In the 1920s, there was a dinner at which the physicist Robert W. Wood was asked to respond to a toast. This was a time when people stood up, made a toast, and then selected someone to respond. Nobody knew what toast they’d be asked to reply to, so it was a challenge for the quick-witted.
In this case the toast was: “To physics and metaphysics.” Now by metaphysics was meant something like philosophy — truths that you could get to just by thinking about them. Wood took a second, glanced about him, and answered along these lines:
The physicist has an idea, he said. The more he thinks it through, the more sense it makes to him. He goes to the scientific literature, and the more he reads, the more promising the idea seems. Thus prepared, he devises an experiment to test the idea. The experiment is painstaking. Many possibilities are eliminated or taken into account; the accuracy of the measurement is refined. At the end of all this work, the experiment is completed and … the idea is shown to be worthless. The physicist then discards the idea, frees his mind from the clutter of error, and moves on to something else. The difference between physics and metaphysics, Wood concluded, is that the metaphysicist has no laboratory.