Quote from Professor Roger Penrose speaking on BBC Radio 4 'Start the week - A Theory of Everything? 20th June 2016.

There is a deep paradox in quantum mechanics, it's a contradiction, and it's hardly ever pointed out as a contradiction. And this contradiction is actually quite a simple one, it's that you have one procedure to describe how things evolve - the Schrödinger equation, (or 'Unitary Evolution' as it's called,) and another which is what you do when you make a measurement. And, if your measuring apparatus was going to follow the Schrödinger equation it wouldn't produce any results at all - it would never have 'A or B' , you'd never have any probabilities. You have to have two incompatible procedures in order to make the theory work. And they are actually inconsistent with each other. And so there has to be something wrong at some level.

As an example, a Geiger counter, in the process of detecting radioactive emissions which are indeterminate until detected, is itself made of particles which are indeterminate - nevertheless it still 'clicks or not clicks'.

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