A throwaway comment in Che Tibby's latest caught my eye:
All I have to say is this, the truly great theories are really, really, hard to understand. Once upon a time there were only two people in the world who understood the theory of relativity. Einstein, and some smart-arse. These days everybody knows that if you send a clock into space at the speed of light when it gets back to Earth it's only advanced five minutes while society has advanced a billion years. Or something.
Just by way of establishing my smart-arse credentials, the above-mentioned smart-arse was the astrophysicist Sir Arthur Eddington, who translated some of Einstein's work from German into English. And the time-dilation example Che uses is an example of Special Relativity; it was General Relativity that was "only understood by two people". The former deals with observers moving at constant speed with respect to one another, and results in time varying along with velocity depending on the frame of reference used. The latter throws in observers who are speeding up and slowing down as well, and reconceptualises gravity as the curvature of space (resulting in all those irritating examples where people roll marbles across rubber sheets). It also utilises the Lovecraftian horror of tensor calculus, which drives people insane and ruins their hair.
As for complexity, being difficult to understand is often simply a sign that someone is a bad writer, or that they are applying the old strategy of "if you can't blind them with brilliance, baffle them with bullshit". In fact, where science is concerned, it's simplicity and elegence which are appreaciated, not complexity. All the "greatest" scientific theories - natural selection, Newton's Laws, Maxwell's Equations, even special relativity - are all at their heart extremely simple ideas which will frequently fit on a T-shirt.