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Old 28th September 2009, 01:54 AM   #41
martu
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Originally Posted by Reality Check View Post
That is right. Before the photons are mingled the ions are not entangled. If the photons are then detected within the 15 ns window the ions should be entangled. This is then demonstrated to be the case with the detection of the hyperfine state of the ions.
So do you have any other objections to my idea?
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Old 28th September 2009, 01:56 AM   #42
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Originally Posted by Tumbleweed View Post
I read your link and it seems to infer that this entanglement involves a mechanical system. One pair of ions is set vibrating, the other pair responds. So we get back to the Mars thing again: If I set two ions vibrating on Earth, two entangled particles do likewise on Mars. Why is this not an instantaneous switch?
Because you couldn't use it as a switch. Unless you can show me how?
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Old 28th September 2009, 03:29 AM   #43
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Originally Posted by martu View Post
So do you have any other objections to my idea?
Other than it does not work, no.
Entangled objects are entangled because their quantum states are entangled, not because you state that they were at the same position and time. The theory and experiments shows that the objects need not be at the same position or time.

IMO - there is probably an experiment out there that has 2 entangled photons emitted from the same atom at different times.

Note that the entangled photons in this case not only start from different positions but they also start at different times. Within a 15 ns window does not mean that the photons were emitted at the exact some time. You might say that time begins when they entangle at the half-silvered mirror but then what about their effect on the ions?

You also have the entangled ions which are definitely at different positions and they can emit the (non-entangled) photons at different times within the 15 ns window.

Last edited by Reality Check; 28th September 2009 at 03:39 AM.
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Old 28th September 2009, 03:59 AM   #44
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Originally Posted by martu View Post
What are these standard techniques? Do they involve bringing the entangled pairs together at one point in space and time?
You should be able to look up the standard techniques yourself.
They usually involve lasers of specific frequencies to place ions in specific quantum states.

Originally Posted by martu View Post
From this paper Entanglement concentration in Bose-Einstein condensates
Bose-Einstein condensates fit my picture as you have to ‘distribute’ the entanglement which I would say is bringing two particles together at the same point in time then doing this over and over again resulting in all the atoms sharing a point in time.
It does not fit your picture (note the word teleportation in the abstract).

The paper's abstract is quite clear that the technique is about concentrating the degree of entanglements of atoms that make up a Bose-Einstein condensates.
Quote:
We propose a scheme for demonstrating entanglement swapping (i.e. teleportation of entanglement) using trapped Bose-Einstein condensates. This is accomplished by detection of the total number of atoms leaking out of two adjacent traps. We describe how this scheme may be used to concentrate entanglement shared between two parties in the form of entangled condensates
At no time during the process are all the atoms in the Bose-Einstein condensates at the same point in space or time.

Note that the entanglement is "teleported", i.e. the atoms are never close to each other.
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Old 28th September 2009, 04:37 AM   #45
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Originally Posted by Tumbleweed View Post
I read your link and it seems to infer that this entanglement involves a mechanical system. One pair of ions is set vibrating, the other pair responds. So we get back to the Mars thing again: If I set two ions vibrating on Earth, two entangled particles do likewise on Mars. Why is this not an instantaneous switch?
In the Copenhagen interpretation, because it's random. In MW, because both things happen (so it's effectively random in each).

Originally Posted by martu View Post
What are these standard techniques? Do they involve bringing the entangled pairs together at one point in space and time?
No.

Quote:
Bose-Einstein condensates fit my picture as you have to ‘distribute’ the entanglement which I would say is bringing two particles together at the same point in time then doing this over and over again resulting in all the atoms sharing a point in time.
No, the atoms never come together. Two atoms can become entangled by (for example) exchanging a photon or other particle between them.
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Old 28th September 2009, 05:16 AM   #46
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Originally Posted by Reality Check View Post
Other than it does not work, no.
Entangled objects are entangled because their quantum states are entangled, not because you state that they were at the same position and time. The theory and experiments shows that the objects need not be at the same position or time. .
You need to follow it through. The following describes the independent events that occur, Event 1 is the emission of one of the photons, Event 2 is the emission of the other and Event 3 is the mingling of the photons.

Event 1:

Ion1 and Photon1 are at the same place and time. Result Ion1 and Photon1 become entangled.

Event 2

Ion2 and Photon2 are at the same place and time. Result Ion2 and Photon2 become entangled.

Event 3

Photon1 and Photon2 are at the same place and time. Result Photon1 and Photon2 become entangled. But we have also have to consider that Photon1 and Photon2 are at the same point in time as Ion1 and Ion2 respectively. Consequence? Ion1 and Ion2 are at the same point in time also and become entangled.

This is logically consistent do you agree?

It also predicts that only some runs will produce entanglement as the photons will not consistently meet at the same point at the beam splitter. I admit I can’t follow the reasons in the text as to why they only get so few correlations can you enlighten me?

Also this sentence:

Originally Posted by Reality Check View Post
Entangled objects are entangled because their quantum states are entangled, not because you state that they were at the same position and time.
Says things are entangled because they are entangled, a tautology. Why are entangled objects entangled in your opinion?

Originally Posted by Reality Check View Post
IMO - there is probably an experiment out there that has 2 entangled photons emitted from the same atom at different times.
This would show me wrong without a doubt but I can’t find an example of this at all.

Originally Posted by Reality Check View Post
Note that the entangled photons in this case not only start from different positions but they also start at different times. Within a 15 ns window does not mean that the photons were emitted at the exact some time. You might say that time begins when they entangle at the half-silvered mirror but then what about their effect on the ions?

You also have the entangled ions which are definitely at different positions and they can emit the (non-entangled) photons at different times within the 15 ns window.
See above for a description of the three events.
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Old 28th September 2009, 05:19 AM   #47
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Originally Posted by Reality Check View Post
You should be able to look up the standard techniques yourself.
They usually involve lasers of specific frequencies to place ions in specific quantum states.


It does not fit your picture (note the word teleportation in the abstract).

The paper's abstract is quite clear that the technique is about concentrating the degree of entanglements of atoms that make up a Bose-Einstein condensates.


At no time during the process are all the atoms in the Bose-Einstein condensates at the same point in space or time.

Note that the entanglement is "teleported", i.e. the atoms are never close to each other.
I will look into this a bit more, thanks for the information.

Note that my description of the 3 events in my post above does not require that the atoms are close to each as long as they were, at one point at least, at the same point in time as a carrier particle like a photon. This is how the entanglement is 'teleported'.
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Old 28th September 2009, 05:21 AM   #48
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Originally Posted by sol invictus View Post
No, the atoms never come together. Two atoms can become entangled by (for example) exchanging a photon or other particle between them.
Yes as I describe in my 3 events above.
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Old 28th September 2009, 05:34 AM   #49
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Originally Posted by martu View Post
Originally Posted by Reality Check
IMO - there is probably an experiment out there that has 2 entangled photons emitted from the same atom at different times.
This would show me wrong without a doubt but I can’t find an example of this at all.
I don't understand your idea at any level, so I can't comment whether this will show it to be wrong. But it's certainly true that the same atom can and will emit 2 photons at different times, and the two photons will be entangled with each other.

For example an atom in an excited state that decays to its ground state in two stages, by emitting two separate photons.
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Old 28th September 2009, 05:39 AM   #50
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Here you go. Slightly more complex than what I had in mind, but it does the job:

"Thus, the excited atom emits a first photon, entangled with the atom in ground states as discussed before [14]. In the second part, the atom is subsequently excited by the pump, and emits a second photon and swaps its entanglement with the first photon (already outside the cavity) to the second photon. The whole process now generates an entangled photon pair."
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Old 28th September 2009, 05:42 AM   #51
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Originally Posted by sol invictus View Post
I don't understand your idea at any level, so I can't comment whether this will show it to be wrong. But it's certainly true that the same atom can and will emit 2 photons at different times, and the two photons will be entangled with each other.

For example an atom in an excited state that decays to its ground state in two stages, by emitting two separate photons.
Ok thanks do you have a link that details this process please? My cursory Google search was inconclusive.

ETA: Just caught post 50 ignore this thanks sol
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Old 28th September 2009, 06:32 AM   #52
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Originally Posted by sol invictus View Post
Here you go. Slightly more complex than what I had in mind, but it does the job:

"Thus, the excited atom emits a first photon, entangled with the atom in ground states as discussed before [14]. In the second part, the atom is subsequently excited by the pump, and emits a second photon and swaps its entanglement with the first photon (already outside the cavity) to the second photon. The whole process now generates an entangled photon pair."
This fits with what I am saying actually. We have two events:

Event 1:
Atom emits photon1 at a unique point in time. Atom and photon1 are now entangled.

Event 2:
Atom emits photon2 at a unique point in time. Atom and photon2 are now entangled. However the Atom is already at the same point in time as photon1 hence photon1 and photon2 are now at the same point in time and consequently entangled.

I doubt this will help as you can’t seem to follow what I’m saying unfortunately. I will probably have to write all this out mathematically.

Thanks all this has been helpful.
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Old 28th September 2009, 06:34 AM   #53
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Originally Posted by martu View Post
See above for a description of the three events.
Your 3 events are nothing to do with the experiment.
The real events as described in the experiment are:
Event 1:
Ion1 emits Photon1. They are not at the same place and time. They are not entangled.
In QM the ion and the electron emitting the photon have no set position - rather they have a probability distribution in space.
If you like the "place" of the ion is the average position of its nucleus and the "place" of the photon is the average position of the electron emitting it. These are different.

Event 2
Ion2 emits Photon2. They are not at the same place and time. They are not entangled.

Event 3
Photon1 and Photon2 are not at the same place and time. They are in the region of the half-silvered mirror. They not entangled.

Event 4.
Only those events that the detector shows that Photon1 and Photon2 are in the 15 nanosecond window are selected. Result: Ion1 and Ion2 are entangled. Photon1 and Photon2 are entangled.

It is the detection that causes the entanglement.
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Old 28th September 2009, 07:01 AM   #54
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Originally Posted by martu View Post
This fits with what I am saying actually.
Probably the question to ask you is, what are you trying to accomplish? QM and QFT already describe entangled phenomena in a certain way. They give sharp, mathematical predictions that have been born out of tens of thousands of sophisticated experiments. So they're clearly either correct or very good approximations to correct.

But they don't describe entanglement in anything like the language you're suggesting (since your theory contains no math I can't say anything more than that). So, what are you after? Are you trying to find an entirely new theory that will replace QM and QFT? Or are you simply trying to find a way to explain in words how entanglement is possible? If it's the first, forget the words and write a real theory, with math. If it's the second, why can't I connect the words you're saying to what I know about QM and QFT?
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Old 28th September 2009, 08:23 AM   #55
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Originally Posted by Reality Check View Post
Your 3 events are nothing to do with the experiment.
The real events as described in the experiment are:
Event 1:
Ion1 emits Photon1. They are not at the same place and time. They are not entangled.
In QM the ion and the electron emitting the photon have no set position - rather they have a probability distribution in space.
Ok I am obviously missing something.

If you can spare me more time can you tell me why the bolded part is true? The text flatly contradicts this:

Page 17 first column third paragraph:

Quote:
Before the two photons mingle at the beamsplitter's half mirror, the only quantum entanglement is between each ion and the photon it emitted
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Old 28th September 2009, 08:46 AM   #56
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Originally Posted by sol invictus View Post
Probably the question to ask you is, what are you trying to accomplish? QM and QFT already describe entangled phenomena in a certain way. They give sharp, mathematical predictions that have been born out of tens of thousands of sophisticated experiments. So they're clearly either correct or very good approximations to correct.

But they don't describe entanglement in anything like the language you're suggesting (since your theory contains no math I can't say anything more than that). So, what are you after? Are you trying to find an entirely new theory that will replace QM and QFT? Or are you simply trying to find a way to explain in words how entanglement is possible? If it's the first, forget the words and write a real theory, with math. If it's the second, why can't I connect the words you're saying to what I know about QM and QFT?
No I am not trying to replace anything at all in fact it was the discussion of Bell’s theorem in the deterministic thread which led me here. I accept QM and QFT as being correct, experiment tells us this (for now, new evidence in the future and so on…). So it’s the bolded sentence, to your question:

Originally Posted by sol invictus View Post
why can't I connect the words you're saying to what I know about QM and QFT?
Because we speak different languages when it comes to physics. Ok perhaps not different languages but you are fluent whereas I have some basic conversational physics. But I can follow most of the maths, I spent too much of my time at university on the rugby pitch or in the bar but I did manage to get a maths degree while I was there.

The whole idea is based on postulating whether we can say things can be next to each other or touching in time in the same way they can be touching each other in space. If we can and the maths works then messages between them will be instantaneous much the same way that messages between objects touching in space are instantaneous. Instantaneous messages are required for entanglement and here we are.

Does this sound like complete nonsense from the off?
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Old 28th September 2009, 12:03 PM   #57
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Originally Posted by martu View Post
Ok I am obviously missing something.

If you can spare me more time can you tell me why the bolded part is true? The text flatly contradicts this:

Page 17 first column third paragraph:
The bolded part is wrong. It should be "They (the two photons) are not entangled)" and only for the second event.

More points about why the "touching in time" concept has nothing to do with quantum entanglement (other than the theory has nothing about this and the experiment contradicts it).

It also applies if there are 2 unconnected atoms that just happen to emit photons at the same time. In other words it states that quantum entanglement is a common state in emissions such as starlight or lasers. Scientists are obviously wasting their time doing all these complex quantum entanglement experiments .

Take a state that is a combination of 2 independent states, i.e. the 2 wave functions are added together. Plug them into the time dependent Schrödinger equation. What you get out after some time is still 2 wave functions that are added together. The states are still independent and have not mixed. The states have not mixed. A measurement on one state will have no effect on the other state.
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Old 28th September 2009, 12:13 PM   #58
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Originally Posted by martu View Post
The whole idea is based on postulating whether we can say things can be next to each other or touching in time in the same way they can be touching each other in space. If we can and the maths works then messages between them will be instantaneous much the same way that messages between objects touching in space are instantaneous. Instantaneous messages are required for entanglement and here we are.

Does this sound like complete nonsense from the off?
It is right up to the last sentence which is "complete nonsense" .
There are no messages, i.e. as in information passing between the photons at speeds greater then light.
Entanglement imples instantaneous collapse of the wave function. Instantaneous messages do not make quantutum states entangled. Instantaneous messages do not require that the photons be touching.

What entanglement requires is entanglment of the quantum states. If the quantum states are not intangled then a measurement of one photon will not effect the other photon.

ETA:
You seem to think that "touching in time" means instantaneous messages (the second to last sentence). This is not true.
If the message speed is finite then the space between the photons means a finite time for the messages to travel.
If the message speed is infinite then it does not matter whether the photons are "touching in time" or not. All messages between any photons at any point in spacetime are instantaneous.

Last edited by Reality Check; 28th September 2009 at 12:43 PM.
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Old 28th September 2009, 09:01 PM   #59
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I've gone back to your OP to try to make sense of it.

Originally Posted by martu View Post
At the creation of a pair of entangled particles we can say that the time of creation for each photon is equal, that is for a pair of entangled photons p1 and p2

te1 = te2 = 0

where ten is the creation time of photon n.

Here we’re going to use a slightly modified spacetime diagram, in this spacetime diagram the x axis and y axis represent the spatial dimensions and the time axis, ct, is the z axis perpendicular to the (x, y) plane. The z dimension is suppressed to help us picture what is going on.
Fine.

Quote:
Picture the two entangled photons as created at the point (0, 0, 0) and they go in opposite directions along the x axis. So for our entangled photons p1 and p2 we can say at the time of emission

(x1, y1) = (x2, y2) = (0, 0)

And also

(dx1/dy1) = (dx2/dy2)
OK.

Quote:
Here is the extra step – our time axis is not a plane but a line.
Huh? The time axis is always a line, it's an axis. Did you mean the opposite?

Quote:
What does that mean? Well it means for each event en we define it’s spatial and temporal co-ordinates not as (x, y, t) but (x, y) and (t) that is we plot the path of an object through time as a line in the (x, y) plane and a different line ‘up’ the time axis. If your spacetime diagram is on a page our path through time can be represented as a line coming out of the page. All objects move ‘up’ the time axis at the same rate, c.
That makes no sense. Objects occupy one location at any given time, and that location changes as a function of time. Therefore the trajectory of an object through spacetime is indeed a line, but it's a single line and it's at some angle to the z-axis that's less than or equal to 45 degrees on your diagram.

Quote:
A consequence of this is that for our entangled pair of photons they travel ‘up’ the time line together, at least until one of them experiences an event.
No idea what you mean. The photons are flying off in opposite directions AND advancing in time; they are detected some distance away in different places some time after they were emitted.

Quote:
Or to put it another way at any time tn the two photons will be on the t axis at the same point.
But that would mean both photons remain at x=y=0, which they don't.

Originally Posted by martu View Post
No I am not trying to replace anything at all in fact it was the discussion of Bell’s theorem in the deterministic thread which led me here. I accept QM and QFT as being correct, experiment tells us this (for now, new evidence in the future and so on…).
Right, OK, that's why I went back to the OP.

Quote:
Instantaneous messages are required for entanglement and here we are.
No, they're not. In MW there is nothing instantaneous, everything is local, nothing suddenly changes.
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Old 29th September 2009, 03:19 AM   #60
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Originally Posted by Reality Check View Post
The bolded part is wrong. It should be "They (the two photons) are not entangled)" and only for the second event.

More points about why the "touching in time" concept has nothing to do with quantum entanglement (other than the theory has nothing about this and the experiment contradicts it).
You agree that the ion and the photon are entangled as the text clearly states?

Originally Posted by Reality Check View Post
It also applies if there are 2 unconnected atoms that just happen to emit photons at the same time. In other words it states that quantum entanglement is a common state in emissions such as starlight or lasers. Scientists are obviously wasting their time doing all these complex quantum entanglement experiments .
Firstly no it doesn’t apply if two atoms are unconnected remember that bit about being at the same place too?

Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments. Or am I wrong again?

Originally Posted by Reality Check View Post
Take a state that is a combination of 2 independent states, i.e. the 2 wave functions are added together. Plug them into the time dependent Schrödinger equation. What you get out after some time is still 2 wave functions that are added together. The states are still independent and have not mixed. The states have not mixed. A measurement on one state will have no effect on the other state.
I know this and haven’t said they will mix. I am struggling to get my message across, bear with me.
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Old 29th September 2009, 03:24 AM   #61
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Originally Posted by Reality Check View Post
It is right up to the last sentence which is "complete nonsense" .
There are no messages, i.e. as in information passing between the photons at speeds greater then light.
Entanglement imples instantaneous collapse of the wave function. Instantaneous messages do not make quantutum states entangled. Instantaneous messages do not require that the photons be touching.

What entanglement requires is entanglment of the quantum states. If the quantum states are not intangled then a measurement of one photon will not effect the other photon.
You keep repeating that entanglement requires entanglement which doesn’t explain anything does it?

Originally Posted by Reality Check View Post
ETA:
You seem to think that "touching in time" means instantaneous messages (the second to last sentence). This is not true.
If the message speed is finite then the space between the photons means a finite time for the messages to travel.
If the message speed is infinite then it does not matter whether the photons are "touching in time" or not. All messages between any photons at any point in spacetime are instantaneous.
Consider this – we have two hypothetical identical rigid objects A and B and they are touching (spatially). If I push A then B will also be pushed. OK? What is the time difference between the push of A and the push of B?
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Old 29th September 2009, 03:56 AM   #62
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Originally Posted by sol invictus View Post
Huh? The time axis is always a line, it's an axis. Did you mean the opposite?
No I meant that the time for any event is found on the z axis so if we consider (x, y) to be our spatial plane the time co-ordinate is always at some point (0, 0, t). The event’s spatial location will be at (x, y) so to get a complete description of an event we have the spatial coordinates (x, y) and a time coordinate (t). But we do not plot (x, y, t) we plot (x, y) and separately (t), consider the time co-ordinate as the clock for this event.

Originally Posted by sol invictus View Post
That makes no sense. Objects occupy one location at any given time, and that location changes as a function of time. Therefore the trajectory of an object through spacetime is indeed a line, but it's a single line and it's at some angle to the z-axis that's less than or equal to 45 degrees on your diagram.
Consider the simple example of two entangled photons created by Spontaneous Parametric Down Conversion. At the time that the single photon ‘splits’ into two photons we have

p1 is at location (x1, y1)
p2 is at location (x2, y2)

where

(x1, y1) = (x2, y2)

For simplicity assume that the photons are travelling in opposite directions along the x axis.

To say the photon are at the same point in time and entangled is to say that

t1 = t2

until one experiences a new event. They share a clock which moves along the time axis.

So after 1 second we have on the x, y plane

p1 is at location (-c, 0)
p2 is at location (c, 0)

but on the time axis we have

p1 is at time c
p2 is at time c

touching in time.

Originally Posted by sol invictus View Post
No idea what you mean. The photons are flying off in opposite directions AND advancing in time; they are detected some distance away in different places some time after they were emitted.
ct1 = ct2

I am running out of words to be honest, I think I’ll have a go at writing this out mathematically.
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Old 29th September 2009, 04:15 AM   #63
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Originally Posted by martu View Post
No I meant that the time for any event is found on the z axis so if we consider (x, y) to be our spatial plane the time co-ordinate is always at some point (0, 0, t). The event’s spatial location will be at (x, y) so to get a complete description of an event we have the spatial coordinates (x, y) and a time coordinate (t). But we do not plot (x, y, t) we plot (x, y) and separately (t), consider the time co-ordinate as the clock for this event.
I understand those words, but what's the point of following that procedure? We draw these plots so that we can tell where the particles are. Doing things your way we'll have two lines for each particle, neither of which represents its position.

Worse, those lines can intersect or coincide even when the particles are not entangled and never interact. For example two pairs of particles produced at different times at the same point would produce four coinciding lines, even though the two pairs might not be entangled with each other. Similarly two particles that actually coincide and therefore can interact cannot be distinguished from two particles that pass across the same point at different times and therefore cannot interact.

Basically this way of drawing diagrams removes lots of relevant information, which is not the point of making a plot. And we cannot even interpret the one piece of info that two t-axis lines coincide to determine anything, as you can see from that example.

As for the math, it simply isn't the case in standard QM that two entangled particles "coincide", or that the time axis is relevant to them in any special way compared to non-entangled particles. "Entangled" means nothing more and nothing less than that the full state cannot be written as a product of a state for particle 1 times a state for particle 2.

Last edited by sol invictus; 29th September 2009 at 04:18 AM.
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Old 29th September 2009, 04:54 AM   #64
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Originally Posted by martu View Post
You agree that the ion and the photon are entangled as the text clearly states?
Yes. Each ion is entangled with the photon that it emits.

Originally Posted by martu View Post
Firstly no it doesn’t apply if two atoms are unconnected remember that bit about being at the same place too?
You need to state your concept more clearly then.
Remember that if you state it mathematically then you will have to the prove that an entangled quantum state emerges from your mathematics.
So far you have not even got close to that.

If your concept is that two objects that are ever in the same place at the same time, e.g. the 2 photons in your OP, will have their quantum states magically entangled somehow then the 2 ion experiment proves your concept to be wrong.

The ions are never in the same place. The ions are never "touching in time". But they are entangled.
Thus the formation of entangled quantum states does not need the objects being entangled to be in the same place at any time nor does it need for them to be "touching in time".

This makes the rest of your post (and this thread) moot.
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Old 29th September 2009, 05:09 AM   #65
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Originally Posted by martu View Post
You keep repeating that entanglement requires entanglement which doesn’t explain anything does it?
It explains everything. It is the entanglement that explains the behaviour of the entangled objects.
Your concept explains nothing. All it is is the assumption by you that something that has nothing to to with quantum entanglement will somehow magically create entanglement. Theory and experiment disproves this.

Originally Posted by martu View Post
Consider this – we have two hypothetical identical rigid objects A and B and they are touching (spatially). If I push A then B will also be pushed. OK? What is the time difference between the push of A and the push of B?
Why consider that? It has nothing to do with any quantum entanglemnet experiment. At the point that the measurments are made the entangled particles are not "touching (spatially)".

I will wait for you to come back with the mathematical treatment of your concept before comenting further. It will be interesting to see how you get entangled states from your concept.

My guess is that you will start with 2 systems in pure quantum states, allow them to be at the same position, set t = 0, plug the composite system into Schrödinger's equation and get .... a composite system consisting of pure quantum states!
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Old 29th September 2009, 09:34 AM   #66
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Thanks both of you, this conversation has helped me understand a few things. You're both right about the maths and maybe I am trying to use words (badly obviously) to describe the existing maths as you suggest Reality Check, I honestly hadn’t thought of that. It’s one thing to follow the maths (as I can when I read a physics text) it’s another to fully understand it, as you’re both probably aware you don’t really grasp the maths behind something until you use it.

I'll be back with some maths if I can. Thanks again.
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Old 29th September 2009, 09:37 AM   #67
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Originally Posted by martu View Post
Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments. Or am I wrong again?
Sorry one final thing I meant to add to my previous post, Reality Check is my statement above correct?
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Old 29th September 2009, 11:48 AM   #68
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Originally Posted by martu View Post
Sorry one final thing I meant to add to my previous post, Reality Check is my statement above correct?
I do not know.

IMO Entanglement is not common given that it needs the quantum states to be manipulated using things that do not appear often in nature, e.g. lasers, specific configurations of magnetic fields (NMR), etc.

Last edited by Reality Check; 29th September 2009 at 11:54 AM.
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Old 29th September 2009, 01:14 PM   #69
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Originally Posted by Reality Check View Post
I do not know.

IMO Entanglement is not common given that it needs the quantum states to be manipulated using things that do not appear often in nature, e.g. lasers, specific configurations of magnetic fields (NMR), etc.
If we assume that events exists where the parties are not entangled we have to conclude that events exist where one, or more, of the conservation laws is violated.
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Old 29th September 2009, 03:56 PM   #70
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Originally Posted by martu View Post
If we assume that events exists where the parties are not entangled we have to conclude that events exist where one, or more, of the conservation laws is violated.
I do not now what you mean.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept). Which one, or more, of the conservation laws is violated in that case?

Last edited by Reality Check; 29th September 2009 at 03:58 PM.
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Old 30th September 2009, 02:40 AM   #71
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Originally Posted by Reality Check View Post
I do not now what you mean.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept). Which one, or more, of the conservation laws is violated in that case?
Really? What experiments show electrons colliding resulting in no entanglement where decoherence hasn't occurred?

Maybe I am way off here but I thought if any two elctrons collided spin would have to be conserved after the collision. Not only spin but any conserved property hence we can say they are entangled.
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Old 30th September 2009, 03:47 AM   #72
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Originally Posted by martu View Post
Really? What experiments show electrons colliding resulting in no entanglement where decoherence hasn't occurred?

Maybe I am way off here but I thought if any two elctrons collided spin would have to be conserved after the collision. Not only spin but any conserved property hence we can say they are entangled.
I do not know of any such experiments. But the fact that the electrons are in pure quantum states (not really mentioned in my post) means that they are never entangled to start with and can never be entangled by the collision.

And yes spin is conserved during the collision. So what?
So is energy, mass and charge.

Last edited by Reality Check; 30th September 2009 at 03:51 AM.
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Old 30th September 2009, 04:38 AM   #73
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Originally Posted by martu View Post
Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments.
That's correct.

Originally Posted by Reality Check View Post
There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept).
Actually Martu is correct: they will be entangled in that case.

Originally Posted by Reality Check View Post
But the fact that the electrons are in pure quantum states (not really mentioned in my post) means that they are never entangled to start with and can never be entangled by the collision.
I think you're confusing entanglement with mixing here. "Entangled states" usually refers to pure states, and unentangled states can become entangled via interactions.
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Old 30th September 2009, 04:55 AM   #74
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Originally Posted by sol invictus View Post
Actually Martu is correct: they will be entangled in that case.
Stopped clocks and all that.....

Thanks for the clarification.
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