What is the longest wave-lenght of a photon?

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Discussion Overview

The discussion revolves around the concept of the longest wavelength of a photon, exploring theoretical limits, practical considerations, and the nature of photons as quantum entities. Participants examine the implications of wavelength in the context of electromagnetic waves and detection challenges.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants suggest there is no simply defined upper limit for the wavelength of light, with one proposing the length of the universe as a practical limit.
  • Others question the rationale behind the universe's length being a limit, noting that radio waves can have wavelengths much larger than physical spaces.
  • A participant mentions that in cases of black holes and distant regions of the universe, wavelengths may be redshifted into infinitely long wavelengths.
  • It is argued that photons do not 'have a wavelength' in a classical sense, as they are quantum entities, and that the associated electromagnetic wave has a wavelength instead.
  • Some participants highlight that while there is no fundamental maximum for wavelength, very low frequency electromagnetic waves correspond to low energy photons, making detection increasingly difficult.
  • Concerns are raised about the practical challenges of generating and detecting very low frequency signals, with one participant noting the need for large antennas to intercept such signals.
  • Another participant counters that generating low frequency signals is not inherently difficult, but emphasizes the importance of signal-to-noise ratio in detection.
  • Discussion also touches on the relationship between electromagnetic waves and their propagation, particularly in guided systems versus free space.
  • One participant states that electromagnetic theory imposes no upper limit on wavelength, while another mentions that generating a wave of infinite wavelength would take an infinite amount of time.
  • Questions are raised about the smallest frequency of an electromagnetic wave, with responses indicating that the smallest frequency is theoretically zero.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the longest wavelength of a photon, the implications of quantum mechanics on the concept of wavelength, and the practical challenges of detection. The discussion remains unresolved with no consensus reached.

Contextual Notes

Limitations include the dependence on definitions of wavelength and frequency, as well as unresolved mathematical implications regarding the generation and detection of low frequency electromagnetic waves.

meyol99
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What is the longest wave-lenght of a photon particle in the nature and can it be longer?
 
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There is no simply defined upper limit for the wavelength of light. I suppose one mught argue the length of the universe is a practical limit.
 
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Why would the length of the universe be a limit? I am sure there are radio waves in my room right with wave lengths much bigger than my room. Am I missing something?

Also, in the cases of black holes and places in the universe too far away for us to view, aren't these red shifted into infinitely long wavelengths?
 
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In theory there is no longest wavelength. As a practical matter, the length of the universe may be the longest in existence.
 
Mevludin Licina said:
What is the longest wave-lenght of a photon particle in the nature and can it be longer?
Your question is fundamentally flawed, I'm afraid because it's harder than that, in fact. Photons do not 'have a wavelength'. They are not classical particles but quantum entities. What you 'are allowed' to say is that the EM wave they are associated with, has a wavelength. There is no fundamental maximum for wavelength but EM at very low frequencies has very low energy photons and becomes harder and harder to detect because you just can't make receiving equipment that can 'extract' the signal out of the space it's traveling through. (The antenna would have to be several thousand km long to intercept a 50Hz signal)
 
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sophiecentaur said:
Your question is fundamentally flawed, I'm afraid because it's harder than that, in fact. Photons do not 'have a wavelength'. They are not classical particles but quantum entities. What you 'are allowed' to say is that the EM wave they are associated with, has a wavelength. There is no fundamental maximum for wavelength but EM at very low frequencies has very low energy photons and becomes harder and harder to detect because you just can't make receiving equipment that can 'extract' the signal out of the space it's traveling through. (The antenna would have to be several thousand km long to intercept a 50Hz signal)
In addition they would be very hard to generate.
 
sophiecentaur said:
Your question is fundamentally flawed, I'm afraid because it's harder than that, in fact. Photons do not 'have a wavelength'. They are not classical particles but quantum entities. What you 'are allowed' to say is that the EM wave they are associated with, has a wavelength. There is no fundamental maximum for wavelength but EM at very low frequencies has very low energy photons and becomes harder and harder to detect because you just can't make receiving equipment that can 'extract' the signal out of the space it's traveling through. (The antenna would have to be several thousand km long to intercept a 50Hz signal)
why can battery-operated amplifiers and oscilloscopes pick up the mains noise (50 Hz in Europe) when you touch the input cable?
 
mathman said:
In addition they would be very hard to generate.
Not at all hard to generate - all you need to do is to move electrons around with a low frequency electric field. The problem is to generate and radiate enough power at that frequency to be detected remotely in the presence of the ubiquitous noise. All problems in life come down to Signal To Noise Ratio. :smile:
 
derek10 said:
why can battery-operated amplifiers and oscilloscopes pick up the mains noise (50 Hz in Europe) when you touch the input cable?
Because the em wave is not a 'launched wave, traveling free through space but guided on the wire. To launch a significant level of signal into space. from a circuit, it has to be 'matched', which requires a radiating structure that's not much smaller than one wavelength. A wire / person link is a totally different situation.
 
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EM theory imposes no upper limit.
It will take an infinite time to generate a wave of infinite wavelength.
What on Earth (or in the universe) do you have in mind with this question?
 
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The other variant of my question would be what is the smallest frequency of an EM wave
a) in general ?
b) detetected ?
 
  • #12
Same answers. The smallest frequency is zero (as far as EM theory is concerned) and it would take an infinite time to detect it.
 

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