188
PHYSICS OF IDE IMPOSSIBLE
matter always drops down to its lowest energy state, the prospect of
negative energy was potentially disastrous. It meant that all electrons
would eventually tumble down to infinite negative energy, hence
Dirac's theory would be unstable. So Dirac invented the concept of the
"Dirac sea." He envisioned that all negative energy states were already
filled up, and hence an electron could not tumble down into negative
energy. Hence the universe was stable. Also a gamma ray might occasionally collide with an electron sitting in a negative energy state and
kick it up into a state of positive energy. We would then see the gamma
ray turn into an electron and a "hole" develop in the Dirac sea. This
hole would act like a bubble in the vacuum; that is, it would have a
positive charge and the same mass as the original electron. In other
words, the hole would behave like an antielectron. So in this picture
antimatter consists of "bubbles" in the Dirac sea.
Just a few years after Dirac made this astounding prediction, Carl
Anderson actually discovered the antielectron (for which Dirac won
the Nobel Prize in 1933).
In other words, antimatter exists because the Dirac equation has
two types of solutions, one for matter, and one for antimatter. (And this
in turn is the outcome of special relativity.)
Not only did the Dirac equation predict the existence of antimatter;
it also predicted the "spin" of the electron. Subatomic particles can
spin, much like a spinning top. The spin of the electron, in turn, is crucial to understanding the flow of electrons in transistors and semiconductors, which form the basis of modern electronics.
Stephen Hawking regrets that Dirac did not patent his equation. He
writes, "Dirac would have made a fortune if he had patented the Dirac
equation. He would have had a royalty on every television, Walkman,
video game and computer."
Today Dirac's celebrated equation is etched in the stone of Westminster Abbey, not far from the tomb of Isaac Newton. In the entire
world, it is perhaps the only equation given this distinctive honor.
PHYSICS OF IDE IMPOSSIBLE
matter always drops down to its lowest energy state, the prospect of
negative energy was potentially disastrous. It meant that all electrons
would eventually tumble down to infinite negative energy, hence
Dirac's theory would be unstable. So Dirac invented the concept of the
"Dirac sea." He envisioned that all negative energy states were already
filled up, and hence an electron could not tumble down into negative
energy. Hence the universe was stable. Also a gamma ray might occasionally collide with an electron sitting in a negative energy state and
kick it up into a state of positive energy. We would then see the gamma
ray turn into an electron and a "hole" develop in the Dirac sea. This
hole would act like a bubble in the vacuum; that is, it would have a
positive charge and the same mass as the original electron. In other
words, the hole would behave like an antielectron. So in this picture
antimatter consists of "bubbles" in the Dirac sea.
Just a few years after Dirac made this astounding prediction, Carl
Anderson actually discovered the antielectron (for which Dirac won
the Nobel Prize in 1933).
In other words, antimatter exists because the Dirac equation has
two types of solutions, one for matter, and one for antimatter. (And this
in turn is the outcome of special relativity.)
Not only did the Dirac equation predict the existence of antimatter;
it also predicted the "spin" of the electron. Subatomic particles can
spin, much like a spinning top. The spin of the electron, in turn, is crucial to understanding the flow of electrons in transistors and semiconductors, which form the basis of modern electronics.
Stephen Hawking regrets that Dirac did not patent his equation. He
writes, "Dirac would have made a fortune if he had patented the Dirac
equation. He would have had a royalty on every television, Walkman,
video game and computer."
Today Dirac's celebrated equation is etched in the stone of Westminster Abbey, not far from the tomb of Isaac Newton. In the entire
world, it is perhaps the only equation given this distinctive honor.