How Einstein saved magnet theory

Magnetism is one of the most bizarre of known classical physics phenomena, with many counter intuitive effects. Even weirder, when one uses Maxwell’s equations (the laws that describe electromagnetism) and traditional Galilean relativity, you can see that magnetism makes no sense at all. However, when one uses Einstein’s theory of relativity, it all makes perfect sense. In this video, Fermilab’s Dr. Don Lincoln helps sort it all out.
Magnetism for parallel wires:
• Magnetism (10 of 13) M...
Magnetism for parallel wires:
• Magnetic Field of a Wire
Purcell simplified:
physics.weber.edu/schroeder/m...
Purcell E M and Morin D J 2013 Electricity and Magnetism Harvard University Mass. Third edition pp 259-264.
Length contraction video:
• Length contraction: th...
Fermilab physics 101:
www.fnal.gov/pub/science/part...
Fermilab home page:
fnal.gov

[@willi-fg2dh]

there once was a fencer named Fisk whose action was exceedingly brisk so fast was his action the Lorentz contraction reduced his rapier to a disk.

[@romanski5811]

If you pass by the Earth fast enough, then the Earth is flat.

[@willi-fg2dh]

@@romanski5811 nah . . . that only happens if the Earth passes by you.

[@aranos6269]

Both scenarios are same.

[@badbrain3185]

This can only be observed by one being perpendicular to the sword.

[@Newtspeare]

There once was a man called Don Who was ever so easy to con He made a great hash Of physics' worst trash And all that he said was wrong.

[@mikecannon6529]

I heard this in passing about 45 years ago. It stuck with me but I never managed to chase down the details. Thank you.

[@jackieking1522]

I did know this.... was taught it 55 years ago and remember the feeling of amazement that relativity at such gentle speeds could so precisely explain electromagnetism. Thanks for bringing it all back.... it will help me fade away with a smile.

[@CarBENbased]

That was nuts... I was getting more confused but you set me up perfectly for it to click when you brought in the length contraction animation! I'd love to see a video on how this applies to permanent magnets and maybe even induced temporary magnetism.

[@frederf3227]

I remember this explanation from school. I suppose given that E and M must function in all reference frames you could derive special (probably also general) relativity from the known results. The fact the E is M and M is E through relativistic transformations is so cool. Also it shows just how insanely charge dense normal matter is.

[@muraliavarma]

This is actually insane. So relativistic effects of magnetism happen at such low speeds too? I should probably read the math behind it but one observer's magnetism is another one's electricity? Truly mind blowing!

[@brothermine2292]

Depending on the observer's motion, it could be a sum of both magnetism and the electric force that explains the total force on the charged particle.

[@TrixieWolf]

This must be where ICP gets their name. :V

[@douglasstrother6584]

It's pretty wild that the generation of magnetic fields by currents is an everyday relativistic phenomena (tiny charge density imbalance), and ferromagnetism is an everyday quantum phenomenon (tiny atomic current loops).

[@kreynolds1123]

The relativistic effects being so tiny and the strength of electromagnetic effects in lab frame or charged particle frame of reference is simply a testimony to the strength of electromagnetism and the very large number of particles involved in a length of wire. Gravity by contrast is orders of magnitude much weaker.

[@fg786]

Electric forces are really strong compared to gravity, so it's not at all surprising that low speeds are already have tremendous effects.

[@philippk736]

How does all of that work for freely moving charges in a vacuum without the presence of the opposite charge as in the wire?

[@bramfran4326]

Thanks for sheding light on (mysterious) magnetism and for providing source with more info. I would absolutely love to see an explanation of why inductors and transformers work the way they do using only this phenomenon!

[@regth8208]

Always a pleasure to learn from these videos. Thank you to everyone involved with these presentations!

[@tenbear5]

if you’re capable of thought, this is a terrible piece.

[@tensaisenshi]

I've heard of this before, but your way of explaining it really clears things up. Now I can say that I know, rather than having heard of this effect. Thanks.

[@SiqueScarface]

Albert Einstein invented Special Relativity to explain Magnetism in his 1905 paper "On the Electrodynamics of moving bodies", where his starting point was the apparent asymmetry of a moving wire and a stationary magnet vs. a stationary wire and a moving magnet.

[@danieloberhofer9035]

And here I was, thinking it was really about trains, because of all the train examples and whatnot...

[@SiqueScarface]

@@danieloberhofer9035 Die Arbeit heißt im Original "Zur Elektrodynamik bewegter Körper" und erschien in den "Annalen der Physik" 1905. In dieser Arbeit leitet Albert Einstein die Gleichungen der Speziellen Relativitätstheorie her: "Man denke z. B. an die elektrodynamische Wechselwirkung zwischen einem Magneten und einem Leiter. Das beobachtbare Phanomen hängt hier nur ab von der Relativbewegung von Leiter und Magnet, während nach der üblichen Auffassung die beiden Fälle, daß der eine oder der andere dieser Körper der bewegte sei, streng voneinander zu trennen sind." (Womit auch klar ist, wo der Begriff Relativitätstheorie ursprünglich herkommt.)

[@Ebani]

@@danieloberhofer9035 Actually Einstein didn't invent it, he just used the work of myriads other scientists before him. Which is why none of the special relativity concepts bear his name other than "Einstein's special relativity theory", which is but a summary of everything other scientist already found. His genius was making sense of all the things other geniuses found 💁‍♂

[@estranhokonsta]

​@@Ebani Lol. The same can be said of every scientists. It isn't for no reason that Newton wrote "If I have seen further it is by standing on the shoulders of Giants". Note that even that metaphor is way older than Newton.

[@sudazima]

@@estranhokonsta newton said the standing on giants thing in response to someone who was very small, implying he would not contribute at all.

[@Brindlebrother]

3:56 The physicist: "Everything I just told you is right" Me who's not a physicist: "Welp, that's good enough for me"

[@Earwaxfire909]

This is a good start. I would also note that the Coulomb force is so strong that even a small change in charge density produces a noticeable effect. Also the mass of proton charged nuclei is much greater than electrons and that makes them move slower giving rise to the greater special relativistic contraction of the flow of electrons in the frame of the outside charge observer. It would be fun to look at the difference between AC and DC currents.

[@mrtienphysics666]

what about the random root square speed? and also how about the fact that electrons are Bloch waves inside?

[@Earwaxfire909]

@@mrtienphysics666 It does get fun really quickly!

[@misterlau5246]

Well, let's modulate those with laser and we'll obtain some FOCK photon states

[@theultimatereductionist7592]

I wish he would quantify the cause and the effect, wish he'd show the math I'm sure it's not too hard.

[@InssiAjaton]

Regarding the note about the polarity naming of current flow, I recall an old (older than me) book describing an electrolytic solution. It could and indeed had been used as a rectifier. And because the "material" - positive ions flow was chemically more evident than any flow of the electrons, that became the positive direction. So, the polarity was established by wet chemistry instead of either solid state or gaseous state observations. Such a funny thought!

[@corradoghinamo9935]

Phenomenally clear explanation. Congratulations

[@jeffi49]

As always, I truly enjoyed your videos. Thank you, to make the effort to outreach the community.

I had to study the Berkley Physics Course books in the 70´s at the Groningen University so I got familiar then with the idea that magnetism comes from a special relativistic effect. As far as I can remember the explanation was set up differently in the book, but the idea is the same and at the time I was really excited by explanation.

[@himanshukhanna2589]

The concentration of charge due to length contraction causes electrical repulsion thus resulting in what is called the magnetic force. But how does that work for two point charged particles?

[@sapelesteve]

Yet another magnetic example of Dr. Don's mind blowing video's! 👍👍💥💥

[@misterschifano]

Dr. Don Lincoln with the classic hits, taking us all the way back to 1905, baby! Albert Einstein featuring James... Clerk... Maxwell for this mix, you know it, get your right hand in the air for On the Electrodynamics of Moving Bodies! ⚡

[@misterphmpg8106]

Hi Don, I imagine these very tiny relativistic effects on the moving electrons do matter in the macroscopic world because there are trillions and trillions of them and they add up to a macroscopically measurable force. But what happens if only two of them pass each other along their way? They interact by exchanging a virtual photon, so how does quantum mechanics fit into this picture? Do those exchanged virtual photons between the wires also add up to make that electric force? Should be, but for me that makes it even wilder to imagine... thanks for your amazing video! And: if you look at many comments below it's amazing how easy it is to get dozens of nobel prize winners to pop up by just mentioning SRT. THAT is Einsteins most magical force it seems.

[@warrenarnold]

Hey what about stationary permanent magnets, how can they be explained with the wire theory?

[@skibaa1]

wow, this is amazing. Relativistic effects at 1mm/s, magnetism explained without those weird right hand rules, exactly what I missed in the high school. May be I would become some magnet engineer if I saw this video at my 16 :)

[@kumagoro]

Fermilab videos .... are everything!

[@jesseschwab1813]

Thanks for this solid review of the basics. So the relative motion of the charges contracts them, effectively concentrating their potency. There is fertile soil here.

[@linuxificator]

I've done the calculations long time ago, it works great, but if B is entirely a relativistic effect of moving E, how would one describe an EM wave? I've been searching for that, but I cannot find it.

[@humicroav215]

Wouldn't an EM wave be the exact same phenomena just oscillating? Instead of charge moving uniformly in one direction, it changes direction. Acceleration is required to create electromagnetic waves and the change in direction is the acceleration. We describe the oscillation by its relationship to time as frequency and its relationship to the speed of light by wavelength.

[@hanifarroisimukhlis5989]

You have to derive a 4-vector field. In that case, relativistic effects looks like a 4-rotation of the vectors.

[@AstroAri504]

Hi Dr. Don! Can you do a video on the difference between magnetism and electromagnetism? I'm having trouble understand why like poles on a magnet repel, while like charges on an electromagnet attract.

[@drdon5205]

It's more complicated than the video here, but it's the same thing. For like poles, the electric field is similar to like charges, while for opposite poles, the contraction is more like concentrating opposite charges. It's >>much

[@stefanyankov3801]

I also would like to see if relativistic effects can explain the permanent magnets. Permanent magnets attract or repel each other without presence of moving charges, right?

[@drdon5205]

@@stefanyankov3801 No. Remember that electrons both move and spin within atoms.

[@constpegasus]

I need to watch this again. Thank you Mr Lincoln.

[@vb6database]

I absolutely love your content!! Keep making it!

[@jeremyelser8957]

How does the shortening of the charges themselves equate to a shortening of the spaces between them? The space between them isn't moving and wouldn't contract, I'd think. Why doesn't the external charge just see bigger-than-normal gaps between smaller-than-normal charges?

[@vincentbrown4926]

My question as well.

[@MRichK]

Quick hopefully useful rake: If two charges are moving past you at some speed relative to your rest frame then they are in a different frame - one moving at their speed relative to you. >Everything< in that reference frame looks shortened in that direction to you including the space between the particles. Think of them as ticks on a ruler. The ruler shrinks so the ticks look closer together to you. The fact that there is no material ruler there, doesn't mean there isn't the "frame ruler".

[@herbertniesler320]

On top of that, the length contraction does not depend on the direction of current flow. The effect should be the same in either direction. Switching the charges you look at when you "change" current flow direction does not make physical sense.

[@unduloid]

Remember: It's OK to be a little crazy!

[@bandotasif]

I love these videos. Entertaining and informative. I so wish I had these when I was in school.

[@Czechbound]

That was great. I remember asking the science teacher in high school why the textbook said it the charge moved in a direction that seemed to be completely the opposite of how he had explained that electricity worked. "It just is the way it is" was his response. I knew I was right !

[@spoddie]

If Insane Clown Posse don't understand magnets, then I have no chance

[@mehdibenseghir663]

You seriously rock! Physics is the most noble science there is.

[@anthempt3edits]

It’s everything!

[@keithwald5349]

Well, Einstein's original paper on special relativity was called "On the Electrodynamics of Moving Bodies." He starts right away by pointing out the bothersome asymmetry in the usual description of induced emf in a stationary loop with a moving magnet inserted, versus the magnetic force on the charges in a moving loop surrounding a stationary magnet. He then discusses the lack of reference frame inherent in Maxwell's equations, with which Newton's laws don't jibe. The paper is remarkably easy to read for anyone with limited mathematical background. In special relativity, the math is surprisingly simple, although the ideas are not so easy. (This is in contrast to most other topics in physics, like generaly relativity or quantum field theory, where the math is definitely _not_ simple - nor are the ideas.)

[@leonhardtkristensen4093]

A good reason for that is as I have understod it Albert Einstein wasn't all that good at mathematics. He had a very good mind to find new ideas. This is why I can't understand that todays Physicians demand that an idea is calculated through before they even want to consider it.

[@skywatcherextraordinaire7014]

Wow yes this concept never fully made sense to me until now, well done great explanings!

[@kredwol2103]

Jesse Pinkman saved magnet theory

[@douglasstrother6584]

It's pretty wild that the generation of magnetic fields by currents is an everyday relativistic phenomena, and ferromagnetism is an everyday quantum phenomenon.

[@DrDeuteron]

Light is both

[@aaronperelmuter8433]

What’s not wild at all is that you put that exact same comment, word for word on more than one video. Doug, it got old before you even did it, time dilation in reverse!

[@rahularyaphysicist]

Oh my god I love Sir Don’s Explanations, he made me love physics

[@twrandy]

I first learnt this theory in Veritasium's channel, feel quite skeptical about it, so I did a rough calculation: Assuming 1A current flow through φ8mm wire --> electron drift speed ~10^-5m/s order--> Length contraction about 1/10^13 order, for 1m wire moving electrons are packed in (1 - 10^-13)m less Electron density in conducting metal 10^28/m^3 order --> In φ8mm wire there are 5x10^23 free electrons / m Which means positive charges in 10^-12m contribute to the "magnetic field" In 10^-12m distance, positive charge number equal to electron number if there is no current, so there is 5x10^10 difference between positive and negative charges in 1m wire That's 1.6x10^-19 x 5x10^10 = 9 x 10^-9 C electric field built because of the 1A current flow, if we can really apply specific relativity into this equation Could someone please try to verify if 9x10^09C electric field does equal to the magnetic field of a φ8mm wire with 1A current?

[@c00ckiez]

My puny mammal brain can barely handle these ideas. Great video!

[@brendabeamerford4555]

Consciousness power three sets all captives free no longer at the mercy of the child mind mammalian Beast mind rule of Self in our world

[@nanoalt8127]

​@@brendabeamerford4555What are you smoking?

[@SolaceEasy]

Yepper, lost me. I can usually keep up.

[@WokeandProud]

​@@brendabeamerford4555Get help.

[@brendabeamerford4555]

@@nanoalt8127 metatron's Matrix smoking hot light is fire light is water light is wind light is Earth... Quantum Light is TIME SPACE SPACE TIME LIVEING IAMO IN ALL IAM LIGHT The Reciprocal Value of Rest Mass Energy = TIME (Rest). The Infinite Arithmetic Progression (‘Infinite Sum’ = (1+2+3+4+5+…..-1/12) AND the Infinite Multiplicative Progression (‘Infinite Product’/Factorial) = (1x2x3x4x5x…..τ^1/4; where τ = 2π). The Infinite Sum and the Infinite Product inform the Universal ‘Infinite’ Right Triangle possessing a Hypotenuse ((Infinite Sum/2) value of 4.166666 (=1/.24); Height (Infinite Product^1/2) value of 3.85415 (=1/.259); and Base of 1.583233 (1/.631618); Rest Mass Energy is defined by a Right Triangle’s Height, whereas its Total Mass Energy is defined as Rest Mass Energy + Momentum (Kinetic Energy); its Hypotenuse defines the Infinite Sum/2. The modular configuration is due to θ° forming Mod1/.62; The Hypotenuse/Height defines the Logarithmic Base value (1.08 and its powers at each successive interval). The Inverse reciprocal (1/x) equations of the above define the Precessional Period both at Rest Time (1/.259 x 10^5) and at Total Time (1/.24 x 10^5); this differential accounts for additional momentum/velocity that occurs when the Solar System approaches its Binary Partner Star: Sirius A, contracting the time (Mass-Time Dilation) on the short arc of the cycle to only 21,600 years; versus the long end of the cycle being 25,920 years, the mean value being therefore approx 24,000 years-. These relationships yield a NEW UNIVERSAL EQUATION for 1/TIME (Rest) = ((Infinite Sum/2 - Infinite Product ^1/2)*((Infinite Sum/2) + ((Infinite Sum/2 + Infinite Product)^1/2)…..finding the solution to the Sum-Product as Right Triangles was a serious breakthrough that has now led our Research Team toward entirely new understandings in Physics. Using our recent discovery of Pythagorean Factorization: Factor 1 = 2.583433 (which is also equal to the Square Root of the Gravitational Constant 6.674 x 10^-11 (N*m^2)/kg^2. Interestingly, 258.3433 ≈ e*(360°). The other factor in the equation is 1/(2.4)^2….. and ALL of the above found in a single ‘Infinite’ Right Triangle derived from the ‘Infinite Sum’ and the ‘Infinite Product’ Arithmetic Progression values of Integers……MeTAtron's MAtriX3x3 OM'E... "The All is Mind; the Universe is Mental." "As above, so below; as below, so above.” "Nothing rests; everything moves; everything vibrates." Everything is ALLMIND369 OVEONE IAM=O=QuantuM⚖️ ALLMIND IN 3in1MINDS Body Spirit OVE light*3÷7 color*3÷7 sound*3÷7.. 7SUMS CREATION ALLMIND frequency vibration in THOUGHTS charge ●■☆MC² in WAVES OVE 3SOUNDs7 1Frequency. ... Amplitude. ... 2Timbre. ... Envelope. ... ***3Velocity. ... Wavelength. ... Phase =SUM.7 🎯3 ⚡Lights7: 1 radio waves,÷ microwaves, 2infrared (IR)÷ visible light, ***3ultraviolet ÷ X-rays Sum Gamma rays SUM7x 🎯6 🌈COLORs 7 1 Red÷ Orange 2Yellow÷ Green ***3. Blue÷ Indigo SUM Violet SUM7 🎯9 In seven colors seven notes seven lights in infinite divisions ALL TOGETHER Creating all living systems, Creating All living bodies, Creating all gravity, Creating all matter.. IN ElectroMAGnetic geometrical symmetrical fractal order HerMEs TrisMAjistus THOTH TimesFaceInEnergy.com Light Never Dies death is our illusion through the terrible twos of childhood in Mercy Mercy Me and our promise rest is real.. Prisoners law in three power three sets all captives free 3Consciousness says I see you Mirror Mirror I see me wisdoms wisdom's wisdoms unconditional love and forgiveness is key

[@MathisGries-ml5qv]

It might be an odd tangent, but I think people shouldn't have mocked "F###ing Magnets, how do they work?" Precisely because if this. People think they understand middle school level physics, but they don't realize that their understanding of physics is basically 100 years outdated.

[@mountfairweather]

???

[@RyJones]

As a former ICP fan, I had to defend that constantly.

[@RyJones]

@@mountfairweathersearch for insane clown posse and magnets

[@xtieburn]

Haha, the lyrics had nothing to do with the complexity of the subject and how many people get it wrong. It was about mystifying the topic and science denial. Just read the very next lines of the song.* They absolutely deserved every bit of the mockery they got. *Violent J rolled back the 'liars' claim made in those lyrics and said it was more about scientific explanations destroying the wonder of things, which personally I think is also daft and wrong, but then how would he know? Hes never actually listened to any of them...

[@MathisGries-ml5qv]

@@xtieburn I don't claim to have any insight into what these literal clowns were thinking, and I frankly don't care. What I do know is that the memes overwhelmingly focussed on that one specific part of the lyrics and did not include the lines that followed. I also know that tons of people felt prompted to provide explanations that overwhelmingly did not rise above middle school level physics. My point is simply that that even among people who have reached what would be considered a respectable level of education, the percentage of people who can properly explain how magnets work is vanishingly small.

[@warrenchu6319]

Replication of Ampere's Law using Special Relativiy: The magnetic field is a pseudo electric force field created by moving charges as explained in the video. Charged particles move PERPENDICULAR to the magnetic field lines of force: f = qV x B. That's why B points orthogonally to both the electric field and the current in the wire. Illustrating how the B field around a wire carrying a current is formed: Using the right-hand rule for E, B and v, if you place vector B at the end of vector E, as you rotate 360 degrees the E vector radiating from the wire, B will form a circle centered on the wire, where E is the pseudo electric field formed by moving charges. This is Ampere's Law.

[@TheyCallMeNewb]

Awesome stuff squeezed between nonpareil opening and closing cards!

[@flatisland]

8:56 is the relativistic effect really due to the moving electrons or due to the difference of the electric potential which propagates at nearly c?

[@ivarwind]

I knew this already, but it's always good to see it explained again. It illustrates several important concepts in physics. First the full meaning of relativity in physical laws - two observers should agree on the general laws, but they may not, indeed often will not agree on the exact explanation for a specific observation, not even on which forces are involved. Second, it illustrates length contraction as a phenomenon that has observable effects in everyday life! And third, the electromagnetic force is mindbogglingly strong - even the vanishingly small length contraction of the electron spacings in a wire suffices to generate a charge imbalance large enough to lift objects against the gravitational pull of the Earth.

[@leonhardtkristensen4093]

You forget that according to Einstein there is no gravitadional pull of the earth. It is space time that is bend. Personally I am yet to be convinced that the Physicians current explanation is correct. In my oppinion it is only one way of looking at it.

[@ytfeh]

Well done and clear video on this matter. I learned something new.

[@FrancoisBothaZA]

Others also asked this, but how does this extrapolate (if at all) to how electromagnetic waves work. I know the 2 components are orthogonal, but does relativity explain it too?

[@dtmelanson]

Always great content. Thank you.

[@mcpr5971]

Great video. A good companion to this is describing gravity in terms of time dilation. I don't remember the exact explanation but The Science Asylum did a great video on it. Something about time running slower on one end of a solid object means it feels a force in that direction, aka gravity.

[@misterlau5246]

I watched a S. A. Video where Nick Lucid explained the same as this video, but I think he put a squirrel there to be the observer for the different reference frames you have there.

[@kennethreese2193]

If this happens to be a rebuttal of sorts against a snarky and some what rude attack on your channel that just happened to be based on misunderstanding this exact phenomenon, then you sir, are truly a mastor teacher. While it takes alot of smarts to be able to teach this as well as you do it takes profound wisdom to respond like this.

[@LynxUrbain]

So cool ! A new video from Don @ Fermilab and "PBS Space Time", on the same day !

[@markhuebner7580]

Great finish! A little confusing to have that teaser in the middle though!

[@Blake_47]

Those ideas might not be as rigorous as they should be the explanation is the length contracted negative charge is matching the positive charge but in a rest frame that contracted wire expands back that reduces the charge density and the wire is no more neutral

[@jako_ronin]

But does that effect of length contraction reduce the fundamental charge that each particle carries? Or do the wire "fit more charges" because their length is now shorter?

[@nathanielkilmer5022]

What I don't understand is, why would the space between each electron contract? Shouldn't each individual electron contract in length while the distance between particles remains the same, and thus the effective charge density for a given length of wire remain the same?

[@alsmith20000]

I've heard this explanation before. Thanks for the links to other sources (I haven't checked these out yet) but two significant unanswered questions stick out for me: 1. special relativity has extremely non-linear properties but we learn even in high school physics that magnetic field strength is directly proportional to current; how can a highly non-linear phenomenon give rise to a linear one?. 2. How does this relate to magnetic materials with aligned electron spins?

[@apostolakisl]

If the charges are moving faster and contract (become closer together), but the wire they are in is not moving (or at least is not moving differently for the positive and negatives contained within) and thus is not contracted (or at least contracted the same for both pos and neg charges), would that not mean that you need more of one charge or the other in the wire? Where did the extra charge come from?

[@godfreypigott]

For current to flow the wire needs to form a loop. On the return leg the spacing of the opposite charge is contracted.

[@helder4u]

WOW the world needs more teachers like this

[@fabiocaetanofigueiredo1353]

What a fantastic explanation! Thanks

[@larrytanner4725]

I am amazed. By the Lorentz contraction equation, the relative lengths would be or the order of 1 part in 1,000,000 or less. It is amazing that such a difference could result in a significant magnetic force between the wires. Amazed.

[@SpeakerWiggin49]

Wow, the Lorentz contraction of the "moving" opposite electric charge is a super weird way to get an electric charge effect. It's almost like the opposite of camera perspective distortion, but also not, cause it's about change in position over time, so it's 4D perspective, and cameras produce 2D images...

[@PhotoshopArt]

This is the best channel for science.

[@Zeusz310]

what about 2 single (point like) charges moving relative each other? Does that create a magnetic field?

[@BGTsoundandvision]

When I was I kid I wanted to better understand how the electric guitar worked. That led me to electromagnetism and an interest in physics. Thanks for the video. All this brings us to Jimi Hendrix and then our minds really get blown.

[@tokajileo5928]

can the Lorentz contraction be applied to planck length? i.e can we experience a length less than planck lenght this way? and if not, why not if all lengths contract?

[@SlowToe]

Thanks Don. Mission accomplished 🤯

[@NFGF61]

I am pretty sure Purcell was my textbook in my Physics understanding course in 1981! And this was in Brazil!

[@dinnoel3147]

Classical/Newtonian physics appears to also explain magnetism. It goes like this: Particles are being bombarded by bosons (or by some other forms of energy) at the same rate from all sides equally. At the same time, they shoot out bosons to all other the place also at some steady rate. Since no other changes, space around is “flat”, I.e. boson pressure if equal in all points of space, thus Newton’s 3rd law “keeps” everything at rest. Then electricity begin to flow. Electrons start slow march from - to +. Despite the very slow pace, moving electrons generate disturbance in boson field. Sort of like a passing vehicle create air wave. Particles now experience unequal boson pressure (which we call magnetism) that forces stuff to move. Since particles physically move now, they create even more distortion but grabbing bosons that otherwise would hit other particles, and at the same time bombard others with own bosons at different rate. That new disturbance in turn creates additional difference in electric potentials and thus secondary electric field. And this goes on and on until all particles finally find themselves in a condition of equal forces from all other the place at exactly the same time. That would also explain electromagnetic wave: like a pendulum, particles try to compensate, overshoot (because bosons have limited speed and arrive with delay), move to opposite direction, start compensating again, overshoot again, and on and on. Also, would explain why no magnetic monopole was ever found. Or rather every single particle is such a “monopole” and they all equally compensate each other and stay in state of rest until something introduces initial disturbance.

[@lugyd1xdone195]

Thank you, I've been puzzled by this exact thing!

[@hanks.9833]

My take is that the electromagnetic field generates forces on charges that appear as the classical electric (coulomb) or classical magnetic force depending on the frame of reference, and the difference shows when motion of charges exist. The confusion arises when we mix special relativity with the classical concepts.

[@narfwhals7843]

The confusion doesn't only arise when we mix SR with pre SR electromagnetism. The confusion arises from the lack of reference frame in Maxwell's Equations. The confusion is what _leads_ to Special Relativity. Read Einstein's original paper "on the electrodynamics of moving bodies". It is not too difficult.

[@thekaxmax]

Veritasium and Minutephysics covered this in a connected pair of vids. Good to find about the Einstein link.

[@standoasis]

Then why doesn’t a stationary charge feel the relativistic force from a current? From a stationary charge POV, the + and - charges in the wire are running at different speed and hence have different density.

[@invisiblekincajou]

What will happen with electron beam (charges without wire and thus no positive charges here) shooting somewhere near another charge? or maybe two electron beams. Or just two electrons in that same beam.

[@tresajessygeorge210]

THANK YOU... PROF. DR. LINCOLN...!!!

[@stevewebber707]

Fascinating topic, that I am sad I hadn't heard about sooner. It does bring a question to mind though. Wouldn't this make the existence of a magnetic monopole even more unlikely? Also since the magnetism is defined by spatial contraction, what would that mean to magnetism on the scale of a single set of charges, such as a single proton and electron?

[@richard84738]

That is amazing to consider that the super advanced modern concepts of Einstein and Special Relativity can shed light on something we basically cracked a couple hundred years ago in magnets. So fun to see there are constantly new details of the world to probe, even the parts we thought were "finished". The work of science is never done, and as this video shows, is not just a case of "ever more precision" like some detractors say.

[@user-qo4hc6jf1l]

So the resistance get each charges when goes through by in the wire and how much pure medium is wire source ?

[@joseluisblanco8074]

Why do positive/negative charges in the wire move at different speeds when seen from the charge reference frame?

[@Pottery4Life]

Thank you very much, sir.

[@iand6541]

Thanks for the video!

[@jjll6741]

Are there moving charge inside a magnet? Does relativity work the same way to magnetic force involving magnets as does electric current in a wire?

[@jeremyocassan]

Help. I'm hung up on the relative movement of the + test charge to the + and -- charges in the wire. If the test charge isn't moving relative to the wire in which is flowing a + current it isn't moving only relative to the fixed -- charges of the wire, giving no length contraction. It would see length contraction in the moving + charges in the wire, thus net repulsion? I can only get the test charge (in my head) to feel no attractive/repulsive force if it travels at half the speed of the wire current, where it sees both the stationary -- and current + charges equally length contracted going equally as fast in opposite directions relative to the test charge. What am I not getting straight?

[@belatar]

"for magnetism, both charges need to be moving": if you bring in relativity then as soon as one charge is moving there will always be an observer to whom both are moving. how does that add up?

[@Jar.in.a.Bottle]

It is my understanding that if you extend the same logic to two differently moving observers, they will not agree on the measurable electric/magnetic ratios of the same objects measured. But they can agree on the same universal outcomes of those differing measurements to a very high degree of accuracy by using Einstein's equations.

[@danielhooke6115]

Thanks for explaining that. 🙂

[@zeesan9004]

sir , I have one doubt , when the charge is stationary, from its frame the negative charges are moving and being contracted in length, so shoundn't the charge feel that negative charge is greater in density and feel force? but why the don't?

[@KatjaTgirl]

Thank you for this clear and amazing explanation. Electrons themselves are also tiny magnets. Does this mean that the spin of an electron represents actual movement inside of the electron to create this magnetic field?

[@narfwhals7843]

No it does not represent real motion. But it means you can _think_ about it as if it did, as long as you're careful. But it does represent real angular momentum. And the magnetic field is related to momentum in space.

[@Skagamaster]

Does this imply currents of like charges, without any opposing charges (such as those made in accelerators), will always be repulsive?

[@warrenchu6319]

6:55 The stand-alone stationary charge is ATTRACTED to the wire. 7:38 The stand-alone moving charge is now REPELED by the wire. Please explain.

[@plexiglasscorn]

Do isotopes influence electrical resistance of metal because last orbital electron have slightly different quantum energy values from different distribution of protons in the nucleus?

[@PropellerSteve]

Thanks for sharing.

[@VR_Wizard]

Are the electrons move at near light speed in the millimeter range so length contraction can be used here? I am thinking of jumping araunt in between the atoms at very high speeds, not comming very far but still moving fast when trying to track a single electron.

[@narfwhals7843]

The electrons move _very_ slowly on average. But the electric force is so strong and there are so many electrons that you don't need high speeds for relativistic effects to become relevant. He talks about this near the end of the video.

[@VR_Wizard]

@@narfwhals7843 He doesn't say that it has to do with the strength of the electric fields or the amount of electrons. He just says the distances are tiny. Why we can still expect relavistic effects here is not well explained. I only know the effect from particles moving quickly. That is my quistion. Do the affects take place because electrons move very quickly in random paths between the atoms not making much of a distance because of that? Could we create an electron beam and slow down the electrons so the effect dissapears? Would it work for a single electron at slow speed? Or is it as you said the sheer amount of electrons causes the same effect as length distraction but than it would be a different explaination to the one using speed alone.

[@justintime9714]

Why does the space between the moving charges contract although its not co-moving with the charges?

[@GlennThompson]

So, what exerts/transmits the force?????

[@stevenglowacki8576]

When I first learned about Magnetism and was told it was a related phenomenon to electricity, I concluded that "magnetic forces" were fake forces, and that what we call magnetism must just be a side effect of moving charges, but I never could figure out how it actually worked. I even learned the basics of relativity from other sources, and they didn't specifically mention the connection with electromagnetism, most likely because they focused on measurable length contraction and not the ridiculously tiny amount that's the source of magentism. It wasn't until much, much later, when I was graduated from college and just learning for fun that I came across the connection as this video describe. It still seems mysterious to me, so I try to keep refreshed on how exactly it works.

[@katg-gk5ox]

Nice!! I used to love the Berkeley series!

[@orthoplex64]

Please make a follow-up for permanent magnets

[@dusandusoleil]

Please reply to. The magnetic field around the magnet, what are the particles?

[@jkinkamo]

So, these electric push and pull forces explain the precession of quantum current loops?

[@danielcordes6523]

Hi Don, first of all thank you for this video. Looking ta this explanation some question came to me. What happen with electrons not in a wire. I mean electron beams in the vacuum. Do they join or appart if flowing at the same direction?, because in this case there would not be protons. Thank you and regards again.