Does quantum entanglement imply faster than light communication? (Intermediate)

You seem quite convinced that information cannot travel faster than light.

However, as I read it, I clearly remembered an article sent out by NASA, which describes the possibilities and exciting consequences of the property called entanglement. Do you and your fellow colleuges simply not believe in it, or is this a new result which will change our interpretation of relative physics?

Great question! Quantum entanglement is a really interesting phenomena and one that we all enjoyed worrying about in our quantum mechanics and relativity classes!

The way people get around the idea that entanglement implies instantaneous communication is that no actual information is passed when the entangled particles affect each other. The argument is as follows (using a non-QM example):

Say you agree to send out two beams of light to your two friends who live on opposite sides of the galaxy (you live in the middle). Ahead of time you tell them that if one of the beams of light is red the other will be blue. So you send the blue beam to your friend on one side and immediately she knows that your other friend is receiving a red beam at the same time. Aha! You say, my friends have now communicated at a speed faster than the speed of light and violated relativity, but no real information has been passed between them. You have told both of them at a normal sub-luminal speed about what you just did and that's all. (A way of proving there's no faster than light communication is that you could lie and send them both the same coloured beam of light and they would never know!).

With QM is gets a bit more complicated because theoretically no-one knows the state of the particle until it has been observed, but you still cannot affect the state of the particle so the argument is the same.

There is a nice article about this stuff here which talks about the EPR (Einstein-Podolsky-Rosen) paradox. Einstein and his colleagues were very uncomfortable when they heard about quantum entanglement and devised the EPR paradox to 'prove' that it couldn't be true (meaning that while you hadn't observed the particle yet it still has a state). It was proved in one line of algebra that this idea of "hidden" variables couldn't be true.

As I said above though, quantum entanglement still does not imply faster than light communication. You cannot affect which state the particle goes into, even though it doesn't 'decide' on its state until you observe it.


About the Author

Karen Masters

Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.

Twitter:  @KarenLMasters

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