[ngcles]

Hi AlexN & All,

Alex wrote:

"Whilst opinions are free and everyone has one, for someone who spends a lot of time looking at other galaxies, and knowing how many planets are within our own galaxy... don't you think there is more than a 'slim' chance, that quite a few of the thousands of other galaxies out there have planets, and that a fair few of them would be able to sustain life, and of that few, at least a couple WOULD sustain life... It seems incredibly likely to me..."

Well, I can't share your opinion but hey, it's just an opinion -- like yours. I might well be wrong and if ET lands I'll be more than happy to meet them and I'm sure we'd (The Earthlings) benefit from the relationship. But I just don't think it is going to happen. This is the way I look at it.

It is true that there are a hell of a lot of stars in the Milky Way. The latest estimates place it somewhere between 200 and 300 billion with the higher end figure somewhat more likely. But among those stars, I think there is a (comparatively) very, very small number that are suitable candidates that could develop life, let alone intelligent life, let alone intelligent life that is more (much more) advanced than our own and capable of traversing inter-stellar space in reasonable time-frames and happens to coincide with the time when there happens to be intelligent life emerging on this planet.

The variety of stars in the Universe is simply extraordinary. But you need a star that has a mass small enough that it won't burn-out quickly, but needs to be big enough to make a habitable zone far enough from the star that any Earth-like planet doesn't end up with tidally locked rotation. Probably 99.9% + stars have no hope of fitting the bill. Too big, too small or are in the wrong environment. Realistically you need a G0 to G3 star. Even at F8, you've slashed the main-sequence life of the star to about 4 billion years -- not long enough you'd think. In the Milky Way, there are maybe 5,000,000 that fit that bill reasonably well. Then it has to have the correct metal content so that all the elements for life and the elements that make up terrestrial planets are present -- slash a zero off. It has to be in the right part of the galaxy -- to close to the centre and too much going on to be habitable. Too far out -- not enough metal -- take off 80% and were down to 100,000.

You can basically discount a very large majority if not virtually all the binaries. We're down to 40,000.

You can then take out nearly all the systems that have giant planets orbiting close to the host star -- these form way out and migrate in wreaking destruction in their path. From the systems we've found so far, these seem very, very common. Knock out maybe 80% (I think this is a conservative estimate) of that 40,000 leaving 8,000. Then of that 8,000 how many will have an terrestrial sized planets, lets say 1/2 -- were down to 4,000. Of those with terrestrial planets how many will fall neatly into the habitable zone at the right time? Lets say 20% and were down to 800.

So at least on my reckoning 800 Earth-like planets out there in the Milky Way. How many will actually have life -- and personally I don't think like is easy to just start spontaneously. Lets say 1/2 (again I think this is very conservative) -- we're down to 400.

How many develop advanced multi-cellular life -- lets say 5% (again conservative I think) and were at 20 stars. Of that 20 how many manage to avoid the manifold pit-falls like comet-strikes, close supernovae, Gamma-ry bursts etc etc go on to harbour intelligent, self-aware life that are capable of using tools and solving complex problems -- lets say 25% and were left with 5 Earths. Of that 5 with intelligent life how many will go on to solve the riddles of physics and master interstellar travel? One or two at most I'd think and were likely to be one of those two within a few hundred years -- leaving exactly 1 other and they have to find us.

Not a big figure now, and in all likelihood they have to be reasonably close-by (say 10,000 ly) to us to visit -- even with extremely advanced tech. But hey, its just my opinion. I might be wrong. I'd love to meet "ET", I just don't think its going to happen. And tie it in with the topic of the thread I don't think it has happened. Again, maybe I'm wrong -- I'd welcome solid evidence of, or proof to the contrary.

Standing in the way of that of course, as we understand the laws of physics at present light-speed travel is a big no-no. Maybe we'll find a way around that, maybe not -- at present I personally don't think we will find a way around it.

As for proof that we went to the Moon -- there is abundant proof. Just look at the rocks for a start ... The Russians never blew the cover (and they would of had they had even the slightest suspicions) , the retro-reflectors on the surface and the 1000+ people who would have to have been in on the conspiracy and all kept their trap's shut for almost 40 years. It is much easier to imagine we did indeed go to the Moon. The evidence is overwhelming. A super-dooper high-res photo would only show a dot -- no more. Pretty easy to doctor up so why bother. The proof we went is convincing.

Best,

Les D