I believe there is something out there, with all the galaxys we know of and plenty that we dont know of I think it would be very naive of us to think we are the only life which exists.
Also if you think how far technology has come in just a few hundred years imagine how far it would have developed in say 1000 or 1000000 years?
It could well be that in 1000 or 1000000 humans cracked time travel, they could be humans from the future coming to study life in the past.
But if they are UFOs they are smart to keep there distance.
Seems with the human race anything we dont understand we seem to kill, sad but true.