I'd like to assume and believe one and many exist anyway, it's an interesting thought rather than the depressing one that the Human race is the only sentient, highly intelligent and fairly advanced civilization in our galaxy and by extension (The universe)
So they exist. They've seen our radio signals, seen our little lumps of metal with outdated radio transmitters and equipment being sent out into space all over the solar system, Voyager 1 and 2 may have flown right by their giant (probably invisible) spaceships while they laughed at them
They've seen Earth and have mapped our planet, know of us as the Human race, a civilized (to most extents) and sufficiently advanced civilization (to be engaged in rudimentary space travel and exploration) - and know all about us
But they're refusing to make themselves known, start trade, communications or relations with us and our planet as a whole. Why?
Would it just end up being like 'V' in real life? (An alien race show up out of the blue, have 29 massive spaceships hover over our major cities under the pretense of peace and a relationship but are actually sinister and want to take over our world for resources or whatever, enslave the human race blah blah blah) or just refer to any alien invasion movie ever made
Would visiting aliens making themselves known simply always be hostile or oppressive to us eventually?
It begs the question, if they're so advanced and above us in every way, why even bother coming to our earth and having any relations with us as we wouldn't benefit or affect them in anyway - thus we would never know they exist as they wouldn't want us to know
Perhaps we're not recognised as sentient life by the Aliens. Or they have a strict non-interference policy except for scientific research and therefore only target lonely spinsters and alcoholic rednecks so the truth never comes out.
Or maybe, like Vorlons, they're secretly controlling our civilizations until we're advanced enough to be of use rather than simple exploitation a la colonialism.
Because their government spending cuts mean they can't provide aid to Earth. Even aliens have to make cuts, ye know.
Aliens don't visit us because:
a) Although I think they exist, odds are that they evolved on a planet very far away and there may only be a handful of similarly intelligent beings in the galaxy
b) It takes a very long time to get anywhere without developing some kind of way to open wormholes in space-time, which seems a bit fanciful even though they do exist
c) Why would anyone come to check out this star above all others? It's a very ordinary, small star as far as the galaxy goes
Amongst other reasons
Because they still havnt figured out faster than light technology yet.
The fact that they haven't "come to say hi" doesn't necessarily mean that they don't exist. They could simply be too far away or be extremely advanced but not have sufficient technology to travel light years.
I find it strange that people presume that alien civilisation is highly advanced. It's just as likely that they are less advanced than we are. There could even be a planet full of animals or bacteria that haven't developed any technology.
You can travel a billion light years in 3 seconds without faster than light travel as long as you accelerate enough.
Negged by someone who needs to lern to special relativity. Hmm.
Maybe we're not as interesting as we think we are.
There's a theory that the alien civilisations would have to be peaceful because if they weren't they wouldn't really be able to make serious technological advancements without ending up killing each other first. I suppose this is reflected in our world. The more peaceful nations are generally the more technologically advanced.
I suppose to be at the point where you can travel distances faster than the speed of light the civillastion would have developed quite a bit.
They're probably asking the same question about us
Maybe they just couldn't care less for us? Picture them as us now, and earth as an anthill. See?