Quantum Entanglement?

[blike]

Do scientists know exactly the mechanism by which photons are quantumly entangled?

 

I've heard reports that they "communicate" with each other at +c speeds. Do they know how this works?

 

In the experiment performed with entangled photons traveling through sheets of metal [Nature (vol 418, p 304)] the photon was converted to electron waves which passed through the metal, then re-emitted the photon on the other side, which was still entangled.

 

How are they entangled, and how would this entanglement remain in tact with the electron waves?

[blike]

ahem *bump* since no one seems to know :/

[fafalone]

I'll answer tomorrow, it's too late to think about it

[Radical Edward]

Ultimately it is all to do with the wierd quantum uncertainty, in much the same way that you can have a superposition of states (i.e. a particle that is spinning up and down at the same time) you effectively create a state between the two particles that is described as an entangled state - there isn't really any mechanism.

 

here's a link to my lecturer's notes on it if you can be bothered to trawl through the maths!

 

http://www.threetowers.net/lectures.pdf

[blike]

Thanks for the link edward

[Guest Unregistered]

no problem. I hope you have more fun churning through it than I did!

[Radical Edward]

oops, unregistered is me by the way.. I forgot to log in.

[Guest Unregistered]

An example of something being entangled: consider two particles with a total spin of zero, each one of them goes off to the opposite side of the galaxy from the other. If you measure the spin of one of them and find it to be (for example) +1, since spin is conserved, when the other one is measured it will be -1. They are entangled because when the spin of one is determined by someone measuring it, the other one's spin is determined even though it's incredibly far away.

 

This can't be used to communicate though, since you have no way of knowing what the particle's spin will be before you measure it - eg if you decide that you'll send a binary digit, where if the other particle's spin is positive the bit is 1 and negative the bit is 0, you don't know for certain which bit value you'll send because you dont know the particles state until you measure it.

[Radical Edward]

you could use it for encryption though, and effectively send a key at up tp 2c.

[blike]

I thought information couldn't be transferred faster than c?

[Radical Edward]

the key would be an entirely random key though.

[Guest Hogslayer]

Is this along the same lines as molecular information exchange? I remember reading something about electron spin, and how if you separate electrons from the same atom, and change the spin of one, the other will change. Is this along the same lines?

 

If anyone can provide good search keywords or even better, non-technical links for further review, I would appreciate it.

[mastersamwise]

im not absoloutely sure that you could change the spin of an electron?

How could you be cure what you were seeing was not some sort of quantum tunneliung effect?

i'd be interested in the article if you have it!

[JaKiri]

You can change the spin of an electron by putting it in a magnetic field.

[Guest jp-zeal]

The phenomenon of entanglement (discovered by Einstien, Podolsky & Rosen) infact presents with one of the most intriguing of modern day mystries. I dont think any of the scientists would be able to answer u r query.

[mastersamwise]

As a general note i have to say that although i concede that quantum physic is one of the most powerful tools of undertanding the world that we have had to date I have to err on the side of Einstein, he never truly accepted the field and i have to say i agreee; it has lead to some 'interesting' theories that noone can prove or disprove.

I may sound old fashioned but surely this is contrary to the very nature of science (empirical facts and all that....)

[JaKiri]

Well, 'proof' isn't empirical for a start.

 

Secondly, without quantum physics you explain to me the photoelectric effect, or any of the other myriad experiments that empirically proove the standard model?

 

Saying there's no proof for a very commonly accepted (and taught) part of physics is at best a gross underestimation of the physics community.

[Kedas]

first I want to say I don't know much about QM and I'm just giving some ideas to hear what you think.

 

I was thinking most of what we do is based on: if we understand the smaller part then we wil also understand the bigger part.

 

The 'smaller' parts defines what the bigger part wil do.

 

maybe there is a level where this turns around where the bigger part defines what the smaller part should do.

 

so if we would have one part of a whole part and somewhere far away the other part.

by manipulating one part we schould be able to communicate.

and then the big question will be how fast or will nature have shown al his cards and reveal that (almost) infinite speed exist.

(you have to admit that that would be very exciting)

It are just ideas so you don't have to tell me this doesn't match with current theories.

 

I think this quote is also on it place here:

"If we knew what it was we were doing, it would not be called research, would it?" [Albert Einstein]

[Kettle]

Does anyone know what distances have been involved thus far when scientists have measured the link between the two particles? Are we talking miniscule distances? Other side of the room? Down the hall? etc.

 

Thanks

[Kedas]

Originally posted by Kettle

Does anyone know what distances have been involved thus far when scientists have measured the link between the two particles? Are we talking miniscule distances? Other side of the room? Down the hall? etc.

 

Thanks

 

Max 100 kilometres it seems http://www.newscientist.com/hottopics/quantum/quantum.jsp?id=ns99993802

[Kettle]

That is just SO strange (yet decidedly cool).

 

So, considering the speeds and distances that have been recorded in quantum entanglement experiments, does anyone think that inter-dimensional travel might be involved (or have I just seen B5 one too many times?).

 

I mean, if you alter the spin of one electron and immediately record an identical change in the other entangled electron, rather than saying that this change has been communicated at faster than light speeds, could you say that this connection exists outside of our dimension?

 

I really hate using the term Dimension - it's so Star Trek

[Guest DHill]

mastersamwise said in post #16 :

As a general note i have to say that although i concede that quantum physic is one of the most powerful tools of undertanding the world that we have had to date I have to err on the side of Einstein, he never truly accepted the field and i have to say i agreee; it has lead to some 'interesting' theories that noone can prove or disprove.

I may sound old fashioned but surely this is contrary to the very nature of science (empirical facts and all that....)

 

I've wondered a lot about that. I can't tell if it was a pride issue with Einstein or if he had any justification for it. Possibly it was an ego thing, given that his greatest contributions came in 1905 and then 1915, and suddenly a bunch of new and interesting young minds come in and revolutionize science all over again? Just a thought.

 

Quantum Mechanics is a strange field because there are only a few models that can be easily solved. It begins so simply. Write down the Hamiltonian, and solve. But that only goes so far. In condensed matter, for example, the favorite Hamiltonian is some version of a harmonic oscillator or a free electron, but with further inspection one will quickly find that pencil and paper are inadequate for more detailed solutions, and turn to the computer.

 

Maybe it will seem more clear after a few hundred years (if we last that long). In the way that the procedures of Lagrangian mechanics simplify Newtonian mechanics, maybe there is something equally simple for quantum that has not yet arrived (?).

[rebeldog]

You must have heard about the experiment in Switzerland when 2 entangled photons were split and sent in opposite directions (about 7 km each way) with a counter at each end. The counters would randomly count photons at their end. There was statistical evidence to suggest that a photon knew its partner had been counted (observed) at the opposite end. This could mean that particles are communicating at c+ speeds when they become aware of each other when counted or observed. A crazy and beutiful situation has arisen which opens up god knows what!

[JaKiri]

You must not have read the thread on Scienceforums.net when RadicalEdward explained (or at least posted the link to the explanation) of this phenomenon and how it doesn't break the c speed limit.

[bigjnorman]

yeah, all entanglement really does is show that their is a correleation between probabilities of the particles,

 

an even more impressive experiment was done using gravitational lensing of a distant star's photons, just having a detector along one of the paths was enough to make the photons "choose" one path or the other even though they should have "chosen" which path, or both, millions of years ago. ( i can't remember if wheeler did this or not)