Einstein and "spooky actions"

[zaybu]

What about circumstances where theta is greater than 1?

Theta greater than 1 means you're dealing with an angle greater than 180 degrees. The shadow would be on the left instead of the right, and the equation would yield the same result.

At theta = 1, your hand is covering the light, hence no shadow to measure its velocity.

 

[PolyHedral]

Theta greater than 1 means you're dealing with an angle greater than 180 degrees. The shadow would be on the left instead of the right, and the equation would yield the same result.

At theta = 1, your hand is covering the light, hence no shadow to measure its velocity.

A theta greater than one corresponds to an angle greater than 60 or so degrees. (There are 2pi, not 2 radians in a circle.) Importantly, it means that S > L, which means your stated conclusion is wrong.

 

[Mr Spinkles]

Ok, I understand what you're saying now.

One worry I had was that I would be able to send a message to someone and he'd be able to relay the message to a third guy faster than I'd be able to, but the triangle inequality takes care of that.

A guy on the screen doesn't see the dot as moving faster than light even though we do. Going back to the light year sized spherical setup I mentioned earlier with the source moving pi/2 radians in five seconds. (and now I see why the dot moves across the screen in 5 seconds) It helped me to imagine that I have guys with their own laser pointers positioned on the screen at thetas {0, pi/10 , pi/5 , 3pi/10 , 2pi/5 , pi/2} If each guy shines his pointer at the guy at 0 once the initial dot hits his position, then the guy at 0 will get a signal from the 1st guy about a third of a year after he see's the original dot. Now if each guy sent a signal to every other guy as soon as he received the initial dot, they could use that information to conclude that the source sees the dot move faster than light.

Does that seem reasonable, or am I just rambling?

Yes that seems reasonable.

I prefer to say "the dot moved at this speed" in this frame, rather than "someone saw it move at this speed". To me it's simpler to talk about what actually happened in this frame, because the theory says everyone in this frame will agree if they are competent observers. Once we realize this, we needn't worry ourselves about the additional complexity of lots of observers coordinating lots of light signals .... we only need to consider one reference frame + the system of interest.

It's only when we want to consider what happens in a different frame (moving relative to the original) that we need Lorentz transforms.

 

[zaybu]

A theta greater than one corresponds to an angle greater than 60 or so degrees. (There are 2pi, not 2 radians in a circle.) Importantly, it means that S > L, which means your stated conclusion is wrong.

Ok, I see the confusion: it should read sin (theta/2) = 1, therefore theta = 180.

In the diagram, theta should read theta/2, and for small angle, sin(theta/2) ≈ theta/2. Here's the revised diagram

 

[Mr Spinkles]

In this case, you need QM only for the observation that the spins are either up or down. In classical physics, the spin of an object, be it planet earth or a top, can have any value. But at subatomic scale, it is quantized along a given axis. For that, you need QM to explain this result. But for the correlation of Alice's data and Bob's data, plain old fashion classical physics can explain that.

Emphasis added. Another contradiction. Even assuming quantization of spin, the correlations violate Bell's theorem which you called "classical logic", and you yourself said "quantum logic" was required to explain the strength of the correlations.

Doesn't it worry you that you constantly contradict yourself, and your sources? It's incredible that you still haven't admitted that you were incorrect to say the way I wrote down the singlet was "wrong", when it's right there in your Susskind lecture notes.

Anyway, when you say "classical physics" can explain the correlation are you referring to your conservation of angular momentum argument? You aren't saying that each particle "really" had a definite spin-up or down beforehand, just statistically described by QM, are you?

That physics is weird is perpetuated by people like you. Once you understand the mathemsatical framework of QM and GR, there's little mystery left, except how to quantize gravity or explain the hierarchy problem. But these are not weird, just problems we haven't figured out how to solve.

"Weird" is a subjective judgment. The mathematical formalism of QM however is not subjective, so that should be our focus. You were wise to carefully avoid this when I spelled it out in post #307:

I notice you still have not explained how one particle, by itself, can even be in a "singlet" state. Again it's just math. The singlet state is a sum of two-particle spin eigenstates, |up,down> + |down,up> (neglecting a factor for normalization). The possible results of Alice's measurement are the eigenkets of the appropriate operator applied to that state. Those eigenkets are, of course, |up,down>, and |down,up>, which we can simply read off from the state since we chose to write the singlet state as a sum of terms in the spin basis. Each of these eigenkets is just the (tensor) product of the single-particle spin eigenstates. For example, |up,down> = |up>|down>. That state means that particle 1 is in the |up> state AND particle 2 is in the |down> state. It means they are not entangled. It means neither particle is in the singlet state. |up>|down> is the state you write down if someone gives you particle 1 in state |up>, AND particle 2 is in state |down>, without any mention that they may have previously been in an entangled singlet state together.

So when Alice measures a singlet, the state that results from her measurement cannot be a single-particle spin eigenstate |up>, or |down>, according to the rules of QM. Those are NOT possibilities, since they are NOT eigenkets of the appropriate operator applied to the singlet. Instead, the only possibilities are the eigenkets |up>|down> or |down>|up>. In other words, BOTH particles must go to a spin-eigenstate, and NEITHER particle can remain in the singlet state after Alice's measurement. According to the rules of QM. It's just math.

If we assume that Alice knows before doing her measurement that the total spin is zero. What else could it be but zero?

I haven't a clue, that's why you were wrong in post #301 when you suggested we don't know the total spin of the singlet before Alice measures. Yet another contradiction for zaybu.

Assuming Alice knows the conservation of angular momementum, she will know that (2) is also zero.

Please show the calculation explicitly. After Alice measures, (2) = Total spin = spin of Alice's particle + spin of Bob's particle = ...? Spin of Alice's particle = up. Spin of Bob's particle = ... ? (Does Bob's particle have a definite spin? At one point you were saying Bob's particle remains in the singlet state! )

This is where you are muddling up the case. On a theoretical basis, the total spin is zero, and all parties know that, but until it is measured experimentally, we can't confirm it.

We can't confirm it until we measure it, yes. But we can know it's there before we measure it. And after we measure it, we can conclude it was there beforehand. That is the simplest assumption and in this case, QM demands it. (Normally QM says a measurement changes the state, but in the case of Bob's measurement QM says both particles were already in spin eigenstates, whether Bob measures or not.)

 

[zaybu]

Emphasis added. Another contradiction. Even assuming quantization of spin, the correlations violate Bell's theorem which you called "classical logic", and you yourself said "quantum logic" was required to explain the strength of the correlations.

Again you're putting words in my mouth I didn't say. The correlation in our scenario is one thing, and Bell's theorem is another. His inequality, which can be derived by Venn's diagram, was trying to prove whether there are hidden parameters or not. You are trying to prove that the wave function is real, and when it collapses, a spooky action at a distance makes sure the law angular momentum is conserved. So stop confusing your troubles with your speculative unfounded theory with Bell's theorem.

It's incredible that you still haven't admitted that you were incorrect to say the way I wrote down the singlet was "wrong", when it's right there in your Susskind lecture notes.

Susskind has a different purpose in mind. His was to show that a quantum system will violate Bell's theorem on theoretical grounds, never mind on experimental grounds. In no way this prove your twisted theory of spooky action.

Anyway, when you say "classical physics" can explain the correlation are you referring to your conservation of angular momentum argument?

Oh wow, you've got that one right.

You aren't saying that each particle "really" had a definite spin-up or down beforehand, just statistically described by QM, are you?

I don't know where you got that. It seems you are grasping at straws. If we knew that the spin was in a definite state beforehand, we wouldn't need QM, which is a theory of probability.

I haven't a clue, that's why you were wrong in post #301 when you suggested we don't know the total spin of the singlet before Alice measures. Yet another contradiction for zaybu.

There's no contradiction, but more of your misunderstanding that is at play. In the first scenario, it hadn't been spelled out clearly if Alice knew that Bob was going to measure an entangled state. So for a while I was asking you from which POV your questions were assuming. That is why I came up with the second scenario so that it would be very clear that she didn't know.

Normally QM says a measurement changes the state

Again, this shows you are still hung up on the "wave collapse" misconception. All we can say is before making the measurement, we don't know in what state it is, that's why we write as a linear combination of ↑↓. After measurement, it will be either this ↑ or that ↓. What it was in the real world beforehand, we don't know. The state vector does not represent a real thing in itself. Just the probabilities.

 

[PolyHedral]

What it was in the real world beforehand, we don't know.

What it is in the real world is up-down. To say otherwise implies hidden variables, which are verboten.

 

[idav]

We can't confirm it until we measure it, yes. But we can know it's there before we measure it. And after we measure it, we can conclude it was there beforehand. That is the simplest assumption and in this case, QM demands it. (Normally QM says a measurement changes the state, but in the case of Bob's measurement QM says both particles were already in spin eigenstates, whether Bob measures or not.)

What we can't conclude is whether the first particle changed the state of the second. Over and over they will correspond one up one down and vice versa. It will always come out as QM states but QM hasn't shown how. It is easier to conclude that both Alice and Bobs particles were at the spin they end up measuring otherwise you have to say that Alices particle collapsing caused Bobs to collapse as well which points to spooky action. When Alice particle collapses there is no way to tell if Bobs had collapsed as well, at least not in the way they did the measurement.

 

[zaybu]

What it is in the real world is up-down. To say otherwise implies hidden variables, which are verboten.

It's your interpretation, which comes closer to Sprinkles than mine. Yours is saying that the particle "exists" as up and down simultaneously. I'm saying the state vector doesn't represent the existence of anything but mathematical probabilities.

 

[PolyHedral]

It's your interpretation, which comes closer to Sprinkles than mine. Yours is saying that the particle "exists" as up and down simultaneously. I'm saying the state vector doesn't represent the existence of anything but mathematical probabilities.

So what do you think is "real?" Is the particle "really" up or down, even though the state vector says otherwise?

 

[zaybu]

So what do you think is "real?" Is the particle "really" up or down, even though the state vector says otherwise?

We don't have that knowledge before measurement. We only know that once the spin is measured, it is quantized in a given direction. And remember that the spin has three components. So even after measurement, we only know one of three components, we still don't know the other two.

 

[PolyHedral]

We don't have that knowledge before measurement. We only know that once the spin is measured, it is quantized in a given direction. And remember that the spin has three components. So even after measurement, we only know one of three components, we still don't know the other two.

You didn't answer the question. In an ontological sense, is a particle "really" definitely spinning either up or down even when the state vector says its both?

 

[zaybu]

You didn't answer the question. In an ontological sense, is a particle "really" definitely spinning either up or down even when the state vector says its both?

Can't we even say that it's a particle because it also behaves as a wave in different circumstances? Is it a particle or a wave? What we can safely say is: in one set of circumstances, it behaves like a particle; in a different set of circumstances, it behaves like a wave. The state vector is a mathematical tool that avoids this dilemma as it is written to take care of what we can measure. It contains the probabilities that are possible. But only a measurement will confirm its state. But it doesn't answer the question of "Is it a particle or a wave?" as there is nothing in the classical world in which we live that corresponds exactly like to what is happening at the subatomic scale.

 

[idav]

You didn't answer the question. In an ontological sense, is a particle "really" definitely spinning either up or down even when the state vector says its both?

IMO yes. That's what the results of the double slit imply to me, the particle pretends to be a wave even so it is a particle. The same with the two states. It may act as if it is in two states but it is not in reality. Just my opinion I'd love this verified of course.

 

[Mr Spinkles]

What it is in the real world is up-down. To say otherwise implies hidden variables ...

Exactly right (according to quantum mechanics, that is). Frubals.

 

[PolyHedral]

Exactly right (according to quantum mechanics, that is). Frubals.

Non-local hidden variables are technically permitted, but those are spooky action at a distance, so aren't really helpful.

 

[idav]

Non-local hidden variables are technically permitted, but those are spooky action at a distance, so aren't really helpful.

Seems odd that the claim is that the particle is in two states at once yet is only in one state when observed. QM hasn't even told us how a particle can be in literally two places at once as the math eludes to. Great for calculating probablity, as if a whole wave is going through instead of a single particle. Not useful in actually saying what the particle is doing.

There are other interpretations.
https://hekla.ipgp.fr/IMG/pdf/Couder-Fort_PRL_2006.pdf

 

[PolyHedral]

Seems odd that the claim is that the particle is in two states at once yet is only in one state when observed. QM hasn't even told us how a particle can be in literally two places at once as the math eludes to. Great for calculating probablity, as if a whole wave is going through instead of a single particle. Not useful in actually saying what the particle is doing.

Why not just take the equation at face value? Say that the object you're dealing with actually is this complex-valued self-interacting field that you get entangled with, and voila, no ontology issue.

 

[idav]

Why not just take the equation at face value? Say that the object you're dealing with actually is this complex-valued self-interacting field that you get entangled with, and voila, no ontology issue.

Are you trying to spook me, cause it's working.

 

[zaybu]

Why not just take the equation at face value? Say that the object you're dealing with actually is this complex-valued self-interacting field that you get entangled with, and voila, no ontology issue.

That was the initial programme behind classical physics. But the universe is not cooperating at subatomic level. QM is a theory of probability. And that's why Einstein didn't like it with his "God doesn't play dice with the universe". Tough luck.