In July 7, 1947 an object crashed in a ranch in Roswell, New Mexico. The theories behind what may have happened there varies, but the most common explanation is that an space aircraft, coming from other world is what have crashed there that day. The official story says that an experimental surveillance balloon is what was recovered by the U.S. military. The probability that a spaceship crashed on Earth is remote, in fact, the probability that life from outer space visit us is remote.
The probability is remote because too many conditions must be met so that life from outer space may visit us. Here are some of the conditions that should be met.
- There should be stars with planets (That is easy)
- There should be planets where life may be held (Less common, but easy)
- The life in such planets should evolve into intelligent life (Not so easy)
- That intelligent life have to appear in the same window of time we are existing (Not easy)
- That intelligent life that happens to occur in our same small time frame, have to find us. (Difficult)
The last two points are the harder to comply. We know there are planets out there capable to support life, but in this time? How much time did it take to the earth to be able to support life, how much time took life to evolve into intelligent life, and finally how much time are we going to be here?
What happened here, may happen in another planet, for sure, but to happen in the same time and near enough from here for them to find us. I really do not think so.
So, unless we are an experiment of some bigger civilization, unless they have planted life in our planet, is really hard to think that some outer space civilization is going to exist in our time frame and that it may find us.
It took our planet since its creation 4.500 millions of years to have intelligent life, and we may not be here in another million of years, so, do the math.