be depressing reason indeed.