# Theoretical Limit on Frequency?

## Main Question or Discussion Point

Is there is theoretical limit on how large a frequency (or how small a wavelength) an EM wave can have?

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the frequency available is continuous and has no upper or lower bound, so there is no finite lower limit or upper limit on the possible energy of a photon. On the upper side, there are practical limits because you have limited mechanisms for creating really high energy photons. Low energy photons abound, but when you get below radio frequencies, the photon energies are so tiny compared to room temperature thermal energy that you really never see them as distinct quantized entities - they are swamped in the background.

xantox
Gold Member
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Meir Achuz
Homework Helper
Gold Member
Is there is theoretical limit on how large a frequency (or how small a wavelength) an EM wave can have?
No.........

mjsd
Homework Helper
Is there is theoretical limit on how large a frequency (or how small a wavelength) an EM wave can have?
unfortunately, many of the physical theories we have are strictly valid at a relatively low energy... since freq is related to energy... so you may have problems when things go extremely large... but that doesn't mean there is definitely a limit..it is just a statement saying that we don't know ..yet

If there is a limit then either the Doppler's shift is completely wrong for ultra high frequency or there is a bound (less than c) on how fast one can travel with respect to a source of a light.

actually if you pump enough energy into a photon it will entually become a different kind of boson, I forgot the particulars however.

If there is a limit then either the Doppler's shift is completely wrong for ultra high frequency or there is a bound (less than c) on how fast one can travel with respect to a source of a light.
How can you draw this conclusion?

in Doppler's effect, the frequency goes to infinity as one approaches a light source close to the speed of light... so if there is a limit on how high frequency goes and Doppler's effect is correct, then there is limit (lower than c) on how fast one can travel toward a light source. similarly, if there is a lower bound on frequency, then there is a limit (lower than c) on how fast one can travel away from a light source.

xantox
Gold Member
That is correct, invariance of the Planck energy scale could require at least a modification of special relativity so that blueshifting is only possible asymptotically up to Planck energy (or so that Planck length may not be Lorentz-contracted into a smaller length, etc). At worst, special relativity could break completely at this scale.

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in Doppler's effect, the frequency goes to infinity as one approaches a light source close to the speed of light... so if there is a limit on how high frequency goes and Doppler's effect is correct, then there is limit (lower than c) on how fast one can travel toward a light source. similarly, if there is a lower bound on frequency, then there is a limit (lower than c) on how fast one can travel away from a light source.
So what happens in a photon-photon collision? There should be infinite frequencys involved?

lightarrow:
Infinities are very frequently serious problems in physics.

actually if you pump enough energy into a photon it will entually become a different kind of boson, I forgot the particulars however.
This doesn't sound correct. No matter how great the energy of a photon is, there is always another frame, where the energy is arbitrarily small. If a photon could change into another particle, it should not depend on the chosen frame.

lightarrow:
Infinities are very frequently serious problems in physics.
Certainly. I didn't mean that tim_lou's conclusion have to be wrong, I know doppler effect equation and how it works. Mine was just a question.
Of course I know that a reference frame where a photon is stationary doesn't exist, but what he said makes one think! it's an interesting consideration!

(Nice the joke with "frequently"!)