• tim wood
    9k
    Sorry, MU, not interested. You can braid your arguments any way you like. But for the topic of this thread, I refer you to the exchange noted just above, that I had no part in. I do note I said if you insisted on cause, I would ask you to define exactly what a cause is. And you ignored that.
  • flannel jesus
    1.7k


    I thought it would be worth potentially elucidating why the non-local causality of Copenhagen was problematic for Einstein (why he called it spooky action at a distance) and why it remains problematic for other physicists. None of this is meant to be proof that it can't be correct, only an explanation for why it isn't taken at face value as obviously the correct interpretation.

    Physicists, for what you might call "aesthetic" reasons, have I think always tended preferred local causality rather than instantaneous-across-distances causality since physics was even a thing. Einstein himself changed that from a mere aesthetic preference to something a bit more substantial.

    Einstein is of course credited with Relativity, and specifically of interest to this conversation is Relativity of Simultaneity. If you observe two events, one over here and one over there, you may be able to say "this event happened before that event". Einstein's relativity of simultaneity says there is some other observer in some other reference frame who can say the opposite "that event happened before this event" - and in relativity, it's not that one of you is right and the other is wrong. You're both right, in your own reference frame.

    Now, when events are happening locally, everyone agrees which one happened before the other one. This problem of disagreeing order of events only happens with events that are separated in space.

    So, back to Bell's Theorem. You're at a reserch facility. At the middle, you have an apparatus that generates entangled electrons and sends one east, to you, 50m, and one west, to your research partner Alice, 50.000000001m - she's very slightly further away from the middle than you. So, you generate an entangled electron pair, you measure the spin as Up, Alice measure's the spin as Down just a tiny fraction of a second later. The causal narrative of Copenhagen says, you measured your electron as Up, then immediately, faster than light, the virtual worlds collapsed and guaranteed that Alice would measure her spin as Down.

    Relativity of simultaneity says, there's some equally valid reference frame where actually, Alice measured the spin as Down first, and that's what caused the collapse of the virtual worlds, the wave function, which caused you to measure yours as Up.

    When you combine Relativity with Copenhagen, you get this strange picture of causality. You can't objectively, universally say A caused B, because it's equally valid to say B caused A. THIS is what "spooky action at a distance" means. This is what's spooky about it. This is why Einstein couldn't stand QM when he first learned of it.

    Again, this doesn't mean Copenhagen is incorrect, it's just meant to give you some context as to why some people aren't satisfied with Copenhagen.
  • Metaphysician Undercover
    12.8k
    On your view, why does it matter what material the conductor is composed of, or what the cross sectional area of the conductor is?wonderer1

    I made a reply to tim wood's statement of opinion "the electron is particle-like, and only cloudlike in the sense that it moves around really, really fast." On the other hand, it is my opinion that the transmission of energy through a field cannot be adequately represented as particles moving really really fast. In fact, what I've been arguing is that the representation of such energy transmission as through particles is completely wrong. This is compatible with what flannel jesus is arguing, that the outcome of Bells theorem is that the classical representation of energy as the property of bodies (particles in this case) is fundamentally inadequate.

    Of course "the body" of the conductor plays a role, and that's why I argued elsewhere in the "Entangled Embodied Subjectivity" thread, that it makes no sense to talk about "just the field", as if the field could exist without the body. This specific problem, I believe is due to the deficiencies in our understanding and conceptualization of what is called "the field".

    Since there is no ether identified as the medium within which the waves exist, the only substance which this concept is grounded in is the body which the field is a property of. Establishing the correct relationship between body and field is problematic in current conceptualizations. If the ether which is logically required to support the real existence of waves, was identified such that its real properties could be tested, this would allow us to conceptualize independent existence of the waves, enabling us to properly conceive of the waves as prior in time to the body, and therefore the appearance of a body (particles, atoms, molecules, etc.) as property of the waves. But this implies a conception of the waves which would be completely distinct from the current "field".
  • flannel jesus
    1.7k
    Since there is no ether identified as the medium within which the waves exist, the only substance which this concept is grounded in is the body which the field is a property of. Establishing the correct relationship between body and field is problematic in current conceptualizations. If the ether which is logically required to support the real existence of waves, was identified such that its real properties could be tested, this would allow us to conceptualize independent existence of the waves, enabling us to properly conceive of the waves as prior in time to the body, and therefore the appearance of a body (particles, atoms, molecules, etc.) as property of the waves. But this implies a conception of the waves which would be completely distinct from the current "field".Metaphysician Undercover

    You got me interested, so I googled this up:

    https://physics.stackexchange.com/questions/308413/ether-vs-quantum-field-theory

    Just posting it here because it's interesting. Maybe you'll find it as interesting as I did.

    I do think the usual idea of the fields is that the waves aren't distinct from the field, the waves are literally perturbations of the field. I don't know if there's any conception of quantum fields where the waves are somehow distinct from the field, never heard of that idea before.
  • hypericin
    1.5k


    Interesting. Does MW "solve" this somehow?
  • flannel jesus
    1.7k
    yes, world splitting is not a global event. World splitting in MWI actually happens at the speed of causality.
  • hypericin
    1.5k
    In that case, I hereby modify my "theory", the virtual world collapsing also happens at the speed of causality (aka light?) :P

    This means that MW and Copenhagen aren't just interpretations, they are different theories, and there must be a way to test their differing predictions, right?
  • flannel jesus
    1.7k
    if it happens at the speed of causality in your interpretation, then you're left with explaining what's happening on Alice's side when she measures DOWN after Bob measured UP. Do 2 Alices exist at once, one who saw down and one who saw up?

    Many worlds does, in fact, have 2 Alices, and 2 Bob's, which is why the worlds don't have to split globally immediately. But in your idea, there aren't 2 real Alices in 2 real worlds, which means you've got some tricky things to deal with.

    If you believe there's only ever one real Alice and one real Bob, then the worlds CAN'T just split at the speed of causality. They have to split fast enough so that Alice's result is guaranteed to be opposite to Bobs, but the split can only begin happening as soon as Bob has measured. It takes near instantaneous casualty to make that happen.
  • flannel jesus
    1.7k
    if my above explanation isn't sufficient to make it clear why single-world Copenhagen type interpretations require faster than speed of light communication to happen, I'm happy to illustrate in much more detail.

    Also, just clarifying something I said a couple posts ago - the phrase "speed of causality" means "slower than or equal to the speed of light".
  • hypericin
    1.5k

    :chin: Lemme think about it. Feel free to elaborate if you like, you've got a real knack for it, I love your lucid explanations.
  • flannel jesus
    1.7k
    Thank you, I'll try to make it brief. It's truly just a differently-detailed example from before, but hopefully the new details are illuminating.

    If you believe there is only one Alice and one Bob, then imagine a scenario like this.

    You've got the entangled-photon emitter, emitting one photon East and one photon West like before. Bob is east, waiting to receive the photon 10 light seconds away. Alice is west, waiting to receive the photon 11 light seconds away.

    At t=0s, the photons are emitted. At t=1, both photons are in their way to Alice and Bob respectively, BUT crucially the photons have an indeterminate spin at this moment, right? Because they haven't been measured.

    At t=9, both photons are close to their respective destinations, but crucially still with indeterminate spins. Same thing at t=9.9999 right?

    At t=10, Bob gets his photon and measures it as spin Up. At this moment, Alice still has not received her photon. Now, if you want this to all happen with only speed of light level causality, the problem starts to become clear:

    Alice's photon is still unmeasured at t=10, and Bobs has only just been measured 20 light seconds away, which means Alice's photon must still be indeterminate, right? It was indeterminate at t=9.9999, and nothing casually exists that would have changed that in the meanwhile in our example, right?

    So, here's the problem. Bob has measured Up. Bob knows for a fact Alice will measure Down. But Alice's photon is still indeterminate, and the information required to make Alice's photon collapse to "Down", at t=10, has 1 second to make it to Alice's photon. It has 1 second to travel 20-21 light seconds, to make Alice's photon spin state collapse to the matching value.

    It has 1 second to travel 20-21 light seconds. The information has to travel over 20 times the speed of light to achieve this.

    This is why you can't just believe in a single real world and say "my virtual worlds collapse at the speed of light".

    I hope that makes sense.
  • tim wood
    9k
    If you believe there is only one Aliceflannel jesus
    And if you believe there are two or more Alices, and ultimately there have to be as many as needed, are they the same? Or are they different? If the same, then how does that work? And if different then not the same, and thus not Alice.

    Much is made of the spin of the particles being not well-defined until measured, but the point is that they are measured. Further, we're not dealing with events at the quantum level, but real observed events at the macro-level, namely the readings of machines.

    MW is a fun story, until you think about it even a little bit. After all, to "solve" what seems to be a problem, at least in understanding, requires the ad hoc creation of as many new worlds as needed, without one word as to how that can be! Well there is one word: Magic!
  • flannel jesus
    1.7k
    I appreciate your feedback. However, the post you're replying to is purely about why Copenhagen family of interpretations require non local casualty.
  • wonderer1
    1.8k
    Since there is no ether identified as the medium within which the waves exist, the only substance which this concept is grounded in is the body which the field is a property of. Establishing the correct relationship between body and field is problematic in current conceptualizations. If the ether which is logically required to support the real existence of waves, was identified such that its real properties could be tested, this would allow us to conceptualize independent existence of the waves, enabling us to properly conceive of the waves as prior in time to the body, and therefore the appearance of a body (particles, atoms, molecules, etc.) as property of the waves. But this implies a conception of the waves which would be completely distinct from the current "field".Metaphysician Undercover

    I find it strange, the way you seem to get hung up on words being used in ways you disapprove of. Analogies play an important role in the way humans communicate things with each other and the use of "wave" to convey somewhat analogical things about electromagnetic fields has been going on for longer than either of us have been alive. It looks to me like you are fighting a losing battle.

    What do you see as a problem, with having a notion of "wave" that needs nothing more than space to propagate through?
  • hypericin
    1.5k
    I hope that makes sense.flannel jesus
    Yes. I retract my amendment, my theory as originally stated stands: the virtual worlds collapse immediately.

    When you combine Relativity with Copenhagen, you get this strange picture of causality. You can't objectively, universally say A caused B, because it's equally valid to say B caused A. THIS is what "spooky action at a distance" means. This is what's spooky about it. This is why Einstein couldn't stand QM when he first learned of it.flannel jesus

    I think the word "causality" is misused when applied to virtual worlds collapsing. "Causality" in the physical, actual world involves the action of forces. You can't have a situation where A can cause B, or B can cause A, depending on the frame of reference. This is illegal *not* because it bothers our intuition, but because forces are asymmetric: you can't generally get the same result if you change the sequence. The universe can't allow that, because there is only one actual world, and this would result in multiple conflicting versions of reality.

    The collapse of a virtual world into actual is not caused by a force (though it can be triggered by a force). Could a force somehow push or pull a virtual world into actuality? It doesn't make sense. Rather, this operates at a deeper level, it's the underlying logic of the universe that makes causal interaction via forces possible. Unlike forces, collapses are symmetric, so it doesn't matter if A or B happens first in different frames of reference, what matters is that the outcome is the same.
  • tim wood
    9k
    Fair enough. The non-local causality is called "entanglement" as you well know. Now I'm thinking that no one understands entanglement - do you know anyone who does?

    Btw, I admire your description in terms of light seconds; it was very clear. And above you described a not-so-simple relativistic effect in which the sequence of events A and B can depend on the frame of reference (FoR). I think that's right but only for events that are space-like separated. That is, in no FoR does the target shoot the gun. The events at Alice's and Bob's detectors are not space-like separated. Thus while different observers may see a different sequence, the actual sequence is preserved in the FoR of the detectors. And this gets complicated to think about.
  • Metaphysician Undercover
    12.8k
    I do think the usual idea of the fields is that the waves aren't distinct from the field, the waves are literally perturbations of the field. I don't know if there's any conception of quantum fields where the waves are somehow distinct from the field, never heard of that idea before.flannel jesus

    I think what is needed here is a clear understanding of what is a "field". Wikipedia tells me that it is a geometrical representation which assigns values to various points in space. The values will
    change as time passes.

    What I would say, is that the changing values of the field are a representation of the real wave motion (a motion which would require an ether). However, there is no ether identified, so there is no real wave motion which can be identified. However, the field representation does show the transmission of energy through the thing represented as a field. So many physicists are inclined to just think of the field as the thing which is real, and forget about the real waves which the field represents.

    I find it strange, the way you seem to get hung up on words being used in ways you disapprove of. Analogies play an important role in the way humans communicate things with each other and the use of "wave" to convey somewhat analogical things about electromagnetic fields has been going on for longer than either of us have been alive. It looks to me like you are fighting a losing battle.

    What do you see as a problem, with having a notion of "wave" that needs nothing more than space to propagate through?
    wonderer1

    I've studied enough physics to know that a wave is an activity of a substance. That's simply what a wave is, and all waves are understood through modeling the movement of the particles within that substance. That's what a wave is, a specific type of activity of a substance which involves an interaction of its particles. Therefore a wave in empty space is simply impossible because there would be no particles there to make the wave. Yet we know from observation, rainbows, and other refractions, that light must consist of waves, therefore there must be a substance there which is waving.
  • flannel jesus
    1.7k
    are you eschewing a casual explanation altogether? If not, how does the casual narrative look?

    I also want to take the opportunity again to clarify that the stuff I'm presenting is only meant to illustrate a tension between relativity and Copenhagen. It doesn't mean that Copenhagen must be incorrect, AND it may be that the tension is resolvable anyway. I'm by no means attempting to convince you to change your mind. I just think all this stuff is interesting to think about.
  • flannel jesus
    1.7k
    The events at Alice's and Bob's detectors are not space-like separated.tim wood

    Being many light seconds apart is exactly an example of what it means to be space-like separated, no? They are... separated in space.

    Thank you for the kind words btw
  • flannel jesus
    1.7k
    Really interesting read.
  • tim wood
    9k
    Being many light seconds apart is exactly an example of what it means to be space-like separated, no? They are... separated in space.flannel jesus

    My bad, if bad. In the frame of reference that includes Alice and Bob, and the particle emitter, all parts of the experiment are time-like related. At the moment of detection, yes, a momentary space-like relation. That the instant of non-local effect. I invite you to listen to this:
    https://www.youtube.com/watch?v=OduDEz77h9U&t=830s
    You can speed it up to however fast you can listen. He makes the point that what Bell's theorem rules out is any strictly local theory (thus non-locality) At about 21:00. And that Bell's theorem in not about hidden variables(!) 24:00. The whole worth the listen
  • EricH
    587
    Yet we know from observation, rainbows, and other refractions, that light must consist of waves, therefore there must be a substance there which is waving.Metaphysician Undercover

    Perhaps I'm misunderstanding you, but the Michelson–Morley experiment disproved that idea.
  • flannel jesus
    1.7k
    I invite you to listen to this:
    https://www.youtube.com/watch?v=OduDEz77h9U&t=830s
    You can speed it up to however fast you can listen. He makes the point that what Bell's theorem rules out is any strictly local theory (thus non-locality) At about 21:00. And that Bell's theorem in not about hidden variables(!) 24:00. The whole worth the listen
    tim wood

    He's championing a particular interpretation, or class of interpretations here - pilot wave theory, which some argue has evolved since its invention into Bohmian mechanics. That's certainly an interpretation I have had my eye on for a long time, definitely worthy of thought and attention.

    Every interpretation has its own way of answering to Bells Theorem - how a particular interpretation answers to Bells Theorem is a big part of the flavour of the interpretation itself. It's like a trade off - in order to answer to Bells Theorem, you have to choose something you want to keep in physics and choose something else you're okay with losing. Some interpretations are okay with losing "locality", for example. Some are okay with losing "realism".

    That's kinda what's fascinating about qm - it took all of physicists intuitions and said, you can't keep all of them! You've got to let go of something. If you want to keep this, say goodbye to that.
  • hypericin
    1.5k
    are you eschewing a casual explanation altogether? If not, how does the casual narrative look?flannel jesus

    So, Alice and Bob are 11 and 10 light seconds away respectively from a dual photon emission. Charles is at the emission site, and Dave is travelling at high speed in a spaceship, away from Bob, towards Alice.

    When Alice and Bob measure their spins of +A,-A, they immediately send signals telling the result. Charles measures Bob's first, and believes Bob "caused" the virtual world to become actual where Alice measures +A. Dave believes Alice received the photon first, and "caused" the virtual world to become actual, where Bob measures -A.

    Both are equally correct. "Cause" is in quotes to distinguish it from ordinary cause and effect, which always involves forces. I'm speculating that this situation is OK, because unlike with forces, the resolution of virtual worlds into the actual world is invariant wrt sequence. No matter the frame of reference, the end result is the same, that Alice and Bob occupy the same actual world, and measure the opposite spin.

    How this cosmic bookkeeping actually works might be beyond our ken.

    I'm by no means attempting to convince you to change your mind. I just think all this stuff is interesting to think about.flannel jesus

    :100: Absolutely
  • flannel jesus
    1.7k
    No matter the frame of reference, the end result is the same, that Alice and Bob measure the opposite spin.hypericin

    The question, I guess, is what sort of mechanism allows the universe to guarantee that their measurements are opposite? That's the casual explanation I was looking for.

    It's easy to guarantee opposite results if the values are pre-set as soon as the photons leave the emission site, but that's exactly what Bells Theorem seems to disallow. The mechanism for Many Worlds is called "decoherence", but that requires 2 bobs and 2 Alices. What's the mechanism in your view?
  • hypericin
    1.5k

    :chin: :chin: :chin:
    It's the right question, and a doozy... I'll have to get back to you on that one!
  • flannel jesus
    1.7k
    I thought you were going with some sort of acausal view, or at least alternative-causality view, when you were saying it doesn't matter if a causes b or b causes a. Alternative causality is something that comes up in QM sometimes.

    For example, Tim Woods linked video above seems to promote the Pilot Wave family of theories, and some of those involve a sort of retro-causality - there's some "thing" that goes to the future, finds out what value needs to obtain, and then comes back in time and takes that value. Not all versions of pilot wave take that approach, but some do. I think I have some work to do to understand more about pilot wave / Bohmian ideas.

    Anyway, please tag me in your next post if you have a development here.
  • hypericin
    1.5k
    there's some "thing" that goes to the future, finds out what value needs to obtain, and then comes back in time and takes that value.flannel jesus

    Sounds pretty unaesthetic to me. If it comes to that I might prefer MWI.
  • Metaphysician Undercover
    12.8k
    Perhaps I'm misunderstanding you, but the Michelson–Morley experiment disproved that idea.EricH

    I don't think you misunderstand me, but I do think you misunderstand what the M-M experiments disproved.
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