Does the force of a single photon act in 1 dimension?

[jcatom]

If it does, is there a way to calculate what the force of a single photon would be if it were acting in 3 dimensions?

 

[jedishrfu]

particles absorb photons and change energy states so I guess there's some momentum transfer but we don't think of a photon as providing a force on something.

I do know that they talk about sunlight pushing against a sail as a means to travel in outer space:

http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/sunlight_exerts_pressure.htm

perhaps you can determine it from this article.

 

[jcatom]

I'm pretty poor with using the correct terminology. Maybe I can rephrase and the question will make more sense.

The fundamental interactions, in this case the electromagnetic interaction, have a strength relative to each other.

So maybe the word is 'strength' instead of 'force' (the photon is sometimes called the force-carrier of the electromagnetic interaction, which is why I got confused).

 

[jcatom]

Maybe this is better--dropping the reference to single photons:

Gravitation occurs in 3 spatial dimensions. Does electromagnetism occur in only 1 spatial dimension?

If I'm framing this question correctly and if electromagnetism does occur in 1 spatial dimension, would there be a way to calculate its strength if it were to occur in 3?

 

[tom.stoer]

The formulation of a QFT depends on the spatial dimension D. For the el.-mag. interaction and the gravitational interaction you have a 'potential'
D=1: linear
D=2: logarithmic
D=3,4,...: ~ r^-(D-2)

You cannot say anything referring the relative strength.

 

[jcatom]

I've seen in several places that gravitation as a fundamental force is weak compared to electromagnetism. If gravity=1 then EM=10^36.

What I'm asking is: if EM is linear, could there be a calculation to find what it's strength...or potential would be if it were like gravity and acting in 3 spatial dimensions at once?

 

[jedishrfu]

I've seen in several places that gravitation as a fundamental force is weak compared to electromagnetism. If gravity=1 then EM=10^36.

What I'm asking is: if EM is linear, could there be a calculation to find what it's strength...or potential would be if it were like gravity and acting in 3 spatial dimensions at once?

I still don't understand why you keep going back to the 1 dimensional case. We live in a 3D world where gravity and EM emanate in all directions from a source.

Are you thinking about a StarTrek tractor beam or a laser? These would be directed along a line.

 

[jcatom]

That's why I initially referred to a single photon, which goes in a single direction. Or, is absorbed at a single point. I know that it acts like a wave before that.

 

[jcatom]

Let's try it as a thought experiment (please forgive me if I use the wrong terms, I'll do my best to clarify if needed).

If we have some massive object like a planet, a rock or something that is perfectly spherical and then measure out some radius from the center there would be an imaginary sphere at that distance around the object.

The gravity of the massive object would be 'felt' equally by an object located at any point located on that spherical plane.

This central massive object is also radiating light and if a single photon could and were to interact with the imaginary sphere this interaction would take place at a single point.

I'm asking if that single photon radiated outward from the massive object in the way that gravity does, in all three spatial dimensions at once, what would be the difference in force, strength, or whatever term works here compared to the force or strength of the point-like photon?

 

[chill_factor]

how do you know the photon is NOT propagating outwards in 3-D? Can you detect that photon while its in flight? no. can you detect that photon without destroying it? no. so how do you know that photon is not everywhere in 3-D all at once, and that once you detect it, its gone?

 

[jcatom]

I know that it is considered to be everywhere at once until it is detected. But when it is detected it is at a single point.

The question is if it could be detected at all points on the imaginary spherical plane at once (which I know it can't) what would the difference in strength be as compared to the single point which we detect in reality?

 

[jedishrfu]

I know that it is considered to be everywhere at once until it is detected. But when it is detected it is at a single point.

The question is if it could be detected at all points on the imaginary spherical plane at once (which I know it can't) what would the difference in strength be as compared to the single point which we detect in reality?

I think the best you're going to get is the NASA article I posted earlier about solar pressure where you could try to determine the effect of one photon on an object.

 

[jcatom]

So Wikipedia may be a hated thing to reference by some or all, but when I talk about strength there's a good chart here that shows what I'm talking about. The 'relative strength' mentioned in this chart is the same as what I've read in several other places about the befuddling weakness of gravity.

http://en.wikipedia.org/wiki/Fundamental_force#Overview

 

[jedishrfu]

Okay, I think the chart is referring to the force felt from a charged source or the magnetic field felt from a magnetic source not the force felt from a single photon.

So for example, two electrons would repel each other 10^38 times more than they would attract.

 

[jcatom]

More than they would attract through gravitation?

 

[jedishrfu]

More than they would attract through gravitation?

yes electric field is 10^38 times stronger than gravitation

 

[jcatom]

So from another page:

"In [URL='https://www.physicsforums.com/insights/paqft-idea-references/']perturbative quantum field theory, the forces between particles are mediated by other particles. The electromagnetic force between two electrons is caused by an exchange of photons."[/URL]

 

[jedishrfu]

JC I think this thread has run its course.

We just don't know the answer to what you're asking. In the article you referenced yes photons are mediators of EM field but given that its QM you can't start to think in a Classical Mechanical way about a single photon pushing the other particle.

Do you see what I mean? I can't explain it further I'm not a PhD level physicist.

I do hope you got some insight out of the thread that can help answer your question in the future but I think we've run out of stuff to say.

 

[jcatom]

Well, thanks for trying.

My disconnect comes when I read about the quanta of the electromagnetic field (photons) carrying the force between particles. That through the exchange of photons the energy contained in the electromagnetic field is moved from one place to another. I know that it isn't thought to bounce off of the other particle--that a photon is emitted from one particle then absorbed by another particle which then becomes more energetic or emits a photon of its own and so on. It is the means for exchanging energy between particles that are separated. It must do something.

 

[ZapperZ]

The problem here is that you are asking about quantum field theory, but trying to learn it in a handwaving fashion. So inevitably, many of us try to answer it via analogies. While doing it this way might have some benefits, it really isn't a very accurate picture of the physics. So at some point, if you want to dig in deeper, you need to decide if you really need to learn the actual physics. There are limits to what can be done superficially here.

Zz.

 

[jcatom]

I'm not trying to convince anyone of anything, just trying to understand. I'm also not trying to bug anyone. I've read a lot over the years and have several questions, but seem to have trouble asking them correctly.

 

[jedishrfu]

one way you could look at this is suppose the sun issues one photon. It travels out in all directions as an EM wave and when the wave encounters a particle it collapses to a photon and is absorbed by the particle.

Imagine the sun to be a bees nest and the photon is a swarm of bees going out evenly spaced in all directions and one bee runs into a honey pot. The swarm is an EM wave.

The bee telepathically calls all the other bees to where he is (wave collapse). The honey pot now has a swarm of bees on it (particle captured the photon and gained some momentum and mass via higher energy from photon).

 

[jcatom]

Right, wave-particle duality. I've read about the double-slit experiments and how a single photon can even interfere with itself when it is in a wavelike state.

My question is about that moment/point of interaction--the collapse of the wave-function. When there is suddenly a single photon, does that interaction take place in a single spatial dimension? The photon has no mass so it's hard to see how it could be more than that. I'm leaving the time dimension out right now.

 

[ZapperZ]

Right, wave-particle duality. I've read about the double-slit experiments and how a single photon can even interfere with itself when it is in a wavelike state.

My question is about that moment/point of interaction--the collapse of the wave-function. When there is suddenly a single photon, does that interaction take place in a single spatial dimension? The photon has no mass so it's hard to see how it could be more than that. I'm leaving the time dimension out right now.

I am a bit puzzled on your obsession with "dimensions" here. Can you point out any physics in which the spatial dimensions plays a role in such interactions.

Take note that if you even just look at the geometry of such an interaction, you already need more than just one, unless you always confine things to be head-on collisions, which is often unlikely. So already you know that the dynamics must be described at least in 2D.

Take note that there's a distinct difference between something that moves in 1D versus something that lives in an exclusively 1D universe or space. The physics is very different (for example, look at the electronic density of states in 1D, 2D, and 3D). I think you are mixing those two and it makes it very confusing to figure out what exactly you are seeking here. It is also compounded by the fact that we keep having to take several steps backwards to be able to explain the physics of what you are using.

You might also want to take a look at our https://www.physicsforums.com/forumdisplay.php?f=209 in the General Physics forum, IF you think you are about to tackle this "particle-wave" duality.

Zz.

 

[jcatom]

I don't mind being wrong, but I'm not 'obsessed' with anything either. Nor do I think that disparaging remarks towards people here engender respect. 'Obsession' almost always carries a negative connotation.

Wouldn't a massive particle of the smallest size exert a gravitational 'pull' (which I know is not the right word) on every other massive particle around it? Gravity in the way that Einstein described it is a curvature of spacetime in 3D--not really like the dumbed-down 2D representation of a grid that has a hole in the middle that we often see.

 

[ZapperZ]

I don't mind being wrong, but I'm not 'obsessed' with anything either. Nor do I think that disparaging remarks towards people here engender respect. 'Obsession' almost always carries a negative connotation.

Wouldn't a massive particle of the smallest size exert a gravitational 'pull' (which I know is not the right word) on every other massive particle around it? Gravity in the way that Einstein described it is a curvature of spacetime in 3D--not really like the dumbed-down 2D representation of a grid that has a hole in the middle that we often see.

Yes, but what does that have anything to do with the discussion here? You asked if a single photon "acts" in 1D. I've given you an example (non-head on collision) in which one can see that the dynamics can't be confined to 1D. Doesn't that already answer your question?

So I am no longer sure what it is that you're trying to get at, since you already were given the answer. It may not be the answer you want, but Nature often doesn't care about what we want.

Zz.

 

[jedishrfu]

Yes, but what does that have anything to do with the discussion here? You asked if a single photon "acts" in 1D. I've given you an example (non-head on collision) in which one can see that the dynamics can't be confined to 1D. Doesn't that already answer your question?

So I am no longer sure what it is that you're trying to get at, since you already were given the answer. It may not be the answer you want, but Nature often doesn't care about what we want.

Zz.

Good ending point so let's close this discussion now.

 

[jcatom]

I was responding to this question "Can you point out any physics in which the spatial dimensions plays a role in such interactions."

Certainly didn't expect such animosity or condescension. Thanks I guess.

 

[jedishrfu]

I was responding to this question "Can you point out any physics in which the spatial dimensions plays a role in such interactions."

Certainly didn't expect such animosity or condescension. Thanks I guess.

Hi JC,

There's no animosity or condescension here. The thread has run its course. I don't think we know of a book that can answer this question directly.

The only thing I've seen is that mathematically for two dimensions forces like gravity would work as 1/r and for 3D its 1/r^2 and the higher you go to say dimension n then its 1/r^(n-1) strength. Basically the surface of an n dimensional sphere with the force radiating in all directions.

Try not to conflate the ideas and analogies used in Classical Mechanics with similar ideas in Quantum Mechanics. I think that's where you rconfusion lies but it seems we just don't have the necessary insight to help you overcome this.

Keep thinking.

Regards,

Jedishrfu

 

[MikeGomez]

Gravitation occurs in 3 spatial dimensions. Does electromagnetism occur in only 1 spatial dimension?

Jcatom, I think your mistake is that you are comparing the 3 dimensional falloff of gravitational strength with the 1 dimensional path of a single photon. This is an improper comparison. You must compare the 3 dimensional case for both, or 1 dimensional case for both, for a proper comparison.

-------------------------------------------------------------------------------
3 dimensional case: (I’ve drawn it in 2D not 3D, but you get the point)

The attached image is a 2d picture I made to represent the gravitational field around a planet. It gets weaker further from the planet by the inverse square law.

The attached image is also a 2d picture of a spherical light source showing irradiance, or flux density of the light. The strength falls off as the square of the distance from the source, exactly the same as gravitation.

You see, the inverse square law for gravity (or light) is not due to the nature of gravitation or light, it is due to the amount of gravitation or light per unit of area. The further from the emitting object, the more surface area you have with a given amount of gravitation or light.

-----------------------------------------------------------------------------
1 dimensional case:

A single photon of light does not diminish as the inverse square of the distance; rather it is the amount of photons per unit area which decreases. We don’t know the exact nature of gravitation, but if we image some photon or quantized unit of gravitation, that case would be the same as for your 1 dimensional light photon (i.e. it would not diminish with distance).
-----------------------------------------------------------------------------

 

[jcatom]

Keep thinking.

Regards,

Jedishrfu

I will and thanks again. I'll also do better about quoting so that the direction of my response is more obvious.

We don’t know the exact nature of gravitation, but if we image some photon or quantized unit of gravitation, that case would be the same as for your 1 dimensional light photon (i.e. it would not diminish with distance).

Thanks for the response.

The difference I see is that a photon is in some sense everywhere at once until it interacts with something. Upon interaction the wavelike photon is suddenly in one specific place in time and the dispersed energy is concentrated at that point.

Gravity doesn't seem to be like this at all. I know that there is the theoretical graviton, but nobody has figured that out. Would gravity suddenly be at a single point in time when it interacts with a massive body, taking the energy (or whatever the best term is) from a dispersed area and collapsing down to a single point in time?

 

[ZapperZ]

The difference I see is that a photon is in some sense everywhere at once until it interacts with something. Upon interaction the wavelike photon is suddenly in one specific place in time and the dispersed energy is concentrated at that point.

Gravity doesn't seem to be like this at all. I know that there is the theoretical graviton, but nobody has figured that out. Would gravity suddenly be at a single point in time when it interacts with a massive body, taking the energy (or whatever the best term is) from a dispersed area and collapsing down to a single point in time?

Where does it say that a photon is everywhere at once?

Zz.

 

[tom.stoer]

In one dimension the potential is linear, i.e. ~ |x-y|

In addition there is no photon in one dimension, except for a zero-mode. The reason is that gauge fixing eliminates always two polarizations, but in one dimension there are only two spacetime-directions, so the photon field can be gauged away.

What remains is a static Coulomb potential ~ |x-y| and a single quantum mechanical d.o.f.

 

[MikeGomez]

The difference I see is that a photon is in some sense everywhere at once until it interacts with something.

Why do you believe that? Please provide references.

If a photon were everywhere at once, there would be no "until it interacts with something" because it would already be interacting with everything everywhere. It doesn't make sense to me.

 

[jcatom]

Well in comment #22 of this thread jedishrfu says

one way you could look at this is suppose the sun issues one photon. It travels out in all directions as an EM wave and when the wave encounters a particle it collapses to a photon and is absorbed by the particle.

and chill_factor asks

so how do you know that photon is not everywhere in 3-D all at once, and that once you detect it, its gone?

Both, I assume, are talking about the same thing that I am. 'Everywhere at once' was a poor phrase to use. I'm talking about the wavefunction collapse.