ilovephysics.com :: free online physics help, tutorials, forums, classes, misconceptions in / Entanglement Question

Trak · 2005-08-10 16:39:32

When two photons are entangled and one of them is measured then as I understand it the other one becomes polarized.
I was wondering if it is possible to tell when this happens?
For example:
If alice has one of the entangled photons and Bob has the other then if Alice measures her photon but doesn't tell Bob, can Bob find out that his photon has changed?

Last edited by Trak (2005-08-10 16:41:45)

Chris · 2005-08-10 16:59:32

Trak wrote:
If alice has one of the entangled photons and Bob has the other then if Alice measures her photon but doesn't tell Bob, can Bob find out that his photon has changed?

Yes. Google "Bell's Inequality" and "Innsbruck Experiment."

Trak · 2005-08-10 17:18:55

In that case, can information be passed between Alice and Bob simply based on the fact that Bob's photon has changed. It isn't important to know what value it has changed into just that it has changed.

For example:
Alice is going home from work and she has agreed to let Bob know when she gets home.
So when she gets home she measures her photon which immediately causes Bob's photon to change, so therefore he knows that Alice is home.
Doesn't this mean that information has been teleported instantaneously without the use of a classical channel?

Since I know from reading about this stuff that isn't possible I am wondering why I am wrong?

Chris · 2005-08-10 18:14:02

Alice is going home from work and she has agreed to let Bob know when she gets home.
So when she gets home she measures her photon which immediately causes Bob's photon to change, so therefore he knows that Alice is home.
Doesn't this mean that information has been teleported instantaneously without the use of a classical channel?

No experiment will be able to prove a true "instantaneous" interaction. But there have been experiments done that showed "information" passed at 10,000 times the speed of light.

Since I know from reading about this stuff that isn't possible I am wondering why I am wrong?

Why is it not possible? Experiment seems to disagree.

See: http://plato.stanford.edu/entries/qt-entangle/

Announcement

#1 2005-08-10 16:39:32

Entanglement Question

#2 2005-08-10 16:59:32

Re: Entanglement Question

Trak wrote:

#3 2005-08-10 17:18:55

Re: Entanglement Question

#4 2005-08-10 18:14:02

Re: Entanglement Question

Board footer