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My argument for these kind of questions (Why are the surroundings exactly right for life?) is always:

If they weren't exactly how they are now, there would be nobody to ask this question.

The universe itself is like a huge laboratory. There are an uncountable number of suns and an uncountable number of planets surrounding them.

The way I grasped just how huge the universe is was when I looked at this image made by the Hubble telescope closely. Remember our galaxy, the Milky Way? The star closest to our solar system is so far away that we couldn't reach it in our lifetime. When looking at an image of our galaxy, our sun is just lost in the huge sea of stars anyways. Now look at that picture Hubble shot. How many galaxies can you count? Every single galaxy of these is about the same size as ours (for human proportions anyways). They are just hanging around there randomly, and those are just the ones we can see with our current technology.

Every single planet in all of the galaxies has unique properties that might or might not be suitable for life. For the tiny number of planets of these that are suitable for life (which probably is still an uncountable number), there is a tiny tiny chance that life will actually happen. For those where life actually happens, on only a tiny tiny amount of them a species develops that is sophisticated enough to actually ask these questions. However, since there is such a large pool of potential planets, this is still a viable number (just how large this number is, is still under discussion in science).

For me personally, alien life is a fact (based on my knowledge of statistics). The only question is whether we can actually communicate with any of them, due to the huge distances.

    Well, if there were/ar intelligent lifeforms on another planet, that coincidentially happened to have started the same time we did, and they were to have focused on advancing their knowledge of all things, and were not obsessed with greed and mutual destruction, they could have probably been here thousands of years ago.

    Thankfully, we invented television and radio broadcasts. If they happen to come anywhere near us, they'll have the luxury of seeing how vile humanity in general is. The signals will weaken with distance, but with a little luck, they'll be able to clean up a signal somewhere between 75 to 100 light years out. When they get to about 45 to 50 light years out, they'll see how we would treat prospective visitors. Kill them first, and steal their technology later. And that's only alien related science fiction. Factual war radio and television broadcasts will paint the rest of the picture for them.

    We have set up our own warning beacons that no one should *ever* approach this desolate rock on the end of a lonely spiral arm of this galaxy.

    Assuming they stop in the occasional system to look and listen, if they stopped around any of the 1,400 stars (133 like our sun) within 50 light years of Earth, they'd know to avoid us at all costs.

    If we developed FTL travel, wouldn't we take such broadcasts as a warning?

betelgeuse is in orion's armpit, so it's only going to blow his arm off

luckily for orion the star that's going to blow isn't the one at the tip of his dick:

http://upload.wikimedia.org/wikipedia/commons/9/91/Orion_constelation_PP3_map_PL.jpg

oh wait... M42 already IS a nebula. he's already blown his interstellar load

http://www.atlasoftheuniverse.com/nebulae/m42.html

cosmic spooge

apparently orion gets too easily sexually excited when he's hunting

wait, i'm sorry, it's not his dick, it's his SWORD

http://upload.wikimedia.org/wikipedia/en/c/ce/Orionurania.jpg

riiiight

that's what the ancients were thinking?

riiight

Ooh, thanks... that's a sweet map of the neighborhood!

Try here for a really cool representation of the universe

A few hundred years ago it was nearly impossible and highly, highly impractical to load up goods and persons on little wooden ships and sail them across the Atlantic. Yet we did. And yes, we colonized as we went. Did we, though, colonize every single leaf of grass we passed over? Not exactly. There are still wild areas of this Earth, even with humans being able to readily and easily travel to each inch of it.

We haven't colonized the whole planet YET. Ask again after 10,000 years of population pressure and resource depletion. The only factors which prevent this from being inevitable is the need for ecosystem balance (e.g. deforestation v. global warming), lack of suitability or desirability (e.g. Antarctica), or sentimental attachment (e.g. parks and nature preserves).

This doesn't work at the level of planets, and it ignores extra-planetary colonization via orbital structures that exploit the mineral and other resources of an uninhabitable world.

Is it not even remotely possible that another, more attractive system is nearby, and that was the one colonized?

Oh, yes. But how likely is it that no where in the galaxy has been colonized within the span of time that it would take for a radio signal to reach us?

For SETI purposes, we usually only consider stars within 50 light years of us because those are systems that our first radio signals could have reached that could have responded to us in time. Just in that small volume of space, there are 133 stars like our own sun and roughly 1400 total star systems. No one colonized any of these systems?

Okay, so maybe we live in a 50 ly radius "nature park." (Not that I can fathom what one principle would unify all these systems as "protected" instead of treating them individually, but we'll go with that.) What about radio signals from worlds that weren't aware of us at the time they were broadcasting? Why don't we see radar signals within 200 to 600 light-years?

That is a range of less than .1% of the width of the Milky Way (but good enough to cover the thickness), but for us not to have seen someone by now, they would have had to have evolved to space flight sometime in the past few hundred million years -- which is trivial compared to the age of the galaxy. Either we're one of the first (on a galactic time-scale), no one is interested in exploration, or we're alone.

At this point, if there's anyone else out there, they are so far out that we'll have millennia to prepare to meet them. We may as well just operate under the assumption that they aren't there because they'll have no impact on us any time soon.

Yes! That's why whenever I look at the sky I can only see 133 stars.

http://www.atlasoftheuniverse.com/50lys.html

High-tech masks and data gloves not withstanding, I've wondered why there's no plan to shoot unmanned ships to the nearest ten or twenty star systems even if it's 100 - 200 years before they get there and we start getting data back and even if in the meantime technology advances enough to make these initial ships pointless - e.g. warp drive is developed. There's a reasonably good chance that FTL travel won't be developed in the next 1,000 years (if ever) so why not try to accomplish something in the nearer term?

Is it possible to aim well enough to place a ship in orbit of a star 8 - 30 light years or so away? How much could we learn about a star system with a satellite orbiting a star at a distance roughly the same as between Jupiter and Saturn for example? Would it be any better than current or near-future Earth based imaging can provide? If such a satellite came into orbit of our solar system sent by another civilization, would we readily be able to detect it?

In the range of 20lyrs there are about 100 stars, in the range of 250lyrs about 260000.

See: http://www.atlasoftheuniverse.com/

angel'o'sphere

Here's a cool website that has some of the brightest stars within 50 Light years. Here's to getting a signal in 30 or so years. http://www.atlasoftheuniverse.com/50lys.html

Has it crossed anyone's mind that we could be alone? Bacteria and other forms of life aside, is there any reason to believe that galaxies team with life, just because there are so many? Something like 90% of the solar systems out there contain *nothing* but gasses, a bunch more have planets too far or too close to their sun. Still more are in flux- near black holes, and pulsars and the like. I'd love to see something out there, too, but I'm a little dubious about the likelihood. There are perhaps a million combinations of circumstances that allow us to be, and be here. Everything from a precise gravity to an orbiting moon; it's not a simple circumstance.

Very true, but I think the point is that there are staggering numbers involved, so the probability that we're the only form of life is incredibly small. According to "The Universe within 14 billion Light Years", there are 350 billion large galaxies and 7 trillion dwarf galaxies in the visible universe, comprised of 30 billion trillion stars (3e22). Even when you start being pretty pessimistic about the conditions required for life you'll still end up with more than one planet being suitable.

Cheers,

Roger