With the rapid acceleration of technology, we should be able to travel to other stars in our galaxy within the next few centuries (conservatively). If there are alien civilizations out there, certainly some should be more than a few centuries ahead of us in developing. So the question is, why haven’t we seen or heard from any of them? I believe there are three possible explanations:
- There are no other intelligent beings out there.
- There are some intelligent beings but the speed of light has limited them from reaching us yet.
- There are intelligent beings and they are keeping themselves hidden from us for some reason.
Let’s look at each of these possibilities:
There are no other intelligent beings out there. The Drake equation attempts to determine the number of intelligent civilizations in the universe from the rate of star formation * fraction of stars that have planets * number of planets that are habitable per planet bearing star * fraction of these that develop life * fraction of life that becomes intelligent * fraction of which are willing and able to communicate * expected lifetime of such a civilization. The first few variables in this equation are known and there are likely billions of planets in the universe. The question is, how many are habitable, how frequently does life form, and how frequently does it become intelligent. Perhaps the collision that created our abnormally large moon (which creates our tides) and large tilt angle (which creates our seasons) was necessary to get life started. Maybe the asteroid that wiped out the dinosaurs was vital for us to evolve. We are the only intelligent (speaking, tool-using, etc) beings on our planet, so perhaps intelligent life doesn’t evolve very often. If even a small fraction of the planets out there bore intelligent life then our universe would be teeming with it, and certainly we would have seen some by now.
There are some intelligent beings but the speed of light has limited them from reaching us yet. Perhaps there is some intelligent life out there but they are rare and far away. While there are some 30 billion trillion stars in the visible universe, there are only about 600 million stars within 5000 light years and 260,000 stars within 250 light years. If faster than light travel is impossible (through wormholes or any other means) then any communication or contact with another civilization would likely have to travel across space for thousands of years to reach us. So while it seems unlikely that we’re the most advanced ones out there, if we’re at least within 5,000 years then we won’t have seen anyone yet (although 5000 years is nothing on the cosmic scale either). But certainly if there was life out there that wanted to contact us and it was possible to travel faster than the speed of light, we would have seen some by now.
There are intelligent beings and they are keeping themselves hidden from us for some reason. It’s also possible that aliens are out there but are hiding themselves from us, following some “Prime Directive” like in Star Trek. It seems unlikely that every alien race would adhere to this rule if there really were that many of them out there.
So what conclusion can we come to? If there are aliens out there, either its impossible to travel faster than the speed of light or they want to remain hidden. Or perhaps the impact that created our planet and our moon, and the other circumstances surrounding our planet’s beginnings, life’s beginning on Earth, and our evolution, are so rare that we are a once-in-the-universe kind of thing.