In Back to the Future, to get Marty back to 1985, it looks to me like the Doc connects a cable to the pole with the weather vane on top of the clock tower and fastens the other end to a light pole on the other side of the road. They need the power of the lightning to transport Marty to the future.
They know what time the lightning strikes, because the clock is stopped by the lightning and Marty has the pamphlet from the future with the time on.
Marty drives the DeLorean, the lightning strikes and goes along the cable. All goes according to plan and Marty is transported to the future.
- If the lightning strikes the pole and travels along the cable to the ground, would not the clock be bypassed and therefore not be stopped?
- If so, would this not constitute a time paradox?