If you were to say to a physicist in 1899 that in 1999, a hundred years later, moving images would be transmitted into homes all over the world from satellites in the sky; that bombs of unimaginable power would threaten the species; that antibiotics would abolish infectious disease but that disease would fight back; that women would have the vote, and pills to control reproduction; that millions of people would take to the air every hour in aircraft capable of taking off and landing without human touch; that you could cross the Atlantic at two thousand miles an hour; that humankind would travel to the moon, and then lose interest; that microscopes would be able to see individual atoms; that people would carry telephones weighing a few ounces, and speak anywhere in the world without wires; or that most of these miracles depended on devices the size of a postage stamp, which utilized a new theory called quantum mechanics - if you said all this, the physicist would almost certainly pronounce you mad.

Most of these developments could not have been predicted in 1899, because prevailing scientific theory said they were impossible. And for the few developments that were not impossible, such as airplanes, the sheer scale of their eventual use would have defied comprehension. One might have imagined an airplane - but ten thousand airplanes in the air at the same time would have been beyond imagining.

So it is fair to say that even the most informed scientists, standing on the threshold of the twentieth century, had no idea what was to come.

Now that we stand on the threshold of the twenty-first century, the situation is oddly similar. Once again, physicists believe the physical world has been explained, and that no further revolutions lie ahead. Because of prior history, they no longer express this view publicly, but they think it just the same. Some observers have even gone so far as to argue that science as a discipline has finished its work; that there is nothing important left for science to discover.