There's a novel titled Glasshouse, by Charles Stross, where members of a far future civilization sign up to live in a simulated mid-20th century town. At one point the protagonist disassembles a flashlight and discovers that it's just a flashlight-shaped case containing a small wormhole whose other end is in close orbit around a star. No one knew how to make an LED or incandescent bulb, or understood enough about early electronic components to hook one up to a switch and a battery. It was easier to make a wormhole generator and stick it in a metal tube.