Microbial/bacterial life outside earth is extra terrestrial life.
Yes, That is highly likely to exist.
Thus "aliens" exist, we only need to find it.
Only a fool would believe we're alone in this universe.
As for actual intelligent life, it's possible.
Will we find them/contact them? possibly not.
Think about Star trek's prime directive.
Space faring beings can't interfere with the development of "primitive" species.
It could very well be that they are observing us at this very moment.
If, infact there's no such thing would be true and the opposite would be more likely, then extra terrestrial intelligent life would've already be on its way to harvest this planet.
One would travel... 600 lightyears (give or take a few) just to say hello.
We'd be nothing but resources to them.
As for actual war... (what many would believe)
Come on, think for once.
We pose no threat to them, they are highly technologically advanced.
All our "smart" weaponry runs on circuits, they could just blast one gigantic EMP at our planet and all our weapons (except the normal firearms) would be disabled.
TL;DR
Microbial "alien" life, yes, highly unlikely that it won't exist.
Intelligent "alien" life, yes, it might exist but we probably won't be interesting enough to them for actual contact.
