Why we might be alone in the Universe

[polymath257]

The problem is that if life is common in the universe, why have we not detected it? Why have we not seen large-scale technology like Dyson spheres?

One possibility is that we are among the first intelligent agents, at least locally. Since intelligent life could not get started until the basic elements were formed from the first generation of stars, there is an earliest time in the universe when life *could* get started. It may well be that our sun is one of the first stars to have planets with enough of the basic materials for life to form. Again, at least in our galaxy.

Next, maybe life developed rather quickly on Earth and we are one of the first intelligent races. Even if we are a mere 10,000 years ahead of others, that makes a significant difference in our abilities to detect other life. If everywhere else is still at stages like what was on the Earth prior to 200 years ago, then there is no chance we would detect another species given *our* technology.

Yet another is the 'dark forest' possibility: those species that announce their existence are ruthlessly exterminated by the species that already exist. So any species that still exists keeps quite for its own survival. Who knows? Perhaps some teardrop shaped, strong force 'bomb' is already on its way to destroy our sun?

Kudos for whoever gets the reference.

[Brian37]

The problem is that if life is common in the universe, why have we not detected it? Why have we not seen large-scale technology like Dyson spheres?

One possibility is that we are among the first intelligent agents, at least locally. Since intelligent life could not get started until the basic elements were formed from the first generation of stars, there is an earliest time in the universe when life *could* get started. It may well be that our sun is one of the first stars to have planets with enough of the basic materials for life to form. Again, at least in our galaxy.

Next, maybe life developed rather quickly on Earth and we are one of the first intelligent races. Even if we are a mere 10,000 years ahead of others, that makes a significant difference in our abilities to detect other life. If everywhere else is still at stages like what was on the Earth prior to 200 years ago, then there is no chance we would detect another species given *our* technology.

Yet another is the 'dark forest' possibility: those species that announce their existence are ruthlessly exterminated by the species that already exist. So any species that still exists keeps quite for its own survival. Who knows? Perhaps some teardrop shaped, strong force 'bomb' is already on its way to destroy our sun?

Kudos for whoever gets the reference.

Because the universe is FRIGGEN HUGE.....

Put it this way, imagine trying to find 4 needles in a haystack as large as our solar system. We might get lucky and detect communication, but even then alot of that would depend on our species to focus resources to do that instead of spending it on weapons and war. 

It is more likely than not, that life exists elsewhere, but again, because of distance it makes it extremely hard to figure out where life would likely survive in the universe. But we do know right now, water exists elsewhere which is the most important thing for life to exist.

[Gawdzilla Sama]

It may be that life is common but technological civilizations are vanishingly rare, like one per million galaxies. For now we should act as if we are the galaxy's (or even the universe's) one shot at a star-spanning civilization. If we don't do it, there's a good chance it will never get done. And that would be sad, IMHO.

But wouldn't every civilization that reaches our current point have the same chance? Remember, we're a second generation star.

[Anomalocaris]

It may be that life is common but technological civilizations are vanishingly rare, like one per million galaxies. For now we should act as if we are the galaxy's (or even the universe's) one shot at a star-spanning civilization. If we don't do it, there's a good chance it will never get done. And that would be sad, IMHO.

But wouldn't every civilization that reaches our current point have the same chance? Remember, we're a second generation star.

Ours is actually at least a third generation star.   It could be of a fourth, fifth, or higher generation, but certainly no less than the third generation.  But rocky planets can not form around first generation stars, because the interstellar medium shortly after the Big Bang were devoid of metals.   Rocky planets were unlikely to form around second generation stars also because metals were still scarce.   Only with third or higher generation stars would one likely find native rocky planets in orbit.

[polymath257]

The problem is that if life is common in the universe, why have we not detected it? Why have we not seen large-scale technology like Dyson spheres?

One possibility is that we are among the first intelligent agents, at least locally. Since intelligent life could not get started until the basic elements were formed from the first generation of stars, there is an earliest time in the universe when life *could* get started. It may well be that our sun is one of the first stars to have planets with enough of the basic materials for life to form. Again, at least in our galaxy.

Next, maybe life developed rather quickly on Earth and we are one of the first intelligent races. Even if we are a mere 10,000 years ahead of others, that makes a significant difference in our abilities to detect other life. If everywhere else is still at stages like what was on the Earth prior to 200 years ago, then there is no chance we would detect another species given *our* technology.

Yet another is the 'dark forest' possibility: those species that announce their existence are ruthlessly exterminated by the species that already exist. So any species that still exists keeps quite for its own survival. Who knows? Perhaps some teardrop shaped, strong force 'bomb' is already on its way to destroy our sun?

Kudos for whoever gets the reference.

Because the universe is FRIGGEN HUGE.....

Put it this way, imagine trying to find 4 needles in a haystack as large as our solar system. We might get lucky and detect communication, but even then alot of that would depend on our species to focus resources to do that instead of spending it on weapons and war. 

It is more likely than not, that life exists elsewhere, but again, because of distance it makes it extremely hard to figure out where life would likely survive in the universe. But we do know right now, water exists elsewhere which is the most important thing for life to exist.

But again, make the distinction between life at the bacterial level (which I agree is most likely quite common) and life at the technological level. At this point we have no chance of detecting non-technological life beyond our solar system.

But, if there was a technology at the level of manipulating stars, there is a decent chance we could detect it. There was even a false signal recently thinking there might be construction of a Dyson sphere around a nearby star.

Detecting those 4 needles becomes a lot easier if they are luminous. The question is, if there are truly advanced technologies out there, why are they dark to us? And if not, why not?

[Mister Agenda]

It may be that life is common but technological civilizations are vanishingly rare, like one per million galaxies. For now we should act as if we are the galaxy's (or even the universe's) one shot at a star-spanning civilization. If we don't do it, there's a good chance it will never get done. And that would be sad, IMHO.

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.

[polymath257]

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.

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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).

[Gawdzilla Sama]

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.

ONLY if they use some system that we can detect.

[Brian37]

Because the universe is FRIGGEN HUGE.....

Put it this way, imagine trying to find 4 needles in a haystack as large as our solar system. We might get lucky and detect communication, but even then alot of that would depend on our species to focus resources to do that instead of spending it on weapons and war. 

It is more likely than not, that life exists elsewhere, but again, because of distance it makes it extremely hard to figure out where life would likely survive in the universe. But we do know right now, water exists elsewhere which is the most important thing for life to exist.

But again, make the distinction between life at the bacterial level (which I agree is most likely quite common) and life at the technological level. At this point we have no chance of detecting non-technological life beyond our solar system.

But, if there was a technology at the level of manipulating stars, there is a decent chance we could detect it. There was even a false signal recently thinking there might be construction of a Dyson sphere around a nearby star.

Detecting those 4 needles becomes a lot easier if they are luminous. The question is, if there are truly advanced technologies out there, why are they dark to us? And if not, why not?

Again, even life at our level would be likely too. But again, the universe is so big, it is still that needle/haystack for them and us.

Distance. While there could even be more advance life then ours, because of distance, it would most likely be just as stuck locally where it is, like we are, even if it had a slightly longer range.  I will say this though, if I were intelligent alien life, and spotted us, with the way we behave to each other now, I wouldn't try to contact us even if I could. We are a very violent species.

I really do think you are over complicating this. It only takes water and amino acids for evolution to occur. As individual atoms, those atoms are plentiful in the universe. But no, I still do not buy any Area 51 or Roswell crap. 

In theory if we could go to every rocky planet in the universe, as big as it is, we should expect to find life at our intellectual level. But again, distance and time and energy are going to make it almost impossible for life to communicate with each other over those distances.

[AFTT47]

Yet another is the 'dark forest' possibility: those species that announce their existence are ruthlessly exterminated by the species that already exist. So any species that still exists keeps quite for its own survival.

Negative on that because you can't hide even if you want to.

If there is an aggressive species out there hell-bent on wiping out potential rivals, they will build super-thin telescope mirrors with the diameter of planets. With such telescopes, they could image any planet in the galaxy.

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While there could even be more advance life then ours, because of distance, it would most likely be just as stuck locally where it is, like we are, even if it had a slightly longer range.

No, Brian. I pointed out the fallacy of that in another thread recently so I'm not going to repeat the whole thing. The cosmic speed limit of the speed of light is NOT a deal breaker for interstellar travel. No technological civilization is "stuck" except by temporary lack of resources. Known physics is not a barrier.