Question: do you need plutonium to power a time traveling car?

Rik Allen answered on 11 Mar 2015:

Hmm – There might be bigger problems than how to power it. The best science at the moment says is’t impossible – but scientists should always be prepared to be proved wrong. They use plutonium for some satellites etc, but it might not be the safest thing to use for cars.
If we can solve the problem of nuclear fusion – rather than nuclear fission – then running cars on water would be more interesting to me.