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Physicists provide support for retrocausal quantum theory

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Re: Physicists provide support for retrocausal quantum theory

#71

Post by eximius »

ridewinter wrote: post #33
mikeash wrote: post #24

Earlier quoted context omitted.

That seems to be begging the question. Qubits do more than this universe is capable of, therefore there must be multiple universes. The obvious refutation is: qubits don't do more than this universe is capable of, because the universe does not run on classical limits. 10^80 atoms implying on the order of 10^80 computations that can be done implicitly assumes that these things operate on classical-ish rules. There's a…

Explain the double slit experiment to me. The single photon somehow calculates the interference pattern with photons that don't exist, in our world at least. If there's not parallel universes, how does a single atom calculate that interference pattern? Where do those calculations occur? All other theories say it happens by magic and give all sorts of complicated non-real obfuscations to explain it.

What? So in other universes the interference pattern is wrong?

A photon isn't a computer. It doesn't compute. It acts according to some nature which we equate with computation.

Re: Physicists provide support for retrocausal quantum theory

#72

Post by mabbo »

ridewinter wrote: post #50
TheOtherHobbes wrote: post #46

Earlier quoted context omitted.

There are no photons. There are only photon-like events, with associated probabilities and scattering processes. It's a lot easier to assume that reality is the visible output of an heroically counter-intuitive but relatively tractable probabilistic calculation process, than it is to assume there are infinite universes with poorly defined boundary conditions between them and even more poorly defined properties, and t…

That's exactly what I'm saying! All other explanations say something confusing and obfuscating like "there are no photons". Many-worlds keeps it simple and says "there are photons, and the reason they behave like that is because they're interacting with parallel universes". You can't explain why they behave like that, so you say that the photon isn't really real, and have a complicated explanation of it.

> All other explanations say something confusing

The problem here is that you want an explanation that is intuitive and easy for you to grasp. What if the true answer is one that is too hard for you (or maybe any human) to easily understand?

Our brains aren't evolved for understanding the true nature of the universe, they're evolved for reproducing and surviving in a very simple world. We're using re-purposed hardware for a very different task- we shouldn't be surprised that it's difficult.

Re: Physicists provide support for retrocausal quantum theory

#73

Post by [deleted] »

ridewinter wrote: post #15

The many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain quantum effects. It's so rare to find clear explanations, but they do exist. My favorite from David Deutsch, a main creator of the idea of quantum computing: To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s al…

[deleted]

Re: Physicists provide support for retrocausal quantum theory

#74

Post by euyyn »

ridewinter wrote: post #51
mikeash wrote: post #47

Earlier quoted context omitted.

The atom is a wave, which can interfere with itself.

I think Deutsch would say there isn't actually a wave-particle duality. That's just an obfuscation that doesn't have any reality to it. Many-worlds has a much simpler explanation - there is simply a particle that interacts with particles in parallel universes that produce a wave-like interference effect.

I think you can just dispose of the concept of particle and everything works fine as waves (with discrete levels where the boundary conditions force so, and with collapse when coupled to a macroscopic system that restricts the possible states).

Re: Physicists provide support for retrocausal quantum theory

#75

Post by [deleted] »

petters wrote: post #19
woliveirajr wrote: post #11

> First, to clarify (...) It does not mean that signals can be communicated from the future to the past(...) instead, retrocausality means (... it) can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past. So, hard to explain in layman words: future can't transmit…

That explanation still seems to allow faster than light communication.

[deleted]

Re: Physicists provide support for retrocausal quantum theory

#76

Post by euyyn »

miltondts wrote: post #34
Lxr wrote: post #18

I never fully understood the Bell experiments. How exactly do they discount hidden variables?

They don't here is what Bell said: "There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experi…

Ok, and barred that?

Re: Physicists provide support for retrocausal quantum theory

#77

Post by jostylr »

BoiledCabbage wrote: post #70
ridewinter wrote: post #50

Earlier quoted context omitted.

That's exactly what I'm saying! All other explanations say something confusing and obfuscating like "there are no photons". Many-worlds keeps it simple and says "there are photons, and the reason they behave like that is because they're interacting with parallel universes". You can't explain why they behave like that, so you say that the photon isn't really real, and have a complicated explanation of it.

Clearly this is all subjective, but Pilot Wave theory (De Broglie & Bohm) is the simplest least "crazy" of all the explanations. Horribly simplified: Space isn't empty, there is an "ether". Matter moving through the ether interacts with it and produces waves just like a very light boat in a lake - these crests and troughs exactly line up with the magical waveform. All of the quantum behavior we see is explained by th…

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, including MW. The novel part of PWT, that of particles having definite locations at all times being guided by the wave, is quite ordinary.

Re: Physicists provide support for retrocausal quantum theory

#78

Post by alasdair_ »

rf15 wrote: post #35
mirekrusin wrote: post #13

// WARN: because past is static, to support retrocausal influence, we're spawning alternative universes which are joined on retrocausal action choice - this slows down The Simulation and, if abused, can exhaust resources and crash.

don't remind me that people actually believe that you can infer the existence of a simulation only with data points that are created and controlled by it.

There doesn't seem to be anything wrong with this basic idea. As a (bad) analogy, think about how computer code can be written to detect whether or not it is running inside a virtual machine or on a "real" device. It's usually almost impossible to tell but by probing at the extremes and forcing the system to do things that never happen under common usage, it's possible. (It's also possible to break out of the system entirely and gain access to the host OS sometimes, but perhaps that's taking things too far :)

Re: Physicists provide support for retrocausal quantum theory

#79

Post by graycat »

ridewinter wrote: post #33
mikeash wrote: post #24

Earlier quoted context omitted.

That seems to be begging the question. Qubits do more than this universe is capable of, therefore there must be multiple universes. The obvious refutation is: qubits don't do more than this universe is capable of, because the universe does not run on classical limits. 10^80 atoms implying on the order of 10^80 computations that can be done implicitly assumes that these things operate on classical-ish rules. There's a…

Explain the double slit experiment to me. The single photon somehow calculates the interference pattern with photons that don't exist, in our world at least. If there's not parallel universes, how does a single atom calculate that interference pattern? Where do those calculations occur? All other theories say it happens by magic and give all sorts of complicated non-real obfuscations to explain it.

Double slit experiment? It appears that some people, e.g., Feynman, believe that this experiment is profound. I don't have an explanation as good as I would like, but from what I studied in physics class, reading Feynman, etc. here's my explanation.

So, shoot a photon, or an electron, neutron, proton, alpha particle, etc., at the double slit barrier. Only one particle, please.

Well, now give up on the idea that we shot a particle. F'get about particles because they don't exist and only seem to exist from some interactions. Instead of a particle, what we shoot at the target is a wave or, in quantum mechanics, a wave function.

So, the wave function hits the barrier. Nearly all that wave function hits the barrier and disappears. Why? Because physics can't think of anything else it could do. So, what is left are the two parts of the wave function that pass through the two slits. Now that one wave function is in two pieces, but no energy has been lost bumping into the barrier and squeezing through the double slits (amazing thing a wave function) -- but maybe with some barriers some of the wave function is reflected, but let's leave that to the next semester!

The two pieces of the wave function that went through the slits continue on to our array of detectors. As wave functions tend to do, especially as they pass through a small hole or slit, they spread out. By the time the two parts of the wave function hit the detectors, they overlap. But, they are just two parts of the same wave function. So, they interfere and create a sine wave pattern at the detectors. Well one of the detectors, at random, gets a detection of the particle.

So, lesson: What travels is a wave, not a point like particle. The wave can be split into two parts and come back together, and then it interferes with itself in a way different from having waves from two independent (I hope the physics people do say independent instead of uncorrelated) particles hitting the detectors. When the wave is detected the detection is at a point as if there were a particle. Moreover, there is no more than one detection, as if there were a particle.

Still, there are no particles; it's just that when a wave function interacts, say, at a detector, it interacts at a point, just some one point, as if it were a point particle. Amazing.

Amazing experiment.

Generalize the experiment some and get the Michelson-Morley experiment, even more amazing.

Re: Physicists provide support for retrocausal quantum theory

#80

Post by AnimalMuppet »

ridewinter wrote: post #50
TheOtherHobbes wrote: post #46

Earlier quoted context omitted.

There are no photons. There are only photon-like events, with associated probabilities and scattering processes. It's a lot easier to assume that reality is the visible output of an heroically counter-intuitive but relatively tractable probabilistic calculation process, than it is to assume there are infinite universes with poorly defined boundary conditions between them and even more poorly defined properties, and t…

That's exactly what I'm saying! All other explanations say something confusing and obfuscating like "there are no photons". Many-worlds keeps it simple and says "there are photons, and the reason they behave like that is because they're interacting with parallel universes". You can't explain why they behave like that, so you say that the photon isn't really real, and have a complicated explanation of it.

> All other explanations say something confusing and obfuscating like "there are no photons". Many-worlds keeps it simple and says "there are photons

OK so far...

> and the reason they behave like that is because they're interacting with parallel universes.

No longer OK. You consider that the simple explanation? You don't think that's obfuscating at least as much as "there are no photons" does?

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