![]() Textbook quantum theory holds that the interaction between particles is instantaneous. If this is indeed the case, relativity is safe. But physicists expect that what happens between entangled particles can't be harnessed for true communication, essentially because there is no way anyone can control the "messages", or influences, that pass between particles. ![]() What relativity forbids is faster-than-light communication. This seems to put quantum theory in conflict with relativity, but there is a subtlety which irons out the tension. But according to Einstein nothing, and that includes information, can travel faster than light. Experiments have shown that the messages that pass between particles would have to travel more than 10,000 times faster than light. The second explanation gets into trouble with Einstein's theory of relativity. But both theory and experiment have shown, time and time again, that the inequality doesn't hold: nothing in the past can have determined the particles' properties at the time of measurement. He showed that if the behaviour of two entangled particles were down to a past cause, then measurements of their properties would have to satisfy a particular inequality, now called Bell's inequality. The first explanation was ruled out in the 1960s by the physicist John Bell. The other is that the two electrons are communicating with each other, sending messages that travel so fast that the interaction appears instantaneous. One is that something in the past, some cause we have not yet discovered, determined what the spin of the two electrons was going to be. There are two common sense explanations for what is going on here. (For another example of entanglement and Einstein's criticism of it see this article.) It's a strange effect, but it has been demonstrated in the lab many times. Now if you measure the spin of one of two entangled electrons and find it pointing up, then immediately the spin of the other, if measured, will be pointing down, no matter how far away it is. When you measure the spin of an electron you will find it pointing either up or down. An example is a property of electrons called spin. Have once interacted can remain linked even when they are Image: Timothy Yeo, Centre for Quantum Technologies at National University of Singapore.Įinstein's "spooky action" shows up when we are dealing with so-called entanglement: two particles that The observation and confirmation of the fact takes place retrospectively - but this doesn't detract from the fact that the wavefunction will be demonstrated to have collapsed simultaneously across a vast distance - something is acting on them at faster than light speed.Spooky action at a distance. Particle A observed on Neptune at midday will have the same state of spin as Particle B observed at an equal time on Earth. Information from Spaceman A cannot be sent from Neptune to Earth at faster than light.īut - my question is - who cares about spaceman - or any conscious entity sending information -the fact is the entangled particles themselves are affected at faster than light speed. So, Spaceman A on Neptune, cannot send a morse-coded message to Earth using quantum entangled particles - the need to force a particle to choose a state releases the entangled particle at the other end from behaving (instantaneously) in a determined matter. I understand that the Bell Paradox - and non-locality - prevents information being exchanged in a faster than light matter. So, don't be fooled by the title of my question.
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