Two entangled particles. Particle A is in the pocket of a man who is 10 billion light years away from Earth, and he walking away from Earth (so according to Lorentz transformation in his time it is 150 years into the past on earth). He measures the particle spin. Would we have seen the entangled particle on earth with the same spin 150 years ago? Is it that simple? And if we had seen that particle 150 years ago, we could predict the spin of the far away particle.

  • $\begingroup$ Suppose I have two marbles, one blue, one red. I choose one at random and, without looking, give it to my friend, who promptly flies to another continent (or, if you like, to the Andromeda Galaxy). By looking at the marble I have, I can instantly predict which marble my friend has, no matter how far away he is. No quantum weirdness involved at all, they're just ordinary marbles. Where's the paradox? $\endgroup$ Jan 5, 2020 at 23:18
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    $\begingroup$ Essentially, you can't just declare that two entangled particles exist. How was the entanglement created, and how did Particle A subsequently get into the faraway man's pocket? $\endgroup$ Jan 5, 2020 at 23:20
  • $\begingroup$ @probably_someone this is a question about timing of simultaneous events. Can two simultaneous events occur 150 years apart because of Lorentz transformation? $\endgroup$ Jan 5, 2020 at 23:47
  • $\begingroup$ Which two specific events did you have in mind? Also, keep in mind that whether two events are simultaneous depends on your reference frame - if two events are simultaneous in one frame, they won't necessarily be simultaneous in another frame. $\endgroup$ Jan 5, 2020 at 23:50
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    $\begingroup$ Let us continue this discussion in chat. $\endgroup$ Jan 6, 2020 at 0:15

1 Answer 1


Based on the discussions and chats, my original supposition was incorrect. The correct interpretation is that in the Earth time frame for me, it is January 6, 2020. In the spaceman's time frame on the far away planet, for him, it is January 6, 2020. But in the spaceman's time frame, once he starts walking he would consider that, on Earth, it is 150 years ago in 1870. Regardless of this, when we both open our box on January 6, 2020 in our own time frames, the particles would be in sync.


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