Hello, lazy writer here. Got a question for you all; apologies if it's been asked before or needs to be moved. Assuming an advanced civilization controlled the Milky May for a period of ~16 gigayears (from the galaxy's formation until the merger with Andromeda) and had all that time to work on it, and was willing to go to any length (up to and including engineering supermassive black holes, converting all the available mass in the galaxy using von Neumann machines, etc.), what mega-engineering scenarios could said entities plausibly use to construct a time machine capable of sending a nano-scale piece of common matter back gigayears, one way, to before the galaxy existed? The question doesn't assume any particular cosmological model. Exotic matter OK. And no need to think about causality paradoxes because let's say the displaced matter will have no effect on the past once it gets there. I'm just asking for some thoughts on how a civilization with extreme tunnel vision and practically infinite time might conceivably accomplish this kind of thing, in hopes of giving my plot device at least a veneer of plausibility to shield it from inevitable nitpicking. I have actually tried to research this myself - honest. But this is where my grasp of physics runs out, and with all the suggestions out there, it's difficult to judge the barely plausible from the less so.