Hadron Supercollider - How does smashing protons reveal facts of the inception of our universe?

Question

How does smashing protons at high velocity reveal how our universe was formed? At some point, wouldn't the atoms need to come together in order to form planets etc? I am a curious student- not a physicist.

Answer 1

The current cosmological model, lovingly called "the big bang", assumes that the universe went from a very hot, very dense state to the currently observed state of low density and low temperature. So far everything that we have learned about physics tells us that this cooling process was fairly "smooth", with exception of a very rapid early phase that is called "inflation". We know very little about the physics during inflation.

Some time after inflation was finished, however, the universe would have gone trough a number of so called "eras", during which different physical effects dominated that are accessible to us experimentally. One of these eras happened at energies and densities that we can partially re-create in very small volumes in our accelerator experiments. So that's basically the time of the early universe that we can study by smashing protons together at LHC.

Later times (at lower energy and density) can be studied with nuclear physics and plasma physics. And in order to learn something about ever earlier times, we need particles with ever higher energies, far higher than those than can be made in an accelerator like LHC at the moment. Some of that data can come from cosmic ray observations and, hopefully, we will have future accelerators that will allow us to look back that far.