[Q] "Frequency" of a photon

[Restless Archer]

Hi everyone.

 

Why is it acceptable to talk of the frequency of a photon - a massless particle traveling at the speed f light? What does it really mean?

 

Thanks.

A.

[CraigD]

An excellent question! :thumbs_up

 

For most purposes, the frequency of a photon is just a relative measure of various useful qualities, such as the angle at which it is refracted by a particular medium, or how much energy it imparts to an electron in an atom of some material. From this, it’s not clear that frequency – the number of occurrences of some regularly recurring phenomenon in some duration of time, or if an alternative explanation would server as well. For example, might photons associated with higher frequencies and thus higher energy (which is directly proportional to frequency, ie: [math]E = hv[/math] where [math]E[/math] is energy, [math]v[/math] frequency, and [math]h[/math] a constant) not have, say, just have proportionally more mass?

 

When one looks at wave-like behaviors of light, it becomes clear why the frequency of a photon is truly some that could, in principle if not in practice, be counted in much the way one can count the number of water wave crests pass a fixed point, or the movement of the diaphragm of a microphone moved by sound waves.

 

For example, the interference pattern recorded on a photographic plate or detector array after passing through a double slit apparatus is identical in all but scale one produced by water waves passing through a similar apparatus. Interferometry can be used to precisely determine distance to within increments smaller than the wavelength ([math]v/c[/math], where [math]c[/math] is the speed of light) of the light used.

 

So, while it’s not practically possible to determine the frequency of a photon by a simple counting processes, as we can with water waves or sound waves, we can reproducibly determine it with great precision using indirect methods that can be performed with very simple instruments (a workable spectrometer can be made with paper, tape, and nearly any sharp-edged material, such as is illustrated in Make Your Own Spectrometer|Orbiting Frog)

[RanchDressing]

Please also remember the flip side of the matter at hand. Matter is measured to have a wavelength also. (Wavelength and frequency are the reciprocal 'flip sides' of each other.

 

See: De Broglie hypothesis - Wikipedia, the free encyclopedia

[Little Bang]

f = MC^2/h

[enorbet2]

As Science has progressed particularly into the realm of the very small, it becomes harder and harder to understand because of the lack of frame of reference. So many of us were brought up with the idea of an atom as being something like a mini solar system, plus we tend to prefer thinking of things as somehow solid, that it's difficult to comprehend that things look solid because of perspective and feel solid because of fields of force. The fact that gravity does not somehow pull us into the Earth displays that Gravity is many orders of magnitude weaker than atomic forces since we as well as the Earth are mostly space.

 

As vast as the distances are in Space they are proportionately greater within the atom, mostly space, or so it appears with our present instruments. (The Planck Scale is unknown.) Furthermore the foundation of General Relativity and Quantum Mechanics is based on that beautiful experiment to which CraigD alludes wherin it is shown that fundamental particles are the embodiment of E=MC^2, that a better term might be "wavicles" because they can act as either particles or waves. They, including photons, behave as both. This does not appear to be mere conjecture. Aside from the double-slit experiment, electron microscopes produce "pictures" exactly through the action of their higher frequency as compared to photons. The vibration is shorter so electron microscopes can "see" things too small for the longer photon vibrations. The reason we cannot yet, or possibly ever, "see" at Planck Scale is from lack of waves of sufficiently shorter wavelength. The characteristic of sub atomic particles, or wavicles, to behave as vibrations is partly what launched String Theory(s). These vibrating strings are not thought to be solid either. It's a wild world!