The Secrets of Feynman Diagrams

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Unlock the secrets of Feynman Diagrams. Part 5 in our Quantum Field Theory series. And if you're submitting an answer to our challenge question email your answer by August 2nd to pbsspacetime [AT] gmail.com with the subject line "Feynman Diagram Challenge."

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Feynman’s path integral shows us that, to properly calculate the probability of a particle traveling from point A to point B, we need to add up the contributions from all conceivable paths between those points – including the impossible paths! In fact we can go even further: according to Feynman’s approach, every conceivable happening that leads from a measured initial state to a measured final state DOES in a sense happen. To calculate the probability of any quantum system evolving from one state into any other state we need to sum over every conceivable intermediate state. This is impossible because there are infinite possible intermediate states.

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