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Waldo
06-16-2014, 09:18 AM
Sci-fi question here. How close are photons spaced?

Imagine a beam of light constantly emitting photons for the duration of the experiment. A photon bounces off a sensor, how much time passes until the second, and third photons hit the sensor. Would this measure the distance between photons?

noranne
06-16-2014, 10:21 AM
Well photons aren't exactly like marbles. They're actually a wave AND a particle. Yeah it's weird. And the more precisely its position is known, the less precisely its velocity is known, so detecting on a sensor like that would

I would say probably the more useful measurement would be the wavelength of the light. Based on the energy of the photons, their waves would have a different period. Blue light, for example, has a wavelength of 475 nm.

When you're getting down to the level of photons, you're pretty heavily into quantum territory, which defies neat explanations. :)

girlyswot
06-16-2014, 01:26 PM
Sci-fi question here. How close are photons spaced?

That... isn't how they work.


Imagine a beam of light constantly emitting photons for the duration of the experiment. A photon bounces off a sensor, how much time passes until the second, and third photons hit the sensor. Would this measure the distance between photons?

No.

Telergic
06-16-2014, 06:35 PM
Let us attempt a better answer than "no".

In most situations light behaves like a wave. Photons that participate in a wave are superimposed and lose all individuality, and so their spacing is meaningless. With macroscopic instruments you can indeed measure a single photon, but you rarely see individual photons, and in most situations their wave-nature dominates the experiment. Of course an electronic detector itself is where the photoelectric effect dominates, and it's there that photons have a particle nature, but their density is only meaningful when they are detected one at a time, which is rarely the case in real-world situations.

However, there is a sort of fake photon density measure you can come up with based on the total energy of light received over time that may be helpful to the OP.

You can compute individual photon energy based on the frequency of light -- that is the sole determinant of energy in this case, so all photons emitted by a monochrome laser have the same energy -- and you can measure the amplitude of an electromagnetic signal over time. Divide the total energy of the signal by the individual photon energy for the frequency and you get the effective number of photons that would be received over time if indeed they were individual particles with no wave-nature. From this figure, the duration of the experiment, and the cross-sectional area of the detector used in the experiment, you can compute a number that would be the density of photons per square or cubic meter if indeed photons were traveling through space as particles. They're not traveling through space as individual particles, to be sure, but that figure might at least convey some sense of an answer to the OP's question.

The arithmetic is left as an exercise for the student.

WeaselFire
06-16-2014, 10:24 PM
Sci-fi question here. How close are photons spaced?
Answering that might get you a Nobel prize. Or at least a chair at a decent university. :)

Now, what exactly do you need for your story?

Jeff

benbradley
06-17-2014, 07:08 AM
At very low light levels you CAN measure each photon with this device:
http://en.wikipedia.org/wiki/Photomultiplier

If you could figure out, say, what intensity of light gives an average of one photon per second and compare that to the intensity of light you're thinking of (I don't know how to do this offhand), you could just multiply by the intensity ratio and get a number for photons per second. Then you can divide that into the distance light travels in a second (about 186,000 miles - more accurate values are available in books and online), and you'll have a number for the average distance between photons.

I won't get into the discussion of whether or not this value is meaningful.

Michael Davis
06-18-2014, 02:26 PM
Photos occur when some stimuli of energy causes an electron to jump valence shells, they're not just sitting around waiting to pop up. In terms of predicting their regularity, like one responder noted, not sure in the uncertain world of quantum mechanisms that's even possible unless you use probability functions vs absolute statements. Yeah, the world of the tiny is weird.