Einstein and "spooky actions"

[Mr Spinkles]

If Bob makes no measurement, his particle stays in a singlet state.

However, within my explanation: there are no singlet states ...

:biglaugh: :clap
Incredible. Seeing your route blocked at every turn, you've decided to retrace your steps and declare the thing we were talking about never existed to begin with! Someone call the Nobel committee and the publishers of all our textbooks, a guy on the internet says physics is wrong. Bravo for having the courage to retreat in the face of certain humiliation.

Look, if you are going to abandon your current argument and try out a new one, at least be honest about it. Don't just throw different arguments at the wall to see what sticks. Your own sources, namely the Susskind lecture notes you posted in support of your argument, contradict you: "the singlet state [is] the simplest quantum system that exhibits entanglement". What an odd thing to say about something that does not exist ...

 

[Mr Spinkles]

The interpretation of the experiment results are the question. My position fits what the link describes as the realist position. That the particle was always at C and qm couldnt determine it until measurement.

Okay. But if that is your interpretation, you still have to accept nonlocality (and I believe on this point even zaybu agrees).

 

[idav]

Okay. But if that is your interpretation, you still have to accept nonlocality (and I believe on this point even zaybu agrees).

Not really when qm is only making it seem as if an particle is on two places at once while it isnt in reality. Both a particle and a wave, a particle that acts as a wave but really is still a particle at one single point.

 

[Mr Spinkles]

Not really when qm is only making it seem as if an particle is on two places at once while it isnt in reality. Both a particle and a wave, a particle that acts as a wave but really is still a particle at one single point.

Read the link. All of it. Carefully.

 

[zaybu]

Incredible. Seeing your route blocked at every turn, you've decided to retrace your steps and declare the thing we were talking about never existed to begin with! Someone call the Nobel committee and the publishers of all our textbooks, a guy on the internet says physics is wrong. Bravo for having the courage to retreat in the face of certain humiliation.

The concept of a singlet is part of a theory, it's not a fact. I hope you understand the difference. Now if a concept is redundant in explaining a fact, then why use it ? I understand why you want to use the concept of a singlet in your explanation in order for you to fill in with your spooky action at a distance. But like I said before, it's superfluous.

Your own sources, namely the Susskind lecture notes you posted in support of your argument, contradict you: "the singlet state [is] the simplest quantum system that exhibits entanglement". What an odd thing to say about something that does not exist ...

What Sussking is saying is true within a theory. But in the cases we have discussed, it is only necessary within your explanation, but one has to consider all the trappings it brings - an unnecessary singlet with spooky action at a distance to prop up the whole argument. OTOH, one can explain the data without those trappings.

 

[zaybu]

Not really when qm is only making it seem as if an particle is on two places at once while it isnt in reality. Both a particle and a wave, a particle that acts as a wave but really is still a particle at one single point.

Right, the double-slit experiment with one particle at a time clearly indicates that the wavefunction in QM gives a statistical distribution of the particles. Basically, waves are just made of particles. A whole lot of them makes a wave. There's no weirdness, and certainly, no spooky action at a distance.

 

[PolyHedral]

You mean, depending on the relative speed of your reference frame, right? Everyone in Alice and Bob's inertial frame agrees (or can be made to agree) on what happened, no matter where they are standing.

Yes, but I also haven't done the maths in enough detail to exclude someone standing closer to Bob than Alice and co-moving with them.

To be precise, Bob's observable universe is not confined to his past light cone. He can observe the emission of a photon traveling at light speed, for example, even if the emission occurred outside his past light cone, but not at the present moment--in Bob's future, he can observe it.

IOW, once the emission event has entered his past lightcone. That's the definition of the lightcone.

Additionally, superluminal propagation (a shadow, for example, or the propagation of the max height of a wave) can be observed by Bob at the present moment, even if it started outside his past light cone, as long as the propagation does not carry information, energy, etc. from one place to another faster than light.

I'm interested in knowing how Bob can percieve the shadow of an event that's happened outside his lightcone.

Relativity simply says that causal events cannot occur outside Bob's past light cone.

Fudge! Kludge! Inelegance! Relativistic classical mechanics says nothing propogates faster than light, it's only when we try to throw this entanglement thing in that we have to make the distinction.

However, the effect of Alice's measurement on Bob's particle is statistical, not causal. Alice's measurement can indeed change Bob's particle from the singlet to a spin eigenstate...

Sounds like either causality or hidden variables to me.

Furthermore, since BOTH particles go from the singlet state to a spin eigenstate at the exact moment Alice measures, no spin angular momentum is carried from Alice to Bob faster-than-light.

What exact moment? Who says?

 

[PolyHedral]

Right, the double-slit experiment with one particle at a time clearly indicates that the wavefunction in QM gives a statistical distribution of the particles. Basically, waves are just made of particles. A whole lot of them makes a wave. There's no weirdness, and certainly, no spooky action at a distance.

So explain how this experiemnt works.

 

[idav]

Right, the double-slit experiment with one particle at a time clearly indicates that the wavefunction in QM gives a statistical distribution of the particles. Basically, waves are just made of particles. A whole lot of them makes a wave. There's no weirdness, and certainly, no spooky action at a distance.

Thats one of the issues though. The particle acts as a wave even when sent one particle at a time. Not that its in two places at once but the interference pattern indicates a particle interfering with itself.

 

[zaybu]

So explain how this experiemnt works.

This is the explanation given for one of the experiment:

Following the analysis given above, we see that in Fig. 4a and b, 100% of the output impinges upon detector B. This is true even if the light intensity is reduced so that only one photon at a time travels through the apparatus. The explanation for this is the same as for the double-slit experiment: it appears as if the wave function of each individual photon travels both paths and engages in interference at the last beam splitter, so that only the wave to B is constructive. In Fig. 4a, although the photon is illustrated as having taken the "northern" branch of the interferometer, it interferes with itself so that only detector B detects the photon. The same holds for Fig. 4b, although the photon is considered to have taken the "southern" branch of the interferometer.
Fig. 4c illustrates the situation where an obstacle has been introduced on the "southern" branch of the interferometer. 50% of the photons are deflected by mirror M, and the remaining photons are split 25% to detector A, and 25% to detector B.
Fig. 4d illustrates the fundamental paradox raised by this demonstration. An individual photon arriving at detector A must have traversed the "northern" path and could not have interacted with mirror M. The arrival of a photon at detector A constitutes proof that an obstacle exists on the "southern" path, but there is no exchange of energy between the photon and obstacle M. How could the photon possibly have acquired information about M without an exchange of energy? This is an example of counterfactual measurement in quantum physics.

What I take from this is that they are sending light, not one photon at a time. So in that case, you need to describe what's happening in terms of waves, not photons, which unfortunately they do. So you get a paradox. In the double-slit experminent in which one photon is sent at a time, you get grainy points hitting the screen, and only after a certain time, when thousands and thousands of photons have hit the screen do you see the bright and dark fringes that we customarily see when light ( read, gazillions of photons) shines through the double-slit. So unless they do this experiment with sending one photon at a time, the paradox will remain. I hope one day they do it.

 

[PolyHedral]

This is the explanation given for one of the experiment:



What I take from this is that they are sending light, not one photon at a time. So in that case, you need to describe what's happening in terms of waves, not photons, which unfortunately they do. So you get a paradox. In the double-slit experminent in which one photon is sent at a time, you get grainy points hitting the screen, and only after a certain time, when thousands and thousands of photons have hit the screen do you see the bright and dark fringes that we customarily see when light ( read, gazillions of photons) shines through the double-slit. So unless they do this experiment with sending one photon at a time, the paradox will remain. I hope one day they do it.

You are misreading. They send one photon at a time, and find that it interferes with itself.

 

[zaybu]

Thats one of the issues though. The particle acts as a wave even when sent one particle at a time. Not that its in two places at once but the interference pattern indicates a particle interfering with itself.

Only after thousands and thousands of photons have hit the screen do we see the classical bright and dark fringes. We can't conclude that the particle has interfered with itself.

 

[zaybu]

You are misreading. They send one photon at a time, and find that it interferes with itself.

I don't find in the text where this is said. Can you? Never mind I found it.

 

[PolyHedral]

Only after thousands and thousands of photons have hit the screen do we see the classical bright and dark fringes. We can't conclude that the particle has interfered with itself.

If the photons were billiard balls, we'd expect to see exactly two bars of light, exactly behind the slits. We do not. Since only one photon is in the apparatus at any given time, what can it be interfering with to produce the wave pattern, if not itself?

Remember, you can't label photons. You will get the exact same results from sending 2000 photon through the apparatus as you would if you built 2000 copies of the apparatus and sent one photon through each. Since that's the case, how would we get a wave pattern when we aggregated the apparatuses together?

I don't find in the text where this is said. Can you? Never mind I found it.

I understood "This is true even if the light intensity is reduced so that only one photon at a time travels through the apparatus." to mean that when the experiment is performed with individual photons, the results are as though the photon interfered with itself.

 

[zaybu]

I understood "This is true even if the light intensity is reduced so that only one photon at a time travels through the apparatus." to mean that when the experiment is performed with individual photons, the results are as though the photon interfered with itself.

Yes, I found it, that's why I wrote "never mind" after my hasty response.

The 50% arriving at C is easy to explain. When there is no obstacle, 50% of photons go by the northern branch, 50% by the southern branch. So if an obstacle (mirror) is placed in the southern branch, they will end up at C, hence the 50%.

The numbers at A and B are more difficult to find an explanation. And right now, I don't have one. I will need to think about this. And it's late. So I'll get some sleep, and come back tomorrow.

 

[zaybu]

I understood "This is true even if the light intensity is reduced so that only one photon at a time travels through the apparatus." to mean that when the experiment is performed with individual photons, the results are as though the photon interfered with itself.

Yes, I found it, that's why I wrote "never mind" after my hasty response.

The 50% arriving at C is easy to explain. When there is no obstacle, 50% of photons go by the northern branch, 50% by the southern branch. So if an obstacle (mirror) is placed in the southern branch, they will end up at C, hence the 50%.

The numbers at A and B are more difficult to find an explanation. And right now, I don't have one. I will need to think about this. And it's late. So I'll get some sleep, and come back tomorrow.

Ok. The numbers at detectors A and B in fig4c can be explained. The northern branch photons go through the beam-spitter (bottom right-hand corner), and so half of them go to A, the other half to B.

1/2 x 50% = 25%

NOTE: the question at bottom of fig 4, "How does one single photon observed at A know about the existence of an obstacle at M?" is the wrong question to ask. Fig 4c can be explained as I did above.

What is the real troublesome, and still unexplanable to me are the numbers in fig4a (or fig4b), which read as: 0% in detector A, and 100% in detector B.

Now the explanation given: "it appears as if the wave function of each individual photon travels both paths and engages in interference at the last beam splitter, so that only the wave to B is constructive."

This does not explain the data. Even if the photons would interfer constructively with itself at the beam-splitter(bottom right-hand corner), after that, each wave should continue along their path, and 50% should go to A, 50% to B. But we don't get that, instead we get 100% at B, none at A. That would mean the wave coming from the southern branch moving from left to right, goes 100% (of 50%)through the beam-splitter(bottom right-hand corner), IOW, doesn't split and continues to B (depicted in fig 4b), while the northern branch, which is now moving downward after reflection with the mirror(top right-hand corner), but now makes an extraordinary 90 degree turn at the beam-splitter (bottom right-hand corner), without splitting to move 100% ( of 50%) from left to right to reach B (depicted in fig 4a)!!!

So this experiment does not in anyway prove that a single photon interfers with itself. Nevertheless it is still a mystery why 100% go to B, and none to A:

(1) Why there is no splitting at the beam-splitter(lower right-hand corner) for both branches,
(2) why the northern branch, going from up to down, makes a 90 degree turn to go to the right (fig4a), and the southern branch goes straight through( fig4b).

So whether we take either the wave picture or the particle picture of the photon, we should get 50% at A , 50% at B. The result 100% at B, and none to A is definitely weird. However it does show that our classical classification of matter into two bins - one for particles, the other for waves - doesn't work at sub-atomic scale. Both picture fails to account for the data. And it doesn't prove spooky action at a distance, either.


https://en.wikipedia.org/wiki/Mach–Zehnder_interferometer#Counterfactual_measurement

 

[Reptillian]

Interesting conversation still going on. Quantum Mechanics 101, the individual photons in the double slit experiment behave like particles when interacting with the screen, but behave like waves when they pass through the slits...unless you close one slit to find out which one they traveled through, or put detectors at the slits to find out which one it passed through before heading on to the screen...then all of a sudden they change their behavior to travel like particles. What's that photon doing when we're not measuring it? Nature doesn't seem to want you to know. Either that or there is some sort of a problem with our classical ideas like wave or particle...these may just be "big scale" ideas that our monkey brains create to help us make sense of our world.

I'm interested in knowing how Bob can percieve the shadow of an event that's happened outside his lightcone.

Let's imagine that you're on the inside of a gigantic Dyson Sphere (DS) and that the star in the center rotates. Let's that we've set up light detectors in a grid all over the surface of the DS (to measure the solar power per unit area or something) Now imagine that a big old sunspot occurs on the surface of the star...detectors in the shadow of the sunspot on our DS will measure less power per unit area. As the star rotates, the detected shadow will move across our DS. If the DS is big enough and the star rotates fast enough, then it's possible for the shadow to move faster than the speed of light across the surface of our DS with nothing causal really travelling faster than light.

 

[PolyHedral]

Let's imagine that you're on the inside of a gigantic Dyson Sphere (DS) and that the star in the center rotates. Let's that we've set up light detectors in a grid all over the surface of the DS (to measure the solar power per unit area or something) Now imagine that a big old sunspot occurs on the surface of the star...detectors in the shadow of the sunspot on our DS will measure less power per unit area. As the star rotates, the detected shadow will move across our DS. If the DS is big enough and the star rotates fast enough, then it's possible for the shadow to move faster than the speed of light across the surface of our DS with nothing causal really travelling faster than light.

What does this look like for someone standing on the surface of the DS?

 

[zaybu]

So explain how this experiemnt works.

Following post #336, I think I have found a solution to the Mach-Zehnder interferometer. I will work out the detail and post it on my blog. Then I'll let you know when that is done. What's surprising is that the solution is very simple if you use vectors.

 

[Reptillian]

What does this look like for someone standing on the surface of the DS?

I'm not sure. I'm betting it looks weird to say the least....I'm trying to make it easier to imagine by thinking of half the star being blocked out with a massive sunspot to sort of simulate night on the surface of the sphere, but it isn't helping...the best I can come up with is a kind of murky twilight. IDK