# B How To Consistently Explain Electromagnetism With Relativity

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1. Nov 30, 2017

### Ibix

That explanation works as long as you are happy to ignore the acceleration phase and just consider "before and after". There are a number of complications during the acceleration.

Yes. Note that this is a highly unrealistic electron drift velocity. Typical speeds are around 10-5m/s, yielding a separation change of around one part in 1026.

2. Nov 30, 2017

### Staff: Mentor

I disagree. As was pointed out earlier, you needed other people (using the mathematical formulas) to tell you the strength of each interaction. Your approach can help you understand the math, but it simply cannot substitute for the math.

It is not only inefficient, it is also insufficient.

But I am not the one who said your graphs were wrong, that was you. I am just telling you why: they are wrong because they are the outcome of a fundamentally flawed approach.

Another fundamental flaw of this approach is that you are attempting to “explain electromagnetism with relativity” when you don’t know relativity. How does that make sense as an approach? In order to avoid learning electromagnetism directly you are now trying to learn general relativity, but general relativity is a substantially more difficult subject.

If an advanced second grader asked you to explain multiplication tables using logarithms when they don’t know logarithms, would you not recommend a different approach to multiplication?

Case in point...

Last edited: Nov 30, 2017
3. Nov 30, 2017

### Geocentricist

Awesome! That's fine since I'm not illustrating the acceleration.

You're right.

4. Nov 30, 2017

### Geocentricist

How's this? Is this correct? Obviously didn't put as much effort as I did in the other ones.

5. Nov 30, 2017

### A.T.

DrGreg's diagram is better because it shows at least two electrons in each case, so you see their spacing:

For two identical currents duplicate the lower part of the loop.

For two opposite currents look at the lower and the upper part of the loop.

Last edited: Dec 1, 2017
6. Dec 22, 2017

### Geocentricist

DrGreg's diagram is not suited for my purposes since there are too many particles and also, not a simple ratio of electrons to protons in each frame. Is mine correct?

Last edited: Dec 22, 2017
7. Dec 22, 2017

### A.T.

Just enough to have at least two electrons in each case, so you see their spacing. The perfect amount.

What is a simple ratio? What non simple ratios do you see in DrGregs diagram?

It doesn't show enough particles to tell.

8. Dec 22, 2017

### Geocentricist

In one frame the ratio is 0.25 which is harder to work with than mine which is 0.5. Not a big difference but I want to keep things simple as possible!

Sure it does, the ratio is all that matters and you must assume the segment I've shown is representative of the ratio of the entire wire

9. Dec 22, 2017

### A.T.

The ratios are 1:1, 1:2 and 1:4. Doesn't get simpler than that, if you want to show all cases (3 ratios).

10. Dec 22, 2017

### Geocentricist

Ah you're right.

I have a question about the magnetic force. If the strength of the electric repulsion between two electrons co-moving at 87% the speed of light is 1 then is the strength of the magnetic attraction between them 0.5? And if the electrons are moving in opposite directions is the magnetic force repulsive or is it simply halved in strength and still attractive?

11. Dec 22, 2017

### Ibix

See post #76.

12. Dec 22, 2017

### Geocentricist

That gives me a formula but it doesn't answer the question for me. If you don't want to tell me just say you don't feel like figuring it out. jartsa was helpful but you are not

13. Dec 22, 2017

### Staff: Mentor

The formula answers the question. (I recognize your previously stated distaste for math, but it is undeniably essential for exactly this specific question and it does no good to berate someone for answering a mathematical question with math)

14. Dec 23, 2017

### Ibix

If you are asking us to check your working, post your working. If you are just guessing, all the tools are available on this thread for you to be able to answer your own question without guesswork. Try. Post your working or say where you get stuck.

15. Dec 24, 2017

### Geocentricist

I've just been told two co-moving electrons will not experience a magnetic force that pulls them towards each other. Is this true?? I thought this was like the main reason for two wires with identical currents attracting ...

16. Dec 24, 2017

### pervect

Staff Emeritus
It's hard to give a complete and correct description in words without math, but I'll say what I can. In a frame where the two electrons are moving, there is both an electric and a magnetic force. In a frame where the electrons are at rest (relative to the frame), there is only an electric force.

There are well defined transformation laws for how the components of the force transform, but it's hard to describe in non-technical language without mathematics. In technical language, we say that the forces transforms in a covariant manner.

In general, the difficulty in describe how things transformation when one changes frame is a limitation of your non-mathematical approach.

It's a bit like how length contraction works, but the details are different.

17. Dec 24, 2017

### Staff: Mentor

Didn’t we discuss this at quite some length earlier in this thread?

18. Dec 24, 2017

### Geocentricist

Yes, and from what I understood, your position was two co-moving electrons experience an attractive magnetic force towards each other. Or at least that's what I thought jartsa was telling me. And I thought I had it down until someone on another forum mentioned the argument I will elaborate on below.

The argument against this that was given me is if there is an attractive magnetic force and repulsive electric force in the frame where they are moving, but only a repulsive electric force in the frame where they are stationary, the frames do not agree on whether the electrons are moving towards each other or moving apart, or at least they don't agree on how fast they are moving apart. What is wrong with this argument? The only resolution I can think of is that the repulsive electric force in the frame where they are moving is stronger than it is in the frame where they are stationary, although I don't see why this should be the case that the electric force is stronger when the electrons are moving than when they are not.

19. Dec 24, 2017

### Staff: Mentor

They experience an attractive magnetic force in frames where they are moving and a repulsive electric force in all frames. The net force is repulsive in all frames

The frames all agree that the net force is repulsive. They do not agree on how fast they are moving apart

Last edited: Dec 24, 2017
20. Dec 24, 2017

### Ibix

Also, why would you expect the electrons to move apart at the same rate as measured in different frames?