SETI research: what can we now rule out?

Great Debates
1

The Fermi Paradox dates from 1950. The SETI Institute was established in 1985. We haven’t yet discovered any aliens. Are there scenarios that we can rule out, if only probabilistically?

One is tempted to say, “Star Trek or space opera”. I’ll leave that for someone else.

Some might say, “Basically nothing.” Sam Stone pushes a line like this in the FQ: What is the end game of SETI? and other threads, though I’m guessing he might not go quite that far.

My take: I think we can tentatively rule out a galaxy with a large number of advanced civilizations that want civilizations like ours to know about them. “Advanced” means > > 2100 technology. I can’t say the same for 1950-2050 style civilizations. An advanced civilization could figure out what a culture like ours would notice and then do something that we would notice. Can we go further than that? (Or does even that go too far, for some values of “large”?).

We haven’t located any galactic or stellar level Dyson spheres. Is there anything we can conclude from that, if only in a limited way?

I mean there must be some conclusions we can hypothesize, if only tentatively.

2

Perhaps we can rule out the universe having a large number of Dyson galactic supercivilizations. Alien Supercivilizations Absent from 100,000 Nearby Galaxies - Scientific American

3

Personally, I rule out our current ability to detect other civilizations.

4

Dark forest hypothesis?

5

I’m inclined to side with the “we know almost nothing” side of the argument. The problem is that our sample size from which to draw conclusions is hopelessly small, so we have to make a lot of fanciful assumptions, which may well be completely wrong.

Just about the only assumption in which we can have some level of confidence – though that might be wrong, too – is the assumption that complex life, or indeed probably any life at all – must necessarily be based on carbon. That puts constraints on the conditions under which life could develop and flourish. But there’s very little else that we can assume with any confidence.

Our search for life thus far has been very local and based on incredibly limited evidence. Within the solar system, only Mars has been explored to any meaningful extent, and other candidates for life like the oceans of Europa and Enceladus are a complete wildcard. On a larger scale, our efforts to detect signs of distant intelligent civilizations elsewhere in the galaxy are based on highly conjectural approaches and, moreover, are also intrinsically local. This is because our galaxy has a radius of nearly 53,000 light years, and we’re located in quite a remote part of it. The “downtown” part where the action is is clustered around the center, and that’s around 26,000 light years away.

These vast distances not only make any signs of other civilizations almost impossibly hard to detect even if we knew what to look for, but it also introduces temporal factors. What was the state of our own technological civilization a mere thousand years ago? When did we first start broadcasting potentially detectable radio waves, and how much longer will we continue to do so? And, indeed, the development of science and technology was arguably a total fluke; we lived for tens of thousands of years in more or less our present form and developed virtually nothing at all, and may well have continued that way for thousands more, but for a quirk of fate that started the ball rolling on the exponential growth of scientific knowledge and its applications.

All of which means that if we expect to detect signs of distant civilizations, we not only have to be looking at exactly the right place in the unbelievable vastness of space, but we have to be looking at exactly the right time, because the signals may last much less than the thousands of years they took to get to us before the civilization either died out or moved on to different endeavors, and that’s assuming such signals are even theoretically detectable against the background noise of the universe.

As for “Dyson spheres” and the like, any notions about what sorts of technologies super-advanced civilizations might create is so speculative that it doesn’t even rise to the level of scientific hypotheses, even though it’s often dressed up that way. It’s pretty much science fiction.

6

Not at all. I’m making a somewhat more extreme case than in @Wolfpup’s excellent post.

We know nothing at all. We don’t know what to look for, we don’t know if we have the right equipment, we are extrapolating from our single data point of nothingness. Whether there are other civilizations and what, if any, they do is not understood sufficiently to make any assumptions. The finger is pointed at us. That’s the extrapolation that the actual evidence leads to.

Whether to continue efforts is a different issue.

7

If we’d been searching for signs of life for the last 100,000 years, I think the lack of resulting data would be meaningful.

What we’ve got is the equivalent of turning on the kitchen light for 1/8th of a second, seeing no mice on the countertop, and wondering why, given that we think we may have mice.

8

Any advanced civilization we’d be able to detect would have to be either extremely close or extremely ancient. We’ve only been generating radio signals for 100 years or so, so there’s only about a 200 light year diameter ‘shell’ of outward-traveling radio signals around the Earth. That’s nothing. Any civilization further away than that looking our way would detect zilch.

And…maybe there aren’t many, or even any, ancient advanced civilizations out there. Maybe we are at least among the first civilizations. Somebody’s got to be first, why not us? I proposed this in a similar SDMB thread a few years ago and got slightly ridiculed, but here’s my homework:

  • The universe is estimated to be around 14.5 billion years old.
  • It took about 10 billion years for heavier elements to form-- the heavy elements need to form in larger stars than our Sun, then become supernovas, explode and scatter the elements through space. So 10 billion years had to go by before the universe had a complex enough array of elements to support life.
  • Earth is estimated to be around 4.5 billion years old, and life began around 4 billion years ago, about as soon as conditions on Earth allowed it.

That could still leave spans of hundreds of thousands of years, give or take, but if you accept that the above estimates are correct ( a big if, perhaps) then it would be unlikely for an advanced civilization to have formed say, millions of years before us.

9

I’m comfortable ruling out life forms on the Moon.

10

I think “know” and “rule out” is the wrong framing.

Certain things have become less likely based on our observations, but advanced ETs are the ultimate “all bets are off” – we have no idea what might motivate them. Still, the lack of any kind of signal or megastructure across quadrillions of stars I think should actually make us lean more towards the proposition that there’s no-one there, as disappointed as I am with that conclusion.

On the more positive side, there are bad solutions we can rule out, like “planets are rare”. It appears that the majority of stars have planets.

11

“Millions of years” is an awfully short time, compared to billions. If there was just one star where the processes needed for life and evolution of intelligence proceeded just one percent of one percent faster than they did for us, the resulting civilization would be a few million years ahead of us. Now, we don’t know exactly all of the processes needed for life and evolution of intelligence, so we can’t say for sure what the absolute minimum amount of time for it is, but it seems implausible that we’re within 0.01% of the absolute minimum.

12

I’ve made that point before - one could imagine scientists in the first intelligent looking around and confidently declaring near zero odds that they arefirst, given the size and age of the universe.

That doesn’t mean that we are that civilization, of course. But even something as unlikely as being the first in the universe is happening to SOMEONE…

13

I don’t know that I agree with this bit, though. There’s no reason why a dinosaur species couldn’t have eventually evolved intelligence, for example (after all, corvids and parrots are quite intelligent and did eventually evolve from that stock). So if a lineage of birds evolves towards intelligence 100 million years ago at the height of the donosaur age, they could specialize further for 30 million years or so and then have millions of years to develop technologically (hopefully they can redirect asteroids by 65 MYA!) which should be plenty of time to conquer the galaxy even without FTL.

So, if Earth’s life evolved as early as life in the universe could have evolved, and many Earth-like worlds of the same age exist, one in which the intelligent animal group rose to dominance tens of millions of years sooner is easily imaginable.

14

(replying to post #12)
Absolutely, but who would even dispute that? I have heard people confidently assert that there are no other intelligent species out there, I’ve never heard anyone claim there never will be.

Anyway, being the “ancient ones” does make everything we’re doing seem much cooler. My car is not a piece of trash, it’s a future precursor relic :slight_smile:

15

True. I do agree that “we’re the first” is probably not the most plausible argument for the Fermi Paradox.

Another pet theory of mine, which I touched on in a similar thread here just a couple days ago, is that life may be common throughout the galaxy, but intelligent life may be vanishingly rare. And intelligent life that has the means to manipulate its environment in such a way as to be able to develop technology may be even more rare.

Evolution is all about adaptation to environment. Intelligence is one adaptation but it’s by no means a necessary one. Insects and arachnids are supremely adapted to their environment. There’s no guarantee that given (X) time for a species to evolve that it will become intelligent and technologically capable. Even for animals that are intelligent, like dolphins, it would be difficult for them to start building things with flippers.

I’ve read speculation that our big brains are sort of a side effect of evolving to be tool-using creatures-- our brain capacity grew to accommodate hands that were increasingly nimble. So we evolved to be tool-using tinkerers and the intellectual capacity was a secondary thing.

16

Well, I’d guess that if intelligent life other than us doesn’t exist, then no matter how long it takes us to expand - even if a planet can only add send out one colony ship every million years - that’s still likely to let us colonize the entire galaxy an order of magnitude faster than the time scale of new intelligent life evolving.

Sort of like how abiogenesis only happened successfully once and all life is related, because once life appeared it quickly spread to all available niches before it could happen again.

IF intelligent life in the universe is so rare that we are the only example, I think it’s likely that means that it is so rare that we or our descendants will spread out before it can happen again no matter how long we take doing it.

17

Yes, I’d agree with all that.

I’m just saying, I don’t think there’s much distinction between “we are alone” and “we are first” in practice. Aside religious reasons, I don’t think many people are going to agree with the former and not the latter.

18

I’m still of the opinion that the optimists and believers in the Fermi paradox vastly underestimate the difficulty of interstellar, much less intergalactic, travel. I think that’s the bottleneck. I’m of the belief that life is probably common (I wouldn’t be at all surprised if we find evidence that Mars used to be inhabited, that some of the moons of Jupiter and Saturn have life in a subterranean ocean, or maybe even in the upper atmospheres of Venus or the gas giants), intelligent life rare but not so rare as one in a trillion or some crazy number like that, but that the difficulty in making the journey between solar systems is just too difficult for any species to make the journey. Which means the only civilizations that have made contact with aliens are those lucky enough to have two or more planets or moons in the same solar system that developed civilizations.

19

Well, we’ve been doing radio astronomy for almost a hundred years now, so we could probably conclude that no aliens within a hundred light years have been putting out radio signals strong enough for us to detect in the previous up to a hundred years or so. That is, a radio signal sent in 1840 would have been detected in 1940, but one sent in 1940 is still on its way. Every year the bubble of what we can have detected gets one light year larger, while the time frame gets one year longer.

Spacetime gives people headaches!

20

But under known physics the journey isn’t all that difficult, just time consuming.

If you have a society that lives in habitats in orbit of various planetary bodies in our own solar system, and I don’t think that’s unreasonable to expect in the next few centuries, much less millenia - then shoving a space station so that it will reach another star in a hundred years is not all that difficult.