Tuesday's Horizon on BBC2, Who's Afraid of a Big Black Hole?, was a case study on showing the unshowable and explaining the inexplicable.
Black holes aren't just hard to film - the very laws of physics say they can't be filmed. It was a challenge director Stephen Cooter faced by filming his interviewees in semi-darkness and showing a lot of swirly clouds in blackness. Well, what can you do?
More interesting was his use of an old-fashioned blackboard to explain the physics behind black holes.
In the sequence below, Cooter breaks Einstein's first law of documentary making (well, if he'd had time to come up with one): never leave the viewer unable to understand what your contributors are talking about.
Professor Michio Kaku chalked formulae on the board, explaining what he was doing, but leaving non-physicists adrift. We had been told this was "something so disturbing [Einstein's] theory breaks down completely". But it was nothing we could follow - until the good prof got to the point. Having shown that the formula for black holes had to include infinity, he concluded that "in the real world, there's no such thing as infinity; therefore there's a fundamental flaw in the formulation of Einstein's theory."
It was a conclusion worth reaching and, to my mind, justified the Dr Who-style jargon that got us there. Even if we didn't understand the details, by letting the prof spell them out to his own satisfaction, Cooter had revealed the nature of the argument. If the prof had only been allowed to state his conclusion, we would have been denied an insight into the debate.
So, let's not be dogmatic about requiring programme-makers to exclude incomprehensible stuff. Sometimes the audience can get the flavour of an argument, or an idea of what kind of evidence is being brought to bear, even if they can't follow every line that's uttered.
