Suppose Alice and Bob are both asked to prepare a meal. Alice likes Chinese, Bob likes Italian. They each pick their favorite recipe, shop at the local specialty store, and carefully follow the instructions. But when they take their dishes out of the oven, they are in for a big surprise. The two meals turn out to be identical. We can imagine the existential questions Alice and Bob must ask themselves. How can different ingredients produce the same dish? What does it even mean to cook Chinese or Italian? And is their approach to preparing food totally flawed?
This is exactly the perplexity experienced by quantum physicists. They have found many examples of two completely different descriptions of the same physical system. In the case of physics, instead of meats and sauces, the ingredients are particles and forces; the recipes are mathematical formulas encoding the interactions; and the cooking process is the quantization procedure that turns equations into the probabilities of physical phenomena. Just like Alice and Bob, quantum physicists wonder how different recipes lead to the same outcomes.
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