There’s a well-known refrain in a song from The Sound of Music that suggests “nothing comes from nothing.” This phrase could just as well have been sung by a physicist. There is something inherently wrong with the idea that something comes from nothing.
There is a principle of physics that whenever we see a particle of matter created out of the vacuum of space, we expect to see an antimatter particle created at the same point of space.The matter and antimatter can annihilate to form pure energy. So we never see a matter particle created without its partner, an antimatter particle.
The announcement this month by the leader of the Alpha Magnetic Spectrometer instrument, put into space last year by NASA, stated that they see more high-energy positrons (the electron’s antiparticle) than expected by theory. The question is: Where are these antimatter particles coming from?
The AMS results are solid and leave no doubt that there are lots of high-energy positrons coming in at all directions from sources outside the solar system. What AMS really measures is the ratio of electrons to positrons.
Theoretical calculations predict that this ratio should get smaller as the particle’s energy increases. But the AMS data show that the ratio starts to drop, then starts to rise at high energy. This suggests that there is some unknown source creating high-energy positrons without creating the corresponding electrons. Could it be that collisions between dark-matter particles are causing this excess of positrons from space?
Since we don’t know anything about dark matter — even if it’s a particle — then perhaps the physics of dark-matter collisions is different from the usual laws of physics.
Whatever the mechanism is for dark-matter collisions, we can only guess for now. Although there are laboratory experiments being done to search for such collisions, so far we have come up empty-handed.
Meanwhile, we have some hard data from AMS that outer space is a bit stranger than we expected. Something out there is creating these high-energy positrons, and we don’t know what it is.
This brings me to another strange question: Why are we even here? As I mentioned before, the current laws of physics say that when a particle is created from a source of energy, its anti-particle is created at the same time.
So where is all of the antimatter? If there are equal amounts of matter and antimatter, then these should annihilate each other, leaving a universe of pure energy. The fact that you’re reading this column is proof that the universe has more matter than antimatter. How did this happen? It turns out that there is a known law of physics that allows for a tiny asymmetry in how matter and antimatter are treated. It goes by the name “CP violation,” and its mathematics is devilishly difficult to describe.
However, the main point here is that this small violation is not sufficient to explain the matter dominance of the universe. This suggests that something is missing in the known laws of physics.
So where does this leave us? My answer is that the universe is a much stranger place than you might think. That is, unless you happen to be a dark-matter theorist.
Kenneth Hicks is a professor of physics and astronomy at Ohio University in Athens.