The many guises of quantum theory
Why does reality only seem to coalesce into a definite state when you make a measurement? The answer depends on your preferred view of the quantum world
Copenhagen interpretation
The “shut up and calculate” view: the quantum world does not exist in any meaningful sense without measurements.
Many worlds interpretation
Make a measurement and the universe splits, taking you into the parallel world where you got the result you did.
Objective collapse
Spread-out quantum states are collapsing into definite states all the time. Your clodhopping measurement just helps things on their way.
Quantum Bayesianism
Quantum uncertainty is not intrinsic to reality – it has to do with your own lack of knowledge about whatever you are attempting to measure.
Information
When you measure something, you extract some physical form of information from it, forcing it into a high-definition state.
Bohmian mechanics
Reality is guided by pilot waves; measurement just discovers what reality is up to, in the same way as classical physics (
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