1. There is life outside of Earth
This is easy to believe because it's almost a reality. We've already had discoveries about life that have made us rethink how life is formed in the first place (obligatory XKCD). Panspermia is a nice theory that life on Earth originated from space. Can't say I believe that is true, but I cannot believe Earth is the only place in all the universe that has life.
2. There is intelligent out there.
I just established my belief there is life out there, so now we just have to figure the probably of life evolving into something intelligent. Taking a brief look at our own history, it took 4.5 billion years before intelligent life happened. Over that time there were five extinction level events. I am not a black and white kind of guy, so it would not be fair to say all five were the same or even the term "extinction level" is 100% accurate. To keep things simple though let's just say it took Earth 5 tries before intelligent live happened.
Even that model is not accurate. Looking at time on a geological scale, the dinosaurs were around for millions of years and they never made it to the moon. While we did it and we've only been around for tens of thousands (maybe there is some debate there too). Based on that I have to conclude there is more to intelligent life than waiting for it to happen. How you interpret that; chance, alien seeding, divine intervention, or whatever is up to you.
I also have to conclude, all things being equal, if it happened here then it can happen somewhere else. Which brings me to the Drake Equation. While the Wikipedia article is interesting, let me simplify it. Basically Frank Drake looked up and thought, "Hey there are a lot of stars, what if only a small percentage of those stars had planets, and only a small percentage of those planets could support life, and a small percentage of those planets produced intelligent life like ours....how many planets would be left?" After some maths, the number is still pretty darn high.
Of course, the flip side to that argument is a paradox, also an interesting Wikipedia article. But to dumb it down Enrico Fermi chatted over lunch with some friends and wondered, "With as old as the universe is (almost14 billion years) why have we not seen aliens?" He has a point.
Think about where we we will be in 100 years, a 1000 years, or 1,000,000 years (I need the commas with more zeros). Considering how far we've advanced I'd think our ability to travel through space with ease is less than 1000 years away. Maybe we won't go far, but by golly we'll be all over the solar system. In 1,000,000 years it's difficult to imagine--there may be no Earth but we'll be somewhere. Perhaps we are the future cockroaches of the universe.
To me it's not far fetched to think intelligent life is ultra-rare. Ultimately it took me about 13.75 ± 0.11 billion years to write this blog post, and there could be people on other planets (notice the politically correct alien terminology already in use) all over our galaxy thinking the exact same things and posting it in their blogs. It's not that we're not there, or they're not there, we're just all so far away we can't see each other yet.
Or maybe, while I'm on this rant, they are about 1000 years ahead of us exploring their local region of space watching us from the exoplanet telescopes (of course they may only be seeing dinosaurs but we're not going off on that tangent today) wondering when we'll be able to look back at them (or their dinosaurs).
There is a rather extensive section on the Fermi Paradox Wikipedia page with theories to it's solution. One or two is similar to mine just written with more eloquence.
3. They're not here yet (unfortunately)
After all that, I believe there is life, I believe there is intelligent life, but I cannot say for certain the aliens are here. I love to read about this stuff too. There is a ridiculously detailed section on Wikipedia about paranormal activity and UFO's get their fair share. As much as I enjoy reading about the unexplained I also enjoy reading about the explained. I used to be very one sided on this. I used to be the guy that would say, "yeah huh there are aliens and here is why" and then never even think there was an opposing view point.
I cannot help but think of Occam's razor (warning: gross over simplification coming), which basically states the simplest solution is usually right. When you have a situation where 3 in 25 people make an extraordinary claim we are forced to conclude some one is wrong.
I'm not saying people don't see UFOs. I'm just saying they might not be aliens. We live in an extraordinary world that we are just barely beginning to understand. All I'm saying is the odds of aliens be slim.
Just take an example like Roswell. Simple Earthlings have made traveling safer. Driving is safer, flying is safer, even space travel is safer. Assuming that trend, we will always strive to make travel safer. Now lets pretend we can travel to distant solar systems, and one has life, and we've decided on some sort of Star Trek like Prime Directive... I'd like to think our space craft would be one of the safest things ever built? The odds of us crashing would be ridiculous. Yet the flip side of that argument "ultra advanced aliens crashed landed" is the basis of the Roswell story.
Don't get me wrong, there are some really compelling alien stories. Here are some of my favorites.
- Late 19th Century "Mystery Airships"
- Roswell (just because I don't believe it was aliens doesn't mean there aren't some interesting things that happened--I'm partial to the "Russian's did it" theory).
- Whitley Strieber (but I hate the cover of his book)
- Betty and Barney Hill Incident (finally a link not to Wikipedia)
- Rendlesham Forest incident
And I could be totally wrong. They're here, they're looking at you right now, they're reading over your shoulder. I just wonder how could they be so far advanced, yet so careless to be caught? My side-theory is that if they are here they are the ultimate pranksters.
In conclusion, I haven't seen them. I want to see them. All my experience with aliens, abductions, conspericies, comes second hand. To be honest it makes me a little jealous.
3.1 If they are here they're friendly
Otherwise we'd already be dead.