On the social construction of electrons

One interesting fact about electrons is that they are all literally identical. And I really do mean completely and literally identical, in the sense of sharing all properties. Yes, even the spatial distribution of their wavefunctions.

To illustrate how this is possible, consider a simple scenario, where we have two electrons, one at point A, and the other at point B. At first it would seem that electron 1 has a different location from electron 2. But in fact, the universe is in a quantum superposition of two states–the first state has electron 1 at A and electron 2 at B, while the second state has electron 2 at A and electron 1 at B. So even though we observe electrons at two distinct locations, the two electrons involved are actually identical.

The fact that electrons are identical has really important consequences.  One consequence is the Pauli Exclusion Principle, which states that no single state can be occupied by two electrons simultaneously. So when we have a large atom, electrons will occupy many different orbitals of the atom, instead of having all electrons occupy the one orbital with lowest energy.

Of course, it’s not really practical to think of it this way all the time. Generally we prefer to think of each electron as being at a distinct location, and then we tack on additional rules like the Pauli Exclusion Principle.

The point is that the individuality of electrons is an idea that arises from practical necessity, and not from the fundamental physics. Practical necessities arise from social context. And in principle, a different social context could have different needs that are better fulfilled by some other way of thinking about it. Therefore, the concept of individual electrons is a social construct.

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Why are physics talks so bad?

As I get closer to the end of my PhD, I wanted to talk about why grad school sucks so much. For my first complaint, let’s talk about physics talks. I’m not referring to popular stuff like Stephen Hawking’s TED Talk or whatever. I’m referring to talks given by physicists to other physicists in their field.

By design, a physics talk starts out with a broadly accessible introduction, and dives into technical details that only two people in the audience understand. This is followed by a Q&A where those two people ask (apparently) extremely intelligent questions, and everyone else silently feels stupid as they listen to arguments over arcane details.

When I started out my PhD, approximately 0% of physics talks made sense. I thought that maybe when I got further into my PhD I would understand much more. Nope! Now, maybe 10% of talks make sense. And even that high rate comes from knowing when to avoid going to a talk in the first place.

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Trump’s past light cone

When Trump was elected, and for many months following, people kept on talking about why he was elected. What caused it? This conversation irritates me deeply, because people lack a base-level understanding of what causation is. But I’ve waited to say anything because I thought it might be too crass to insert a philosophical discussion into a political one, at least while it was still hot.

Cause and effect is often thought to be a fundamental part of the way the world works, but I and other physicists understand that it is not. For a brief explanation, I recommend this video by Sean Carroll. It is better to think of causality as an emergent property, more in the realm of philosophy than physics.

What does physics have to say about the cause of Trump’s election? It’s everything in Trump’s past lightcone! It was the DNC, it was Clinton, it was Comey, it was Russia, it was neoliberalism, it was identity politics, it was ancient supernovae. This answer is rather naive, but what did you expect from us? Physics can’t provide all the answers.

When we talk about causes, we’re typically just selecting a few things from the past lightcone, and highlighting those things as important. In philosophy, this is known as causal selection. Sean Carroll talks a little bit about causal selection. He says that one way of thinking about it is that a cause is something that has great leverage over the future. But that’s just one way we might think about it.

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Quantum games

Last March, I attended the APS March Meeting, which is the largest annual physics conference in the country (and perhaps world?). During the conference, one of the particularly memorable sessions was about quantum gamification, making games using concepts from quantum physics.

Quantum games are an interesting concept, because usually “physics-based games” are only based on classical physics, specifically gravity and collision. The point of having a physics-based game is to have a relatively complex system where you don’t need to teach players every single detail, because they already have an intuition for how gravity and collision work. But obviously, when it comes to quantum physics, players don’t have an intuition, thus the physics must serve some other purpose.

In most of these games, the nominal purpose is either (a) teach physics, or (b) use player data to help physicists. Although I get the sense that the nominal purpose is not always the true purpose. I’m not that confident in the value of collecting player data, and suspect that the true purpose is more about public outreach. And some of the “outreach” projects kinda felt like they were just a way for physicists to do something fun. Well, whatever persuades people to give you grant money.

Anyways, let’s check out some of these games.

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How peer review works

Even if you’ve never been involved in scientific research, you’re probably aware that it involves a process called “peer review”. I want to take a minute to explain how this actually works. This is based on my personal experience, although I think much of it generalizes to other academic fields, including those outside of science.

1. Sending to referees

It starts with the submission of a manuscript to a journal. A lot of work has already gone into the manuscript, including input from collaborators and colleagues, but this is where peer review formally begins.

The journal assigns the manuscript to an editor, and then the editor chooses a few (usually 3) referees to look at the paper. Now, choosing referees can be quite difficult, because they need to be close enough to the field that they can understand and critique the manuscript. In fact, it’s common for referees to decline, because they think the manuscript is too far outside their field. And yet, referees can’t be so close that they’re direct competitors. Authors typically provide a list of competitors to the editor to avoid conflict of interest (or even worse, theft of ideas). But editors aren’t required to follow this advice, and authors never know because they don’t know the names of the referees.

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Physics and p-values

In science, there is something called the “replicability crisis”–the fact that the results of most studies cannot be replicated. This appears to mainly come from psychology and medicine, where meta-studies have found low replicability rates. But it likely generalizes to other scientific fields as well.

At least, when people talk about the replicability crisis, they definitely seem to believe that it generalizes to all fields. And yet, one of the most commonly discussed practices is p-hacking. Excuse me, folks, but I’m pretty sure that p-hacking does not generalize to physics. In my research, we don’t calculate p-values at all!

(Background: p-hacking is the problematic practice of tweaking statistical analysis until you get a p-value that is just barely low enough to technically count as statistically significant. FiveThirtyEight has a neat toy so you can try p-hacking yourself.)

Here I speculate why p-values rarely appear in physics, and what sort of problems we have in their place.
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Stabilizing an inverted pendulum

Like many physicists, I have a fondness for simple physical systems that behave in unexpected ways. Here’s a demo known as “Kapitza’s pendulum”.

For those who didn’t watch the video, it shows an ordinary pendulum attached to a motor. Then the motor starts moving up and down 58 times per second. While the motor is running, the pendulum stands upright, and stays upright even when knocked to the side.

Kapitza’s Pendulum is easily understood by anyone with a degree in physics. But for everyone else, here’s an explanation that could be understood with high school physics.

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