This is a follow-up to Phil's post, "The Great Filter."

NPR published a great radio segment a couple of weeks ago titled "Lucy's Laugh Enlivens the Solar System." It's about television and radio being broadcast into space. It's 6 minutes long. Have a listen. I'll wait.

...

"I Love Lucy" and other shows of that era were broadcast over 57 years ago. That means that original broadcast has traveled over 57 light years. There are many other star systems in that range, but astronomer Chris Impey points out the Lucy wouldn't be detectable over the cosmic background noise past, say, Pluto. And apparently there's no foreseeable technology out there that could improve on that. If you're thinking that future broadcasts will be stronger, well, it doesn't seem to be going that way. Our planet has gotten quieter cosmically-speaking since the heyday of Lucy.

This would seem to indicate that SETI is likely to fail, but such failure doesn't rule out the existence of other civilizations.