Like many here I find the subject of finding life on other planets fascinating and consider it inevitable. What's interesting is that the estimate of planet incidence is seemingly much higher than originally postulated by the Drake Equation [1].

A factor in the development of life, especially sentient life, is metallicity [2]. Almost all of the first 100 elements naturally occur on Earth. This is pretty amazing. Nuclear fusion in stars naturally produces elements up to iron [3]. S-capture is thought to produce elements up to Bismuth (atomic number 83). Elements higher than this are thought to be produced only in supernovae or other cataclysmic events.

It's amazing to think that enough time has gone by in the Universe to take the abundant hydrogen and helium, form stars, have those stars run out of fuel and enough of them explode to scatter their elements to form heavy planets around later stars.

While heavy elements may not be required for life it seems less likely that starfaring sentience can form without them. Semiconductors for example require an odd mix of heavy elements.

It seems amazing that even we exist given that you need metals, a long-lived and stable star, likely billions of years of evolution, a sufficiently stable (and probably geologically active) planet with an atmosphere that has water in liquid form (a pretty narrow temperature band even taking into account different atmospheric pressures) and no cataclysmic events to happen in all that time (it seems to have been ~65 million years since the last big one).

It may just be that sentient life is fleeting. We've had "civilization" for X0,000 years, which is the blink of an eye. It's entirely possible we'll wipe ourselves out due to war or simply lack of (sufficiently cheap) resources in another blink. The problem isn't lack of resources. They are plentiful in space. The problem is the cost of getting them if energy is anything other than free.

Additionally interstellar distances seem almost unconquerably large that one has to wonder if we'll ever meet another sentient life form face to face (assuming they have faces).

Even if we do, one wonder what evolved elsewhere for facilitate communication. Will they see? Will the wavelengths of light they see cross over ours at all? These are questions we can only really speculate about.

It's also been suggested (by Hawking among others) that we really don't want to meet a much more advanced species as it will probably be bad for us, perhaps even an Outside Context Problem [4] and it seems unlikely given the rate of change we're experiencing that another civilization will be at the same point as us.

We could of course be "first". I mean someone has to be right? It does seem unlikely however. But I suspect there were many "firsts" (in the sense that they evolved independently and without any contact or evidence of other species).

The seeming lack of self-replicating robots, something we'll almost certainly be able to build and start filling the galaxy with within a thousand years I'm sure, is also somewhat puzzling.

Personally I just hope we find evidence of extraterrestial life sometime soon as it will settle [5] a whole bunch of issues about us being "special" (in the typically religious sense).

[1]: http://en.wikipedia.org/wiki/Drake_equation

[2]: https://en.wikipedia.org/wiki/Metallicity

[3]: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/nucsyn.html...

[4]: http://en.wikipedia.org/wiki/Excession#Outside_Context_Probl...

[5]: http://xkcd.com/1235/