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The Fermi Paradox Again

Entry 1839, on 2017-02-23 at 20:49:53 (Rating 1, Science)

NASA recently announced the discovery of 7 Earth-like planets orbiting the relatively close star, Trappist-1, and that 3 are in the "Goldilocks Zone" (not too hot, not too cold). It is now expected (at least I have heard this although I don't think it is officially stated anywhere) that almost all stars have planets and that a significant fraction of them might have conditions similar to Earth.

This is significant because for many years no one knew how many planets existed in the universe (although there were some discoveries going back to 1988 it was only Kepler, HARPS, and some other new advanced telescopes more recently that lead to significant numbers of discoveries). So it was generally assumed that planets were common but there was no way of knowing.

Another great mystery of the universe is how likely is life to arise and under what conditions. Here we are even worse off than with the planets because we are literally working with a sample size of 1. No other life has been discovered outside of the Earth, although there have been some interesting discoveries on Mars, none have lead to any proof of even primitive life.

It is generally assumed that life will have to be broadly similar to what we have here on Earth. I don't mean similar in any superficial sense but in broad principles. So it will be based on carbon, because carbon is the only element in the universe which bonds to other atoms (and itself) with sufficient complexity to form molecules suitable to base life on. We also know that the elements we know about are the only ones which can exist in the universe.

The chemistry of life also requires a solvent, and water is the obvious choice. So these chemical requirements limit the temperature and other factors that life would need, which is why we are so interested in "Earth-like" planets which are big enough to have strong gravity, are the right temperature to allow liquid water, and have solid surfaces allowing water to pool and to provide the other elements that life might need.

Note that it is possible that life might be able to exist in a wider variety of conditions but I'll stick to these, fairly conservative, assumptions.

Even when all the conditions are just right, or within certain limits, it's hard to know how often life might arise. Experiments in the lab and some observations of molecules in space indicate it might be really likely, but the failure to find life on Mars seems to contradict this.

But even if there was only one chance in a billion of life arising if conditions were suitable, that still means these should be a lot of it in our galaxy alone, and a lot more in the universe as a whole.

There are about half a trillion stars in our galaxy (although this number has gone up and down a bit, the latest number I heard was at this high end) and each star seems to have multiple planets (let's say 10 as an approximation) and it's likely that at least one might be in the correct temperature zone (some stars might have none in this zone but other, like Trappist-1, have many). This seems to indicate that there are as many Earth-like planets as there are stars.

A recent Hubble survey indicated there might be 2 trillion galaxies in the observable universe. So we have 2 trillion galaxies x 500 billion stars x 10 planets x 1/10 Earth-like, giving one trillion trillion places where life might evolve in the observable universe.

These numbers could be off by many orders of magnitude but who cares? Even if we are a billion times too optimistic that still means a thousand trillion places!

I have talked about the Fermi Paradox - the fact that according to best calculations there should be a lot of advanced life around, yet we never see it - in previous blog posts so I won't go into that again here except to say we aren't much further ahead in resolving it!

There is hope though. As telescope technology advances there will be techniques available which seemed impossible in the past. Detecting a planet orbiting another star is an incredible achievement in itself (the stars are really big and bright but at the distances of other stars the planets are very dim and small). But it should be possible to actually study their atmospheres in the future by analysing the light shining through the atmosphere from the star.

In that case it should be possible to learn a lot more about conditions on the planet (temperature, pressure, what elements are present, etc) and to even detect the chemical signatures of life.

And there are even serious proposals now to design small, robotic spacecraft which can be sent to close stars in a reasonable time (by reasonable here we mean decades rather than tens of thousands of years needed by current spacecraft). We know the closest star, a mere 4.2 light years (42 trillion kilometers) away, has a planet but it is unlikely to be suitable for life, but other relatively close stars could also be explored this way.

So how long will it be before we know that life exists on other planets? I predict hints of its existence within 10 years, strong evidence within 30, and proof within 50. And at that point, depending on the circumstances, it should be obvious just how likely life is. I predict we will start finding evidence for it everywhere.

But I still can't get past the problem presented by the Fermi Paradox. If life arises frequently, why don't we see signs of advanced, intelligent life? Maybe intelligence isn't a good evolutionary trait. And, especially given the state of the world at the moment, that is a worrying thought.

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