The Weight of the Proton

The proton has been measured and found lacking in weight. The difference between the expected weight and the measured weight was a full three standard deviations, which means that the proton was substantially lighter than previously thought.

At first glance, this may not seem like a big deal. However, the implications of this when it comes to theories related to nuclear fusion and stars are significant.

According to the standard solar model, stars are fueled by hydrogen fusion in a super dense and super hot core. Mass of single protons are turned into heat through a two step process in which four protons and two electrons are fused together to produce helium.

Atomic nuclei of hydrogen, deuterium, helium, lithium and beryllium

First, energy is spent in order to fuse two and two protons together to form deuterium. Then, energy is released when two and two deuterium atoms are fused together to form helium.

The overall process is exothermic, but with the proton smaller in mass than originally thought, the energy that can be released through fusion is smaller as well.

This follows directly from the energy equation E = mc². If the mass of the proton is smaller, the energy associated with it is correspondingly smaller.

The fact that single protons are lighter than thought is a big deal. It puts the standard model of stars into doubt, and it makes controlled hydrogen fusion less likely to deliver on its promise of limitless free energy.