Monday, May 17, 2010

The Langston Field and Thermodynamics

Here I'm analyzing some further implications of the Langston Field. We're going to get into some thermodynamics and what that implies for spaceships and weapons in the Terrible Secret of Space.

I stated in the last post that the field radiates like a black body. The question is, what exactly does that mean? Black body radiation describes the way that stuff gives off light depending on how hot it is. The interesting thing about black body radiation is that it doesn't depend on what size, or shape, or color, or even if the object in question is a communist. It only depends on the temperature. An incandescent light bulb shines because that filament is really, really hot. You're emitting infra-red radiation right now, you can't tell because you eyes don't see at that wavelength. The SWAT team that just cut your power and battered down your door can see them, though. Their heat vision goggles sense the heat you're emitting, and can tell by the wavelength the difference between you (100 degrees) and your nightstand (70 degrees.)

So we said that the shields shift up the color spectrum as they take damage, taking in heat and emitting it like a black body. But since black body's don't care what's doing the emitting, we can figure out how hot the shield is. Let's say the ship blows up when it's emitting light at a wavelength of about 400 nanometers. That's in the deep purple region of colors. Just before it overloads, the shield is going to hit a temperature of about 7250 kelvin. That's plenty enough to melt and boil tungsten or what have you. There are some problems raised by that; how do you see out of one of these shields? I mean, it's black. It stops light. There's no way to get it to stop "dangerous" light like lasers but not "useful" light like, oh, the stuff that shows you where your opponent is. You could build cameras on metal poles and stick them through the shields (the shields will allow matter to pass, and electric signals should be able to get through). And then someone actually shoots you enough, your cameras melt off and you're blind again. Well before the explosion point.

I'm thinking the answer to that is that you can open holes in your own shield. This is suboptimal in combat because someone might try to shoot through your holes, but necessary. I mean, you've got to shoot your laser cannons out, right? Blasting it into your own shield seems counterproductive. Also, your fusion drive has to shoot materials out the back, if they get caught in the shield you won't go anywhere.

That's not the biggest problem, though. Remember how black bodies radiate solely based on their temperature? Exactly how much do they radiate? There's an equation for that (I won't post it, partly because you can't be bothered with it and partly because I can't be bothered with getting the Greek symbols and formatting equations in a text file). The amount of energy emitted is proportional to the fourth power of the temperature. Not just squared or cubed, raised to the fourth power. What's 7250 to the fourth? Roughly 2.7 quadrillion (thanks Windows Calculator!). Quadrillion, as in even the federal deficit hasn't gotten that large yet. The proportion factors are all pretty small decimals, but we end up with a huge number nonetheless. Let's say a spaceship has a spherical shield with a 100 meter radius. Now heat that ship up to the explosion point. Just before it's exploding that ship will be emitting a kiloton of energy in black body radiation every second.

A kiloton of energy every second. Remember Hiroshima? In one minute a spaceship like that could duplicate the effects.

Now let's go over the disturbing implications of that. And not just it's uses as a superweapon. (If you're gonna do that, why not just lob the atom bombs and cut out the middle man?) If the spaceship is radiating kilotons of energy, how much energy do you have to put in to keep pushing the shield temperature up? At some point you're lobbing atom bombs at it to make sure the damn thing doesn't cool down on you, let alone cook off. You can probably do it with H bombs, but your laser batteries might fall short. Weapons are going to have to be culled because we're gonna have to ask ourselves "neat as this is, is it really as destructive as an atom bomb?". Naturally this saddens me.

Now, if you're emitting that much energy, how close do I want to fly to you? Forget the explosion (for the moment) My shields will be heating up just going by. Probably not going to be a major concern for another ship. But let's say we're having a battle in orbit over the planet. You detonate enough atom bombs directly above the atmosphere and you'll pump in enough heat to affect the weather. I haven't done any calculations about this, but you might start fires or kill crops or some such.

For that matter, what about using a shield as a weapon? If you take a starship, nuke it profusely and then send it hurtling through someone's atmosphere, set so that the final collision will overload the shield you can create an explosion that makes your garden variety atomic bomb weep. You've got all the energy of those nukes plus the energy of a giant freaking meteor hitting stored in the shield. You could raze continents with those. Y'know, as if you couldn't with enough nukes already.

(There are also conservation of momentum problems here that I didn't consider. Particle hits shield makes sense. Shield hits planet makes less sense. Does it slow the planet enough to overload the shield? For collisions of any velocity?)

That brings up another question. How much energy exactly can one of these shields absorb? I'm gonna have to talk about Specific Heat here, and how it's totally inapplicable to the problem at hand but I'm going to use it nonetheless. Specific heat is a measure of how much energy something can hold. For a given mass, different materials will hold different amounts of heat. An experiment! Take a mass of iron, boil it in water. Take an equal mass of water. Dump them both out on a snowbank, and see which one melts more snow. You'll get more melting from the water because even though they're undergoing the same change in temperature the water can hold more heat than the iron. It has a higher specific heat.

Now drop an atom bomb on that snowbank. The snow will melt and vaporize. So will that chunk of iron. And anything else in the nearby area. You could build a chunk of iron large enough to not melt when you hit it with a nuke, but it'd take a lot of iron. (At least you could build one if the heat conducted at an infinite rate; as it stands the nuke is still going to leave a crater.) The question is, what specific heat do those fancy schmancy Langston fields have, what with the not cooking off with the first nuke that comes their way? Well, it's hard to say. Y'see, the shields are force field, and they don't exactly have a mass. (Ok, all energy has a mass, thanks Mr. Einstein, but I can't wrap my head around asking about the specific heat of a quantity of heat. The question makes even less sense than my twisted diction.) Specific heat depends on having a mass. So the question doesn't even apply.

But, as I stated earlier, I'm not going to let that stand in the way of Science! We can work out a volume for these shields (say a 3 meter shell on a 97 meter warship to get that 100 meter shield I was talking about). We can throw in a "density" factor so that we can work out an effective mass, and from there we can figure out exactly what sort of heat capacity the shields have to have. If some practical joker took away your Langston field and substituted water for it, it'd have a known density (1) and heat capacity (4 point something). We could calculate how much energy the water would absorb before it'd heat to the requisite 7250 kelvin. Assuming, of course, the wildly unphysical notion that the water would stick around to be heated and not boil off the very first chance it gets. But the heat, the heat could be provided by a single atom bomb, blasting through your shields and wrecking your ship.

This will not do. Fortunately, our shields aren't made out of water, but are pulled form the figurative aether. By fiddling with the heat capacity factor we can work out a shield that will not only survive the first nuke but several more, changing into pretty colors and radiating energy and doing all the other wonderful things I'm counting on the Langston field to do. Roughly, I expect this handwaved heat capacity to be a hundred million times larger than that of water.

I doubt this is the last I have to say about Langston fields. But it's good enough for now.

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