There is a problem in the impracticality of deep-space travel though, to be honest I don't think we'll ever colonise another planet

Moving a self-sufficient colony around these vast distances at speeds that'll be worth the trip has some basic requirements for generating some momentum, and there aren't a lot of options on the horizon for doing so. Tricks like using a planet's gravity to get a boost and using space elevators are good for getting from zero to planet-speed, but further than that we can't add much more on

Also we know the physical limitations of a perfect fuel (matter/anti-matter) so it's not necessarily a lack of imagination, it's just that there's no unwritten rule that the universe has to be able to provide us with a physical means for space travel, at the moment it's looking impossible

(And going back to the original topic this is what you'd expect with a lack of signals from well established intelligent life)

if intelligence is unsustainable then you are suggesting that from the time they came into existence until roughly 10,000 years ago humans were not intelligent creatures

Humans were intelligent, it is only their technology level that was low. Maybe high technology level is unsustainable?

that is my thought process exactly

technology is not a direct refelection of intelligence by the way

Is intelligence sustainable? Well, the answer to the standard Fermi paradox has already been given, so I don't see why that's in issue. However, the question is still interesting to consider, and most possibilities are a bit "chilling" to some.

Personally, I think that intelligence is not, by it's very nature, unsustainable. Then again, I do not think that anger and hate by their very nature are "bad" emotions; there is a proper time and place to feel them. Likewise, there is a proper set of circumstances in which "intelligence" is both sustainable and desirable. These circumstances naturally require that the intelligent beings be intelligent enough to not kill each other off. We've not quite reached this point, but we're getting there (I hope). So long as "intelligent" races are wise enough to not wipe themselves out, I see no problem with intelligence's sustainability.

The real question is, can this happen? We'd all certainly like to think so. It's denial is not a manifest contradiction; we can imagine an intelligent society where everyone gets along and beings try to further the greater good over their own personal desires. Is it practical? I don't believe so. Evolutionary nature is based around the idea of conflict; the "better" survive and pass their genes on, and the weak die off and remove their genes from the pool. My astronomy teacher put it very bluntly to us when he said, "Your brains are wired to do three things: eat, avoid being eaten, and mate. You aren't designed to understand the mysteries of the universe."

Oops, hit the post button too soon. To continue:

Naturally, because there isn't enough for everyone to eat, we're thrust into conflict. Even if we can somehow sustainably provide food and basic living conditions for all people, we'll still, in all likelihood, be put into conflict of ideas. It is my opinion that our brains simply cannot function as they are intended to without conflict. This is good for us as a species. Conflict fuels change, and change hopefully fuels progression. There is no "golden age" which we'll never surpass; we can always get better.

But can we somehow express our conflict without resorting to violence? Sadly, we aren't all Lincolns and Douglases. There will always be at least a few individuals who will prefer to use their fists instead of their tongues. Nevertheless, perhaps the more peacefully inclined of the human race can forcibly suppress those more dissident elements. It might even be possible, with more advance psychology, to "cure" them of their violent tendencies. However, I find this improbable. All that needs to happen is for two violent men (or women) to slip into opposing positions of great power, and humanity will be done for.

In sum, I personally think that intelligence, if created by the standard evolutionary model, is unsustainable. Remnants from earlier evolutionary stages will continue to reside in the species, and somewhere down the line, the species will destroy itself. We came really close in October of 1962, and that was only a few years after we had developed the power to completely eradicate ourselves. We're programmed for conflict, and something will eventually disturb the status quo. Whether that be some rise of the machines (a la Terminator), a scientific experiment gone horribly wrong (LHC, I'm looking at you [not really, some super-virus is more likely]), or simply a thermonuclear war, it will end in our destruction. Then again, I tend to be a pessimist, in the hopes that I will be pleasantly surprised. Usually, I'm wrong.

For a look at my personal beliefs as to how humanity will develop, see the book Accelerando by Charles Stross; the complete text of which can be found at http://www.accelerando.org/book/

Well, it's quite likely that all intelligence will ultimately arise due to evolutionary processes. Evolution doesn't naturally make us competitive, it just makes us selfish. If it benefits us most to co-operate, then for sure we'll co-operate... hence, societies.

There's no reason that conflict can't be the catalyst for our progress, since it frequently is... technology always progresses fastest between two or more highly competitive countries/corporations. Self-interest has managed to take us this far, and look at all the fantastic things we have now! All produced because we want to survive and attract mates!

Kestas is right that momentum is a highly limiting factor... but that doesn't restrict us from colonizing the Moon or Mars if we had the technology and energy to make it habitable. Planets outside our solar system would take a long, long, time to reach, but that doesn't make them entirely unfeasible. Certainly, no corporation today would consider launching into space to exploit resources but that's just because there are still resources to exploit here on Earth and because there isn't too much legislation regarding space and claiming rights. However... as resources become rarer here, while demand continues to increase with population, we might find a few courageous countries/corporations extending their reach to space in order to exploit vast untapped resources. The same leap will be made when population densities can justify moving beyond the solar system for economic gain.

"Most of the so-called "developed" countries already have negative birth-rates. The same thing will happen in a century or three all over the world."

That's why, thanks for answering for me, Denzel.

Can you see when you're travelling at the speed of light?

Can you throw a ball in front of you when you're traveling at the speed of light?

I don't know much about physics but I'll hazard guess on this one. Speed is relative, so if you were traveling at the speed of light (relative to a stationary observer), and you threw the ball in front of you at 30 km/h, it would move away from you at 30 km/h.
As far as the observer on the ground is concerned, as an object approaches the speed of light time slows down relative to the stationary observer. So as far as the observer is concerned watching you, time would stop, and for the ball, time would go backwards.
That's my uneducated guess anyway lol.

Actually I think I am wrong about the ball. Apparently at super high velocities speeds don't add they way the do normally. So if you are travelling at the speed of light and you throw a ball it will also be moving at the speed of light. Over my head.

You cant travel at the speed of light :-|

I was aware of that. I assumed Invictus's question was hypothetical.

Everyone seems to assume the developed worlds birth rate is fixed but the developing world's isn't. I read an article out there once that the low birth rate thing will evolutionarly phase itself out. The women with maternal instincts will be having the babies and thus produce more women with maternal instincts. This negative growth thing we are experiencing is only temporary. Just throwing it out there.

Sorry if thats contributing to the side track, but we won't just die out because we all get abortions.

To Glorious and others: what you're basically talking about is governed by Einstein's theory of special relativity, which describes movement of particles in non-curved spacetime (curved spacetime is governed by Einstein's theory of general relativity, which is a bit more complex in terms of mathematics). The basic condition is that the speed of light in vacuum is constant in any inertial frame (an inertial frame can be thought of as a coordinate system that moves at constant speed, i.e. no acceleration). At velocities much smaller than the speed of light, this doesn't cause any noticable effects. However, once velocities become comparable to the speed of light, weird so-called relativistic effects start to appear. For example, when you're on a spaceship travelling at a velocity near the speed of ligth, your vision will be limited to a narrow cone that extends to the front and back of your direction of movement. If you're somehow moving AT the speed of light (not possible unless you're a massless particle), the cone will have narrowed to a single point. Other weird effects are spacetime contractions and time dilation. As Kestas correctly states, it's impossible for a massive object to travel at the speed of light, only massless particles (photons) are able to and to them, all movement will appear instantaneous. The reason why massive objects cannot reach the speed of light is because the amount of energy needed to accelerate a massive object grows exponentially as one nears the speed of light. In order to propel a massive object to the speed of light one would need an infinite amount of energy.

The basic fact is that an event (such as the throwing of a ball off of a spaceship) will be perceived differently by moving and stationary observers. It's really difficult to explain without use of illustrations, and besides, I had too many beers yesterday so I've probably made a terrible mess out of this explanation already ;) I encourage you to take a look at the wiki-article on special relativity:
http://en.wikipedia.org/wiki/Special_relativity
it explains things much better than I'm able to.

Thanks Wotan. I was hoping you might chip into this discussion.

@Invictus & spyman: you wouldn't be able to throw a ball in front of a spaceship travelling at near-light speed because of the energy needed to propel it to that speed.

There are a good number of examples of these relativistic effects: usually they involve spaceships travelling at near-light speed, lightbulbs that emit flashes and how observers travelling at different speeds perceive them. To us, relativistic effects sometime produce anti-intuitive (i.e. weird) results which seem irreconcilable with our normal perception of space and time. But this is simply because our perception is a result of our darwinian evolution, and hence our minds are evolutionary 'programmed' to think in terms of massive objects moving at sub-luminal velocities and space and time as separate phenomena, rather than in terms of massless objects moving at the speed of light and a unified concept of spacetime. Anyway, the validity of special relativity has been established through countless observations over the past century (for example, time dilation has been verified through observing the decay times of cosmic rays in the Earth's atmosphere) and Nature conforms beautifully to Einstein's theory, so the only problem is really for us to intuitively grasp it.

@spyman: you're welcome :) Not the best post I ever wrote, I'm afraid... ;)

Reading through the earlier posts, I found it puzzling that so many of you seem to think that we cannot expect to colonize the solar neighborhood because we will be swallowed up by the Sun or because the accelerated expansion of the Universe will eventually cause heat-death. While certainly not incorrect per se, you seem to miss the fact that the time-scale involved in both these scenarios are absolutely immense compared to our own evolutionary history. As a species, we've been here for 500.000 - a couple of million years (depending on how you choose to delineate humans vs. proto-humans, the issue is not settled as far as I know). The Sun will burn out in another 4 billion years; that's about as long as there has been life on this planet and in that time span, single-celled organisms have evolved into sentient beings capable of spacetravel and nuclear fission. Imagine what we would evolve into in another 4 billion years! The heat-death of the Universe (if it happens, that's not settled either, although it looks like the most likely outcome judging from current observational evidence) has a much, much longer time-scale, although I don't remember exactly how long (and it's also model-dependent). So what I'm saying is that we won't have to worry about these things as we will have ceased to be humans and will have evolved into something entirely different (or terrestrial life will have ceased to exist entirely) by the time where these events take place. A planet-killer meteor is highly unlikely, but still a much more serious concern for us as a species now, as far as I can tell. But the most important concern, and one that we should devote all our energy and intelligence to is to make sure our planet remains habitable until we're able to colonize other planets. This is as much a scientific issue (creating green technologies that can reverse global warming, for example) as a socio-economic one (fighting poverty and social inequity).

According to the Fermi paradox calculations an intelligent civilization could colonize the galaxy in as little as 10 million years.
Here is a truncated synopsis of the idea: an intelligent life form evolves on a planet to the point where it develops interstellar travel (at sub-light speeds).
It then send a few colonizing ships out to prospective star systems thus seeding new civilizations. With a thousand years or so these new civilizations send out more colonizing space ships. Thus over time the number of seeds increases exponentially.
Given the age of the universe, and the number of stars in the universe, and the opportunities for intelligent life to evolve (assuming that it isn't just a once off freak occurance) why isn't the universe teaming with life?

Sorry Wotan I just realized you explained Fermi's Paradox in more depth earlier in the thread - and why you think it isn't really a paradox.

No worries ;) I think the uncertainties in the parameters of the Drake equation (http://en.wikipedia.org/wiki/Drake_equation) are so large that the 'Fermi paradox' cannot strictly be considered a true paradox. The 10 million year time-scale that you mention can certainly be accomodated by current observations, but so can a time-scale of 10 billion years; it's just a question of tweaking the values of the individual parameters. In my humble opinion, further observational constraints on the parameters are needed before we can say anything meaningful about it.

spyman: For one, there are a million catastrophes that could stop such a civ from starting. What if we had another meteor hit us causing another ice age before we could stop it?

The point of the paradox is not that there is one opportunity for one intelligent civilization to develop, but multiple opportunities. The fact that not every intelligent civilization will develop into an interstellar civilization is factored into the Drake equation. However as Wotan has pointed out the parameters of the Drake equation can be tweaked, thus increasing the likelihood of other intelligent life in the universe of decreasing the likelihood.
http://www.fermisparadox.com/
http://www.fermisparadox.com/Fermi-paradox.htm

typo.. *or decreasing the likelihood.

There are uncountable opportunities.

But with how much everything needs to be JUST RIGHT before interstellar colonization becomes possible, it's believable that every chance of it happening so far in the universe has been some combination of the following:
1) An almost-but-not-quite success (failure by a small margin)
2) Too many light years away to ever contact us
3) Wiped out prematurely by something going wrong