The evidence for the Big Bang is overwhelming, but the exact details on how the universe we all know and love came to be are still a bit vague.

One particular phase, which we are currently beginning to test in the lab, is the Big Bang nucleosynthesis, the time when the first nuclei came together. This happened between a few tenths of a second and about 20 minutes after the Big Bang, when the universe was billions of degrees above zero.

In a paper published in Physical Review Letters, William Detmold from MIT and his co-authors show how their novel approach, called lattice quantum chromodynamics, can be used to reproduce the nucleosynthesis process in an accurate way.

"You start off with very high-energy particles that cool down as the universe expands, and eventually you are left with a soup of quarks and gluons, which are strongly interacting particles, and they form into protons and neutrons," Detmold said in a statement. "Once you have protons and neutrons, the next stage is for those protons and neutrons to come together and start making more complicated things – primarily deuterons, which interact with other neutrons and protons and start forming heavier elements, such as Helium-4, the alpha particle."

The code tested in this mimics the interaction between the fundamental quarks and the gluons, which are carriers of the strong nuclear force. As the name suggests, they “glue” the protons and neutrons together. To make the calculation computationally cheap, the team considered quarks with 10 to 20 times their physical mass.

"For simple things like calculating the mass of the proton, we just put in the physical values of the quark masses and go from there," added Detmold. "But this reaction is much more complicated, so we can't currently do the entire thing using the actual physical values of the quark masses."

Although the calculation doesn’t obtain the correct physical numbers, it correctly reproduces the process through direct calculation. This opens the door to calculating the values of other processes that have not been measured experimentally yet.

This approach shows that we can model the true nature of complex nuclear reactions from their fundamental components (quark, gluons, and their interactions) without having to resort to too many oversimplifications.