Antimatter

:For the physics of antimatter, see the article on antiparticles.

History

In 1928 Paul Dirac developed a relativistic equation for the electron, now known as the Dirac equation. Curiously, the equation was found to have negative energy solutions in addition to the normal positive ones. This presented a problem, as electrons tend toward the lowest possible energy level; energies of negative infinity are nonsensical. As a way of getting around this, Dirac proposed that the vacuum can be considered a "sea" of negative energy, the Dirac sea. Any electrons would therefore have to sit on top of the sea.

Related Topics:
1928 - Paul Dirac - Relativistic - Electron - Dirac equation - Dirac sea

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Thinking further, Dirac found that a "hole" in the sea would have a positive charge. At first he thought that this was the proton, but Hermann Weyl pointed out the hole should have the same mass as the electron. The existence of this particle, the positron, was confirmed experimentally in 1932 by Carl D. Anderson.

Related Topics:
Proton - Hermann Weyl - Positron - 1932 - Carl D. Anderson

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Today's standard model shows that every particle has an antiparticle, for which each additive quantum number has the negative of the value it has for the normal matter particle. The sign reversal applies only to quantum numbers (properties) which are additive, such as charge, but not to mass, for example. The positron has the opposite charge but the same mass as the electron. An atom of antihydrogen is composed of a negatively-charged antiproton being orbited by a positively-charged positron.

Related Topics:
Standard model - Quantum number - Charge - Mass - Positron - Atom - Antihydrogen - Antiproton - Orbited

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