We live in a galaxy where the Keppler space telescope has shown one fifth of the stars surveyed to have an Earth-like planet in the so called Goldilocks zone. That refers to the zone around a star where a planet could experience temperatures ranges similar to those on Earth theoretically allowing for the possibility of liquid water and life. So basically we talking about amounts in access of 3000 of the 150,000 sampled thus far.
With that many planets capable of supporting life, it still doesn’t mean that they do. The suggestion here is that they could allow human-type life but there is the additional requirement that the life evolve. To run into another species in while traversing the galaxy could require, basing it on one of Earth’s numbers, 2.7 billion years to possibly become a space faring society. (This bases life on radiometric dating)
To further break it down; that these Earth-like planets are habitable is merely a guess. An educated guess, but no equipment developed as yet can analyze the atmosphere or detect light experienced on the surface though there are certainly plans to try and get there.
Does life exists in the galaxy? If it is viewed as a game of numbers; probably, but that is just life. Is that life single cell or walking upright?
And what about the planets that are inhospitable to our form of life? Extremophiles here on Earth show that life is possible and can thrive even under the harshest of terms.
Seems the more we know, the more questions we have. In this galaxy alone there are over 50 billion planets. (Our Solar System is 27,000 light years from the center of it!) To go out further, there are estimated to be hundreds of billions of galaxies in the Universe. With those kind of numbers it is hard to imagine that there isn’t an ET!
I wonder, does ET wonder if he is alone in the Universe too?