Moshkiae
I think the biggest problem is that we're stuck on our own "physics" and do not believe that there are other type of organisms out there that live in completely different environments that we can not conceive.
Gotta love how egocentric the science is in that matter. WE'RE defining what is out there in the universe, instead of that universe defining for us what there is and there is not!
The crux of the matter is precicely that.. matter.
For as far as we can see into and towards the edge of our universe the laws of physics as we know them seem to apply equaly, as our predictions sujest they should.
By definition this would require that life as we know it here would require similar conditions elsewhere.
Life "as we know it" being based around Carbon, Hydrogen and Oxygen. (with trace elements). If you try to create a life cycle based on different elements you get into all sorts of problems of energy gradients that don't work, reaction products that are too solid or stable to be re-used, temperature incompatabilies, etc..
You can only look for what you know.
That being said, the universality of the laws of physics would sujest that carbon, hydrogen and oxygen would be just as abundent elsewhere in the universe as they are on Earth, so there is no reason to doubt the possiblity of other carbon based life in the universe, even if proving its existence may prove futile.
And now back to your regular program.