Also superposition of which particles exist in the first place.According to the Many Worlds Interpretation of quantum mechanics, the entire universe is in a massive superposition for all quantum states of every particle. — Marchesk
Observers as such play no role. Think systems in a state, such as a classic rock at time T. Anything that rock has measured (a subset of what's in its past light cone) is part of the entangled state of that system.A potential issue arises here. What of all the entanglements that don't support observers?
If you want to define 'world' that way, sure, but it's just a language definition then. The physics cares not if it is observed by say something you'd qualify with the word 'conscious', which seems to be what you're hinting as being an observer.Which means observers are fundamental for saying what counts as a world.
Yes.The universal wave equation makes no such distinctions. In fact, "observers" and "worlds" are classical concepts.
Yes. — noAxioms
Observers as such play no role. Think systems in a state, such as a classic rock at time T. Anything that rock has measured (a subset of what's in its past light cone) is part of the entangled state of that system. — noAxioms
No, a world is not a relation with an observer. Not sure where you get this. If you like, you can assign a world in relation to an event-state, but calling the system an observer seems to suggest a very different interpretation. — noAxioms
I don't see how classical observations in any way would have difficulty 'squaring' with that to which I answered 'Yes'.Problem is you have to square this with actual observations, which have classical results when a measurement is performed. — Marchesk
Just so, but I'm not claiming rocks are the source of quantum theory. They only obey it, acting as a classic system as much as any human-body system (dead, alive, asleep, whatever), which is after all still just a classical physical system differing from the rock only in arrangement of material.I'll refer you back to what Bohr had to say regarding experiments. Experiments have to be described in terms of the language of performing the experiment, not the mathematical formalism used to model what happens during the experiment. Rocks didn't come up with the Schrodinger equation or the Born rule. Physicists did after observing or learning about experimental results.
I think you're going to need to define your use of the word 'observer' here, because I don't think we both agree with this given the common definition. I can think of only one obscure interpretation of quantum physics (Wigner) in which a living thing plays a special role, and even Wigner abandoned it after some time.If there's no observation, there's no world, since as we both agree, a world is a system that appears to be classical.
What Everett does NOT postulate:
"At certain magic instances, the the world undergoes some sort of metaphysical “split” into two branches that subsequently never interact" — Tegmark
Yes, a classical rock takes measurements. If that makes it an observer, then fine. It doesn't need to know about Schrodinger's equation in order to measure a classical world. If you don't count that as an observation, then I completely disagree with your statement above. — noAxioms
I talk of universes splitting. It's part of the language of the subject.Sean Carrol, a current proponent of MWI, talks of universes splitting. — Marchesk
Don't know what you mean by this. Certainly not that empirical evidence of rocks constitute a falsification of MWI. A rock is a system and a system is part of MWI. A rock, in a state, can be described by a wave function. It very probably is not a closed system.There aren't classical rocks or observations in MWI. — Marchesk
Our classical appearance needs to be part of a valid solution to the universal wave function, and nothing says it is not.Some physicists, mathematicians and philosophers say the wave function describes the universe. If it does, then the classical appearance of our world needs to be derivable from that equation. — Marchesk
Think systems in a state, such as a classic rock at time T. — noAxioms
Not sure exactly what he suggests or how he words it, but there seems to be problems with two different universes (one with each measurement) existing. If there's all these universes/worlds and they exist, the more probable ones either have to 'exist more' than the lesser ones, or maybe there's just more of them. What does it even mean for one thing to exist harder than another?Sean Carrol, a current proponent of MWI, talks of universes splitting. — Marchesk
Hossenfelder indeed seems to find issues the interpretation. This seems to be part of a series taking down each of the interpretations in turn, with a similar argument. Anyway, which comment in there (at what time) do you think counters my suggestion that a rock in a certain state is part of a valid solution to the universal wave function at some time in the past of the rock state?Sabine Hossenfelder says it's not — Marchesk
Yes, there should.There should even be some human-like observers seeing a rock teleport some distance — Marchesk
As an old math person my suspicion is that "superposition" and "collapse of wave function" is nothing more than experimenting to discover which of multiple solutions of the partial differential equations describing phenomena actually apply in a particular instance. Multi worlds I consider science fantasy. — jgill
If, as is my understanding, there is no way to decide on a correct interpretation of QM empirically, it becomes not fantasy, but metaphysics. Or maybe just baloney. — T Clark
Q: You’ve written critically about the Many Worlds (or Everettian) Interpretation of quantum mechanics. What are its main shortcomings?
A: Its main shortcoming is simply this: The interpretation is completely contentless. I am not exaggerating or trying to be rhetorical. It is not that the interpretation is too hard to believe or too nonintuitive or too outlandish for physicists to handle the truth (remember the movie A Few Good Men?) It is just that the interpretation actually does not say anything whatsoever about reality. I say this despite all the fluff of the science-writing press and a few otherwise reputable physicists, like Sean Carroll, who seem to believe this vision of the world religiously.
For me, the most important point is that the interpretation depends upon no particular or actual detail of the mathematics of quantum theory. No detail that is, except possibly on an erroneous analysis of the meaning of “quantum measurement” introduced by John von Neumann in the 1930s, which is based on a reading of quantum states as if they are states of reality. Some interpretations of quantum theory, such as the one known as QBism, reject that analysis.
Q: So your position is that the Many Worlds Interpretation isn’t useful because it doesn’t constrain our theories of physics?
A: Allow me to get a bit technical to try to get the point across: Would Many Worlds work if quantum mechanics were based on real vector spaces instead of on complex ones? I would say yes. Would it also work if quantum mechanics used a different product structure than the tensor product? Yes. Would it work if quantum mechanics were nonunitary, i.e., didn’t obey the Schroedinger equation? Yes. And so it goes. One could even have a Many Worlds Interpretation of classical physics — as David Wallace, one of the most careful philosophers of the Many Worlds interpretation, once reluctantly admitted in a conference I attended.
The Many Worlds Interpretation just boils down to this: Whenever a coin is tossed (or any process occurs) the world splits. But who would know the difference if that were not true? What does this vision have to do with any of the details of physics? — Qanta
Don't know how to answer this. All interpretations are supposed to yield the same empirical results, so if there is an empirical problem to be solved (like getting a quantum computer to work), the problem is with quantum theory.What in your view is the problem for which MWI is a solution? — Wayfarer
MWI is and isn't a realist interpretation. It, like any almost all interpretations (QBism included), does not hold to the principle of counterfactual definiteness (that things really exist in the absence of measurement). Only under that principle is there 'spooky action at a distance", or faster-than-light cause/effect.It is just that the interpretation actually does not say anything whatsoever about reality. — Quanta interview
Such a statement can be crafted of any interpretation.Whenever a coin is tossed (or any process occurs) the world splits. But who would know the difference if that were not true? What does this vision have to do with any of the details of physics? — Qanta
I think (for what it's worth, probably not much) that there are more and less credible interpretations. I rather like Chris Fuchs QBism, — Wayfarer
there is no way to decide on a correct interpretation of QM empirically — T Clark
Well go on then, split the universe! :party: — Agent Smith
What in your view is the problem for which MWI is a solution?
Don't know how to answer this. — noAxioms
Just did, nobody noticed. Or ever will. — Wayfarer
If one is seriously averse to wave function collapse, the list of interpretations on wiki (about 13) has only half of them supporting collapse. Point is, there are others to choose from besides MWI.Might I suggest that the motive for accepting the MWI interpretation is to avoid the philosophical conundrum of the 'collapse of the wave function'? — Wayfarer
OK, this is like a double slit setup with a which-slit detector behaves differently than a setup without one. That's not especially profound. If you get into the act of observing now changes something in the past, that's quite interpretation dependent.to wit 'The observer effect is the phenomenon in which the act of observation alters the behavior of the subject of observation'
Again an interpretation dependent statement. Not all interpretations suggest that a thing an exist in multiple states simultaneously. Bohmian mechanics for instance has but one state for anything. It is a hard realist interpretation where stuff is where it is. On the other hand, it necessitates backwards causation where decision not yet made can affect what a particle does now. I personally find that more offensive than collapse.This is due to the ambgious nature of sub-atomic particles, which means that they can exist in multiple states simultaneously.
Causing what to assume a definite state? The particle? Only some interpretations suggest this. With some (original Copenhagen for instance), the wave function is epistemological, describing only what one knows about a system. You take a measurement and your knowledge of the system changes, but the system is not affected by your acquisition of this knowledge.When an observer measures a particular property of a particle, they are effectively collapsing the wave-function of that particle, causing it to assume a definite state
Something you apparently consider a substantial cost. I'm fine with that since I don't hold to the premise that there should be only one world, especially in the absence of evidence supporting that premise. My dismissal of MWI comes from other grounds.The approach of the MWI is to declare that the so-called wave-function collapse doesn't occur - but at the cost of there being many worlds.
So I guess I need to ask what you mean by an act of observation being considered 'causal'. — noAxioms
I don't hold to the premise that there should be only one world, especially in the absence of evidence supporting that premise. — noAxioms
With some (original Copenhagen for instance), the wave function is epistemological, describing only what one knows about a system. You take a measurement and your knowledge of the system changes, but the system is not affected by your acquisition of this knowledge. — noAxioms
Don't get the last bit. It would seem that if you measured something's location, it is the location possibility which gets reduced to some much smaller deviation, and the others (momentum say) which are still just probabilities of what will be measured. The first bit talks about 'existing in a specific place' which is counterfactual terminology. Most interpretations do not hold to counterfactual definiteness, which means particles don't have actual positions (and other properties) in the absence of measurement. BM would say a photon exists en-route. Just pointing out the minefield of using terms like 'exists' which are defined differently from one interpretation to the next.That prior to observation the particle doesn't exist in any specific place, that its possible properties are described by the wave-function, and that the act of measurement reduces all of the possibilities, except for the one in which it was measured, to zero. — Wayfarer
The measurement changed the wavefunction (relative to to the screen at least), so yea, that was caused by the interaction. Did the measurement change the photon? No, it's more like the photon caused the measurement. I'm trying to see the problem here.So that's how the act of observation is considered causal. Is that not correct?
Don't know much about QBism, but it sounds a bit like all the idealism stops being pulled out. It defines existence in terms of beliefs and such, if I read it right.I don't recall reading anything like that about Bohr and Heisenberg's interpretation, it seems more like QBism which I mentioned above.
Don't get the last bit. It would seem that if you measured something's location, it is the location possibility which gets reduced to some much smaller deviation, and the others (momentum say) which are still just probabilities of what will be measured. — noAxioms
Q: Does that mean that, as Arthur Eddington put it, the stuff of the world is mind stuff?
QBism would say, it’s not that the world is built up from stuff on “the outside” as the Greeks would have had it. Nor is it built up from stuff on “the inside” as the idealists, like George Berkeley and Eddington, would have it. Rather, the stuff of the world is in the character of what each of us encounters every living moment — stuff that is neither inside nor outside, but prior to the very notion of a cut between the two at all.
A potential issue arises here. What of all the entanglements that don't support observers? Those aren't considered worlds since there's no observers for things to appear classical. Which means observers are fundamental for saying what counts as a world. — Marchesk
“Worlds” are mutually dynamically isolated structures instantiated within the quantum state, which are structurally and dynamically “quasiclassical”. The existence of these “worlds” is established by decoherence theory. — Decoherence and Ontology - David Wallace
However, the structural approach is committed to an approach to the mind which ... denies observers some uniquely special status, but describes them as emergent as structures and patterns in lower-level physics (specifically, in lower-level classical physics, itself to emerge from unitary quantum physics via decoherence); — Everett and Structure - David Wallace
That being said, my understanding is that the probabilities we use to calculate the likelihood of what to expect when a measurement is made still needs to be derived within the Schrodinger equation in a self-consistent manner without adding it in post hoc, since the wave function is supposed to describe the universe we live in, if MWI is true. So deriving the Born rule within MWI is an ongoing project. — Marchesk
↪180 Proof He has a very interesting idea on how to put MWI and wave-function collapse interpretations to the test. Assuming we can build a conscious AGI quantum computer. — Marchesk
I didn't get where in the 2nd vid that Deutsch suggested some kind of empirical test that should yield different results from one interpretation to the next. I'm very skeptical of that. — noAxioms
6:12 Deutsch: When we have quantum computers, we will be able to have very large, very complex entities existing in super positions. So, in principle, I suggested long ago before this was remotely on the cards experimentally, that if we had a quantum computer on which an artificial-intelligence program was running, say, with human level artificial-intelligence then this entity would be able to experience interference in its own consciousness.
6:46 Arndt: Well, some people would say that your consciousness would collapse your reality.
6:50 Deutsch: Yes, so if that happened that would refute the Everettian interpretation or, as I would say, it would refute quantum theory. That would be a very interesting problem and that's one of the reasons why scaling up both the size and the complexity and the mass of phenomena that I experimentally observe, but that can only be explained by quantum theory, is very important.
7:17 Arndt: I fully agree. We need to do that.
7:21 Deutsch: We just need to close the gap between that and the AI because the AI would not be having this conversation. Or, at least, the AI would not be able to make the argument that you just made. It would have to say I've only got evidence of many worlds on the scale of my mind, but not bigger so - and I guess that will always be true. — Are There Many Worlds? David Deutsch in conversation with Markus Arndt
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