Why do we see no other intelligent civilizations? (Fermi)

[Maroza]

Civilizations destroy themselves with technology before space travel

Evolution to and conditions for intelligent life is rare to nonexistent

I would have to say a combination of these two factors. I would have to guess that intelligent life is rare but not terribly uncommon. Those life forms that do come about, that are not killed by the environment or competition with other species, are often killed with their own technology for one reason or anther. As such intelligent life that achieves interstellar travel would be a rather rare phenomena.

That's my SWAG (Scientific Wild Ass Guess).

Or hell, maybe we're like ants, uninteresting and blissfully unaware of all the shit going on around us.

[Tmutarakhan]

Not in any focussed direction. Our radio emissions are such a pathetically small fraction of the radio emission of Jupiter, let alone the sun, that at distances of light-year they could not possibly be picked out.

Wouldn't hat depend on how sensitive the detection equipment used is? (And of course how powerful the computers used to sift out our radio signals)

The random fluctuations in the background noise are many orders of magnitude above the "signal". There really wouldn't be any way to even know that there was anything to "sift out", let alone any way to distinguish which of the tiny fluctuations which you could note was any more significant than any other little fluctuations.

[Sidhae]

First, let's look at the Universe as a kind of computer, all contained within being information. Every process, no matter how complex, that takes place within, is effectively a program in operation, including life and ultimately, the essence of individual beings. Their manifestation in the material universe is in that case but a projection of their essence, much like this text you now read is but a manifestation of otherwise invisible information on your monitor.

Now, if that is the case, then obviously all living beings have a soul, a program that defines how they are manifest in the material universe.

By extension, that would imply there exist sapient beings far more advanced than us, who are aware and familiar with the principles of how this underlying programmature of the Universe works and how to manipulate it. If that is so, that would remove the need for them to construct spacecraft, enabling them to travel interstellar distances simply by projecting their essence, and to manifest themselves via avatars suited to native environment of their destination world, much like we create our customized avatars in video games - in other words, aliens could walk among us without us even recognizing them as such.

Think of it as yourself being an NPC in a video game - would you be able to recognize player characters if you were not aware of being a video game character? Could you find it plausible that the character next to you is an avatar of some being from a world outside your own, or believe that such a world even exists?

To put it short - maybe we all live in the Matrix, a computer simulation run by some outside force, which would explain the absence of aliens.

---

Or maybe we are simply being extremely arrogant by assuming that spacefaring civilizations should be interested in visiting our world, which is really but a rock orbiting an insignificant star in the ass end of the Galaxy. There's no doubt there exist such civilizations, but the chances of them coming across us are extremely slim. They could very well be having a major colony in Alpha Centauri system just a few light years away and never know we're here.

[Samuraikoku]

Think of it as yourself being an NPC in a video game - would you be able to recognize player characters if you were not aware of being a video game character?

Deadpool can. Marvel Ultimate Alliance 2.

The Warcraft III units can as well, if one repeatedly clicks on them.

[Tyrants]

I like the idea of Earth being an enclosure in an intergalactic zoo. "Look kids, a primitive race busily evolving."

[Salandriagado]

First, let's look at the Universe as a kind of computer, all contained within being information. Every process, no matter how complex, that takes place within, is effectively a program in operation, including life and ultimately, the essence of individual beings. Their manifestation in the material universe is in that case but a projection of their essence, much like this text you now read is but a manifestation of otherwise invisible information on your monitor.

Now, if that is the case, then obviously all living beings have a soul, a program that defines how they are manifest in the material universe.

That does not follow.

By extension, that would imply there exist sapient beings far more advanced than us, who are aware and familiar with the principles of how this underlying programmature of the Universe works and how to manipulate it.

That also does not follow.

If that is so, that would remove the need for them to construct spacecraft, enabling them to travel interstellar distances simply by projecting their essence, and to manifest themselves via avatars suited to native environment of their destination world, much like we create our customized avatars in video games - in other words, aliens could walk among us without us even recognizing them as such.

This doesn't follow from any of the above.

Think of it as yourself being an NPC in a video game - would you be able to recognize player characters if you were not aware of being a video game character? Could you find it plausible that the character next to you is an avatar of some being from a world outside your own, or believe that such a world even exists?

This has no connection to anything else in the post.

To put it short - maybe we all live in the Matrix, a computer simulation run by some outside force, which would explain the absence of aliens.

Not particularly well.

Or maybe we are simply being extremely arrogant by assuming that spacefaring civilizations should be interested in visiting our world, which is really but a rock orbiting an insignificant star in the ass end of the Galaxy. There's no doubt there exist such civilizations, but the chances of them coming across us are extremely slim. They could very well be having a major colony in Alpha Centauri system just a few light years away and never know we're here.

This is more like it.

[Fort Kick Ass]

I feel like we are seen as a violent race to other intelligent life forms and they try to avoid our species. Whoever they is sees us as primitive, unevolved, and destructive and to avoid until we prove we are "worthy" of interacting with the outside.

[Our Most Resplendent Goddess Sen]

I chose "Evolution to and conditions for intelligent life is rare to nonexistent", however that's not exact.

I'm more into 'space is just too darn big' -explanation.

Let's do a magnitude estimation, with optimistic numbers from the hat:
- Spacefaring species: 1000
- Ships/probes dedicated to scouting star systems: 10,000 per species
- Average probe velocity during travel: c/2
- Average stellar density: 1 per cubic parsec -> ie. closest star is roughly 1 parsec away -> ie. probe is 6 years in transit
- Average research time per system: Negligible

Average research speed of all the spacefaring species combined:
1000 * 10000/6 years = 1,67 million star systems per year

Now, size of our galaxy:
- 200 000 000 000 to 400 000 000 000 stars.
- Perhaps 1/4 is habitable

Which totals to an average research frequency of a habitable star system:
Once every 30 000 to 60 000 years.

Also, let's not forget this:
- Average time to report home: 300 years
- Average time to react back: 600 years

So, perhaps there are aliens over there but they need not have visited this place in tens of thousands of years EVEN if they were actively probing nearby stars.

Problem: with the stated level of propulsion technology it is completely trivial for said civilization to colonize the entire galaxy.

All of it.

Probably inside of half a million years.

[Salandriagado]

I chose "Evolution to and conditions for intelligent life is rare to nonexistent", however that's not exact.

I'm more into 'space is just too darn big' -explanation.

Let's do a magnitude estimation, with optimistic numbers from the hat:
- Spacefaring species: 1000
- Ships/probes dedicated to scouting star systems: 10,000 per species
- Average probe velocity during travel: c/2
- Average stellar density: 1 per cubic parsec -> ie. closest star is roughly 1 parsec away -> ie. probe is 6 years in transit
- Average research time per system: Negligible

Average research speed of all the spacefaring species combined:
1000 * 10000/6 years = 1,67 million star systems per year

Now, size of our galaxy:
- 200 000 000 000 to 400 000 000 000 stars.
- Perhaps 1/4 is habitable

Which totals to an average research frequency of a habitable star system:
Once every 30 000 to 60 000 years.

Also, let's not forget this:
- Average time to report home: 300 years
- Average time to react back: 600 years

So, perhaps there are aliens over there but they need not have visited this place in tens of thousands of years EVEN if they were actively probing nearby stars.

Problem: with the stated level of propulsion technology it is completely trivial for said civilization to colonize the entire galaxy.

All of it.

Probably inside of half a million years.

No it isn't. Not in the slightest. That just simply isn't true in any way, shape or form.

[Our Most Resplendent Goddess Sen]

Problem: with the stated level of propulsion technology it is completely trivial for said civilization to colonize the entire galaxy.

All of it.

Probably inside of half a million years.

No it isn't. Not in the slightest. That just simply isn't true in any way, shape or form.

Except it is.

The stated level of propulsion technology is as far beyond the level of propulsion technology required to make it trivial as, say, a nuclear-propelled ship is beyond a handmade rowboat.

[Genivaria]

Carl Sagan's novel Contact submits the idea that warmongering cultures and species tend to kill themselves off before ever making it into space.

[Samuraikoku]

Carl Sagan's novel Contact submits the idea that warmongering cultures and species tend to kill themselves off before ever making it into space.

Lest we return to Mon'Tau, the Terror.

[Salandriagado]

No it isn't. Not in the slightest. That just simply isn't true in any way, shape or form.

Except it is.

The stated level of propulsion technology is as far beyond the level of propulsion technology required to make it trivial as, say, a nuclear-propelled ship is beyond a handmade rowboat.

Go on then. Work out the cost and manufacturing capacity necessary. Straight up distance/time calculations don't work.

[Wonder bread Inc]

Hopefully we can find a bread planet...

[Sobaeg]

Hopefully we can find a bread planet...

that gives us more than one loaf before we head home

[Sobaeg]

Carl Sagan's novel Contact submits the idea that warmongering cultures and species tend to kill themselves off before ever making it into space.

nope - dr steven greer meets with aliens all the time, they are peaceful
does noone take his science skills srsly?

[Martean]

Anyway, I think we would kill ourselves before we managed to find any other planet. Look what we've been doing for 1 million years: Fight. We are just animals but instead of fighting with our hands we throw nuclear bombs to the countries we don't like. Imagine what we could do with super technology, a minor war in the Middle East of 10,000 from today could kill hundreds of millions.

We were intelligent enough to create weapons, but he haven't been intelligent enough to NOT use them.

[Sobaeg]

Anyway, I think we would kill ourselves before we managed to find any other planet. Look what we've been doing for 1 million years: Fight. We are just animals but instead of fighting with our hands we throw nuclear bombs to the countries we don't like. Imagine what we could do with super technology, a minor war in the Middle East of 10,000 from today could kill hundreds of millions.

We were intelligent enough to create weapons, but he haven't been intelligent enough to NOT use them.

what do you mean, we are constantly not nuking other nations like usa china etc.

[Martean]

Anyway, I think we would kill ourselves before we managed to find any other planet. Look what we've been doing for 1 million years: Fight. We are just animals but instead of fighting with our hands we throw nuclear bombs to the countries we don't like. Imagine what we could do with super technology, a minor war in the Middle East of 10,000 from today could kill hundreds of millions.

We were intelligent enough to create weapons, but he haven't been intelligent enough to NOT use them.

what do you mean, we are constantly not nuking other nations like usa china etc.

We almost did it. And apart from war there is: Global warming, Pandemics, Asteroids, Hungers, Financial Crisis... And that to mention the ''not sci-fi'' forms of dissapearing as a race.

[Our Most Resplendent Goddess Sen]

Except it is.

The stated level of propulsion technology is as far beyond the level of propulsion technology required to make it trivial as, say, a nuclear-propelled ship is beyond a handmade rowboat.

Go on then. Work out the cost and manufacturing capacity necessary. Straight up distance/time calculations don't work.

Using the most conservative possible interpretation of the technology required to meet that mission profile, a single developed solar system is capable of deploying ten thousand interstellar probes, each of which is equipped with a propulsion system far beyond any in the literature and capable of supporting its own fuel and maintenance needs without outside assistance. At that hilarious level of technical ability, the dominant limiting factors for colonization with fast vessels (the time until colonies can send out their own missions and the maximum range of the starship) become largely irrelevant and you're back to being limited by your starship's maximum velocity.

With more plausible technology, you're looking at several million years to spread across the galaxy. But his assumptions are pretty hilarious.

[Priory Academy USSR]

Maybe there are dozens of advanced civilisations out there; just not as advanced as us? Take for example, a medieval-esque technology level. We would have no clue they existed, and we would have no clue we existed, even if wesent every last radiowave on Earth at them.
At the same time, life might have taken a different route on other planets. There could be a world where ants (or similar creatures) dominate everything, building super-tall colonies, and even some level of collective conscienceness. Could we tell they are out there? No.

Of course, as with a lot of things extra-terrestrial, this is pure speculation.

[Salandriagado]

Go on then. Work out the cost and manufacturing capacity necessary. Straight up distance/time calculations don't work.

Using the most conservative possible interpretation of the technology required to meet that mission profile, a single developed solar system is capable

That isn't the same as "will".

of deploying ten thousand interstellar probes, each of which is equipped with a propulsion system far beyond any in the literature and capable of supporting its own fuel and maintenance needs without outside assistance. At that hilarious level of technical ability, the dominant limiting factors for colonization with fast vessels (the time until colonies can send out their own missions and the maximum range of the starship) become largely irrelevant and you're back to being limited by your starship's maximum velocity.

Presuming that you a) want to; and b) have a population growing quickly enough (why on earth would it be growing at all?).

With more plausible technology, you're looking at several million years to spread across the galaxy. But his assumptions are pretty hilarious.[/quote]

[His Noodliness the FSM]

Since when are we intelligent life?

[UNIverseVERSE]

Easy. The galaxy is too big.

There are somewhere north of 100 billion stars in the Milky Way. Of these, somewhere over 20% are of the rough type of our Sun. Currently it looks like perhaps 30% of stars have planets, but we're only just getting good at detecting Earth-like planets. Let's ballpark it at 10%, for a low estimate. Then maybe 10% of those will sit in the habitable zone of their star (generalising recklessly from the Milky way). So that's .2% of star systems with a suitable planet for life to develop on.

Or in numbers, 200 million.

For how probable it is that intelligent life develops, well, you can just pick your own number for that. But it's got to be greater than 0%. How about one one-thousandth of a percent? That makes it pretty unlikely.

So then we've only got 2000 intelligent life forms out there, give or take a factor of 10^3 at least (the floor, after all, is 1).

Deduction the first, then is that aliens exist.

Modern humans have been around for roughly fifty thousand years (citing from Wikipedia). So let's assume we'll be around another 50k years, and that we'll be sending out radio signals for all of that time. But we won't make any significant expansion out of the solar system, although we will colonise other planets and moons within it. And, because otherwise we can just give our aliens any characteristics we want, let's assume they're fundamentally similar to humans in this way.

So there's only a fifty thousand year window you can detect an arbitrary intelligent species in. Take 2000 such species, and then that's a total of 100 million years. Or about the duration of the dinosaurs.

Entire civilisations can trivially have risen and fallen throughout the entire history of the galaxy without one ever being within the same time as us.

In the time it takes for their first radio emissions to reach us, a civilisation on the far side of the galaxy (100 thousand light years) can rise and fall again.

Meanwhile, we've only been listening well for perhaps 50 years at the outside, now. In that time, even if 2k other alien species reached technological maturity at the same time we have, the chance of any of them being within the very close neighbourhood of earth they would need to be is minute.

Of course, there is a whole universe out there. So by the same statistical arguments that show it is fantastically unlikely we will ever detect another trace of intelligent life, we can show it is nearly certain that somewhere, there is another intelligent species, with computers, who are sitting there and asking "are we alone in the universe?".

[Meryuma]

The universe is infinitesimally vast and interstellar travel is infinitesimally hard.

Leaving aside the fact that infinitesimal is the exact opposite of the word you're looking for, neither of these is correct.

I kinda derped up. I could've sworn "infinitesemally large" was a thing people said but whatever.

Also, how else would you describe the scale of the universe from the perspective of a single species if not as unimaginably huge and and how do you propose interstellar travel can be made likely or at least realistically plausible?