I’d never even considered this until Den Of Geek reader ‘HarrisonFord’ (we assume he’s the real one) raised it in our discussion of Back To The Future Part III last week. And it’s this: there has to be two time machines in 1885.

Much of the third film is spent trying to find new ways to get the Delorean that Marty travelled back from 1955 in up to 88mph. But what about the time machine that Doc got sent in, when it was struck by lightning at the end of Back To The Future Part II? That’s the one that he stores in a cave for 70 years (although it’s still damaged, to be fair, as the Doc sends instructions forward in time). And given that it’s established that we can have two Docs and two Martys at the same point in time, why can’t we have two cars?

Now, there’s some argument as to whether Doc has either drained the car of fluid, or left it with a full tank of fuel. Either way, there’s surely something of use in the second car.

Of course, there are arguments why that car can’t be touched. Firstly, there’s the old paradox rule that would destroy the universe, although by the third film, the Doc is getting far more liberal with the laws of time. And secondly, if the alternative car was used, then Marty – are you following this? – wouldn’t have been able to get back to 1885 in the first place. Because if it was fundamentally tampered with or used, that’d make it either redundant of non-existent in 1955. Which would, of course, create a paradox to bring down the universe, as you well know.