Setting: a small old-fashioned but very tidy office. Its narrow window overlooks a big city. The walls are decorated with framed certificates, a few family pictures, and a majestic portrait of Emperor Wilhelm II. At the massive wooden desk in the middle of the room sits a small middle-aged man, dressed in very accurate clothing and wearing half-moon spectacles. He now sharpens a pencil, wipes the shavings methodically into a tray specifically allocated for that purpose, and proceeds to scribble a few notes onto a document in front of him. After a short while he presses a red button to his si ..read more

It’s that time of the year again: grad school applications are soon due! You have dutifully selected a good set of schools, following the “reach/middle/safe” principle; you’ve secured writers for your letters of recommendation; you’ve filled out many forms; maybe you also have submitted GRE or TOEFL or IELTS scores—and now you look with dread at that pristinely empty text document on the screen in front of you, titled “Statement of Purpose”. The cursor goes blink, but your mind is blank. To be honest: I don’t know for sure what that feels like. I have never applied for graduate school in the ..read more

Warning: this post is a bit wonkish. Math ahead!  Controlling the Covid-19 pandemic requires testing and contact tracing, but the usefulness of tests declines if getting results takes too long: a week is no longer unusual, and there have been reports of three week waits. Given that the standard PCR tests, which try to identify viral RNA in the sample, involve sophisticated biochemistry that requires ingredients that are in limited supply, one wonders: aren’t there simpler, faster tests? There are: antigen tests, which instead look for viral proteins. But the problem is that they are n ..read more

This blog post started as a humble thread on Twitter, which turned out to be unexpectedly popular. Several readers commented that the subject might be easier to digest in a format that’s more appropriate for long-form presentations. And so I’ve decided to port the content to this blog, too. The main theme is of course the same: I’d like to expose you to one of the many fun quirks of special relativity—velocity addition—and then try to convince you that the result is actually not quite as weird as it appears at first look. (Actually, towards the end I’ve collected a few additional thoughts, m ..read more

The arrival of several highly effective vaccines has dramatically changed the landscape of the Covid-19 pandemic. Remarkably, though, a considerable fraction of people are hesitant to get immunized—for reasons that would be fitting material for a different blog post, but which right now I will sidestep. What interests me here, instead, is how this hesitancy affects the ongoing pandemic—especially in the light of common statements we hear very often in this context. For instance, Dr. Rochelle Walensky, director of the CDC, has warned that Covid-19 is becoming a “pandemic of the unvaccinated ..read more

by Markus Deserno One of the fundamental facts of statistical physics is that microscopic systems are subject to constant thermal fluctuations. They are fundamentally random, but still exhibit many regularities that permit us to learn a great deal about those systems. For instance, any individual quadratic degree of freedom of the form $\frac{1}{2}Kx^2$ has an expected value of the energy equal to half the thermal energy, or $\frac{1}{2}k_{\rm B}T$. This so-called equipartition theorem in particular implies that we can measure the spring constant $K$, provided we can measure the variance o ..read more

by Amirali Hossein Biological lipid membranes divide eukaryotic cells into compartments with specialized functionality and play a central role in controlling the flow of matter and information between them. Their main building blocks are hundreds of different types of lipids, and the lipid composition of the two leaflets of many bilayer membranes is known to not be the same. This asymmetry is believed to be present in all domains of life and therefore ought to play an important functional role. While there are various proteins responsible for transporting lipids between membrane leaflets ..read more

A delightful pastime in mathematics is to think about really big numbers. And unlike many other mathematical mind games, this is one that has captured the imagination of a much wider community. It is fun to think about a million, a billion, or a trillion, and then picture how big they are, and how much bigger each subsequent number is than the previous one. This game is hard to continue, though, simply because we run out of names. The next step is huge powers of ten. A thousand is $10$ times $10$ times $10$, or $10^3$. A million is $6$ such factors, $10^6$, and a billion and trillion are ..read more

Towards the end of the year, here’s one more blog post that’s a bit wonkish, but teaches an important lesson. It’s about statistics, and about one of the many ways in which it can be counterintuitive. Almost all statistics discussed in the everyday press deals with averages, and maybe fluctuations around averages. As we all know, this can already be confusing enough. But here we wish to deal with the opposite problem: instead of wanting to know what will most likely happen, we will be interested in events that are very rare. In other words, we want to focus on the stuff that is exactly the o ..read more

by Samuel Foley Lipid membranes are fundamentally important structures in all branches of life. Not only do they form the boundary of living cells, they also perform a multitude of roles within them. To deeply understand these fluid membranes and their properties is then essential for explaining the mechanics of life at these scales. An important property of biological membranes which has recently moved to the forefront of research is the asymmetry of their constituent layers, as discussed in a previous post on this blog. While experiment will always be the gold standard of scientific kn ..read more