Anti-Matter

In particle physics and quantum chemistry, antimatter is the extension of the concept of the antiparticle to matter, whereby anti-matter is composed of antiparticles in the same way that normal matter is composed of particles. For example, an anti-electron (a positron, an electron with a positive charge) and an anti-proton (a proton with a negative charge) could form an anti-hydrogen atom in the same way that an electron and a proton form a normal hydrogen atom. Furthermore, mixing of matter and antimatter would lead to the annihilation of both in the same way as mixing of antiparticle and particle does, thus giving rise to high-energy photons (gamma rays) or other particle-antiparticle pairs.

The particles resulting from matter-antimatter annihilation are endowed with energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original matter-antimatter pair, which is often quite large.

There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely antimatter instead, and what might be possible if antimatter could be harnessed, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the greatest unsolved problems in physics.

In December 1927, Paul Dirac developed a relativistic equation for the electron, now known as the Dirac Equation. Shockingly, the equation was found to have negative-energy solutions in addition to the normal positive ones. This presented a problem, as electrons tend toward the lowest possible energy level; energies of negative infinity are nonsensical. As a way of getting around this, Dirac proposed that the vacuum is filled with a “sea” of negative-energy electrons, the Dirac Sea. Any real electrons would therefore have to sit on top of the sea, having positive energy. Thinking further, Dirac found that a “hole” in the sea would have a positive charge.

At first he thought this was the proton, but Hermann Weyl pointed out that the hole should have the same mass as the electron. The existence of this particle, the positron, was confirmed experimentally in 1932 by Carl D. Anderson. During this period, antimatter was sometimes also known as “contraterrene matter”.

Today’s Standard Model shows that every particle has an antiparticle, for which each additive quantum number has the negative of the value it has for the normal matter particle. The sign reversal applies only to quantum numbers (properties) which are additive, such as charge, but not to mass, for example. The positron has the opposite charge but the same mass as the electron. For particles whose additive quantum numbers are all zero, the particle may be its own antiparticle; such particles include the photon and the neutral pion.

Antimatter cannot be stored in a container made of ordinary matter because antimatter reacts with any matter it touches, annihilating itself and the container. Antimatter that is composed of charged particle can be contained by a combination of an electric field and a magnetic field in a device known as the Penning trap. This device cannot, however, contain antimatter that consists of uncharged particles.

The one most important question that arises in a young mind such as you and me is that if antimatter reacts with any matter it touches, then it must react with the light which is composed of photons, imposing a challenge to its visibility.

If you knew a little bit more physics, you’d know that antiparticles don’t differ from particles by anything, except electric charge. They have the same mass, the same spin, the same energy. Since mass is equivalent to energy, then pure energy (the 2 gamma photons) can be converted to mass (the particle and its antiparticle) and vice-versa, mass (particles with rest mass) go into pure energy (gamma photons).

Actually, the problem is a bit more tricky or subtle. The two photons should be one photon and one anti-photon, but since photons are charge-less (by their nature), the photon and the anti-photon are identical and thus no reaction takes place.

 

”When there is darkness, there is light…When there is heaven, there is hell…And when there is matter, there is antimatter…”
-Angels and Demons by Dan Brown