Giordano Bruno would have been proud. In 1600, the Italian monk was burned at the stake at Piazza dei Fiori in central Rome for, among some very serious theological offenses (e.g. Mary wasn't a virgin, the Holy Trinity was a scam, etc.), stating that every star in the sky was a sun and that each one of them had its own court of planets. Bruno even put forward the notion that, just like our own planet, these worlds would have living beings and plants. Well, a couple of weeks ago a team at the Southern European Observatory announced the discovery of another 32 extrasolar planets, putting the present count at over 400!
This is exciting science, changing our collective worldview. Yes, many have suspected that there were planets surrounding stars, even in ancient Greece. Why should our solar system be so special? The existence of planets is actually a natural consequence of how we understand stars are born, from the collapse of huge clouds of hydrogen, sprinkled with some (or many, it depends) of the elements of the periodic table. But one thing is to think planets are out here; another is to actually detect them. In science, seeing is believing.
If the Milky Way alone has about 300 billion stars and most of these stars have planets (and some will also have moons), we are talking over a trillion worlds in our own galaxy. A mind boggling number of worlds, each of them different: different chemical composition, may or not have magnetic fields, may or not have an atmosphere, moons, liquid water, frozen water, axial tilt... There is an emerging field of astronomy called "comparative planetology". To learn about many worlds we need to compare them, how they were formed, what's their chemical composition, their distance from their parent star, mass, radius, etc.
Of course, the question in everyone's mind is how common "other earths" are. Are there other worlds with similar characteristics to our own? If so, would life have developed there as it did here? What kind of life would that be? Simple? Complex? We don't know. And, in fact, opinions vary wildly, although we can group them roughly in two camps: the astronomers and the biologists. (Of course, as with any generalization, this one fails. But it's practical.) The astronomers look at the big numbers, the trillions of worlds and claim that, yes, life is out there, and we are just one of an enormous crowd of "typical observers". So, they believe that not just life but intelligent life is all over the place. The biologists are more skeptical. Look at the story of life on Earth, they claim, and you will see that things are more complicated than that. First, for about 2 billions years, life here was pretty simple, unicellular blobs called prokaryotic cells. Only in the last 500 million years or so things got more interesting, and life became multicellular. How can we be sure that complex life will evolve elsewhere? Does evolution necessarily lead to complexity? (And here is a tease for my fellow bloggers in the bio field...) I'd say not. Natural selection has no grand plan toward complex life forms. Whoever fits well into the current environmental conditions will do better. If we are here, it's because of a series of fluke accidents. In this case, we are pretty rare. And precious. Not sure Bruno would have liked this too much.
5 comments:
Marcelo, whenever I talk with astronomers they seem far more positive about the possibilities for complex life forms than when I talk with evolutionary biologists. Somehow I get the impression that the biologists think truely complex (to say nothing of intelligence) life may require so many accidents that it would be very rare.
I wonder this impression is about the divide between the feels is real.
Well, then I guess you have the same impression I reported on my text. I think the divide is real, and it springs from a somewhat naïve view astronomers have of evolution and life. It's the old thing about necessary vs. sufficient. To have life as we know it (I'll abstain from other kinds...) we need liquid water, a sustainable energy source, the right chemicals, and they must also be at high enough concentrations to get the reactions jump-started. But, just having this stuff together is no guarantee that life will get going. And much less complex life. To say that the universe is filled with "typical observers" like us is, I think, quite premature. As Fermi said, "Where is Everybody?" But this is something that I will for sure get back to in the near future.
I sometimes find myself in the awkward position of explaining to my non-astronomer friends that even though there may be 10 billion planets in the galaxy, if the odds of complex life are 1 in 100 billion then you simply run out of planets.
It always makes me feel like Debbie Downer.
The book Rare Earth comes to mind as an eye opening argument that complex life may be very hard to come by.
@Adam and Marcelo. What are our expectations for aliveness and intelligence? If the universe were truly alive and intelligent, should we see a universe organized more like urbane utopias? Does a galaxy void of human consciousness mean that it's void of intelligence itself? Why wouldn't a galaxy such as that be considered as something emodying intelligence?
Marcelo, you end with your sense of our being rare and precious. This is an unusual voice. Usually, the voice I hear from science culture is that because we are so rare, we're basically a statistical anomaly: for anyone who understands statistical reality, will know that weighting such an anomaly with any significance wouldn't be rational and good statistical science.
Ah! but being a statistical anomaly, a rare oddity in the cold, dead cosmic vastness, is precisely what makes us precious. In other words, we are precious because we are rare and aware of it. I am glad you think this is an unusual voice in the current scientific culture. It is indeed, and we are trying to create a scientific counter-culture, much more engaged with the culture of humanism than the norm. I might add, this unusual voice is a badly needed one, a theme I explore in much more detail in my upcoming book (april 2010) and that will certainly be part of these exchanges. Thanks for your comment.
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