June 06, 2016 at 01:25AM

Today I Learned: 1) ...about a proposed system of interstellar travel involving laser propulsion. This isn't a new idea at all, but I did learn some new tidbits, as well as a proposed *implementation* that's gotten some early-stage funding. The basic idea of laser propulsion comes roughly from the solar sail idea. The spacecraft would have (or be) a large solar sail, but instead of being powered by solar ejecta, it would be pushed by a laser, beaming power from Earth, Earth orbit, or some other, more convenient location. The nice thing about laser propulsion is that the spacecraft would require virtually no fuel -- all the actual power generation would occur at the launch site. The only problem is that you can't really decelerate at the other end... but it's the only vaguely-plausible mechanism we currently have for getting things to the speeds required for interstellar travel. One thing I didn't know about is that there's a recently-proposed project at NASA to actually build these things, along with a proof-of-concept grant to show that it could plausibly work. The *really* cool thing... well, there's a couple of cool things, but the *most* cool thing about this particular project is that it's designed to be *scalable* in the sense that NASA can start by building a small, kilowatt-scale laser for short-distance, low-mass flights, then scale it up by either building progressively larger lasers or building *more* of the small ones. That means there's a smooth path from proof-of-concept prototypes through dozen-gigawatt-scale interstellar probe launchers. The *other* really cool thing about the laser propulsion system is the sheer ridiculousness of what it can do once scaled up. The ultimate goal is to build a 50-100 gigawatt orbital laser (with a total mass of about 100 times that of the ISS) that would be capable of accellerating a wafer-thin, several-kg probe to about a quarter of the speed of light. In 10 minutes. At that speed, we could get a probe to Alpha Centauri in about 17 years after launch, which means we'd have telemetry from that probe about 21 years after launch. The younger among us could be hearing back from another star system *in our lifetimes*. 2) I've noticed while interacting with high schoolers on the subject of biology that I'm often surprised about what the students know... and also by what they don't know. That makes it really hard to teach effectively. Today I learned that this is one of the big known problems in teaching, and that there are a ton of tricks and tips out in the literature for getting around it. For example, I also learned today about the idea of an "exit ticket". In a class with an exit ticket, a student can't leave the class until they've filled out some kind of "ticket" with a problem solution, an answer to a question, or simply a self-evaluation of how well that student understood everything from the class. It's a simple way of getting some valuable feedback about what everyone knows, doesn't know, or thinks they know but don't. Thanks to Kamila Laliv Goldin for sending me down this educational path! 3) ...how to play Netrunner! It's a cyberpunk asymmetric strategy card game where one player takes on the role of a corporation, trying to advance corporate agendas, while the other player takes on the role of a hacker who tries to reveal, steal, or otherwise disrupt those agendas. There's a lot of hacking and a level of tech-speak I find quite pleasing. Thanks to Andrey Shur for teaching me!