The Quantum Experiment that ALMOST broke Locality


Hey Crazies. Back in August of 1959, two physicists published a paper in The Physical Review. They suggested that, maybe, we’ve been imagining the electromagnetic field all wrong. They even outlined an experiment to prove it. An experiment that almost broke locality. This episode was made possible by generous supporters on Patreon. OK, first order of business: What the heck is locality? It’s easily one of the most important principles in all of physics. It states that the behavior of an object or particle should only be influenced by events or phenomena at the location of said object or particle. The universe is inherently local. In other words, for two things to affect each other they have to be at the same place. It’s kind of a big deal. And not like Big Deal Clone,like an actual big deal. Hey! Anyway, most forces require physical contact to work. Things have to touch each other. But, even before quantum mechanics came along, we knew this locality principle had a few notable exceptions. Gravity being the most obvious. It seems to be able to reach out over unimaginable distances. It makes this squirrel fall near the surface of the Earth. But it also keeps the Moon in orbit around the Earth and the planets around the Sun, and the stars inside the galaxy. Which, you know, seems a little strange. But, rather than give up on locality, we considered the possibility that, maybe, that affect isn’t direct. Instead of the Earth affecting this rock, maybe the Earth does something to space and it’s the space that actually affects the rock. It’s something we call a field: a number or set of numbers assigned to points in space. In classical or Newtonian physics, that field is made up of arrows called vectors. In general relativity, it’s made up of curvature tensors, but it’s still a field. It’s a number or set of numbers assigned to points in space. Isn’t that a little mathematical? Yes, but so is everything else in physics. Lots of mathematical things represent something real. For example, we represent motion with a velocity arrow. The motion is real. The velocity arrow is not. It’s just the math that represents the real thing. The same is true for this gravitational field. I mean, it’s not like my hand is hitting a bunch of arrows right now. But locality says the Earth can’t affect this rock directly, so the force must be due to something located where the rock is. We call that a gravitational field and represent it with a bunch of arrows. It’s not a substance or a fluid or anything, but it’s something. Something is there. And, whatever it is, it preserves the principle of locality. The Earth creates a field and it’s that field that affects the rock. We can very easily extend this concept to electricity and magnetism. Charges don’t affect each other over a distance. One charge creates an electric field and that field affects the second charge. Magnets don’t affect each other over a distance either. One magnet creates a magnetic field and that field affects the second magnet. Locality is preserved. Or is it?! In this video, we learned the behavior of a particle is described by a wave. Something we call a quantum wave function. I also mentioned that wave was unobservable and that’s true. It is. But, if we have two particles, we might be able to see a difference. This wave could have started here or here or even here. As time plays out, you can see these waves are out of sync. We say they’re out of phase in time. But all three of those waves describe the same particle. It’s something we call global phase invariance. You want the wave to start here instead of here. Quantum particle don’t care! The probabilities you calculate from that wave function will be exactly the same regardless. But, back in 1959, two physicists proposed an experiment that calls everything into question. Say we’ve got a device that emits electrons that are all in-phase. That means their waves are all synced. If we separate two of those electrons and then bring them back together, they should still be in-phase. And that’s exactly what happens when we do the experiment. We get a pattern on a detector screen that is consistent with two waves in-phase. Wait, what’s that screen made of? What kind of electron device? How are you separating the electrons? None of that matters! Don’t get hung up on unimportant details. All that matters here is that they’re in-phase at the end. How we got there is completely irrelevant. OK, so we get a pattern on a detector screen that is consistent with two waves in-phase. Everything is fine so far. No problems at all. Now let’s consider a second device called a solenoid. That’s just a long densely-packed coil of wire, nothing too fancy. If we run an electric current through that wire, we’ll get a magnetic field, but only inside the coil. Outside the coil, the field is so weak, you might as well just say it’s zero. Things start to get weird when we use this coil in our experiment. Say we place the coil in the middle, so the two electrons go around the outside. There’s no field out there, so the principle of locality says they shouldn’t be affected. Things should only be affected by other things at their location. Except those electrons are affected. We get a different pattern on the detector screen. The electron waves are out-of-phase. What? What? What?! I know, right?! Somehow the magnetic field here is affecting the electrons all the way out here. That shouldn’t be possible. So do we finally give up on locality then? Eh, not so fast. This phase effect is called the Aharonov-Bohm Effect after the two physicists who proposed the experiment. Thankfully, those same two physicists phys physicist? phys phys physicist? Thankfully, those same two physicists also proposed a solution. What if there is something in the space the electrons are passing through? We know there’s no magnetic field, but maybe the magnetic field isn’t the best way to look at this. In basic mechanics, you normally use forces and Newton’s second law. That’s where electric and magnetic fields are the most useful. An electric field is a force per unit charge. It tells you how much force could be exerted on a charge at that point. The magnetic field does the same thing for magnets and moving charges. The two of them together allow us to find an electromagnetic force. But forces are not the only way to look at a situation. Sometimes, energy and momentum can give you a deeper insight. Take this battery for example. It has a voltage of 1.5 volts and a volt is just a joule per coulomb, an energy per unit charge. What that means is the energy at the positive end of the battery is 1.5 volts higher than the energy at the negative end of the battery. That number isn’t just limited to those two locations though. This battery assigns a number like that to every point in space. It’s something we call the electric potential. And, since that number is assigned to every point in space, it’s a field. A scalar field. This number tells us the energy that one coulomb of charge would receive from the battery at each location in space. However, the solenoid in our experiment doesn’t have an electric potential around it. It has a magnetic potential! Which fulfills a similar purpose, but for momentum instead of energy. Since momentum is a vector, so is the magnetic potential, which is why we call it a vector potential. We have one of these magnetic potential fields outside our solenoid. And it solves our locality problem. The electrons in our experiment pass right through that magnetic potential and it predicts the phase difference we see on the detection screen. So, locality, it’s kind of a big deal. Things should only be affected by other things at their location. It’s a principle we see obeyed over and over and over again. If you want to affect something over a distance, You’ve got to send something between you and that thing. Maybe that exchange happens because of a physical object. Ugh! Ouch! Maybe it happens because there’s some kind of field. But, no matter what, even in weird quantum experiments like this one, there is something local. Locality must be preserved at all costs. So, do you have any questions? Please ask in the comments. Thanks for liking and sharing this video. Don’t forget to subscribe if you’d like to keep up with us. If you like what we do and have it spare, please consider pledging on Patreon. Even a dollar a month helps keep things stable around here. And until next time, remember, it’s OK to be a little crazy. Wait, what about quantum entanglement? Aww, sh…. The featured comment comes from Feynstein 100. who pointed out how amazing the quantum wave function is. I admit, it is amazing, but that doesn’t make it real. It’s more like a coded message. In order to make sense of it, you have to decode it first. It’s the decoded information that’s real. Anyway, thanks for watching.

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100 thoughts on “The Quantum Experiment that ALMOST broke Locality

  1. Buuut what those fields are made of?? Do we know?? It is just a Mathematical representation?? Do we know if they are made of actual stuff??

  2. I've been wondering… if Gravity affect all object with mass inside its gravitational field, does magnet also affect every thing in its field? Is it because what it pulls and pushes cancels out that it isn't get attracted?

  3. "WHAT ABOUT QUANTUM ENTANGLEMENT???"
    Thank you – that was literally the question going through my head through out this entire video. 🙂
    Doesn't Bell's Inequality and the Alain Aspect experiment refute absolute locality?
    (And yes, I know what's coming: it doesn't because it doesn't carry any information the experimenter can influence, so it's not really alocality in any meaningful sense… but that always feels like a cop out…)

  4. The good old Berry's phase.
    It video kind of makes me appreciate what I studied in detail, something that rarely happens with youtube videos. So it was a weird experience.

  5. But locality may be broken in the quantum entanglement phenomenon. Moreover Bell's test experiment tell us that we must abandon either locality or realism (or maybe both) since the theory of hidden variables proposed by Einstein fails to explains the result of the experiment

  6. I was just about to ask about quantum entanglement violating the locality principle…..and then they had a little blurb about it at the end.

  7. Locality is bullshit. Universe is non local. Field is not entity that exist. It is effect of object communication. There is no field hanging unused. Communication between all objects in universe is instant, otherwise all objects would be in chaos out of sync with each other

  8. Couldn't we also propose that the wave function of the electrons exists partly inside the solenoid where the magnetic field is 'significant'? Sorry, my maths is crap so I cannot tell if this will affect the phase of the electrons or not.

  9. It's the creation of INFORMATION that makes the difference, hence the two experimets represent two different quantum process.

  10. What is that fluid thing u r talking about in space
    Is the gravitational force nothing but same as why small and less weight object start moving when high speed fan start rotating…
    I am going crazy!!!

  11. In another video, you described how all electrical charges have a magnetic field. So as your coil has a magnetic field and you not only believe electrons are real,, they too must, (being a so called charge carrying particle.) They must also have a magnetic field surrounding them. Could you please explain why there seems to be interference between your coils magnetic field and the field a magnetic field a so called electron must have?

  12. What about correlations due to entanglement? No, they cannot be used for communication (or other causal effects). But how do the entanglement correlations come to be? 
    Huh? Huh? How do they?

    Anyway, I say this is an excellent video. I learned.

  13. So, it is really about the wider meaning and implication of Locality; it is not simply something I can physically grab or look at, but context specific. Quantum entanglement has its own 'locality', starting from it's inception.

  14. I don’t understand why you say that the information “decoded” from the quantum wave function is any more “real” than the wavefunction. What do you even mean by “real”? This seems like a question of ontology, which is a hairy subject I think.

  15. Hey, in electron positron annihilation 2 photons are formed with one electron and positron, but one photon gives one electron and positron in pair production process.How?

  16. Contacting body forces are principally if not entirely electrostatic fields. So, in the end, all energy/momentum transfers are due to fields.

  17. 5:05 But "weak" is different from "zero". Why it is not enough to explain this experiment?
    And how are locality and quantum entanglement conciled?

  18. If we can imagine it. It must be real.
    Right?
    Right.
    I saw an unicorn once.
    It was great.

    Shame you have to teach every fly how to behave.
    Learning is a process I mostly enjoy but oh boy you guys are fast I cant keep up.
    You gotta warry of that, I might die from lack of knowledge.

  19. So qhat youre telling me is that the thingy can go around the mabob and end up being a thingamajig?

    Well ill be damned

  20. So, this David Bohm guy….. I seem to remember he did another paper which had a huge impact. I also seem to remember you promising to make a video on the result of that paper over a year ago. Any chance of this video being made before the United States gets a new President?

  21. Nick, if mass orbiting the earth is actually in a state of free fall how comes its orbit doesnt excellerate by the g constant 9.8 m/s?

    p.s. thanks for answering my last question about the difference between wave function and wave length

  22. Seems like a field is just a way of representing things in a way that doesn't break locality. Cheating, if you like!

  23. I remembered in your previous video, the DJ clone said because asylum crazies think deep, so I was wondering, how to think deep?

  24. So if locality exists then how does spooky action at a distance or quantum entanglement influence particles that are extremely far apart? You can make a change to one particle and instantaneously see that change. The other particle regardless of how far apart they are. I’d love to know how locality explains thatBecause I honestly am having a hard time wrapping my brain around it.

    Also, I posted my question before reaching the end of the video and it appears as though you asked the same thing LOL!

  25. I… Really want to understand how magnetic potential, yet no force, affects the electrons' wave functions

    This shift in perspective is making me question a lot of things-
    School and college only barely hinted at this through the first law of thermodynamics
    Never have I seen a potential alone, yet no corresponding force, affect a system

  26. The Ahranonov Bohm effect is more profound than simply locality. It was one of my topics in my undergraduate assignments. The idea is that the E & M fields are real, but the electric potential field ( q ) and the magnetic vector potential field ( A ) were mathematical constructs and without physical reality. The AB effect demonstrates that A is real, and has measurable effects.

    The Grad x A gives the magnetic field strength. So A alone should have no effect. However, changing the phase of the A field can have measurable effects on the path of the electrons. A is therefore a real physical field in its own right.

  27. I feel like the explanation of magnetic potential was a bit too cursory. I'm used to electric potential from batteries, it's fairly intuitive, but I'm not aware of magnetic potential — which before this video I would've assumed is just the magnetic field not interacting with anything. But, but, Nick says there's an effectively zero magnetic field outside the solenoid. Examples, please!

  28. But in order for the electrons to be affected they must interact with magnetism. But electrons to have magnetic properties should mean that they have moving electric charges on them. But electrons "are" the quantised charges. Is this how spin comes along or am I totally lost?

  29. Great video (as always) about an amazing experiment! However, you could add something regarding the gauge freedom in the electromagnetic potentials. In my first contact with the AB effect this blew my mind!

  30. What about Quantum Entanglement?

    But well in theory it can also be explained. Like by taking consideration of dimensions.

    Well Science Asylum , How you explain it?

  31. But the electromagnetic potentials can't be deirectly observed, they are in a way similar to what you said about the wave function: you have to decode it. This is reflected by the gauge invariance. So what do you say about that? Because looking at it this way, the electromagnetic potential field isn't a real vector field that directly corresponds to something real, is it? (I know gauge transformations don't change the closed line integral of the A field, but still.)

  32. Locality must be preserved. That's not a very spiritual statement. What about entanglement and sending information into the past?

  33. The magnetic field outside the solenoid is weak do to the iron/ferrous core at the center?

    In auto repair, we use capacitive probes on ignition coils, which are inductors, but I don't think they're actually solenoids. The capacitive probes, as I understand it, respond to the electric field, not a magnetic field, so that we can measure voltage (namely we just want the waveform to analyze and actual voltage isn't all that important).

  34. If the earth curves spacetime and due to the curve in the time axis of the squirrel, it's future points towards the Earth, then why does the squirrel not fall when it is placed on a table. (I mean when table exerts a force on it) Does the table reverses that curvature in the squirrel's time axis? Also, why would the table even apply force on the squirrel if gravity isn't even a force. What the heck is the table even trying to balance by the applying a normal reaction force?

  35. Small point: The negative side is 1.5 volts higher, not the positive side. Electron flow is from negative to positive because electrons have a negative charge.

  36. Nick: “Locality must be preserved at all costs.”

    Quantum entanglement: “Hold my beer.”

    Question clone: “I’m holding your beer good and tight.”

    Nerd clone: Holds breath and tries desperately not to say anything.

    Rocket clone: “Can I go back to Earth? We’ve been doing this twin paradox thing for three hours!”

  37. Not sure this is how gravity works, both a stone and a planet affect each other, it's just that planet is much more massive.
    That solenoid might be made in China and cause shortcuts.

  38. Tachions, actual dimensions passing through our universe in imaging work planes doing other things. Sister universes freezing and thawing in the bulk of higher Klein bottle pivot table spreadsheed gauss plank periodic diett.

  39. You explain complex (even though non-immaginary, ok couldn't resist…) things with a smile and the ability to keep your spectators curious and absorbed …
    You might be a little crazy; you're definitely a great teacher!

  40. Locality and linearity shouldn't be confused. It is understandable that changes propagates using neighbours, more like Butterfly effect. But , set of neighbours need not be linear. If we draw crazy nonlinear shape of neighbours, then actions will appear to not obey locality.
    Things gets even interesting if we consider fractional points and multi-dimensional space. Also, linearity doesn't continue as usual between points 0 and 1, straight line appears to bend if we use equation of line.
    Considering multi-dimensional effect, fractional points and different properties of materials, locality may not be as obvious as linearity. Extreme locality wold be then random like, defying definition of locality itself. So we may not understand how things are operating in the universe. As of now our sensor, intelligence and devices are bound by linearity.
    Edit, fractional points: we say something is at point X,Y,Z in space and other is at say X+1, Y+1, Z+1. But there could be unknown things between X and X+1.

  41. Why does the magnetic vector potential affect the electrons but not other things(If if did affect other things, wouldn't that just be the same as a normal magnetic field)? BTW great video as always, love watching them.

  42. There are no unimportant details when most of the understanding is math. Relativity changes length mass and time to keep light speed constant, and no one even questions it. Get rid of the strong force and then figure out why charge changes in tight clumps. You’ll change the world. I bet that the field is changed by some resonant mechanism. Put that in your book.

  43. A great explanation of locality. Of course even locality is down to fields and action at a distance albeit an extremely small one, no two things physically touch, they repel when the fields around the outer electrons interact. You explained before that a field simply exists around a particle it's not emitted by it, it's still a big mystery how this happens.

  44. So in the end there simply is a magnetic field around it? Or what else is a magnetic potential if not the magnetic field itself? I dont quite get it…
    Whats the difference between the magnetic potential and the field?

  45. So in the end there simply is a magnetic field around it? Or what else is a magnetic potential if not the magnetic field itself? I dont quite get it…
    Whats the difference between the magnetic potential and the field?

  46. So in the end there simply is a magnetic field around it? Or what else is a magnetic potential if not the magnetic field itself? I dont quite get it…
    Whats the difference between the magnetic potential and the field?

  47. Say we place the coil in the middle, so the two electrons go around the outside
    'round the outside
    'round the outside

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