Photon Duration & Wavelength: Exploring the Mysteries

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In summary, the conversation discusses the concept of photons and their behavior in electromagnetic (EM) waves. The expert explains that photons are quantum particles and cannot be understood in a classical way. They are not like the carrier of an AM station, but rather similar to a Keyed Morse Code transmission. The length of a burst of photons, the frequencies in it, and the amplitude of the EM field all depend on the source that's generating the wave. The energy and frequency are used to characterize a photon, and they also have angular momentum. The expert recommends reading Feynman's "QED: The strange theory of light and matter" for a better understanding of photons.
  • #1
Averyuniquename
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Perhaps this a question that make no sense or has no answer but...
I understand an EM wave is not like the carrier of an AM station but rather similar to a Keyed Morse Code transmission. In other words bust of trains ow waves
If my description is correct
How long the burst last?
How many wavelenghts it contains?
I know the photon energy is determined by the frequency but there are different solutions.
Is the energy determined by the length of duration, or by the amplitude of the EM field?
What is the order of magnitude of the EM field amplitude?
 
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  • #2
Averyuniquename said:
I understand an EM wave is not like the carrier of an AM station but rather similar to a Keyed Morse Code transmission. In other words bust of trains ow waves
You're right, the question "How long is a photon?" doesn't make sense. But neither does this part - radio transmissions like the carrier of an AM station are EM waves.
If my description is correct
How long the burst last?
How many wavelenghts it contains?
I know the photon energy is determined by the frequency but there are different solutions.
Is the energy determined by the length of duration, or by the amplitude of the EM field?
What is the order of magnitude of the EM field amplitude?
The behavior of the EM field in a wave is described by Maxwell's equations from classical physics; photons aren't involved and introducing them only adds confusion. The length of a burst of EM radiation, the frequencies in it, and the amplitude of the EM field all depend on the source that's generating the wave.
 
  • #3
You have asked "that question" that causes people most trouble when they want photons to be 'familiar' objects. Photons are not like that. They are Quantum Particles and not little bullets (or even long ones). They have no Extent and you could say they only exist whilst they are interacting at each end. The Energy is carried by a wave. You just can't think classically; you don't need to. The 'length of time' i think has to depend on which particular system they interact with - like the bandwidth and rise times of a conventional receiver. But that's much too classical really.
And welcome to p f btw.
 
  • #4
Thanks for your answers
I wrote "I understand an EM wave is not like the carrier of..." Sorry but that is not what I meant to write and confused people.
I wanted to write Photon instead of EM Wave.
If an atom emit a photon something must be able to be said about.
Is a Photon a EM wave? We talk about wave length and frequency. Can we say a Photon has a polarization? Does it interact instantly or take a finite time to that?
 
  • #5
What quantity is used to characterize a photon?
 
  • #6
George Jones said:
What quantity is used to characterize a photon?
Energy and frequency or are you implying there are no characteristics ascribed to it, other than speed?
 
  • #7
Is energy related to (spatial) momentum?
 
  • #8
I understand you think you are posting stimulating questions but you are not helping. If I posted a inappropriate question, like what gender are angels, then stir me in a direction that leads to better understanding.
 
  • #9
If you're trying to ask what a photon is, you could give this thread a try: https://www.physicsforums.com/threads/what-is-a-photon.879128/#post-5522356

And yes... "How long is a photon?" is indeed like asking about the gender of angels.

Often when people first hear that photons are "particles" they form a mental model that light is made up of photons the way a flowing river is made up of water molecules, that there's a stream of photons moving from the light source to whatever is illuminated by that light. That mental model feels natural, but it's hopelessly misleading. A better (but still imperfect - there's no substitute for a proper quantum electrodynamics textbook) model says that photons appear when electromagnetic radiation interacts with matter.

Feynman's "QED: The strange theory of light and matter" is the only layman-friendly equation-free description of QED that I know of. A key point in Feynman's treatment is the that the theory is not about photons moving through space from one point to another, but about the probability of a photon being detected (that is, it delivers a quantum of energy to something) at a given point in space.
 
Last edited:
  • #10
George Jones said:
Is energy related to (spatial) momentum?
Yes, for a photon in vacuum, E = cp
Photons also have angular momentum.
 
  • #11
Nugatory said:
If you're trying to ask what a photon is, you could give this thread a try: https://www.physicsforums.com/threads/what-is-a-photon.879128/#post-5522356

And yes... "How long is a photon?" is indeed like asking about the gender of angels.

Often when people first hear that photons are "particles" they form a mental model that light is made up of photons the way a flowing river is made up of water molecules, that there's a stream of photons moving from the light source to whatever is illuminated by that light. That mental model feels natural, but it's hopelessly misleading. A better (but still imperfect - there's no substitute for a proper quantum electrodynamics textbook) model says that photons appear when electromagnetic radiation interacts with matter.

Feynman's "QED: The strange theory of light and matter" is the only layman-friendly equation-free description of QED that I know of. A key point in Feynman's treatment is the that the theory is not about photons moving through space from one point to another, but about the probability of a photon being detected (that is, it delivers a quantum of energy to something) at a given point in space.
Nugatory said:
If you're trying to ask what a photon is, you could give this thread a try: https://www.physicsforums.com/threads/what-is-a-photon.879128/#post-5522356

And yes... "How long is a photon?" is indeed like asking about the gender of angels.

Often when people first hear that photons are "particles" they form a mental model that light is made up of photons the way a flowing river is made up of water molecules, that there's a stream of photons moving from the light source to whatever is illuminated by that light. That mental model feels natural, but it's hopelessly misleading. A better (but still imperfect - there's no substitute for a proper quantum electrodynamics textbook) model says that photons appear when electromagnetic radiation interacts with matter.

Feynman's "QED: The strange theory of light and matter" is the only layman-friendly equation-free description of QED that I know of. A key point in Feynman's treatment is the that the theory is not about photons moving through space from one point to another, but about the probability of a photon being detected (that is, it delivers a quantum of energy to something) at a given point in space.
Thanks, that was helpful.
 
  • #12
Khashishi said:
Yes, for a photon in vacuum, E = cp

I was trying to use the Socratic method to illustrate that photons are characterized by precise values of momenta, and thus cannot be characterized by positions along something like a classical trajectory.
 
  • #13
George Jones said:
I was trying to use the Socratic method to illustrate that photons are characterized by precise values of momenta, and thus cannot be characterized by positions along something like a classical trajectory.
OK thanks. So since the momentum is known the position uncertainty is infinite, therefore it can be anywhere or nowhere. It make no sense to confine it in space.
 
  • #14
Averyuniquename said:
OK thanks. So since the momentum is known the position uncertainty is infinite, therefore it can be anywhere or nowhere. It make no sense to confine it in space.

Yes, this is what I was trying to at, but I suspect that his is just hand-waving. I sometimes like hand-waving arguments, but I also like what Griffiths wrote in his elementary particles book,"When you hear a physicist invoke the uncertainty principle, keep a hand on your wallet." :biggrin:

At a substantially more technical level, there isn't a position operator for photons.
 
  • #15
The problem here is that this is all about the "position" operator, and not a "size" operator. There is no "size" operator here that can immediately spits out a value upon measurement.

An off-shoot of what George Jones did here is to ask you for ALL the properties and characteristics of "a photon". We can define its momentum, it's wavelength, etc... etc... But nowhere in the complete list of characteristics here is there anything resembling a "size" or volume. A photon is never defined as having such a thing.

So yes, when you ask for a length or a size, you ARE asking about the gender of angels, because a photon is never defined that way.

Zz.
 
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  • #16
I think of it this way: if a photon were generated by one particular source (a particular atom with a particular transition) then everything about that transition would need to be the same for another different atom with a different electron arrangement or the photon could be 'too long or too short' to be absorbed. But EM energy is transferred perfectly well from one system to another.
So Photons have to be identical and with a few characteristics as possible - i.e. their energy and nothing more.
 
  • #17
Averyuniquename said:
Perhaps this a question that make no sense or has no answer but...
I understand an EM wave is not like the carrier of an AM station but rather similar to a Keyed Morse Code transmission. In other words bust of trains ow waves
If my description is correct
How long the burst last?
How many wavelenghts it contains?
I know the photon energy is determined by the frequency but there are different solutions.
Is the energy determined by the length of duration, or by the amplitude of the EM field?
What is the order of magnitude of the EM field amplitude?

The strange thing about this whole thread, and the reason why I didn't join in the "fun" from the very beginning is that, the original post has a rather significant misunderstanding. If you read the post carefully, the part where the OP mentioned "bust (sic) of trains ow (sic) waves" and "How long the burst last", this is NOT the "size of a photon", but rather the pulse length of the EM wave!

This is what I found rather odd, because radio and TV transmission is cw, not in pulse mode. The beginning premise, at least according to me, was completely false, and it made the rest of the discussion rather strange.

Zz.
 
  • #18
ZapperZ said:
radio and TV transmission is cw, not in pulse mode.
There are plenty of 'pulses' in TV signals and even in some Audio programmes. But the times of those pulses are longer than 1ns.

I do agree that the OP was very imprecise in the way the question was formed, though. The idea that a received CW signal consists of string of photons (once it hits the receiver, that is) is not too ridiculous.
 
  • #19
sophiecentaur said:
They have no Extent and you could say they only exist whilst they are interacting at each end.

How do you explain the interference pattern in the double-slit experiment with single photons without extend?
 
  • #20
DrStupid said:
How do you explain the interference pattern in the double-slit experiment with single photons without extend?
No defined extent. Where are you trying to take this?
 
  • #21
sophiecentaur said:
No defined extent.

That's something different than "no Extent".

sophiecentaur said:
Where are you trying to take this?

Your answer shows that you already got it.
 
  • #22
DrStupid said:
Your answer shows that you already got it.
:smile:
 

Related to Photon Duration & Wavelength: Exploring the Mysteries

1. What is a photon's duration?

A photon's duration refers to the amount of time it exists as a particle before it is either absorbed or released by an atom or molecule. This duration is extremely short, typically measured in nanoseconds (10^-9 seconds).

2. How is a photon's duration related to its wavelength?

A photon's duration is directly related to its wavelength. The shorter the wavelength, the higher the energy and the shorter the duration. This is because the wavelength of a photon is inversely proportional to its frequency, and higher frequency photons have more energy and therefore have shorter durations.

3. How does the duration of a photon impact its behavior?

The duration of a photon plays a crucial role in its behavior. For example, in the double-slit experiment, the duration of a photon determines the amount of time it takes for the photon to travel from the source to the detector, and this affects the interference pattern observed. In addition, the duration of a photon can also determine its interactions with other particles and how it is affected by external forces.

4. Can the duration of a photon be measured?

Yes, the duration of a photon can be measured using advanced techniques such as ultrafast laser spectroscopy. This involves using short laser pulses to create and detect changes in the energy levels of atoms or molecules, allowing for the measurement of a photon's duration.

5. How do scientists study the mysteries of photon duration and wavelength?

Scientists use a variety of experimental techniques, such as spectroscopy, interferometry, and quantum optics, to study the behavior of photons and their duration. They also use mathematical models and theories, such as the wave-particle duality of light, to understand and explain the mysteries of photon duration and wavelength.

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