I didn’t write about the Nobel Prize in Physics the day it was awarded because it was awarded in an area of physics that I’m not very familiar with and I needed to educate myself.
The area concerned is “topological phases and phase transitions” in matter. It is not entirely unknown to me. Steve Bramwell, a leading expert in the field, is a member of my department at UCL, and I was fortunate to hear him speak about his work. He’s been pretty busy doing interviews since Tuesday and is quoted here in the Guardian article about the price.
While trying to educate myself, I came across a great explanation of the general ideas behind the award from Brian Skinner at MIT, and I don’t think I can improve it. If you want to understand the ideas and why they are important, I heartily recommend his article (written before the award ceremony) ¹.
Without rehashing that, I just want to add something that really fascinates me about this type of physics.
A key concept is the idea of topological defects, illustrated in Skinner’s article by a flaw in a zipper or a swirl in a field of arrows. These defects have many of the same features that we see in the so-called “fundamental” particles of the Standard Model of Physics. Some of the mysterious properties of these particles become a little more intuitive when the particles are represented as vortices.
For example, the ‘Pauli Exclusion Principle’ prevents electrons from overlapping and forces them to occupy different energy levels around the atomic nucleus. These energy levels are responsible for all of the chemical properties of the elements in the periodic table, so it is an important principle to understand. I have a hard time imagining how this could work for fundamental electrons. However, if you look at the eddies in Skinner’s illustrations, it’s easy to see why they can’t get too close – the arrows are simply pointing in the wrong direction.
These topological ideas even naturally give rise to the idea of quantization itself. You can’t gradually switch between two topologically different shapes – for example, a bagel and a Swedish pretzel (see video). You have to make a quantum leap. In topological terms, you need to connect or disconnect.
So from one point of view this physics looks more fundamental than the search for the smallest constituents of matter. It is the physics of deep principles that these constituents seem to obey.
On the other hand, all discussion of these principles in relation to zippers and arrows (or bagels) assumes that the zippers and arrows and the forces exist between them. The experimental observations and applications are seen in solids, and the little arrows are magnetic atoms or molecules. All of them have to be made of something, and in the end they are made up of the quarks and electrons of the Standard Model. Once you get to that stage, all you have to do is say that electrons behave like defects in a quantum field. You don’t have a mechanistic model for this field so call it basic. Indeed it could be.
I’m just saying that there are two senses in which physics can be “basic”. The question arises, what is the core of everything – what are the smallest parts of the universe? But there are also rationale that work in many different systems on many different scales.
These topological phases are the expression of some new principles with far-reaching consequences. That is why its discovery is so important.
¹ Its swirling arrow diagrams are also beautiful to look at. One of the key achievements behind the award is the ‘Kosterlitz-Thouless phase transition’, which corresponds to a temperature at which eddies and anti-eddies separate from each other. This is illustrated by the nice animation in the middle of the article. Thanks to Stephen Curry and Aatish Bhatia for bringing this article to my attention.
Jon Butterworth’s book Smashing Physics is available in Canada and the United States as “Most Wanted Particle”.