(Feb 28, 2018 05:35 AM)C C Wrote: One of the world's most respected theoretical physicists Michio Kaku
He's better known as a science popularizer than as a researcher. I'm sure he's a competent physicist though. I like his popular science books.
Quote:has predicted that humans will make contact with an alien civilisation within this century. While he doesn't know if we'll be able to talk back to them by then, Kaku thinks that humans will detect aliens before 2100 by listening in to their radio communications.
That assumes that the aliens will have a technological civilization. Anatomically modern human beings have existed on earth for 100,000 years or more (and human-like hominins for more than a million years), but the industrial revolution was only about 200 years ago. We have only had modern science for less than 400 years.
It isn't clear whether advanced aliens would be using radio for communications purposes either. We only started using radio about 100 years ago and are already switching over to fiber-optics and optoelectronics. An alien civilization would have to be at a particular stage in its evolution to be putting out lots of radio communications.
So not only would there have to be an alien civilization within range, putting out communications with an energy that would defy the inverse-square law between here and there, it would have to be located at a distance so that its perhaps-narrow temporal window of energetic radio emissions corresponds to its distance from us in light years. (Otherwise their emissions would have passed us by or not gotten here yet.)
And that assumes that they are interested in any of that.
My own guess is that life is scattered very thinly though our galaxy. (Unless my panspermia speculations turn out to be true, in which case it might be abundant.) That's because the initial chemical origin of life seems to me to be a very low probability event. Very fortuitous. (We can test panspermia with Mars. If Mars once had conditions hospitable to life and it indeed once had life similar chemically to our own, then that similarity would be strong evidence of some common origin.)
But whatever 'life' appears elsewhere (in the sense of self-reproducing chemical replicators) with a totally different origin might be very different from how we conceive of life from our own sample size of one.
Then we would have to imagine an evolutionary history that leads to heterotrophic animal-like things that display complex behavior. Those have existed on Earth for the last 500 million years (in a history of life dating back at least 3.5 billion years). (And radio for only 100 years...) It's conceivable that evolutionary history on other planets may go in very different directions from how it unfolded here.
Then we would have to imagine any complex aliens having human-like psychologies. But maybe their motivations aren't anything like ours. (Maybe they are solitaries and have no interest in communication, maybe they are more like social insects, or maybe possibilities that we can't even imagine.)
All in all, detecting alien signals seems like a very low probability hope to me. I nevertheless strongly support SETI just on the off-chance it succeeds.
But unlike Michio Kaku, I don't think that it's tremendously likely.