A small bird was starving one winter. It was so cold, he couldn't fly any more, and he fell to the road. Just then a horse-cart passed over him, and the horse dropped a huge load of dung on him. The dung warmed the bird, and the seeds in it fed him. Soon he was feeling so cheerful he started to hop around and sing. The commotion attracted the attention of a passing wolf, who pulled the bird out of the dung and ate him.
This story has three lessons. First, the one who puts you in deep doo-doo is not necessarily your enemy. Second, the one who pulls you out of deep doo-doo is not necessarily your friend. And third, if you're full of doo-doo, don't draw attention to yourself.
I keep the last lesson in mind when thinking about SETI, the Search for Extra-Terrestrial Intelligence in the Universe. SETI proceeds by combing the universe for radio signals that meet certain statistical criteria for being non-random and non-repetitive - in other words, not of natural origin. But suppose that some ET were out there looking for us. For a long time, say 5 billion years, there would be nothing. Then a faint glimmer of radio signals starting around a century ago. Then analog television shows from about 60 years ago. But this year, television has gone digital - which looks more like random noise to those statistical algorithms. We are going quiet, going out of radio frequency existence after only a century or so. Odds are very slim that any ET would be looking our way during that brief period of time. Which means that odds are we won't be found.
And that is a very comforting thought. Consider the energy it takes for interstellar travel. Let's say that an alien civilization had a spaceship weighing 10 metric tonnes, that it could accelerate to 99% the speed of light. If such a thing experienced brake failure (accidentally or otherwise) it would hit whatever was in its path with an energy of 5x1020 Joules, or 100,000 megatons TNT equivalent. That's more than enough to smash a planet. And we wouldn't even see it coming, because the light from it would be moving barely ahead of it. By the time we detected it, it would be too late think much about it, much less to to do anything about it.
Maybe that's why SETI hasn't found anything. Maybe all those ETs out there have done the same simple calculation that I've just done, and have decided not to draw attention to themselves. Our digital revolution is making us appear to go radio quiet. Let us continue, for in the grand scheme of interstellar society, we may be the little bird.