Not singling anyone out here but generally speaking, I think the thing that most people who believe in extraterrestrial visitations don't seem to grasp is the vastness of space and the limits of speed and time. I find it difficult to believe that other alien races can do what we believe to be physically impossible. I'm not talking about technology. If we took some of our current technology even back 100 years it would be beyond comprehension. If we took most of it back 300 years it would be witchcraft.
But what has advanced just as quickly as our technology is our understanding of how the universe works. Just as electricity and magnetism are two sides of a single coin, space and time are connected, velocity and mass are connected. Energy, mass and acceleration are a vicious circle. The more an object accelerates, the more mass it gains, the more mass it gains the more energy it takes to accelerate it. Even a single proton would take an infinite amount of energy to reach light speed. This is true for everything in the universe with mass.
Now, personally I'm going under the assumption that an alien race would require a planet near a sun to evolve. The closest star to us is about 4 light years away. There's 3 of them actually and two of them are part of a binary system and after that they start to range between 6 to 10 light years away and beyond. Even traveling at half the speed of light it would take about 10 years to get to the closest star, that's a one way trip at about 500 million kilometers per hour. I'm not even going to mention the amount of energy it would take to accelerate even a tiny craft to 500 million kph. I think the Mars Rover topped out at about 20,000 kph. 1/25000th of our desired speed and it carried a craft about the size of a Mini Cooper.
Now since we're talking about actual aliens visiting you have to put some sort of species on the craft which opens a whole new can of worms. How do you get a human (or alien) up to 500 million kph? Well, If you give yourself a month to achieve that speed and you're a very small human or alien you can keep the g-force down to about the same as an extreme rollercoaster ride. (Maybe around 3g) Which makes for a rather uncomfortable 30 days. Or you can give yourself a year and comfortably accelerate to half the speed of light but then you'll need a similar amount of time to decelerate and that's not counting the problem of navigation. You could sit quite comfortably in a craft at 500 million kph and if the speed and direction was constant you could even get up and walk around. The problem is that even the slightest change in direction would fling everything and everyone in the craft in the opposite direction. A car traveling at 100 kph changes lanes too fast and you spill your coffee. Imagine trying to turn even slightly at 500,000 times that speed. Even if you plotted a constant arc from point A to point B with the minimum curve the passengers in the craft with feel a constant g- force in the opposite direction of the curve for the entire duration of the trip. Inertia is a bitch.
And I didn't bother with the amount of energy it takes to accelerate earlier because of the amount of energy it takes to sustain the crew for the trip. Any species is going to require a renewable source of oxygen, carbon dioxide, helium or what ever it breathes, a food supply either stored or renewed, a navigation system, lights, heat, communication for 10 years each way and that is just to the nearest star. To get to the next batch of stars after that, double everything I just said.
This is part of why I don't believe aliens have visited earth. I've never believed that we are alone in the universe or even that we are the only intelligent species. The problem is that any other species in the universe (unless they are subatomic particles) are bound by the same Newtonian laws of physics as we are regardless of their technology.
I could probably write an entire book on why I think it's simply not possible for an intelligent alien species to get from there to here and why the odds are almost zero that they would evolve within 100 or even 1000 light years of us, much less 4 or 10 but I've just bored you with 3 or 4 paragraphs of it. Imagine reading a hundred pages.
, I know you are a 100% science type of guy, I am also upto a certain extent, science in it`s many shapes and forms has answered so many questions, but, i`m also a staunch believer in the process of elimination, which helps (most times) for those answers where science fears to tread,
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