I always go back to people like Drake and Shostak. They seem pretty convinced that "they" are out there, but the problem is that there’s no known way to communicate with them due to distance and time. If there’s a way to solve this problem, please let me know. Sagan and others seemed to think that if we could communicate (a very big if), then we could exchange our knowledge, but how exactly could you do that? The problems appear insurmountable.

Humanity has undertaken massive projects that took hundreds of years before (~2,000 years for all of the great wall of China).

As long as they're less than a few thousands light years out, I don't think that communication would be impossible.

I’m with you. But is it reasonable to assume that we can understand each other and share knowledge between the stars. From what I understand, it’s extremely unlikely. After all, we can barely communicate with species other than our own.

I think we'd better hope that we're alone. If creatures like us are common then that's bad new for us, because "life that behaves like humans and exists for millions of years" and "a galaxy that hasn't been completely filled long before now" are mutually-exclusive states. If we have any chance at all of conquering the stars we'll be doing it alone.

This is a reformulation of the Great Filter argument. Are there any good counterarguments?

Sure, plenty. They just mostly require us to change over time. Maybe sapient species mature and don't feel the need to ever expand, for millions of years. Maybe interstellar travel is so hard nobody ever does it nor do they make machines that do. What worries me, though, is it doesn't seem that impossible. It seems like if humans exist long enough one of us is going to make and launch a Von Neumann probe that eats the entire galaxy. The fact no alien species has makes me think we're far and away more likely to go extinct long before attaining that capability.

I remember a line from a sci-fi novel: "We only consider a species mature when you could put the power to destroy the world into the hands of every single individual with complete confidence that none of them will ever use it." I think we're, eventually, doomed.

I still have my doubts. I agree it feels true, and yet every "earthlike" planet found so far is nothing like the Earth. How many exoplanets have been found, and how many of those are Earth-size planets with a large moon in the habitable zone of a sun-like star? Because it's entirely possible that all of those are necessary.

Because as inevitable as life may seem, it's also fragile. Practically the entire universe is extremely hostile to it, with the exception of a small layer on the surface of this one planet. Radiation will destroy life, so we need a thick atmosphere and a strong magnetic field, something of the rocky planets in our solar system, only our planet has. The focus is mostly on water and the Goldilocks Zone, but it's entirely possible that there are a lot more requirements to make life possible.

I want to believe there's lots of life out there, but I don't want to be suckered into wishful thinking; evidence does matter.

> I'm perfectly comfortable with things being true even sans iron clad rigorous proof. If you limit your worldview to only that which has been rigorously proven you miss out on a lot of necessary and interesting truths, I think.

A sensible outlook in general. And I frankly think it's true of everybody, even if some people claim otherwise. Most of the human experience is not provable or falsifiable, yet we experience it and believe it.

> How many exoplanets have been found, and how many of those are Earth-size planets with a large moon in the habitable zone of a sun-like star?

I think this is down to how we look at the moment. One of the main ways we find exoplanets is to notice the star dimming with a regular frequency. This gets harder as the orbital time increases, as you need multiple observations of the planet transiting the star to conclude that it's a planet. This means that the vast majority of the exoplanets we know about have relatively short orbital periods, and the characteristics that go with that (e.g. they're close to their stars, therefore less likely to have moons, and if we consider them to be in the 'habitable zone', then their stars are relatively dim).

Actually, the fact that we've found so many exoplanets that fit in the relatively limited criteria that we can detect, suggests to me that there are probably a lot of exoplanets of all kinds, that we're just not as good at detecting yet.