|Is this guy watching us? Probably not.|
To make the statement "We have been visited by creatures not of this planet" is making some very wild assumptions. Some of them are so wild that they fall under the realm of insanity. And I don't feel at all that saying so is an exaggeration.
Let's start with the most basic of those assumptions: our planet is worth caring about. Even if there are creatures out there, unknown to us, with technology to reach our planet, the trip would be long and arduous. So out of all the planets in the night sky, they decide upon ours to visit and study. People forget how vast the universe really is. Let me explain this in a matter of figures. Pluto is the farthest planet from the sun. (I'm typing this in Illinois, and Pluto is still considered a planet by Illinois law.) Pluto is around 5.7 billion kilometers from Earth. At the closest, they're 4.3 billion kilometers apart. The estimate I found online says that it would take us around 23 years to get to Pluto. The alien society that is presumably watching us is farther away than Pluto. (I know that's an assumption, but it's a rather safe one to make.) So either they've already explored all the the planets in between here and there, or they picked us out to be their main focus. What would make us so special? It's a hard question to answer, really.
But let's assume they did want to study Earth, either from process of elimination or by conscious choice. So they have a trip that, like I said, is long and arduous. So when they arrive, how does this alien society study us? Secretively. According to many UFO enthusiasts, aliens have been visiting our planet for centuries, some even say millennia. And, according to some UFO enthusiasts, it must be the same society, as all of their crafts are similar--disk shaped, with no apparent thrusters or propulsion systems. So clearly, they've been making this trek for a long time. Why not land and say hello? Let's put ourselves in their position. Most people agree that these are scientific missions. If we sent astronauts to a planet on a scientific mission, are we just going to hover in the clouds or are we going to land? Ask any scientist. If we make that journey, which even to Mars would take several years, you can be damned sure we're going to land. If it's a military mission, then why now attack already? They clearly have more advanced technology. It seems illogical, and there's a reason for that.
Now, one might argue that maybe we're not being visited by the same society of aliens. Reasonable enough, at first glance. Perhaps this explains why they've not landed. Maybe one society showed up and decided not to land, and another one happened to do the same, followed by another and another, each one more wary that the last. If you can't already see why this is a ridiculous hypothesis, I'll explain. The likelihood of one society of aliens coming to Earth and not making themselves well-known is not high, but it is still possible. The likelihood of two societies doing the same thing is so low that it's laughable. An explanation does lend itself to the multiple societies theory though. If so many societies of aliens have visited us, and we've never visited a single one of them, we're clearly the dummies of the galaxy and it's no wonder why none of these more advanced societies want to stop by and chat.
But a major chink in this theory is that, as near as we can tell, there are no planets in our solar system that have life on them except our own. If you believe in evolution, then you'll agree that is stands to reason that the creation of life is so rare that two planets having life on them and being near enough for interplanetary space travel to be possible, is highly unlikely. If you believe God put us here, then it also stands to reason that He only created life on planets that were a good distance apart. Maybe he even limited it to one life-filled planet per galaxy. That seems just as likely as Him creating life on every planet. You could also go with C.S. Lewis' proposition from Out of the Silent Planet that since we are a fallen race, the other races of the universe are forbid from canoodling with us.
Going back to interplanetary travel, the belief that other planets have obtained this while we remain without it is presupposing quite a few things as well. The first and foremost being, if not beyond lightspeed travel, a fuel source better than anything we've come up with. Now, as for lightspeed or beyond lightspeed travel, it's not bloody likely. I was disappointed when I found out that scientists are pretty sure that it's impossible to achieve, but they're probably right. Is it possible that aliens uncovered some truth that has evaded us? Yes. But science is science all over the universe, and what's true for earth is probably true for any other society out there. As for an alternate fuel, let me say this: if we're to travel to Mars, it's believed by many scientist that it'll have to be a colonial expedition. The reason for this is, there's simply no way to go there with enough fuel to bring us back. The heavier an object is, the more fuel is needs to propel it. Simple enough, right? The more fuel held on a ship, the heavier it is. The heavier it is, the more fuel needs to be held on the ship. You see the dilemma? Aliens would have to overcome this obstacle as well, which is a rather tall hurdle to leap over.
Another assumption caused by the notion of interplanetary travel is this: you assume that the alien society is more advanced then our own. This, at first glance, seems like a harmless assumption, but when you really think about it, what is there to say we're not the most advanced beings in the universe? There's nothing disproving that hypothesis, but nothing proving it as well. What we do know is that we're more advanced then, say, fish. How do I know that? Fish can't breath on land, and that's why you never see fish getting out of the water of their on volition. Humans can't breath under water. So what did we do? We constructed devices to give us that ability. (Humans, 1; fish, 0.) The point being, there might be life on other planets, but there's nothing to say whether that life is an ageless telepathic civilization that has unlocked the mysteries of science, or just fish.
|Millions of billions seems smaller until you see it.|
There are literally millions of billions of planets in the universe, at a conservative estimate. Yes, there is likely life on at least one other planet than our own. But why should we think that out of those millions of billions of planets, two planets would both form intelligent life (not just fish), at least one develop the technology for traveling through space, and both be near enough for one or both to make contact? With those types of numbers, yes, it is possible. But any reasonable thinker also has to see that it's a pretty big assumption, and in logical thinking, we should always avoid such large assumptions.