> - definitive sink to send all of our nuclear waste (it would be the /dev/null of the Solar System)

Now, black holes probably aren't known to be gateways to other locations, but that comment made me wonder what if they are, and dumping our hazardous waste in them has far reaching consequences somewhere else, then that in turn made me think of what other cosmic-scale consequences of alien technology might be out there.

I mean, if a civilization has planet-spanning tech, their "waste products" could be on the scale of planets too. Somewhere, a species must be burning through solar systems like we're burning the Amazon.