For much of human history, we have subscribed to the notion of the infinite.
The universe is infinite in size. Matter can be cut up into infinitely smaller and smaller slices. The past is infinite with no beginning.
Much of this can be attributed to the Greek philosopher Aristotle and this view has impacted our modern lives. Many people still believe in the infinite. They argue we will never run out of fossil fuels or fish in the seas or animals on the land, despite all evidence to the contrary. They also argue the only way forward economically is through perpetual inflation.
However, with modern science, we now know there are limits. In particular, the universe had a beginning in a singularity which "exploded" and brought forth all that is.
I put exploded in quotes because it was not an explosion in the same sense as we might see in the movies or at a mine site.
For one thing, it was both much smaller and much larger than anything we can imagine. For another, it wasn't an explosion into anything else. That is, it wasn't a Death Star scattering into fragmented pieces against the backdrop of a black universe.
The big bang created the universe and as such it created all of the space and matter within itself. It was over in a matter of minutes by our reckoning although it took a few hundred thousand years before the universe eventually settled down to contain atoms and molecules.
We have a fairly good theory for how this all might have occurred, but there is one aspect still plaguing modern science.
We know energy can be used to create matter - this is what Einstein's famous equation tells us. Energy and matter are related to one another by the square of the speed of light or a factor of about 10 to the seventeenth power.
But every experiment carried out so far indicates when creating matter, we also create anti-matter.
For every particle created, we also get an anti-particle. Furthermore, when they meet, these particles collapse back to the energy from which they were made.
If this is the case, though, why is there any matter in the universe? If the energy of the big bang generated all of the matter in the universe, it should have created an equal amount of anti-matter.
The collision of the matter and anti-matter particles should have resulted in annihilation. The universe should be filled with nothing but photons.
The Standard Model contains a small asymmetry in the Weak Force, which allowed for one more particle of matter out of every billion pairs of matter and anti-matter.
That tiny amount - a one part per billion discrepancy - may have been enough.
Of course, theories need to be tested.
At CERN, the scientists are making anti-hydrogen atoms and with care even anti-hydrogen molecules. It is not easy work. Hydrogen is composed of an electron orbiting a proton. It is the simplest of all atomic structures.
Anti-hydrogen is made by getting a positron to orbit an anti-proton. Both of these components can be made fairly easily at CERN. However, they are moving close to the speed of light when they are created.
They need to be decelerated quickly in a manner which does not bring them into contact with any matter.
For the scientists at CERN, manipulating charged particles is fairly straightforward.
The tricky part comes when they are combined to form neutral anti-hydrogen atoms. A special magnetic trap needed to be constructed which would hold the atoms in place. As a result, it takes 90,000 positrons and anti-protons to generate 25,000 anti-hydrogen atoms, but of these only 14 are successfully slowed and trapped during each trial.
The results are worth it, though, as the hydrogen atom is one of the best understood objects in our universe. Its spectroscopy has been measured with a precision on the order of parts per billion or parts per trillion.
Last January, scientists reported the results of their observations for the 1s-2s transition for anti-hydrogen. Within the present experimental limits, they match the spectra for hydrogen exactly. The results provide further validation of the Standard Model for physics.
More experiments will need to be carried out and other spectroscopic transition examined before anti-hydrogen and hydrogen can be declared as twins.
Still the experiments on symmetry and tests of the theory are certainly reaching maturity at CERN.
In conjunction with other work on the antiproton-electron mass ratio and the antiproton charge-to-mass ratio, work on antihydrogen may answer questions on the fundamental symmetries underlying the universe. The answer to why there is matter in the universe may be within reach over the next decade.
Of course, matter only makes up a small part of the universe. We still don't understand dark matter and dark energy.
