Antimatter
- nicolelyu812
- Feb 26, 2024
- 2 min read
Updated: Mar 31, 2024
"Hi there, I'm your antiparticle!"
"What....? I have an "anti" counterpart??"
Antimatter might sound fictional, but it is very much true in existence. Straightforwardly speaking, antimatter is substance composed of subatomic antiparticles. Antiparticles have the same mass and spin as ordinary particles, but opposite charge (electric charge, weak isospin, colour charge), number (baryon number, lepton number), etc. When matter meets antimatter, they annihilate - whoosh - and a huuuuge amount of energy is produced. The mass has successfully been converted to energy using E = mc^2.
There are 2 separate notation for antimatter: adding a bar above the letter representing the particle e.g. u becomes ū, or reverse the sign of the particle which denotes its electric charge e.g. e- becomes e+.
This term “antimatter” was first coined by Arthur Schuster in 1898, albeit a speculation. Paul Dirac kickstarted the modern theory of antimatter with a paper in 1928, in which he realized that the relativistic version of the Schrödinger wave function predict for antielectrons. At 2 August 1932, Carl D. Anderson first discovered them in a cloud chamber and named antielectrons “positrons”.
Huh? So what is it actually?
Good questions. There are several theories of what they actually are and how they came into existence. One follows the Dirac Hole Theory, a modern one is called the quantum field theory, and the other concerns time. They are extremely interesting and check out the specific articles about them!
Antimatter in our lives
Antimatter might be closer to our daily lives than you might think. Beta negative (β−) decay occur naturally, and this process produces an anti-electron neutrino (as well as other products). Beta-positive decay, on the other hand, produces a positron (as well as other products). Antimatter also occurs in cosmic ray collisions with Earth’s atmosphere.
When a particle collide with its corresponding antiparticle, they annihilate and their mass is converted to energy (E = mc^2), which is released through gamma photons traveling in opposite directions (for momentum conservation). This reaction is used in medical imaging, e.g. PET (positron emission tomography). Antiparticles can form anti-atoms, with antihelium being the most complex every artificially produced and observed.
Baryogenesis
Evidence proved that in the observable universe, it is almost ordinary matter in its entirely instead of an equal amount of matter and antimatter, this asymmetry, or the problem of baryogenesis, remains one of the unsolved problems in physics. Also do check out the more detailed article about baryogenesis!
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