Ah, SMAC, how do I love thee? Let me count the ways.

Sid Meier’s Alpha Centauri is spoken of in hushed, reverent tones amongst a certain segment of the 4X gaming community, and for good reason: if you happen to like sci-fi, like I do, it is hands-down the best Civ-a-like game ever released. This isn’t down to how it plays, particularly, since if you suck away the sci-fi coating what you’ll find inside looks very much like Civilization 2 in terms of mechanics. Firaxis could have done much worse than base their game on Civ 2, but aside from a few bolted-on additions like the unit workshop and the social engineering interface replacing static forms of government, Alpha Centauri didn’t make any groundbreaking changes to the basic formula. What it did do was seamlessly weave that formula into a coherent sci-fi universe in a way that no other game has before or since.

The premise of the game is that a near-future humanity, locked in its final death throes, has built and launched a massive colonisation spaceship towards the Alpha Centauri trinary star system in the hopes of preserving something of the human race. Just as the ship – the ironically-named Unity — comes to the end of its decades long journey and approaches the Alpha Centauri system, factional infighting amongst the ship’s crew comes to a head and the Unity is sabotaged. Each faction escapes the ship in a landing craft and heads on down to the surface of the only inhabitable planet in the system. Displaying even less imagination than I do when it comes to naming things, the colonists dub their new home “Planet” and start scrabbling together the basic niceties required to start rebuilding human civilisation.

But not human civilisation as we know it. The different factions that formed on the Unity did not do so along national or organisational lines; instead they sprang up around charismatic leaders with their own personal ideologies about how future society should be run. This gives each of the seven factions a distinct thematic flavour in the way they play. Ironically for a big lefty like myself I’ve always been partial to Nwabudike Morgan’s ultra-capitalist settlements, where the enormous production outputs come at a cost of massive ecological damage and an increased upkeep cost due to pampered Morganite workers demanding the most opulent and wasteful settlements possible. The antithesis of the Morganites is Chairman Yang’s Human Hive, a totalitarian nightmare that combines the most extreme aspects of communism and fascism to great effect, where the population lives and works crammed into gigantic underground settlements that are basically massively upscaled versions of ant colonies. Then there’s Deidre Skye’s Gaian society, who aren’t your typical treehuggers because they have absolutely no qualms about siccing tame brain-devouring mindworms on you if you piss them off. Prokhor Zakharov’s University, Miriam Godwinson’s Believers, even Commissioner Pravin Lal’s wishy-washy remnant of the UN Peacekeeping forces – they all serve to give the opposing factions a level of personality above and beyond “Montuzema is a dick”.

The different factions are just one part of the rich background tapestry woven with loving care by Firaxis. They provide a political pretext for all the plotting and wars that take place before and after Planetfall, but the terraforming of Planet itself is also one of the key features of the game. Civilization games have always let you improve the areas around your cities, and the early ones hit you with nasty pollution penalties if you overexploited the land, but Alpha Centauri is the only one that I’m aware of that took it from being a major element of the gameplay to possibly the central tenet of the game. It’s to be expected given that the colonisation of an alien world would require a level of adaptation of the surrounding environment far above and beyond irrigating a few fields with water from a nearby river and calling it a day, but what strikes me about the terraforming in Alpha Centauri is the lengths Firaxis went to to create the illusion of an actual functioning ecology that you were disrupting with your “improvements”. Unless you take social engineering traits that reduce your ecological impact on Planet, screwing with it in a big way can have very unpleasant consequences because it is a living system and it will try to defend itself by zerging your bases with huge mindworm boils or reclaiming developed land by force-growing impenetrable fungus forests (thus incidentally providing a plausible rationale for the game’s barbarian units).

And of course because this is the future, and because you have magic future technology, the scale of the changes you can make dwarfs anything else seen in a 4X. The one thing that has always stuck with me are the Mohole mines; enormous holes bored all the way down to the bottom of Planet’s crust to extract valuable minerals that incidentally also happen to release vast amounts of heat from the planetary interior. Not only is this going to piss off the indigenous flora and fauna, but if you don’t want the sea levels to start rising you’ll have to counterbalance this extra heat with an artificial cooling mechanism like an enormous solar shade launched into space. It’s still all very simplified – mostly so that the player actually has a chance of understanding it – but it is nevertheless a system. It has domino effects that can lead to unintended consequences. Your ability to tamper with this system grows as you discover increasingly exotic future technology, as does the scale of the risk and the rewards.

Technology! I could genuinely write a short thesis just on how amazing Alpha Centauri’s technology tree is. Humanity starts out on Planet with only the most basic of resources, barely subsisting until you complete the first couple of tiers of the tech tree which focus on adapting to the new environment and recreating a functioning society out of nothing, as well as perfecting a few avenues of science that are works in progress today (string theory, anyone)? Researching these techs gives you the social engineering options, terraforming methods and base facilities to go beyond simple survival; improvement promotes growth and growth permits a larger industrial and scientific base, allowing you to tackle the near-future stuff like fusion power, mastering the quantum states problem inherent in photons and waves, and also the small matter of growing the industrial base to the point where you can start launching stuff back up into space again. And then after this intermediary stage comes the far-future stuff: stasis fields, unified field theory, controlled singularities and so on.

What I like about the Alpha Centauri tech tree isn’t just the way it flows smoothly from survival to prosperity to becoming a Kardashev Type I civilization, which is basically sci-fi catnip as far as I’m concerned. No, it’s the plausibility of the whole thing. Rather than somebody going “Right, we need a technology that will confer game ability X, let’s make something up,” this thing has instead been written by people who have at least a basic understanding of where science is likely to be going over the next few centuries. It gets rather speculative towards the end, and the timescale is rather compressed (if you ask me) in order to fit with the game’s one year per turn mechanic, but the underlying structure of it is perfectly sound. It first tackles the problems confronting scientists now, moves on to the things we think we might be able to do if we ever did solve those problems, and wisely leaves the hand-wavy space magic stuff towards the very end of the tree where it can’t concretely be ruled out because of all this other more believable tech that’s been researched. If you asked me for a roadmap of scientific progress over the next two centuries I’d probably just hand you Alpha Centauri’s tech tree. It’s like somebody managed to recreate the Civilization tech tree without the benefit of having actually had it happen so they know how it all turned out. Incredible.

Finally there’s the little atmosphere-building touches. The Secret Project (read World Wonder) movies have yet to be bettered, as far as I’m concerned. They’re not bombastic CGI experiences meant to reward the player for finishing the wonder; instead they’re far subtler pieces of work that, a lot of the time, actually give you second thoughts about whether or not the all-seeing AI policeman you just built was really a good idea. They rely on a lot of real-life camera footage that can occasionally make for genuinely uncomfortable viewing, and many of them focus on technological advance as a double-edged sword as we grow further apart from our squishy biological origins, in particular this one which is the only work of fiction I’m aware of to mention the probable downside of a “teleportation” device. The various quotes from faction leaders and other sources are scattered throughout the game, playing whenever you discover a technology or build a base facility for the first time, and these too tend towards being thought-provoking rather than the current trend of a cool/ironic one-liner about how awesome the thing you just researched is. As you play the game you’re getting this constant commentary that tells you about the world and also hints at the deeper sociological and ideological struggles that are going on behind the scenes as humanity struggles to adapt to an uncertain future on an alien planet.

I think limiting myself to just talking about Alpha Centauri’s world-building and atmosphere was a wise move, otherwise I could probably go on for ever. It’s a sci-fi 4X so it has to pay more attention to that side of things in order to get you invested in its universe, but what I really like about Alpha Centauri – and the thing that makes it unique, as far as I know – is how utterly the developers embraced the idea and wove it into the fundamental DNA of the gameplay. Galactic Civilizations 2 failed at building any sort of believable world whatsoever. Master of Orion 2 succeeded, which one of the reasons it’s so good, but it always treated it in a rather space opera-ish fashion as rather incidental to the actual process of playing the game. Alpha Centauri on the other hand doesn’t use a sci-fi universe to serve gameplay goals; rather, it is a sci-fi universe from top to bottom, and if you know nothing about planetary science and ecology you could do a hell of a lot worse for an education than playing a couple of games of SMAC on a medium difficulty setting. The base game is even on GoG now, look. Go and play it.

(Also you can occasionally throw out quotes from Nietzsche’s Thus Spoke Zarathrustra thanks to having heard them so many times in the datalinks. Your friends will be impressed to bits, I promise you.)

The post In Praise Of: Alpha Centauri. appeared first on The Scientific Gamer.

How do atmospheres work? As it turns out, the same way as everything else; that is, the gas molecules making up a planet’s atmosphere are bound to it by the planet’s gravity. However, there are some key differences. Inside the atmosphere all the different gas molecules are constantly moving around, colliding with each other, exchanging energy and then moving off in different directions. This means there are a couple of special rules that apply thanks to the difference in behaviour between a gas molecule and the unwieldy mass of squishy cells and organs that makes up the average human being. The general behaviour of a gas is described by the equation

where P is the pressure of its gas, V is its volume, N is the number of molecules of gas enclosed in that volume, k is something called the Boltzmann constant and T is the temperature of the gas in Kelvin.

The Boltzmann constant is necessary because temperature is not a property that can be applied to an individual gas molecule. There is no such thing as a gas molecule with a temperature of 300K; instead, the molecule will be moving at such-and-such a speed which gives it a certain kinetic energy, which will be different from the speed and energy of an adjacent molecule in the same volume. This speed is constantly changing as the molecule collides with other molecules and loses or gains energy, making it impossible to get discrete speed/energy measurements for a single gas molecule. The only way we can deal with a gas in any meaningful sense is by measuring the average kinetic energy of all the molecules inside it; this is expressed as its temperature. So in order to convert temperature — a measure designed to describe the general behaviour of a whole bunch of gas molecules — to the energy of a single molecule of the gas, we need to chuck in the Boltzmann constant k. The general idea is that the quantity kT will be on the order of (that is, somewhere close to, but probably not the same as) the energy of a given gas molecule in the volume V.

Understanding the difference between temperature and the kinetic energy of a single molecule is important for understanding how atmospheres work. All the gas molecules in a planet’s atmosphere are whizzing around at completely different speeds and kinetic energies even though the atmosphere itself has a certain temperature T. Most of the molecule velocities will cluster around the molecule speed described by that temperature T, but there will be many, many outliers which travel slower or faster. The range of molecule speeds and how they change with temperature is described by something called the Maxwell-Boltzmann distribution.

That graph may look a bit bewildering, but hopefully once I’ve explained what’s going on it won’t be all that complicated. The number on the vertical (or y) axis is the probability function, while the number on the horizontal x-axis is the speed of the molecule. What the graph is describing is what the probability is of a certain molecule in a gas travelling at a certain speed given a temperature a. If a single molecule has a 0.6 (or 60%) chance of travelling at a certain speed, then it follows that 60% of all the molecules in the gas will be travelling at that speed. The three different coloured plots on the graph show how this probability distribution changes at three different relative temperatures, a = 1, 2 and 5.

So from the graph we can see that for a low temperature of 1, all the gas molecules will be tightly clustered around a speed of 1-2, with none of them exceeding a speed of five³. Increasing the temperature to 2 changes the shape of the distribution; the average speed of a gas molecule is now 3-4 but the range of speeds at which the gas molecules as a whole travel is now much larger, as shown by the wider base and shallow peak of the distribution. Finally, for a high temperature of 5 the speeds of the gas molecules are much more evenly distributed, with a small peak at about 7 but with a long tail that stretches off all the way up to 15.

This long tail is the thing that interests us. Even if the temperature of an atmosphere is low, and the majority of the gas molecules in it are travelling at low speeds, some of the molecules will be travelling faster. A few of them will be travelling much faster – and if they’re travelling fast enough, they’ll reach what is called the planet’s escape velocity.

The escape velocity is a measure of how fast something has to be going in order to escape the planet’s gravity well permanently. You could strap yourself into a rocket and blast yourself into space, but if your rocket wasn’t powerful enough to propel you up to escape velocity before it ran out of fuel you’d eventually plummet back down to Earth if you didn’t manage to get into a stable orbit. The escape velocity changes from planet to planet as every planet has a different mass and therefore a different level of gravity, and furthermore since the gravitational force a planet exerts on an object diminishes the further away that object is from it, the escape velocity is greatest at the surface of a planet and diminishes as you progress upwards into space.

Now that we have all the background information down, we can finally start to look at why atmospheres are the way are. In reality atmospheres are not composed of a single homogenous gas but instead a whole variety of different elements. Even inside an atmosphere with a single uniform temperature the heavier gas molecules such as nitrogen and oxygen might have the same kinetic energy as a hydrogen molecule, but they’ll be travelling at lower speeds thanks to their greater mass. This causes the various gaseous elements inside an atmosphere to differentiate themselves according to weight; the heavier, slower stuff can’t get very far off the ground and is found close to the surface, while the lighter molecules can and slowly migrate to the higher portions of the atmosphere over time. If a molecule is light enough and the air around it is thin enough (so that it doesn’t get its direction of travel changed by a collision with another molecule) then the velocity of that molecule can easily exceed the planet’s escape velocity and escape into space – and this is true even if the temperature isn’t high enough for the average velocity of a gas molecule to exceed the escape velocity because the long tail of the Maxwell distribution ensures that some of the molecules will be moving fast enough, causing the planet to slowly (or not so slowly) bleed portions of its atmosphere away into space.

How likely a given molecule of gas is to remain part of the atmosphere can be calculated mathematically. My notes here don’t go into the specifics of how the Maxwell distribution and the interactions between molecules dictate this, but if a molecular constituent’s thermal velocity is near one-third the escape velocity, then about half of that molecule type will have escaped from the atmosphere within weeks. If the thermal velocity is one-fifth of the escape velocity, then the planet will lose half of that molecule type after a billion years. And if the thermal velocity is one-tenth of the escape velocity, then the planet will retain that molecular constituent indefinitely.

Therefore we run two parallel equations.

where G is the gravitational constant and k is the Boltzmann constant.

Everything in these equations that isn’t a number or a constant is a property that affects the likelihood of a planet losing a certain type of gas – the mass of the planet, the radius of the planet (since gravity diminishes the further away you go from the centre of mass), the temperature of the atmosphere and the mass of the gas molecule. If, at the end of the day, v_thermal is more than 0.1 v_escape, the planet will eventually lose that gas type. How much more v_thermal is is what dictates how quickly this happens.

From this the compositions of the atmospheres of the planets become much clearer. Earth has very little hydrogen or helium in its atmosphere because it’s not massive enough to hold on to them. Jupiter has no such problems (not to mention forming in an area where light materials were much more abundant) and so it’s still got most of its primordial hydrogen – this is why Jupiter and the other outer planets are referred to as gas giants. Mars is a relatively light planet and so much of its atmosphere has seeped away over time, but it still retains a fair amount of the heavier stuff such as carbon dioxide. Poor old Mercury gets hit with a double whammy: not only is it situated very close to the Sun — raising its surface temperature and thus its escape rate — but it’s also constantly being blasted by the solar wind which also serves to strip away atmosphere, as a result of which it doesn’t really have one any more.

So how is this all relevant to the terraforming argument? Well, if we run the equations above for an oxygen molecule in the Martian atmosphere we get a mean thermal velocity of 630 metres per second. Mars has an escape velocity of 5 kilometres per second. While Mars is losing oxygen molecules to thermal escape over time it’s doing it very slowly. This means that the fact that Mars has a crappy atmosphere in terms of potential human habitation has very little to do with how small it is, and is in fact heavily related to two other factors:

• Attrition by the solar wind; something we don’t have to worry about so much here on Earth thanks to the magnetosphere.
• Mars getting absolutely creamed by asteroid/comet impacts (along with every other terrestrial planet) during the Late Heavy Bombardment. Like, so much so that there’s still chunks of Mars dating from around about then floating around the Solar System which occasionally fall to Earth. This is because the impacts were so violent they threw up ejecta and debris from the surface so high and so fast that they reached escape velocity and were never seen again. From the point of view of Mars, anyway. If the Late Heavy Bombardment did that sort of thing to solid rock, imagine what it did to the atmosphere.

The first point is something that any prospective terraformers would still have to worry about, and given the lack of any magnetosphere on Mars the solar wind is likely to contribute far more to atmosphere loss than thermal escape. Barring some sort of cataclysmic event we don’t have to worry about the second ever happening again, at least over human timescales. As a result, while any Martian atmosphere we generate would dissipate relatively quickly, that “relatively” is relatively to the lifetime of the planets and the Solar System. In timescales relevant to humans even the most pessimistic estimates have a usable Martian atmosphere sticking around for 200,000 – 300,000 years, and it’s more likely that it’d last for a million plus. Are we really going to say terraforming the Martian surface isn’t worth it because the atmosphere will “only” last for 300,000 years?

1. It was a talk for kids aged 12-16 so I couldn’t say what I really thought of them.

2. The moral of this story is either that you should never use even mild language like “crazy lunatics” in case there are some crazy lunatics in your audience, or else that no matter what you do you should be prepared to go through life inadvertently offending an awful lot of people.

3. This graph uses dimensionless measures because the shape of it will be the same no matter what system of measurement you use to measure the temperature and speed of the gas.

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