Why We Haven't Heard From Other Civilizations

To believe that there are no other advanced civilizations in the universe is absurd. The place is just too big, millions, billions, trillions of other places. So why don't we hear from them? OK, so they might not drop by, but a nice telegram, a radio braodcast, something. Are they snubbing us?
[As an aside, I'm not one, obviously, who believes that aliens have "dropped by." In my opinion, if a craft lands, the whole world would be aware of it in a very short time. Our ability, as a species, to make information public knowlege is part of what makes us an advanced civilization. If you believe in conspiracies, you have never met a journalist.]

It's not for lack of trying. We listen with fabulously delicate electronic equipment that could hear an ordinary radio antenna across a distance that is bigger than humans can grasp or imagine. Nothing. Nada. Zilch. Why?

Think of the radio waves that our civilization generates. Nicely modulated, easy to detect. But we've only been broadcasting for a dozen decades and already we are slipping out of braodcasting nice easy to detect waves to one more closely resembling random noise (and therefore, by the laws of information theory, more efficient). So we wouldn't necessarily see it as non-natural.

The signal we've output that we ourselves could detect is a sphere that spreads at the speed of light, but it is hollow. The stuff inside is stuff we will output in a few years that we wouldn't recognize ourselves. This radio wave is a thin hollow shell. It may be 150 years thick but before it passes another civilization, it will perhaps be millions or billions of lightyears in diameter. Remember, the universe is vast. Things are very very far apart. That planet's civilization has only 150 years to catch a radio signal. What are the chances that they are in the situation to detect them just as the shell passes?

It may happen, but the odds are very low.