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Let's imagine the following thought experiment,

Two particles, A and B are entangled on the Earth. As decided, Alice (a friend of Bob) stays on the Earth with the A and Bob travels with the B to a light years distant planet named X. There was a contract between Alice and Bob that, at some point of time in future if Bob finds the B's spin in UP direction, he will destroy the planet X otherwise he won't. Now, at the point of time in future, when Alice measures the A's spin and finds it DOWN that instantaneously means Bob is destroying the planet X (because, Bob finds B's spin UP).

Now, for particularly this thought experiment, it appears to me that, Alex is receiving the information that "Bob is destroying the planet X" faster than light speed. What am I missing?

Note: as a newbie to the field of quantum physics, I might be missing very basic stuff. Nevertheless, I am requesting to audience to suggest me to improve my query if it has any area of improvement before downvoting/closing the post because, this questing the really genuinely sticking my head.

Sazzad Hissain Khan
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1 Answers1

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The answer lies in the definition of information. If Alice measures its particle in the "up"state, she knows that Bob's particle is in the "down" state. However, this is not considered to be information. The idea of saying that information can not travel faster than light contains the concept that only one person knows something, and that this information is communicated to a second person. Therefore, even if Alice and Bob agree that Bob performs a definite action depending on the outcome of his experiment, e.g.

  • if Bob obtains "up" in his measurement, he will destroying the earth, and
  • if Bob measures "down", he will destroying the sun,

Alice does not gain any new information by taking the measurement. The communication of the information, which experimental result has which consequence, took place before the measurement was performed. Alice and Bob simply correlated the faith of an object to a random event. The fact that the result of the measurement is random incorporates the "informationless property". If Alice and Bob measure a sequence of entangle particle pairs, each observer obtains a random sequence. The fact that the two random sequences are correlated does not change the fact that each sequence is random.

In order to communicate information between Alice and Bob, one of them has to imprint his/her information onto the particle. However, if Alice manipulates her particle to be definitely in the "up"-state, and then performs her measurement, the entanglement between the two distant particles is lost. While Alice measures her particle in the "up" state, Bob measures his particle in an arbitrary state, and not necessarily in the "down" state. Therefore, by loosing the entanglement the correlation of the two measurements was lost. Again, no information is communicated.

This considerations also apply to the so called weak measurements. Unfortunately, Physics does not provide "free lunches".

NotMe
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