科技网络公司纷纷布局 区块链“爆款”应用离我们还有多远？
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| 15 hours ago | comment | added | Ján Lalinský | @KP99 That an actual stochastic radiation background is present is an additional assumption adopted by the so-called stochastic electrodynamics (Timothy Boyer, Trevor Marshall, Emilio Santos), but the idea, even if intriguing, has problems, and it is not how QT of radiation describes things. | |
| 15 hours ago | comment | added | Ján Lalinský | @KP99 The zero point fluctuations aren't classical fluctuations in time, they're just a strange formal property of the field operators that they have non-zero dispersion in the field ground state, but nothing changes in time, so it's not radiation. There is a numerical coincidence in that rate of spontaneous emission is close to the rate of stimulated emission we would get for an hypothetical stochastic radiation background with spectral density $\propto \omega^3$, but there is no such actual radiation background in QT of radiation. | |
| 15 hours ago | comment | added | Ján Lalinský | @KP99 No, that is all wrong. Oscillating charged systems radiate on their own already in classical EM theory, spontaneous emission goes back to Larmor at least. One needs relativistic theory to describe this, not quantum theory. In quantum theory of spontaneous emission, one needs relativistic description of the field, or at least very many oscillators coupled to the system. EM fluctuations are not needed as an independent assumption, that's more of a red herring due to some confusion about zero point energy and vacuum fluctuations. | |
| 15 hours ago | comment | added | KP99 | I see ????. But I thought spontaneous emission was really a quantum phenomena. In literature, this emission is attributed to vacuum fluctuations | |
| 17 hours ago | comment | added | Ján Lalinský | @KP99 no, I meant just radiating dipole in classical electrodynamics, without random radiation background. Such background can modify details of the process, make it stochastic, but even without it, the dipole will lose energy and its emission will decay in time. | |
| 17 hours ago | comment | added | KP99 | Ooh..is it stochastic electrodynamics? I guess a decay amplitude is inevitable if the system is leaking energy to it's surrounding | |
| 18 hours ago | comment | added | Ján Lalinský | @KP99 you're welcome. You've got it. Also it helps to think about what classical EM theory predicts about spontaneous emission - it's a pulse of radiation in all directions, with decaying amplitude. The Fourier resolution of such a decaying pulse always has to have all wide spectrum of frequencies active in it. QT also has to have a decaying pulse, so the different frequencies have to be present. | |
| 18 hours ago | vote | accept | KP99 | ||
| 18 hours ago | comment | added | KP99 | Thank you for the response. I guess, I missed the fact that initial state wasn't an eigenstate of the full Hamiltonian...so there is no sharp energy value defined for it. The different frequencies are mostly centered around $k_0c$ as we see in Weisskopf-Wigner approximation. | |
| 21 hours ago | history | edited | Ján Lalinský | CC BY-SA 4.0 |
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| 21 hours ago | history | edited | Ján Lalinský | CC BY-SA 4.0 |
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| 22 hours ago | history | answered | Ján Lalinský | CC BY-SA 4.0 |