New high-speed video reveals the physics of a finger snap

It all happens in a snap. New high-speed video exposes the blink-and-you’ll-miss-it physics behind snapping your fingers.

The footage reveals the extreme speed at which the gesture occurs, and shows that friction plus the compressibility of the finger pads are key to humans’ ability to snap properly, researchers report November 17 in Journal of the Royal Society Interface.

Finger snaps last only about seven milliseconds — that’s roughly 20 times as fast as the blink of an eye, says biophysicist Saad Bhamla of Georgia Tech in Atlanta. After slipping off the thumb, the middle finger rotates at a rate up to 7.8 degrees per millisecond, nearly what a professional baseball pitcher’s arm can achieve, the team found. And a snapping finger accelerates almost three times as fast as pitchers’ arms.

When covered with high-friction rubber or low-friction lubricant, fingers made snaps that fell flat, the team found, indicating that bare fingers have a level of friction ideal for a speedy snap (SN: 8/1/19). That friction between thumb and middle finger allows energy to be stored before it’s suddenly unleashed. Too little friction means less pent-up energy and a slower snap. But too much friction impedes the finger’s release, also slowing the snap.

Bhamla and colleagues were inspired by a scene in the 2018 movie Avengers: Infinity War. The supervillain Thanos snaps his fingers while wearing a supernatural metal glove, obliterating half of the universe’s life. The team wondered if it would be possible to snap while wearing a rigid glove. Typically, when the fingers press together in a snap, they compress, increasing the contact area and friction between them. So the researchers tested snapping with fingers covered by hard thimbles. Sure enough, the snaps were sluggish.

So Thanos’ snap would have been a dud. No superheroes needed: Physics saves the day.

How social stressors mark our genes

Jenny Tung
Evolutionary anthropologist
Duke University

Jenny Tung, featured in 2018, studies how social environments — including social status, relationships and isolation — influence primates’ genes and health. Her study subjects have included captive rhesus macaques and wild baboons.

What has been the most notable progress in your work since 2018?
We have built layers of complexity onto [our] initial story. A few years ago we were showing that it’s possible for social interactions to have profound effects on the function of our genome. And now we’re trying to derive a much better understanding of how and why and when, and what are the exceptions.

The other thing I’m really excited about is our ability to move away from this very powerful but very artificial system using captive primates and to ask about what’s going on in the field with wild monkeys. I’ve studied wild baboons in Kenya for many, many years. We know a lot about the social environments, the social experiences. And now with the ability to collect some simple blood samples, we’re also seeing strong signatures of things like social status and social integration, social bonds, social connectedness in the function of these animals’ genomes. That’s pretty exciting because lab studies are powerful and wonderful, but there’s always this question of, “Well, is this real in the real world?”

You were named a MacArthur Fellow in 2019. What have you been pursuing since?
It was a real honor. It has encouraged us to continue down some of these paths … and to also do some more comparative work and think about species beyond the ones that I have traditionally studied. So in the past few years, I’ve picked up work in other social mammals — wild meerkats and these very social rodents called mole rats — that have their own advantages in giving us insight into how our social world has shaped both how we came to be, our evolutionary past, and how we do day to day in our present.

I’ve been doing more work on something that’s an old love of mine: trying to understand the evolutionary consequences of intermixing between different primates. The population of baboons that I study in Kenya actually sits right at the edge of where the ranges of two different species of baboons meet. And so this population is intermixed between one species, the Anubis baboon, and this other species, the yellow baboon.… We think those patterns of intermixture influence some things about what [the animals] look like, how they behave and so on.…

We know that [humans] have also intermixed a lot with some groups that don’t even exist today, like Neandertals and Denisovans. That process of admixture that we observe right now in living primates [is] potentially relevant to understanding our species’s history.

What are some of the greatest challenges you’ve faced since 2018?
In many ways, I felt very fortunate during the pandemic; as an academic with tenure, I have a secure job. But we were also home with a 3-year-old for a long stretch. I spend usually at least a month a year in Kenya, and I have since 2006. But not in 2020. We had to figure out some way of keeping [the research] continuous without any ability to travel there. We have a permanent staff in Kenya — they are Kenyan — who are very important to us and have been working with our project in some cases for many decades, and they were having their own issues, and isolation, and risks in the face of a lot of uncertainty.

I spend a lot of time in my research life thinking about social interactions. And every species that I study … they live in groups. And humans, to a large extent, we live together. We didn’t evolve to be on our own for a long period of time. And so I spent a lot of time reading and thinking and working on, “Why when you don’t have the right sort of social connections, why does your risk of death just shoot up? What’s the consequence of chronic social stress?” One of the things that I really appreciate in a more visceral manner [now] is how important my social network is to me. I think that we’re all looking for ways to connect during the pandemic. And that’s when your personal experience and the things that you’re writing papers about and thinking about really collide.

— Interview by Aina Abell

A stunning simulation re-creates how M87’s black hole launches plasma jets

From the maw of the supermassive black hole at the center of the galaxy M87, two enormous jets stream thousands of light-years into space. Scientists still don’t fully understand the physics behind the jets, which are made of a mix of electrically charged particles, or plasma (SN: 3/24/21). But they are “really, really amazing,” says astrophysicist Alejandro Cruz-Osorio of Goethe University Frankfurt. So he and colleagues created a computer simulation of M87’s black hole and the swirling gas that surrounds it in an accretion disk. The aim: Figure out how this black hole — already famous for posing for a picture in 2019 (SN: 4/10/19) — became such a jet-setter.

Under the right conditions, that simulation produces jets that match observations of M87, the researchers report November 4 in Nature Astronomy. The black hole twists up spiraling magnetic fields that surround two high-energy beams of electrons and other charged particles. The results suggest that the black hole must be spinning rapidly, at more than half its maximum speed allowed by the laws of physics and possibly as much as 94 percent of its maximum possible speed.

Getting the energies of the jets’ electrons right turned out to be crucial. When magnetic fields in the jets rearrange in a process known as magnetic reconnection (SN: 8/3/21), electrons get accelerated, resulting in more of them having very high energies. This effect was not included in earlier simulations, but it was key to getting the simulated jets to act like real-world counterparts.