Does antimatter actually exist? I have heard that everything has an opposite therefore matter also has one. Also I have heard that it doesn't exist anywhere on earth because on coming in contact with any kind of matter it decomposes. Please answer as I really want to know about this.

Yes, anti-matter do exist. But certainly not on earth. Like, everything has an opposite, like protons-elections, heaven-hell etc, there is also an opposite, anti-matter. Anti-matter, when comes in direct contact with matter, annihilate to give pure energy in the form of photons. A very small amount of anti-matter has however been created by CERN and is kept between magnetic field so as to keep it away from matter. Since, it gives pure energy, therefore reserch has been carried out to look to it as a future renewable-source of energy, but for now it is not possible, as the input cost is very high than the output cost.

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Dear student,

A particle and its antimatter particle annihilate when they meet: they disappear and their kinetic plus rest-mass energy is converted into other particles (E = mc²). For example, when an electron and a positron annihilate at rest, two gamma rays, each with energy 511 keV, are produced. These gamma rays go off in opposite directions because both energy and momentum must be conserved. The annihilation of positrons and electrons is the basis of Positron Emission Tomography (PET) discussed in the section on Applications (Chapter 14). When a proton and an antiproton annihilate at rest, other particles are usually produced, but the total kinetic plus rest mass energies of these products adds up to twice the rest mass energy of the proton (2 x 938 MeV).

Antimatter is also produced in some radioactive decays. When ¹⁴C decays, a neutron decays to a proton plus an electron and an electron antineutrino, . When ¹⁹Ne decays, a proton decays to a neutron plus a positron, e⁺, and an electron neutrino, .

¹⁴C --> ¹⁴N + e^- +

¹⁹Ne --> ¹⁹F + e⁺ +

The neutrino and electron are leptons while the antineutrino and positron are anti-leptons. Leptons are point-like particles that interact with the electromagnetic, weak and gravitational interaction, but not the strong interaction. An antilepton is an antiparticle. In each reaction, one lepton and one antilepton is produced. These processes show a fundamental law of physics - that for each new lepton that is produced there is a corresponding new antilepton.

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