Re: Could alien astromoners recognize Earth as possibly M-cl
Bad Bishop said:
Proponents of the Galactic Habitable Zone concept are not ignorant hayseeds who who got C’s and D’s in Evolution. They are, in fact, real astronomers (unlike some people here in this forum).
Exactly. Scientists are very specialized, often too much so. Those who are experts in one scientific field are often quite lacking in knowledge of other fields. That's not a childish insult, merely a fact. The proponents of the GHZ hypothesis have claimed that galactic catastrophism would prevent the evolution of higher forms of life. Meanwhile, evolutionary biologists have been reporting evidence that evolution on Earth has proceeded at its fastest during periods of heavy catastrophism, and have modeled the mechanisms by which catastrophism promotes evolution by creating both the stresses to encourage change and the opening of ecological niches to allow for it.
So clearly, the formulators of the GHZ hypothesis were unaware of recent developments in evolutionary biology, developments that emphatically contradict one of their main claims. Not a matter of opinion or ideology or name-calling, but something that is demonstrable from the data alone.
Back to the GHZ, the idea that harsh conditions in space may prevent the development of complex life is anything but a fallacious assumption. We only have to review the examples of the moon and the planet Mercury. The chances for life on either are slim at best because of the extreme conditions--severe heat, cold, radiation, gravitational effects, etc.--that exist there.
If you understand the GHZ hypothesis at all, you know perfectly well that that isn't even remotely what it's referring to. The idea is that in zones of heavy astronomical catastrophism, worlds that
are Earthlike and inhabited by simple life would be subject to frequent supernova irradiation and catastrophic climate change from gas clouds passing betwen them and their primary stars. Also that the heavy radiation in such star formation zones would prevent the formation of planetary systems in the first place, which is a valid point of the hypothesis (perhaps, given that our understanding of planet formation is still too tentative to say anything definitively), but at most it would only reduce the number of habitable worlds inward of the GHZ, not preclude the existence of any. They also suggest that the higher proportion of heavy elements inward of the GHZ would result in, to put it simply, rockier systems with more debris, leading to more asteroid bombardment and thus more cataclysms.
Conversely, the model states that beyond the GHZ, stars would be too poor in heavy elements for much planet formation to occur at all. Again, a plausible postulate, but uncertain given that our understanding of planet formation is very much in flux at the moment. And again, it would only be a statistical difference: it would reduce the number of inhabited worlds in the region, not preclude them altogether. But in the papers I've read from the proponents of this hypothesis, they speak as though it meant there could be no life whatsoever beyond the GHZ.
Even the name "galactic habitable zone" plays into this bias by implying that regions beyond it are completely uninhabitable. It would be more valid to call it something like the galactic temperate zone: the region where conditions are most amenable to life, but hardly the only region where it can thrive.
I find it interesting that you denounce one hypothesis, and then use careful language so that you don’t go too far out on a limb with your own.
There's no "denouncing" here. This is science, not politics or religion, so such ideologically loaded language has no relevance. I'm
criticizing it based on evidence and logic, which is what is supposed to be done with scientific postulates. I will gladly consider any evidence or logic-based arguments to the contrary, because I love learning new things and thinking about new possibilities. But you haven't offered me any -- just rhetoric and non sequiturs.
is required?
