"Magnets, how do they work?"

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Thevoiceofreason

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"Magnets, how do they work?"
« on: July 17, 2010, 02:21:02 AM »
To not derail the ISS thread, I've made this topic to discuss how magnets work.
The Insane Clown Posse reference aside, magnetic force is mediated by the photon, the particle for light aka electromagnetic radiation.
key word magnetic their. The relationship between the photon and magnetism has been demonstrated in the lab, by deferring the momentum of the photon with a magnet.

Magnets work, because each electron is constantly spewing forth virtual photons is magnetic waves. These waves are created by the angular momentum of the electron. Each virtual photon (named so due to its short lifespan) carries with it kinetic energy and momentum.
When the photon hits another electron, that momentum is transferred, and the wave's energy turns into the added kinetic energy of the receiving magnet.

If you think about it, its like a game of medicine ball, but the math is a little different, because the magnetic momentum (for lack of better words) does not always carry the same sign as its velocity. In swapping particles, the kinetic energy of the photons (which some people call potential energy) turns into the kinetic energy of the magnets, thus causing attraction or repulsion

Re: "Magnets, how do they work?"
« Reply #1 on: July 17, 2010, 03:53:55 AM »
can they do work?

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Tom Bishop

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Re: "Magnets, how do they work?"
« Reply #2 on: July 18, 2010, 12:05:19 AM »
So how does a magnetic photon pull a body?

How can a particle pull?

In a game of medicine ball, I'm not being pulled towards my partner. If anything, when I throw the ball it's propelling me away.
« Last Edit: July 18, 2010, 12:47:20 AM by Tom Bishop »

Re: "Magnets, how do they work?"
« Reply #3 on: July 18, 2010, 01:34:48 AM »
Quantum fields can impart negative momentum like two negative charges repelling. This is another good examples oh ther limitations of analogies as I was discussing in the next thread.

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Tom Bishop

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Re: "Magnets, how do they work?"
« Reply #4 on: July 18, 2010, 02:14:13 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)
« Last Edit: July 18, 2010, 02:45:09 AM by Tom Bishop »

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EireEngineer

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Re: "Magnets, how do they work?"
« Reply #5 on: July 18, 2010, 03:04:38 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Its very possible.  Stranger things than that have been observed at the quantum level.
If you are not part of the solution, you are part of the precipitate.

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Re: "Magnets, how do they work?"
« Reply #6 on: July 18, 2010, 03:08:17 AM »
momentum is a vector quantity. As such, it is described by 3 real numbers. If any of these components is negative, it means that component is in the opposite direction of the positive sense of the particular axis.

Re: "Magnets, how do they work?"
« Reply #7 on: July 18, 2010, 01:10:02 PM »
Actually its described by 4 real numbers in this case.

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Re: "Magnets, how do they work?"
« Reply #8 on: July 18, 2010, 05:18:03 PM »
Actually its described by 4 real numbers in this case.

Actually, it isn't.

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #9 on: July 18, 2010, 08:12:53 PM »
So how does a magnetic photon pull a body?

How can a particle pull?

In a game of medicine ball, I'm not being pulled towards my partner. If anything, when I throw the ball it's propelling me away.

lrn2 mathematics.
In medicine balls the math controlling the momentum only has one sign.
in the case of the photon, it has negative and positive values.
Again, I'm not an expert, use the google or a library for more info

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #10 on: July 18, 2010, 08:22:48 PM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

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Raver

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Re: "Magnets, how do they work?"
« Reply #11 on: July 19, 2010, 04:36:01 AM »
Quote
In a game of medicine ball, I'm not being pulled towards my partner.

Actually you are, you just can't feel it, one could measure it though, you would get different results depending on the ball and how fat you are.
Quote from: Gen. Douchebag
Quote from: Raver
Why? You a pedo out for delicious loli?
Sure, whatever

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Raist

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Re: "Magnets, how do they work?"
« Reply #12 on: July 19, 2010, 11:17:09 PM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

Re: "Magnets, how do they work?"
« Reply #13 on: July 20, 2010, 10:05:44 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

Yep hence (partly) the virtual part. This is why analogies to classical physics are not always useful. Sometimes the analogy gets lost in translation.

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #14 on: July 21, 2010, 04:57:26 PM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

No not really, it has to do with the magnetic moment.
The physics is beyond the scope of this forum, but it is all explained by Quantum Electrodynamics aka QED.
This sight explains it fairly well, and is accessible to anyone with basic understanding of physics
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/virtual_particles.html

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #15 on: July 21, 2010, 05:05:28 PM »
I'd suggest that anyone who really wants to know more than my attempt at an explanation,
go here: http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/virtual_particles.html

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Raist

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Re: "Magnets, how do they work?"
« Reply #16 on: July 22, 2010, 01:02:37 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

No not really, it has to do with the magnetic moment.
The physics is beyond the scope of this forum, but it is all explained by Quantum Electrodynamics aka QED.
This sight explains it fairly well, and is accessible to anyone with basic understanding of physics
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/virtual_particles.html

But you said it transfers its momentum to the particle. Which is it?

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #17 on: July 22, 2010, 05:27:54 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

No not really, it has to do with the magnetic moment.
The physics is beyond the scope of this forum, but it is all explained by Quantum Electrodynamics aka QED.
This sight explains it fairly well, and is accessible to anyone with basic understanding of physics
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/virtual_particles.html

But you said it transfers its momentum to the particle. Which is it?

It does transfer momentum.
but you can't think of it exactly like a bullet or a ball, that's just an analogy.
look at the link, it explains it almost in full

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Re: "Magnets, how do they work?"
« Reply #18 on: July 22, 2010, 05:36:49 AM »
We will not look at random links. You probably have no idea what magnetism actually is, so please don't try explaining it for us.

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Raist

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Re: "Magnets, how do they work?"
« Reply #19 on: July 22, 2010, 10:49:12 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

No not really, it has to do with the magnetic moment.
The physics is beyond the scope of this forum, but it is all explained by Quantum Electrodynamics aka QED.
This sight explains it fairly well, and is accessible to anyone with basic understanding of physics
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/virtual_particles.html

But you said it transfers its momentum to the particle. Which is it?

It does transfer momentum.
but you can't think of it exactly like a bullet or a ball, that's just an analogy.
look at the link, it explains it almost in full

....

I'm just trying to figure out why you tried to explain it if your explanation isn't what actually happens.

Re: "Magnets, how do they work?"
« Reply #20 on: July 22, 2010, 03:08:20 PM »
I think thats why its called an analogy. Its very hard to come up with analogies for purely quantum phenomena with every day examples. I always used the example of two people on boats throwing balls between them. Each time someone catches the ball they move a little bit. This to first order explains the particle exchange idea of quantum field theory. It doesn't really allow you to go much deeper. The analogy doesn't go to the point of virtual particles but then it still serves a purpose depending on the audience.

If your doing a talk to the general public then you use the balls and a boat, as you don't know the base level of science. If you taking to high school science students you can start talking about the idea of momentum as a vector and as a more abstract quantity. If you have physics students at the upper end of high school or early university you can start to talk about virtual particles because they know special relativity and the basic ideas of quantum mechanics. Theres not much point talking about infinite quantum harmonic oscillators and S-matrices. So the explanation isn't exactly what happens but it'll give you a handle. Theres a difference between transferring momentum and transferring its momentum.

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Raist

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Re: "Magnets, how do they work?"
« Reply #21 on: July 22, 2010, 08:24:26 PM »
yeah, but he didn't use an analogy, he lied.

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EireEngineer

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Re: "Magnets, how do they work?"
« Reply #22 on: July 23, 2010, 04:20:35 AM »
We will not look at random links. You probably have no idea what magnetism actually is, so please don't try explaining it for us.
Talk about willfully obtuse! lol

The most obvious problem with a simple, classical picture of virtual particles is that this sort of behavior can't possibly result in attractive forces.  If I throw a ball at you, the recoil pushes me back; when you catch the ball, you are pushed away from me.  How can this attract us to each other?  The answer lies in Heisenberg's uncertainty principle.

Suppose that we are trying to calculate the probability (or, actually, the probability amplitude) that some amount of momentum, p, gets transferred between a couple of particles that are fairly well- localized.  The uncertainty principle says that definite momentum is associated with a huge uncertainty in position.  A virtual particle with momentum p corresponds to a plane wave filling all of space, with no definite position at all.  It doesn't matter which way the momentum points; that just determines how the wavefronts are oriented.  Since the wave is everywhere, the photon can be created by one particle and absorbed by the other, no matter where they are.  If the momentum transferred by the wave points in the direction from the receiving particle to the emitting one, the effect is that of an attractive force.

The moral is that the lines in a Feynman diagram are not to be interpreted literally as the paths of classical particles.  Usually, in fact, this interpretation applies to an even lesser extent than in my example, since in most Feynman diagrams the incoming and outgoing particles are not very well localized; they're supposed to be plane waves too.

The uncertainty principle opens up the possibility that a virtual photon could impart a momentum that corresponds to an attractive force as well as to a repulsive one.  But you may well ask what makes the force repulsive for like charges and attractive for opposite charges!  Does the virtual photon know what kind of particle it's going to hit?

It's hard even for particle physicists to see this using the Feynman diagram rules of QED, because they're usually formulated in a manner designed to answer a completely different question: that of the probability of particles in plane-wave states scattering off of each other at various angles.  Here, though, we want to understand what nudges a couple of particles that are just sitting around some distance apart--to explain the experiment you may have done in high school, in which charged balls of aluminum foil repel each other when hanging from strings.  We want to do this using virtual particles.  It can be done.
If you are not part of the solution, you are part of the precipitate.

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #23 on: July 24, 2010, 10:14:14 AM »
So a magnetic photon hits the side of an object's surface and it causes "negative momentum"?

 ::)

Hits the side of an object?
The messenger photon hits the charged particles, which transfers the momentum.
Remember the whole f=ma thing?
well in this case the force is negative, or at least it is facing the opposite direction.
This is hard to imagine, because in the case of the medicine ball, the electron-electron repulsion that transfers the force is only repulsive, i.e. when you touch a ball you don't get sucked into it.

But the math allows charges to be negative and positive.

So the photon has momentum in the opposite direction from which it is traveling?

No not really, it has to do with the magnetic moment.
The physics is beyond the scope of this forum, but it is all explained by Quantum Electrodynamics aka QED.
This sight explains it fairly well, and is accessible to anyone with basic understanding of physics
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/virtual_particles.html

But you said it transfers its momentum to the particle. Which is it?

It does transfer momentum.
but you can't think of it exactly like a bullet or a ball, that's just an analogy.
look at the link, it explains it almost in full

....

I'm just trying to figure out why you tried to explain it if your explanation isn't what actually happens.

As I have stated before, I am not an expert, I tried to give an analogy of my own understanding, but the complete explanation is in the link. The point I was demonstrating, was that the energy that is later turned into kinetic energy of the charged particles (potential energy), is carried by the virtual photons. That way, energy is not being created, just transferred.
« Last Edit: July 24, 2010, 10:20:02 AM by Thevoiceofreason »

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #24 on: July 24, 2010, 10:15:03 AM »
We will not look at random links. You probably have no idea what magnetism actually is, so please don't try explaining it for us.

So you don't want to look at a link that tells you how magnetism works, in a thread about how magnetism works. Ok

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #25 on: July 24, 2010, 10:17:21 AM »
We will not look at random links. You probably have no idea what magnetism actually is, so please don't try explaining it for us.
Talk about willfully obtuse! lol

The most obvious problem with a simple, classical picture of virtual particles is that this sort of behavior can't possibly result in attractive forces.  If I throw a ball at you, the recoil pushes me back; when you catch the ball, you are pushed away from me.  How can this attract us to each other?  The answer lies in Heisenberg's uncertainty principle.

Suppose that we are trying to calculate the probability (or, actually, the probability amplitude) that some amount of momentum, p, gets transferred between a couple of particles that are fairly well- localized.  The uncertainty principle says that definite momentum is associated with a huge uncertainty in position.  A virtual particle with momentum p corresponds to a plane wave filling all of space, with no definite position at all.  It doesn't matter which way the momentum points; that just determines how the wavefronts are oriented.  Since the wave is everywhere, the photon can be created by one particle and absorbed by the other, no matter where they are.  If the momentum transferred by the wave points in the direction from the receiving particle to the emitting one, the effect is that of an attractive force.

The moral is that the lines in a Feynman diagram are not to be interpreted literally as the paths of classical particles.  Usually, in fact, this interpretation applies to an even lesser extent than in my example, since in most Feynman diagrams the incoming and outgoing particles are not very well localized; they're supposed to be plane waves too.

The uncertainty principle opens up the possibility that a virtual photon could impart a momentum that corresponds to an attractive force as well as to a repulsive one.  But you may well ask what makes the force repulsive for like charges and attractive for opposite charges!  Does the virtual photon know what kind of particle it's going to hit?

It's hard even for particle physicists to see this using the Feynman diagram rules of QED, because they're usually formulated in a manner designed to answer a completely different question: that of the probability of particles in plane-wave states scattering off of each other at various angles.  Here, though, we want to understand what nudges a couple of particles that are just sitting around some distance apart--to explain the experiment you may have done in high school, in which charged balls of aluminum foil repel each other when hanging from strings.  We want to do this using virtual particles.  It can be done.

This.
It's from the link

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Re: "Magnets, how do they work?"
« Reply #26 on: July 24, 2010, 10:53:46 AM »
The quoted text describes any interaction mediated through the exchange of virtual particles, not just magnetism. If you actually knew what you were talking about, you would know that magnetism is only one face of a fundamental interaction called the electromagnetic interaction. QED stands for Quantum Electrodynamics, not even mentioning the word magnetism.

Magnetic interaction between elementary particles (such as two electrons) is negligible compared to the electrostatic Coulomb interaction. It is only when the electrostatic Coulomb interaction between the particles of a complicated system, such as the atom of a transition metal with half filled f sub-shell, cancels that we are left with the magnetic interaction as the most dominant one. Magnetism, as seen on a macroscopic scale, is almost exclusively a product of the atoms' valence electrons' orbital and spin magnetic moments adding up collectively to give a measurable effect. The virtual photon exchange picture you describe is practically useless for such considerations.

Re: "Magnets, how do they work?"
« Reply #27 on: July 24, 2010, 03:10:50 PM »
Magnetic fields and electic fields are actually the same thing just in different frames of reference, so they must have the same mediating particle. I might even be kind enough to provide the derivation but its probably on wiki, so ill only be accused of copying it

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Re: "Magnets, how do they work?"
« Reply #28 on: July 24, 2010, 04:19:12 PM »
Magnetic fields and electic fields are actually the same thing just in different frames of reference, so they must have the same mediating particle. I might even be kind enough to provide the derivation but its probably on wiki, so ill only be accused of copying it

They are not the same thing, they are different parts of a unified reality. If you use the language of field theory, force has little meaning. When we discuss fundamental interactions, one uses the concept of an action. There is an action for a charged particle in an electromagnetic field and there is an action for the field itself. The action contains information about the dynamics of the EM field and the particle field (in Quantum Field Theory, everything is assigned a particular kind of field).

So, saying magnets emit virtual photons is completely bogus.

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Thevoiceofreason

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Re: "Magnets, how do they work?"
« Reply #29 on: July 24, 2010, 04:50:19 PM »
The quoted text describes any interaction mediated through the exchange of virtual particles, not just magnetism. If you actually knew what you were talking about, you would know that magnetism is only one face of a fundamental interaction called the electromagnetic interaction. QED stands for Quantum Electrodynamics, not even mentioning the word magnetism.

Magnetic interaction between elementary particles (such as two electrons) is negligible compared to the electrostatic Coulomb interaction. It is only when the electrostatic Coulomb interaction between the particles of a complicated system, such as the atom of a transition metal with half filled f sub-shell, cancels that we are left with the magnetic interaction as the most dominant one. Magnetism, as seen on a macroscopic scale, is almost exclusively a product of the atoms' valence electrons' orbital and spin magnetic moments adding up collectively to give a measurable effect. The virtual photon exchange picture you describe is practically useless for such considerations.

the example shown is for electric force. If you read through it you'll see that he says magnetism works in a similar manner.
Also http://en.wikipedia.org/wiki/Magnetic_field#Quantum_electrodynamics.

Stop talking about things that you don't understand. If you don't think magnetism is a part of QED, that is only evidence that you have no idea what you are talking about. Magnetism is always a result of the exchange of virtual photons. lrn2 standard model+ quantum physics