In Honor of the UFO Congressional Hearing

There is almost certainly intelligent life elsewhere in the universe. Probably lots of it. Also, UFOs are bunk.

If there are, say, a million species that could build spaceships, that would average out to one every 1.3 x 10^4 light years if the universe was only one dimension. Since it's not, it comes out to, I guess, something like one every 1.44 x 10^8 cubic light years.

Now suppose they developed interstellar travel, and they could afford to send a hundred ships cruising to see what's what, knowing of course that it would be thousands of years before they found out what they learned (say everyone but us lives a really long time). If they sent them out at their equators, every three degrees, by the time they had traveled just one light year, they would be separated from each other by approximately 3.6 x 10^11 miles. That's a very, very large gap in the search pattern.

So, they aren't going to get here by accident and certainly not the several different kinds the conspiracy people envision. How about detecting us somehow and coming here specifically?

The strongest radio station I ever heard of was WGN. It was, I think, fifty thousand watts. Let's pretend that the entire earth is fifty thousand watts going in all directions, all the time.

Radio waves get weaker as they travel by something called the inverse square law (basically, the energy spreads out into a sphere, and the inverse square is the math that describes that).

At one light year distant, the inverse square equation looks like 5.0 x 10^4 / 3.6 x 10^26, ie 10^-22 or .00000000000000000000001 watts. I'm not even sure if that is one whole photon.

Suffice to say that you wouldn't notice it with the most sensitive detector ever made. And, that's only if the aliens happen to be only one light year away and if they happen to have their super-sensitive radio telescope pointed exactly at us.

How likely is that? Space is really big, and we are really small, so the precision of the aim required to see us is insane, and the numbers are too. Riffing off the example of spaceships, if they put one of their super-duper radio telescopes every one degree around their planet, that would take 65 thousand of them, and it would have the same problem as spaceships. 

Suppose the aliens are around Earth's closest neighbor, Proxima Centauri. Around 4 light years from here. That means there would be a gap of 4 x 10^11 miles between each telescope's sight lines (a tenth of a light year, give or take). But, it's worse because this is outer space. For each telescope, there would be a region of 16*10^22 square miles in which we could be missed. And, that is for the closest star.

Bottom line, even if interstellar travel weren't out of the question, it would take an insane stroke of luck on the order of winning the big lottery a thousand times in a row for them to find us.