I’d go back to the 1970s, the dawning of personal computer growth in it’s beginnings. I’d take every single idea and patent from today and collect them all in a multiple series of binders. I would spend weeks holed up in some apartment, jotting notes, re-directing credits to me.
I would be the founding father of hundreds of technological inventions, way before they were even thought up. Flash Drives? My idea. Compact Discs? My idea. SSDs? My idea.
Everything will be my idea and I’ll be biding my time, pitching ideas and profiting off of the patents that I sell and my ideas alone, with little to no work involved. By the turn of the 2000s, I’ll be unfathomably recognized and wealthy.
You’d probably kill those civilizations off entirely with the germs and viruses you bring back.