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Physicists provide support for retrocausal quantum theory

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Re: Physicists provide support for retrocausal quantum theory

#111

Post by mikeash »

Simon_says wrote: post #96
mikeash wrote: post #82

Earlier quoted context omitted.

Feynman said, "I think I can safely say that nobody understands quantum mechanics." This is a guy who won the Nobel Prize for work in quantum mechanics. QM does not line up with human intuition at all. It looks like this is a fundamental issue with how the universe works, not a problem with our explanations. And really, that shouldn't be any surprise. There's no reason to expect the universe's workings to match our i…

Feynman said that quote in 1965, and it may have been true when he said it. The Many-Worlds Interpretation was technically invented before then (1957), but was a fringe theory and not disseminated much prior to the 1980s. I don't think you could get away with saying the same quote today.

Implying that many-worlds is the key to unlocking true understanding of QM? What's the basis for that?

Re: Physicists provide support for retrocausal quantum theory

#112

Post by Simon_says »

mikeash wrote: post #111
Simon_says wrote: post #96

Earlier quoted context omitted.

Feynman said that quote in 1965, and it may have been true when he said it. The Many-Worlds Interpretation was technically invented before then (1957), but was a fringe theory and not disseminated much prior to the 1980s. I don't think you could get away with saying the same quote today.

Implying that many-worlds is the key to unlocking true understanding of QM? What's the basis for that?

Yea, that's exactly what I'm implying. As for the basis for it -- I'm not sure how to put it. Every other interpretation is deeply confused, but MWI gives a deterministic, algorithmic, and non-mysterious explanation.

MWI may or may not be correct, but an adherent definitely would not say they "don't understand" QM.

Re: Physicists provide support for retrocausal quantum theory

#113

Post by gnaritas »

mikeash wrote: post #110
gnaritas wrote: post #92

Earlier quoted context omitted.

Maths are models of reality which may or may not be correct and can only be verified by comparing them to reality. While they serve as the most simple way to explain reality, don't confuse them with reality. The map is not the territory.

What prompts this reply? I'm not saying that math is reality, merely that solid mathematical models have been the foundation of progress in science, not "explanations."

I just don't agree with what you're saying, progress comes from understanding reality via some intuition, understanding and intuition lead to the development of testable models. Testable mathematical models are the result of progress in science, not the foundation of it.

Re: Physicists provide support for retrocausal quantum theory

#114

Post by jostylr »

BoiledCabbage wrote: post #102
jostylr wrote: post #77

Earlier quoted context omitted.

While one can take a bit of issue with using the ether as analogy for a number of reasons, the most important difference to keep in mind is that the wave function exists in configuration space. For 10^80 particles, this is a space with 3^(10^80) dimensions. This is the source of nonlocality. While PWT is the most sensible to me, it is strange though solely because of the wave function which is common to all theories,…

So here I may be stepping past my knowledge, but I thought that the reason for appearing to require so many would be simply due to using the wrong "basis" to calculate the wave function. Or separating the concept of how to generate the wave function from the values it produces. Via analogy, let's imaging the perfectly still lake. In the lake at an (x,y) position is a mechanical oscillator which moves up and down and…

Error: Yes, it should be 310^80. I think my brain was half-writing the dimension and half-writing the more useful view of (R^3)^10^80. Thanks for catching that.

As for your analogy, I don't quite follow. The actual physical model is that of the oscillators, more or less. The wave is the mathematical abstraction that does allow us to replace it with a function. In terms of information, the wave has more detail, but it is abstracted into a nice form. I think we agree on this.

But the quantum wave function is serving a different role. The water wave is something that varies over the 2d space. As we look at different values, we change the x and y coordinates to see the new values. In that sense, it is 2d.

For the quantum wave function, if we keep all but one of the 10^80 particles in the same exact position, but we vary the position of that one particle, we do get different values of the wave function and it does matter to all the particles as it will affect the gradient vector defining the velocity vector of each of the particles. The change is not localized to just the one particle that is changing, but impacts all particles.

Of course, most of the time, practically speaking, changes by one particle will not make a difference, but situations such as present in Bell's Theorem and quantum computing are exceptions to this.

Fundamentally, the current state of all the particles is needed to be known in order to know what part of the wave function is needed. That is the sense in which the dimension is not 3, but 310^80.

Re: Physicists provide support for retrocausal quantum theory

#115

Post by mikeash »

Simon_says wrote: post #112
mikeash wrote: post #111

Earlier quoted context omitted.

Implying that many-worlds is the key to unlocking true understanding of QM? What's the basis for that?

Yea, that's exactly what I'm implying. As for the basis for it -- I'm not sure how to put it. Every other interpretation is deeply confused, but MWI gives a deterministic, algorithmic, and non-mysterious explanation. MWI may or may not be correct, but an adherent definitely would not say they "don't understand" QM.

I thought the various competing interpretations of QM were all exactly equivalent when it came time to actually crank through the math in an algorithmic fashion.

Re: Physicists provide support for retrocausal quantum theory

#116

Post by Simon_says »

mikeash wrote: post #115
Simon_says wrote: post #112

Earlier quoted context omitted.

Yea, that's exactly what I'm implying. As for the basis for it -- I'm not sure how to put it. Every other interpretation is deeply confused, but MWI gives a deterministic, algorithmic, and non-mysterious explanation. MWI may or may not be correct, but an adherent definitely would not say they "don't understand" QM.

I thought the various competing interpretations of QM were all exactly equivalent when it came time to actually crank through the math in an algorithmic fashion.

Not exactly equivalent.

The Copenhagen Interpretation has a pretty big theoretical hole in that the condition for when a wavefunction collapse occurs is not defined within the theory itself. Supposedly collapse occurs during a "measurement". Well, what's a measurement? Your measuring apparatus are all made up of matter that supposed to be following the same fundamental physical laws. I think you'd be hard pressed to write a computer program that takes as input a description of all the particles and their wavefunctions and compute when a measurement occurs. In practice, scientists doing calculations under the Copenhagen Interpretation will choose the points in time to perform a collapse so that the calculations match experimental results. This is what I mean when I say that Copenhagen is non-algorithmic. That's a forgivable mistake if you invent your theory before the idea of an algorithm is formalized (as was CI), but today it's not a forgivable mistake.

If you decide to fix the problem with Copenhagen Interpretation by explicitly defining that a measurement is when X happens for some X, then you've allowed for an experiment whose results can differentiate between Copenhagen and Many Worlds. MWI says that different parts of the wave function can affect each other no matter how distant, though the effect size decreases exponentially with distance. So set up an experiment so that X occurs and then be able to measure interference from distant parts of the wavefunction that are either present (in MWI) or not present (in CI). That distinguishes the interpretations via experiment.

Re: Physicists provide support for retrocausal quantum theory

#117

Post by JadeNB »

gnaritas wrote: post #113
mikeash wrote: post #110

Earlier quoted context omitted.

What prompts this reply? I'm not saying that math is reality, merely that solid mathematical models have been the foundation of progress in science, not "explanations."

I just don't agree with what you're saying, progress comes from understanding reality via some intuition, understanding and intuition lead to the development of testable models. Testable mathematical models are the result of progress in science, not the foundation of it.

> Testable mathematical models are the result of progress in science, not the foundation of it.

I think that the information can flow either way. For example, the existence of anti-matter, and portions of quantum mechanics (and, let's say, much of Witten's scientific work—though here I am tossing out a bit of folk knowledge, and couldn't point to anything in particular), are examples of letting the math guide the physics.

Re: Physicists provide support for retrocausal quantum theory

#118

Post by JadeNB »

opportune wrote: post #36
JadeNB wrote: post #31

Earlier quoted context omitted.

> My favorite from David Deutsch, a main creator of the idea of quantum computing: It's interesting, but this "I challenge you to answer a philosophical (not scientific) question in a way that I find acceptable" approach surely skirts uncomfortably close to dogmatically creationist arguments. (For the record, my answer, which certainly wouldn't satisfy Deutsch, is: it works because the math proves it works; there's n…

I agree with you. I think the need for philosophical justification stems from our desire to reconcile quantum computing with our classical computing/physics models. But just because we desire such a thing doesn't mean there exists a reasonable one. What I think the truth really is, is that we don't encounter quantum superpositions in an obvious way in our day to day lives. So it's inherently "weird" for us, especiall…

> But that doesn't mean it's wrong, it just means that one of our evolved instincts isn't applicable on a quantum scale.

I think that this puts it very well. If a theory doesn't fit with our intuition, then it might mean that the theory is wrong; but it's at least plausible that our intuition is wrong, and goes from plausible to overwhelmingly likely once the theory is backed up by experimental data. (Anyone, even or especially a scientist, who dogmatically trusts his or her intuition over science probably could do with a quick refresher in cognitive biases.)

Re: Physicists provide support for retrocausal quantum theory

#119

Post by gnaritas »

JadeNB wrote: post #117
gnaritas wrote: post #113

Earlier quoted context omitted.

I just don't agree with what you're saying, progress comes from understanding reality via some intuition, understanding and intuition lead to the development of testable models. Testable mathematical models are the result of progress in science, not the foundation of it.

> Testable mathematical models are the result of progress in science, not the foundation of it. I think that the information can flow either way. For example, the existence of anti-matter, and portions of quantum mechanics (and, let's say, much of Witten's scientific work—though here I am tossing out a bit of folk knowledge, and couldn't point to anything in particular), are examples of letting the math guide the phy…

The math certainly points at places to look for physics, so yes I agree to a point, but the math itself didn't just happen, it came from a mathematician using his intuition and understanding of physics to explore possible ideas that might be true with most of the possible maths not leading to possible physics. Math is just a language to communicate ideas accurately, those ideas however came from someones intuition about what should be. The math it led to is a result of a process, not the creator of it, the model the math lays out could be right or could be wrong and as such simply points out possible places for experimental physicists to go searching. The math didn't come first, the intuition came first, the mathematical model second, and the physical proof last.

Re: Physicists provide support for retrocausal quantum theory

#120

Post by mikeash »

Simon_says wrote: post #116
mikeash wrote: post #115

Earlier quoted context omitted.

I thought the various competing interpretations of QM were all exactly equivalent when it came time to actually crank through the math in an algorithmic fashion.

Not exactly equivalent . The Copenhagen Interpretation has a pretty big theoretical hole in that the condition for when a wavefunction collapse occurs is not defined within the theory itself. Supposedly collapse occurs during a "measurement". Well, what's a measurement? Your measuring apparatus are all made up of matter that supposed to be following the same fundamental physical laws. I think you'd be hard pressed to…

Thanks. I must have gotten mixed up with the equivalence of some of these interpretations, and the lack of actual experiments to distinguish the others.
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