| || |
Seeing the man on the moon
February 18, 2013 - Harry Eagar
Friday, I went to the monthly astronomy lecture at Maikalani expecting to hear more about Fermi's paradox. It turned out the paradox (more about that later) was only a stepping stone to the big news, which is that astronomers are plotting to build the largest telescope ever to search for habitable planets within 50 light-years.
Jeff Kuhn, the lecturer and head of the Haleakala Observatory of the University of Hawaii Institute for Astronomy, modestly described himself as just a cog in an international venture to build The Colossus, but he's the project director and, I suspect the concept is mostly his.
The-Colossus.com is already a private corporation with an (unnamed) capitalist backing it. I was surprised to learn from Jeff that for the past 150 years, all the successive largest telescopes have been built with private money and that the cost, in constant dollars, has remained the same -- the Yerkes was $6 million and the Colossus will be about a billion, which is what $6 million was a century ago.
(Apparently Jeff does not count the Russian 6-meter telescope, which was larger than Palomar when finished, but since it was built in the cloudy Caucasus Mountains was never used for anything much.)
Russian theory is better than Russian practice, and Jeff takes off from a half-century old idea about advanced civilizations. As they advance, they need more and more energy. The Colossus is intended to spot an extrasolar planet whose inhabitants use 1% or more of their star's energy. (Earth is at about 0.4%.)
Civilizations acquire more and more information and storing it takes energy -- think of Google's server farms and their huge air conditioning bills, multiplied many times. The laws of thermodynamics require that light energy, once absorbed, be re-emitted as heat. ("The real global warming," says Jeff, like me a skeptic about what might be considered AGW-lite that people are demonstrating against.)
As a result, a planet in its star's habitable zone will, once it acquires a sufficiently advanced life, be dim in visible light and bright in infrared. Even if the aliens don't want to signal their presence to the nearest, perhaps hostile advanced lifeforms, they cannot help it.
No telescope can even almost spot this optically dim, bright infrared planet, in part because even the biggest is not big enough, and in part because each successive biggest telescope is built to see more and more of the Universe.The Colossus would be designed to focus on something as small as a planet at 50 light-years distance -- it could also see a man (your size) on the moon, or the surface of a distant star. (This is why I suspect Jeff is behind the concept; Haleakala Observatory is a solar specialist.)
To do the job, the team has designed a group of 60 8-meter mirrors arranged in a circle about 250 feet across. Ideal sites would be the same as ideal sites for other giant telescopes, Hawaii or Chile.
The cost is estimated to be half that of current proposals for next successive biggest (general) 'scope, about a billion.
With money, it could be up in 5 years, but it would require nightly observations of the 60 nearest stars for several years to accumulate the tiny differences that would spot the planet.
Which brings us back to Fermi's paradox, which asks why, if life is common in the Galaxy, we don't hear from those other guys? Jeff notes that as discoveries have accumulated, each successive one tells us that Earth is nothing special. If Earth has life, then lots of other stars should have planets with life.
I buy this argument, if you consider the statistical event under scrutiny to be the likelihood of advanced life. If Earth is like billions of other planets, then at least millions ought also to have life. It's the old Drake equation.
The thing about the Drake equation, though, is that it is almost all unknowns. Usually it is said that the only known factor is that there is life on Earth -- the factor for life-in-the-universe is 1.
But I am more interested in biology than in physics, and there is another known factor hidden in the Drake equation (though I have never seen it discussed). We know how long it took from the beginning of one-celled life to multi-celled life.
If we guess that, once multi-cellular life (or something close to it) occurs, intelligence necessarily follows (through the power of natural selection, which we know operates wherever there is life), then advanced life should be common.
However, there's an "if" that the astrophysicists do not (so far as I know) worry about. What if the 3 billion years it took to reach eukaryosis -- a hard fact -- is fast? Our experience must be on either the short side or the long side of average. We don't know which, although it is more likely we were on the fast track.
The reason is that the lifespan of the Galaxy is finite. It might be that given enough time, advanced life almost always results, but we are not given unlimited time. Compared to 3 billion years, we have only a little time to work with. If the average time to eukaryosis is, say, 6 billion or 9 billion years, then advanced life will be scarce, because not enough time has passed yet.
The statistic of interest then is not something close to 1 (life almost everywhere), but the number of microbial interactions that have to occur before one microbe absorbs another without digesting it and also manages to incorporate its machinery in its own output.
Put that way, the number of missed opportunities before our success must have exceeded the number of particles in the universe, and life begins to look most improbable. "Accidental" as Jeff expressed it when I asked him about it.
In that case, Jeff said, the Colossus would find nothing, and that would tell us something.
My own sense of it, based on the fact that almost every time we learn more about a biological process it turns out to be way more complicated than it looked, is that the progression from one cell to many probably required an intermediate step, perhaps evolution of a virus that coated a microbe and prepared it for absorption without digestion. Or something.
Anyway, Fermi's paradox is like the question of theodicy. Religionists ask themselves, if god is good, how can there be evil, and tie themselves in knots trying to put constraints on a putatively omnipotent Big Spook. Much easier to answer if you propose that god is not good. Fermi's paradox fades if life is scarce.
No comments posted for this article.
Post a Comment
The inner Solar system (only terrestrial planets) as seen at 50 light years away from the Sun by the Colossus. The Sun to Mars distance will be seen at the angle of about 100 milliarcseconds. The sizes of the planets and the Sun on this image are not scaled with the distance.