Being an age-old fan of Back to the Future (the trilogy), I have the occasional Marty McFly type dream.

Maybe I could go back 50-odd years and somehow marry the lovely lady I had a crush on in my high school days (my then best friend's Mum, P.H. (1944-2009), God bless her soul; linked photo is taken from the public domain). But in that parallel universe, my best friend couldn't then exist (!) and we couldn't have that. Also, life as a coloured person in the 1960s (in a majority white western country) wasn't necessarily always all that flash, even if the music sounded much better than most of today's filth.

Being able to use the time machine only one time poses an interesting dilemma, a very different situation from the BBC TV show Goodnight Sweetheart with its time portal, the novel 11/22/63 with similar, or of course Back to the Future (1,21 GW a prerequisite!).