JohnW
Posts: 3217
Joined: Aug. 2006
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| Quote (dheddle @ Nov. 04 2009,11:10) | | Quote (Chayanov @ Nov. 04 2009,12:20) | | Quote (Albatrossity2 @ Nov. 04 2009,12:09) | | Quote (dheddle @ Nov. 04 2009,11:58) | | You have to have a transparent atmosphere in the visible part of the spectrum —and that permits astronomy. |
Do you think it is possible that the "visible part of the spectrum" is so-named because we (the wonderful entities focusing on how wonderful it is that we are here in this wonderful situation) have photoreceptors that work with the light that makes it through our atmosphere?
Do you think it is possible that organisms on other planets with other atmospheres admitting other wavelengths might have photoreceptors that work at those wavelengths?
Sheesh. |
Wait, you mean if we could see different wavelengths then we would have a completely different definition of "visible"? But then that means the fine-tuning argument isn't an argument at all. |
Come on. No it is not possible. The reason is Carbon chemistry. First of all there are, at first glance, three facts in play here.
1) The sun has a peak wavelength.
2) The atmosphere is narrowly transparent
3) Our eyes are sensitive to certain wavelengths.
Now the fact that all three coincide is remarkable. Of course evolution is a perfectly reasonable explanation as to why our eyes are sensitive to the peak of the sun’s spectrum. But (as far as I know) there is no strong evolutionary argument as to why the atmosphere must be (narrowly) transparent at the same wavelengths. (Not much UV or IR gets through.) That seems to be luck. Furthermore chemistry is chemistry, and (if Louis the chemist is around he can correct me) it is also true that the energy levels of many carbon molecules—which would be the same anywhere—have much overlap with what we call visible light—enabling, for example, photosynthesis.
In other words, if our atmosphere was transparent to UV and not visible light would there be a viable replacement for photosynthesis? Would our eyes have evolved to be sensitive to UV and ignore the sun’s peak wavelengths? Or would we still have evolved to be sensitive to the sun’s peak—but would have had an opaque sky? (and therefore no astronomy.) The answer is none of the above—most likely we wouldn’t be here. So the PP result stands—again in a sort of common sense way. Complex life probably requires the coincidence of an atmosphere transparent at the peak of its sun’s emission, and probably that has to be in what we call visible light. At least that is a serious and obvious advantage, and as a consequence it enables Astronomy. |
The three don't need to coincide. A planet orbiting a red dwarf (with a peak in the infra-red) at a much closer distance would work just fine*. As long as enough radiation gets to the surface for photosynthesis to take place, it doesn't really matter how much gets absorbed or reflected at other wavelengths. So the position of the radiation peak doen't really matter.
* A planet orbiting a blue/UV star at a greater distance would also work, although they tend to have other problems (like going supernova in a couple of million years) making them unsuitable for life.
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Math is just a language of reality. Its a waste of time to know it. - Robert Byers
There isn't any probability that the letter d is in the word "mathematics"... Â The correct answer would be "not even 0" - JoeG
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