Zero - Charles Seife [66]
Matter waves are not so different from string waves. Just as a guitar string of a given size is not capable of playing every possible note—some waves are “forbidden” from appearing on the string—some particle waves are forbidden from being inside a box. Put two metal plates close together, for instance, and you can’t fit every sort of particle inside. Only those whose waves match the size of the box are allowed in (Figure 49).
Figure 48: Forbidden notes on a guitar string
Casimir realized that the forbidden particle waves would affect the zero-point energy of the vacuum, since particles are everywhere winking in and out of existence. If you put two metal plates close together and some of those particles aren’t allowed between the plates, then there are more particles on the outside of the plates than on the inside. The undiminished zoo of particles presses on the outside of the plates, and without the full complement on the inside, the plates are crushed together, even in the deepest vacuum. This is the force of the vacuum, a force produced by nothing at all. This is the Casimir effect.
Figure 49: The Casimir effect
Though the Casimir force—a mysterious, phantom force exerted by nothing at all—seems like science fiction, it exists. It is a tiny force and very difficult to measure, but in 1995 the physicist Steven Lamoreaux measured the Casimir effect directly. By putting two gold-covered plates on a sensitive twist-measuring device, he determined how much force it took to counteract the Casimir force between them. The answer—about the weight of one slice of an ant that’s been chopped into 30,000 pieces—agreed with Casimir’s theory. Lamoreaux had measured the force exerted by empty space.
The Relativistic Zero: The Black Hole
[The star,] like the Cheshire cat, fades from view. One leaves behind only its grin, the other, only its gravitational attraction.
—JOHN WHEELER
Zero in quantum mechanics invests the vacuum with infinite energy. A zero in the other great modern theory—relativity—creates another paradox: the infinite nothing of the black hole.
Like quantum mechanics, the theory of relativity was born in light; this time it was the speed of light that caused the trouble. Most objects in the universe don’t have a speed that every observer can agree on. For instance, imagine a small boy who is throwing stones in all directions. For an observer approaching the boy, the stones seem to be going faster than for an observer who is running away; the velocity of the stones seems to depend on your direction and speed. In the same way, the speed of light should depend on whether you are running toward or running away from the lightbulb that’s shining on you. In 1887 the American physicists Albert Michelson and Edward Morley tried to measure this effect. They were baffled when they found no difference; the speed of light was the same in every direction. How could this be?
Again, it was the young Einstein who had the answer in 1905. And again, very simple assumptions would have enormous consequences.
The first assumption Einstein made seems fairly obvious. Einstein stated that if a number of people watch the same phenomenon—say, the flight of a raven toward a tree, the laws of physics are the same for each observer. If you compare the notes of a person on the ground and a person on a train moving parallel to the raven, they would disagree about the speed of the raven and the tree. But the eventual outcome of the flight is the same: after a few seconds, the raven arrives at the tree. Both observers agree on the final result, though they might disagree about some of the details. This is the principle of relativity. (In the special theory of relativity, which we are discussing here, there are restrictions on the kind of motion that is allowed. Each observer must be moving with constant velocity in a straight line. In other words, they can’t feel an acceleration. With the general theory of relativity, the restrictions are removed.)
The second assumption is a little more