How Special Relativity Makes Magnets Work
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- čas přidán 22. 09. 2013
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Magnetism seems like a pretty magical phenomenon. Rocks that attract or repel each other at a distance - that's really cool - and electric current in a wire interacts in the same way. What's even more amazing is how it works. We normally think of special relativity as having little bearing on our lives because everything happens at such low speeds that relativistic effects are negligible. But when you consider the large number of charges in a wire and the strength of the electric interaction, you can see that electromagnets function thanks to the special relativistic effect of length contraction. In a frame of reference moving with the charges, there is an electric field that creates a force on the charges. But in the lab frame, there is no electric field so it must be a magnetic field creating the force. Hence we see that a magnetic field is what an electric field becomes when an electrically charged object starts moving.
I was inspired to make this video by Prof. Eric Mazur mazur.harvard.edu/emdetails.php
Huge thank you to Ralph at the School of Physics, University of Sydney for helping us out with all this magnetic gear. Thanks also to geology for loaning the rocks.
This video was filmed in the studio at the University of New South Wales - thanks to all the staff there for their time and support.
Music: Firefly in a Fairytale, Nathaniel Schroeder, and Love Lost (Instrumental) by Temper Trap licensed from CueSongs.com
On my fourth viewing of this video, I realized I was looking at... a cat-ion.
This is fantastic I'm so glad you pointed it out
too bad anions aren't called dogions
WHY DID HE NOT TELL US HIS GLORIOUS PUN????
Because everyone has already heard it before. Or at least, anyone with a half-way decent high school chemistry teacher . . . .
Or because they aren't living in an English-speaking world
"You are looking slim."
"Only in your frame of reference."
- how is this not a famous quote? XD
+Martin Verrisin lol so true
+Martin Verrisin it is now
+Martin Verrisin XD XD i think you just made it a quote
xD
What about when someone tells me "You are looking fat"?
What should I say?
Just saw this 7-year-old video. "A magnetic field is just an electric field viewed from another reference frame." Extraordinary!
Agree fully.
This is why magnets blow my emf reader off the charts!!!
Unfortunately the video is wrong.
As is shown In "Is magnetic field due to an electric current a relativistic effect?" by Oleg D Jefimenko available to download on Internet, if one assumes that the interaction between moving electric charges is entirely due to the magnetic field, then the same relativistic force transformation equations make it imperative that a second f ield-this time the electric field-is also present. Therefore, since it is impossible to interpret both the electric and the magnetic field as relativistic effects, one must conclude that neither field is a relativistic effect.
It is a very spread missconception. Several authors have asserted that the magnetic f ield due to an electric current is a relativistic effect. This assertion is based on the fact that if one assumes that the interaction between electric charges is entirely due to the electric field, then the relativistic force transformation equations make it imperative that a second field-the magnetic field-is present when the charges are moving
@@drslump9314 I just read through that paper. Not being a mathematician, I doubt my ability to explain the concept clearly to anybody. (The acid test for understanding a thing).
However.., if pressed.., at 1:30 in the video, the fact that the electrons are moving ought to invoke the same relative principle. But it doesn't.
You can't have it both ways. -That is, you can't have a relativistic effect only when the cat is moving, but not when the electrons are moving. Which means the theory doesn't work.
@@MarkOakleyComics it is an interesting reading.
it shows that what he said in 2:44 is completely wrong. Neither field is a relativistic effect.
Some animations are missleseading. I.e. Electrons drift velocity is slower than a tortoise. Some topics are not even mentioned as the role of surface charges
Dude wtf are you serious , I have been asking this question like millions of times too professors and teachers but noone wanted to give me an answer. This channel is sacred for me from now on
someone like me.
its true though magnetic field is just electric field in a diff. frame of reference, and solves a lot of issues with force fields in general in 19th century, Lorentz found that before Einstein...
This is a very good educational video, but it is just a special case. For example, a single charge also produces a magnetic field. That can not be explained by applying relativity in this fashion. Advanced maths and Lorentz transformations come in there.
@@_BerKill_ someone like me as well
me too i haven't got any answers until i watched this 😮 8 years wow this is amazing
What Schroedinger was trying to say with his cat analogy: Quantum superposition makes no sense.
What Derek learned from Shroedinger's analogy: All analogies are better with cats
It represent cat-ions
Even scientist are obsessed with pussies
He was making fun of the stupid people who used re-equalization to basically screw up quantum theory, which they did and hence why it makes no sense now.
Wife (While jogging): Honey, am I looking slim?
husband: Not even in my frame of reference?
So hows your single life going now
Trust me, after 20 years in wifey prison, single life feels friggin' awesome! xD
@ki kus Is that supposed to be sarcasm or what? What led you to believe i got offended, I implied that his wife got offended and divorced him. Sorry Im confus
@ki kus idiot
Destro Metro I didn’t understand your joke can you please explain it again ASAP??
"A Magnetic field is just an Electric Field viewed from a different frame of reference." Thank you for that mind-blowing definition. I always viewed Electromagnetism from a classical point of view and just started studying Special Relativity, but thanks to this video I see another connection between both theories. Thanks a lot man, you literally made my day!
But it is not...
"Is magnetic field due to an electric current a relativistic effect?" by Oleg D Jefimenko available to download.
It shows it is impossible to interpret both the electric and the magnetic field as relativistic effects.
I'll admit I'm also convinced that it's not true. When you do a simple thought experiment of imagining only moving electrons inside the wire (no protons or neutrons) and then an outside electron, one case where the outside electron isn't moving, and then another case where the outside electron is moving in the same direction and speed as the electrons inside the wire.
When we do this thought experiment, classic electromagnetism contradicts what you would predict happening when comparing it to the theory where the magnetic force is only a result of the electric force combined with relativity.
What happened to electric field and magnetic field are perpendicular to each other and interchange their energy in electromagnetic wave??
@@drslump9314 You got wrong what bit though. There is no real world difference between magnetic fields and electric fields, they are one and the same. We use these terms because they make "more sense" in a Newtonian worldview.
But the universe is not Newtonian.
@@drslump9314 jefimenkos eq are illuminatin, but a current is just a charge viewed from a moving frame
For those who ask themselves, why the electrons dont come closer together in the lab frame: I think its because only the electrons become contracted not the space in between. Hence, the density of charge doesn't change. When the cat moves, everything it sees is contracted, since everything (also the space between the postitiv charges) moves and the density of positive charges increases. Just my approach though
This is a very clear view of why the stationary electron stills sees the cable as neutral, while the moving electron does not. Thanks for sharing,
Omg thanks. I thought it was infuriating no one noticed that this was not explained by the video
This should be the top comment. This was my biggest question coming out of the video.
i also think the fact that the positive ions are contracted plus the egative ones spread out means that the forces stack up wich is why it's negligable from the lab point of reference
I have been struggling with this for long and this explanation seems to solve it very clearly. Thanks.
Our Prof linked this video as part of his lecture. So I have to ask: Is this part of the exam?
Ur lucky to have a professor lime him.
According to Schrodinger it will be both on the exam and not on the exam.
And the answer is - Doesn't matter!
@@SumNutOnU2b I literally just watched a video on Schrodinger lol.
@Max....you saw @Donks comment and watched that video for the sole purpose of leaving that comment. Also does this have anything to do with the confounding fact that some people are rubber and some people are glue?? Unfortunately I’m glue and I’d like to change that if possible.
In the case when cat is at rest and it sees electrons moving, the electrons are more densely accumulated and the positive charges are spread out. So according to this logic, even rest charge must interact with magnetic field.
The length contraction happened in 1D but density is 3D. This is a contraction without necessarily density increase. The density should be determined such that the total charge is zero relative to positive particles reference frame, happens to be the same as the observer or anything "at rest".
Alex Yang please explain it more deeply. I didn't get what you said about 1D and 3D density
Emergy Man you are absolutely right. There is a flaw in this videos explanation.
Electromagnets might offer a simpler case for illustration. In the loops of wire of an electromagnet, the current is flowing so the electrons in each successive loop are all in the same frame of reference and so are the (to us) stationary nuclei. But to the electrons the nuclei are moving and seem slightly closer together(making the next wire-loop over seem positively charged) and to the nuclei the electrons seem a bit closer together (making the next wire-loop seem negatively charged), so the loops all attract one another, because there is a slight curvature of the spacetime-like manifold that constitutes the force applied by the electric field.
Ya ur right but only if the wire is thick enough to carry so many free electrons and even if it is thick charge wouldn't interact as due to resistance in wire the current decreases
I’ve been teaching high school physics for 32 years, I and I’m still learning such cool things thanks to amazing videos like this one.
Hey buddy..
I too teach physics in India would love to learn from your experience.
If I can get any of ur contact
Would be very grateful if you teach whatever you learn to your students as well😊
Marks are not everything
These amazing concepts will make physics both easy and fascinating for them
I know you meant it well, but tbh that's a bit sad (nothing against you!!). How aren't physics teachers required to know this, what kind of joke is uni degree for a highschool (that means right until university right?) teacher to not know this.. So confusing how bad "our" education is before uni and then you go to uni and everything is over 9000 and all profs are angry because you didn't learn it in highschool.. wtf:D
@@ibonitog , if understanding relativity were required then there wouldn't be any high school physics teachers!
@@HR-yd5ib yeah and that is sad.. in my high school, special relativity e.g. was part of the final year curriculum.
Why the wire has no charge in the rest frame: The electrons do initially experience length contraction as they start moving, but they repel each other and spread out to restore neutral charge. The same can't happen with the protons because they can't move freely in the material.
Why a single moving electron produces a magnetic field: The electric field caused by the electron also moves along with the electron, causing it to contract and increase its density.
The contraction is not comparable to compression of air for example
I agree and I think the wire should have electric field from rest frame like the way you mentioned, which cause the magnetic needle to deflects
Why does the electrons get less dense when the cat moves in frame with them then? Shouldn't their mutual repulsiveness space them out evenly again?
A positively charged cat is a cation.
Love it!!!
richard meagher oh goood noooo. Why. Why???????
richard meagher if he wanted you be a idiot, he say, "all know it all's comment Bellow"
Pawsitively charged
@@fgvcosmic6752 Oh this went way fur ther than I thought it wood. Joy!
Trying to be flirty with nerds:
"You're looking slim"
"only in your frame of reference"
isnt that like an insult?? that one should move at high speeds to perceive you as slim ,i.e you hella fat XD
Why is the wire neutral when current flows through it? Shouldn’t the electrons experience length-contraction from our point of view? Shouldn’t a stationary cat therefore be attracted to the wire?
From our point of view there is a magnetic field due to the current which is why the cat is also repelled
@@Blegie he means, when the cat is not moving. In the Video he says, that there is no force on the cat, but the electrons are moving and should be contracted out of both perspectives.
i was looking for this comment
@Fabian Wittmann yes exactly. And also, he says that the flow of electrons is ever so slightly spread out from the point of view of the moving positively charged cat. Is that right though? There’s no such thing as reversed lenght contraction right?
I Completely AGREE. In fact we should start demanding the link to the papers or demonstrations, otherwise these animations are just misleading or incomplete
I was always told electromagnetism is a relativistic correction on a moving electric field but I’ve never actually had that explained. Thanks heaps for that.
electromagnetism is analogous to you moving a spoon in a cup of coffee. if you move it, fluid from all sides rushes into the lower pressure density area right after the displaced fluid. the whole universe is a fluid, charges are a measurement of fluid (or its pressure) density around matter , which in itself is just stacked fluid waves locked in a standing wave motion by having just the correct wavelengths to perpetually push each other, and whos perpetual movement creates a perpetually lower fluid pressure density around the standing wave, which is called gravity on the subatomic, incoherent scale, and magnetic field when only looking at the stacked force of coherent pull from all the tiny mass units which are aligned to pull together in magnets. there is no need for any kind of relativistic nothing. the amount of charge density might be the same in the entire wire, but the moving charges create an area with lower charge density right behind the displaced charges, which compels the charged behind them and in front of them to move, causing a chain reacting in the wire. the non zero local charge density comes from the transmitted pressure impulse creates by the battery, or more specifically the induced movement. You could use relativistic language to describe this, but it is just semantic confusion for something very simple. you dont stir your coffee with the speed of light, but it still makes the coffee in your cup implode into the center of the lower pressure created by you moving the spoon. you would not use relativistic language in that case, yet the same implosive field is created, just in another medium. the faster you move the more implosive the coffee becomes, and if you were fast enough and pushed only in one direction, a vortex would form that would approach a phi golden vortex spiral more and more with increasing speed. a magnetic field made visible in 3 dimensions looks like a double phi golden ratio vortex, cause it is an implosive field . In text books, the spiral shape is not shown, and the field lines are instead depicted as straight, but thats not true and comes from only doing visual experiments on a 2 dimensional plane, which doesnt show the golden ratio vortices.
my point is that its all just changing pressure and fluid dynamics. the entire universe is just a single unified superfluid with its waves forming standing waves, and all fields are just pressure differencials ultimately caused by perpetual standing waves creating perpetual areas of lower pressure, and them stacking on top to appear particle like on a larger scale. in reality, the electrons moving in the wire do not exist as countable units, they are actually an amount of fluid literally flowing through the wire after getting pushed out of their pressure neutralizing areas around the standing waves which form the copper atoms, and that movement creates an implosive force around the wire just like in the cup.
I got it! I finally got it! I was wondering, from the stationary point of view, why the electrons don't contract and attract the positive cat. It is because from the moving cat's point of view the entire world - the positive nuclei and the wire along with it - is moving. That is why the space between the positive charges contract. Because that space itself (i.e. the wire they're in) is moving in this frame of reference.
From the stationary point of view, however, only the electrons themselves are moving. This only means that the electrons are squished down a bit and get flatter, but the space between them (again, the conducting wire) is stationary. Therefore the distance between charges remains the same and there is no change in the charge density.
I feel so happy right now.
Edit: It turns out this intepretation is not entire correct. In a simplified scenario of two co-accelerating bodies there are basically two possibilities (or more like two ends of a spectrum). If the distance between them stay *constant from the bodies' pov* it will *contract* from an observer's pov. If the distance stays *constant from an observer's pov* it will *expand* from the bodies' pov. It depends on how/when that acceleration is applied to the different bodies. Look up Bell's spaceship paradox for more info.
But the electrons in a wire seem more complicated than just some constant acceleration. Not sure how exactly it works... but i guess it does.
If the electrons contract but the space around them doesn't follow-up, what is there between the end of space and the electron? And does it occupy no space to not create distance? wtffffff Ok, it's late here now, am I confusing things?
Ropbastos I'm researching this right now. If you want to PM me (if that's possible on CZcams), I could show you what I've found and we could discuss it.
Ropbastos
It's the protons that contract, and it's space itself that is contracting.
You've got to remember it's not just the time that is relative, it's space AND time that are relative. That's what the illustration of the squished car was all about. From one relative framework (stationary observer watching moving car), the car is squished. From another framework (moving car watching stationary observer), it isn't. In fact, it's the outside observer who is squished! It's not a perception thing, either. Any means of measurement the stationary observer uses to measure the car comes up with a shorter length than the driver of that car would find if measured from his own frame of reference. The car is literally shorter for the stationary observer.
So for the cat and the wire, the protons in the wire really are closer together than the electrons when the cat is moving, causing the positive cat to be repelled by the now slightly positive wire. From a stationary observer's perspective, however, the wire remains neutral.
Jeffery Wells "From the stationary point of view, however, only the electrons themselves are moving. This only means that the electrons are squished down a bit and get flatter, but the space between them (again, the conducting wire) is stationary." I'm referring to this part of the main comment. From "Derek's" pov it would be the electrons contracting, no?
By the analogy in the video, when the camera is stationary, the car squishes while the space (background) remains unchanged. But when the camera moves, the whole space is moving backward in it's frame, so the whole space (background) squishes, hence making its content (positive ions in case of wire) less dense.
I feel so happy right now as well. Thanks for helping, Volbla. :)
At primary school I never understood why magnets work... Now I see why it never gets explained to kids;)
xD
exactly!
even adult cant understand
I never understood too... And now I do
@@JanKowalski-wb2fv i still dont haha. here he has a moving charge. but what happens when i put a magnet here? does it have moving charges and thats why its gonna have a “magnetic field”?
1:20 "so if there were... a positively charged cat nearby,"
*cat dying sfx*
I absolutely love you guys, this is a such a great explanation it literally filled me with joy since I have been trying to understand what magnetism is for months now, but have been unable to find a satisfying answer. The work you guys do is so so so important and I am extremely grateful for this video and all the work you guys do.
6 years of Electrical Engineering curriculum which included extensive study in EM and I was never taught this...... I'm somewhat disappointed in my university. I actually think I asked this specifically: "I understand all the effects of a magnetic field, but what IS it fundamentally?" and after some discussion of permeability and Maxwell's equations I lamented that no one in that class, professor included, actually knew. We could all describe a magnetic field by its effects and influences and even the qualities and characteristics of materials that can support a magnetic field and the methods of inducing one, but not what it actually is. Thank you so much for this video. I can now (at least more fully) answer that question "What IS a magnetic field".
+djscurge that's why you should study physics and not just EE
+djscurge, I came across this in an intro EM textbook at Uni and it blew me away. It was like a "holy crap, of course" moment. But Maxwell's Eqns were like a beautiful derivation based on laws found from experiment, whereas the Relativity argument was more like a logical derivation from first principles.
+UteChewb Wow. Can I know which EM textbook you is it?
loo xavier
This was a long time ago but I kept the book because it was so amazing. It is "Electromagnetic Fields and Waves" by Lorrain and Corson. It not only has a solid treatment of EM but it has plenty of examples with detailed explanations. Googling, it appears there is a pdf of the 3rd edition available on the internet.
The text gives an in-depth (intermediate level) intro to electrostatics and then before getting into magnetism it covers special relativity. :) I'm sure there are more up to date texts available but I don't know them.
+djscurge Don't feel bad about your university curriculum. This is not something that you can teach freshman or even juniors right away. It takes some time to be able to recieve and understand it. This is honestly not something that would be relevant for most EE programs - we teach it to Physics students in their third year.
I just want to say a BIG THANK YOU for your videos having captions in so many different languages. I started watching your videos and it was a struggle to try to understand English and Physics at the same time. When I saw that you have captions in my language I screamed of happiness! (This sounds weird but I have just realized the eager I have to learn Science) thank you, thank you! It's truly a beautiful thing that your channel is spreading knowledge to so many people all over the world. That's huge.
bonjour
Which language do you prefer???
Which language do you speak?!
In India, Juli is a Dog's Name.....😆😂🤣🤧😅
@@gopalkrishna3803 I think it's a very disrespectful comment. Don't downgrade India's name please
I am not sure if the explanation can be correct. The Lorentz factor at the speed shown at 3:27 is only 1+5*10^(-25), meaning that the relativistic effect is only 5^5*10^(-25) (because at 0 speed the Lorentz factor is exactly 1). Now I assume a copper wire and proceed to making only a rough calculation with orders of magnitude, which will surfice for my purpose. 1 kg of copper has about 10^24 atoms, and each atom has 11 valence electrons (which are the free electrons in a copper wire), so there are about 10^25 free electrons per kg copper. So if the magnetism is caused by special relativity, there would only be about the charge of 1 electron difference per 1 kg of copper wire. The charge of 1 electron is about 10^(-19) coloumbs, which would not be enough to observe the strong forces that you get, if you e.g. use a coil with 1 kg of copper wire. So either the ecplanation is wrong, or the drift velocity mentioned at 3:27 is wrong.
Eczacly!
I can not thank you enough for this brilliant video!
For years now this question has been bugging me but most explanations weren't sticking with me. This was presented so clear that it will finally stick in my head.
I always look forward to your videos!
But what if the cat is not moving? Aren't the electrons moving relative to the cat, which means more density of electron and thus pulling the cat?
+Michael Englo It is a mistake in the video. With the cat not moving with respect to the atoms in the wire, the positively charged ions (atoms) appear to the cat at the expected distance, whereas the electrons moving past appear to the cat foreshortened and closer together, and therefore a net negative charge from the cat's point of view. So yes, you are correct, the stationary cat feels attraction to the stationary wire with negative electron current flow.
+Steve Greenfield Someone else in the comments explained that that's not correct. According to special relativity, the electrons themselves would experience length contraction in the stationary cat's frame, but the space between them would not since it's not the space that's moving relative to the cat. Electrons are essentially point charges, so the length contraction of an electron itself has no effect, and the wire remains neutral in the stationary cat's frame.
The length contraction affects the electrons as a group, because they are moving as a group. The spacing appears the same from the electron's frame of reference, but the group has shrunk in length from the cat's point of view.
Actually, someone else had a better explanation. In reality, both the nuclei and the electrons are moving. In the stationary cat's frame, the nuclei move back and forth but the electrons move around in a way that almost immediately neutralizes any charge imbalance caused by the movement of nuclei, even when a current is flowing, so that the wire remains electrically neutral. When the cat is moving, however, there is no way for the electrons to neutralize the charge imbalance since the electrons appear less dense than the nuclei.
There is no difference. Imagine this:
Reverse charges in the wire, with a stationary cat. Stationary negative charges, positive charges moving to the right, stationary positive cat.
From the cat's reference frame, negative charges appear normal. Positive charges appear to be closer together and so the cat is repelled.
This is exactly the same as the cat moving to the right with the negative charges moving to the right at the same speed.
When speaking of something as stationary, this is misleading. Because you can only speak of motion in relation to some other frame of reference. So a stationary cat is a cat stationary with respect to -you-, but you aren't part of the picture. The cat is either stationary with respect to the wire, or stationary with respect to the electrons. In each case, everything that is moving relative to the cat appears to the cat as subject to Lorentz contraction. That includes the entire universe.
www.mtholyoke.edu/courses/tdray/phys310/electromag.pdf
"If you can't explain it simply, you don't understand it well enough." - Richard Feynman
Bro he is not Feynman but einstein
Nah it was Feynman.. check it
"We stumbled on this archival BBC interview with American theoretical physicist Richard Feynman over the weekend, and just couldn't stop watching. Filmed as part of the 1983 TV program Fun to Imagine, the interview takes a rather tense turn when the interviewer poses what I'm sure seemed like a very simple question in his head: If you hold two magnets with the same poles close, you'll feel a force pushing them away, and if they have opposite poles, they will snap together. "What I want to know is, what's going on between these two bits of metal?" he says, as Feynman does little to mask his annoyance. "Why are they doing that, or how are they doing that?"
For those who haven't seen this clip before, Feynman's response to what anyone would consider a perfectly reasonable question is somewhat off-putting. To be perfectly honest, Feynman initially comes off as a bit of a jerk whose "delicate genius" has been needlessly disturbed. But through his obstinance, Feynman admits that it's actually an excellent question, but one he simply cannot answer in terms that a layperson can understand.
"How does a person answer why something happens?" Feynman responds, before launching into an analogy about "why" Aunt Minny slipped on some ice and ended up in hospital. Just as you can't fully explain that scenario without discussing the fundamentals of fluid dynamics, and why you can't properly answer "Why is the sky blue?" without also explaining the concept of Rayleigh scattering, he says you can't explain why magnets behave the way they do to a layperson without first explaining the concept of electromagnetic forces to them. And who knows if they'll even understand that?
Feynman tells his interviewer:
"I can't explain that attraction in terms of anything else that's familiar to you. For example, if I said the magnets attract like as if they were connected by rubber bands, I would be cheating you. Because they're not connected by rubber bands ... and if you were curious enough, you'd ask me why rubber bands tend to pull back together again, and I would end up explaining that in terms of electrical forces, which are the very things that I'm trying to use the rubber bands to explain, so I have cheated very badly, you see."
www.sciencealert.com/watch-richard-feynman-on-why-he-can-t-tell-you-how-magnets-work
@@Chicken_Little_Syndrome he couldn't explain it to an average person and washes hands saying that they're so average and uneducated that they have to understand principles behind it that they're also too much for their little mind? He's not wrong, but it's no excuse for someone on the "TOP" of historical scientists and idolatred icon and for anyone "educated".
It was *Einstein!!*
One question of the college EM course examine was that : calculate the E & M of two parallel moving charges with speed V (relative to the observer) in terms of the frames of the charges and the observer with Lorentz transformations. In the observer frame, there's force inbetween due to the interaction of a magnetic generated by one of the moving charge and the other moving charge; in the charges' frame , it's the static electric repelling(or attraction) force of the two charges.
this is my favorite veritasium video of them all on his channel, i had goosebumps man. you have my respect sir...
When the cat was stationary, negative charge was moving with respect to it, so distance between -ve charge should become less and the wire should attract the positively charged cat when it was stationary. Moreover, if the cat starts to move in the direction opposite to the electrons, it should feel even higher force of attraction.
Because the animation in the video is misleading. In reality, you should visualize the positive charges as holes that move opposite to electrons. So they both have equal and opposite velocities so the net effect will make the wire neutral in charge
You need to go to back to Maxwell and ether and magnetism separated from electricity. Read Robert Sungenis.
The electrons all move on separate trajectories such that their spacing is unchanged . They do not constitute a solid object subject to relativistic stresses
@@DrDeuteronif that would need true it would be unaffected by the moving cat as out would not change. Motion is relative. From the cat perspective it is never moving. The electrons in the wire only change speed and it direction
but then in your frame of reference the negative electrons are moving , and are 'slimer' and so they are more dense,so should'nt the cat attract to the wire
it's just that narrator's frame of reference doesn't matter to the cat and the wire.
Indeed. The explanation is ridiculous.
Thank you so much for the explanation, man!
Just one problem with that: in a metal, we don't explain conduction using holes. Not that it's relevant to your explanation but it's just an FYI.
YiFan Tey there are no "holes". The positive charges are the positive ions in the metallic lattice.
@Veritasium In a circuit, superficial charge are necessary. Charge density is very small but they do have to exist. If not how would we explain the existence of an electric field. It was already known by Weber. It has been discussed more recently by H Härtel and Assis.
From my point of view, cats are only attracted to wires that have christmas lights and are plugged in!
help I'm stuck in an infinite "click here" loop between Veritasium telling me to go to Minute Physics and Minute Physics telling me to come here :-(
Break the loop check out Quantum Atom Theory!!!
> Click here < to escape the loop.
There you go. You're welcome.
Do not worry my suggestion-abiding friend! CTRL+F4 will break the cycle!
Destroy the power plug and incinerate your computer. Problem solved.
so... If the cat is not moving, it is the negative charges that are contracting. Therefore there is a higher negative charge density, and the cat is attracted ?
Guillaume Lemaigre No - that confused me too at first.
If electrons are moving right, protons are moving left. There's a sea of ions, positiv and negative, and electron drift also results in positive charges drifting in the opposite direction. From a still point of view, both contract in the same magnitude, and so there's no net charge.
Steven Wang No. That's wrong. In the stationary cat's frame of reference the protons are not moving!
ricomajestic Well, not necessarily the protons are moving. But with electrons moving to the right, essentially positive charges are moving left.
Take a neutral charge and a positive charge:
± +
Suppose the electron jumps to the right:
+ ±
The electron has jumped to the right, but essentially, the positive charge is moving left. So you're right - no, the protons don't move, but yes, the positive charges are moving left as the electrons move right.
Steven, it depends on the frame of reference. From a stationary cat frame of reference (i.e.- a cat that is not moving relative to the wire), the protons are not moving but the electrons are moving to the right. However, from the electron's frame of reference the protons (and cat) are moving to the left.
Steven Wang Ok that's much more clear. But still...
Just explain me why an electromagnet atract then a piece of metal (like iron). Because the iron is not moving but is still attracted... it just feels like it contradict itself somewhere.
(i know for sure that magnetism is really well explained by relativity in term of moving electric charges, but on the concept side, it's not clear to me.)
I just saw a video talking about this video but I cant really understand it, but with this I can fully grasp whats happening and the formation of magnectic field when current passing through!
I watched so many videos to understand this and I eventually got it. It really helped me understand it when you looked at the repulsion of the positively charged cat from the cat's and an observer's frame of reference Some insist that there's no such thing as magnetic force whereas from an observer's frame of reference it makes sense to say the cat is repelled due to the magnetic force.
The results are the same and thats the main thing. Thanks 🙏👍🏻
So I watched your video. You sent me to MinutePhysics, then they sent me to you, then you sent me to them, then they sent me to you... HOW DO I GET OUT OF THIS CYCLE???
**Old woman's voice** It's been ...... 84 years.......
Alan Jay Its called an youtube loop.You are stuck for eternity.
Arghya Sen Awh Naaaaawwwwwwwwh!!
+Alan Jay LOL omg
+Alan Jay Want to know how to keep an inquisitive CZcamsr busy?
+Alan Jay, That's what you get when two great persons collaborate.
I have seen comments questioning this explanation by saying that the electrons appear to contract when they start moving, creating a net negative charge and thus acting on the cat even when it is stationary. I also had this thought when I watched the video. However, when the electrons start moving and appear to contract from the wire's and a stationary observer's reference frame, the electrons will repel each other from the perspective of the wire and stationary observer until the density of both types of charge are the same. On the other hand, this spreading cannot happen from the perspective of the moving observer because the positive charges are metal ions that are bonded to each other; these charges cannot spread out without stretching and lengthening the wire. The electrons likely cannot contract and neutralize the wire from a moving reference frame because they are being forcefully pulled forward by the electric field that started the current in the first place.
Thanks! I was really confused and the comment sections of those questions were filled with hate comments (unlike most science vidoes)
You're welcome.
not convincing. Good for the try though. This question needs addressing
Girlfriend: "I'm pregnant!"
Boyfriend: "Not in my frame of reference."
😎🎶YEAAAAAHH🎶
*drives away*
Thank you once again for this video. I have always wondered the effects of magnet and possible relationship with relativity.
i think he forgot to mention this
When the cat is stationary, in its frame
the only things moving are the electrons
(and not the space between them). So the electrons get squished but the distance between its centers is the same, and the charge density remains the same.
However when the cat is moving everything moves except the electrons, in the cat frame. So the protons and the space between them contracts, effectively changing the charge density and creating an electric force in the cat frame, or a magnetic force in the stationary frame
EDIT- this is my own explaination and I came up with it on my own and I was in 9th class when I came up with this answer one year ago now I am in 10th so I have only some knowledge about relativity and there are lot of new things to learn so maybe this explaination is wrong in that case please correct me. And this is my father's account if you are thinking why I look old
I think that special relativity is also applicable to the space time fabric as a whole along with subatomic particles like the proton and electrons and also the members of the elementary particles.
Thanks very much.. I have been very confused about this from a long time
Thanks for the explanation. I immediately looked into the comment section expecting that someone must have addressed this issue.
@@shashankknp smart bro
that is, when a rocket flies at a sublight speed, shrinks not the length of the rocket (from nose to tail) visible by us, but the atoms of which it consists?
If the electrons are moving relative to a stationary observer, won't they be contracted, and thus have a higher density of negative ions compared to positive ions, and thus be negatively charged to the observer?
I thinks, bcz of drift velocity are very very small w.r.t to normal movement...
This is because the wire tries to remain neutral under a current so the "real" density of electrons has to decrease slightly to keep the zero charge with the moving electrons. The protons are not moving so they determine the new density of electrons, which has to be the correct one to keep the wire neutral. That's the reason that the proton outside the wire sees no charge when it's not moving relative to the protons. (Sorry for my english)
Lot of confusion here stems from a little oversimplification in this video. The positive charges--or rather, the distribution of positive charge--is in reality not actually static but moves in the *opposite* direction as that of the negative charges.
Basically, you can loosely think of it as if an electron migrates away from a nucleus in some direction towards some other positive charge then it's former location because more positive, while the latter becomes more neutral. So, you have like a net negative charge movement or stream in one direction, together with a positive-like charge movement or stream in the opposite direction. So, from a rest charge perspective these opposing streams merely cancel one another out and the so-called "current-carrying" wire overall actually appears simply neutral. But, if that external charge happens to *just so ever budge* into the direction of one of these streams, then it will experience that whole associated effect (magnetic repulsion or attraction) due to the length contraction phenomenon presented in this video.
@@MikeSmith-vb8ul Thank you. Your clarification really helped me out.
@@MikeSmith-vb8ul By that logic, if the cat-ion moved in the same direction as the protons, it would "see" the electrons moving in the opposite direction and thus become more densely packed. And so it would be attracted to them... But that's not what actually happens, is it?
If you are wondering why moving electrons do not cause length contraction when the cat is stationary, electrons are little more complicated than simple pictures of protons. Free electrons in metal, that's what they make a conductor, are nevery stationary at room temperature. They actually constantly move really fast (~ 1 million m/s) and are scattered off by protons and other electrons. Without electric field, they move to all different direction and that's why we don't see any effect. When electric field is applied, their moving directions are slightly drifted and their overall collective motion becomes what we call "current". It's not like they all of a sudden align and start marching in a single direction altogether. Therefore, you cannot simply apply special relativity to those electrons.
For protons, however, they are mostly tightly bound to the lattice structure. Thus, they are stationary and we do observe length contraction when the observer moves fast and that creates net nonzero electric fields as this video explains.
P.S 1: electron contraction is not something you would consider under any circumstances. When you try to measure the contraction of an electron, uncertaintly principle dominates and you lose the idea of how fast the electron is. Thus what's the speed to compute the contraction?
P.S. 2: If electron's size is macroscopic and they are all aligned in a single direction, both their size and the spacing get contracted.
The actual nature of conduction only obscures this thought experiment. Here, electrons move on trajectories such that their spacing is unchanged, by definition.
At 2:23 you discuss about the the density of positive charges increases and positive cat will repel if we see them wrt moving cat's frame of reference, but i am so confused that at 1:36 the electrons are also moving but did not come closer and the charge density of negative charges not increases so our cat does not feel force of attraction due to higher negative charge density when cat is stationary.
And what if only one charge is moving.
Plz correct me if I am thinking wrong and missing something.
I've returned to this video so many times throughout the years, I love it, and it's something I never hear people talk about. This is brilliant!
This is absolutely friekin insane!!! I can’t believe my ears and eyes. Relative magnetism. Phenomenal!
Saw this video now, after 10 years it was uploaded to CZcams thanks to one of my dear friends. This is so engrossing 🙏🏼🙏🏼🙏🏼 never in my wildest imagination I would’ve thought in this direction. Truly amazing! Thanks 🙏🏼 😊
*Question:* but what about the case where cat is stationary? Electrons are moving so they should contract, and protons are stationary so they should stretch. Overall, there should be a net negative charge which should attract the "cat-ion". But it doesn't...
I know the force on cat is _F = qvB_ and since v = 0 there is no force. So what happenes here????
But, from your point of view, the ELECTRONS are moving, so their seperation should be "ever so slightly" contracted, and since the positive charges aren't moving so there should be a higher density of negative charges in the wire from my point of view and the cat should be attracted to the wire
Woah! Mind blown... I had no idea! So totally cool, relativity is awesome
I really wish Veritasium could explain some of the workings of human body.
Your videos,topics and explanations are outstanding and so are the production methods very interesting.
Remember learning/calculating this in first year uni physics - thought it was so amazing. Still do.
mm something doesn't quite make sense though. If the cat isn't moving and the electrons are, then aren't the electrons contracted in the cat's frame of reference? Therefore shouldn't there be high density of electrons, causing the cat to be attracted to the wire?
I'm gonna just copy and paste a response from another person answering virtually the same question. He explained it really nicely.
From "Bob Badeer" a couple of months ago:
"In Derek's reference frame, yes electrons are moving and the distance between them is effectively 'slimmer' in his reference frame. But consider this, overall the wire is also neutral. It has to be since applying an electrical current doesn't make a conductor ionized (non neutral) overall. So what's going on?
Each time an electron moves from atom A to atom B, atom A has lost 1 electron (it is now positively charged) while B has gained one more electron (it is now negatively charged). It's as if atom B gave a positive charge to A instead of A giving an electron to B. That positive charge is an electron hole. Think of it as money. You have a 100$ bill and I have none. I give a -100$ bill to you : it cancels out your 100$ bill making your net worth 0 while I have lost a -100$ making me richer by a 100$ (2 negatives make a positive). Wealth hasn't been created nor destroyed, only transferred.
When an electron moves from A to B, an electron hole moves from B to A at the same time. So in Derek's frame, electrons are moving but holes are also moving at the same speed (thus having the same relativistic effects) making it neutral.
In the cat's frame, electrons aren't moving anymore but holes are moving in the opposite direction twice as fast making the wire clearly positively charged thanks to relativistic effects. If you reverse the current, you'd reverse the direction in which holes and electrons are moving. In this scenario, electrons are moving in the opposite direction while holes are stationary in the cat's frame. That is why inverting polarity inverts the magnetic field.
Now clearly, the absence of an electron isn't a real particle : it's just a region of space with no electron in it. So where does this positive charge-like effect comes from? From the atom's protons. Remember, we are talking about atoms here and atoms are made up of negative charges (electrons) and positive charges (protons). So when an atom has less electrons than protons, it is ionized (cation or positively charged)."
That explanation 8sn't satisfactory either.
If the positive charges come from the protons, then the positive charges are relatively stationary in the wire....thus no relativistic effects for things in the wires inertial frame.
The explanation is insufficient to explain any number of real world phenomena:
-even without protons, for example electrons shot down an evacuated tube, the magnetic field is created and will alter the path of moving charged particles.
-nothing in the original explanation of follow up attempts explains why a charged particle moving directly toward or away from a current carrying conductor experiences a force that turns it away from directly into or away from the wire. If it were correctly modeled by electrostatic attraction/repulsion, the path would not experience this turning.
Ben Griffin I agree, I don't think that happens, because it's like watching a screen, even if you see a jet dash away in a movie, nothing's really moving, the led lights just turn on in sequential order so the positive charges aren't really being length contracted.
Dont worry. Most stuff makes no sense in Einstein theories. If you start to consider them seriously and not as an abstract you will get to paradoxes, division by zero, infinite densities or zero volume and negative radius etc.
No wonder Nobel committee did not gave him Nobel for that.
oldi184, says the guy who has "100 Reasons Why Evolution is So Stupid" in his playlist.
Arghh! You guys are just alternating me between these two channels repeatedly. I'll still do it for the love of science 😊✌🏽
Omg. The electromagnetism midterm is coming and I just didn't understand chapter 5: Fields of moving charge after the lecture but this video really helps clear my mind and trigger curiousity. Thank you so much.
Wow! What a neat, simple and to the point explanation! Love it
I feel the more I understand it the more confused I am. So how does the electromagnet attract a not moving metal object then?
A not moving metal object has metal atoms with electrons circulating around them. This creates a "magnetic field" for every atom (called magnetic moment, not literally) which lines up with other such magnetic fields of other atoms to temporarily create a magnet with two poles (given if the metal shows paramagnetism)
A circulating electron is like current across a circular loop, so like a ultra small version of a solenoid
@@mukherjee.p exactly, magnets. But in the video he presents a charged particle not an magnet.. and isn't this only a phenomena with AC current? I'm also confused
@@ivarnyman3417 Well Yeah but not only for AC. Any moving charged particle produces a magnetic field (on top of the electric field it already had). You move an electron (somehow) (doesn't even have to be in a circuit or anything. Simply moving it through space) and it'll create a very small magnetic field. That's the theory
magnetic field lines want to be in the (permeable) metal, it lowers the field energy the closer the metal gets to the magnetic. Energy changing with position is a force.
how come at 1:18 the cat doesn't experience a force when it isn't moving?
I thought that because the electrons are drifting by minutely then they are slightly more dense and contracted and stuff per the video, doesn't that mean the wire will have more negative electrons and be attracting the cat?
Where have I gone wrong?
I feel that it is wrong. If someone considers the twin paradox resolution, it says even though the observer in moving frame of reference seems the time is dilated in stationary frame (with respect to whatever), the actual time dilation happens only for the frame of reference that is moving. They reason this by accounting for the effect of acceleration (may be based on general relativity) for the moving observer before it becomes an inertial frame. Similarly, we can say that the actual length contraction happens only for the cat and not the wire. So then, how could the explanation in the video stands correct?
that video was great,for first time i have grasped the concept of special relativity,i used to float anyway.thanks veritasium keep your lane
You brought the relativity spark back in me. I was losing mine. Thanks for this amazingly simplified video.
I've watched 5 videos today on what magnetism is and none of them actually explained what the "field" is made of or how it comes out of the material and back in again
This is the fun part. Mathematically, quantum electrodynamics is by far the best model we've got, but it's cutting edge. I mean, we know fields occupy space, possess energy and momentum, and interact with each other, but we just don't know yet whether they're made of anything more fundamental than themselves, nor if "field" even gives an ideal picture of what's going on. But assuming it does, a particle is a sustained oscillation propagating through spacetime. Each particular type of particle has a corresponding field. Electrons are oscillations of the electron field, and they continually cause momentary fluctuations/disturbances in the electromagnetic field (the field for photons). These disturbances can't be detected directly as they don't have all the right traits to become particles, so we call them a virtual particle and debate whether or not they exist. One way to imagine it is that all the possible positions in spacetime have a state, and each field is like a huge spreadsheet woven throughout, applying formulas to every position. Due to the uncertainty principle, we can't pinpoint an exact position, there are fluctuations everywhere, and the smaller the region we try to observe, the bigger those fluctuations get.
With a normal object, the momentary disturbances aren't aligned in any special way so their effects are cancelled out. However, a magnet's unpaired electrons have been aligned so that they have the same 'spin', the effect being that they disturb the electromagnetic field in a consistent way. Electrons of certain other objects then acquire momentum in a common direction when they absorb the disturbances (which are otherwise reabsorbed by the magnet). The arrowed lines drawn coming out of the material and back in show the direction that the acquired momentum goes. But the disturbances themselves reach outwards in straight lines from the magnet in all directions.
Classical electromagnetism doesn't reflect physical reality, it's just a (really good) mathematical model. Even quantum field theory seems to fall apart in certain circumstances, so we don't have an absolute picture of reality. This is frustrating, but I think being able to visualize electromagnetic waves and fields is still really useful.
I like the Thunderbolts project. They have hundreds of videos trying to illustrate what electricity and magnetism could be. The best I've heard is that magnetism is an effect of ions interacting linearly, instead of in a waveform, with the "ether" (space-time.) People don't like that word because it's archaic. But, I understand that a fundamental geometry of reality has been "found" and that's what I think they mean, even if they don't realize it. Anyways, it's been illustrated that the magnetic force is similar to tugging a rope and feeling the effect, as apposed to whipping the rope and waiting to feel the wave, on the other end. This is why there is an "instantaneous" effect when compared to something with a "limited" speed such as light.
look up Magnetism - Ken Wheeler: czcams.com/play/PLjz0SgxcrlEbksk1t13CfZt1p6F8wg2ZH.html
Electricity and magnetism oppositional forces. They are the same differing only by degree and temperature. When what a magnet approaches absolute zero, it's loses electrical potential and becomes heavily magnetized eventually entering a Quantum locking state were you can position the magnet in three dimensional space and it will remain locked in that position like you were holding it with clamps. Inversely the hotter the metal becomes the more charged the electrical potential increases and the less magnetic it becomes until it reaches its Curie temperature at which point loses magnetism. Everything in science can be thought of in this way, everything has a pole and an opposite Force which is exactly the same, but separated by degree. You can think of magnetism/electricity like an ethereal water, it works very similar. Water evaporates off of the surface of the ocean into hot humid air which condenses into water which then falls to Earth where it is absorbed and eventually mkes it was back to the ocean. A magnet exposed to changing or oscillating poles creates a magnetic field which like evaporation fills the air with electrical potential (humid air) which then collects or inducts the electrical out of the air and and eventually returns to ground or earth.
Excellent description of relativity and magnetism.
Great explanation and discussion. I am pleasantly surprised by the number of people who are animated by such questions. Makes me feel more “normal”.
See the is why I love quantum physics and general relativity, its when you understand the physics is when your head starts to spin, not when you don't understand it ;)
2:30 How dare you push that cat over. 🤣
5 years later! & This video perfectly brings back a sense of nostalgia...
Déjà vu
Derek has got much better at explaining stuff since then!
This explanation doesn't work. Special relativity says there is no preferred inertial frame of reference. So when the Cation is not moving with respect to the wire ( and it's positive charges) the moving negative charges should appear closer together and the Cation should be attracted to the wire.
That is not the case though. The Cation is only attracted to the wire when it is moving with respect to the wire (and it's positive charges) in a direction antiparalell (or with an antiparalell component).
exactly Ben; no preferred inertial frame of reference; they can't even memorize the things they were supposed to memorize, let alone question those things
I agree, this explanation makes no sense. When the cat is stationary, the moving negative charges shall contract and attract the cat.
@@TheMyrkiriad I'm just going to point out that he did say we should assume that at a "stationary" perspective the positive and negative ions had identical density... ( 1:15 and 1:32 ) So, no It shouldn't be attracted.
I was going to type something similar but you've got it covered. These people spewing this pseudo intellectual nonsense are really starting to do my head in.
@@mysty0 I notice how nobody in this two year old comment thread actually linked a better explanation or did anything except go "nuh uh!" Also, Jimeny Christmas, people. It's a 4 minute video, not a semester long lecture on quantum effects and fundamental forces. If any of you putzes have a better explanation, I'm all ears, and I'm sure the creators are, too.
"You are looking slim"
"Only in your frame of reference"
-Albert Einstein
Wow, mind blown. Never thought of this perspective before. Thanks for the video
when the cat is stationary and the electrons are moving to the right, why electrons don't have a higher spatial charge density than the protons due to length contraction, causing an attractive force on the cat? Since you are explaining the repulsive force in case of moving cat (from the cat perspective) as: protons are moving to the left, electrons and the cat are both stationary, which is the same scenario from our perspective when the cat is stationary and electrons are moving to the right.
Same doubt
Why doesn't a stationary charge feel a force, since the density of electrons moving in the wire should be higher due to special relativity, giving the wire an overall negative charge.
***** It doesn't. mindstormmaster The density of the moving electrons is not higher. The electric field from the voltage source, which causes the electric current, accelerates every electron in the same way, leaving their distance unchanged as measured in the rest frame of the stationary charge. Consequently, due to special relativity the distance of the electrons must be greater in the rest frame of the electrons.
question: from the observer frame of refference does the electrons also contracts? if so then the observer would be able to observe the special relativity effect on the kitty right?
Awesome.🔥😀 Truly blew my mind. I had heard that electric and magnetic forces are same but never had I been able to connect then how. Your video visualised me that. Thank you😀
This is brilliant. Never thought of magnetic fields this way!
This is a really difficult topic. Props to you guys for tackling it. And y'all did a fantastic job, IMHO.
There WAS one logic fart, though: If you have a neutral wire and then start pushing electrons through it, the positive cat would be attracted to it if it's not moving, because length contraction would affect the electron current.
The way experimentalists deal with this problem is that they charge the wire very, very, very slightly positively after they start the current flowing. By testing to see how charges respond to the wire, they find the spot where the Lorentz force (total force due to electromagnetism) is zero.
Fantastic video. Explained it even better than my professors did.
If "magnetism" is due to length contraction, wouldn't this mean that if the drift velocity of the electrons is 1 cm / minute relative to the wire, then the "magnetic field lines" themselves would drift at 0.5 cm / minute longitudinally down the wire?
Stated another way, is it fair to say that given that the "magnetic field" only manifests when a "net" length contraction of the field affects the test charge, any change away from the frame of reference where this doesn't happen to that charge can be likened to cause of a movement across the field lines?
Wrong.
gozags65
You are responding to a question, so by "Wrong" I assume what you actually meant is "No".
Okay. Thanks for answering!
kmarinas86 gozag's answer (static magnetic field lines) is accurate on anything but the smallest scales, at which point magnetic fields don't really exist anyway (quantum physics is weird). His answer was great; I can't really add anything to it.
Sorry if I misled you; the last class I took on relativistic electrodynamics was about three years ago, and none of my research hinges on relativistic electron interactions, so so I may have forgotten a bit.
However, any physics undergraduate at a real university has at least been exposed to apparatus that use charged wires to explore quantum effects. In this, at least, I'm justified in my confidence.
wouldn't a stationary "cat" see the electrons as moving past it and thus the electrons would contract while the protons spread out? causing a greater negative charge and an attractive force on the cat?
Relativity still blows my mind. And also I noticed Derek was young in this video and realised it was posted 10 years ago😂
"A magnetic field is just an electric field viewed from another frame of reference " 🙏🏻🙏🏻🙏🏻🙏🏻it blowed my mind
Russians: *start closing in on Berlin
Hitler: 0:46
Omg i haughed so hard XD
lmao
nice one
I had a nice laugh at that
LMAO
Day 62 : I'm still going back and forth from Veritasium to Minute Physics.
"A magnetic field is just an electric field viewed from another reference frame." 7 years later, today, I learnt something really important that my college years failed to teach
Ten years later, and the "only in your frame of reference" joke still gets me xD
this is imho the best video of veritasium! :o
But when the cat is not moving, the electrons are moving relative to it and the protons are stationary relative to it right? Won't the separation of electrons be reduced as they are moving relative to the cat and the protons more widely spaced between each other as they are stationary relative to the cat? Won't there the wire then become negatively charged and attracts the cat? Your attention is much appreciated!
Thanks for crediting the music! Made it easy to find :)
I HAVE BEEN ASKING MY TEACHERS THIS QUESTION ABOUT MAGNETIC VS ELECTRO FIELDS MY WHOLE LIFE, AND YOU FIBNALLY ANSWERED IT. OH MY GOD.
Why is the stationary cat not attracted to the wire? The electrons are moving, and thus slim down.?
Yeah, I have the same question...
It depends on the frame of refrence
They are moving relatively to a stationary observer. Why aren't they closer together? Why the wire "resolves itself" as neutral for a stationary observer, and not in some other way?
Luiz Sarchis I don't understand what you said :/
maby cos of the cats charge
Veritasium But if the cat is not moving, the electrons are moving with respect to it whereas protons are not so the electrons should be denser. Doesn't that mean that the cat will be attracted to the electromagnet?
"A magnetic field is just an electric field viewed from a different frame of reference." This is incorrect. I realize that the following explanation is verbose and dense, but it must be said, and maybe we can find a more digestible way to convey this to the public. It is true that a transformation from one frame to another changes the components of the electromagnetic tensor. With the above statement, one might be tempted to model electromagnetism with electric fields only and a lorentz transformation. That is incorrect. Electromagnetism is represented by a tensor. Some of those components we conveniently call the "electric field" and some we conveniently call the "magnetic field". The fact that we have given special names to components of this tensor is probably an historical accident that Maxwell's equations were defined before relativity or tensor calculus was invented. The components of the electromagnetic tensor transform via Lorentz transformation, and in some frames some of those components may be zero. However, this fact does not negate the tensorial nature of electromagnetism, nor does it get rid of the components that we call "magnetic field". Length contraction alone does not explain the Lorentz transformation of the electromagnetic tensor.
but this is a special case, where Derek has F_0j = F_j0 = 0, where F_ij = -F_ji is non zero, and a four current with J_0 = 0 and J_z non-zero, then he transforms it to Henry frame where everything is nonzero, except the electron's 3-current vanishes. The most sensible way to say it is that Henry's electric field is a transform of Derek's magnetic field (because Henry's positive charge density is a transformation of Derek's two canceling J_0's that only cancel in Dereks frame). fwiw.
I have seen this bad generalization in textbooks, now people repeat this everywhere and its difficult to revert the misinformation.
@@DrDeuteron indeed, but then they use this special case to say something general about how electric fields transform. The problem here is that they are trying to explain a relativistic effect with classical ideas.
This is so wel explained damn, such a difficult matter explained in a short amount of time.
you sir, just saved me a lot of time understanding my physics class...
It's pretty amazing that special relativity explains electromagnetism.
2:25
Shouldn't the electrons be contracted in the reference when the cat is at rest?🤔 So, would make the wire negatively charge and the cat would be attracted to the wire.. not repel?
Someone explain what I am missing... Thank you :)
Ya i have the same question, if you find the answer plz tell me
I was also looking for this same doubt in the comment section and got yours..
We share the same brain
No because the SPACE between electrons in NOT moving and electrons themselves have no size.
This is probably why Kaluza-Klein theory even works. In simple terms it extends general relativity into 5 dimensions, assuming there is some scalar field in the fifth dimension. When you solve the new field equations, maxwell’s equations and the normal GR field equations magically appear.
0:52 that contracted car looks hilarious lmaaao
What I took from this video: POSITIVE CHARGES REPEL CATS! WE CAN FIGHT THEM WITH POSITIVITY!
*everyone think happy thoughts OH GOD THEY'RE HERE HIDE!!!*
+Daniel Hale *keep thinking happy thoughts we just might be able to fly away!!*
+Daniel Hale
Oh, but that will never happen.
+Daniel Hale PREACH BROTHER!!! RISE AGAINST THE CATS!!!!!!!!!!!
Your positivity would attract negative cats.
actually, (cations) are pawwsitively charged!
I just learned more about magnets than I have in a lifetime. Thank you!
Wow ! That's crazy ! I never thought it could be so, thanks for this video .