4 ms·
Such conceptually dense language! Isn't the average amplitude of every wave just zero?
by knodi123 6y ago
Such conceptually dense language! Isn't the average amplitude of every wave just zero?
- danbruc 6y agoThe amplitude is the difference between maximum and minimum, not the momentary value of a wave at some point.
- frabert 6y agoThen how can the average amplitude be zero? If at any point the amplitude is nonzero, it must be positive (as it is the absolute value of the difference), thus the average can only be positive
- ben_w 6y agoIIRC the minimum is supposed to be 0.5 photons of any given wavelength. This is what gets called “zero point energy”. Except there are ways to go below that, like a Casimir cavity. I find these things confusing because when people explain Casimir cavities they never bother to say why the justification for zero point energy existing in the first place doesn’t apply within the cavity.
- fsh 6y agoIndeed this is not possible for a classical wave. However, in a quantum description there exists a so-called "vacuum state" for which the expectation value of the electric field operator vanishes at all times, but the expectation value of the square of this operator does not. In the classical approximation of quantum optics, the expectation value of the electric field operator corresponds to the amplitude of the classical wave, whereas the expectation value of the square of the electric field operator corresponds to so-called shot (or quantum) noise on the classical wave. Of course in nature there is no such thing as a "classical wave", so this description has to break down at some point. This is the case for vacuum fluctuations which simply do not have a classical explanation.
- bollu 6y agoDoes this have to do with the fact that the wave is complex-valued?
- raxxorrax 6y agoWould be disappointed at the "wave" at that point.
- stallmanite 6y agoHmm, at least with an audio waveform one can have a DC offset wherein the average is not zero.
- alanbernstein 6y agoThe DC offset does not manifest when the waveform is translated into sound, which is an actual propagating wave, the appropriate analogy to light.
- phonethrowaway 6y agoparticle/wave duality. it means neither fully encapsulates "light".
- sharpneli 6y agoAlmost but not quite. With light the electric field can go negative and the average is generally 0. With sound in air the pressure component has a ”DC” offset of 1bar and it cannot go negative, you will just get nonlinear effects when you start nearing that limit.
- deleted 6y ago[deleted]
- macawfish 6y agoThe DC offset can be considered as approximating a low frequency component that is so low frequency, relative to the measurement window, that it appears to be constant. I think in the case described here, the zero average amplitude thing has to do with something a little bit different.