Eukaryotic cells are ones with nuclei and other organelles such as mitochrondria (Flora and Fauna)- prokaryotic ones without (like bacteria). So Mhaze is quoting is it is very unlikely for prokaryotic cells to evolve into Eukaryotic cells so it takes an extremely long time. Interesting. I think we have to wait for some more studies to confirm this hypothesis.

To Mhaze- Pretty robust journal article though.

Oh, BTW, those links got the Drake equation wrong. Here's the correct version:

http://xkcd.com/384/

Although I think an equation that is probably a bit more useful is the Flake equation:

http://xkcd.com/718/

Space is quite big. Time is quite long. On the one hand, it's possible that there are countless universes alongside, above and below, our own, which is big enough. On the other hand, it's possible that there have been countless Big Bangs even just in our own universe, with its bits and pieces being blasted out and then sucked back in again, over, say, thirty billion years, countless times.

So, it's possible that, somewhere out there, there is the odd planet with some form of life on it. But the chances of comparable life, life with which we can communicate on a roughly even level, that isn't, say, a billion years in advance of us, or a billion years behind, is probably a bit remote. Only a hundred years in advance or behind us, even more remoter.

Meanwhile, back in the real world, we have enough resources to feed everybody, if it were shared around. There are regions on this planet which are barely developed, given with our latest technology, if people could get hold of it. So as world population growth slows down, perhaps to ZPG by 2100, and as efficient productive technology becomes cheaper for developing countries across the world, the need to go to some other planet will diminish (like, say, growing tomatoes at the South Pole: possible but a bit expensive), along with the realisation that we are effectively alone in the multi-verse.

There's work to do on our own planet without getting too worked up about others. If they're there, and their inhabitants want to contact us for some reason, they will, in due course. If not, then no.

Joe

I find this whole topic fascinating. Especially the size of 'Space'. Many more smarter than I, understand this Big Bang; what exactly exploded? A massive planet, leaving bits of itself floating about, in what's now known as our universe? With the various constituent planets like Mars, Earth, Venus, etc. part of that huge planet that exploded causing the Big Bang?

If we were to fire a missile into space, and it never hit or collided with anything, where would it end up? If it strikes the edge of what we now know, through the immense reach of our Radio telescopes, what's the other side of it? Admittedly, almost childlike questions I agree, but are there any answers?

Canem Malum,

Re Eukaryotic cells. I first came across this when watching a talk by Brian Cox in which he finally came down on the side of us being alone in the observable universe. He mentioned that the current theory is that Eukaryotic cells have evolved only once. That is all flora/fauna have evolved from one cell that broke the code of evolving from a bacteria. I then researched it and it seems to be the prevailing view these days and the research is more around why only once. There's actually a lot out there about it...

http://www.newscientist.com/article/dn18734-why-complex-life-probably-evolved-only-once/

http://news.nationalgeographic.com/news/2010/05/100513-science-evolution-darwin-single-ancestor/

http://rstb.royalsocietypublishing.org/content/royptb/368/1622/20120266.full.pdf

That's a mere sample.

The ramifications of that are enormous. Endosymbiosis is the theory that "one Prokaryotic cell such as bacteria engulfing another Prokaryotic cell and that cell escapes digestion and therefore lives inside the cell. Now this creates a symbiotic relationship where the engulfed cell provides energy and nutrients and in return the engulfed cell receives protection." (Waggoner, 2001). So in the untold centillions of interactions where one Prokaryotic absorbed another only one ever resulted in a Eukaryotic cell.

So even if Prokaryotic style life emerged on some other planet, the chances of it advancing beyond that stage is minute.

And that's before we even begin to consider why and how single celled Eukaryotic life evolved into multi-cellular life.

" I think we have to wait for some more studies to confirm this hypothesis."

True. But at this point it seems to be, as best I can tell as a mere interested observer, that the theory is widely accepted.

So if you marry the utter unlikeliness of Eukaryotic life with theories like the Great Filter and the Drake equation, you end up, as these authors have shown, with a high likelihood that we are alone.