I’m not sure what you mean. If something is “shared”, but this something contains no information, how can we know that it was shared? In what sense does this something even exist?
The perfect correlation of entangled particles is well established, and very cool, but perfect correlation does not require sharing of “something”. The perfect correlation is baked into the system from the start, from local interactions only.
Indeed. I’m not completely sure what point you are trying to make, but my point is not a hidden variable point. The states can be in a perfectly correlated superposition without any hidden variables, and still not “share anything” upon collapse into an eigenstate.
I will concede that it looks a lot like one particle somehow tells the other “hey, I just collapsed into the |1> state, so now you need to as well”, but at a closer look this seems to happen on its own without any such message being shared. In particular, while the collapse of one state causes the collapse of the other, there is no physical way to distinguish between a state that was collapsed due to entanglement, and one that wasn’t. At least not until you send a sub-FTL signal to explain what happened.
So if physically, the state of particle 1 before and after particle 2 was measured is indistinguishable, how can we say that “something” was shared from particle 2 to particle 1?
I mean you can setup a source of entangled particles and two very far detectors that would do measurements roughly at the same time on each particle in such a way that information traveling at the speed of light wouldn’t have time to travel the distance between both detectors.
You can then just gather roughly simultaneous measurements and at a later time join the datasets from both detectors to see what one measured vs the other for each pair.
If I understand correctly the current observations show that collapsing the state of one of the particle influences the other all the way at the other detector. Since there’s no hidden variables that predetermine the result of measurements while the result of the collapse is random, and the fact that particles still respect the correlation over any distance is why there seem to be a FTL communication between the particles.
Something has to be communicated between the particles for the influence to work FTL, but it also seem we cannot leverage this phenomenon to send “actual information” this way :/
edit: Important point with that experiment: once the particles have been observed, if you try the experiment a second time using the same particles, then you’ll get different results, this time in line with hidden variables because the particle’s state already collapsed.
I fully understand the concept of entanglement and the experiments you mention, but I’m still to understand what you mean when you say “something” is being transmitted between the particles.
As you say, this “something” cannot contain information, and it also cannot influence the particle physically, since there is no way to distinguish the physical state of the particle before and after it receives this “something”. So the signal contains nothing, and has no effect on physical reality. That sounds a lot like “nothing” rather than “something”.
I completely get the argument that somehow the two particles must agree on what result to give, but in the theory this is just a consequence of how entanglement and measurements work. No transmission required.
The message transferred between the particles supposedly FTL does contain information though. What I meant was that we cannot encode our own arbitrary information on top of it. The message has a physical effect on reality, without it the state we find the particles in cannot be respected.
Just reconsider this: If we agree that the result of a measurement is totally random (no hidden variable predetermining the result of the measurement) but that once we measure and know the state of one particle then we know with certainty the state of the other particle (entanglement): information about the collapse of the first measured particle was shared to the other so that it’s no longer random.
edit: If your argument is about “sharing information doesn’t imply transmission” then let’s stop here and leave this thread agreeing that “information was shared” :)
I have no opinions on what shape the information sharing takes. Nor am I interested in guessing.
The “message” does not have any local effect on reality - when you measure your particle, you have no way of figuring out if its partner was already measured elsewhere. The effect it does have is on the global state, maintaining the correlation that was encoded from the start.
If you write up the density matrix for the system before and after measurement of one of the particles, you can see that while the density matrix changes, it does not change in a way one can measure.
What I will concede is that before the first measurement the global state is |00>+|11>, afterwards it is |00> or |11>. This projection appears to happen instantaneously, no matter the distance, which is indeed faster than light.
But calling the wave function collapse a signal or a message or a transfer of information is misleading, I would say. In your example, we know that the initial state is |00>+|11>, and that the result of the first measurement is then, say, 1. Then no further information is required to know that the other measurement will result in 1. No messages required, no hidden variables, simply the process of elimination.
I would like to say that this is indeed a confusing subject, but that the math is clear, and that I am arguing what is my impression of the mainstream view in the field.
I’m not sure what you mean. If something is “shared”, but this something contains no information, how can we know that it was shared? In what sense does this something even exist?
The perfect correlation of entangled particles is well established, and very cool, but perfect correlation does not require sharing of “something”. The perfect correlation is baked into the system from the start, from local interactions only.
The 2022 nobel prize was given to experimentalists that observed the violation of Bell’s inequality.
https://en.m.wikipedia.org/wiki/Bell's_theorem https://en.m.wikipedia.org/wiki/Quantum_nonlocality
I’m genuinely not an expert but I get it to mean that there aren’t hidden variables created alongside the entangled particles.
Indeed. I’m not completely sure what point you are trying to make, but my point is not a hidden variable point. The states can be in a perfectly correlated superposition without any hidden variables, and still not “share anything” upon collapse into an eigenstate.
I will concede that it looks a lot like one particle somehow tells the other “hey, I just collapsed into the |1> state, so now you need to as well”, but at a closer look this seems to happen on its own without any such message being shared. In particular, while the collapse of one state causes the collapse of the other, there is no physical way to distinguish between a state that was collapsed due to entanglement, and one that wasn’t. At least not until you send a sub-FTL signal to explain what happened.
So if physically, the state of particle 1 before and after particle 2 was measured is indistinguishable, how can we say that “something” was shared from particle 2 to particle 1?
I mean you can setup a source of entangled particles and two very far detectors that would do measurements roughly at the same time on each particle in such a way that information traveling at the speed of light wouldn’t have time to travel the distance between both detectors.
You can then just gather roughly simultaneous measurements and at a later time join the datasets from both detectors to see what one measured vs the other for each pair.
If I understand correctly the current observations show that collapsing the state of one of the particle influences the other all the way at the other detector. Since there’s no hidden variables that predetermine the result of measurements while the result of the collapse is random, and the fact that particles still respect the correlation over any distance is why there seem to be a FTL communication between the particles.
Something has to be communicated between the particles for the influence to work FTL, but it also seem we cannot leverage this phenomenon to send “actual information” this way :/
edit: Important point with that experiment: once the particles have been observed, if you try the experiment a second time using the same particles, then you’ll get different results, this time in line with hidden variables because the particle’s state already collapsed.
I fully understand the concept of entanglement and the experiments you mention, but I’m still to understand what you mean when you say “something” is being transmitted between the particles.
As you say, this “something” cannot contain information, and it also cannot influence the particle physically, since there is no way to distinguish the physical state of the particle before and after it receives this “something”. So the signal contains nothing, and has no effect on physical reality. That sounds a lot like “nothing” rather than “something”.
I completely get the argument that somehow the two particles must agree on what result to give, but in the theory this is just a consequence of how entanglement and measurements work. No transmission required.
The message transferred between the particles supposedly FTL does contain information though. What I meant was that we cannot encode our own arbitrary information on top of it. The message has a physical effect on reality, without it the state we find the particles in cannot be respected.
Just reconsider this: If we agree that the result of a measurement is totally random (no hidden variable predetermining the result of the measurement) but that once we measure and know the state of one particle then we know with certainty the state of the other particle (entanglement): information about the collapse of the first measured particle was shared to the other so that it’s no longer random.
edit: If your argument is about “sharing information doesn’t imply transmission” then let’s stop here and leave this thread agreeing that “information was shared” :)
I have no opinions on what shape the information sharing takes. Nor am I interested in guessing.
The “message” does not have any local effect on reality - when you measure your particle, you have no way of figuring out if its partner was already measured elsewhere. The effect it does have is on the global state, maintaining the correlation that was encoded from the start.
If you write up the density matrix for the system before and after measurement of one of the particles, you can see that while the density matrix changes, it does not change in a way one can measure.
What I will concede is that before the first measurement the global state is |00>+|11>, afterwards it is |00> or |11>. This projection appears to happen instantaneously, no matter the distance, which is indeed faster than light.
But calling the wave function collapse a signal or a message or a transfer of information is misleading, I would say. In your example, we know that the initial state is |00>+|11>, and that the result of the first measurement is then, say, 1. Then no further information is required to know that the other measurement will result in 1. No messages required, no hidden variables, simply the process of elimination.
I would like to say that this is indeed a confusing subject, but that the math is clear, and that I am arguing what is my impression of the mainstream view in the field.