"I mean, why would we believe that other than residual religious dogma?"
Because when we look out into the universe, it looks like we expect it to look when it is dead, not full of life, some significant percentage of which becomes intelligent. Nothing that looks like Dyson spheres of any form (recalling that the "solid shell" is actually only a special case), nothing that looks like curated stellar evolution (very high-end stuff but a truly advanced civilization will not want to leave stars just randomly flying around a galaxy and exploding), very very little that could even conceivably be a ship traveling between the stars (which turns out with any physically-plausible propulsion mechanism to be visible from a very long ways away and would show very clear blue/red shift changes), nothing that doesn't appear entirely natural.
This isn't the whole story (maybe they're hiding, maybe our idea of the top end of tech is wrong, maybe they're all virtual, maybe they escaped into another, friendlier dimension, maybe they all kill themselves, maybe the universe is soaked with simple life but this article is essentially correct and complex intelligent life really is a 10^-1000 event, etc.), but it is not true that the claim that complex life must be hard is some sort of stupid idea in light of the size of the universe. Arguably it's actually the claim best supported by the evidence at this time.
People are really bad at thinking about small probabilities even on the scale of one out of a million, and it's not impossible that complex intelligent life turns out to be one out of 10^1000 or worse; we simply don't know. It is not hard to come up with calculations that plausibly set the odds of advanced life occurring even once in the universe as less than 50/50 without having to make stuff up. Our ignorance dominates our knowledge here.
Where exactly would we be seeing all this stuff? I mean, how closely can we even look on planets in our galaxy? We are still discovering trillions of new galaxies here and there.
Our reach is virtually zero in the context of the universe. It seems from our vantage point, I would expect the universe to look exactly the same whether it was bustling with life or we were the only ones.
I had never thought about searching for Dyson spheres (it made me replay a part from The Big Lebowski where the dude says, "We'll that's fucking interesting man."), but they strike me as a incredibly hard thing to search for. Don't we see into the universe with the energy escaping from stars, galaxies, etc..? If some species were able to actually harvest the output of a star to anything approaching 100%, wouldn't it be exactly the type of thing we would never see?
> Arguably it's actually the best claim supported by evidence
Unless I am fundamentally wrong about the resolution of our map of the universe, I don't think there is any evidence either way unless you believe in any 'encounters'
"If some species were able to actually harvest the output of a star to anything approaching 100%, wouldn't it be exactly the type of thing we would never see?"
You'd still have residual heat. Some have suggested that what we'd see is awfully similar to red giants though I rather expect we'd still see something odd about them.
Besides, the one you really should have focused on is star-traversing ships. They're visible from a really long ways away.
"I would expect the universe to look exactly the same whether it was bustling with life or we were the only ones."
Allow me to re-add in the word "intelligent" to your "life". The universe looks the way it would be expected to work if absolutely nobody ever makes it off their planet to any reasonable degree, or there is no other intelligent life out there. Or we just happen to be the "precursors".
Part of the problem with this debate is that most people are still participating in it with very 1960s ideas about the limits of technology, very Star Trek ideas about what technologically sophisticated aliens will be like. Of course the Federation could be floating around out there without us knowing, with its starships powered by magic, its technologies powered by magic, and humanoid aliens scattered about everywhere due to magic. (Yes, I know about the episode in question.) But that's not what it looks like. In reality, a modern conception of what a technologically-sophisticated culture would do results in a lot of things visible from a very great distance, the ones I previously mentioned before. And we see 0 of them.
Personally I do not put much stock in the idea that intelligent life is abundant and easy and not a single one of them ever decides to go to another star. For such a society it just isn't that hard and the payoff of being the first in a star system is incomprehensibly enormous, well out of proportion to the difficulty of getting there. Something about standard story of easy, abundant intelligent life is very very wrong, and the most parsimonious explanation is that intelligent life is in fact not easy or abundant.
What? No. If there is residual heat you aren't capturing all the energy.
> In reality, a modern conception of what a technologically-sophisticated culture would do results in a lot of things visible from a very great distance, the ones I previously mentioned before. And we see 0 of them.
This appears to be the crux of your argument. Can you go into or point to a place where I can find out more about what these ships would supposedly look like?
I think the fact that we will almost certainly need a paradigm change before we can really conceive of interstellar travel combined with the radical shift in conceived ideas following a paradigm shift, current guesses about what a super advanced culture's vehicles act like doesn't really hold much weight for me.
You can't capture all the energy. Basic thermodynamics. You have to black-body radiate away the heat of the star driving the system, or the only alternative is that it is all collecting within the system, cooking everybody within in a fairly short period of time.
I argue on the basis of real science that we know, not because we know it all but because we can't argue on the basis of science we don't know about. Given that, we damn well can make some guesses about what a space ship will look like, which inevitably includes some form of propulsion involving either the expulsion of very, very hot matter (to get optimum mass efficiency, propellant will be at a premium and no point dumping it out the back cold) or light directly (unlikely but at least plausible) in a directional manner.
The topic came up a few months ago during the discussions on whether it is rational for an alien civilization to summarily execute any other civilizations it discovers with relativistic planet-killers, but unfortunately trying to Google up a specific discussion about spaceships and relativistic projectiles is an exercise in futility. Still, work the math on what it takes to get a decent payload (at least several thousand tons would be nice) up to ~.1c, and then recognize that thanks to Newton's laws, the resulting mass-energy number you find must actually be coming out the back of your spacecraft in as close to a single direction as possible. Possibly literally as a laser, though as I said I'm pretty skeptical about the utility of a pure light-drive. It's pretty damned bright.
Look, I hate to be offensive, but if you don't fail basic thermodynamics and you actually take seriously the real science we already know, we don't have to retreat into romantic cliches about how we can't possibly understand advanced cultures. We can in fact put bounds on things if our understandings are basically correct, and if our understandings are basically incorrect then frankly we have bigger problems than the question of alien life.
The upshot of this, going back to your first post, is that if either of us is retreating into "religious dogma", romantic conceptions of reality held onto despite rational examinations of the evidence and science, taking shelter in the possibility of who-knows-what magic science may produce in the future and refusing to use what we already know, it's you, not me.
Look, it's not offensive but I do think what you're saying is naive.
Lets take a step back into the 1500s and talk about what an advanced culture able to move thousands of tons of goods from one side of the country to the otherside in a matter of days would look like. or what being able to search all of the worlds knowledge instantly would look like, etc etc. Any of their guesses are necessarily limited to their 'limited' perspectives.
We have had numerous paradigm shifts since then, each giving fundamentally new ways to conceive of problems, and I think it's incredibly likely that we will undergo another paradigm shift with regard to physics/space travel before our society is leaving the solar system, let alone the galaxy. If that's the case it's not an unnecessary romantic conception, it's a necessary repercussion of a historically verifiable phenomenon, paradigms change, and so do ways of thinking about problems.
Besides, I still don't understand how we are seeing a several-ton payload going .1c in a galaxy we just discovered.
I guess I just don't see a compelling argument that we would, from our vantage point and with our tools be able to make any type of reasonable observation against a hypothesis about other intelligent life.
To play the role of "guy who links to a relevant wikipedia page" again, the conflict between the fact that we've seen no observations of intelligent life out there and our estimates that our life is not unique is known as the Fermi Paradox (http://en.wikipedia.org/wiki/Fermi_paradox). Once again, you may already know this, but it will hopefully be interesting reading to someone else.
Because when we look out into the universe, it looks like we expect it to look when it is dead, not full of life, some significant percentage of which becomes intelligent. Nothing that looks like Dyson spheres of any form (recalling that the "solid shell" is actually only a special case), nothing that looks like curated stellar evolution (very high-end stuff but a truly advanced civilization will not want to leave stars just randomly flying around a galaxy and exploding), very very little that could even conceivably be a ship traveling between the stars (which turns out with any physically-plausible propulsion mechanism to be visible from a very long ways away and would show very clear blue/red shift changes), nothing that doesn't appear entirely natural.
This isn't the whole story (maybe they're hiding, maybe our idea of the top end of tech is wrong, maybe they're all virtual, maybe they escaped into another, friendlier dimension, maybe they all kill themselves, maybe the universe is soaked with simple life but this article is essentially correct and complex intelligent life really is a 10^-1000 event, etc.), but it is not true that the claim that complex life must be hard is some sort of stupid idea in light of the size of the universe. Arguably it's actually the claim best supported by the evidence at this time.
People are really bad at thinking about small probabilities even on the scale of one out of a million, and it's not impossible that complex intelligent life turns out to be one out of 10^1000 or worse; we simply don't know. It is not hard to come up with calculations that plausibly set the odds of advanced life occurring even once in the universe as less than 50/50 without having to make stuff up. Our ignorance dominates our knowledge here.