Enrico Fermi once proposed the famous question, "Where are they?", in reference to extraterrestrial intelligence (ETI). He was implying that if extraterrestrials existed, then we should be visited by them. This is a logical conclusion assuming a certain population of intelligent life within our Galaxy, because a number of these civilizations would have existed much longer than our own and would have overcome the immense difficulties of interstellar space travel. Since we do not have "hard evidence" that we are being visited, the conclusion is that ETIs must not exist.
However, since we exist, we know it is possible for the universe to produce intelligent life, but how probable is our existence? Although we know that there are many stars like our sun with probable planetary systems similar to our solar system, some astronomers argue that we are unique in the universe, requiring just the right galaxy, supernova rate, star, moon, magnetic field, thickness of crust, quantity of greenhouse gases, etc. Other astronomers believe our own Galaxy is full of intelligent life, despite Fermi's question. There is no consensus among astronomers, biologist, and other scientists regarding the answer to this question, and it may be a long time before there is.
My answer is "here we are" implying that since we exist, there are (or will be) most likely other intelligent life forms in the universe (if not the Galaxy). If we make the simple and reasonable assumption that we are not a fluke, then our universe has -- at the very least -- a significant probability (say 50%) of producing at least one intelligent life form (us) in 10 billion years. If this is the case, then there is a good chance that there is at least one or a handful of other intelligent civilization in the universe right now or will evolve in the future.
The above argument is consistent with Occam's razor: accept the simplest explanation with the fewest assumptions and reject more fantastic and convoluted explanations. Since we exist, the simplest explanation is that the entire universe had a reasonable probability of producing at least one intelligent life form: us. Remember the universe is a big place -- much bigger than our Galaxy. The universe consists of at least 100 billion galaxies. Further, it is going to exist for a long, long time before entropy (like the slow running down of a clock) or collapse overtake it, and therefore life will continue to evolve over the eons in the universe's vastness.
Additionally, it is not inconceivable that our own race may perish in a thousand or million or billion years, and another intelligent life form evolves on this planet before our sun dies (another 5 billion years).
Let us increase the probability somewhat and suppose (purely hypothetical) that there is a 50% chance of life evolving once every 5 billion years per 100 million galaxies. This doesn't sound like much. However, when we take into account the size of the universe, it translates into hundreds of ETIs right now, and many tens of thousands over the lifetime of the universe. Further, no one ETI would ever contact another.
One footnote should be made. While the majority of scientists would say we have no "hard evidence" of ETIs, I am not as convinced as I once was that we have not already been visited. The reports of abductions, etc. cannot, in my mind, be 100% dismissed as fantasy. Although this may turn out to be the case.
God is working in the lives of these intelligent creatures also, just as He works with us. Jesus may have come to countless planets throughout the universe in the form of the intelligent life which lives there. Note in the following quote of Jesus that He uses the article "this" instead of "the" implying that our world is not unique. "Jesus answered, 'You belong to this world here below, but I come from above. You are from this world, but I am not from this world' " (John 8:23). Of course the tremendous wicked spiritual forces, which hinder God's work on this planet, are also at work on other planets. The struggle to find God would doubtless be difficult for other intelligent civilizations just as it is difficult for us. However, it is not hard to suppose that some societies might do better than others. Some might be very close to God while others are very far away.