I spend rather a lot of time thinking about the problem of other civilizations, and why haven't we found any yet. And while I have my own set of reasons: for example, what if at least some of them evolved at the bottom of an ocean, which is covered with ice like Europa and so they somehow never got around to get all the way through that ice layer?

Anyway, I'm also taking a cruise next month (stick with me, this is all connected) and I'm aware of the problem of cruise ships dumping garbage and waste directly into the ocean. So then I thought, what if star ships do the same thing? What if we stumbled across evidence of extra-terrestrial civilization by its garbage?

There's a story there somewhere. I do write science fiction, and I'm adequate at the short story level, but that idea is really a novel.

Must remember that we only discovered radio wavelengths about 50-60 years ago. Before that we would be considered a dead planet. SETI is looking for radio signals and without them the planets they explore are dead.

If there are radio waves from a limited period in a species' development, they'd likely be drowned out completely by all the background noise from space. That means we can rest easy that Hitler's speeches and "My Mother the Car" won't be picked up by alien species who would then assume we're complete pushovers and should be invaded.

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

Seems like there are a lot of empty planets from which one could get resources like gold or diamonds.

I was watching an episode of Stargate Universe not too long ago and realized that when visiting a distant planet you might meet something that wants to eat you. (Star Trek always had their planets filled with beautiful women)

We tend to think we are so strong but we are only as strong as we have conquered a specific area and rid it of other animals/plants that might want to eat us.

It's good book written by an astronomer. He basically works through I think 50 arguments on this issue. Pretty interesting book. There's a little in there about the origins of SETI, to.

civilization in the Milky Way (or hell, even the entire local group).

That still means there are over 100 billion civilizations and we wouldn't be able to detect any of them, most likely.

the budding astrophysicist. He had not yet known of this (he currently does research in galaxy formation and evolution) but was quite fascinated.

Another 1420 years before they receive the Jack Benny Show.
But we should be able to watch their old tv shows.

Very interesting news. Something to keep an eye on.

..."spotted a strange mess of objects whirling around a distant star." The existence of objects is hypothesized to account for the star's extreme variations in brightness, but no objects have been sighted. The most interesting hypothesis, though unlikely, is that extraterrestrials have put objects in orbit around the star to harvest the star's energy for their use.

http://www.washingtonpost.com/news/morning-mix/wp/2015/10/15/the-strange-star-that-has-serious-scientists-talking-about-an-alien-megastructure/

Obviously

https://en.wikipedia.org/wiki/Dyson_sphere