[AntiGuv]

First of all, there's every plausibility that life is common but that technological civilizations do not arise fairly frequently. Out of millions and millions of species on Earth, only one has developed a technological civilization. Moreover, that particular evolutionary tree took some 600 million years in order to accomplish the task..

Secondly, you again assume not only that other species would have personality characteristics conducive to interstellar expansion, but also that interstellar travel, migration, colonization, and communication are all relatively plausible, effortless, and attractive.

Consider if you will, an Earth where near-luminal travel were available - tomorrow. How many people would want to take such a trip? Where would they go? Let's say they hop on over to the next earthlike planet. They would be essentially cut off from Earth. One communication signal would take at least a decade to travel back and forth.

What would they do once they're on that planet? What if the planet turns out unsuitable? What if they have a mutiny along the way? A civil war? They have to establish the colony. For what? Are they dissidents, or whatever? Now, how long will it take for them to set up a another expansive, resource gathering civilization? In order to send out more colonies. What are their motivations? Or, do they wait for this new world to fill up first. What if their civilization collapses?

The questions proliferate ad infinitum. The fact of the matter is that: we do not see indications of other civilizations, which suggests that other civilizations do not expand to fill the galaxy, and we don't know precisely why that is...

[AntiGuv]

And, some more points. What if we are the first (assuming we're the first, since we don't know yet)? Someone has to be first.. What if there are half a dozen other civilizations out there, with perhaps one or two expanding - slowly? What if the one - or twenty - that are expanding simply don't find our system especially suitable for their interests? What if we just can't recognize their communications? (Especially if they have a superluminal means of communication). What if they have much more languid reproduction rates; much shorter lifespans; what if they're marine?

what if, what if, what if.. All we know is that at least one (but probably more) what ifs apply, assuming 'they' are out there, which they probably are..

[alnitak]

First of all, there's every plausibility that life is common but that technological civilizations do not arise fairly frequently. Out of millions and millions of species on Earth, only one has developed a technological civilization. Moreover, that particular evolutionary tree took some 600 million years in order to accomplish the task..

Exactly! That's what the Fermi Paradox argument says - there are no other civilizations in the galaxy.

Secondly, you again assume not only that other species would have personality characteristics conducive to interstellar expansion, but also that interstellar travel, migration, colonization, and communication are all relatively plausible, effortless, and attractive.

I'm not assuming anything, I'm trying to reason it out. Read my post #32, penultimate paragraph, again for why I think your argument about other technological civilizations not colonizing the galaxy is wrong.

Secondly, you're lumping things together to make it sound more impressive, but in reality interstellar travel implies migration, colonization and communication. There's really only one bone of contention - is interstellar travel possible?

I never said they were plausible, effortless or attractive. The only one of those three conditions we can comment on with any certainty is "effortless" - certainly, it won't be!

[BillCompton]

Some fine points.

First of all, there's every plausibility that life is common but that technological civilizations do not arise fairly frequently. Out of millions and millions of species on Earth, only one has developed a technological civilization. Moreover, that particular evolutionary tree took some 600 million years in order to accomplish the task..

It is true, no doubt, that life takes a long time to develop. But earth has a 100% batting average at producing intelligent life. I don't think you can use Earth as an example of how intelligent life is unlikely to emerge.

Secondly, you again assume not only that other species would have personality characteristics conducive to interstellar expansion, but also that interstellar travel, migration, colonization, and communication are all relatively plausible, effortless, and attractive.

Your point, if I understand it, is that some intelligent life might have the characteristics you describe. My point is that if _ever_ there were an exception, that life form would quickly consume the galaxy.

What would they do once they're on that planet? What if the planet turns out unsuitable? What if they have a mutiny along the way? A civil war? They have to establish the colony. For what?

I agree that it has yet to be established that we can long exist with advanced technology. But if we can, then you have to assume a space colony would also be able to persist even with advanced technology. The engine for expansion, of course, is resources. When earth is out, which it almost certainly will be in a million years, what will man do? Die quietly? I doubt it. We will try to solve the problem. The only solution is too obtain resources elsewhere and we will seek to create habitats elsewhere. I think this urge, always assuming a super-bug doesn't wipe us out first, will inevitably lead to colonizing space.

The questions proliferate ad infinitum. The fact of the matter is that: we do not see indications of other civilizations, which suggests that other civilizations do not expand to fill the galaxy, and we don't know precisely why that is...

Why do you assume they are there?