Are you a fan of Star Trek? If you are or if you have ever seen it, you surely know that their spaceship, the Enterprise, runs on antimatter: the reactors rely on matter-antimatter annihilation (total destruction) for energy production.
Even if you have read Angels and Demons by Dan Brown, you probably remember that the protagonist, Robert Langdon, was chasing a man who had stolen a cylinder containing antimatter in order to destroy Vatican city.
But what is this so famous antimatter and who discovered it?
Dirac was the first physicist who hypothesized the existence of antielectrons (antiparticles endowed with the same electron mass but with a positive charge) studying the movement of electrons; this theory was later confirmed by Carl Anderson, who discovered positive electrons, named positrons. Other physicists discovered antineutrons, antiprotons and antihydrogen atoms , so Charles Janet envisaged a complete periodic table of antimatter.
Nowadays, some physicist have hypothesized the possible existence of antiplanets, antistars, antigalaxies and even an antiuniverse! Their aspect would be very similar to our universe, galaxies, etc., so no one could distinguish its real content.
I think that an example will clarify the concept of antimatter: imagine you stamp out a coin from a metal sheet: you get a coin and a hole in the sheet that we can call “anticoin”. This is what happens when energy transforms into matter: you produce both particles and their mirror images, antiparticles. Energy is necessary to create them, so when you bring them back together (the annihilation that fuels Star Trek Enterprise) this energy is released, as if you put the coin back into the hole and you get the original metal sheet.
All the particles around us were created from energy just after the Big Bang, indeed according to Einstein’s theory (E = mc2 ) mass is concentrated energy. New particles and antiparticles were created thanks to the very very high temperature, and then annihilated back into energy.
Matter is always created with antimatter, so originally there must have been the same amounts of particles and antiparticles. However, scientists haven’t yet discovered why this symmetry was broken and matter “won” over antimatter: for every billion antimatter particles, there were a billion plus one matter particles. But what has become of all antimatter particles? They were transformed into energy after the annihilation with the matter particles; one second after the Big Bang temperature had dropped too low to create new particle-antiparticle pairs and only that small surplus of particles survived. The result of matter-antimatter annihilation is the cosmic background radiation, while we’re all made from the remaining matter.
A source of antimatter are cosmic rays: when they hit the outer atmosphere, they’re mainly fast-moving, high-energy protons; then they collide with atoms in the air and some of the collision energy transforms into new pairs of particles and antiparticles.
The most important laboratory where physicists always “play” with particles and antiparticles is CERN (European organization for Nuclear Research) in Switzerland. Their goal is to know these particles better and to understand what we and the universe are made of. The recent progress of this organization is remarkable, for example researchers have captured some antihydrogen atoms for 16 minutes last summer: they’re made up of positrons and antiprotons and they’re contained in complex traps called magnetic bottles.
When electron and positron meet they annihilate, but, at high energy, they can rematerialize as new particles and antiparticles: this is what happened at Cern; at a low energy, however, it’s used in different ways, for example to study how the brain works in the technique called Positron Emission Tomography (PET).
If the mixing of matter and antimatter is the most powerful source that a starship could use to travel huge distances every week, why don’t we use it as fuel? I think it’s a bit complicated because it’s difficult to produce, but I guess that scientists will find new ways to get it in the future.
Can you imagine a universe powered by antimatter?
Science fiction is not so far away…
Look at this interesting video in which Fermilab scientist Don Lincoln describes antimatter and its properties.