It is 50/50: Either they do or they dont
July 28, 2011 5:49 PM Subscribe
Are We Alone In the Universe? New Analysis Says Maybe
posted by Potomac Avenue (111 comments total)
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In a new paper published on arXiv.org
, astrophysicist David Spiegel at Princeton University and physicist Edwin Turner at the University of Tokyo argue...using a statistical method called Bayesian reasoning...that the life here on Earth could be common, or it could be extremely rare — there's no reason to prefer one conclusion over the other.
Salient quote from the article:
While it's true that life arose quickly on Earth (within the planet's first few hundred million years), the researchers point out that if it hadn't done so, there wouldn't have been enough time for intelligent life — humans — to have evolved. So, in effect, we're biased. It took at least 3.5 billion years for intelligent life to evolve on Earth, and the only reason we're able to contemplate the likelihood of life today is that its evolution happened to get started early. This requisite good luck is entirely independent of the actual probability of life emerging on a habitable planet.
"Although life began on this planet fairly soon after the Earth became habitable, this fact is consistent with … life being arbitrarily rare in the Universe," the authors state. In the paper, they prove this statement mathematically.
Their result doesn't mean we're alone — only that there's no reason to think otherwise. "[A] Bayesian enthusiast of extraterrestrial life should be significantly encouraged by the rapid appearance of life on the early Earth but cannot be highly confident on that basis," the authors conclude. Our own existence implies very little about how many other times life has arisen.
from the paper:
By constructing a simple model of the probability of abiogenesis, we calculate a Bayesian estimate of its posterior probability, given the data that life emerged fairly early in Earth’s history and that, billions of years later, sentient creatures noted this fact and considered its implications. We find that, given only this very limited empirical information, the choice of Bayesian prior for the abiogenesis proba- bility parameter has a dominant influence on the computed posterior probability. Thus, although life began on this planet fairly soon after the Earth became habitable, this fact is consistent with an arbitrarily low intrinsic probability of abiogenesis for plausible uninformative priors, and therefore with life being arbitrarily rare in the Univers
of the analysis already emerging