RE: Why we might be alone in the Universe
May 10, 2019 at 11:15 am
(This post was last modified: May 10, 2019 at 11:28 am by polymath257.)
(May 10, 2019 at 10:54 am)Mister Agenda Wrote:(May 10, 2019 at 9:43 am)Gawdzilla Sama Wrote: But wouldn't every civilization that reaches our current point have the same chance? Remember, we're a second generation star.
Well, I could think of situations where they wouldn't have the same chance (no nearby planets, impractical life support requirements, aren't even aware of other stars because their atmosphere is too opaque or their vision is too different or they rely on another primary sense entirely), but in general, another technological civilization like ours would have the same chance. If it exists. And practically, if a galaxy a billion light years away is teeming with alien civilizations that got started a million years ago, there's little likelihood we'll ever gain awareness of their existence. The only way we discover another technological civilization is if it's close enough to us in space and time to be perceptible within the lifespan of our species. If there is such a civilization, I hope it's close enough to someday discover; but until we confirm the existence of another technological civilization, I think we should proceed as if we're it, because we might be.
Let's do this. Suppose that technological civilizations pop up in large spiral galaxies every 50 million years or so. Suppose that they last, say, 500,000 years. Suppose that the signal they send out is strong enough to be detected to a distance of 100 million light years and they do so continuously for that 500,000 years. There are about 200 galaxies within that distance from us and about a 1 in 100 chance of overlap. So we would, in this extreme case, be able to detect 2 other civilizations.
If, instead, the civilization only lasts 50,000 years on an average, then we would detect *no* other species.
Are these numbers reasonable? I don't know. Multicellular life has existed on Earth for 700 million years or so, but we have only had technology that could potentially be detected in a close star system for the last 100 years. How many other planets make it to multicellularity? At what rate are intelligent species produced? How long do they last? I don't know.
But if you think that species have a finite time of existence, then it is quite possible we will simply never detect another civilization even if they are 'common' in some senses.
I'd also point out that intelligent life is not very likely to originate in elliptical galaxies. They tend to be very 'metal' poor, meaning they don't have many elements past helium. While this isn't absolute, it makes life much less likely there. To find the larger elements, you have to go to large spiral galaxies (like our own).
