Ask any question you want about Physics

originally posted by: Pirvonen
a reply to: Nochzwei
Any movement of any charge creates a magnetic field. Any change in a magnetic field creates an electric field. A changing electric field generates a change in magnetic field. And so it goes, propagating on at the speed of light.

Movement of an electron, except when on an undisturbed orbital around the nucleus, is movement of a charge that gives rise to electromagnetic waves. Vibration of a molecule is the motion of charges, giving rise to electromagnetic waves. And so it goes.

So when for ex. you move a bar magnet in space, the mag field in space is changing and it will generate em waves?

Nochzwei[/post]

So when for ex. you move a bar magnet in space, the mag field in space is changing and it will generate em waves?

Yes.

This can be pretty damn useful sometimes.

en.wikipedia.org...

originally posted by: ImaFungi
a reply to: mbkennel

Ok, so that first graphic shows the field all surrounding the charged particle being effected. Would this be EM radiation propagating away from that charged particle, in all directions surrounding the particle (at least on some 2d plane, perpendicular to direction of acceleration maybe)?

This is all I was getting at. Arb seems to think, that graphic should only show 1 field line around the charged particle waving when the particle is accelerated, as that is what he says a photon being emitted from a moment of accelerated charged particle resulting in EM radiation, is.

The electron is 3d. No such thing, essence, quanta, can exist in any way, that is not at least 3d.

Make at least one statement that supports your faith in less than 3d electron. A math paper that defines the electron as being a less than 3d object, has nothing to do with reality, that has to do with symbols on paper, that do not corroborate to reality, everything is rounded and skewed, I am after closest to truth, the electron not existing in 3d can not be a statement that is closest to truth. It is silly to even argue with you, you are absolutely wrong. One way to destroy your stance, is to ask you to state the first particle that is 3d (I am sure you will have trouble understanding what I mean for reasons obviously not obvious to you, but I mean to say, if electron is not 3d according to ignorance and idiocy, what particles moving up in dimension, is the first particle that is 3d...you are an absolute mongrel, disgusting, filthy intellect. garbage.)

It's not known for sure but theory and experiment suggest it's a point particle.
The whole point of quantum objects is that they do not act like actual 3D objects. The electron exists in an electron cloud made of probable electrons and you can't have an electron that is still because if you know the position exactly then the momentum is completely unknown.

I was just reading about point particles on physics forum, this quote touches on the subject nicely:
This discussion of "point particles" is also rather strange. Point particles in physics means that the spatial extent of the object has no detectable consequence. So if you care that much about "actual observation", this would be it. Our "actual observation" based on measurements from area of study such as condensed matter physics, gives a direct result that many of these particles are point particles. To say that they have a spatial extent does not match our "actual observation". We have no ability to say that these have any. Not only that, the theory that describes them as point particles produces the SAME prediction as experiment.

The electron field is something of a mathematical concept but you could say it's a field made up of virtual electrons zipping in and out of existence and when you add some energy to that field you get an actual electron.
But all the quantum weirdness is still there.

The first particle that you could say is 3D is probably any particle that you can break up with high energy collisions.

a reply to: Nochzwei

Waving a bar magnet around will generate EM waves, but only over a very tiny area. Let me park myself at a point in space near the magnet. The change I see at my location due to the motion of the bar magnet is compensated by the motion of the other end of the magnet. There is a small EM effect, but it is short-circuited against the other parts of the bar magnet´s field. No matter what crazy flips you make the magnet do, there is at any time one part of the magnetic field going one way and another part going the opposite way, cancelling the long-range effects. In a tiny area very near the magnet there is a non-propragating EM field, however.

If you were able to make the magnetic field grow and shrink, that would give rise to a propagating magnetic field. Perhaps a hinged, V-shaped structure?

originally posted by: joelr
The first particle that you could say is 3D is probably any particle that you can break up with high energy collisions.

Hey, imafungi? The electron has to spin 720 degrees in a single rotation, too. Not 360. 720. Enjoy visualizing that one.

originally posted by: Pirvonen
a reply to: Nochzwei

Waving a bar magnet around will generate EM waves, but only over a very tiny area. Let me park myself at a point in space near the magnet. The change I see at my location due to the motion of the bar magnet is compensated by the motion of the other end of the magnet. There is a small EM effect, but it is short-circuited against the other parts of the bar magnet´s field. No matter what crazy flips you make the magnet do, there is at any time one part of the magnetic field going one way and another part going the opposite way, cancelling the long-range effects.

You can, in fact, get propagating radiation from time-varying magnetic dipoles. Witness NMR (and google magnetic dipole radiation).

Technologically, for classical radios electric dipole radiation is much more important as it's stronger by a factor of 1/(v/c)^2 than magnetic dipole, (magnetic dipole is on same order in multiple expansion as electric quadrupole) but magnetic dipole radiation can be important in atomic and nuclear physics. Maybe pulsars too---they're an enormous nucleus.

In practice the power radiated by waving a bar magnet by humans is really minuscule.

If you were able to make the magnetic field grow and shrink, that would give rise to a propagating magnetic field. Perhaps a hinged, V-shaped structure?

How about a time varying electromagnet? Or a nucleus with non-zero spin & magnetic moment?

a reply to: mbkennel
I can wrap my nogging around a magnetic dipole, or its equivalent current loop element. And what is an electromagnet other than a somewhat large number of current loops The "ferrite antenna" that can be found in some transistor radios is the reciprocal case, so a time-varying electromagnet should definitely be a source of propagating EM fields.

I noticed your link to NMR, and while anything that has to do with particle physics tends to make me feel fuzzy, at least I can not see any counterargument to the spin-magnet being an EM source or sink. I believe you are right, and I will continue to not think about it.

originally posted by: Bedlam

originally posted by: joelr
The first particle that you could say is 3D is probably any particle that you can break up with high energy collisions.

Hey, imafungi? The electron has to spin 720 degrees in a single rotation, too. Not 360. 720. Enjoy visualizing that one.

Right, there is that too. I think particles with spin 1/2 have to be rotated 720 degrees to be back in their original phase state. Do they rotate through a different dimension? Don't know.
Even that though is nebulous because you cannot measure exact spin of a single particle because of the uncertainty principle. You can measure collections of similar particles.
They are not particles (3D type objects) or waves. They are things that possess both characteristics. It really depends on how you measure it.

originally posted by: joelr

Point particles in physics means that the spatial extent of the object has no detectable consequence

"...the spatial extent of the object has no detectable consequence"

As a statement, does not equal:

"An object exists which has no spatial extent"

originally posted by: Bedlam

originally posted by: joelr
The first particle that you could say is 3D is probably any particle that you can break up with high energy collisions.

Hey, imafungi? The electron has to spin 720 degrees in a single rotation, too. Not 360. 720. Enjoy visualizing that one.

Explain what you mean by 'has to', and explain what you are referring to?

a reply to: ImaFungi

If you were to pick a spot and turn until you were in the same position, you'd go through 360 degrees of rotation.

In order for an electron to complete a rotation, it has to turn 720 degrees.

originally posted by: circlemaker
a reply to: Pirvonen

a reply to: Bedlam

You missed my point...

Here's perhaps a better example: If space was occupied by a single object, how would the object know when it's rotating? There would be nothing else in space to measure that rotation. Hence my question: what is it relative to? Is there some invisible frame of reference that's attached to the object at birth?

Once you settle on choosing the exact object you are referring to in your example, you must consider what that object exactly and entirely is; Molecules, which are made of atoms, which are made of subatomic particles etc.

So an object is molecules in an organization relative to one another. If you started to rotate that object (if it was hypothetically the only object in the universe) would the molecules 'feel' an energetic difference? According to the energy expended and shared which creates the bonded nature of the object, wouldnt there be a physical difference to the molecules local relationship with others, if they collectively began to be rotated?

Now, if your question is about the thought experiment starting mid rotation, and in this scenario the velocity of rotation would never slow or speed down at all, than I have no clue, I suppose the proper thought would be that that circumstance would be the ultimate truth of that perspective of reality, 'any hypothetical conscious observers on this spinning object' would reckon that the only balanced existence they know of, would be to our agreed upon perspective, a rotating one. Surely they could I suppose, mathematically define what to them would be 'average/normal/"stationary" as 0 and then imagine an object that rotated incrementally faster and incrementally slower...but I am not sure.

I suppose we can just change this question to, if only the earth existed in all the universe, (and somehow) humans existed on earth, and earth was rotating, how would humans know it was rotating?

Well first of all, this is a messy path to go down, as there would be no sun, so no light, and so we are already muddled in hypotheticals, because once you say there is light, then I suppose that can be a tool that would be useable perhaps to discover that the earth was rotating?

originally posted by: Bedlam
a reply to: ImaFungi

If you were to pick a spot and turn until you were in the same position, you'd go through 360 degrees of rotation.

In order for an electron to complete a rotation, it has to turn 720 degrees.

Says who and what?

What 3d shape would the electron be most comparable to?

What dimensional shape of your choosing would the electron be most comparable to?

Generally describe the experiment set up, in how it is determined that the object electron, has one end defined (call it pole S) and another opposite end defined (call it pole N) and that starting in the experiment with pole S facing me, the object electron spins 360 degrees (all tautologically defined, mind you, the very meaning of opposites and rotations of the shape those opposites are a part of) and the S pole is not facing me. The onus is on you.

originally posted by: ImaFungi

originally posted by: Bedlam
a reply to: ImaFungi

If you were to pick a spot and turn until you were in the same position, you'd go through 360 degrees of rotation.

In order for an electron to complete a rotation, it has to turn 720 degrees.

Says who and what?

What 3d shape would the electron be most comparable to?

What dimensional shape of your choosing would the electron be most comparable to?

Generally describe the experiment set up, in how it is determined that the object electron, has one end defined (call it pole S) and another opposite end defined (call it pole N) and that starting in the experiment with pole S facing me, the object electron spins 360 degrees (all tautologically defined, mind you, the very meaning of opposites and rotations of the shape those opposites are a part of) and the S pole is not facing me. The onus is on you.

The spin space the electron rotates through is not the common Euclidean space of x,y,z of classical physics and our common experience. Because in that space of physical x,y,z, and as represented by common Euler angles, rotation through 360 degrees gets you back to where you started.

Think of another hidden 2-d space of spinors attached everywhere to x,y,z,t of the electron field. It's sort of like it's a point on the x,y,z side, but a vector on the hidden 2-d intrinsic spin space.

If you object that it's not intuitive, I will agree, but don't throw insults, because it's right.

You need to learn more about physics and abstract mathematics.

a reply to: ImaFungi

Neutron interferometer experiments can demonstrate this behavior.

You pass one of the neutron beams through a magnetic field to cause 360 deg rotation and get destructive interference, while it is constructive without the magnetic field, or for 720 * n degree rotations.

originally posted by: moebius
You pass one of the neutron beams through a magnetic field to cause 360 deg rotation and get destructive interference, while it is constructive without the magnetic field, or for 720 * n degree rotations.

Interesting, especially given your screen name

originally posted by: mbkennel

originally posted by: ImaFungi

originally posted by: Bedlam
a reply to: ImaFungi

If you were to pick a spot and turn until you were in the same position, you'd go through 360 degrees of rotation.

In order for an electron to complete a rotation, it has to turn 720 degrees.

Says who and what?

What 3d shape would the electron be most comparable to?

What dimensional shape of your choosing would the electron be most comparable to?

Generally describe the experiment set up, in how it is determined that the object electron, has one end defined (call it pole S) and another opposite end defined (call it pole N) and that starting in the experiment with pole S facing me, the object electron spins 360 degrees (all tautologically defined, mind you, the very meaning of opposites and rotations of the shape those opposites are a part of) and the S pole is not facing me. The onus is on you.

The spin space the electron rotates through is not the common Euclidean space of x,y,z of classical physics and our common experience. Because in that space of physical x,y,z, and as represented by common Euler angles, rotation through 360 degrees gets you back to where you started.

Think of another hidden 2-d space of spinors attached everywhere to x,y,z,t of the electron field. It's sort of like it's a point on the x,y,z side, but a vector on the hidden 2-d intrinsic spin space.

If you object that it's not intuitive, I will agree, but don't throw insults, because it's right.

You need to learn more about physics and abstract mathematics.

I asked Bedlem, to describe the experiment. In which you would in a moment, know which way the end you defined as 'end S' was facing you; then the means by which you would be certain you were rotating the electron; then by the means by which you would be certain you were rotating the electron exactly 360 degrees.

After you answer those general questions, we can progress further into this topic.

originally posted by: ImaFungi
I asked Bedlem, to describe the experiment. In which you would in a moment, know which way the end you defined as 'end S' was facing you; then the means by which you would be certain you were rotating the electron; then by the means by which you would be certain you were rotating the electron exactly 360 degrees.

After you answer those general questions, we can progress further into this topic.

It gets back to Stern-Gerlach.

Since you can't "see" marks on an electron, you have to determine the spin other ways. Ones that generally preclude the direct visualization that you are fond of. And that's true for most quantum problems.

Stern-Gerlach proved that electrons have 1/2 spin, as do all fermions, as far as I know.

Having 1/2 spins causes (mathematically) a requirement for some behaviors, and a 720 degree rotation is one. You can thank eigenspinors for that one.

The prettiest and least cluttered direct demonstration of 1/2 spin fermions having a 4pi rotation is Rauch 1975. For only $35 bucks you can download the paper.

Oh, and electrons are dimensionless points. Looked at some ways classically, it can seem like they have radii. Think of it as a tiny LED seen in a fog bank at a distance. It'll look like a round ball. But it doesn't look that way when you get closer.

All that to say, you can't leave the classical world where things you visualize in your head may have some correlation to what's real - you were 'designed' to process that. But when you start looking under the hood, things stop being what you'd think. And you're NOT 'designed' to directly visualize it. Thus do you need maths.

Trying to think of electrons as little balls of plastic with red/white marks on and insisting that's all need be done is not going to get you into the horrifying world of quantum mechanics.

Spin not being what I visualized as spin...exactly... was where I found I had to abandon direct visualization.

If you were to look back through the history of a number of turn-of-the-last-century scientific development, and you won't. you'll see that they were amassing a metric crapton of problems with classical physics. Some were elephant-in-the-room unignorable. There were a LOT of observations of phenomena that could not be explained classically, because we were getting good enough instruments to see that something else was going on. That's when it dawned on people that quantized solutions explained a lot of the more basic things they were seeing, and away it went. The problem is, right about the time it took off, the math became non-trivial. Autodidacts and math-averse folks were tossed in the ditch after a lot of flailing and gnashing of teeth that this couldn't be real. But it was real. It explains what is being seen. Better, as the thing developed, it quickly became predictive, and you could do experiments to confirm the math, instead of the maths not quite matching the experiments any more as had been going on.

It's real, man. There are just a huge #heap of things that require math because you cannot visualize them productively. Spin is one. Hell, even basic things you have to do (well, I do anyway) regularly aren't something you should waste time visualizing. EM field theory is one. Curl, grad, divergence, convolution, you just can't describe these things well in your head as a picture, like a ball rolling down a ramp. Yet, it's part of so many neat things that couldn't be done other ways. Hell, I defy you to sit down and do something as commonplace as "visualize" a digital filter design. Without calculus level maths, you aren't going to be able to. Yet they work. And you can't visualize exactly how it's going to come out unless you do the math.

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a reply to: Bedlam

What's sort of mind-blowing is that after your professors finally beat you into accepting that electron spin absolutely, positively, is not a classical phenomenon (which is true), you might learn about the insufficiently-well-known Einstein/de-Haas experiment. Which showed that electron spin, as amplified through ferromagnets, really is almost just like plain old angular momentum. (More specifically it can be turned into macroscopic angular momentum).

Sort of like the completely illogical Catholic trinity after the Council of Nicea (it's both definitely different, and yet the same thing), but with actual experimental evidence.

One of the linked texts, and many teachers, say that the word 'spin' used for an electron was a bad analogy with classical physics, but I disagree. It was so named at the time for good reasons---Einstein/deHaas result was before Stern-Gerlach and the discovery of quantum spin.

The experimental paper that Bedlam alluded to is here:

www.physic.ut.ee...

Since you can't measure a single electron, and you can't draw dots on it to know its spin, all quantum mechanical experiments will use statistical ensembles and magnetic fields to manipulate the spin.

This relies on another property of electrons (and protons and neutrons), that they have a magnetic moment pointing in the direction of the spin, so you can externally manipulate this and see the effects through magnetism.

The experiment uses neutrons (which do have a magnetic interaction even though they are net uncharged, because neutrons, unlike electrons, are composed of quarks which have charges). Because regular electrons would interact much too much with matter to see the effect.

In a nutshell, the 720 degrees rotation in spin space happens when there is precession of the particles in an external magnetic field. As it travels the particle 'turns' in the otherwise invisible 2-d spin space which you can think of as being attached to the particle in the 3-d physical space everywhere, and the turning in this spin space gets back to the starting point after 720 degrees.

If it had been a macroscopic magnetized body in regular 3-d space the precession would return to its initial point after 360 degrees as the rotation would be in normal 3-d physical space.

originally posted by: Bedlam
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