[goatlover]

You're assuming the probability for life, or at least intelligent life forming, is a lot greater than the amount of habitable places in the observable universe, such that there would be many civilizations. But we don't know what the probability is. It could be rather low, approaching the number of habitable worlds, such that we're alone or very rare, spread apart by vast distances of space and time.

Would explain the lack of evidence just as well.

[naikrovek]

I'd bet that the types of life that may exist in the universe far outclass our narrow definition of life. I get why we only look for life like ours, and I'm quite sure we're excluding the vast majority of life by narrowing the scope so much.

I'm saying that there are absolutely many more habitable planets around than we believe there to be, even among the planets we've observed. We just don't know what to look for, because we don't know what's possible.

"Life, uh, finds a way."

[sph]

That's just a fallacy because we're life and surrounded by life and want to believe it's everywhere.

But the little we've explored of space, it's just dead rocks. There is literally nothing that has suggested a hint of life outside our atmosphere.

I'm not completely discounting alien life, I'm saying all we have now is hope, wishful thinking and not a shred of proof.

[mpalmer]

There are multiple problems with the claim that a lack of evidence for intelligent life makes it more likely that it doesn't exist.

First, the further out we look, the less recent our data. Every event we observe that's more than 200 light-years away happened before slavery was abolished in the U.S., and well before Earth's first radio emission.

I'm not saying we shouldn't base conclusions on evidence, but I will say that our ability to gather _current_ data about our surroundings is limited to an infinitesimal fraction of the universe. Worse, it degrades with distance. Bacteria were there, but we couldn't see them for a long time. (They were theorized, though, their existence reasoned out and later proved with evidence)

Second, unlike bacteria intelligent life is...well, you know. Suppose we're the last ones to the interstellar party, or at least not the first. We come in, blasting radio waves like a toddler, BEEP BEEP BEEP BEEP. No signal hygiene whatsoever. Our neighbors on the other hand likely learned a long time ago to hide their presence from all but those they trust, and certainly from those on a lower technological playing field.

If the intelligence we're trying to prove can consciously avoid us finding out about them, then taking absence of evidence as evidence of anything becomes suspect.

Of all the intelligences that could exist - not just those we could detect, mind you - what percentage of those do you think are more advanced than us?

[neuronic]

It's not a fallacy because that would imply you know better. You don't. Wishful thinking maybe, but not a fallacy.

[msrenee]

If you asked scientists 30 years ago about some of the extremophile life that we now know to exist, they'd have thought you were insane. They've recently found microbes loving in an asphalt lake in Trinidad. It doesn't have to be an with x% oxygen and x% CO2 and whatever else to support life. It doesn't have to be between -30 and 90 degrees C for things to survive. There's organisms out there that use sulfur compounds for respiration in the way we do oxygen.

So either whatever caused life on Earth was completely unique and couldn't have happened anywhere else, or there's a very good chance there's other life out there. The universe is huge and it's hard for me to believe that earth is the only place where the parameters were met to cause life. From there, it's hard for me to believe that those life forms couldn't adapt to circumstances that are beyond our wildest imagination.

[taylorius]

Why is it a fallacy to believe life is elsewhere in the universe? It seems the most likely possibility to me. Of course we have no proof either way - because we've not really looked anywhere (we're not able to, yet), apart from the moon, and a few tens of square metres of Mars (both of which we knew, a priori were barren rocks - but at least they're not too far away). That doesn't make the idea of other life in the universe "wishful thinking", surely?

[mr_mitm]

> It seems the most likely possibility to me

Why though? Surely you did not do a statistical analysis, because there are too many unknowns:

What is the likelihood of life (as we know it) forming on a given planet? What is the likelihood it will become multicellular? Life on earth was prokaryotic for billions of years and the Cambrian explosion is not yet entirely understood. How likely will it become intelligent? Remember, we don't have any reason to believe that intelligence is in any way a "goal" of evolution. Even if it does, will they have the resources necessary for becoming a technological species? Maybe dolphins are super intelligent, but living in the water and not having opposable thumbs sucks if you want to make tools and perhaps harness the power of fire to build even better tools and machines.

That does not even take into account the various catastrophic events that can happen in the universe where we do not have a good idea of how likely they are. What if a meteor hits at the wrong time? What about gamma ray bursts? What if a Carrington-type event wipes out all electronics? For all we know, these could happen with an average frequency of 100-200 years. Do we have an idea of how likely it is that the climate on a planet stays somewhat stable for a few hundred million years so it doesn't spontaneously become a planet like venus? We just don't have enough data points to assign probabilities there.

So yes, I believe it is largely wishful thinking.

[taylorius]

Ok, we don't know how likely life is to evolve in the universe. It could range from impossibly hard (though it cant actually be that, because we exist) to easy enough that it has occurred many times. Of all those possibilities, what difficulty range would result in it occurring once (on earth), but never again - despite the billions and billions of planets that exist. A very, very fine tuned difficulty - or to put it another way, the earth would need to be super,super unique, to be the only place capable of life in the entire universe. That strikes me as less likely that it occurring multiple times.

[naikrovek]

We don't know all forms that life can take. We simply do not know what is possible outside our own tiny realm, and our understanding is limited because of that.

In 1000 years, do you think we won't have discovered forms of life that we would say are impossible today? We've discovered things we thought were impossible just 20 years ago!

[goatlover]

Maybe so, but what chance do have of detecting those life forms outside of our solar system? At least for now, a technosignature is our best bet, and as interesting as discovering an extremophile on some moon around a planet circling a brown dwarf would be, finding out we're not alone as a communicating civilization is what people really want to know.

[neuronic]

Habitable for organic life.

While I can't fathom anything else I still believe it's hubris to believe we understand what forms of life may exist in the universe. Maybe we exist right along something else and will never notice each other.

[Teever]

That's the point.

We're looking for what we can recognize as life.

[Grimburger]

> the amount of habitable places in the observable universe

Based on the range of extremophiles we have from just one planet, that's a lot more than you might think:

* -20 to 120 degrees celsius

* 1,100 bar pressure

* ph 1 to 11

* 6000 Gy radiation (a CT scan is about 6 mGy)