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Electrons are not just like photons. It's tempting to say that, but there are some significant differences that can lead you in error if you think in this pictu
by rnhmjoj 1y ago
Electrons are not just like photons. It's tempting to say that, but there are some significant differences that can lead you in error if you think in this picture.
First of all, if you think of a photon as some small ball, not that's not what it is. Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
Unlike photons, electrons have a position operator, so in principle you can measure and say where one electron is. The same is impossible for photons. Also electrons have a mass, but photon are massless. This means you can have motionless electrons, but this is impossible for photons: they always move at the speed of light. Electrons have a non-relativistic classical limit, while photon do not.
W. E. Lamb used to say that people should be required a license for the use of the word "photon", because it can be very misleading.
- whatshisface 1y agoWhy don't photons have a position operator?
- mcnamaratw 1y agoIt’s really not accurate to say that a photon has no position at all. How would a photodiode work? You have to be careful with this stuff. https://physics.stackexchange.com/questions/492711/whats-the-physical-meaning-of-the-statement-that-photons-dont-have-positions https://physics.stackexchange.com/questions/492711/whats-the...
- westurner 1y agoPhotons certainly appear to have a real physical location with 1e9 FPS imaging capabilities: "Visualizing video at the speed of light — one trillion frames per second" (2012) https://youtube.com/watch?v=EtsXgODHMWk& https://youtube.com/watch?v=EtsXgODHMWk& But is there an identity function for a photon(s), and is "time-polarization" necessary for defining an identity function for photons?
- riskable 1y agoThink of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe. Since it lives and dies in the same instant, it can't have a position—because the moment it exists and the moment it doesn't is exactly the same time. It takes time—even for light—to get from point A to point B. However, the measurement of any positions—relative to the photon itself—will always be the same. It's related to that property of quantum physics that allows two particles to exists in two different places at the same time.
- Izkata 1y ago> > > Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle. > Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe. Would an appropriate analogy be a "glider" from Conway's Game of Life? "Lives and dies in the same instant" isn't exactly the same, but I'm thinking of how no parts of the glider move while the glider as a whole "moves" across the board.