Ok folks, it’s time. We’ve all asked this question, but I’ve been putting off answering it because we all actually know the answer.

How do the Zerg fly in space?

Magic.

There’s a certain point in sci-fi or fantasy where you have to just suspend disbelief and go along for the ride, and I think that the Zerg ability to travel through space is a good example of this. That said, I’d like to take a look at one of the most common explanations that people give to justify the mutalisk’s ability to flap its wings and propel itself through space. As you’ll see, it’s completely implausible.

Now, we know that flapping doesn’t do anything in a vacuum: there’s nothing to provide any resistance, so you can flap all you want and it won’t move you forward. But what if mutalisks used their dragon-like wings as solar sails, catching the photons from a nearby star to cruise through interplanetary space? That might not explain the flapping, but it could explain how they can move, so let’s take a closer look.

The idea behind solar sails is the conservation of momentum. Even though photons of sunlight have no mass, they do have momentum. High school physics tells us that momentum is conserved, so if you have a bunch of photons with momentum being absorbed by a solar sail (or a mutalisk’s leathery wing) then their momentum must be transferred to the thing they’re hitting, exerting a force on it and causing it to move through space. So, how large would a mutalisk’s wings have to be to let it accelerate at a reasonable speed? To figure this out, we need to do a back of the envelope calculation, making some assumptions about how big mutalisks are.

In general, the sizes of units in the game are not reliable: I prefer to consider the cinematics as the authoritative source. So let’s take a look at this cinematic showing Jim Raynor’s battlecruiser being attacked by a swarm of mutalisks.

At about six seconds, one of the mutalisks flies over the right-hand side of the battlecruiser and crosses near a long row of windows. Based on its size compared to the set of windows, I would say that the creatures have a wingspan of around 100 meters and that their tube-like body is about the same length and maybe 5 meters across. If mutalisks are like most earth life, then they are mostly water. to get a rough idea of their weight we can calculate their volume and then multiply by the density of water. A cylinder 5 meters by 100 meters has a volume of about 2000 cubic meters. That would correspond to a whopping 2,000,000 kg or 2000 metric tons!

Now, obviously that’s too big for something to fly in at atmosphere, let alone in space by flapping its wings. But lets be generous and say that maybe mutalisks are made of some very low-density material, and maybe I overestimated their size. What if they were closer to 20 tons? How much oomph would their wings give them if they used them as solar sails. Again I’ll be generous and treat the wings as a square of material 100 meters on a side.

The momentum of a photon is given by: Momentum = Energy/Speed of Light, so near a sun-like star, where most photons are in the visible range, they have an energy of 2-3 electron volts, yielding a momentum of 1.6×10^-27 kg m/s per photon. That’s not much, but a star puts out a lot of photons, so let’s see if that balances it out and gives us a decent thrust.

Let’s say our theoretical mutalisk is orbiting the sun at the same distance as Earth, 150,000,000,000 m from the sun. The sun puts out 3.8×10^26 watts or roughly 8×10^44 photons per second, but that power is spread out in all directions. To figure out how much hits our solar-sailing mutalisk, we have to imagine spreading that power out over a sphere the size of our mutalisk’s orbit with a surface area of 4*pi*R^2 where R is the radius of the orbit. That gives 2.25×10^20 photons per square meter per second.

Solar sails don't make for the most maneuverable spacecraft, and they would be sitting ducks in any sort of space battle.

With a wing area of 100 m x 100 m (10,000 square meters), our mutalisk would intercept around 10^24 photons per second, corresponding to a whopping force of 0.0004 newtons! That’s enough force to accelerate a 20 ton mutalisk up to about 14 miles per hour in a year.

Edit: An astute reader points out that the size of mutalisks is described in the Starcraft novels as being much smaller than I described. They apparently have a wingspan of 20 feet and are only 7 feet long and about a meter across. to me that seems shockingly small, especially compared to the cinematics, and it also seems quite stubby compared to all of the art depicting mutalisks as having a body that is a long tube. Still, we can scale the above results to fit these new dimensions. Given a cylinder 7 feet long and 3.3 feet across, and again assuming a density like water, I get a mass of 1.7 metric tons. If we treat the wings generously as a 20 foot square, then their surface area is 37 square meters, so the thrust on wings of that size as compared to our 10,000 square meter example above would be .0004 newtons x .0037 = 1.5×10^-6 newtons. That’s enough to accelerate our 1700 kg mutalisk all the way up to 0.06 miles per hour in a year! Even assuming a much lower density, it would only accelerate a 170 kg mutalisk up to 0.6 miles per hour in a year.

You might not have followed every step of that (admittedly very crude) calculation, but that final value should give you some idea of how ridiculous it is to say that a Mutalisk’s wings could work as solar sails. Even assuming very large wings and a small body, the acceleration that you get is miniscule. Plus, solar sails are really only good for accelerating away from the star, and Mutalisks are like fighter jets: they need to be able to dodge and weave in all directions very quickly.

Bottom line, I can’t explain how the mutalisks fly in space. Heck, I can’t explain how something that big flies in air! Solar sailing certainly doesn’t cut it, so we’re left where we began. It’s magic. This is a part of the Starcraft Universe that just doesn’t fit with the laws of physics in our own universe, and that’s fine. Mutalisks are still cool, and it’s not like I’m going to stop playing Starcraft because I don’t know how they can fly in space.

Stay tuned: next I’ll take a look at all the non-winged Zerg fliers!

The other day I was playing Starcraft 2 and trying to think of the next topic to tackle here. As I watched a swarm of zerg roaches attack a group of terran marines, I realized that I needed to talk about acid. Two of the new zerg units, the baneling and the roach have acid-based attacks. The baneling is a little suicide bomber that detonates, splashing corrosive acid all over nearby units, while the roach is a nasty armored insect that spews a stream of acid on its foes from a distance.

Banelings doing their thing.

I like both of these units in the game, but they perpetuate a myth about acid that has infested pop culture for years: it is bright neon green. I’m not sure where this idea originated. Maybe it goes back to World War I, when chlorine gas was used as a chemical weapon. It’s not an acid, but it is a nasty caustic chemical that is a sickly green color. Or maybe the green acid idea can be traced back to the movie Alien, where the alien is revealed to have highly acidic blood that looks greenish yellow.

The famous shot of the alien's acidic blood in Alien.

Whatever the origin of the idea, it’s patently false. Most acids are colorless in both their pure form and in solution. Sulfuric acid? Colorless. Hydrochloric acid? Wikipedia says that it is colorless to light-yellow, but I’ve never seen an example that showed any color. Hydrofluoric acid? Colorless.

I don’t know of any acid that is brightly colored, though I admittedly not a chemist. There are probably some nice, colorful organic acids, and it’s certainly possible for acid to be mixed with other colored stuff in a solution, but in the real world acid does not conveniently advertise its corrosiveness by being bright green.

While we’re on the subject, let’s talk about the plausibility of an insect spraying acid, whatever the color may be. This is actually plausible to me. There are plenty of examples of insects that are armed with chemical-based weapons. One of the most famous is the bombardier beetle, which defends itself by blasting a nasty, boiling hot liquid at its attackers. Bee venom contains formic acid, and many ants inject or spray formic acid or other chemicals when they bite.

If we’re willing to suspend disbelief enough to allow the zerg to exist in the first place, I’m also willing to grant that they might use caustic chemicals to attack, since real-world insects do this too.

In a lot of ways, Starcraft 2 is very similar to its predecessor, and I think on the whole that’s a good thing. With the original Starcraft, Blizzard hit on a formula for a compelling game that just worked, so they didn’t need to fix it. With Starcraft 2, they tweaked it instead. There are a lot of familiar units in the new version of the game, but there are also a lot of new ones, as well as new abilities for familiar units that make things interesting. There are also a lot of tiny, careful changes to the gameplay that make everything flow more smoothly.

Tychus Findlay and Jim Raynor at the bar.

For me, the campaign was always the highlight of the original Starcraft and I’m happy to report that it is excellent in Starcraft 2 as well. The story focuses on Jim Raynor who has had a make-over and is now a rugged, scarred mercenary. Instead of a linear storyline with little player choice like in the original game, Starcraft 2′s missions allow a little more flexibility: at any given time there are several missions to choose from. Between missions, you can interact with other characters on your ship. Head to the cantina and share a drink with Tychus Findlay, a rough-and-tumble ex-convict marine. Or go to the lab and see what new technologies Egon Stetman, the stereotypical squeaky-voiced, lab-coat-wearing, socially-awkward scientist has cooked up for you. Or check out the armory and ask Rory Swann – the mechanic who sounds like he belongs on Car Talk and looks like a Warcraft dwarf – to upgrade your mechanical units. Other colorful plot-related characters include the awesomely stereotyped Tosh – a rastafarian rogue ghost operative, complete with voodoo charms and a “ya mon” accent – and the idealistic young ship’s captain Matt Horner, whose clean-cut look and fancy uniform were carefully designed to contrast with Raynor’s bad-boy tattooed arms and sweat-stained t-shirt.

Tosh, the suspicious Jamaican operative. Yes, that is a voodoo doll around his neck.

This interesting bunch of characters  send you on missions following several parallel plotlines that gradually intertwine to lead to the requisite huge battle at the end of the campaign. Each thread of missions is based on that character’s personal interests, and things get interesting when some of the characters disagree on what’s the best next step. All of these interactions are done really well using rendered-on-the-fly cutscenes. Some of these cutscenes are cinematics in their own right (at one point there’s a bar fight which was very well done) but there are also a few of Blizzard’s trademark spectacular pre-rendered cinematics for key plot points.

I really enjoyed the interplay between the missions and the “down time” on the ship: each mission gives you a new type of unit, some “research points” and some cash. The new unit is then available in all future missions and the research points and cash can be used to upgrade your units and hire mercenaries to help you. This adds another layer of customization to the game that worked really well.

Jim Raynor, Matt Horner and Tychus Findlay on the bridge of the Hyperion.

I also loved the variety of the actual campaign missions themselves. There are actually very few missions where you just build an army and destroy the enemy. There’s always something more going on. In one level, lava floods the low ground every few minutes. In another level, hordes of zombies attack you at night, and you have to hold the line until daybreak, when you can take the fight to them. The “hero” levels, where you just get a handful of special units to achieve your obectives, are really excellent too.

The story itself, like the story for the original Starcraft, is passable but not great. The problem with video game stories in general is that they exist primarily to get you to the next mission, so they are often not as developed as one might hope. Compared to most video games, Starcraft 2 has a very good story. Compared to most novels, it’s pretty weak. The writing is mediocre at times as well, with plenty of cliched lines and heavy-handed character development. But it gets the job done, and the fact that there are actual characters, and that they do develop a bit, is actually a great thing to see in a game!

The cantina. You can play some sweet tunes on the jukebox, or watch the latest amusing news broadcast from the Starcraft analog of Fox News.

A final aspect that I want to mention is the overall “feel” of the campaign. There was a certain Firefly-like “space western” vibe going on that I really enjoyed. This shows in everything from the (very good) in-game music, to the characters of Jim Raynor and Tychus Findlay (roughly analogous to Malcom Reynolds and Jayne Cobb in Firefly) to the jukebox on the ship that plays down-home favorites like “Sweet Home Alabama” and “A Zerg, A Shotgun and You“.

Bottom line, Starcraft 2 is a great game. The loving attention to detail that went into every aspect of the game is obvious. The campaign is full of really well-designed missions that lead you through several strands of an intertwining story to an exciting conclusion. The ability to customize your units between missions adds a nice dimension to the gameplay, as does the ability to interact with the various colorful (if blatantly stereotyped) characters on the ship.

And of course, once you’re done with the campaign, there are limitless hours of multiplayer fun to be had. You can work your way up the competitive ladder, or take advantage of the extremely powerful map editor that comes with the game and play custom maps made by other players, some of which are good enough to be separate games in their own right.

If that’s not enough, there are two expansions in the works. The campaign in Starcraft 2: Wings of Liberty is strictly Terran (with a few protoss missions thrown in). Each of the two expansions will focus on one of the other races in the Starcraft universe. I don’t think there are release dates set for the expansions yet, but it’s pretty clear that Starcraft 2 and its expansions will be keeping us busy for a long, long time.

Some of the pre-mission loading screens are pretty awesome too.

A couple weeks ago I took a look at railguns, how they work, and how the ones depicted in Starcraft 2 don’t look much like the real thing. This week I’d like to look at another favorite exotic gun in sci-fi video games: the gauss rifle. In Starcraft, the marines carry gauss rifles that act much like real-world assault rifles. In other games, like Fallout 3 and the Mechwarrior series, gauss rifles are a sniper weapon, used to do lots of damage at a distance with a single shot. So, what is a gauss rifle, really? And is it anything like those depicted in the games?

A gauss rifle (also known as a gauss gun or a coil gun) is actually much simpler than the railguns that I talked about before, but it also is based on electromagnetic forces. In a gauss gun, the barrel is a solenoid: essentially a big coil of wire. If you send a current through a coil of wire, it creates a magnetic field in the middle of the coil. We can use the right hand rule to prove this to ourselves: just point your thumb in the direction of the flowing current, and your fingers will curl in the direction of the magnetic field. Make your thumb follow an imaginary coil and you’ll notice your fingers always point the same way!

Animation of a basic coilgun. Source: Wikipedia

In a gauss rifle, this magnetic field is used to accelerate a magnetic projectile, essentially pulling it along the barrel of the gun. If you were to leave the current on, you’d just get the bullet stuck in the magnetic field, oscillating back and forth, but by carefully timing the current so that it turns off at the right time, the projectile will go flying out the end of the gun. In some cases, several coils in a row are used to accelerate the bullet to very high speeds.

The advantage of a gauss gun is that it is pretty simple, and doesn’t really have many moving parts. The difficulty is in getting the coils to turn on and off at just the right time, and in pumping enough current through the wires to accelerate the projectile without destroying the coils with the heat generated by their electrical resistance. If you’re dealing with a sci-fi setting, you can say that the coils are high temperature superconductors, which gets you around that particular problem.

I don’t know of any actual military uses of rail guns, but there are hobbyists who make them, and based on the videos I’ve found on YouTube, they are at least strong enough to blast holes in various household objects.

As you can see in the video, these aren’t exactly machine guns. It takes a while for the capacitors to store up enough energy to fire the gun, so I don’t know if a gauss rifle would ever work like a machine gun, as they are depicted in Starcraft. I think the sniper rifle role, as seen in Fallout and Mechwarrior is probably more plausible, though I’m not sure there would be any advantage over traditional guns.

My biggest problem with the gauss rifles shown in Starcraft is not the rate of fire. It’s the shell casings. In every cinematic, we see marines blasting away with their guns, casings flying all over the place. Heck, in one of the videos in Starcraft 2, we see a closeup of the casings piling up on the ground as the terrans try to hold off advancing zerg forces. It’s a nice cinematic touch, but why would a gauss rifle have casings? Those are there to hold the gunpowder behind the bullet! If you don’t have any gunpowder, there’s really no need for a casing, is there? I think this is another case where the “cool factor” was most important. The guns carried by marines are called gauss rifles because it sounds cool, not because they’re actually based on real gauss rifles.

The marines in Starcraft sure use a lot of bullet casings considering their gauss rifles don't use gunpowder.

The splash screen for the 'Supernova' mission in Starcraft 2.

Everyone has heard of supernovae, but it seems like there is some unwritten rule that they must never be depicted correctly in popular sci-fi. Starcraft 2 is, sadly, no exception. I don’t think it’s too much of a spoiler to say that there is a mission in the campaign where you have to battle your enemies to gain control of a relic on a planet that is about to be consumed by the fires of a huge blue star that is “going nova”. Or supernova. The words are used interchangeably.

As an astronomer, I always cringe when this happens, so I want to clear up what exactly supernovae and novae are.

The confusion is understandable: both are stellar explosions, and their names imply that a supernova is just a big nova. But in most cases this isn’t true. Let’s consider supernovae first, since by understanding them we will already be well on our way to understanding novae.

A supernova is when a very large star explodes. But that’s the end of a long process, so let’s rewind to the beginning: a star starts off as a ball of (mostly) hydrogen gas that is compacted into a dense sphere by its own gravity. At some point, the immense pressure of all that hydrogen is enough to force the atoms in the star’s core to collide with one another and merge into helium, releasing a huge amount of energy. This process is called fusion, and for most of a star’s life, it sits there turning hydrogen into helium and producing lots of energy. That energy makes the star so hot that it glows, and it also provides the pressure that keeps gravity from crushing the star any more. Most stars are poised in perfect balance with gravity trying to compress them and the nuclear reactions in their cores trying to expand them.

The problem with this lovely equilibrium is that helium is more dense than hydrogen, so it sinks to the core of the star. Eventually, there isn’t enough hydrogen in the core to maintain fusion and the internal energy source fizzles. Without fusion supporting the star, it begins to collapse. The pressure and temperature at the core increases until the helium atoms are colliding often enough and hard enough to form carbon. This produces energy again and prevents the star from collapsing, but the core has shrunk and is much hotter. Surrounding the helium-burning core is a shell of hydrogen burning. The intense radiation from the core puffs up the outer layers of the star, giving it much more surface area. It’s a bit unintuitive, but the surface of the star actually cools down when this happens. It has expanded so much that even though the star is producing more energy than before, that energy is spread out over its much larger surface, and so instead of being a bright white or blue star, the star becomes a red giant.

In really large stars, this cycle repeats many times. When the carbon in the core runs out, it compresses even more until carbon fuses into neon. Neon breaks down to form oxygen, and oxygen fuses with hydrogen, helium and neon to form heavier elements. This process continues, forming layers of fusion in the star’s core. Like an atomic assembly line, each layer uses the products from the layer above it to produce new elements and more energy. Until it reaches iron.

The onion-like layers of a massive star that is about to explode.

Iron is a special element because its nucleus is extremely stable. So stable, that unlike lighter elements, it consumes energy to fuse two iron nuclei together, rather than releasing energy. When a star’s core fills up with iron, it suddenly loses its internal energy source. Gravity, a weak but infinitely patient force, finally wins out over the star’s internal pressure. The star implodes.

As the billions of tons of matter come rushing together at relativistic speeds, all hell breaks loose. Atoms are disintegrated and recombined into exotic isotopes and giant atoms like lead and plutonium and uranium. Every atom in the universe heavier than iron was formed in the chaotic forge of a supernova. Faster than the blink of an eye, the collapse rebounds off of itself and becomes a tremendous explosion that shatters the star and sends all of its newly formed elements streaming into space.

The Crab Nebula was a star once. It exploded as a supernova in 1054, and was so bright that it was visible during the day for 23 days and at night for two years. At its center is the Crab Pulsar: a rapidly spinning neutron star.

That is a supernova. Left behind where the core of the star was is a tiny remnant. If the star was less than about 20 times the mass of the sun, the remnant will be a neutron star: a ball of neutrons the size of a city but with the mass of a star. Neutron stars are among the most awesome objects in the universe. Instead of the pressure due to fusion that supports normal stars, neutron stars are supported by “degeneracy pressure”: the fact that you can’t put two neutrons in the same place.  Neutron stars spin thousands of times per second, they have tremendous magnetic fields, and they are so dense that a teaspoon of neutron star-stuff would weigh about ten million tons. If you dropped that teaspoon on earth, it would punch holes in our planet like it wasn’t even there.

If the star was really big, then even degeneracy pressure isn’t enough to hold up the material left over in the remnant. In this case gravity really does win. The stuff collapses and just continues to collapse forever. It becomes so dense that you would have to go faster than the speed of light to escape its gravity. The core of the star forms a black hole.

Ok, so that’s a supernova. So what’s a nova? A nova is a special case that happens in binary star systems. See, not all stars explode as supernovae and form neutron stars or black holes. Most stars like the sun die a much gentler death, shrugging off their outer shells of gas in a gently expanding nebula and leaving behind a white-hot ball of carbon and oxygen called a white dwarf. In a binary system, one star can evolve to become a white dwarf while the other is still happily burning hydrogen, so you end up with a white dwarf and a normal star orbiting each other. When the second star begins to expand to form a red giant, something weird happens. It can’t expand! Instead, once it grows past a certain size, the white dwarf begins to suck up the outer layers of its neighboring star. Eventually, enough hydrogen accumulates on the surface of the white dwarf for fusion to begin again: boom! The white dwarf lights up as it burns up the fuel it borrowed from its neighbor. But that fuel doesn’t last long, so the star cools down after a little while and waits until it has enough fuel again. That’s a nova. It’s a brief, brilliant flash of light from a dead star that is sucking fuel from its neighbor like a vampire.

A white dwarf steals fuel from its companion until it has enough for fusion to re-start, causing a nova.

Just to complicate things, it is possible for a nova to become a supernova. Eventually, the white dwarf will accumulate so much mass from its neighbor that it can no longer hold itself up against gravity. In a fraction of a second, the white dwarf will collapse and rebound in a supernova explosion. This type of supernova (type Ia)  leaves no remnant, but it always produces the same amount of light, since it always comes from a white dwarf that has the same mass. This makes Type Ia supernova very useful for measuring distance in the universe. If you know how bright something is, and you can see how dim it looks due to distance, you can figure out how far away it is.

So what does all of this have to do with starcraft? Well, in the mission in question, the star is “about to go nova”. But it’s clearly not a white dwarf. If anything, based on the picture it is a blue giant. If we’re meant to understand that it is about to go supernova, then we run into another problem: the planet. Stars that are about to go supernova have expanded to hundreds or thousands of times their original size, and in doing so they typically consume their planets. When the sun becomes a red giant, its surface will be about where Earth is now. Even if the planet was far enough away that it was spared, the solar wind from a giant star would be powerful enough to rip the atmosphere away from a rocky planet easily. In fact, since the star depicted is blue, it probably has such a powerful stellar wind that its cool outer layers have been blown away. The planet would be a radiation-baked wasteland long before the star exploded. And if you were on a planet when its star exploded, you wouldn’t be faced with a slowly advancing wall of fire. The planet would be scorched like a moth in a bug zapper. Poof. A rocky, highly radioactive lump might be left behind.

And finally, you can’t look at a giant star and say “we have four hours before that thing goes supernova!”. It doesn’t work like that. You’d be lucky if you could pinpoint the explosion to within a few million years. Stars evolve on a timescale that is so much longer than anything we’re used to, it’s hard to comprehend.

A swarm of diamondbacks fire their "railguns" at a train.

In the Starcraft 2 campaign, there is a unit called the “diamondback”. It’s a sort of hovertank, and it is useful for hunting down other vehicles because it is armed with dual “rail guns” that can fire while it moves. In the game, the rail guns are depicted as some sort of energy weapon: they fire hot blue beams at the target. This disturbed me because rail guns actually do exist, and they most certainly don’t fire blue energy beams!

So what’s a real rail gun and how do they work? I’m so glad you asked!

To understand how a railgun works, we need to review some basic physics. In fact, railguns are often used as a homework problem in introductory electricity and magnetism! Whenever you have a current flowing through a wire, it generates a magnetic field that circles around the wire. You can use the “right hand rule” to visualize this. If you point the thumb of your right hand in the direction of an electrical current, the direction that your fingers curl is the direction of the magnetic field produced by the current. In a railgun, the power source, the two parallel rails and the conductive projectile form a circuit, with the current flowing from the power supply out one rail, crossing through the projectile, and then back along the second rail. If you use the right hand rule, you can convince yourself that the magnetic field between the rails points upward in between them, as shown in this diagram:

A schematic of a railgun showing the circulating magnetic fields around the rails and the resulting Lorentz force acting on the projectile. (Borrowed from How Stuff Works)

So, we have a current flowing across the projectile, from one rail to the other, producing an upward magnetic field between the rails. When you have a current flowing in a magnetic field, that actually results in a force on the thing carrying the current. That force is perpendicular to the current and the magnetic field, and also follows a form of the “right hand rule”. Point the fingers of your right hand in the direction the current is flowing (in the case of our projectile, it is flowing across the projectile from one rail to the other) and then partially close your hand so that the fingers are now pointing in the direction of the magnetic field (upward for our railgun) and your thumb will point in the direction of the resulting force. For the railgun, the force is along the rails, away from the power supply.

This force is what propels the projectile out of the railgun. The result is a gun that doesn’t use any explosives, but can launch a projectile at enormous speeds. The larger the current, the larger the force on the projectile, and the faster it goes! The rails themselves also are subjected to a huge amount of force trying to push them away from each other, but a well-designed railgun would be able to withstand that.

This photo is from a US Navy railgun test in 2008. The projectile was fired at 2500 meters per second, just a fraction of the velocity intended for the final version of the gun. The "fire" behind the projectile is a plume of plasma, presumably from the erosion of the rails and the projectile during firing.

Railguns aren’t science fiction: they actually exist. The US Navy has tested prototypes of a system that would be able to hit targets hundreds of miles away, and an experimental system developed by the Institute for Advanced Technology has a prototype that could punch right through a tank. The problem with current railguns is that the rails wear out due to the intense heat and forces that they have to withstand for every shot.

Railgun projectiles are much simpler than missiles or even bullets because they don’t contain any explosives. Instead, they do damage because they hit their target at extremely high speeds, and the kinetic energies involved do as much or more damage than explosives. This makes the projectiles much cheaper and safer to store, and if they could be made small enough to be mounted on a vehicle like the diamondbacks in Starcraft 2, they would also be easier to aim than a traditional gun simply because their bullets travel faster. (For very long distance firing such as for the Naval prototypes you still have to account for pesky things like the rotation of the earth, just like regular cannons.) Reloading might also be faster since there wouldn’t be an empty cartridge to eject after every shot.

A diagram showing how the naval railgun would be used. Note that is says for "direct fire" purposes, the projectile reaches the horizon in 6 seconds!

In many ways, the role that the railguns play in Starcraft 2 makes sense: they are intended to take down armored vehicles and can aim and fire rapidly on the fly. This fits perfectly with the advantages that real-world railguns would have over traditional guns! Current railguns are still in development, but I see no reason why in the future there shouldn’t be railguns suitable for the role depicted in Starcraft. My only real complaint about the railguns in Starcraft 2 is that they look like blue energy beams! Maybe they fire so fast the projectile is turned into a beam of plasma? Or maybe blue beams just look cool. I suspect the latter.

The results of a typical AI battle in Starcraft: Brood War. The Protoss basically dominate.

Anyway, before I launch back into the Science of Starcraft, I thought I would share this post about the Computer Science of Starcraft over at Twenty Sided. You may be good enough at Starcraft to regularly beat the AI, but I’m not. I’m just too slow. So I was interested to hear the results of this experiment, where Shamus set up a map with seven AI players and a human observer, and ran it repeatedly, tabulating the results to learn a little more about how the AI ticks. He found (somewhat unexpectedly) that the computer was by far most effective with Protoss and worst with Terrans. He also has some interesting observations about how the AI uses special abilities like the Templar’s psi-storm agains human players and computer players:

I’ve come to suspect that the AI cheats a bit and detects clusters of units which have been grouped by hotkey by human players. This is very naughty if it’s true.

Anyway, it’s an interesting look at the AI of the original Starcraft. The custom map is even available to download if you want to try the experiment yourself!

A zerg swarm, silhouetted against some colorful nebulae as they cross the vacuum of space.

In Starcraft, the biological, hive-minded Zerg can survive and even thrive in the vacuum of space, while the more fragile humans (and presumably the Protoss) require some sort of space suit. So that got me wondering: How plausible is it for living organisms to be able to withstand the vacuum, extreme temperatures and high radiation levels of space?

Fist of all, I’m going to set aside how the Zerg fly around in space. That may be the subject of a future post. I’m more concerned with just the idea of a hydralisk standing on an exposed moon-like surface and not immediately freezing or suffocating or otherwise dying gruesomely.

As you may imagine, NASA is quite interested in how living things react to space-like conditions. Between concerns over contaminating places like Mars and Europa with terrestrial microbes, and that whole “launching humans into space” business, there have actually been a lot of studies done on the topic.

Before we dive into more extreme forms of life, let’s examine what happens to a human exposed to vacuum. I want to clear up one misconception right away: You don’t pop like a balloon in space. Nor do you instantly freeze solid or pass out. It turns out that your circulatory system provides enough pressure so your blood wouldn’t boil even in zero pressure, and you remain conscious as long as the oxygen that’s already in your blood lasts (about 15 seconds). The biggest danger is holding your breath: don’t do it!

Even though humans don't instantly die in space, it still is deadly. That's why so much work goes into designing good space suits for astronauts.

When exposed to vacuum, all the air in a person’s lungs goes rushing out in a vain attempt to fill the void. This can cause serious damage if you try to hold it in, in much the same way that a scuba diver who inhales pressurized air at depth risks fatal lung damage if she holds her breath and then swims to the surface.

You don’t instantly freeze in space because there is no effective way to lose heat! Normally we’re surrounded by air which can convect heat away, but in space the human body is not in contact with other matter, so the only way it can lose heat is by radiating it away as infrared light, which is a very inefficient process. Anyone who has ever used a thermos to keep their coffee warm knows that heat doesn’t transfer through a vacuum very well!

Of course, people still have issues when exposed to space. You can get a nasty sunburn in seconds. You can get the “bends” (another affliction of SCUBA divers, in which bubbles begin to form in the bloodstream and cause damage). There will be tissue damage. Hence the bulky space suits that NASA uses and the bulky space marine suits in Starcraft.

But the point is that even fragile creatures like humans can survive for a few tens of seconds in a pinch. But we want to talk about the Zerg: insect-like creatures that can survive intense radiation and the vacuum of space with little to no damage! How plausible could that be?

Well, let me introduce you to the tardigrade, an insect-like creature that can survive intense radiation and the vacuum of space with little to no damage! Tardigrades, also known as “water bears” are microscopic, water-dwelling, segmented and absurdly durable creatures. They are especially hardy when they are in a state of suspended animation.

Tardigrades (a.k.a. "water bears") - distant relatives of the Zerg?

According to Wikipedia:

Some can survive temperatures of -273°C (-460 °F), close to absolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more radiation than other animals, and almost a decade without water. In September 2007, tardigrades were taken into low Earth orbit on the FOTON-M3 mission and for 10 days were exposed to the vacuum of space. After they were returned to Earth, it was discovered that many of them survived and laid eggs that hatched normally, making these the only animals known to be able to survive the vacuum of space.

There are also plenty of simpler creatures that can survive in extreme conditions. For example, the bacterium deinococcus radiodurans can repair its DNA on the fly, withstanding doses thousands of times higher than the lethal limit for humans. For the zerg to survive long in space, they would need to share this ability to repair radiation damage rapidly.

They would also have to be able to survive without air, and to completely exhale all the air inside them safely before entering space. One possible mechanism to help the zerg survive without air is the creep. Creep provides sustenance to zerg buildings, but if it also could nourish zerg creatures, it might keep them going without the need to breathe. Combine that with a slow metabolism, making any nourishment or oxygen absorbed from the creep last for a while after they leave it, and you might be able to do away with the need to breathe. This is admittedly far-fetched, and would work much better for microscopic creatures with higher surface area to volume ratios.

The problem with a slow metabolism is that extreme temperatures would be problematic. Although an organism doesn’t freeze or burn instantly in space, long-term exposure would still be deadly unless the organism is able to moderate its temperature by matching its metabolism to the amount of energy going in and out while it sits in space. Did you ever wonder why space suits are white? It’s to reflect sunlight! Humans already put off a lot of heat, and it’s already difficult to get rid of it in space, so NASA doesn’t want even more heat from the sun making things too toasty for the astronauts. I’m not sure I have a good way around this for the zerg. Take a look at any zerg swarm and they look pretty active, but that means a high metabolism, producing excess heat that needs to be dealt with and requiring extra calories and, presumably, oxygen which would be difficult to get in space.

Pressure is, in my mind, less of a problem. We know that the zerg have an armored carapace, and since even fragile human tissues can provide enough confining pressure to keep the fluids inside from boiling, I’m willing to believe that the Zerg could survive extreme low pressures.

This hydralisk seems perfectly happy in space. Just look at that big grin!

The question of course, is how the Zerg could evolve in space? But luckily, we can wave our magic wand to explain this point. We’re told in the games that the zerg did not really evolve independently but were engineered by the ancient and powerful Xel’naga, combining many different species. Considering that present-day puny humans are capable of splicing genes from multiple species together to create improved organisms, I have little trouble picturing an advanced intelligence picking and choosing all the right genes to create space-hardy creatures. Maybe the zerg even have a little bit of water bear DNA in them!

I was always a fan of the Protoss: super-advanced technology, powerful units, and those awesome plasma shields protecting everything from the lowliest probe to gigantic carriers. But I always wondered: could those force fields really work?

Well… Sort of.

It really depends on your definition of a force field and what you want to prevent from passing through. Electric and magnetic fields can exert forces on charged objects, so you could call those “force fields.” If you accept that definition, then there have actually been some NASA studies of how to use force fields on spacecraft and lunar bases.

One of the biggest problems facing human space exploration (aside from the politics) is that space is a dangerous place for humans. Even if we can launch people to Mars, there is a lot of radiation out there, both from the sun and from high-energy events out in the galaxy. That’s why two studies at NASA’s Institute for Advanced Concepts (which has, sadly, been canceled due to lack of funding) looked into deflecting the radiation with electromagnetic shields.

A lot of the radiation in space is in the form of charged particles: electrons, protons, and even larger atomic nuclei. If you remember your science classes, charged particles are attracted to objects with an opposite charge and repelled by objects with the same charge. So if you want to protect your lunar base, you just set up some strategically placed charged spheres, like so:

A NASA study suggested using charged spheres above a lunar base to create a force field to deflect radiation.

The other NIAC study focused on protecting the crew during long-duration missions. Even with advances in propulsion technology, it will still take months to get to Mars, and all the while the crew will be bombarded with radiation. Unless their ship is shielded! This concept would shield the spacecraft by using powerful magnetic fields to divert the solar wind plasma. “Plasma” in physics refers to a gas in which the atoms have been stripped of some (or all) of their electrons. That means that the plasma can be shaped by magnetic fields, creating a safe zone where the crew of the ship could stay protected.

You’re actually being protected from radiation by just such a shield right now! The Earth’s magnetic field diverts the solar wind and prevents it from hitting the surface, except at the poles. That’s why you only see auroras at the north and south pole: that is where all the solar wind plasma is being funneled down to hit the upper atmosphere. When the radiation hits the atmosphere, it excites the atoms and causes them to glow in the familiar colors of the aurora. The concept for the shielded ship would essentially create a miniature magnetosphere to protect the crew.

A computer simulation of plasma hitting a magnetic field and being diverted. Red is denser plasma (and therefore more radiation), black is less dense. The researchers confirmed this result in the lab. (Figure from Bamford et al., 2008)

Ok, but let’s be honest: those shields are not nearly as cool as the protoss plasma shields. We want something that can stop bullets! We want to deflect hydralisk spines!

Well, I’m afraid nothing quite so awesome exists yet, but there is one bit of technology that is similar: plasma windows. These are narrow slabs of plasma confined by – you guessed it – magnetic fields. They actually have a lot in common with science fictional plasma shields! The hotter a plasma gets, the more viscous it gets, so plasma windows are actually able to act as a strong barrier between air and hard vacuum. Presumably, with enough energy you could create a plasma window capable of blocking more substantial regular matter. Right now plasma windows are tiny, but again, with a huge supply of energy, they could possibly be made larger. Interestingly, plasma windows do not block laser light or electron beams, so even if larger versions were made, they would not protect against weapons that used those forms of radiation.

Wrapping plasma windows all the way around something in a sphere would be very difficult, and projecting a shield onto a distant target, like the Terran science vessel’s “defensive matrix” capability is definitely not possible with today’s technology and understanding of physics.

So, unfortunately, plasma shields exactly like the ones that protect Protoss units are not realistic, but there are various force fields and plasma-shield-like technologies being developed. We may not be able to keep out bullets or zerglings, but some of the shields being developed block a much more realistic threat to human explorers: radiation.

References:

Lunar Base Electrostatic Shield

Plasma Windows

Bamford, R., Gibson, K., Thornton, A., Bradford, J., Bingham, R., Gargate, L., Silva, L., Fonseca, R., Hapgood, M., Norberg, C., Todd, T., & Stamper, R. (2008). The interaction of a flowing plasma with a dipole magnetic field: measurements and modelling of a diamagnetic cavity relevant to spacecraft protection Plasma Physics and Controlled Fusion, 50 (12) DOI: 10.1088/0741-3335/50/12/124025

The Overmind

Well folks, it looks like I’m not the only one interested in the Science of Starcraft! The gaming site GamePro has a very interesting article taking a look at several aspects of StarCraft science, including teleportation, zerg in space, a hive mind, and hybrid species. They cover each topic pretty quickly but it’s still worth reading. But be sure to check back here! I’ll dig into those and other topics in a lot more depth.