Silicon’s magnetic properties test quantum mechanics to its limits

The world of physics is a bit like a child's bedroom. After sufficient yelling, everything becomes neat and tidy, but open a drawer or look under the bed and an enormous mess is revealed. The neat agreement between experiment and quantum mechanics is a never-ending source of amazement to me. But obtaining that agreement is a bit like the fraught business of straightening out the mess under your kid's bed.

Often, when we think about advancing physics, we turn to the things we can't explain, like the apparent accelerating expansion of the Universe or the pull of gravity. However, we can also (destructively) test quantum mechanics closer to home by making precision measurements on the properties of atoms and ions (atoms with electrons removed).

But that requires comparing experimental results to calculated outcomes. Actual practical calculations of things like the properties of atoms and ions require taking quantum electrodynamics apart, cleaning out under its bed, and generally getting down and dirty with integrals. The hope is that at the end of it all, we can say something useful about the validity of quantum electrodynamics in our Universe.

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