What Happens When Two Identical Photons Travel Parallel in a Vacuum?

[slow]

Hi. Maybe you can help me understand something. Two identical photons travel parallel in a vacuum. I want the lines of their trajectories to be as close to each other as possible.

1. If each photon could observe the other, what would it detect?

2. Is there a minimum separation necessary to prevent photons from collapsing? Or do they never collapse, regardless of how much separation there is between the two lines?

 

[Drakkith]

1. If each photon could observe the other, what would it detect?

This is impossible, so any answer given would be wrong.

2. Is there a minimum separation necessary to prevent photons from collapsing? Or do they never collapse, regardless of how much separation there is between the two lines?

What do you mean by "collapsing"?

 

[sophiecentaur]

Two identical photons travel parallel in a vacuum. I want the lines of their trajectories to be as close to each other as possible.

This is not a model of the photon that works, I'm afraid. The location and size of a photon are not quantities that have any meaning at all. The only occasion when you can say a photon 'is there' is whist it is interacting with an Atom (or many atoms at a time) with a known position. If yo want a narrow beam then you have to approach this with wave theory and conventional optics.

 

[slow]

Hi, Drakkith. I used the word collapse to include any event that starts with two individual photons traveling parallel and ternime with something different, that is, something that is not a pair of parallel individual photons.

Hello sophiecentaur. The initial note of this thread does not mention a photon model. Within what I have been taught, until now we only have the mathematical formulation of some properties of the photon, as energy directly proportional to frequency, spin always equal to a universal constant, phase, polarization, that type of data that are formulated abstractly, without resorting to a physical model. I asked about the separation of the lines, because I do not know what happens with respect to the trajectory. I do not know to what extent there may or may not be uncertainty in the trajectory, so that it may not make sense to imagine a line for each photon and we must imagine something like a cylindrical region whose axis is the line we classically call a ray in the propagation. Instead of pointing to a model, my question points to what I do not know.

 

[Drakkith]

Hi, Drakkith. I used the word collapse to include any event that starts with two individual photons traveling parallel and ternime with something different, that is, something that is not a pair of parallel individual photons.

Well, photons don't interact with each other very well, so you'd be unlikely to get any such event at all.

Hello sophiecentaur. The initial note of this thread does not mention a photon model. Within what I have been taught, until now we only have the mathematical formulation of some properties of the photon, as energy directly proportional to frequency, spin always equal to a universal constant, phase, polarization, that type of data that are formulated abstractly, without resorting to a physical model.

If by "physical model" you mean a model that makes intuitive sense based on our own experiences of life at our own scale, then there is no such model that accurately describes photons. One of the biggest barriers to learning about quantum physics for most people is that common sense and intuition just don't apply to physics at the atomic scale. Things like the uncertainty principle and complementarity aren't observable at the macro scale, so our brains never have a chance to get used to them at an early age and form an intuitive understanding.

I asked about the separation of the lines, because I do not know what happens with respect to the trajectory. I do not know to what extent there may or may not be uncertainty in the trajectory, so that it may not make sense to imagine a line for each photon and we must imagine something like a cylindrical region whose axis is the line we classically call a ray in the propagation. Instead of pointing to a model, my question points to what I do not know.

What happens to a photon prior to being detected is mostly unknown and mostly unknowable. However, we know that photons cannot be said to have a trajectory in the classical sense, as wave diffraction leads to some very strange observations that a classical model of a particle with a well defined trajectory just cannot explain. And that's before we even throw in quantum tunneling and other quantum effects. Usually when we talk about the path of a photon, we are using shorthand for the path through space that you would be most likely to detect a photon.

 

[sophiecentaur]

Hello sophiecentaur. The initial note of this thread does not mention a photon model.

Two identical photons travel parallel in a vacuum. I want the lines of their trajectories to be as close to each other as possible.

I don't understand. You ask a question about photons but deny that you are mentioning photons. OR do you have a problem with the word "model"? The fact that you are introducing photons means you are working to a 'model' but you are not using a valid photon model from the very start.