[pensador (OP)]

Can a photon be visualized?

We can describe a photon as having both wave and particle properties, and predict mathematically what it will do.
The double slit experiment shows clearly it has wave properties.

Quote from: chiralSPO on 05/04/2019 17:32:11
We can use different models to account for the different speeds of light in different materials--one model essentially views the photon as being absorbed and re-emitted repeatedly, and one model just looks at the effective permittivities (both electric and magnetic), and uses that to calculate the speed of light. Both models predict the same speeds (as far as I know), but sometimes it is better to use one model than the other.

This is a little like something I was mulling over a little while ago, and never found any conclusive answers on. Can space be viewed as a material? Ie can a photon passing through free space, be viewed as being absorbed and re-emitted by virtual particles? Thus maybe re-producing a wave effect via a jittery movement through space from virtual particle to virtual particle ?  .

Does anything come out of Feynman diagrams on this? I have not found any answers from my searches.

[alancalverd]

The particle model doesn't predict the speed of light in vacuo because there is nothing there to absorb and re-emit particles.

Maxwell's equations show that you don't need any medium to transmit light, and imply that the speed of light in vacuo is independent of direction, with values of ε₀ and μ₀ chosen arbitrarily to rationalise the system of units in use - they don't refer to the properties of a medium but are the "fudge factors" that make electrostatics and electromagnetics mutually consistent.

[jeffreyH]

To describe observations the mathematics also has to be able to make predictions. These then can be tested and shown to agree with new observations or not. If a certain constant is required to produce those mathematics then it is used. There is no intention to explain why it is needed. It just works. How would you answer the why? How can anyone observe a vacuum?

[pensador (OP)]

Thanks for the replies. I understand the math and the predictions. But I don't think you answered my question

I know that the vacuum of space is not empty, it is full of virtual particles as predicted by the Heisenburg uncertainty principle, which are proven to exist via the Casimir effect. Virtual particles are also the basis for theoretical Hawking radiation around a black hole. ie the Vacuum of space is not empty, this is a known and accepted factoid in the standard models.

Maxwells equations are applicable at the classical level not the quantum level, I was trying to visualize the photon at the quantum level moving through space which is full of virtual particles.

Can a photon passing through free space full of virtual particles, be viewed as being absorbed and re-emitted by the virtual particles? Thus maybe re-producing a wave effect via a jittery movement through space from virtual particle to virtual particle ? A photon will collide or plough through all the quantum foam, so it seems reasonable that it may be being absorbed and reemitted by virtual particles as it whizzes along in some way 

Non local effects observed in entangled photons can not explain the wave effects seen in the double slit experiment, yet if the double slit experiment is performed in multiple separate labs by firing a single photon through the slits, and the results brought together, the wave effect is still observed. Absorbtion and emission of said photon or deflection by virtual particles as it passes through space by virtual particles might produce the wave effect maybe 



 

[alancalverd]

Now you are trying to model a quantum phenomenon with a billiard ball! It is a waste of life. Fact is that we have two models for electromagnetic radiation, a wave model and a particle model, but a model is not the "real thing". We can count individual photon events, thus demonstrating the quantum photoelectric effect, and measure the speed of light, thus demonstrating the validity of Maxwell's continuum wave equations. The virtual particles that populate the vacuum are just that - virtual, not real, beasts that we invent to model the Casimir effect.  If there were indeed collisions between photons and virtual particles, light would be dispersed in a vacuum and not travel in straight lines or at a constant speed.

[pensador (OP)]

The virtual particles that populate the vacuum are just that - virtual, not real, beasts that we invent to model the Casimir effect.  If there were indeed collisions between photons and virtual particles, light would be dispersed in a vacuum and not travel in straight lines or at a constant speed.

Please correct where I am wrong.

Maxwells equations describe the classical view of electromagnetic waves.

A single photon can be viewed as a quantum particle. In quantum theory we can neither assign a precise position nor an exact direction to a particle. The probability to find a quantum object at position x with momentum p can be predicted from the absolute square of the quantum mechanical wave function. |ψ(x,p)|˛

At any given time this probability can assume non-zero values at several even widely separated positions. In that case we say that the object is delocalized and we cannot assign a single well-defined position in space. (just like in the double slit experiment)

In any position measurement on a photon we find a complete photon. Its properties, inertia, energy, polarizability are measurable – they are not diluted or smeared over larger areas of space (suggesting the photon is not a wave perhaps ?)

The HUP predicts virtual particles do exist in space, they do have inertia, and they are proven to exist via the Casimir effect, to suggest otherwise is to deny experimental proof of their existence. It would also be discrediting Hawking Radiation as nonsense which is based on virtual particles around a BH event horizon.

Electrons absorb and emit photons and transmit forces via theoretical virtual particles which MIGHT NOT exist, electrons them selves can borrow energy from the vacuum and repay it. This type of virtual particle helps to balance the math, and maybe the one you are claiming doesnt exist. Conceptually it does.

I accept virtual particles may not present any resistance to a photon, to slow it down or cause it to be deflected. I was asking a question to which I am not sure your analogy of a billiard ball is correct, its more like a bowling ball bashing through ping pong balls, or the Ping Pong ball momentarily absorbing the photon and re-emitting it.

Would I be correct in thinking that the quantum explanation and wave particle explanation, give the same answers?
 

[PmbPhy]

The particle model doesn't predict the speed of light in vacuo because there is nothing there to absorb and re-emit particles.

Let a source emit a photon at A and it arrive at B where a detector registers it. The particle model states that the photon is emitted at and absorbed at B. No need to re-emit. And this holds for distances from 1 nm to any number of light years.

[PmbPhy]

Please correct where I am wrong.

Maxwells equations describe the classical view of electromagnetic waves.

A single photon can be viewed as a quantum particle.

Its not possible to state whether a photon is a particle or a wave unless you state how its observed. That's the essence of the wave-particle duality.

Note that the Schrodinger equation only holds for non-relativistic particles and photons are relativistic particles.

[PmbPhy]

0 spin connotes zero angular momentum

Not true. Angular momentum is the sum of angular momentum associated with angular speed + spin.

sub elementary particles in the space/time fabric are in a ground state

What is a "sub elementary particle"? There's no such thing that I'm aware of. In any case there's no basis to assert that they're in the ground state. That's only possible when a particle is in a potential. And spacetime has little to do with explaining this.

[alancalverd]

The particle model doesn't predict the speed of light in vacuo because there is nothing there to absorb and re-emit particles.

Let a source emit a photon at A and it arrive at B where a detector registers it. The particle model states that the photon is emitted at and absorbed at B. No need to re-emit. And this holds for distances from 1 nm to any number of light years.

Unlike Maxwell, the particle model doesn't predict the speed of light, nor that it is constant for all photons, unless you accept the conclusion of general relativity, i.e. that massless particles must all travel at c. Problem there is that this is an experimental result that is axiomatic to the GR model, not a prediction of the model. Nor is it terribly good at propagating radio waves. Admittedly it all hangs together in the end, but  I don't think GR requires quantisation, nor vice versa.

[alancalverd]

Its not possible to state whether a photon is a particle or a wave unless you state how its observed. That's the essence of the wave-particle duality.

Here's where I get picky about language.

Consider the double slit experiment, with just one particle at a time. If whatever-it-is passes through both slits simultaneously (i.e. a wave), then its energy, mass and charge must be distributed simultaneously across the detector according to the observed diffraction pattern. But nobody has observed a particle with a fractional charge, mass, or increased photon wavelength at any point. What actually happens is that single photons, electrons or entire buckyballs ping into the detector at various positions and the integral of their distribution over umpteen particles looks like a classical interference pattern.

At the time of reaching the slit, our projectile has no way of knowing how or even whether it is going to be detected, so the implications of "duality"  don't make sense.

[pensador (OP)]

Please correct where I am wrong.

Maxwells equations describe the classical view of electromagnetic waves.

A single photon can be viewed as a quantum particle.

Its not possible to state whether a photon is a particle or a wave unless you state how its observed. That's the essence of the wave-particle duality.

Note that the Schrodinger equation only holds for non-relativistic particles and photons are relativistic particles.

Understood, I was trying to visualize or get a mental picture that covered both scenarios of a photon, from a quantum perspective. Wave Particle duality sounds like Schrodingers cat, which might be dead or alive, unless maybe you don't feed it .

Relativistic versions of the Schrodinger equation exist, ie the Klein Gordon equation. https://en.wikipedia.org/wiki/Klein–Gordon_equation and there is relativistic quantum mechanics https://en.wikipedia.org/wiki/Relativistic_quantum_mechanics neither of which give any support to what I was trying to visualize as far as I can see.


Thanks for the reply

[pensador (OP)]

At the time of reaching the slit, our projectile has no way of knowing how or even whether it is going to be detected, so the implications of "duality"  don't make sense.

Not knowing exactly which slit might make it probable 50 50 which slit. However the interference pattern suggests if it is a particle it didn't go in a straight line. Which is where I got stuck in a loop, with absorption and emission

Thanks for the responses.

[pensador (OP)]

Perhaps a better explanation lies in QED
"
How is the double-slit experiment interpreted via quantum field?
Photons are localized lumps of energy, wave packets with a reasonably well-defined position and momentum, with an uncertainty consistent with atandard quantum mechanics. Like waves, photons can be very delocalized. Each photon in a laser beam has the same shape as the classical field by which this beam is described.
In a double-slit experiment with visible light the distance between two slits can be macroscopic, e.g. 0.1 millimeter, or something like that. In order to get an interference pattern, the photon lump should be no smaller than this size. The corresponding volume is filled with a time-changing electromagnetic field, the light beam. This macroscopically large (but in a weak beam possibly very faint) lump of electromagnetic energy falls on the double slit and interferes with itself according to Maxwell equations - its shape becomes that of a superposition of two spherical waves and becomes even more delocalized over a quickly growing region. Then this big but distributed lump of energy reaches the photographic plate and blackens a single silver grain. The photon energy that was previously spread up in a macroscopic region now gets released within a group of few atoms.
"https://www.mat.univie.ac.at/~neum/physfaq/topics/doubleSlit.html
https://en.wikipedia.org/wiki/Quantum_electrodynamics
If the field around photons is reacting with the double slits as it approaches would this negate the need for wave particle duality?

[alancalverd]

You might get away with that for a photon, but not a buckyball.

[pensador (OP)]

You might get away with that for a photon, but not a buckyball.

Why would you think a buckyball double slit experiment would be any different?

Wouldn't it also be represented as a field which interacts with the slits before going through one of them?

I expect the same experiment can equally be performed by firing a single buckey ball in multiple separate locations, and when the results are brought together the wave pattern still exists. Clearly the buckey balls or photons in separate labs will have had no wave interference from the other labs.

The wave interaction is theorized to exist after multiple particles go through one or the other slit producing the waves

With QED the interaction is before the particle goes through the slits and doesnt require wave particle duality, which is hard to visualize, and not very appealing when there is a simpler way of viewing photons and particles.

[pensador (OP)]

Please correct where I am wrong.

Maxwells equations describe the classical view of electromagnetic waves.

A single photon can be viewed as a quantum particle.

Its not possible to state whether a photon is a particle or a wave unless you state how its observed. That's the essence of the wave-particle duality.

Note that the Schrodinger equation only holds for non-relativistic particles and photons are relativistic particles.

Does De Broglie Bohm / Bohemian mechanics give a valid explanation of a photon in your opinion ? A field surrounded by a pilot wave. It is deterministic, and relativistic versions exist. 

A wiki link for them as don't know what I am waffling about to save time googling.
https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory

[alancalverd]

Why would you think a buckyball double slit experiment would be any different?

Because a buckyball is not a "distributed lump of energy" but a projectile with mass and a very definite structure.
 

The wave interaction is theorized to exist after multiple particles go through one or the other slit producing the waves

So an interaction B which occurs after event A determines the outcome of A? I think not. Or does B hang around the slits waiting to direct the second particle, whenever it turns up, based on the message left behind by the first one?

With QED the interaction is before the particle goes through the slits and doesnt require wave particle duality, which is hard to visualize, and not very appealing when there is a simpler way of viewing photons and particles.

So now you want a wave W that travels ahead of a photon p. This can only happen if W travels faster than c, which itself demands some explanation. It also implies that after a sufficiently long distance (say 1000 lightyears) W and p will have become substantially separated. Now suppose p bumps into some interstellar gas. You have a pilot wave entirely independent of its photon, and thus capable of determining the performance of  some other photon. Has this ever been detected? 

[PmbPhy]

Unlike Maxwell, the particle model doesn't predict the speed of light, nor that it is constant for all photons, unless you accept the conclusion of general relativity, i.e. that massless particles must all travel at c.

I said that not to argue that the standard model predicts c but that your argument was fallacious.

BTW - its SR that c is invariant, nor GR. In GR the speed of light varies with the gravitational potential. Einstein showed this in 1907 and 1911.

[pensador (OP)]

Quote from: flummoxed on Yesterday at 10:52:26Why would you think a buckyball double slit experiment would be any different?Because a buckyball is not a "distributed lump of energy" but a projectile with mass and a very definite structure.

If a pilot wave precedes the bucky ball like a photon or electron, then what is the difference. 

The wave interaction is theorized to exist after multiple particles go through one or the other slit producing the waves  So an interaction B which occurs after event A determines the outcome of A? I think not. Or does B hang around the slits waiting to direct the second particle, whenever it turns up, based on the message left behind by the first one?

The double slit experiment can be performed in multiple separate locations on separate days by firing only a single photon or electron or buckey ball at the slits. When the results from all the locations are brought together the double slit result of firing multiple photons is reproduced. Particle A from location A does not affect the results of Particle B from location B, C D E F etc. There is no wave function interactions from Particle A to Particle B in the double slit experiment, especially when the test is performed in separate locations with single photons. 

So now you want a wave W that travels ahead of a photon p. This can only happen if W travels faster than c, which itself demands some explanation. It also implies that after a sufficiently long distance (say 1000 lightyears) W and p will have become substantially separated. Now suppose p bumps into some interstellar gas. You have a pilot wave entirely independent of its photon, and thus capable of determining the performance of  some other photon. Has this ever been detected? 

I did not say the pilot wave was completely independent of the photon, according to what I have read it surrounds it.
Photons, electrons buckey balls etc are all affected by gravity, gravitational waves for instance have been shown to travel at light speed via Ligo results. The gravitational field will surround any particle/packet of energy and arrive at the detectors before said particles.
I am still reading up on Pilot waves, and was hoping for a little guidance BUT
I am pretty damn sure gravity has been detected, this might not be what is meant by a pilot wave but then gravity might be based on entanglement of space, and the pilot wave is explained in Bohemian mechanics as producing a non local effect, which is I think is wordology for entanglement, spooky action.

Unlike Maxwell, the particle model doesn't predict the speed of light, nor that it is constant for all photons, unless you accept the conclusion of general relativity, i.e. that massless particles must all travel at c.

I said that not to argue that the standard model predicts c but that your argument was fallacious.

BTW - its SR that c is invariant, nor GR. In GR the speed of light varies with the gravitational potential. Einstein showed this in 1907 and 1911.

I noted this but decided not to mention it, as I wasn't sure I could back it up. I did not know that Einstein showed that GR predicts the speed of light to be variable in a gravitational field, do you happen to have a reference.

I am pretty convinced that c is constant in free space. If c isn't constant in free space my whole house of cards might collapse. Can you confirm c is the same for everyone under GR and SR relatively speaking. I am not aware of any experiments indicating c is variable in a gravitational field. Are you perhaps referring to the trajectory of light in curved space. Or length of rulers appearing shorter when aligned with a gravitational field in flat space.