It has always seemed unavoidable that measurements (or observations) set off the sudden change from waves to particles, and many think that the consciousness of the experimenter is part of the process.
But now a small minority, growing rapidly and including some of the world's top physicists, think there's a purely physical explanation, and that it's nothing to do with consciousness. To make a measurement, you have to cause an interaction - 'bumping bits of matter together' - and the new idea is that this is the cause of the sudden change.
Two very good physicists explain why they think interactions is a better bet than measurements, and it becomes clear that the new avenue is an important one. But until now, no-one has been able to say why interactions should do that, so the idea has been something of a taboo.
In the film a British physicist, Jonathan Kerr, who has found a theory that explains why interactions should have that effect, discusses his theory and the interactions avenue with Carlo Rovelli and Neil Turok. The script of the film is based on Kerr's book, The Unsolved Puzzle.
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