# Thread: Magnets and Special Relativity

1. Veritasium and MinutePhysics made a video explaining how special relativity makes magnets work.

They did a good job of explaining it but I don't quite understand a couple of things. When the electrons were moving through the wire they weren't length contracted in the same way that the protons were while moving through the wire. Also, if all of the protons are moving at the same speed in one direction, why would the space between them be length contracted? I would think that only the protons themselves would contract. Does anybody have a way to explain this?

2. Originally Posted by Scheuerf
Veritasium and MinutePhysics made a video explaining how special relativity makes magnets work.

They did a good job of explaining it but I don't quite understand a couple of things. When the electrons were moving through the wire they weren't length contracted in the same way that the protons were while moving through the wire. Also, if all of the protons are moving at the same speed in one direction, why would the space between them be length contracted? I would think that only the protons themselves would contract. Does anybody have a way to explain this?
When 2 electron is moving , the electric force between have to go a longer way compare to they aren't moving(The eclectric force have the speed equal speed of light).Therefore the force between electron should be a less than they aren't moving.And surprisingly when we use special relativity to caculate the different between them , they equal to magnetic force between two electron are moving.
Let me do a simple problem.
Two charges are moving in the same direction with the same speed v. And their distance is r0. Using special relativity, electric force have to go a longer distance r=r0/sqrt(1-v^2/c^2). So the force between them is F=(k*q^2/r^2)*(1-v^2/c^2)=kq^2/r^2-(10^-7)*(qv)^2/r^2.
I have thougt about this but we need to work more to explain magnet using special relativity , because we can't use the same principle to explain why magnet can make electricity.

3. Dear Scheuerf...
Originally Posted by Scheuerf
Veritasium and MinutePhysics made a video explaining how special relativity makes magnets work.

They did a good job of explaining it but I don't quite understand a couple of things. When the electrons were moving through the wire they weren't length contracted in the same way that the protons were while moving through the wire. Also, if all of the protons are moving at the same speed in one direction, why would the space between them be length contracted? I would think that only the protons themselves would contract. Does anybody have a way to explain this?
...you question deals with the relative motion of magnet & conductor discussed in Einstein's first paper (OEMBS). You must start by reading the initial part of that paper in order to understand what is going on. Is it Galilean relativity which is correct here?

I cannot answer this for you here but if you post on the Personal & Alternatives thread we can tease it out fully!

Looking forward to it!

TFOLZO

4. Originally Posted by Scheuerf
Veritasium and MinutePhysics made a video explaining how special relativity makes magnets work.

They did a good job of explaining it but I don't quite understand a couple of things. When the electrons were moving through the wire they weren't length contracted in the same way that the protons were while moving through the wire.
Neither the electrons nor the protons are "length contracted" in the movie, the gaps between them are.
Now, the cat (the observer) and the electrons are in the same frame (they move together), so there is no contraction of the gaps between the electrons. But the protons are MOVING wrt the cat, so, in the cat frame of reference, the gaps between protos are decreasing and the proton density becomes higher than the electron density. So, in the cat frame, the wire is no longer neutral, it becomes positively charged. Since the cat is also positively charged, the wire repels the cat via the electrostatic force explained by relativity.

Also, if all of the protons are moving at the same speed in one direction, why would the space between them be length contracted?
Because of the relativistic effect called length contraction.

I would think that only the protons themselves would contract. Does anybody have a way to explain this?
The protons contract as well but their dimensions are very small wrt the gaps between them, so, their contraction is insignificant.

PS: You can safely ignore TFOLZO, he's just a crank.

5. Originally Posted by Scheuerf
Veritasium and MinutePhysics made a video explaining how special relativity makes magnets work.

They did a good job of explaining it but I don't quite understand a couple of things. When the electrons were moving through the wire they weren't length contracted in the same way that the protons were while moving through the wire. Also, if all of the protons are moving at the same speed in one direction, why would the space between them be length contracted? I would think that only the protons themselves would contract. Does anybody have a way to explain this?
I'm not at home right now so I'll look at the video when I get there. One thing I suspect is that the person in the video is talking about the distance between the electrons/protons and not the length of the electron and proton. The electron has no length since it's a point particle. If you have time then look this up in the Feynman lectures and it will explain in detail.

You can download them at Electronic library. Download books free. Finding books See volume II Chapter 25. If you need help after that then please let me know.

6. Originally Posted by Scheuerf
Veritasium and MinutePhysics made a video explaining how special relativity makes magnets work.

They did a good job of explaining it but I don't quite understand a couple of things. When the electrons were moving through the wire they weren't length contracted in the same way that the protons were while moving through the wire. Also, if all of the protons are moving at the same speed in one direction, why would the space between them be length contracted? I would think that only the protons themselves would contract. Does anybody have a way to explain this?
For the first part of your question, you need to bear in mind that in the rest frame of the wire any imbalance in charge would be quickly compensated for by movement of the electrons.

For the second part in relativity all measurements between any two points in the other frame will be length contracted, for the protons and the spaces between them.

7. The modern misconceptions continue.
Originally Posted by Physicist
I'm not at home right now so I'll look at the video when I get there. One thing I suspect is that the person in the video is talking about the distance between the electrons/protons and not the length of the electron and proton. The electron has no length since it's a point particle. If you have time then look this up in the Feynman lectures and it will explain in detail.
The section is red is total BS. Electrons are physically larger than protons or neutrons, hence the latter end up in the middle of the former. Electrons are spinning vortices, the fluid spinning around the magnetic poles as demonstrated by the magnetic (second) quantum number. The refusal of early investigators to use physical models to work out the structure was because the fluid had to orbit faster than light - since the size of the electron varies in its context, being larger in outer space.

Fantasizing about electrons as "point particles" is part of a mathematical agenda of reductionist abstraction - leading to the present failure to develop nuclear fusion, because the vortex structure of subatomic particles is not understood.

TFOLZO

8. Originally Posted by TFOLZO
Electrons are physically larger than protons or neutrons, hence the latter end up in the middle of the former. Electrons are spinning vortices, <snip rest of nonsense>
You are off your Zoloft again Tfolzo.

9. TFLOZO, this forum is dedicated to mainstream physics, and you will keep the contents of your posts to mainstream physics or only post in the Personal Theories and Alternative Hypothesis section, it is up to you. I want to see no more posts from you in the main forums where you argue with the consensus view.

 Posting Permissions
 You may not post new threads You may not post replies You may not post attachments You may not edit your posts   BB code is On Smilies are On [IMG] code is On [VIDEO] code is On HTML code is Off Trackbacks are Off Pingbacks are Off Refbacks are On Forum Rules