# Why does my thought experiment involving entanglement appear to violate the speed of light?

I have a thought experiment that "seems" to allow messages passed at faster than the speed of light. Since that is impossible I'd like to learn what is wrong with my experiment/reasoning. Start with the classic setup where 2 particles (spin up and spin down) are entangled and then sent in opposite directions to locations A and B (possibly even light years apart). Now picture an ensemble of these (each pair is independent of the other pairs). If no observations (measurements) are made at location B then there must be results of measurements at location A that demonstrate superposition, and these results must look different than if observations were made at location B. So now picture an ensemble sent out every second and measurements (which won't start until the first emsembles reach A and B) are made also every second. Now to send a message from B to A one just needs, for each ensemble arriving at B each second, to either observe the ensemble (call it bit '1') or not observe (bit '0'). Then, simultaneously, at A, one just needs to do measurements to determine if each incoming ensemble is in superposition states or not. If superposition then bit='0', if not, then bit='1'. Since the sending and receiving of the messages is simultaneous there is the violation of the speed of light.

• “one just needs to do measurements to determine if each incoming ensemble is in superposition states or not” there is no such local measurement – Dale Dec 9 '18 at 16:56
• Then what action or change is there when they refer to "spooky action at a distance"? If you observe up at B then of course you will observe down at A. How is that different then the particle going to A had always been in the down state. I apologize for my ignorance on this. – steve k Dec 9 '18 at 19:27
• If you do a measurement at A then you have a 50:50 chance of getting spin up or down. Nothing at B changes that. Later if you get a list of measurements from B you will see that they were perfectly anti correlated. That correlation is the spooky action but it conveys no information regardless of what is measured on either side. – Dale Dec 9 '18 at 20:42
• Thanks. I think I see the spooky action now. Both particles are in their own superposition and thus prior to measurement are not in determined (but unknown) states. But they are also "connected" in the sense that when the measurements are made at A and B the results are anti-correlated. Is that correct? – steve k Dec 9 '18 at 21:53
• But there's still one more question I have. Since each particle is in a superposition of up and down, why doesn't an ensemble yield, with the right setup, an interference pattern? – steve k Dec 9 '18 at 21:56

If no observations (measurements) are made at location B then there must be results of measurements at location A that demonstrate superposition, and these results must look different than if observations were made at location B

no they don't look different

• Then what action or change is there when they refer to "spooky action at a distance"? If you observe up at B then of course you will observe down at A. How is that different then the particle going to A had always been in the down state. I apologize for my ignorance on this. – steve k Dec 9 '18 at 19:27
• Bell's inequality show you the difference – Manu de Hanoi Dec 10 '18 at 1:10