Saturday, 7 December 2013

The Waters of Mars

If you haven't seen it, 'The Waters of Mars' is an episode of Dr Who in which some alarming things are discovered about frozen water beneath the Martian surface, and some other alarming things are discovered about the crew of the first manned Martian base (a British one, of course). It is a good yarn and it gave me the idea for this post.

But this is not about strange things in the Martian water, it is more about the water itself and the fact that is seems to be there at all, or possibly it isn't now, but it definitely was once, which is more or less the point.

When I was a kid I read stories by Heinlein and Blish where people (mostly kids, actually) wandered about the surface of Mars and found it a challenging environment but not much more challenging than, say, Antactica. The air pressure was lower and it was a lot colder, but with some breathing apparatus and suitable clothing, trekking across the Martian wastes was practical enough. And there were signs of life. Lichens mostly but, in Heinlein's stories, more sophisticated plants as well as animal life and even intelligent life. There was a sense that the environment had once been a lot more friendly to our kind of life but it had changed for some reason and this was all that was left. The Dr Who episode followed a similar line.

The recent rover missions to Mars support the idea that Mars once had a decent atmosphere and running water on its surface. The two go together. Under very low pressure, such as that on Mars today, water boils even at low temperatures and doesn't exist long in liquid form. So to support the geological findings of old stream beds etc there needs to have been more atmosphere, and for the water to not be frozen, it needs to have been warmer.

The science fiction I read as a kid was more hopeful than the science at the time. Although a few decades earlier some astronomers had suggested there was a global civilisation on Mars, we all knew that it was too tough an environment to support any such thing. Very little atmosphere, harsh radiation and very cold. If there was any life there it was hard to see how it could have started, let alone survived.

Did you spot the mistake there? Actually there are two of them, but the second one is subtle.

The more obvious mistake is the problem of induction. We make observations and we assume that what we see is how things are, which is okay. Then we project those observations to say something like 'it has always been like this' which is not so okay. We also often project them to say 'it is like this everywhere', in this case everywhere on Mars but we are pretty quick to project our findings to everywhere in the universe. For example the speed of light, the law of conservation of mass and even the notion of cause and effect, we assume to apply everywhere. We do this because we don't have better information. When we get better information (evidence that Mars has had a different environment in the past) we find we were wrong and we have to adjust our thinking. Being willing and able to adjust our thinking is a huge virtue, clinging to outmoded ideas in the face of conflicting evidence is not, though sometimes people try and say it is. But adjusting our thinking doesn't solve the problem of induction. We might be wrong about everything because of this.

The less obvious mistake involves just why we keep on inducing things despite it being obvious that we keep getting it wrong. We insist on keeping to the simplest explanation we can come up with. It is so much simpler to assume that things are consistent across space and time, simpler to assume Mars has always been the same as it is now, so that is what we do. Then we find it is more complicated and have to adjust. The simplest explanation seems to be actually never the right answer, though it is a long tradition in science and any other form of knowledge that keeping things as simple as possible is a good thing. But we need to be clear eyed about this. We pick simple explanations because we like them, not because they are in any way better or more true. We simply choose to believe, for the moment, until we are proven wrong anyway, that the simpler explanation is correct.

We think we know how the Martian water got there, something like icy meteorites crashing into the planet, possibly even bringing the strange life forms in the Dr Who episode. But it might have been something completely different that is much more complicated. In fact, it probably was.

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