I really am grateful for JGWeissman for helping me click on the fact that light isn’t something that obeys the wave described by the Maxwell equation, but is that wave. The difference is imagining light as a type of substance compelled to oscillate with the wave pattern, and there being a wave pattern, resulting naturally from causal interactions, that is interpreted by our vision as “light”.
Thus this is the explanation I would give my past self for strikethrough(why light oscillates) what light is:
A charge creates an electromagnetic field. If the charge moves, the electromagnetic field will have to change. However, while the field is defined over infinite space, the field cannot update instantaneously over all of space. Instead, the field updates at the speed of light from the new position of the charge. At a small, fixed moment in time after the point charge has moved, the field has updated within a sphere of a certain radius, but has not yet updated outside this radius. What we call ‘light’ is the defect radiating outward though space like a ripple. When our eyes intercept this defect, we gain information about the point charge’s displacement and -- in some way I don’t understand, and don’t need to for the immediate explanation—the field no longer needs to keep updating and the ripple stops propagating (the waves collapses to an intercepted particle / photon).
So I no longer see light as a thing traveling though space, but as information about an updated field traveling in finite time.
Does this make sense? I suppose it could be completely wrong, but it is what I mean by a ‘mechanical’ explanation.
Oh, and I’ll add that light oscillates because the electric and magnetic fields update each other in finite time, and there is a slight lag, so that the wave has an amplitude. I see this as analogous to predator-prey oscillations in a Lotka-Volterra model; if the fields responded instantaneously there would be no oscillation.
This is a nit-pick, but the oscillation is not because there is any direct delay in the interaction between the electric and magnetic portions, it’s because the electric and magnetic portions effect each other through derivatives. This is similar to how the the acceleration (second time derivative of position) is directly related to position in any number of mechanical oscillators, such as springs, pendulums, and even circular orbits, when viewed right. For light, while there are still two time derivatives, they are coupled so that one time-derivative arises between magnetic and electric, and the other arises between electric and magnetic.
It’s OK—it’s a matter of language, and not being very precise. Very loosely, in the case of a pendulum, you could say that in the upswing of the pendulum, it takes finite time (a delay) for the pendulum to respond to the downward force of gravity and start moving to 0. By the time it gets to 0, it already has momentum in the other direction and overshoots the equilibrium again. I see how this is the result of the dynamics being described by changes in the derivative of the motion, rather than—say—in the direction of motion itself.
There is no delay for the pendulum to respond to gravity, it starts accelerating immediately. There could be a delay before it achieves a velocity large enough to be perceived.
That is broadly correct. The details of the propagation (and even of the electric field before the charge moves) can be derived from the local laws of how how charges and fields interact.
I know you said you don’t need to understand why the field doesn’t need to keep updating, but the way that you detect the light is that it moves a charged electron within a molecule in your eye, and that movement of the charged electron causes a light wave that (along the blocked path) approximately cancels the original wave.
Interesting. That has a nice symmetry, that to intercept light you need to move a charge in your eye that counters the original wave.
What I was referring to particularly was the quantum mechanical aspect: the wave propagates from the source in three dimensions—an expanding sphere of information. Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.
Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.
Well, that is one of the many reasons that points to Many Worlds being superior to Collapse theories.
But if we are talking about light you see with your eye, that actually registers in your brain, there is way more than one photon emitted, and classical electromagnetic theory is a good enough approximation. Photons are roughly a discrete unit of amplitude of the light wave. For a high enough amplitude wave, you can ignore that it is discrete.
Many Worlds made sense to me as a solution when I considered the case of an apparently random choice. Instead of the world collapsing on an arbitrary choice, each world gets one choice. In the case of interaction with a propagating wave of light, though, I don’t see how it would work. Perhaps something is incorrect with my fledgling model of light.
Let’s consider a single photon. That would still propagate as a spherical wave from the source. The wave expands uniformly from the source and I suppose that according to a classical theory (?), that wave could be perceived simultaneously by different people in different places around the source. Even if I interact with the wave by moving an electron that approximately cancels that wave, then my cancellation would propagate only at the speed of light, not instantaneously.
I suppose that according to a classical theory (?), that wave could be perceived simultaneously by different people in different places around the source.
That is indeed what the classical theory says. It is wrong. This is where the assumption that domain of the amplitude is continuous is a bad approximation.
So how would Many Worlds work in this case?
Quantum amplitude flows into separate configurations. For each detector, there is a configuration such that that detector was the only one to detect the photons. There are also configurations where no detector detected it. So, if in some configuration, a detector detects the photon, and goes to check on another detector, it will find that the other detector has not detected the photon, not because some instantaneous space spanning signal collapsed the wave function, but because in that configuration the photon did not go that way.
I see, so the photon left the source as a particle and the wave picture represents the idea that the particle could have been anywhere, until you know which world you’re in.
But the mechanical-model-that-made-me-so-happy was that the photon was actually just the electromagnetic field trying to update. The electromagnetic field would have to update isotropically … it couldn’t just update along the route to a given detector.
Well, there is a similar mechanical model to the evolution of the Schrodinger wave function, which is to particles (including photons) as the electric and magnetic fields are to light in the classical model. This wave function is fundamental, the particles, and the configurations, or “worlds” are derived consequences.
What I was referring to particularly was the quantum mechanical aspect: the wave propagates from the source in three dimensions—an expanding sphere of information. Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.
Well, it you believe in a collapse postulate. Which I don’t think many people around here do.
You know, I didn’t even know that was the same thing as the collapse postulate. So when people talk about the ‘collapse of the wave function’, they’re talking about—for example—the perception of light. OK, sure, that makes sense.
I really am grateful for JGWeissman for helping me click on the fact that light isn’t something that obeys the wave described by the Maxwell equation, but is that wave. The difference is imagining light as a type of substance compelled to oscillate with the wave pattern, and there being a wave pattern, resulting naturally from causal interactions, that is interpreted by our vision as “light”.
Thus this is the explanation I would give my past self for strikethrough(why light oscillates) what light is:
A charge creates an electromagnetic field. If the charge moves, the electromagnetic field will have to change. However, while the field is defined over infinite space, the field cannot update instantaneously over all of space. Instead, the field updates at the speed of light from the new position of the charge. At a small, fixed moment in time after the point charge has moved, the field has updated within a sphere of a certain radius, but has not yet updated outside this radius. What we call ‘light’ is the defect radiating outward though space like a ripple. When our eyes intercept this defect, we gain information about the point charge’s displacement and -- in some way I don’t understand, and don’t need to for the immediate explanation—the field no longer needs to keep updating and the ripple stops propagating (the waves collapses to an intercepted particle / photon).
So I no longer see light as a thing traveling though space, but as information about an updated field traveling in finite time.
Does this make sense? I suppose it could be completely wrong, but it is what I mean by a ‘mechanical’ explanation.
Oh, and I’ll add that light oscillates because the electric and magnetic fields update each other in finite time, and there is a slight lag, so that the wave has an amplitude. I see this as analogous to predator-prey oscillations in a Lotka-Volterra model; if the fields responded instantaneously there would be no oscillation.
This is a nit-pick, but the oscillation is not because there is any direct delay in the interaction between the electric and magnetic portions, it’s because the electric and magnetic portions effect each other through derivatives. This is similar to how the the acceleration (second time derivative of position) is directly related to position in any number of mechanical oscillators, such as springs, pendulums, and even circular orbits, when viewed right. For light, while there are still two time derivatives, they are coupled so that one time-derivative arises between magnetic and electric, and the other arises between electric and magnetic.
I don’t see where Byrnema claimed there was such a direct delay.
Ok, now I am wondering how I completely missed that last paragraph. I agree with your nit-pick.
It’s OK—it’s a matter of language, and not being very precise. Very loosely, in the case of a pendulum, you could say that in the upswing of the pendulum, it takes finite time (a delay) for the pendulum to respond to the downward force of gravity and start moving to 0. By the time it gets to 0, it already has momentum in the other direction and overshoots the equilibrium again. I see how this is the result of the dynamics being described by changes in the derivative of the motion, rather than—say—in the direction of motion itself.
Right. I’d describe that as a delay for gravity to finish overcoming the motion, rather than a delay in response.
There is no delay for the pendulum to respond to gravity, it starts accelerating immediately. There could be a delay before it achieves a velocity large enough to be perceived.
Most excellent. Now, glasshoppah, you are ready to lift the bowl of very hot red coals. Try this
That is broadly correct. The details of the propagation (and even of the electric field before the charge moves) can be derived from the local laws of how how charges and fields interact.
I know you said you don’t need to understand why the field doesn’t need to keep updating, but the way that you detect the light is that it moves a charged electron within a molecule in your eye, and that movement of the charged electron causes a light wave that (along the blocked path) approximately cancels the original wave.
Interesting. That has a nice symmetry, that to intercept light you need to move a charge in your eye that counters the original wave.
What I was referring to particularly was the quantum mechanical aspect: the wave propagates from the source in three dimensions—an expanding sphere of information. Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.
But that’s QM, outside my pay grade.
Well, that is one of the many reasons that points to Many Worlds being superior to Collapse theories.
But if we are talking about light you see with your eye, that actually registers in your brain, there is way more than one photon emitted, and classical electromagnetic theory is a good enough approximation. Photons are roughly a discrete unit of amplitude of the light wave. For a high enough amplitude wave, you can ignore that it is discrete.
Many Worlds made sense to me as a solution when I considered the case of an apparently random choice. Instead of the world collapsing on an arbitrary choice, each world gets one choice. In the case of interaction with a propagating wave of light, though, I don’t see how it would work. Perhaps something is incorrect with my fledgling model of light.
Let’s consider a single photon. That would still propagate as a spherical wave from the source. The wave expands uniformly from the source and I suppose that according to a classical theory (?), that wave could be perceived simultaneously by different people in different places around the source. Even if I interact with the wave by moving an electron that approximately cancels that wave, then my cancellation would propagate only at the speed of light, not instantaneously.
So how would Many Worlds work in this case?
That is indeed what the classical theory says. It is wrong. This is where the assumption that domain of the amplitude is continuous is a bad approximation.
Quantum amplitude flows into separate configurations. For each detector, there is a configuration such that that detector was the only one to detect the photons. There are also configurations where no detector detected it. So, if in some configuration, a detector detects the photon, and goes to check on another detector, it will find that the other detector has not detected the photon, not because some instantaneous space spanning signal collapsed the wave function, but because in that configuration the photon did not go that way.
I see, so the photon left the source as a particle and the wave picture represents the idea that the particle could have been anywhere, until you know which world you’re in.
But the mechanical-model-that-made-me-so-happy was that the photon was actually just the electromagnetic field trying to update. The electromagnetic field would have to update isotropically … it couldn’t just update along the route to a given detector.
Well, there is a similar mechanical model to the evolution of the Schrodinger wave function, which is to particles (including photons) as the electric and magnetic fields are to light in the classical model. This wave function is fundamental, the particles, and the configurations, or “worlds” are derived consequences.
Well, it you believe in a collapse postulate. Which I don’t think many people around here do.
You know, I didn’t even know that was the same thing as the collapse postulate. So when people talk about the ‘collapse of the wave function’, they’re talking about—for example—the perception of light. OK, sure, that makes sense.
So our solution to that was Many Worlds…