Nicole Ackerman | SLAC | USA

Physics is like…

A lot of topics in physics are explained through analogy. While objects rolling down a ramp or colliding are phenomena people have experience with every day, quantum mechanics and relativity are not part of our daily awareness. They are introduced, conceptually, through descriptions we can understand but that don’t fully encompass what is going on. But seeing as “time slows down” and “the cat is both dead and alive” are hard enough to figure out, the analogies are a good place to start.

Non-quantum cats (in Erice)

Particle physicists spend a lot of time on analogies, likely because our work is so far from what most people deal with daily and requires relatively advanced math. While I think neutrino mixing is ‘straight-forward’ and easy to understand from the math, those equations won’t help my non-physics family and friends. How then, can we explain it? At the International Nuclear School in Erice, Prof. Christian Weinheimer presented an experimental parallel with polarized light. A laser beam is polarized, passed through a birefringent crystal, and then split to have each polarization measured with photodiodes. While his talk was geared towards neutrino physicists, the hope was that we could take the technique back and present it to advanced high school and early university students. I’m not sure how many high school students in the US understand polarized light, but it should certainly work with early university students. Not only is the mixing conceptually similar, but the math works in a very similar way as well.

I find myself attempting to explain my experiment and the physics I work on to people who have not had university (or even high school) physics. I think I have finally come up with a good analogy for the design of EXO-200, a time projection chamber. While scintillation light and ionization are not familiar to many people, lightning is. When a decay occurs in our detector, it is like a flash of lightning. The light we see is immediate, followed some time later by the ‘thunder’ (for us, ionization). By measuring the difference in time between the ‘lightning’ and ‘thunder’ we can tell how far away the decay occurred. The biggest flaw in this is that normally light gives information about how big and what orientation the lightning strike was, while thunder only gives a rough direction. For us, it the other way around – the light can’t tell us much about where the decay way but the ionization (‘thunder’) does.

Hopefully I will improve my own physics analogies over time, or hear good ones that others have developed. My recent favorite is comparing dark matter to the unsocial people at a party. Not only does it capture the physics – freeze out, unseen interactions – it also brings to mind the anti-social stereotype that haunts physicists. This should make the analogy easier to remember! My current quest is to find a good analogy for the Taylor Series Expansion. Given enough time and something to write on, I can explain it to someone who knows what the sine wave is. I haven’t found a good way to explain it quickly – to cashier at a store – or to someone who doesn’t know about the sine wave.