Gravity and Levity

A blog about the big ideas in physics, plus a few other things

Latest articles

How can electrons be “topological”?

The following text is an excerpt from a draft of an article that I co-wrote for the magazine Physics Today, together with Prof. Art Ramirez at UC Santa Cruz. The article will appear (edited, and with more professional figures) in the magazine in September. The article attempts to give some intuition about the concept of “topological” electron bands,...

The Physics Olympiad, and finding community

When I was in high school I spent about 2 hours after school every day running track. This was, on the face of it, an unpleasant thing to do. Running is literally painful, and I devoted something like 10% of my waking life to it. So why did I do so much running? It turns out that there were more or less three reasons. First, I was an ambitious kid,...

What it means, and doesn’t mean, to get a job in physics

I have some reasonably momentous personal news: I got a job. And I don’t just mean that I got a job, in the same sense that I’ve been employed doing research ever since getting my PhD. I got the job: the ostensibly permanent faculty position that so many of us have aspired to (and agonized over) since undergrad. I have accepted a faculty position...

How thick is the atmosphere? A derivation of the Boltzmann distribution

Let’s talk about a small question as a way of introducing a big question. How thick is the atmosphere? How far does Earth’s atmosphere extend into space?  In other words, how high can you go in altitude before you start to have difficulty breathing, or your bag of chips explodes, or you need to wear extra sunscreen to protect your skin from UV damage?...

More people should know about Lagrange multipliers

One of the most useful concepts I learned during my first year of graduate school was the method of Lagrange multipliers. This is something that can seem at first like an obscure or technical piece of esoterica – I had never even heard of Lagrange multipliers during my undergraduate physics major, and I would guess that most people with technical degrees...

Squiggle reasoning: the skydiving animals problem

There is a common conception that physics is a business of writing and solving exact equations.  This idea is not untrue, in the sense that physicists generally prefer to produce exact solutions when they can.  But precise equations can be slow: they are often cumbersome to work with and can obscure important concepts with a tedium of error-checking...

Toward a culture of tolerating ignorance

Lately I have seen an increasingly honest, and increasingly public discussion about the feelings of inadequacy that come with trying to be a scientist. For example, here Anshul Kogar writes about the “Crises in Confidence” that almost invariably come with trying to do a PhD. In this really terrific account, Inna Vishik tells the story of her PhD in...

Good enough for me

Today, April 16, is the one day in the year when I use this blog for very personal purposes.  In particular, I reserve the day for remembering Virginia Tech and my time there.  (Past years’ writings are here: 1, 2, 3, 4, 5). If you’re here for physics-related content, just hold on; a new post should be up within a few days.   On the afternoon of...

Game theory of vaccination

How unreasonable is it to not vaccinate your children? I ask this not as a rhetorical question, but as a mathematical one. How do we describe, mathematically, the benefits and risks of vaccination? What does this description tell us about the reasonableness (or unreasonableness) of not vaccinating? These days, most of the debate about vaccination...

surveyor

There used to exist a really wonderful webcomic called Pictures for Sad Children.  A few years ago its creator, John Campbell, grew tired of the project and removed all of it from the internet.  But the comic was hugely influential, and you can find most of its pieces reproduced online if you do a Google search. Lesser known is the author’s smaller...

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