It's a question that we have no way to answer with our current technology. Are we alone in the universe? Are there other forms of intelligent life that are simply passing us by? There are also other options we haven't quite explored yet.
The universe is 13.8 Billion years old, that we know. But how long will the universe last? For all we know it's still fairly early on in it's lifespan(if it even has an end). Who's to say that we aren't the first sentient species to form even within the universe itself? The probability is very small that we're alone, or that we're the first, but it's still a possibility.
Carl Sagan has said that we were created as a way for the universe to observe itself. If this is true, would it not be possible that we are the first attempt at observation? Could it be possible that humans are the only sentient species in existence at this very moment? Well, like I said, it's difficult to test this theory until we can travel through space and explore the farthest reaches.
We could be staring through a telescope, seeing a planet that is essentially millions or billions of years in the past. Who's to say that the planets we're observing haven't formed sentient life that has already taken to the stars? Who's to say that sentient life has come and gone, destroying itself and it's host planet, never to be known of it's existence?
Thinking of alien life makes us wonder about our own place in the universe. We could either be the first explorers out into space, or we could be infants barely learning to crawl compared to other species. There's no way for us to know until we actually get out there and find out!