So what is this site about?
Gravity and Levity is the personal blog of Brian Skinner, a theoretical condensed-matter physicist who began it back in 2009, when he was a PhD student at the University of Minnesota, US. He’s now a postdoc at the Massachusetts Institute of Technology, where his research focuses on the behaviour of strongly correlated electronic systems, such as low-dimensional electron gases and materials such as graphene.
What topics does it cover?
Skinner takes the view that “physics as a whole is much more interesting than my own meagre contributions to it”, and he isn’t really into physics news, politics or gossip either. So, if you’re interested in reading about the latest theoretical condensed-matter research, or about day-to-day life as an academic, you’ve come to the wrong place. Instead, Gravity and Levity focuses on some of the “big ideas” in physics, taking deep but mathematically simple looks at topics such as the size of an electron, the relationship between physics and maths, and why elements containing more than 137 protons cannot exist (at least according to current theory). If you think that sounds like a pretty eclectic list, you’re right, and it doesn’t end there. Skinner has also written posts about the mathematics of basketball, Cooper pairs and even “the field theory of swords”.
Swords? As in, big metal pointy things?
The same. At the end of 2015, Skinner wrote a series of posts about the nature of particles and fields, and in the series’ final post, he began by observing that one could use this same basic framework to describe the behaviour of macroscopic objects – such as swords. The rest of the post explains that a metal sword can be modelled as an orderly lattice of atoms, and describes how its strength and rigidity arises from defects (more specifically, disordered dislocations) in that lattice. Hence, when a blacksmith is forging a sword, “his effort is largely going into creating a tangled knot of dislocations inside the metal”. It’s a beautiful, fascinating and eminently relatable explanation, and that’s exactly what you can expect from reading Gravity and Levity.
Can you give me a sample quote?
From an April 2014 post about the role of symmetry in physics: “I would like to suggest using the phrase ‘to be a perfectly symmetric ass’ as a description of someone who is being paralysed into inaction by symmetry. For example, suppose someone asked you to predict what will happen if you apply a large voltage between a small inner sphere and a large outer sphere that is filled with a weakly conducting plasma. Most of us who had Gauss’s law arguments trained into us would immediately say that an electrical current will flow out from the inner sphere in a radially symmetric way, and consequently that the total current flow will be very small. But most of us would be wrong, because what actually happens is the system figures out very quickly that there is a much lower-energy way to move its current from inner to outer surface. Namely, by creating sharp (symmetry-breaking) pathways with intense current, which produce dielectric breakdown of the plasma and allow the current to flow easily. If you allow symmetry to fool you into thinking that the current will flow slowly and radially, then you…have ‘made a perfectly symmetric ass of yourself’. I say it lovingly, of course, because I make a perfectly symmetric ass of myself all the time.”
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