### Spooky action at a distance?

Einstein said of quantum mechanics that it had a "spooky action at a distance". He wrote a scientific paper with two colleagues (Podolksy and Rosen) on what has become known as the EPR paradox. E, P & R genuinely believed that they had discovered something paradoxical in QM (that's why they wrote the paper), and that therefore QM had to be

*wrong*. What they had

*actually*done (although they didn't realise it) was to show that the universe behaves in stranger ways than they were prepared to believe.

What EPR had stumbled on was one of the consequences of what we now call "quantum entanglement". This entanglement is an obvious consequence of QM, assuming you have an Everett-like interpretation of QM, which I discussed in my earlier posting State vector collapse?.

So, why does EPR annoy me? It because EPR has become a

*wrong*part of QM folklore. Some people think that EPR were

*right*, and

*not*that they were

*wrong*. This manifests itself in various ways, one of which is that people believe that QM somehow allows faster-than-light (or even instantaneous) communication.

This is complete rubbish. Let me tell you why. This description is quite long and detailed, but it has a very simple logic.

I will describe the basics of EPR from the

*correct*point of view, rather than the

*incorrect*point of view that EPR themselves used in their EPR paradox paper. I want to do it this way because I see no point in perpetuating a misunderstanding by presenting the wrong argument first. This means that I change lots of details in order to tell the story the way I want to. Note that I am

*not*going to discuss technical issues relating to particle statistics, because they don't affect the basic "quantum entanglement" result.

Here is the

*correct*version of EPR:

- Create a pair of identical particles (call them A and B) in such a way that their spins in the up/down direction point in
*opposite*directions. This physical state is represented as A↑ B↓ + A↓ B↑, where the spin-arrows ↑ and ↓ are used to denote the direction of spin. Because the particles are*identical*, both ways of assigning spin to the particles (i.e. A↑ B↓*and*A↓ B↑) are*equally valid*, and both possibilities actually and simultaneously occur in practice, so the*real physical situation*is correctly represented as the*sum*A↑ B↓ + A↓ B↑, rather than only*one*or*other*of the pieces A↑ B↓ and A↓ B↑. - Pull the particles apart until they are separated by an
*enormous*distance, but make sure that you don't mess up their spin directions whilst separating them. You could represent this physical state as A↑ ••• B↓ + A↓ ••• B↑, where the ••• indicate the physical separation between A and B. - Introduce two observers U and V who are tasked with observing A and observing B, respectively. The
*real physical situation*is now represented as U (A↑ ••• B↓ + A↓ ••• B↑) V, where I have placed U at the left and V at the right to indicate where they are located (i.e. near to A and near to B, respectively). - The two observers U and V now observe A and B to see what their spins are. The word "observe" here means that an observer interacts with a particle, in such a way that the state of their brain becomes correlated with the state of the particle (this will become clearer below). There are two possible outcomes of this experiment. The brains of U and V become correlated with A↑ ••• B↓ to create the state U↑ A↑ ••• B↓ V↓, or become correlated with A↓ ••• B↑ to create the state U↓ A↓ ••• B↑ V↑ (a spin-arrow ↑ or ↓ written next to U or V means that the observer's brain has observed the corresponding spin). The
*real physical situation*is the*sum*of these two, which is U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑. - The net effect of the observation above is to transform the state from U (A↑ ••• B↓ + A↓ ••• B↑) V to U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑. The process that leads to this transformation is defined in detail by the dynamical equations of QM. Any other conjectured transformation must bring in assumptions from
*outside*the dynamical equations of QM. - These results show that
*either*(U observes A↑*and*V observes B↓)*or*(U observes A↓*and*V observes B↑), which means that what U observes and what V observes are deterministically associated with each other. Even though the particles are separated by an*enormous*distance when they are observed, they nevertheless produce observations in which A↑ is associated with B↓, and A↓ is associated with B↑. - This is the bit that Einstein said was "spooky action at a distance" because he maintained a distinction between the particles being observed, and the observers themselves. He would
*not*accept that the observers were*also*a part of the whole QM state, so he never accepted that U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑ described a*real physical situation*. His view was (in a QM style of notation) that the*real physical situation*was described by (U↑ A↑*or*U↓ A↓)*and*(B↑ V↑*or*B↓ V↓), where (X*or*Y) allows only*one*of X or Y to occur (this is actually an exclusive-or), and (X*and*Y) requires that*both*of X and Y occur. This prescription (i.e. figmant of Einstein's imagination, if you want) is an example of a conjecture that is brought in from*outside*QM, as described in step 5 above. - Thus Einstein thought that the outcome of observing A was a random result that was
*either*A↑*or*A↓, and similarly the outcome of observing B was an*independent*random result that was*either*B↑*or*B↓. He therefore thought that there was no reason why the results for A and B should be correlated with each other, provided that A and B were so far apart that there was no possibility of some other means of communication between them that might cause the results of the observations to be correlated.

In summary, *we* have an advantage over Einstein, because we know that after the observations have been made the (correct) *real physical situation* is actually described by U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑, whereas Einstein simply refused to believe that this was what reality was doing, and insisted that the (incorrect) *real physical situation* was described by (U↑ A↑ *or* U↓ A↓) *and* (B↑ V↑ *or* B↓ V↓). The *correct* description of reality makes it *obvious* that the QM associations were set up when the particles were originally close together, and were then preserved as the particles were pulled apart. The *incorrect* description of reality has been plucked from thin air, based on a prior prejudice about how the universe works, rather than being derived scientifically from QM. No wonder Einstein *wrongly* thought that QM was paradoxical.

The diagram below summarises the steps in the above argument.

**A:**Initial state of the particles A↑ B↓ + A↓ B↑.**B:**State of the particles after being pulled apart A↑ ••• B↓ + A↓ ••• B↑.**C:**Show the observers tasked with observing A and B as yellow squares, which together with the particles describes the state U (A↑ ••• B↓ + A↓ ••• B↑) V*before*the observations have been made.**D:**Show the observers and the particles*after*the observations have been made. This describes the state U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑.

Can we do faster than light (or instantaneous) communication between the A and B particles (which are separated by an *enormous* distance) in the above description?

- If you think like Einstein (who
*never*accepted the reality of states like U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑ in QM) you would say "yes", because you would have no other way of understanding how the observations of A and B came to be deterministically interrelated, and therefore arrive at a paradox (assuming you believe that faster than light travel is paradoxical!), so you would deduce that QM must be wrong because it is what is allowing this faster than light communication to occur. - If you
*do*accept the reality of states like U↑ A↑ ••• B↓ V↓ + U↓ A↓ ••• B↑ V↑ in QM then you have*no*problem in saying that the communication between A and B occurred whilst they were still close together, and that the consequences of this communication are preserved as the particles are pulled apart, and are then "observed" (i.e. correlated with the brain states of U and V).

I used the suggestive "•••" notation to indicate the separation between A and B, because it *also* suggests that A and B are linked together no matter how apart they are. This linking is also called "quantum entanglement".

Spooky action at a distance? No way!

## 6 Comments:

That was

veryhelpful. Okay, you're now officially on my blogroll. I may be coming over to borrow a cup of quantum physics now and then...I see you have added Fact and Fiction to A Future MetaPhysics section on "Quantum Physics". QM isn't the

mainaim of my F&F blog, which is more to do with generalised debunking of pseudo-science (etc). It just happens that there is a lot of rubbish talked in the general area of QM, and I wanted to put this right.What do you think about the following PDF about entanglement?

http://www.flownet.com/ron/QM.pdf

I wanted to send you an email, do you have an address?

Thanks for pointing out "Quantum Mysteries Disentangled". I have had a quick look through it, and it looks to me as if it describes entanglement and measurement in much the same way that I explained them in my original posting. I have not yet had a chance to go through QMD line-by-line, so I might have missed things.

As for my email address, I thought it was rather ironic that someone called "anonymous" should be asking me for it! You can Google for my name, which tells you where my home page is to be found, and you will find my email address there.

Hello, Sir.

If you are still maintaining this blog, could you please tell me whether it will be possible to infer, from what you have mentioned, that activities in heavenly bodies far away from earth, say, Neptune, influence the happenings on the Earth.

Influence of heavenly bodies on happenings such as birth, death, war, etc. is ridiculed as people feel they exert too less force, G or B or any other field to have any significant impact. Would the presence of 'spooky action at a distance' remove the need of such Newtonian force fields?

In my posting you will see that I explain in detail why there is

nosuch thing as "spooky action at a distance", but thereisthe possibility of "quantum entanglement" which can exist even after "force fields" have been switched off, as long as those fields were present in the first place in order to establish the entanglement.The histories of objects that are entangled with each other are mutually correlated no matter how far apart these objects are located, so it would

seemthat you could thereby get long-range influences of the sort that you asked about.However, setting up these entanglements in the first place is

verydifficult if you to avoid destroying the entanglements that you are trying to create, and this requires “laboratory conditions” to achieve success. So I do not expect that entanglement offers a credible way of getting long-range influences of the sort that you asked about.Post a Comment

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