Time for another thought experiment. Or, rather, a puzzle without a good answer yet.

We're getting pretty good at building extremely powerful telescopes. The Kepler planet finder orbiting telescope may have gone functionally offline, but Hubble keeps plugging along, and the James Webb infrared telescope is on the calendar. And when we look out in the universe, we're seeing some pretty amazing stuff.

But what if the stuff we're seeing is even more amazing than we think?

Imagine, if you will, a very high technology non-human civilization living in two star systems (reasonably close to one another, say half of a light year, to make colonizing moderately feasible; that's close enough to share an Oort Cloud) about 10,000 light years from us. About 10,000 years ago, they split into three factions:

The first wants to go full upload, transcend into post-Singularity bit-liness. They've decided to disassemble their entire planetary system into Computronium, creating a web around their home star to absorb energy to support their digital lifestyle. (Charlie Stross describes this process in the later chapters of Accelerando, required reading for anyone who follows this blog.)

The second likes the idea of tearing things apart, but it less enthusiastic about the whole "turn ourselves into software" upload thing. They make use of similar tools to disassemble their own planetary system to create a Dyson Sphere. (The Star Trek: The Next Generation episode "Relics" is probably the best visualization of a Dyson Sphere around.)

The third faction says "the hell with this noise" and wants to bug out. They build a fleet of modified Alcubierre warp-drive ships to zip around the galaxy. This apparently plausible system uses exotic matter to compress a bubble of space-time around the ship, allowing it to travel effectively faster than light, even though within the bubble the ship is still traveling at a reasonable sub-light speed. None of these ships heads to Earth, but some of them head roughly in our direction, such that photons from the ships arrive along with those from the Computronium conversion and the Dyson Sphere construction.

Okay, got it? Three groups, each doing something different, with the light from their ultra-tech activities just now getting to Earth.

What do we see?

What would the disassembly of planetary systems look like? A Dyson Sphere, by definition, blocks out the home star; what would it look like as the Sphere came together? A Computronium web, conversely, need not block the entire star, but would consume quite a bit of energy; would that radiate differently than a "normal" star?

And just what would a warp-bubble-drive ship look like in action? It may only require a ton or two of "exotic matter," but that still translates into enormous amounts of energy being used to push around spacetime like a middle-school bully.

How would we know we're seeing something artificial, rather than a bizarre natural phenomenon?