Quantum entanglement

[little_monkey]

How spooky does it get?

A ..........← ●● →.......... B​

1) Observer A, called Alice, will measure the spin of incoming particle. If it has spin, say, up then she knows that observer B, called Bob, will measure its counter-part particle’s spin to be down.This is like Alice tossing a coin, heads or tails, and say it comes down heads. Her counterpart Bob who may be light years away on the other side of the galaxy, who is also tossing a coin, and now his must come out in this case as tails!

2) Not only that, but Alice can choose whatever axis, an infinity of possibilities, along which the particle spin must quantize as spin up or spin down. Now Bob’s particle, on the other side of the galaxy, must also quantize along the same axis, with the opposite spin. But how does the particle know that?!?

3) Furthermore, a third observer C, called Claude, might be moving towards either Alice or Bob. Suppose that Claude is moving towards Alice, then according to him, she is measuring first, and she decides along which axis the particle spin will quantize. However if at the same time another observer D, called Donna, is moving towards Bob, then according to Donna, it is Bob who makes the first measurement and he decides along which axis the particle will quantize. How can this be??!?? Which is the cause and which is the effect? Accordingly Quantum physics makes no distinction between the two cases?!?

 

[Engyo]

How spooky does it get?

A ..........← ●● →.......... B​

1) Observer A, called Alice, will measure the spin of incoming particle. If it has spin, say, up then she knows that observer B, called Bob, will measure its counter-part particle’s spin to be down.This is like Alice tossing a coin, heads or tails, and say it comes down heads. Her counterpart Bob who may be light years away on the other side of the galaxy, who is also tossing a coin, and now his must come out in this case as tails!

As long as the two coins are entangled.........

2) Not only that, but Alice can choose whatever axis, an infinity of possibilities, along which the particle spin must quantize as spin up or spin down. Now Bob’s particle, on the other side of the galaxy, must also quantize along the same axis, with the opposite spin. But how does the particle know that?!?

Maybe the particles don't know that they are on opposite sides of what to us looks like a very large galaxy - maybe to the particles they are still next to each other, and the distance is all in our minds.

3) Furthermore, a third observer C, called Claude, might be moving towards either Alice or Bob. Suppose that Claude is moving towards Alice, then according to him, she is measuring first, and she decides along which axis the particle spin will quantize. However if at the same time another observer D, called Donna, is moving towards Bob, then according to Donna, it is Bob who makes the first measurement and he decides along which axis the particle will quantize. How can this be??!?? Which is the cause and which is the effect? Accordingly Quantum physics makes no distinction between the two cases?!?

Again, I think the whole problem is that we confuse our sense-experience of the universe with reality. I believe that the reality the particles are operating in is vastly different from what humans perceive.

 

[little_monkey]

I believe that the reality the particles are operating in is vastly different from what humans perceive.

There are 10ˆ80 particles in the universe, each having its own reality?!? :woohoo:

 

[Kungfuzed]

Action at a distance is a mystery to me. Magnetism and gravity make no sense, since objects don't need to touch to affect each other. Considering this, quantum entanglement doesn't seem any less bizzare, it can just work at a greater distance, theoretically.

 

[silvermoon383]

Bear in mind though, this doesn't necessarily imply the passing of information between the 2 particles (coins in the example). We know that of the pair one has to spin up, the other has to spin down. To figure out both, all we have to do is measure 1 of the particles then use the process of elimination to determine the qualities of it's partner.

 

[little_monkey]

Action at a distance is a mystery to me. Magnetism and gravity make no sense, since objects don't need to touch to affect each other. Considering this, quantum entanglement doesn't seem any less bizzare, it can just work at a greater distance, theoretically.

Action at a distance (Newtonian physics) has long been replaced by Quantum Field Theory, oh say, about 80 years ago.

OTOH, Quantum entanglement is so weird that even Einstein was spooked by it.

 

[little_monkey]

Bear in mind though, this doesn't necessarily imply the passing of information between the 2 particles (coins in the example). We know that of the pair one has to spin up, the other has to spin down. To figure out both, all we have to do is measure 1 of the particles then use the process of elimination to determine the qualities of it's partner.

Take two people. Place them in different rooms. Both know when they toss their coins, it's either head or tail. Now, let one tosses a coin, let`s say it is head, the second person in the other tosses his coin, but now according to QE, it must turn up tail! If you don't consider that as weird, you've been watching too many episodes of SUPERNATURAL...


BTW, by the principle of relativity, particle A cannot transfer its information to B faster than the speed of light. So the second particle`s spin will be observed way before the information can arrive.

 

[Engyo]

There are 10ˆ80 particles in the universe, each having its own reality?!? :woohoo:

No, I said that I believe the reality the particles are interacting differs from what we as humans percieve. I didn't say that each one get's its own reality.....although I wouldn't find that necessarily impossible, just improbable.

 

[Troublemane]

when you factor in relativity its really quite simple....anyone recall the "time dilation effect"? As a particle approaches light speed time slows down to zero, and so does space. (because time and space are actually one thing, called SPACETIME. its not 3 dimensions of space and one of time, its 4 dimensions of SPACETIME, one thing).

so space and time contract to zero, so from the perspective of the particles travelling in opposite directions, no time has passed from the moment they left the device to the time they arrive at A and B, and therefor no space between them. They are effectively ONE particle. Its only after they strike the detector(s) that they differentiate and become separate, but thats due to their deceleration from lightspeed/transfer of energy to the detectors.

see, its not all that difficult when you think of it from their perspective, instead of trying to wrap your mind around it from our inertial frame, here on earth.

 

[little_monkey]

when you factor in relativity its really quite simple....anyone recall the "time dilation effect"? As a particle approaches light speed time slows down to zero, and so does space. (because time and space are actually one thing, called SPACETIME. its not 3 dimensions of space and one of time, its 4 dimensions of SPACETIME, one thing).

so space and time contract to zero, so from the perspective of the particles travelling in opposite directions, no time has passed from the moment they left the device to the time they arrive at A and B, and therefor no space between them. They are effectively ONE particle. Its only after they strike the detector(s) that they differentiate and become separate, but thats due to their deceleration from lightspeed/transfer of energy to the detectors.

see, its not all that difficult when you think of it from their perspective, instead of trying to wrap your mind around it from our inertial frame, here on earth.

You are confusing the particle A with the photon it must send to particle B to get its message across.

In case you haven't understood the experiment. At center, two particles are sent in opposite directions, one towards Alice (A), the other towards Bob(B). In order for the first particle (traveling to A) to communicate with the second particle (traveling to B) it must send a photon. That photon can only travel at lightspeed. Therefore the measurement by Bob(b) can take place way before the photon arrive.

BTW, I did not invent this experiment, it was first designed by Schrodinger in 1935.

 

[Engyo]

You are confusing the particle A with the photon it must send to particle B to get its message across.

In case you haven't understood the experiment. At center, two particles are sent in opposite directions, one towards Alice (A), the other towards Bob(B). In order for the first particle (traveling to A) to communicate with the second particle (traveling to B) it must send a photon. That photon can only travel at lightspeed. Therefore the measurement by Bob(b) can take place way before the photon arrive.

BTW, I did not invent this experiment, it was first designed by Schrodinger in 1935.

I don't believe that a photon is sent between the particles.........I think it is that they are linked in some way we don't yet clearly understand, and that to change one is to change the other with much much less than a light-speed delay - which is what quantum entanglement means. If it were necessary to send messages (photons) between the particles then they couldn't be said to be "entangled", could they?

 

[little_monkey]

I don't believe that a photon is sent between the particles.........I think it is that they are linked in some way we don't yet clearly understand, and that to change one is to change the other with much much less than a light-speed delay - which is what quantum entanglement means. If it were necessary to send messages (photons) between the particles then they couldn't be said to be "entangled", could they?

The experiment can go on with or without a photon being sent.The entanglement has nothing to do with the photon. The question of the photon was raised in response to what relativity allows in this experiment, which is that whatever information can take place, that info is restricted by relativity.

The word "entanglement " was used by Schrodinger to signify that somehow there was a connection between the particles as they travel through space, tho' that connection is a mystery. Einstein wrote a paper, often referred as the EPR paradox, in which he was trying to refute the claims made by quantum mechanics.

Read more at: EPR paradox - Wikipedia, the free encyclopedia

 

[Yerda]

On the topic:

Speed of 'instantly' calculated

You have to travel very quickly to be somewhere "in an instant", say scientists - at least 10,000 times the speed of light, to be precise.

Physicists have worked out the speed of "instantly" with an experiment investigating the weird phenomenon of quantum entanglement that connects paired particles.


Channel 4 - News - Speed of 'instantly' calculated

 

[Troublemane]

You are confusing the particle A with the photon it must send to particle B to get its message across.

In case you haven't understood the experiment. At center, two particles are sent in opposite directions, one towards Alice (A), the other towards Bob(B). In order for the first particle (traveling to A) to communicate with the second particle (traveling to B) it must send a photon. That photon can only travel at lightspeed. Therefore the measurement by Bob(b) can take place way before the photon arrive.

BTW, I did not invent this experiment, it was first designed by Schrodinger in 1935.

Nope, i am not confusing anything. You havent paid attention to my explaination. The two particles sent in opposite directions are travelling at either light speed or near light speed, and relativity says that time and space (relative to a particle moving near or at lightspeed) shrinks to zero. So what I am saying is that the two particles flying away from each other at light speed do not experience any time change until they strike the detectors at opposite sides of the galaxy or ..arbitrarily far away.

since they experience no time change they experience no spatial changes either, so from their reference they are still together as one. THATS why we can have one go thru the detector, measured as "up", and know that simultaneously the other has now changed to "down"---because they were both really just the same particle until the moment we measured one.

there really is no mystery about it, unless you insist on believeing in "local" reality as the only reality (i.e.,anything not going light speed).

 

[little_monkey]

Nope, i am not confusing anything. You havent paid attention to my explaination. The two particles sent in opposite directions are travelling at either light speed or near light speed...

The two particles moving away DO NOT need to travel at lightspeed for QE to take place. They can be moving at 3 x 10ˆ4 m/s, an insignificant fraction of the speed of light. Hence, no time dilation and no space contraction can be be invoked to explain QE.

:sorry1:

 

[Troublemane]

then this is not a quantum entanglement experiement

 

[little_monkey]

then this is not a quantum entanglement experiement

Read my post #12.

 

[Troublemane]

the particles have to be subatomic scale in order for quantum effects to be observed, and these particles have two speeds: near light speed, and complete stop. sorry dude, you cant have quantum entanglement between two particles going slower than lightspeed or near light speed, its impossible.

 

[little_monkey]

the particles have to be subatomic scale in order for quantum effects to be observed, and these particles have two speeds: near light speed, and complete stop. sorry dude, you cant have quantum entanglement between two particles going slower than lightspeed or near light speed, its impossible.

Most particles at sub-atomic level move with a speed ≅ 10ˆ5 m/s. Are you saying that electrons and quarks can only exist at the speed of light???

 

[Troublemane]

in experiments with subatomic particles, you need energy to separate them, this will impart velocity to them. if you try and test for quantum entanglement on a particle, it will be travelling at near light speed. you cannot test for quantum entanglement on a non-accelerated particle, one thats either a part of a molecule or just sitting there.

So...there is no quantum entanglement effects with a non-accelerated subatomic particle.