Fermi paradox

[Zohar]

It revolves around estimates of probability of extraterrestrial life in the universe (those being high according to said estimates) and the lack of evidence of ET life - no huge stellar or galactic complexes, no probes, no radio signals and so on.

Or, in the words of Fermi "Where are they?".

First got interested in it when reading Stephen Baxter's Manifold trilogy (which is pretty cool and you should look it up). What do you think?

It seems strange to me that Earth is the only world with (so-called) intelligent lifeforms on it. After all, we see on our own planet how diverse and flexible life is, according to recent findings it has sprung up a lot sooner than we think, as soon as the planet cooled down a bit. So it doesn't seem that unlikely.

Add to that the existence of amino acids in interstellar space... We should see someone or something. Maybe they don't want to show themselves.

[evilbeanfiend]

the size of the universe is big....

we have been transmitting EM waves for, what, 100 years, how many stars are there in 100 ly distance from us? a few hundred i think. there are an awful lot more stars in our galaxy. the next nearest galaxy is 2*10^6 ly away
they wont be able to detect our radio broadcasts for 2 million years.

also we have only be able to resolve extrasolar planets for about 10 years, and only ones in habitable ranges from stars in the last few years so we really haven't checked much of the universe out for life yet

[3.14159265...]

You don't watch star trek or what?

Where do you think the get the cast.. tsk tsk

[Shadowfish]

How could we know about them?

-Interstellar travel is either *really* expensive, or *really* slow.

-I haven't done any calculations here, but your average radio station would not be detectable at a distance of 10 light years. I'm not sure how much power you would need to get a clear signal at that distance, but my guess is a lot.

My guess that there are hundreds of civilizations in this galaxy, and humans will never meet any of them. It sucks, but the distances between stars are enormous, no matter what kind of technology you have.

[skeptical scientist]

It all depends on what you think the density of intelligent life in the universe is. The fact that we haven't seen anyone else probably just means that the density is low enough that this is likely. With a light-speed barrier, one can only communicate with relatively close places (depending on how long one has had the technology to communicate across light-years at all) so if intelligent life is sufficiently distant, we won't have had a chance to communicate at all.

[Zohar]

The point of discussion is that, seeing as there has been a universe for 15 billion years or so, there could easily be very old civilizations (if, and that's a big if, civilizations don't destroy themselves always, eventually).

Such old civs may need to build vast structures in order to support themselves - enslaving star systems, building black holes and so on. Basically, astronomical artifacts so huge we should see them from over here. And so far we haven't.

It doesn't speak about communication of any kind between the civilizations.

[SpitValve]

Such old civs may need to build vast structures in order to support themselves - enslaving star systems, building black holes and so on. Basically, astronomical artifacts so huge we should see them from over here. And so far we haven't.

That or they'll advance enough that they've reduced their required energy input to a pittance

[Maseiken]

This isn't really a Paradox, more of a quandry.
I'm a firm believer in the Multiverse, So, if there aren't any other forms in this 'verse there probably is in another.

Also, the Universe is big, and the odds of a planet being able to support life and somehow gaining the first Vestiges of it are so absurdly small, that any Intelligent life would be a VERY long way off.

This isn't even touching the theory of an infinite universe.

[Doitle]

I beleive another one of the problems with not finding any other life is the fact that once another life form gained the ability to settle on other planets, they would expand at an exponential speed such that they should really be all over the universe. Think about it like this. Once we can colonize other planets, that is a ton more space, for more people, more resources for more ships, and thus we can go colonize even more planets. It snowballs and you have civilizations spreading out very quickly accross the entire galaxy and universe. At least I've heard that argument made a few times in relation to this.

[gmalivuk]

I'm a firm believer in the Multiverse, So, if there aren't any other forms in this 'verse there probably is in another.

Isn't that just as faith-based and untestable a claim as believing in a God who only made life on one planet?

[Andrew]

I beleive another one of the problems with not finding any other life is the fact that once another life form gained the ability to settle on other planets, they would expand at an exponential speed such that they should really be all over the universe. Think about it like this. Once we can colonize other planets, that is a ton more space, for more people, more resources for more ships, and thus we can go colonize even more planets. It snowballs and you have civilizations spreading out very quickly accross the entire galaxy and universe. At least I've heard that argument made a few times in relation to this.

Yeah, but it'd still have to have started out somewhere within the spacetime-cone-thing pointing out of the back of the here-and-now, otherwise we still wouldn't ever see them.

[Shadowfish]

I beleive another one of the problems with not finding any other life is the fact that once another life form gained the ability to settle on other planets, they would expand at an exponential speed such that they should really be all over the universe. Think about it like this. Once we can colonize other planets, that is a ton more space, for more people, more resources for more ships, and thus we can go colonize even more planets. It snowballs and you have civilizations spreading out very quickly accross the entire galaxy and universe. At least I've heard that argument made a few times in relation to this.

Expansion is only exponential if most civilizations decide that the benefits of colonizing other solar systems outweigh the costs. Given the unbelievable costs of colonizing another solar system, I don't think it's safe to assume this.

To give rough idea: getting a 15000 kg truck to half the speed of light costs 1.2 × 10^21 joules. If you covered the entire earth with 100% efficient solar panels, it would take about 250 years to gather this much energy.

edit:Ok, I lied. It would really only take 2 hours to gather that much energy. still, a space ship that will carry enough stuff to start a civilization from scratch will be a lot bigger than a truck.

[gmalivuk]

Some stuff about oh so much energy being needed to send trucks through space, or something.

Bah, humbug!

I say to you and your naysaying!

Though regardless of how little I agree with your pessimism, you're right that growth in general won't be exponential. Unless someone overcomes the speed of light barrier in a practical way, in which case all bets are off.

[electoralfraud]

Such old civs may need to build vast structures in order to support themselves - enslaving star systems, building black holes and so on. Basically, astronomical artifacts so huge we should see them from over here. And so far we haven't.

That or they'll advance enough that they've reduced their required energy input to a pittance

Here Here! Energy efficiency is one of the biggest bottlenecks we have. Once we can really transfer it efficiently and make efficient use of it we'll be... probably doing some pretty neat things, err...

As to the paradox, well sometimes I think I might just believe the great filter... There is something (physical law, complexity principle, whatever) that prevents civilisations from reaching the point where they can effectively colonise large tracts of space. Now this could be anything... Opening micro-blackholes by arsing around with particle colliders too much trying to make physics breakthroughs; lack of truely viable co-operation theories for disarmament once a civilisation goes nuclear; simple inability to move living tissue close enough to lightspeed whilst maintaining coherence; inability to transfer genuine sentient mental states to alternative storage (would negate light-speed fractions with living tissue dilema); that once the technological standard has been reached where genuinely useful space travel is viable it is no longer needed for either volume, matter, energy or research needs; BIG BAD MONSTER/GOD; BIG GOOD MONSTER/GOD; 'Thankyou for playing, your species high score at possible exodus was: 21,376,732,187,623,589,682.09. You are 3rd on the leaderboard so far. If you remain in the top 5 after all qualification rounds have finished you will qualify for...; whatever...

Although most of the time I think it's probably because of the massive scales and scales of probability we're dealing with without knowing whether our data is genuinely accurate or not. Even with optimistic estimates and other sentient life actually existing in the universe at some point, surely the probability of the conditions that there could be contact are very slim indeed?

[evilbeanfiend]

yes energy efficiency and also emission can get better rather than worse with more tech. originally SETI assumed that once a civiliztion had developed radio it would be beaming radio waves out for evermore. iiirc, now they assume that there is a window of a few 100 years or radio emissions which significantly reduces the chances of finding ET life unless it is trying to be found i.e. transmitting a beacon