A big subject - are we alone in the universe in terms of intelligent life?
It seems that there is a great uniformity about the universe. The trillions of stars are all made of the same stuff as our Sun and operate the same way - nuclear fusion of hydrogen atoms into helium. Stars throughout the universe are clustered into galaxies similar to our Milky Way. We are rapidly discovering in the last decade that stars often have planets orbiting around them.
Within our own solar system there are signs that liquid water once existed on the surface of Mars. There is evidence that basic life forms are common to develop even in tough conditions. It may be that animal life can develop in many cases also.
The really tough question is how common is it for intelligent life forms like humanity to develop and to survive. There is the famous Fermi paradox which questions that if other intelligent creatures exist then why have they not already contacted us. This is a very fair question given the timescale and sheer size of the universe. Then there is the SETI (Search for Extra-Terrestrial Intelligence) work which has not produced any startling results in decades of scanning the skies for radio transmissions.
So, are we the only intelligent creatures in the universe or at least in our own galaxy? Oceans of analysis and comment has been written on this subject and there are so many parameters and variables at play.
Here are some comments of my own:
1. Intelligent life, even in our own form, may not develop well enough to communicate long distances through space. There could be many civilizations that never get beyond crude farming or maybe the equivalent of our medieval history. The exploitation of electricity and in particular radio transmission is quite a major leap as it is an invisible and somewhat abstract technology to both understand and to exploit. It is this technology that allows us to attempt to put our mark on the universe. It is conceivable that this leap in technology is never made in many reasonably intelligent races in the universe. Hence they can neither consider traveling or communicating in space and therefore are undetectable to us.
2. Let us assume that there is a civilization that reaches our own level of technology. It is a fair comment to make that when a race reaches our 20th century level of technology that the basics exist to accelerate technological progress at a rapid rate. It is reasonable to assume that the spectacular technological progress we have made in the 20th century will continue at a high pace in the 21st century and beyond. What will we be like in say 1000 years from today - which is a mere microsecond in the timescale of the universe? Will we be so advanced that we have figured out how to travel huge distances in space rapidly, casually and economically? Would we be advanced enough to detect and reach other intelligent life forms? So assuming it is possible to exploit technology in a way we don't even understand yet - it brings back the Fermi Paradox. Why haven't other civilizations developed the same way and not already reached us? Here are a few thoughts of my own:
2.1 There is of course the possibility that there are very few or no examples of super-intelligent life in the Universe. This could be deducted if very advanced animal life was very rare (see my comments in 1. above) or a block in advancement takes place though regular extinctions - meteor impacts and other natural disasters or indeed self destruction through WMD wars.
2.2 A rather tantalizing direction in relation to the Fermi Paradox would be to raise the hypothesis that super intelligent life has already contacted us and is maybe here already! Given all the logical deductions emanating from the uniformity, timescale and massive size of the Universe then it is reasonable to put forward a hypothesis that other intelligent life has detected us or has been visiting us . Maybe we are so wrapped up in what we consider our super-efficient 21st century technologies that we haven't even got the sensory capacity to detect what is all around us. We are so busy searching using our visual and radio communications tools and maybe we are as blind as bats. We could be like a person who spends hours looking for his hat - only to discover it is on his head! I'm going to post a separate analysis into my "They're here!" hypothesis as it is a very interesting and completely plausible subject.