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Cake day: 2024年2月1日

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  • In undergrad I took a class on sleep, and it really stuck with me. I previously had some FOMO-esque aversion to going to bed early, but after that class if I was done with the day and I was tired, I just went to sleep.

    It’s been a good mentality for us now that we have a small kid, too. No shame in going to bed at 8…


  • No, that’s not really a useful way of modeling it for the case of light traveling through a linear medium.

    The absorption/re-emission model implicitly localizes the photons, which is problematic — think about it in an uncertainty principle (or diffraction limit) picture: it implies that the momentum is highly uncertain, which means that the light would get absorbed but re-emitted in every direction, which doesn’t happen. So instead you can make arguments about it being a delocalized photon and being absorbed and re-emitted coherently across the material, but this isn’t really the same thing as the “ping pong balls stopping and starting again” model.

    Another problem is to ask why the light doesn’t change color in a (linear) medium — because if it’s getting absorbed and re-emitted, and is not hitting a nice absorption line, why wouldn’t it change energy by exchanging with the environment/other degrees of freedom? (The answer is it does do this — it’s called Raman scattering, but that is generally a very weak effect.)

    The absorption/emission picture does work for things like fluorescence. But Maxwell’s equations, the Schrödinger equation, QED — these are wave equations.