What is antimatter, and has there been any real-life examples in existence or is it only a theoretical substance?

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I’m placing this under physics but this could indeed fall under chemistry or engineering from what little I understand.

In: Physics

Antimatter is particles with certain properties that are the opposite of matter particles, but are otherwise the same. For example, a positron is an anti-electron. It has the same spin and mass properties as an electron but it is positively charged (while an electron is negatively charged). In the Standard Model, all particles have an antiparticle, although some (if I recall correctly) are considered their own antiparticle.

We have samples of antimatter (at least some antiparticles), and we create and use antimatter in our largest particle accelerators. It is extremely difficult to make and a technical challenge to store, so we have very, very little of it at any point (and what we do have, we typically destroy in particle accelerators).

In physics, the concept of symmetry doesn’t just mean “you can rotate something and it still looks the same.” That is one form of symmetry, but there a lot of others too. Basically, the general definition is that the laws of physics allow you to change something in a certain way without violating the rules. So we have translational symmetry (you can move something around and the laws of physics don’t change), cylindrical symmetry (forces have the same strength at the same distance), and lots of other more advanced ones that I’m not smart enough to describe well.

Physicists use the concept of symmetry to make predictions. The Standard Model of particle physics has some symmetries. One of them is that it predicts some particles will have “twins” that are identical in every way except charge. So an electron’s twin, called a positron, will be the same mass, spin, etc., but will have positive charge instead of negative. And a proton’s twin, called an antiproton, will be the same mass, spin, etc., but will have negative charge instead of positive.

Antimatter is not just theoretical. They have detected it, and they make it in particle accelerators all the time. It also occurs naturally (in very very very small amounts) from cosmic ray collisions.

There are other symmetry predictions that have not been proven though. Supersymmetry predicts particle twins that are the same charge, but have different spin. They would also be much more massive. Those type of particles would take more energy to create in a particle accelerator than we can produce, so supersymmetry has yet to be proven.

Antimatter is basically the same as regular matter except with the opposite charge. For instance, the anti-electron is called a positron. Also, when matter meets antimatter they annihilate each other in a large explosion.

Antimatter has absolutely been observed. Radioactive decay gives off both positrons and electrons. This is even used in medicine with PET scans (positron emitting tomography).

When new matter is created using high energy collisions it appears to have about a 50 percent chance of being either matter or antimatter. Because of this, one of the great mysteries in science is why the universe appears to be almost entirely regular matter.

[Subatomic particles](https://en.wikipedia.org/wiki/Subatomic_particle) have basic properties: mass, spin, charge, flavor, color, etc. A particle will differ from other particles because it has different mass, different spin, different charge, etc.

Antimatter is, particle by particle, everything else the same but the CHARGE is the opposite. For example, electron has -1 charge, positron has +1 charge, but the same mass as the electron.

[Certain nuclear](https://en.wikipedia.org/wiki/Nuclear_reaction) reactions create positrons and other antimatter particles as a result of the reaction.

Doing nuclear reactions in large quantities would result in too much energy being released (or absorbed), at the scale of nuclear reactors / bombs. But, physicists can use [particle accelerators](https://en.wikipedia.org/wiki/Particle_accelerator) to smash into each other a few particles (atoms) at a time, which can result in a few positrons or other antimatter particles.

These can be “pulled out” and “stored” using magnetic fields, because, like electrons, they’re charged so they respond to electric and magnetic fields.

Anyway, a few particles at a time / per second = hundreds of millions of dollars per year to get a few milligrams.

Did OP mean dark matter?