What An Adorable Little Starship

One thing I missed in the past week was the announcement of Breakthrough Starshot, an effort to send the first space probe to another star. Mini-spacecraft going to Alpha Centauri. Didn't see that one coming.

The main difficulty with traveling anywhere in space is weight. Here on earth, we're used to the idea that you can make something faster just by giving it a bigger engine. Sure, you'll be going through fuel faster, but that just means you'll have to stop to refuel more often; you'll still be faster overall. But in space, there's nowhere to refuel; you have to carry it all with you.

That's a limitation you just can't get around: more powerful engines mean that you'll need to carry more fuel, which will weigh down your spaceship and nullify the advantage of the more powerful engines. So with current rocket technology, there's really no way to get to Mars in less than about 18 months, or to Alpha Centauri in less than ten thousand years.

The only way to go faster is to come up with new technology that gets more energy per pound of fuel. Nuclear power would help, though not as much as you might hope. You'd still need a huge amount of fuel, requiring a huge ship. Some people have tried to get around the weight problem by not carrying the fuel with you. One such concept is the Bussard Ramjet. It would scoop up the very few atoms hanging around space and shove them into a nuclear reactor to generate power. Unfortunately, this would require a huge ship, and no one is entirely sure the concept will work.

Another possibility is to provide the energy from elsewhere. That's how this proposal works. For a while people have suggested the idea of a "solar sail." In that concept, the ship would be pushed by the miniscule force of the sunlight hitting it. Of course, because the force is so small, you would need big sails, and even then the force wouldn't be great; but it would be persistent, and over the course of weeks or months, it would add up to great speed, possibly faster than conventional rockets.

But solar sails will only work in the inner solar system. To go further, you'd need some artificial source of light. Of course, to accelerate any reasonably-sized spacecraft, it would have to be an incredibly powerful laser, beyond what we could currently build.

And that's where this proposal comes in: it takes advantage of the fact that we can make the ship very small, and thus very light, so that we could build lasers big enough to accelerate it to high speeds. When you think about it, that's quite symbolic of how our technology works today: in the past, we imagined that we would build starships by creating huge new power sources. We haven't had much luck making those, but we have done better than we ever expected at miniaturizing machines. So it appears we're going to use those technologies to our advantage.

One thing that's surprised me about this story is just how many people are clueless about astronomy. Sure, as a geek who occasionally interacts with non-geeks, I'm aware that many people know words like "galaxy" and "nebula" only from movies, but have no idea what they mean. But I always assumed that in any small group of people, at least one will have seen enough episodes of Cosmos to be astronomically literate.

Yet I saw two different news programs say that this proposal was to send a probe to the nearest galaxy. I can understand a flustered host who was hired mostly for his voice making that mistake, but these were in a recorded voice-over and a bottom-of-the-screen title. That means it would have passed a few people without anyone noticing how embarrassingly inaccurate it was.

I Wanna Grok

There's a principle you may have heard of that if you truly understand something, you should be able to explain it to a six-year-old. If you can't, then you don't really understand it as well as you think you do.

Personally, I think that's a bit harsh. After all, if it were true, we'd have much more educated six-year-olds. It would be more accurate to say that you should be able to explain something to another adult. Of course, that doesn't reflect well on our university professors: Their job is essentially to understand things and explain them to others. Given their success at the latter, it doesn't give me confidence to the former.

That brings me to a sudden realization: I don't believe in String Theory. No, it’s not based on emperical evidence or esoteric mathematics. It's because I don't believe anyone really understands it, because no one seems to be able to explain it.

I know, it's complicated, it's hard to wrap your head around. But there are lots of things that are hard to understand. The Theory of Relativity, Quantum Mechanics: those are also hard to explain. But it can be done; I've seen people do it. But not String Theory. I've seen and read dozens of explanations, and here's what I've learned:

• All the fundamental particles in the universe are actually strings.
• The strings vibrate.
• Somehow this means that there are lots of other dimensions, but they're really small.

That's it! That's not an explanation. If you were explaining it, you'd also tell us things like:

• How does this help us understand how particles behave?
• What do the vibrations do?
• Okay smartass, what are the strings made of?
• For that matter, why are you explaining something simple (particles that are just little points) with something more complicated (strings)?

Science is all about figuring out how the world works. So the joy of learning about science is to gain a greater understanding of our surroundings. I don't want to hear a few disjointed facts; I want to acquire a mental model of the processes of nature. For whatever reason, String Theory proponents haven't put much effort into this. It's probably just that there isn't much incentive for explaining bleeding-edge physics well. But until someone puts some effort into it, I'm going to assume that String Theory is a massive Emperor's New Clothes situation, where no one wants to admit that none of them get it.

Unfortunately, this kind of explanation-that-isn't seems all too common these days. There's an assumption that if you give the context of a thing, together with some ideas you can drop at parties, that's considered explaining it. But really you haven't learned anything useful: you just know enough to sound intellectual during a superficial discussion, assuming you're talking with other people who don't understand it either. It's really unfortunate that in a society where we can communicate information so easily, we're still not good at spreading understanding.

Getting On My Soapbox

It’s summer, so there may be a soapbox derby in your community on an upcoming weekend. Here's something I've always wanted to know: should a soapbox car be heavy or light.

You might instinctively say, "light," because all things being equal, lighter cars are faster.

...but that's when you have an engine pushing the car's mass. In this case, it's gravity pulling the car down. So the weight shouldn't matter, because, as Galileo showed, things fall at the same speed, regardless of mass.

...but that's in a vacuum. In an atmosphere, heavier things fall faster, because they have more force to overcome aerodynamic drag. So a heavier car would be faster.

...but, a heavier car will have more rolling resistance, because the weight of the car will be pushing down on the axles, increasing the friction.

I tried googling this question once before and never got a straight answer. I tried again just now and found someone with experience had answered this. Yes, there are engineers with extensive experience with soapbox cars; surely that’s not a surprise. The answer is, it depends.