Well, nobody actually knows for sure. Some people believe in other life and other people don't. People who believe in God usually don't believe in aliens.
I personally think that they do, I mean the numbers just show it. Scientists are studying Mars because when they sent their two Robot Rovers, (Spirit & Opportunity) to land on Mars' surface in 2003 Opportunity found geological forms that were almost certainly produced by flowing water. In 2004, Spirit found even clearer signs of water, backing up the evidence of its twin. What do you think are the chances of this? Mars, our neighboring planet once had flowing water on its surface. This shows us that a planet doesn't have to be perfect. It only has to be good enough.
If there are Billions of stars with orbiting planet in each Galaxy and then Billions of Galaxies in our Universe. And then we are not even sure if there is more than one Universe. I simply cannot imagine us being the only ones. I wouldn't be surprised if there was a planet with life only 1,000 Light Years away. Planets are too small for us to see so we can't observe them but if we could, we could observe the planet most likely to support life in each Solar System of one trillion times.
What do you think life needs in order to survive? Food, water, heat and oxygen? Maybe for life on Earth but how do we know that other life needs any of those things. It may breathe on carbon dioxide, (a common gas). Maybe it has the same qualities as a robot and doesn't need heat or food & water. In that case then could be life on basically any planet.
How advanced do you think that other aliens are? Do you think that they are highly intelligent and have listed every single other alien in the Universe or do you think that they are pieces of slime? How intelligent are we compared to these other aliens? I do think that aliens are far apart from each other though. And since the fastest thing that we know of is life it wouldn't be possible for aliens to reach us in under millions of years. Just maybe one day we will find out.
