The scientists working at CERN, the European Organization for Nuclear Research, recently made headlines by announcing that the universe should not exist.
Christian Smorra, a researcher at CERN, said, “All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist.”
Particle Theory 101
Most students learn in elementary school that atoms are made of electrons, neutrons, and protons. Later on, they find out that neutrons and protons are made of smaller particles called quarks. These fundamental particles make up everything in everyday life, including people, plants, and planets. Scientists call this matter.
But the universe contains more than just matter. It also contains antimatter. Antimatter is composed of antiparticles, which correspond to particles of ordinary matter. These antiparticles contain many of the same properties of particles, but with opposite charge and different quantum numbers. For example, electrons have antielectrons (called positrons), which have the same mass as electrons but opposite charge. Similarly, neutrons have antineutrons, and protons have antiprotons. From these antiparticles, we could create anti-atoms.
In fact, using antiparticles, we could, in theory, construct an entire anti-periodic table with elements of anti-hydrogen and anti-oxygen. From this table of elements, we could, in theory, create organisms like anti-bacteria, anti-dogs, and even anti-humans.
An Observation
Scientists have discovered that the universe is almost entirely composed of ordinary matter. Antimatter is extremely rare in the universe.
This observation has left scientists scratching their heads. According to the Standard Model of physics, the early universe should have produced equal amounts of matter and antimatter when it formed. But therein lies the problem. When matter and antimatter collide, they annihilate each other.
High-energy photon collisions in the early universe produced particle and antiparticle pairs. But as soon as these pairs collide, they produce photons again. Eventually, the photons in the universe do not have enough energy for particle/antiparticle pair production and only a sea of cooling photons remain. This phenomenon is being experimentally tested at the particle accelerators at CERN.
So, why is there a universe? The short answer is, we don’t exactly know. If the Standard Model is correct, this universe should be nothing but radiation. But it’s not. It’s full of matter, which is a necessary ingredient for life.
Here’s what we do know. There must have been an asymmetry in matter/antimatter pair production. In fact, scientists are able to measure that our universe contains one particle for every billion photons. That is, for every billion anti-particles in the early universe, there were a billion and one particles. This exact ratio would leave the amount of matter and radiation in our observed universe.
Scientists still don’t know what caused this precise asymmetrical ratio. All experimental results point towards symmetry, not asymmetry. Again, Smorra says, “All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist.” He goes on to say, “An asymmetry must exist here somewhere but we simply do not understand where the difference is. What is the source of the symmetry break?”
Asymmetry and Fine-Tuning?
While the source of the asymmetry is not known, this might suggest another case for fine-tuning for life. Obviously, if there is no matter, there can be no life. Life needs matter. Therefore, the asymmetry is a necessary condition for a life-permitting universe.
After asking the question why asymmetry, it’s natural to ask, why this asymmetry? Why one part in a billion? Why not one part in a million, or one part in a trillion, or one part in two?
Our current understanding suggests this is an important ratio for life. A lower matter/antimatter asymmetry results in a universe that contains too little mass, and nothing of interest forms. No planets. No stars. No galaxies. On the other hand, a higher asymmetry results in a universe that would produce too much mass and is too dense for life.
As I said, this suggests fine-tuning, but the physics behind what actually caused the asymmetry is not yet understood. Until then, we’ll have to withhold judgment.