Magnetic fields and Einstein Special Relativity

[moffy]

I had heard that Einstein explained the magnetic field as a relativistic effect of moving charges or Coulomb's Law but never grasped the concept. This video is explained very well and simply using two examples:

1. An electron moving parallel to a current carrying wire (the length contraction bit makes me think the electrons should fall out both ends of the wire).
2. Two electrons moving parallel to one another.

It might be simply a mathematical abstraction, but it is also consistent and predicts reality. Hope you might enjoy it also.

[RoGeorge]

Veritasium has a video about the same topic

[moffy]

Veritasium has a video about the same topic

Thanks RoGeorge, I must say Veritasium isn't my favourite after confusing radio wave radiation/ coupling with power transfer through conductive wires, his notorious light bulb/switch experiment. It is true the EM coupling between the wires 1m apart takes only 1/c seconds, but the power,  what will actually power the light has to travel the full length of said wires.

[RoGeorge]

IIRC the dude from Veritasium it's a physicist, has a PhD in physics, though the PhD theme was teaching physics, but still, he's not a newcomer to physics.

If something seems strange in his videos, that doesn't mean he's talking bullshit, or that he's confused with terminology.  It means that that's how this world we live is:  strange, when compared to practical day-to-day experience.  That strangeness is the state of our current understanding of the world (AKA mainstream physics), the best we have so far.

Don't know any of the Veritasium videos as being wrong about the physics they show.  Sure, one can disagree with mainstream physics, but that's nothing Derek can do about.

[moffy]

IIRC the dude from Veritasium it's a physicist, has a PhD in physics, though the PhD theme was teaching physics, but still, he's not a newcomer to physics.

If something seems strange in his videos, that doesn't mean he's talking bullshit, or that he's confused with terminology.  It means that that's how this world we live is:  strange, when compared to practical day-to-day experience.  That strangeness is the state of our current understanding of the world (AKA mainstream physics), the best we have so far.

Don't know any of the Veritasium videos as being wrong about the physics they show.  Sure, one can disagree with mainstream physics, but that's nothing Derek can do about.

There certainly are quite a number of videos, by various experts, both electrical and physics that take issue with his video about how power is not transmitted through copper wires by the flow of electrons. There is even a part where he says that since voltage is AC, alternating back and forth, how is it possible to transmit power by electron flow? No concept of phasing i.e. +*+ = +, -*- = +. But I don't wish to make this a discussion about whether I agree with Veritasium but rather about the topic.

[sparkydog]

I must say Veritasium isn't my favourite after confusing radio wave radiation/ coupling with power transfer through conductive wires, his notorious light bulb/switch experiment. It is true the EM coupling between the wires 1m apart takes only 1/c seconds, but the power,  what will actually power the light has to travel the full length of said wires.

If you pay a bit more attention, he was also dealing with a hypothetical "magic" light bulb that would turn on if it saw any current; even the negligible current from radiation coupling. As I understood (been a while since I watched the videos), he never claimed that you'd see "full voltage" that quickly.

[T3sl4co1l]

I must say Veritasium isn't my favourite after confusing radio wave radiation/ coupling with power transfer through conductive wires, his notorious light bulb/switch experiment. It is true the EM coupling between the wires 1m apart takes only 1/c seconds, but the power,  what will actually power the light has to travel the full length of said wires.

If you pay a bit more attention, he was also dealing with a hypothetical "magic" light bulb that would turn on if it saw any current; even the negligible current from radiation coupling. As I understood (been a while since I watched the videos), he never claimed that you'd see "full voltage" that quickly.

Oh here we go again...

"Negligible current" is also what's carrying your data along Ethernet cables.  It's just a basic damned transmission line, with some hundreds of ohms impedance (in the scenario).  Current is proportional to voltage and the car battery in the demo would easily light an LED transiently (if dimly; it would have to be done at night).

You can work such a problem with full fields, but ignoring transient/waveguide modes, it reduces to a linear TL.  Radio waves, in the propagating far-field sense, do not apply at all here.

---

As you can see, the amount of misinterpretation, or misinformation, generated on this topic, as a result of that one video, is immense.  It's hard to say if it was actually worth presenting; is it better to be ignorant of a topic entirely, than for some (many? most? how many actually "get it" is hard to say; I would guess they're probably the silent majority, but who knows) to gain understanding, and many to gain an incorrect understanding (or worse yet, be turned off entirely by the controversy and reject any understanding on the topic).

---------------

ANYWAY, regarding relativity and magnetism, yes, it's very simple, trivial really, how to express Maxwell's laws in 4-space; it's one (or two??) equation(s) in a simple relation.  All the complexity is encoded into spacetime itself, the definitions of the variables and tensors used to describe it.  Considering relativity is derived from E&M (Lorentz invariance), this is no accident, and indeed one might say the simplicity is required so as to simplify working with the equations in other terms.

And, conversely -- one can define a gravitomagnetic effect just the same.  It's an apparent or emergent effect, much as magnetism from the relative motion of charges in EM -- which, I forget the particulars, if it's because it arises when you assume proper time in 3-space and thus there has to be some effect corresponding basically to the lack of simultaneity, and this is the result; or if it's a speed-of-light thing where if you assume gravity is instantaneous (it's not) you get unstable orbits but including such an effect puts things back into place; or, these might be wholly equivalent perspectives.  Again, I don't remember exactly.

Tim

[moffy]

You can work such a problem with full fields, but ignoring transient/waveguide modes, it reduces to a linear TL.  Radio waves, in the propagating far-field sense, do not apply at all here.

I agree, my use of the term radio waves instead of EM field was imprecise as it is near field rather than far field. The transmission line analysis is the most precise.

ANYWAY, regarding relativity and magnetism, yes, it's very simple, trivial really, how to express Maxwell's laws in 4-space; it's one (or two??) equation(s) in a simple relation.  All the complexity is encoded into spacetime itself, the definitions of the variables and tensors used to describe it.  Considering relativity is derived from E&M (Lorentz invariance), this is no accident, and indeed one might say the simplicity is required so as to simplify working with the equations in other terms.

And, conversely -- one can define a gravitomagnetic effect just the same.  It's an apparent or emergent effect, much as magnetism from the relative motion of charges in EM -- which, I forget the particulars, if it's because it arises when you assume proper time in 3-space and thus there has to be some effect corresponding basically to the lack of simultaneity, and this is the result; or if it's a speed-of-light thing where if you assume gravity is instantaneous (it's not) you get unstable orbits but including such an effect puts things back into place; or, these might be wholly equivalent perspectives.  Again, I don't remember exactly.

Tim

I must say I don't find the derivation of the magnetic field from the Coulomb effect and the Lorentz transform as obvious as you do, in fact I still find it rather amazing.

[moffy]

I must say Veritasium isn't my favourite after confusing radio wave radiation/ coupling with power transfer through conductive wires, his notorious light bulb/switch experiment. It is true the EM coupling between the wires 1m apart takes only 1/c seconds, but the power,  what will actually power the light has to travel the full length of said wires.

If you pay a bit more attention, he was also dealing with a hypothetical "magic" light bulb that would turn on if it saw any current; even the negligible current from radiation coupling. As I understood (been a while since I watched the videos), he never claimed that you'd see "full voltage" that quickly.

He also made a number of other claims in his video, some of which I mentioned.

[T3sl4co1l]

I must say I don't find the derivation of the magnetic field from the Coulomb effect and the Lorentz transform as obvious as you do, in fact I still find it rather amazing.

I am glossing over quite a lot; and, mind I have no idea how to derive the gravitomagnetic effect myself, just that it apparently exists.

Tim