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What is the Lamb shift in the ground state of a hydrogen atom? Calculate the value of the Lamb shift by considering the energy difference between the 2S1/2 and 2P1/2 states using the perturbation theory approach, taking into account the interactions of the electron with the vacuum fluctuations of the electromagnetic field.
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<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

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The answer is 42.

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