Measuring Wavelength of Photons: Precision & Variation

[f95toli]

It also depends on what type of measurement you are happy with. In a Cs atomic clock we know the frequency (and since we are in a high vacuum the wavelength) to within 1 part in 10^15 and in a good optical clock (using photons of e.g. 700 nm) 1 part in in 10^18.

This is of course an "indirect" measurement of the wavelength

 

[votingmachine]

I feel that the original question had two components and the arguments here tend to mix them up:

How precise can a wavelength of photons be measured

and how much can it vary?
... is there a point where there is no variation anymore - something like a "quantum" of wavelength?

The answer to the question of whether photon wavelengths can be infinitessimally different in wavelengths or are discretely quantized is that they are NOT quantized in wavelengths, but can be ANY wavelength. The argument from the doppler shift is particularly compelling IMO.

The answer to how precisely wavelength can be measured slips into an uncertainty problem. And a technological problem.

But I think the question was primarily if wavelength is quantized, and the measurement issues from uncertainty were a tangential matter.

On that tangential issue, since a photon has momentum, and an atom is generally 0.1 nm or larger, doesn't that imply the wavelength certainty could never be measured beyond about 0.01 nm? (I'm reasoning that p=h/lambda and (delta-p)*(delta-x)=h/4pi ... so if delta-x is the width of an atom, delta-p leads to a delta-lambda of 1/4pi).

 

[davenn]

There are some folks who claim otherwise:

https://physics.aps.org/articles/v11/38

Very interesting and very specialised but under normal conditions, my response still stands

 

[hutchphd]

They did go to a fair amount of effort. I also thought it interesting and couldn't find any flaw in their setup...but this is tricky stuff, mostly beyond my rapidly decreasing attention span.

 

[sophiecentaur]

There are some folks who claim otherwise:

I find that sort of article very disturbing because it suggests that you could take the idea much further and that could upset a lot of basic principles. Another of those trapdoors in Physics.

 

[almostvoid]

Potentially. There's something called a Planck length that could be the limiting lower size of anything in the Universe. The problem is it's not something we're near being able to test, so it's very hypothetical. You can read more about it and what the consequences of it could be here https://newt.phys.unsw.edu.au/einsteinlight/jw/module6_Planck.htm

It also covers a bit if the other part of your question, but many before me have already addressed that.

Hope that helps

It helped me---I write sci fi and this site -above was excellently explained. Thank you