Lattice Nuclear Physics (feat. The Anthropic Principle)

“I’m not a religious man, but if I was, let’s just say that this would be very compelling” – Computational Lattice Gauge Theorist

The spectrum of QCD bound states’ energy levels scales linearly with the input quark degrees of freedom masses, which come directly from the Higgs Mechanism (2013 Nobel Prize) of Electro-weak Symmetry Breaking. Consequently, as the quarks’ acquired Higgs Mechanism induced masses grow, the energy spacings between the Quantum Chromo-Dynamics (QCD, just the more complicated quark-gluon version of electromagnetism we all know and love) bound states also grows. In Lattice QCD, using larger quark masses than what really exist in our universe makes the computational load much more bearable, however doing so also yields basically just Helium nuclei as the available final states, rather than the rich spectrum of final states we are made of and which comprises almost all matter around us (Wikipedia article on the chart of the nuclides). For example, according to a 2013 lattice chiral Effective Field Theory calculation, Epelbaum, et. al. found that life as we know it is only stable to within 2-3% variations of the fundamental parameters of electromagnetism and the quark masses. instead of getting a Carbon-12 nucleus you would just get 3 unbounded alphas (freely moving helium nuclei as pictured below) and most of chemistry and nuclear physics would be totally different.

The standard nuclear reaction process taking 3 Alpha’s and making 1 Carbon-12 nucleus, which theoretically gets modified and ceases to occur spontaneously if the quark masses are taken to be heavier than the observed values. See this set of slides, which get into the Anthropic Principle around slide 45 or so.

Why is our universe the way it is… why does nuclear matter and chemistry sit at just the right set of parameters such that large and complex interactions are possible, instead of just a boring wash of simple particles everywhere? This is another great example of the Anthropic Principle, wherein the fundamental physics that everything around us depends upon looks suspiciously like it is fine tuned to support our existence as we investigate it. The principle argues that this is because all other places or alternate universes that couldn’t support life just don’t have intelligences there to ask why, and so of course the fact that we are able to ask means that our universe is already one of a very small slice of parameters to describe fundamental physics in a livable universe.

However, and most controversially, if you like, you can attribute the many such cosmic coincidences to a higher power or intelligence. Technically that isn’t a valid scientific postulate, but really neither is the Anthropic Principle when stated as such, so it doesn’t really hurt to think about things this way and it is certainly more entertaining to do so. Either way, there is still, as of yet, no satisfactory physical explanation for a great number of the apparently convenient oriented values that so many of these quantities take, which is one of the reasons it is so much fun to study fundamental physics. We have before us some very interesting and often existential questions which can be investigated, and sometimes even answered, with mathematics and experiment by utilizing the scientific method. I invite you to investigate such matters for yourself (this may provide an interesting starting point if you haven’t heard much about the Anthropic Principle before) and to come back here often as I continue to investigate whatever interesting developments in physics I stumble across in my studies.

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