by Ron Kurtus (updated 8 February 2022)
Antimatter is a form of matter that is made up of what are called antiparticles. The antiproton, antineutron and positron are the antiparticles of the proton, neutron and electron, respectively. Those antiparticles are the building blocks of antimatter.
Although various antiparticles have been detected and even created, the only antimatter atoms created thus far are antihydrogen and antihelium.
Just as particle-antiparticle interactions result in a the release of high energy photons or gamma rays, so too would the interaction of matter and antimatter, except with greater energies.
Although you would expect there would be equal amounts of matter and antimatter in the Universe, each in different locations, it seems that most—if not all—of the natural atoms in space are matter.
Apparently, the behavior of antimatter is exactly the same as matter, since everything is the same except for the electrical charges of the particles. The only antimatter atom made by scientists is the anti-hydrogen atom.
When matter and antimatter collide, an enormous amount of energy is released. Although our part of the Universe is made up of matter, it is possible that other parts consist of stars and galaxies made up of antimatter.
Questions you may have include:
- What are an antimatter atoms like?
- What happens when matter and antimatter combine?
- Is there any antimatter in the Universe?
This lesson will answer those questions. Useful tool: Units Conversion
Antimatter atoms consist of antiparticles. The atoms appear similar, except with opposite electrical charges. Their chemical characteristics are the same, as long as they react with other antimatter atoms.
Antiparticles that make up an antimatter atom are the positron (anti-electron), anti proton and antineutron.
The positron has a positive (+) electrical charge, as opposed to the negative (−) charge that an electron has.
The antiproton has a negative (−) electrical charge instead of the positive (+) charge that a proton has. The proton consist of quarks, while the anti proton consists of anti quarks, which have the opposite charge of quarks.
An antineutron. and neutron both have zero (0) electrical charge, but they are made of quarks, which have electrical charges. The neutron is made up of one up quark and two down quarks. The resulting electrical charge of the neutron is: (+2/3) + (-1/3) + (-1/3) = (0). The antineutron. is made up of one anti-up quark and two anti-down quarks. The resulting electrical charge of the neutron is: (-2/3) + (+1/3) + (+1/3) = (0).
(See Antiparticles for more information.)
Atoms comparisonThe illustrations below compares a Helium atom with its antimatter counterpart.
One man-made antimatter particle is the anti-hydrogen atom, consisting of a positron and an antiproton nucleus. Anti-hydrogen atoms can be maintained at extremely low temperatures and held in place by magnetic fields. Once an anti-hydrogen atom strikes the wall of a container or hits some other atom, it is annihilated and results in high-energy gamma rays being emitted.
The anti-helium particle has also been observed from high energy proton-nucleus collisions.
Combining matter and antimatter
When matter comes in contact with antimatter, an enormous amount of energy is given off in the form of electromagnetic radiation. The total of the mass of the two particles is converted into electromagnetic energy through Einstein's famous E = mc² equation.
That means that if a gram of matter (0.001 kg) would come into contact with a gram of antimatter (0.001 kg), the amount of energy that could be released would be E = (0.002)*(9*1016) = 1.8*1014 joules or newton-meters. This is about 40 times greater than the energy of the first atomic bomb.
The tremendous energy released from a small amount would seem to make combining matter and antimatter a great candidate for powering rockets into space. Two things hold such a power source back. One is that we have no source of even a gram of antimatter. The second problem is that there would be no way to contain the antimatter and keep it from coming in contact with matter before it was used.
The result when matter and antimatter combine is electromagnetic radiation in the form of gamma rays, which are high-energy rays with a wavelength shorter than x-rays. When a single atom and its antimatter counterpart combine, the gamma radiation is in the form to two photon particles, moving in the opposite direction.
NOTE: On an individual basis, electromagnetic radiation can be considered to consist of photon particles. When there are a large number of photons, the radiation is considered a waveform.
The reason the photons or gamma radiation move in opposite directions is due to the Law of the Conservation of Momentum. If the photons went in only one direction, that would mean there was a momentum in that direction that was not there before the atoms combined.
Antimatter in the Universe
As far as we can tell, the Universe is made up of matter and not antimatter. But it seems strange that there should be a preference of one type of matter over the other. Or is it possible that one half of the Universe is made up of matter and the other half of antimatter?
Suppose when the Big Bang occurred, the matter went in one direction and the antimatter went in the other direction. This would follow from the Laws of Conservation of Momentum and of Energy.
Everything in our part of the Universe could consist of matter and in the other part, antimatter. Since the Universe is expanding, matter and antimatter would not have a chance to mingle and cause problems. Since photons (light particles) or electromagnetic radiation has no antiparticle, it could go from one part of the Universe to the other with no effect.
Is antigravity possible?
There is a theory that perhaps there is an antigravity. In this theory, objects consisting of antimatter attract other antimatter object through antigravity, just as matter attracts other matter through gravity.
If antigravity exists, then antimatter would repel matter. The only way that matter and antimatter would then come together would be when particles and antiparticles collide in an atomic accelerator.
Antigravity could explain why the Universe is expanding and not even require the Big Bang Theory.
Antimatter is matter that is made up of positrons, antiprotons and antineutrons. The behavior of antimatter is the same as matter, except for the electrical charges of the particles. The only antimatter atom made by man is the anti-hydrogen atom. An enormous amount of energy is released when matter and antimatter collide. Although our part of the Universe is made up of matter, it is possible that other parts consist of stars and galaxies made up of antimatter.
Always do a little extra
Resources and references
Antiparticles - HyperPhysics
Antiparticle - Wikipedia
Particle/Anti-Particle Annihilation - Matt Strassler, Physicist
Electron–positron annihilation - Wikipedia
Particle–antiparticle annihilation - Wikipedia
Antimatter - CERN Partical Accelerator
Anitmatter - Wikipedia
The five greatest mysteries of antimatter - New Scientist Magazine
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