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In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter, and can be thought of as matter with reversed charges and parity, or going backward in time (see CPT symmetry).

Antimatter occurs in natural processes like cosmic ray collisions and some types of radioactive decay. Antiparticles can also be generated at particle accelerators, but only a tiny fraction of these have successfully been bound together in experiments to form antiatoms. No macroscopic amount of antimatter has ever been assembled due to the extreme cost and difficulty of production and handling. Nonetheless, antimatter is an essential component of widely available applications related to beta decay, such as positron emission tomography, radiation therapy, and industrial imaging. In theory, a particle and its antiparticle (for example, a proton and an antiproton) have the same mass, but opposite electric charge, and other differences in quantum numbers. A collision between any particle and its anti-particle partner leads to their mutual annihilation, giving rise to different proportions of intense photons (gamma rays), neutrinos, and sometimes less-massive particle–antiparticle pairs. The majority of the total energy of annihilation emerges in the form of ionizing radiation. If surrounding matter is present, the energy content of this radiation will be absorbed and converted into other forms of energy, such as heat or light. The amount of energy released is usually proportional to the total mass of the collided matter and antimatter, in accordance with the mass–energy equivalence equation, E=mc2. Antiparticles bind with each other to form antimatter, just as ordinary particles bind to form normal matter. For example, a positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an antihydrogen atom. The nuclei of antihelium have been artificially produced, albeit with difficulty, and are the most complex anti-nuclei so far observed. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements. There is strong evidence that the observable universe is composed almost entirely of ordinary matter, as opposed to an equal mixture of matter and antimatter. This asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. The process by which this inequality between matter and antimatter particles is hypothesised to have occurred is called baryogenesis.

Antimatter particles carry the same charge as matter particles, but of opposite sign.

He hypothesized antiatoms, as well as whole antimatter solar systems, and discussed the possibility of matter and antimatter annihilating each other.

If antimatter-dominated regions of space existed, the gamma rays produced in annihilation reactions along the boundary between matter and antimatter regions would be detectable. The presence of the resulting antimatter is detectable by the two gamma rays produced every time positrons annihilate with nearby matter.

These are typically produced at energies far too high to form antimatter atoms (with bound positrons in place of electrons).

This was the first time that neutral antimatter had been trapped. However, CERN only produces 1% of the antimatter Fermilab does, and neither are designed to produce antimatter.

Antimatter cannot be stored in a container made of ordinary matter because antimatter reacts with any matter it touches, annihilating itself and an equal amount of the container. Antimatter in the form of charged particles can be contained by a combination of electric and magnetic fields, in a device called a Penning trap. At high vacuum, the matter or antimatter particles can be trapped and cooled with slightly off-resonant laser radiation using a magneto-optical trap or magnetic trap.

Gravitational interaction of antimatter – Theory of gravity on antimatter

What is Antimatter? (from the Frequently Asked Questions at the Center for Antimatter–Matter Studies)

Quick Facts

• Antiparticles bind with each other to form antimatter, just as ordinary particles bind to form normal matter.
• The amount of energy released is usually proportional to the total mass of the collided matter and antimatter, in accordance with the mass–energy equivalence equation, E=mc2.
• There is strong evidence that the observable universe is composed almost entirely of ordinary matter, as opposed to an equal mixture of matter and antimatter.
• For example, a positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an antihydrogen atom.
• Antimatter occurs in natural processes like cosmic ray collisions and some types of radioactive decay.

Source material: Wikipedia - "Antimatter". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.