I posted a while back about a ball pit I’d installed in my room. Everything in that post was true, but the pictures were a little misleading.

Looking at that, you don’t necessarily realize how cramped those people are. I framed the pictures to make it look larger than it actually was (THAT’S WHAT SHE SAID). In fact, the ball pit was only about the size of a large bathtub or small jacuzzi. In the pictures on the site, it was barely deep enough to be buried in, and when we shrunk the area to make it deeper, it was barely big enough for two people.

When people came in and saw it, they were always startled at how small it was (also what she said). There was no room for hide and seek, and barely even space for surreptitious ball-pit groping. This was a terrible state of affairs. It was nice to sit in, but really, why bother having a ball pit if we were gonna do such a half-assed job of it?

Well, as of this week, the situation has been rectified.

We all chipped in and quintupled the volume of the ball pit. It’s now set up opposite a hacked-together server-projector system (yes, that means Guitar Hero in the ball pit — that’s a controller you see on the left). It’s lined with blankets and foam padding, and is oh so comfortable. We’ve had two people fall asleep in it already.

For sanitary reasons, we of course have a few rules:

It’s still only half the size of the recently-constructed Last.fm ballpit. But it’s finally big enough to really hide in, stretch out, and grab someone’s ass without them being sure who did it.

On the other hand, it has the slightly unnerving effect that we now have no idea how many people are in the apartment at any given time.

For science, the next experiment will be “what do cats think of ball pits?”

A big thanks to khmer for putting together the piano arrangement in today’s comic.

Thanks also to the readers who tried playing it. I hope you didn’t realize what it was until too late.

Holy crap. This strip’s been up for 800 seconds and it’s already the most controversial thing I’ve ever written, beating out comics about cunnilingus, the Obama endorsement, and my making 4chan tiny on the map of the internet. It turns out everyone and their mother has a fruit opinion, and every one of those opinions is now in my inbox.

Just remember to keep some perspective. If you think watermelon is delicious, and I think it’s only so-so, the important thing is that we each find something we like. Who’s to say whose taste is right?

I am. You are wrong; watermelon is overrated.

Also, I have never liked cantaloupe. It brings down otherwise tasty fruit salads. There, I said it.

Solar sails suck.

In a 2002 paper, Laser Elevator: Momentum Transfer Using an Optical Resonator (available at your local school/library, possibly electronically — J. of Spacecraft and Rockets 2002), Thomas R. Meyer et. al. talk about a neat way to get a lot more speed out of light reflection than with a regular solar sail. The basic physics are pretty simple, and it’s a fun subject to think about.

When a photon hits a solar sail, it gives the sail momentum. If the photon has momentum P and bounces off a stationary sail, it looks like this:

Think of where the energy is in this system. Before it hits, the photon has energy E. After it bounces, the photon still has roughly energy E. But the sail’s moving, so where did it get its kinetic energy? (Remember, energy — unlike momentum — has no direction.)

The answer lies in the word “roughly”. The photon loses a tiny fraction of its energy to Doppler shifting when it’s reflected, but only a tiny fraction. It is this tiny fraction that goes into pushing the sail. This is a phenomenally small amount of energy — far less than a percent of what the photon has. That is, not much of the photon’s energy is being used for motion here.

This is why solar sails are so slow. It’s not that light doesn’t have that much energy, it’s that it has so little momentum. If you set a squirrel on a solar sail and shone a laser on the underside, do you know how much power would be required to lift the squirrel? About 1.21 gigawatts.

This is awful. If we were lifting the squirrel with a motor, railgun, or electric catapult, with 1.21 gigawatts we could send it screaming upward at ridiculous speeds.

This is where Meyer and friends come in. They’ve point out a novel way to extract momentum from the photon: bounce it back and forth between the sail and a large mirror (on a planet or moon, perhaps).

With each bounce, the photon loses a little more energy and adds another 2P to the sail’s momentum. The photon can keep this up for thousands of bounces — in their paper, Meyer et. al. found that with reasonable assumptions about available materials and a lot of precision, you could extract 1,000 times the momentum from a photon before diffraction and Dopper shifts killed you. This means you only need 1/1,000th the energy to levitate the squirrel — a mere megawatt.

This isn’t too practical for interstellar travel. It requires something to push off from, and probably couldn’t get you up to the necessary speeds. It may, they suggest, be useful for getting stuff to Pluto and back, since (somewhat like a space elevator) it lets you generate the power any old way you want (a ground nuclear station, solar, etc). But more importantly, it’s kind of neat — it helped me realize some things about photon momentum that I hadn’t quite gotten before. It’s like Feynman says, physics is like sex — it may give practical results, but that’s not why we do it.

Now we’ll let things get sillier. I spent a while trying to brainstorm how to use this with a solar sail (that is, using the sun). I imagined mirrors catching the sun’s light and letting it resonate with a sail.

But you really need lasers for this — regular light spreads out too fast. Maybe a set of lasing cavities orbiting the sun …

Supplemented by a Dyson sphere …

And since by this point we’ll probably have found aliens …

Why settle for interstellar communication when you can have interstellar war? And we could modulate the beam to carry a message — in this case, “FUCK YOU GUYS!”

Space has been a little disappointing for the last few decades. Since the moon, everything has turned out kind of barren. Every SETI-related result of the past 30 years has been disheartening — “there was once water on Mars” doesn’t really do it for me. There are two big exceptions. One is Jupiter and Saturn’s moons, which are still cool and could do with more checking out.

The other is the search for other solar systems. Starting in 1995, we’ve been finding craploads of planets around every star we look at. The better we build our telescopes, the more planets we see. It seems more and more likely that a lot of stars have solar systems like ours. And if Mars could’ve had water, and we have water, water probably isn’t uncommon. Things are looking up for life in the universe, even if they’re looking down for our neighborhood.

I think we haven’t made contact with aliens by radio yet because we’re looking in a very limited set of places, not because they’re not there. I think it’s more likely that ET is using tight-beam lasers to communicate between star systems; it’s silly to expect them to dump powerful uncompressed signals toward us on the few frequencies we’re searching at the times we happen to look toward them. I think it’s very likely that there’s a lot of life out there; we’ve barely started searching.

In the next decade or so, we’re gonna get a lot better at seeing other solar systems. We’ll be getting new planet-finding telescopes built — there’s immediate-future stuff like Kepler, and there’s also the possibility of giant optical arrays in orbit or on the moon that can directly image earth-like planets around other stars. The data will start pouring in soon, and space will be exciting once more.

All that said, most applications of the Drake Equation are pretty shoddy. You can’t extrapolate from one damn data point no matter how much you want to. But this isn’t really Dr. Drake’s fault. He’s doing the best he can.

Edit: Regarding today’s comic: Dr. Drake’s first name is Frank, not Francis. He is an astrophysicist, not a 16th-century British Vice-Admiral. Thank you to the several readers who wrote in to correct me — I had always thought Francis Drake was just one long-lived and supremely-accomplished person.

Remember limericks? They were huge in the mid-20th century, but fell on hard times over the last couple decades. Now so many dirty limericks are a generation out-of-date, and the really clever ones lie neglected and un-retold.

I want more limericks, and I want the cleverest ones collected somewhere. It strikes me that a certain modern system for collecting bits of funny text might be perfect for both these goals.

So, after a moment’s work, I’ve set up LimerickDB.com, which you’ll recognize as similar to bash.org. Submit away, both old and new! Anonymity is encouraged and a respect for meter is required. Dirtiness is not mandatory, but it helps.