# The Frequency of one Photon?

1. Oct 12, 2009

### voxmagnetar

The "Frequency" of one Photon?

If one could measure a photon passing by a given point, what is the time it takes for the leading edge of the theoretical particle of the photon itself to pass by that given point from the leading edge to trailing edge of just the particle size itself (not any fields or wave aspects, just the particle)

The reason why i ask is that one cannot express the "frequency" of just one photon, (you need many to comprise a frequency) and you cannot use (hertz) because that implies the event lasts one complete second which of course the absorption process of one photon would not take. So in effect the answer to my question would be the actual "frequency" of one photon. It will be one cycle per ___________???

2. Oct 12, 2009

### mgb_phys

Re: The "Frequency" of one Photon?

The length of a single photon is a slightly more complex idea - see http://www.lns.cornell.edu/spr/1999-02/msg0014640.html
But it is definitely wrong to think of it as a particle an equally qwrong to picture it as a sine wave going past a point on a graph.

You can certainly measure the frequency/wavelength of a single photon - it's one all the time for faint astronomical objects and is a standard technqiue for some kinds of lab spectroscopy.

The idea that you can't measure a frequency in 'per second' for something taking less than a second is like telling the police office you couldn't have been doing 60mph because you haven't been driving for an hour!

3. Oct 12, 2009

### DrChinese

Re: The "Frequency" of one Photon?

Welcome to PhysicsForums!

Can you be a little more clear regarding your question? As mgb_phys says, there is no particular reason you can't refer to the frequency of a single photon. After all, you can send a single photon through a filter as easily as a group of photons.

4. Oct 13, 2009

### sokrates

Re: The "Frequency" of one Photon?

This is the most hilarious, and at the same time insightful and at the same time informative thread I have read for a long time...!

5. Oct 13, 2009

### DrChinese

Re: The "Frequency" of one Photon?

This reference had an interesting point. He was pointing out that there is a difference between the following photons:

a) Photon with measured energy of 1 Mev and standard deviation of .1 in that value.
b) Photon with measured energy of 1 Mev and standard deviation of .01 in that value.
c) Photon with measured energy of 1 Mev and standard deviation of .001 in that value.

In fact, it is almost as if any particle has associated with it a set of std deviation values for its non-commuting pairs - in addition to the values of the observables themselves. I.e. something which indicates the uncertainty for the observable values. That way, the particle can be sure to yield results consistent with the HUP in future observations.