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the numbers (of stars, planets, etc) even in just our galaxy are so very large that even under rare life assumptions there are still going to be an enormous number of civilizations at any given time, never mind over all history.

The problem is we have no way of estimating the probability of life emerging given favourable conditions. It could be 1x10^-100 for all we know.

Life emerged very early in the geological history of Earth. The probability of this happening is greater under the "P(life|conditions)≈1" model than under the "P(life|conditions)≈0" model. Our historical observations give the "P(life|conditions)≈1" model greater likelihood. It's not exactly proof, but it's enough to convince me.

So that brings up the question, if life happens so readily given the right conditions, how come it only happened once on earth? And I don't buy the explanation that one form out-competed all other forms -- given the diversity that we have now, there can be millions of forms of life all existing at the same place/time. But all instances we have now originated from one single biogenesis event.

So, how do we know that there was only one biogenesis, and not multiple ones that happen to resemble each other (i.e., that DNA-based life is the only thing that ends up working, and it occurred multiple times)? From what I gather, there are many markers in biological molecules, such as the direction certain molecules form (left vs. right, etc), and that multiple biogenesis events would have gotten these in random positions (i.e., your heart on the right side instead of the left side of the body).

> given the diversity that we have now, there can be millions of forms of life all existing at the same place/time.

Sure, each niche favors a different specialist, but why do you think that whichever process led to the emergence of life will be any good at producing competing specialists? I'd think that evolution of existing organisms would be infinitely better at this task, as existing organisms have both a numerical advantage and the strategic advantage of DNA (a "playbook" of previous successful strategies to draw inspiration from).

Very few niches are available for the emergence of life, even though there are clearly many available for the evolution of existing life. The available niches require a level of sophistication that spontaneous process cannot achieve but that evolution can achieve (e.g. photosynthesis).

Actually, given that our star is a third-generation star, you could even ask the question : why wasn't there life in our very own solar system before earth even existed ? Before sol started burning or even coalesce ?

The first generation stars wouldn't have had anything but hydrogen clouds surrounding them, but second generation stars would have had similar amounts of other elements to what we have today floating around them.

Given that "our" biogenesis event happened only the second time it could happen (here and in billions of other solar systems in our galaxy), where the hell are the second generation societies ? Didn't they survive the supernovas ? (possible, I suppose, but not exactly hopeful for our own chances of spreading across the stars). Was there some kind of large scale disaster ? But the question is worse than that, because they should have been spacefaring ... if they had anything like our numbers of satellites, we should have been able to find something, somewhere, right ?

Selection bias.

> Selection bias.

Elaborate. If you're referring to the anthropic principle, I don't see how it's relevant to my argument.

Historical observations of sample size 1?

Not strictly relevant. If your hypothesis is extreme, a single observation can make its posterior probability small. For instance, suppose that Alice gives you a coin and says "it lands on heads 99% of the time" (hypothesis A) but Bob calls BS and says "it looks like a regular quarter, so it should land on heads 50% of the time" (hypothesis B). You assign prior probabilities of 50% to A,B because on one hand you can't imagine how anyone could engineer a coin to land on heads 99% of the time, but on the other hand Alice is a great engineer, so you don't know what to believe. If you flip the coin a single time and get tails, your experiment strongly supports hypothesis B over A. OTOH, if it landed on heads, A would be weakly supported over B. We started with an even prior, so the posterior probability of A,B are proportional to their likelihoods: P(A|t)≈2% and P(B|t)≈98%, while P(A|h)≈66% and P(B|h)≈33%.

Let's say that a typical planet remains habitable for 8b years and it takes 4b years from the emergence of life to the emergence of intelligent life, so according to the anthropic principle life had a 4b year window in which to emerge. Under the model where P(emergence)/time is tiny, the probability of life emerging in the first billion years is ~.25. Under the model where P(emergence)/time≈1, the probability of life emerging in the first billion years is 1. With even priors, the posterior of P(emergence)/time≈1 is 80% and the posterior of P(emergence)/time≈0 is 20%.

It's not scientific proof of anything, but it's enough to make me consider alternative explanations for why life is rare.

Interesting points here: http://www.gwern.net/Colder%20Wars

If there's no FTL, but civilizations can accelerate massive projectiles to near light speed, there's basically no defense against devastating surprise attack. And there's little accountability to allow retaliation.

Basic game theory says either they all destroyed each other, or the survivors are staying very, very quiet.

Planet bust should be visible to our technology. We'll spot one soner or later if colder war is still waged. Plus, it's much harder to cook the entire solar system and planet death isn't the end of the game.

Didn't a rather large asteroid pass between the Earth and the moon recently, and no one even noticed it until it was on the way out?

Just because something should be visible doesn't necessarily mean we'll happen to be looking at the right place at the right time within the right spectrum. There could be a lot we simply don't see.

I mean that we should spot other homeworlds being busted across the galaxy.

There are billions of galaxies, though, and my point is we may still be half-blind, since we've only recently even able to detect exoplanets smaller than Jupiter IIRC. And, if we did see something, we would likely interpret it as a natural event.

It would probably be in the best self-interests of whatever species launched an attack to make it appear like a natural event in any case, so as not to draw attention to their existence from unknown parties (like us.) And a collision that could wipe out a civilization is clearly within the realm of natural possibility since it's happened on Earth in the past (without the civilization part..) so it need not necessarily draw attention to itself.

"Wolves" is a new term to me and I'm having a hard time googling for more reading. Can someone give me a link?

I was puzzled by this as well. I'm not familiar with a "wolf hypothesis" and a google search doesn't turn anything up.

I'm pretty sure he's talking about the Zoo Hypothesis. i.e. our presence is known to other intelligent civilization(s), and for whatever reason they've decided to hide themselves and not engage. Like a village would refer to wolves in the surrounding forest.

For this to work though, you have to have one advanced civilization that has either absorbed the others ("unitary") or powerful enough enforce the rules. Otherwise it would be pretty inevitable that out of a hodge-podge of civilizations one of them would say screw it and engage.

Wolves aren't known for taking other animals, putting them in cages, and staring at them. Wolves are known for eating other animals.

So a prime directive of sorts, perhaps?

I legitimately think we are living in some sort of holographic simulation created by consciousness. I think Thomas Campbell's work is most accurate model of reality I have seen. Check it out:

https://www.youtube.com/watch?v=fT8LaMrn_MM

There's a depressing non-wolf Great Filter argument. What if this sort of scenario is unavoidable for fundamental reasons... possibly involving a combination of thermodynamics, evolutionary dynamics, and game theory.

http://en.wikipedia.org/wiki/Olduvai_theory

For this to be an explanation it would have to be that this "great filter" is so hard to avoid that someone escapes it maybe once per few thousand galaxies per many billions of years.

>We are simulated.

Actually there is a way to tell if the world you're living in is not a simulation. Our world fails this test.

What test?

If these civilisations find some way to communicate or interact at all you can't treat them like independent variables.