Linked Questions

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Masslessness of the electromagnetic field

Why is the electromagnetic field massless? I presume the mass term in the Lagrangian, $$ \dfrac{1}{2}M^2 A_{\mu}A^{\mu}, $$ would "violate" gauge redundancy. But this is what its name indicates: ...
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3answers
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Conservation of momentum for rockets [closed]

I'm reading Kleppner & Kolenkow Example 4.16 on page 140-141 of the second edition and I am confused by something. So we have a rocket in free space. No friction and no gravity. The rocket has ...
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2answers
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How much fuel is needed for a constant-acceleration rocket?

My son and I have been discussing the concept of a constant-acceleration rocket, as described here and here. We're willing to assume advanced technology such as a fusion rocket, which, according to ...

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