Sunday, March 14, 2010

Extraterrestrial life: I am a skeptic

According to "Poll: do you believe in extraterrestrial..." a majority of the readers of that blog think that the extraterrestrial life exists.

Well, while I have probably answered "I don't know", count me as a skeptic.

Czech socialist boss Mr Jiří Quimby Paroubek has promised the voters to do everything he needs to do to keep his feeding trough and to make his socialist dreams come true. If he needs the communist deputies to vote with him, he won't hesitate to team up with them, and if the extraterrestrial aliens ever land in the Czech Republic, he said, he would be working with them on the socialist project, too. Several ETs landed on his rally in the city of Litoměřice and elsewhere.

It seems obvious to me that most people who feel "certain" that there must exist life on other celestial bodies are trying to prove something emotional to themselves. They're trying to overcompensate the centuries in which the people found extraterrestrial life impossible - and in which they thought that life could not evolve naturally and it needed an intelligent creator.

Well, they were wrong but I still think it's kind of difficult for life to evolve. Drake's equation was proposed as a method to calculate the number of ETs. Most often, it was used as a tool to fool ourselves into thinking that life must be almost everywhere.

Some readers of the aforementioned blog say that it's "arrogant" to suggest that ours might be the only living planet. Well, I find such emotional labels irrational and kind of dishonest. Having one living planet or many living planets are just two possible answers to the question. Both of them can be right, both of them can be wrong. It's just stupid to invent insults such as "arrogant" for one of them.

Many of these nearly philosophical questions - which have no known, well-established answers - are often being politicized in this irrational way. Incidentally, the number of other solutions of the stringy equations in the "landscape" that are potentially viable for life is usually politicized in the other way. It's surely "arrogant" if someone thinks that the right theory has 10^{500} solutions qualitatively similar to ours, people say.

Is that really arrogant? Well, it's just a hypothesis. It may be right or wrong but it can't be arrogant. There's a huge evidence that this large number of semirealistic solutions to the equations of quantum gravity actually does exist, and whoever wants to hide himself from this possible answer by rejecting it a priori as an "arrogant" answer is just fooling himself. He's not scientifically honest because the answer is not known for sure and the circumstantial evidence actually suggests that his opinion is incorrect. In science, only arguments matter - while ever more vitriolic methods of mudslinging and propaganda preventing people from considering alternatives don't matter and mustn't matter. It's very important for every scientifically inclined person to frequently emphasize and patiently & politely explain why the likes of Peter Woit are dishonest propagandists and shitheads.

Crichton and the people's illusion of knowledge

Michael Crichton spoke very intelligently about these matters in "Aliens Cause Global Warming" (TRF). Sad he's gone.

Drake's equation expresses the number of ETs as a product of very many quantities - the number of stars, the percentage with planets, their percentage with the right temperature, and dozens of other factors. And the goal of writing them in this way is to say that each factor is pretty high, so the product must be high, too.

In reality, if you write the number of ETs in this way, you don't improve your knowledge of the true number much. Most of the factors are unknown but even if there were some known ones, there is a much higher chance that at least some of them is unknown and might be very small. ;-)

According to Crichton, Drake's equation was a template for a family of pseudosciences that have culminated with man-made global warming. The question is how many people one SUV kills by emitting CO2. ;-) So they suggestively write the result as a product of many quantities - CO2 emissions, percentage that stays in the air, bare climate sensitivity, climate feedback coefficient, the effect of one degree on sea level or rainforests or anything else, the effect of changed sea level on the society, the effect of the changes of the society on the number of people who die, and so on.

They have to work with a very long chain of such factors. Each of them is encoding some influence in a long chain of events and influences. Some people think that by writing such a chain or such a story, they know much more.

But the whole chain may be a very bad approach to answer the original. The longer it is, the more likely it is that the chain has at least one weak or broken link. In fact, it's almost certain that in the AGW case, it's a completely wrong way of looking at the effect of an SUV. The effect of an SUV on anything like the mortality rate in Africa is essentially zero. Every sane scientist knows so.

The chain is a propaganda tool meant to fool people into believing that there is an established story - even though, clearly, almost nothing is really established about the chain. Moreover, all the individual factors in the product are being routinely overestimated. The more factors you work with, the bigger overestimate of the product you get by a fixed overestimate of each of them (in the same direction). :-)

If I return to Drake's equation, well, there almost certainly exist some relatively complex organic molecules somewhere. But is it enough for the evolution industry to kick in? I have significant doubts about it.

For the evolution to work in the conventional, gradual way that ends up with something like a conservative scientist, to choose a proper representative of the relatively intelligent life on Earth, you need the ancestors to use a qualitatively identical set of biological tools and coding schemes, if you allow me to speak very generally. Any qualitative jump could make the gap very serious and unlikely to be transcended.

But you need a lot of copies of the primitive organisms. So the most primitive organisms that are relevant for the expansion of life must already be sophisticated enough for them to be able to
  • reproduce in the life-less environment of the young planet
  • mutate and show the potential for self-improvement (which must allow the complexification of the genetic code without breaking the life story altogether).
It's not an easy business. Life is a miracle and it's amazing that science has made irreligion possible, using the words of Steven Weinberg. It suddenly became plausible - and likely - that no miraculous intervention was ever needed. However, we don't really know how lucky the Earth had to be for the first primitive ancestors of the modern life that were already able to reproduce to emerge.

The simplest organisms of this kind we know are already pretty complex. The human genome is composed out of approximately 3 billion DNA base pairs. That's like 6 billion bits of information - or a gigabyte file, roughly speaking.

Clearly, it would be impossibly unlikely for such a long molecule to be arranged by chance - the probability would be something like 10^{-billions} - much much smaller than the inverse number of particles in the visible Universe (or other things). And Charles Darwin has shown that it wasn't really necessary: life started with simpler codes.

But how much simpler could they really be? How much can you shorten the code so that you get an organism that is able to reproduce? If you manage to shorten to code from 3 billion base pairs to a hundred of them, it could still be way too long to appear by chance because 4^{-100} is an impossibly tiny probability.

Craig Venter's minimalistic organisms has 381 genes which means many more DNA base pairs.

So the DNA-based life probably had to start by a trick from a simpler life. People talk about the RNA primordial life. It might be progress but it needs one more special event - the birth of DNA out of RNA. Moreover, the progress is not too big. RNA must still be pretty complex for the life forms to reproduce.

If you start with something else, like the creation of viable RNA life forms out of some folding proteins, or whatever buzzword you choose, you will face new problems. You will have to include new crucial events in your theory that may be extremely unlikely. The RNA molecules of the first viable RNA life forms were still too long. Their whole segments had to be created as blocks that would later merge. But one needed many of those blocks. Can it be done?

So we don't really know how likely it is for the most elementary living forms similar to ours to emerge, how many "qualitative" and "difficult" steps had to be overcome, and what their probabilities were. So it's silly to claim that we know that life has to be almost everywhere. After all, we only have an experimental upper bound: there's no industrial life except for ours in 50 light years away from the Solar System. As Fermi asked, where are they?

There exists one general reason to think that simple life could appear quickly - or with a high probability. And it's the fact that our geological history indicates that the life on Earth emerged relatively quickly after the planet was created. If we considered an alternative hypothesis that assumes that it is very unlikely for the simple life to emerge, such a hypothesis would predict that it's much more likely for life to flourish in later - or at least generic - stages of the star's life. However, the Sun was young when the primitive life on the Earth began.

Does it prove that the simple life does emerge quickly and easily?

Not really. First of all, the argument above is a probabilistic one. The life could have appeared quickly on a young Earth by a coincidence. However, there are other major reasons why the conclusion could be just incorrect. In particular, the seeds of the life on Earth could have been imported from other celestial bodies. Nature could have worked on these seeds for billions of years, before the Solar System was created. And some primordial seed may have been needed from the moment of recombination. The visible patch of our Universe could have been lucky to have such a seed.

Once again, we don't know. We don't know how much the life on Earth had to import for it to work. The probabilities of Yes vs No must be chosen comparable to 50% in all similar questions because we're qualitatively ignorant about them. We just don't know. It's clear that many things were produced locally on Earth. On the other hand, we know that many things have been imported. All the heavier elements came from an older generation of stars that produced the heavier elements. And they were important.

With a little bit of creativity, you can find loopholes in almost any argument that tries to "settle" the question about the number of ETs in one way or another. So I just don't know the answer. The closest experimental thing we have says that there seems to be no life in thousands of solar-like system in our neighborhood. So it's not quite crazy to assume that we're the only ones. But it's not a proven assumption, either.

Will we know the answer in a foreseeable future? I doubt it. One way to know would be to find another celestial body with (higher) life - which wasn't imported from the Earth. I am ready to bet, up to 50:1 against me, that this won't happen in our or my lifetime. Assuming that I am right, I am afraid that the question about the number of ETs will remain comparably unsettled as it is today for quite some time.

But we may still learn lots of stuff about the physics of life.

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