There’s been a bit of buzz this week about an experiment that has created a “magnetic wormhole” (which was actually released several weeks ago, as you can see from the date on that story, so I’m not quite sure why it’s making news now…). This is analogous to the spacetime wormholes that are a staple of science fiction, only rather than carrying Matthew McConaughey to a giant black hole without passing through the intervening space, it transports a magnetic field from one side of an apparatus to the other without producing any detectable field in between.
This joins a list of other experiments that have observed analogues of exotic phenomena inside other forms of matter– the most recent of these is the discovery of “Weyl fermions,” the subject of a bunch of papers in Nature Physics and this Physics World story (a more technical writeup is available from Physics, as well, which includes a PDF of one recent experiment). There have also been some high-profile experiments making magnetic monopoles, inside solid matter, and in a dilute vapor Bose-Einstein Condensate (the latter experiments included a visiting professor at Union, which is cool).
I’m not going to go into the technical details of these, which are extremely complicated, but the collision of the Weyl fermion and magnetic wormhole pieces in my social media feeds reminded me of a general point that I think is worth a blog post. Back at the Schrödinger Sessions, Prof. Jimmy Williams of JQI (not this kid) gave a talk about condensed matter physics including an excellent introduction to this sort of stuff. At the time, I said “I’m totally going to
steal \borrow that for a blog post,” and now I will…
Prof. Jimmy Williams talking at the Schrodinger Sessions. (Photo by Chad Orzel)
Prof. Jimmy Williams talking at the Schrodinger Sessions. (Photo by Chad Orzel)

The fundamental problem of condensed matter physics is describing the behavior of particles in vast numbers coming together to make a liquid or solid. This is, in principle, a tremendously difficult task, as it involves far too many particles to count– all the electrons and all the nuclei inside whatever you’re trying to describe– and all of them are charged particles that interact with each other via the electromagnetic interaction.Williams pointed out in his talk, though, that if you just start with the simplest, stupidest spherical-cow approximation you can imagine– that is, saying that the atomic nuclei are fixed in place and the electrons are free to move through the resulting matrix without interacting– it works surprisingly well to describe the properties of electrical conductors. We make heavy use of this in our introductory physics courses, because you can understand a lot of material properties just by thinking of conductors as containing electrons that rattle around inside the material moving more or less freely– I wrote up a blog version of this many years ago, explaining how the microscopic motion of
electrons leads to Ohm’s Law.