Web edition: August 12, 2011
Print edition: August 27, 2011; Vol.180 #5 (p. 32)
September 20, 1930 | Vol. 18 | No. 493
Material Objects Seen as Holes in Space by British Scientist
A new idea of the constitution of space was presented when Dr. P.A.M. Dirac, twenty-five year old Cambridge physicist already famous in mathematical circles, announced to the British Association for the Advancement of Science at its recent meeting in Bristol his new theory that there is everywhere an infinite density of negative energy electrons.
Gone is the idea that there is absolutely nothing in a perfect vacuum, for Dr. Dirac said: “A perfect vacuum is now to be considered as a region of space in which all the states of negative energy and none of those of positive energy are occupied.”
Everything that is material to us, all the material things of the universe, are made up of “holes” in this vast space sea of negative energy, according to Dr. Dirac’s theory. In other words, things that actually exist and can be experimented with have positive energy and can be considered to be vacant places in the space of minus or negative energy...
Dr. Dirac told the physicists what they have long wished to know, just what is the nucleus of the hydrogen atom, better known as the proton. He said: “It will be a sort of hole in the distribution of negative energy electrons. To make the hole disappear which we can do by filling it up with an electron of negative energy, we must put into it a negative amount of energy. This means that the hole itself will have a positive energy. It now appears reasonable to interpret this hole as a proton.”
UPDATE | August 27, 2011
Antimatter pops from Dirac math
The Alpha Magnetic Spectrometer, delivered to the International Space Station in May, may offer clues to the nature of antimatter.Math can reveal the secrets of the physical universe, assuming theorists know how to interpret the equations. Physicist Paul Dirac’s prediscovery of antimatter offers perhaps the best example. In the late 1920s, Dirac realized that quantum mechanics was telling him something that other scientists had failed to see: Electrons could have negative energies.
If negative energies are possible, Dirac speculated in 1930, electrons would want to fill up those negative--energy states. A vacuum would thus actually be a sea of negative--energy electrons. If one such electron popped out of the sea, people would see the hole left behind as a positively charged particle of ordinary matter. Because electrons and protons were the only particles then known, Dirac concluded that the holes would be protons.
But a proton’s mass is nearly 2,000 times greater than an electron’s. So Dirac revised his idea, correctly concluding in 1931 that the holes were a new type of particle with the same mass as an electron but a positive charge. Dirac had predicted antimatter.
In 1932, physicist Carl Anderson saw Dirac’s positively charged electron in cloud chamber tracks, dubbing it “positron.” Today physicists know that every particle has an antiparticle, but they don’t yet know for sure why matter instead of anti-matter dominates the universe. —Elizabeth Quill