# Photons “rate of fire”

I'm not sure if this makes any sense but, do photons "discharge" from a source at an infinite rate?

• Interesting and complicated question. I think you can take the energy emission rate and divide it by the average energy of each photon to get an average photo emission rate. I think the strangeness of quantum mechanics makes this only a classical view that isn't truly accurate though. – Brandon Enright Aug 26 '14 at 5:50
• Are you asking whether a photon is created instantaneously? That is, whether the system goes from no photon to one photon in zero time? – John Rennie Aug 26 '14 at 6:13
• Photons are subject to the uncertainty principle. If you try to measure a photon very "quickly", you will lose the information about its frequency/wavelength. In other words... there is really no way to assign an emission/absorption aperture to a photon. That's a property of the measurement device just as much as it is a property of the source that emits them. – CuriousOne Aug 26 '14 at 6:22
• I'm pretty sure the questioner is asking for a rate in # of photons / unit of time. en.wikipedia.org/wiki/Photon_counting – Brandon Enright Aug 26 '14 at 6:25
• @wtoh The apparent speed of the border of the laser dot on the surface of Moon is indeed faster than light, but no information is really transferred. Vsauce has a great recent video on this topic with links to nice visualizations of this. – Void Aug 26 '14 at 11:31

You are asking about the number of photons fired from a device such as a laser at a unit time. We cannot say what the precise number of photons would be at any interval due to a version of the Heisenberg uncertainty principle: $$\Delta E \Delta t \geq \frac{\hbar}{2}$$ It basically states we cannot suppress our uncertainty about energy fluctuations in time, such as in a light source, under a certain limit.
However, for any device we can say with certainty it will not fire an infinite number of photons in any time interval. Why? Because the probability of any distribution of "fire-per-time" can be non-zero for any number, but the total probability of all events has to be normalized, i.e. $$\sum_{i=1}^\infty P( i\; {\rm photons\; in\; given\;time \; interval }) = 1$$ The convergence of the sum has a necessary condition that $$P(\infty {\rm \; photons \; fired}) = {\rm lim}_{i\to \infty} P( i\; {\rm photons\; in\; given\;time \; interval }) = 0$$