[pharke]

If we're talking about galactic distances and timescales I don't see why we couldn't safely assume enough technological advancement for either aliens or humans to modify their own biology to the point where centuries would be a small fraction of your total lifespan. I think the bigger question is why any significant number of people would travel to more than a few star systems if you had to do it slowly. If the system is uninhabited then you would be isolating yourself from the rest of society for a long time. If it's inhabited then you would have the excitement of discovery and contact but it would still be difficult being separated from your own civilization and you would want to return at some point even if just to share what you've learnt.

How many people today travel to places that are completely uninhabited and have no infrastructure in place for getting there? I'm talking end of the road, getting on a bush plane and landing in the middle of an open field kind of isolated. How long do they stay? Same for contacting the few remaining hunter gatherers on the planet. What if those trips took thousands of years instead of a few weeks?

I think there's a big stretch of time for the development of any technological civilization where they spend most of their effort on developing their own solar system and only send small flyby probes to their nearest neighbours. After that there may be an even longer period during which they colonize those near by stars but each colony likely takes an extremely long time to fully develop. The civilization may send out automated probes to look and listen and maybe the occasional explorer or anthropologist but I doubt there are any galaxy conquering civilizations out there.

So I think I do agree that if anything visits us it is likely to be an automated probe. Bracewell probes would be well suited to any chatty civilization that is seeking contact. Von Neumann probes are more suited to brute force exploration.

This is all assuming that the speed of light is the fastest you can travel and communicate. If it isn't, then I'd say all bets are off.

[YurgenJurgensen]

If the Internet has told us anything, it's that as soon as the production of a self-replicating probe becomes accessible to a hobbyist, some people will do it even if there's no benefit to them. And it only takes one. The far future human colonists won't be landing on unspoilt wilderness; they'll be reclaiming systems from some 25th century script kiddy.

[teddyh]

http://www.threepanelsoul.com/comic/tethics