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The Trouble with Quantum Mechanics

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Re: The Trouble with Quantum Mechanics

#61

Post by posterboy »

vorg wrote: post #47
krastanov wrote: post #25

Earlier quoted context omitted.

The entanglement does not break. The entire black hole becomes entangled with the electron left outside (which is less exciting than it sounds). Sure, plenty of thing break if we start talking about unknowns, like the black hole evaporation for instance, but today's physics has a pretty good idea what happens if we just drop one of the electrons in the black hole and measure the other one. We just learn the spin of b…

> if one entangled electron flies into a black hole then we would be able to know its spin by measuring the other one even if light from it won't reach us All the arguments here mention what happens under SR but wouldn't GR be more appropriate? If an electron flies into a black hole, from the frame of reference of the observer doesn't it appear to get closer and closer to the black hole event horizon over time, but n…

Thanks, I wanted to add that, too, but wasn't sure about it. I still am not, because this opens another can of worms. Can a black hole then not grow if from our POV nothing ever enters?

Re: The Trouble with Quantum Mechanics

#62

Post by lisivka »

krastanov wrote: post #32
lisivka wrote: post #30

Earlier quoted context omitted.

Nobody tells that walkers are simulate all quantum behavior and doing that correctly. However, they helps to understand some of quantum puzzles. For example, droplets have spin. Can you predict behavior of the classical droplet spin in compare to the puzzling quantum spin?

But you can do the same with classical setups that mimic some effects from the typical quantum mechanical formulations. Those classical experiments are indeed amusing and interesting, but they do not illuminate the "quantum puzzles", no matter whether they are modeled after pilot wave theory or after quantum mechanics. And very importantly, those amusing demonstrations do not scale! Sure, you can mimic with classical…

So, your prediction for walker droplet spin is that walkers, in kind of Stern and Gerlach experiment, will behave like classical magnets, not like quantum particles, right?

Re: The Trouble with Quantum Mechanics

#63

Post by lisivka »

kkylin wrote: post #23
goatlover wrote: post #13

Earlier quoted context omitted.

There is the silicone oil droplet phenomena which is a classical version of the pilot wave, and it does reproduce some quantum behavior, including the double slit. That a pilot wave has been discovered (granted at macro scale) does make one reconsider. https://youtu.be/WIyTZDHuarQ

As far as I know there is no analog of entanglement in these experiments. If someone has heard or read something in that regard, I'd be interested in a reference!

Nobody even tried to entangle two walkers. AFAIK, uncharged non-magnetic particle without any inclusions (e.g. bubbles) has spin and phase of vibration only. How to entangle them?

Moreover, spin is 3d, walker is 2d, phase is 1d, while our Universe is 3d. It's like studying of 2d/1d projection of 3d world.

Re: The Trouble with Quantum Mechanics

#64

Post by iheartmemcache »

lisper wrote: post #59

This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement. The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recove…

Well the Copenhagen interpretation traditionally requires the act of an 'observer'. I.e., you are not allowed to perform that act of summation on the set of orthonormal vectors in N dimensional Hilbert spaces until an "observer" observes. (That's where that stupid cat came into play and the 'uncertainty' of it being both dead and alive simultaneously until it's 'observed'.) Until this discrete event occurs, the wave function doesn't "collapse" and we're just living in statistical la-la land.

The disagreement lies in "I can mathematically apply the trace function, I'm just not quite sure when".

Alternatively, according to the Everett interpretation (to which I subscribe, and to which you seem to as well) quite a few reputed physicists do believe that the universe "splits" (though not in an actual literal sense, there's nothing ripping the universe physically in two) every time an "observation" occurs and there are lots and lots of occurring simultaneously taken from various frames of reference. This actually makes a lot of sense. Let Sean Carroll https://youtu.be/ZacggH9wB7Y convince (the plural) you.

Re: The Trouble with Quantum Mechanics

#65

Post by n4r9 »

lisper wrote: post #59

This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement. The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recove…

> The measurement problem is a solved problem.

I think this is overselling it slightly. Yes, Everettian style interpretations have helped to shed insight into the reality of the quantum state. Yes, decoherence has helped us to understand physical systems and their interactions with the environment. But if the measurement problem was solved there wouldn't continue to be a swathe of literature on the measurement problem by respected quantum theorists. There are some very good reasons for doubting the validity of many world interpretations. We don't have much of a consensus on what's "really" going on, and I don't believe we will for quite some time.

Re: The Trouble with Quantum Mechanics

#66

Post by opaque »

lisper wrote: post #59

This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement. The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recove…

Decoherence is an extremely useful and elegant mechanism for understanding quantum systems, but unfortunately it doesn't solve the measurement problem. At least not to the satisfaction of most practising physicists. The entanglement and trace operation does produce classical probabilities in the observed sub-system. However, it requires you to make a pretty arbitrary division between the observed system and the wider environment. Why is everything not just entangled with everything else up and up the chain until the entire universe is in superposition? The problem of where the quantum world ends and the classical world begins is still unanswered. This is one of the greatest open questions in physics, likely requiring a unification of general relativity and quantum mechanics before it's resolved.

Re: The Trouble with Quantum Mechanics

#67

Post by lisivka »

krastanov wrote: post #33
ebcode wrote: post #31

Earlier quoted context omitted.

How so? Why should faster-than-light travel imply a reversal of the arrow of time? Can you explain the reasoning?

This wiki page [1] explains why whether two events happen at the same time depends on your reference frame. If you can send signals faster than light then you can send a signal to an even far away and cancel that event. In another reference frame the sending of the signal would have happened after the far-way event has already happened. Hence, due to the "relativity of simultaneity" FTL communication is equivalent to…

By sending a message in two opposite directions, we can achieve 2c speed of information transfer. How that is possible?

Re: The Trouble with Quantum Mechanics

#68

Post by lisivka »

gizmo686 wrote: post #35
ebcode wrote: post #31

Earlier quoted context omitted.

How so? Why should faster-than-light travel imply a reversal of the arrow of time? Can you explain the reasoning?

The idea behind relativity is that the speed of light is constant in all reference frames. [0]. In order for this to work, we "warp" spacetime depending on the velocity of the observer. More concretely, imagine Alice and Bob are moving away from each other at 50% the speed of light. They both observe event some event, X, occur and note the location in space-time. If Alice observes that X occurs in the location (t,x,y…

> From the perspective of Bob, Carol would have traveled backwards, going from Y to X.

So what? It's Bobs problem.

FTL electrons, in medium where speed of light is much less than c, are traveling exactly as you described.

Re: The Trouble with Quantum Mechanics

#69

Post by EGreg »

posterboy wrote: post #61
vorg wrote: post #47

Earlier quoted context omitted.

> if one entangled electron flies into a black hole then we would be able to know its spin by measuring the other one even if light from it won't reach us All the arguments here mention what happens under SR but wouldn't GR be more appropriate? If an electron flies into a black hole, from the frame of reference of the observer doesn't it appear to get closer and closer to the black hole event horizon over time, but n…

Thanks, I wanted to add that, too, but wasn't sure about it. I still am not, because this opens another can of worms. Can a black hole then not grow if from our POV nothing ever enters?

I thought that from the POV of the object falling into the black hole, time stretches.

From our point of view it can very well be sucked in.

Re: The Trouble with Quantum Mechanics

#70

Post by beevai142 »

opaque wrote: post #66
lisper wrote: post #59

This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement. The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recove…

Decoherence is an extremely useful and elegant mechanism for understanding quantum systems, but unfortunately it doesn't solve the measurement problem. At least not to the satisfaction of most practising physicists. The entanglement and trace operation does produce classical probabilities in the observed sub-system. However, it requires you to make a pretty arbitrary division between the observed system and the wider…

This is correct. As it is usually applied in practice in the literature, the measurement device decoheres the quantum system and becomes entangled with it --- and at the end of the calculation, Copenhagen interpretation is applied on the measurement device. It works fine in practice, but in the end it is philosophically just the Copenhagen interpretation.

If something is not accepted by the wider physics community, it's very likely the correctness of the thing in question is not that clear.

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