>>10195608>unable to find that ninth planet that is hiding far beyond pluto
It's a fairly recent idea to explain the weird orbits of KBO's no one knew existed 20 years ago.
It's not like a cold rocky planet orbiting at that distance stands out. If it's there it's a matter of time before its observed.
If you're using FTL though, it's not a bad assumption that you're dealing with very high energies being utilized, that would leave behind a flash at the very least.
You would also see really weird shit happening if one of these ftl ships passed anywhere near you, like redshifted and blueshifted doppelgangers blasting out of nowhere in opposite directions as it zipps by you.
The idea is that advanced enough civilizations shouldn't be hard to detect because of their general energy requirements and size.
As we get the next few generations of telescopes then you'll have the ability to find and study more exoplanets, down to their atmospheric composition, and Life™ of any complexity should leave finger prints that you should be able to detect.
We're also not far away from being able to send at least probes to other stars, so assuming humanity survives, civilization doesn't collapse, and we continue to progress at even current rates means we're not far away from exploring the local neighborhood of our star, and if you can continue to survive, and expand, and explore, then it's not an unreasonable time frame on cosmic scales before you should be able to have a probe in every corner of the galaxy itself.
If there is life, and some of that life is intelligent, and some of it is ahead of us, then at least someone should have tried something like that.
Since we don't see that, then one can assume that either advanced life is super rare, like one per galaxy (or even one per universe in a worst case scenario), we're at the head of the class, or something happens to prevent civilization from becoming extra-solar.