Antimatter

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

The Antiuniverse

Dirac himself was the first to consider the existence of antimatter in an astronomical scale. But it was only after the confirmation of his theory, with the discovery of the positron, antiproton and antineutron that real speculation began on the possible existence of an antiuniverse. In the following years, motivated by basic symmetry principles, it was believed that the universe must consist of both matter and antimatter in equal amounts. If, however there were an isolated system of antimatter in the universe, free from interaction with ordinary matter, no earthbound observation could distinguish its true content, as photons (being their own antiparticle) are the same whether they are in a ?universe? or an ?antiuniverse?.

Related Topics:
Symmetry - Universe

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But assuming large zones of antimatter exist, there must be some boundary where antimatter atoms from the antimatter galaxies or stars will come into contact with normal atoms. In those regions a powerful flux of gamma rays would be produced. This has never been observed despite deployment of very sensitive instruments in space to detect them.

Related Topics:
Galaxies - Stars - Gamma rays

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It is now thought that symmetry was broken in the early universe when charge and parity symmetry was violated (CP-violation). Standard Big Bang cosmology tells us that the universe initially contained equal amounts of matter and antimatter: however particles and antiparticles evolved slightly differently. It was found that a particular heavy unstable particle, which is its own antiparticle, decays slightly more often to positrons (e+) than to electrons (e-). How this accounts for the preponderance of matter over antimatter has not been completely explained. The Standard Model of particle physics does have a way of accommodating a difference between the evolution of matter and antimatter, but it falls short of explaining the net excess of matter in the universe by about 10 orders of magnitude.

Related Topics:
Charge - Parity - Big Bang - Antiparticle - Standard Model - Particle physics

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After Dirac, the sci-fi writers had a field day with visions of antiworlds,

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antistars and antiuniverses, all made of antimatter, and it is still a common plot device, however suppositions of the existence a coeval, antimatter duplicate of this universe are not taken seriously in modern cosmology.

Related Topics:
Plot device - Cosmology

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see: *What is direct CP-violation?

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