Skip to content

Outreach

Diversity and inclusion

  • 2024-present: UoU PASSAGE President
  • 2023-2024: UoU PASSAGE Member
  • 2021-2022: CRC-TR211 Equal Opportunity Committee Member
  • 2017-2018: APS Academic Peer Mentor
  • 2016-2018: APS Bridge Program Mentor

Science Slams

Science Slams are a German outreach program inspired by poetry slams. The idea is you try to give a short public talk that is accessible and entertaining.

Blog posts

In this section I collect attempts to take topics related to my research and make them accessible to a general audience.

Hair's breadth precision

My dad was a manufacturer who ran his own business doing contract work for other nearby companies. These companies would make, for example, some of the parts needed for machines used in factories to create soda cans. One thing that he was always very proud of was the precision with which he could make these parts; in particular he would brag that his product matched specifications “to within a tenth of the thickness of a human hair”. This might seem mundane to some of you engineers, but it is actually a rather impressive feat, especially when you try to visualize how tiny a hair’s breadth is compared to, for example, the soda can.

To see how impressive this feat is, let’s compute the relative precision necessary to manufacture a can to within a tenth of a human hair’s thickness. (This is not exactly the problem they were solving, but it is close enough for point of this discussion.) The largest dimension of a typical North American drink can is its height, which is 12.3 [cm] or 1.23 x 10-1 [m]. Meanwhile a nominal width for the thickness of a human hair is 75 [μm] or 7.5 x 10-5 [m]. This comes out to a relative precision of

rel. prec. = 6.1 x 10-4,

or about six parts in ten thousand! If that number doesn’t mean anything to you, you can get a visual impression of it by simply placing a soda can on top of one of your hairs. Can you tell that the soda can is sitting crookedly, albeit only very, very slightly? I didn’t think you could.

I would now like to connect this story with precision physics. Our current best theory of particle physics is known as the Standard Model (SM). How good is it? Well dear reader, it describes a rather imposing five percent of all matter and energy that exists in the universe. Oh also it doesn’t describe gravity, or explain why there is more matter than antimatter, or explain how neutrinos get their masses. Actually there is a whole laundry list of problems with the SM, which motivates modern high-energy physicists to find so-called Beyond Standard Model (BSM) theories.

Nevertheless we still trust the SM. There are many reasons for this, but the primary reason is this: it gives accurate experimental predictions for physical processes involving, and characteristics of, the fundamental particles that we know for sure exist. These predictions range in precision, but the most precise is that of the electron anomalous magnetic moment.

What is this quantity? The magnetic moment of a charged particle is the torque that particle experiences when you turn on a magnetic field. The electron, being a charged particle, has its own magnetic moment that can be calculated classically. If you repeat this calculation in quantum field theory aka QFT (QFT is the framework on which the SM is based) and are as “lazy” as possible, you will find that the classical result for the magnetic moment changes by an overall factor. We call this factor g, and if you are lazy, you get g=2. If you are more enterprising, you can do harder calculations in QFT to find that g is very slightly different from 2. We label this deviation from 2 “anomalous”, and hence we call (g-2)/2 the “electron anomalous magnetic moment”.

The electron anomalous magnetic moment is, to my knowledge, the single most precisely measured quantity in history, and it agrees with the prediction from theory to more than 10 significant figures. As of the time of this writing, the relative precision with which the electron anomalous magnetic moment is measured is

rel. prec. = 7.3 x 10-13

or about 7 parts in ten trillion. This is about a billion times more precise than the machining of the soda can.

Perhaps we will one day discover a more sophisticated theory than the SM that solves or explains all the issues listed above. But we will never be rid of the SM entirely; it delivers some of the most accurate and precise predictions ever made, so in that regard, it describes reality better than any other scientific theory. Hence it will be an important limiting case of BSM theories, and it will likely continue to be useful at energy scales currently accessible to us.

We’ll probably keep making soda cans about the same though.