# “It doesn’t matter, does it anti-matter ?”

What could be your worst enemy whom you will always feel afraid to touch? He/she looks like you, but he/she is exactly opposite of you, your anti-matter. He/she can exactly perform the trick that you always can do. Because you both preserve a symmetry called the CPT symmetry. C stands for Charge conjugation, P stands for Parity transformation, and T means Time reversal. So even if your anti-matter looks like your twin, once you two come into touch, you both get annihilated.

Anti-matter is made of fundamental particles and we call them anti-particles. Like positron is electron’s anti-particle. Existence of positron was predicted by Paul Dirac in 1928 when found two solutions, one with positive and other negative energy, of the relativistic version of the Schroedinger’s equation (Now we call it Dirac equation). Particles obeying Dirac equation having positive energies and $-e$ charges are electrons, and particles with negative energies and $+e$ charges (the opposite sign in the charge is followed by the C symmetry) are positrons. Four years later positrons were discovered by C. D. Anderson in 1932 and this discovery awarded him Nobel prize in 1936. Similar many other anti-particles, e.g. antiprotons (by Emilio Segrè and Owen Chamberlain in 1955), antineutron (by Bruce Cork in 1956) and probably many others later on. When a particle collides its antparticle they both disappear by emitting energy as a photon (particle version of light). A photon is its own antiparticle and hence it automatically satisfies this collision rule.

However, to see a real matter made out of antiparticles we first need to build a matter, whose smallest unit is the atom. That means to create anti-partner of hydrogen, we need to bring an antiproton and a positron (antielectron) together in a similar way such that the positron orbits around the antiproton. Now this situation is very tricky to produce in the lab since anything in our world is made of matters, so any antiparticle once gets created will interact with its particle counter part present in the real world stuff (say, air, table, wall, etc.) and get annihilated.

The ASACUSA experiment at CERN (Courtesy: CERN)

This is a remarkable achievement since now probably can attempt to answer a few fundamental question:This week people in CERN’s ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) have claimed in their Nature Communication paper the success of creating 80 antihydrogen atoms by applying magnetic fields, detected 2.7 meter downstream after their creation.

1. Do antimatters obey CPT symmetry?

2. Will antihydrogen show the same spectral lines as normal hydrogen does?

3. Why galaxies and stars made out of antimatters have not been observed yet, whereas the Big Bang Theory supports equal amount of matter and antimatter at the beginning of the universe?

3. Do antimatters feel antigravity (instead of getting attracted like matters, two antimatters can feel repulsion from each other) ?

4. Can we use matter and antimatter annihilation energy to fuel up high-speed spaceships?

Useful links:

Antihydrogen project (Max-Planck institute)

The matter-antimatter asymmetry problem (article from CERN)

The other side (my previous blog post)

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