Comment by yawaworht1978

We humans have only our definition of life form. These are limited by physics and our logic. However, we can't even see the whole universe, with no scientific break through, we never will. We don't exactly know the full story of the big bang, we can't explain the very beginning. We don't know what happens in black holes, our logic rules literally breaks down there. I could well be that there are life forms which we couldn't even imagine, which are not limited by our known physics. We know a little bit about space time and gravity and the elements. Dark matter still unexplained, no universal formula for everything in sight, i have seen DNA mentioned, maybe some creatures do not need any DNA. Too many factors are unresolved, we don't know whether there have been, are or will be totally different species. Imagine, at one point in history, earth didn't even exist, before animals, there were only bacteria. Earth lifetime is nothing on the grand scale of things. Humans are a more intelligent version of very common mammals. With a couple more things gone wrong, like a flu or smarter predator animal in the past, humans might have never come to be. I greatly appreciate scientists and people discovering and accumulating the knowledge, and I understand the scientific methods have to be followed accurately, else we diverge into pure speculation. But limiting possible alien life to earth like planets might not be all there is.