What Is the Diameter of a Photon?

[LightningInAJar]

What diameter does a photon have? Does it vary and if so within what range?

 

[BvU]

Hi,

Can you please share with us your definition of 'diameter' in the context of photons ?

And give us a clue at what level you want your answer ?



More links etc in:

Summary:: Interesting video about interpreting 'single photon' interference experiments

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[LightningInAJar]

Hi,

Can you please share with us your definition of 'diameter' in the context of photons ?

And give us a clue at what level you want your answer ?



More links etc in:$\$

Interesting video, but honestly don't understand much of it. Is a photon unlimited in size or 0 dimensional? I am trying to imagine how many photons can be laid next to one another to produce the maximum amount of perceptible visual information from the physical world. I think biologically an eagle's eye might be around the biological limit at 4 to 5 times the visual acuity of a human in that its retina actually needs to pucker mechanically so light doesn't hit flush but at an angle as to activate more photoreceptors. But in terms of camera sensirs with any lens at its disposal I am curious basically what the resolution of reality must be in the visible spectrum.

 

[PeterDonis]

Is a photon unlimited in size or 0 dimensional?

A photon isn't a little ball with a well-defined size, nor is it a point particle. The questions you are asking aren't even well-defined and don't have meaningful answers.

The only real "size" that has meaning for a photon is its wavelength, and that is frame dependent.

 

[LightningInAJar]

A photon isn't a little ball with a well-defined size, nor is it a point particle. The questions you are asking aren't even well-defined and don't have meaningful answers.

The only real "size" that has meaning for a photon is its wavelength, and that is frame dependent.

Can it only be represented as a long vibrating cylinder shape?

 

[PeterDonis]

Can it only be represented as a long vibrating cylinder shape?

I have no idea where that is even coming from. A photon doesn't have a "shape". It's nothing like an ordinary object.

 

[PeterDonis]

I am trying to imagine how many photons can be laid next to one another to produce the maximum amount of perceptible visual information from the physical world.

This is the wrong way to think about it. The acuity of visual information depends on the size of the detecting elements (such as the rod and cone cells in your retina, or the CCD "pixels" in a digital camera's detector, or the size of the individual light-sensitive particles in photographic film) and the wavelength of the light. But the wavelength of the light is not the same as the "size" of any little ball or other ordinary object.

 

[LightningInAJar]

This is the wrong way to think about it. The acuity of visual information depends on the size of the detecting elements (such as the rod and cone cells in your retina, or the CCD "pixels" in a digital camera's detector, or the size of the individual light-sensitive particles in photographic film) and the wavelength of the light. But the wavelength of the light is not the same as the "size" of any little ball or other ordinary object.

If we can't know a photon's size how do we know how many photo sensors it is stimulating? If big enough it could hit more than one?

 

[PeroK]

If we can't know a photon's size how do we know how many photo sensors it is stimulating? If big enough it could hit more than one?

Even if you know nothing else about a photon, you should know that it is a quantum of light. Its interaction with matter is all or nothing.

Your thoughts and questions in this thread are simply not quantum mechanical in nature.

 

[vanhees71]

As is explained in the video quite well, a photon is a specific state of the electromagnetic field as described with relativistic quantum field theory. Since it is a massless field with spin 1, it is not possible to even define a position observable as you always can for massive fields.

What's observable are the probabilities to observe a photon with some detector at a "place" of finite resolution, which is roughly given, e.g., by the pixel size of a CCD camera (like a webcam or the camera of your smartphone).

The best intuitive picture of a photon thus is in terms of a electromagnetic wave rather than a kind of localized particle. The detection probability is proportional to the energy density of the electromagnetic field in close analogy to the "intensity of light" in classical electromagnetism.

 

[mattt]

I am trying to imagine how many photons can be laid next to one another to produce the maximum amount of perceptible visual information from the physical world.

Is planet Jupiter sad because his nephew didn't win Wimbledon last year?

See that not every possible question is a meaningful question.

 

[Spinnor]

In a way that might answer your question consider if you want to make a detailed astronomical map of the night sky like the early astronomers did, you can do a pretty good job with the human eye and the right tools, bright objects in the sky could be mapped by early astronomers with great precision, (experts please chime in with an estimate). To do better you might want a large space based telescope. Telescope "size" and the detector resolution now limit your precision, (experts please chime in again with an estimate).

Similar questions like your have been asked many time including at Physics Forums, see

https://www.physicsforums.com/threads/just-how-big-is-a-photon.555379/

Found in this Google search, "how big is a photon".

Edit, with some thought it seems both cases, the eye and the telescope, what is important, besides the detector, is called the diffraction limit of a telescope, your eye being a small telescope, see Google search, "diffraction limit of a telescope".

https://www.google.com/search?q=dif...7j0i512l9.11263j0j15&sourceid=chrome&ie=UTF-8

 

[PeterDonis]

If we can't know a photon's size how do we know how many photo sensors it is stimulating? If big enough it could hit more than one?

A single photon will never be received by more than one sensor. Photons are quantum mechanical, as others have commented.

 

[sophiecentaur]

Can it only be represented as a long vibrating cylinder shape?

It's really best not to think in terms of a picture of a photon. The only time that a photon can be said to have 'been' anywhere is when it interacts with something. You can have no idea 'where' it was during the time delay between the emission of a photon and the detection of a photon. Bear in mind that a beam of light passing through a hole will have a diffraction pattern all around the edges. That implies something about the region over which a single quantum of that beam's energy (i.e. a photon) can be pretty big in wavelength terms. In fact, to work out the diffraction pattern, you really need to integrate from +∞ to -∞. Photons don't interact so that means every photon has to be regarded as being everywhere at some time. Not the sort of thing you could draw so not a lot of hope of visualising it.

A single photon will never be received by more than one sensor. Photons are quantum mechanical, as others have commented.

To add to the confusion, one photons worth of light going through a lens must be interacting with all the glass for it to arrive at a statistically likely place (i.e. the Image). So the massive lens and the photon must 'know about each other'; it's not just one atom and one photon in the system.

 

[LightningInAJar]

Baffling. It's hard to imagine something that interacts with matter that shares so few of its properties. Kind of like it doesn't really exist in our world?

 

[DaveC426913]

Baffling. It's hard to imagine something that interacts with matter that shares so few of its properties. Kind of like it doesn't really exist in our world?

The physics of nature at its smallest scale often has very poor analogies at our human-centric scale. Don't try to force analogies where there are none. Study it on its own merits.

 

[PeterDonis]

It's hard to imagine something that interacts with matter that shares so few of its properties.

The questions you are asking don't make much more sense for matter (i.e., particles with nonzero rest mass) than they do for photons. There is no one well-defined "size" for an electron any more than there is for a photon.

Kind of like it doesn't really exist in our world?

Nonsense. There are a huge number of directly observable phenomena that show that photons exist.

 

[CoolMint]

Baffling. It's hard to imagine something that interacts with matter that shares so few of its properties. Kind of like it doesn't really exist in our world?

Upon measurement/interaction, you can bet it 100% exists. Outside this narrow context, photons are best treated as quanta of the electromagnetic fields.

 

[sophiecentaur]

Kind of like it doesn't really exist in our world?

We can say that it doesn't exist in a form that we are familiar with. Its whole scale is so far outside out experience that it doesn't fit any of our cosy analogies with familiar objects.
All you can say is that there's something that exhibits certain properties (interacts with some less etherial parts of our experience).
It's the Duck argument again: if it behaves like a duck then we can say it's a duck etc.. All we can do is work with it as if it's a duck but that requires crossed fingers behind our back because, suddenly we can find it's not a duck. Panic panic.

 

[PeterDonis]

Moderator's note: A number of off topic posts have been deleted.

 

[BvU]

Interesting video, but honestly don't understand much of it.

I appreciate your honesty. From the later posts I sense interest and curiosity on the subject of the behaviour of light/photons, so we might try to find an inroad on a more accessible level. I highly recommend Richard Feynman's 'try-out'/layman lectures, given in Auckland (NZ) 1979. A solid block of six hours of physics with a big part dedicated to photons.

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[LightningInAJar]

I appreciate your honesty. From the later posts I sense interest and curiosity on the subject of the behaviour of light/photons, so we might try to find an inroad on a more accessible level. I highly recommend Richard Feynman's 'try-out'/layman lectures, given in Auckland (NZ) 1979. A solid block of six hours of physics with a big part dedicated to photons.

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I will check it out. Hopefully on YouTube also as that site doesn't appear secure.

 

[berkeman]

I will check it out. Hopefully on YouTube also as that site doesn't appear secure.

feynman.com doesn't appear secure to you?

 

[LightningInAJar]

feynman.com doesn't appear secure to you?

Doesn't seem to use encryption.

 

[BvU]

Doesn't seem to use encryption.

Huh ?
Google 'feynman lecture auckland' and get 3 out of 4 on youtube. Better ?

 

[berkeman]

Huh ?
Google 'feynman lecture auckland' and get 3 out of 4 on youtube. Better ?

In fairness, I see now that my Firefox browser does show a warning about the link that was posted, saying that it's not secure. The little bitty warning icon was not obvious to me when I first clicked into the link.