Do they excist? Yes without a doubt. Have they been to earth/contacted earth? I have no idea. My guess is No. Atleast not in the last 500 years.
I am pretty sure that alien life exist. I expect we will find alien life on other parts of our own solar system. I highly doubt they are coming to Earth or have been to Earth other than as microbes on comets.
It's reasonable but I think the odds that no life exists elsewhere in the universe are unlikely. Just consider how vast the Universe is and how the conditions that we know that life can exist on Earth are found already on other places in our own solar system. The chemistry for life is fairly abundant so it seems like the chances are good that life is happening elsewhere. Keep in mind I am talking about "life" in general and not advanced / intelligent life but taking the Drake Equation it is still very likely that intelligent life exists out in the Universe.
It's mathematically impossible that intelligent alien civilizations do not exist -- they are out there and there are millions of them if not billions.
I think many people have no idea what the probability is in this case, I mean people cannot comprehend number of planets that are in this universe(it is just too large a number for people to grasp).
THere have been some powerful observations with trained observers rather than drunken rednecks: Edwards AFB: http://www.aliensthetruth.com/UFO_sightings_famous.php?view=1&ID=7 Bentwater AFB (UK): http://www.history.com/shows/ufo-hunters/videos/raf-bentwaters#raf-bentwaters
It's not unreasonable to think life may exist on other 'planets' ... heck, who's to say life doesn't exist on comets/asteroids/stars? just because we cannot fathom life sustaining in those conditions doesn't mean it's impossible.
As to whether or not aliens have attempted to contact us consider for a moment that we've been trying to contact them for some time. Carl Sagan helped to create the golden record that's attached to the Voyager satellite with the intention that other life forms may encounter the satellite and be able to find Earth based on the data inscribed onto the record.
Maybe other life exists like in presented in the movie Thor. Different cultures believe in different dimensions within the seen and unseen universe containing angels/gods/ET/aliens. Here's some entertaining sci-fi reading from the '40's from ATS: http://www.abovetopsecret.com/forum/thread822858/pg1
Richard Dawkins says its a possibility that Aliens seeded life on earth...but there definitely is no God.
I do think its likely that there is life somewhere on another planet. How sophisticated and intelligent they are is the real question.
First thing I thought of... The universe is a pretty big place. It's bigger than anything anyone has ever dreamed of before. So if it's just us... seems like an awful waste of space. Right? -Jodie Foster, Contact It's hard to imagine how life could not exist out there. As to whether they've made contact or left evidence here, I don't have a real feel. It's possible aliens could have visited our world thousands of years ago or more, since they could have evolved on a very different timeline from us. It's also possible, even likely, that if other intelligent life forms have evolved elsewhere, like us they do not have the ability for interstellar travel. Thus we'll never meet, or even know of each others' existence. Or, we could be the only advanced life in the universe. That just seems... unlikely.
