We don't have any proof one way or the other. We also don't have enough experience dealing with life coming into existence [from nonliving matter] to be able to properly compute the odds of it happening anywhere. Still, the universe is so very large that it seems likely that there may be life on other planets, or (since the universe has been around a while), there may have been life on some planet where it has since all died off, or there might be life on some other planet in the future where it presently does not exist, or all of these.
As for it mattering for us, that seems unlikely, given the extreme distances of space. The Voyager 1 spacecraft was launched in 1977 and is somewhere near the edge of the solar system, barely into interstellar space. (Officially, it seems, it made it to interstellar space in 2012. In other words, it was about a 35 year trip just to the edge of the solar system, which used the gravity of the outer planets to help accelerate the craft.) It will take an extremely long time for it to get to another solar system, even if it were headed in the direction of the nearest one. Solar systems are generally almost incomprehensibly far apart.
You can see how far away Voyager 1 (and the closer Voyager 2) is right now at:
http://voyager.jpl.nasa.gov/where/
Now, if some aliens were advanced enough to make such trips, if they were to visit us, we would likely be totally fucked. Even if they did not have some virus that was, to them, like the common cold, but to us making ebola look like happy fun time, their technology would be such that they could do whatever the hell they wanted with us. And they would almost certainly regard us as inferior beings, unworthy of being considered even close to them (and, we are very far from such hypothetical aliens technologically at least).
But, on the bright side, it may be completely impossible for any beings to have such technology, and so we may not need to worry about anyone visiting us at all.
As for it mattering for us, that seems unlikely, given the extreme distances of space. The Voyager 1 spacecraft was launched in 1977 and is somewhere near the edge of the solar system, barely into interstellar space. (Officially, it seems, it made it to interstellar space in 2012. In other words, it was about a 35 year trip just to the edge of the solar system, which used the gravity of the outer planets to help accelerate the craft.) It will take an extremely long time for it to get to another solar system, even if it were headed in the direction of the nearest one. Solar systems are generally almost incomprehensibly far apart.
You can see how far away Voyager 1 (and the closer Voyager 2) is right now at:
http://voyager.jpl.nasa.gov/where/
Now, if some aliens were advanced enough to make such trips, if they were to visit us, we would likely be totally fucked. Even if they did not have some virus that was, to them, like the common cold, but to us making ebola look like happy fun time, their technology would be such that they could do whatever the hell they wanted with us. And they would almost certainly regard us as inferior beings, unworthy of being considered even close to them (and, we are very far from such hypothetical aliens technologically at least).
But, on the bright side, it may be completely impossible for any beings to have such technology, and so we may not need to worry about anyone visiting us at all.
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.
