Thought experiment:

  1. Entangle a pair of particles.
  2. Package one half of each pair in a special package, and send it out in a nano-spaceship
  3. keep the other half of the pair of entangled particles here on earth
  4. accelerate nano-spaceship to 99.99999999999999% of the speed of light using a number of tiny cyclotrons

Due to Lorentz contraction,

$$ L = L _\text{0} \sqrt {1 - \frac {v^{2}}{c^{2}}} $$

In one years time, the spaceship would have traveled 93B ly away from us.

After one year of travel, the spaceship could be preconfigured to detect the CMB in the direction of travel, and then trigger their quantum entangled particle to send a '0' or a '1' depending on whether the CMB was detected.

Repeat this process using any number of spaceships in any number of directions, and soon you would experimentally show how big the universe really is.

Any problems?


marked as duplicate by Pulsar, rob May 16 '18 at 3:32

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  • $\begingroup$ The cosmic microwave background can be detected right here on Earth. $\endgroup$ – D. Halsey May 15 '18 at 23:58
  • $\begingroup$ The basic mistake in the thinking is that it is a classical proposal, not a quantum mechanical one. example : "package 1/2" . The act of packaging means interactions, interactions means breaking of entanglement because a new quantum mechanical state is involved. $\endgroup$ – anna v May 16 '18 at 4:22

Except sometimes in science fiction, entanglement doesn't work that way. Entanglement depends on indeterminacy. Entangled particles have a correlated property such as spin orientation, but that entanglement depends on the spin orientation of neither particle being known at the outset. Later, we can measure the spin orientation of one particle and it will tell us the spin orientation of the other (as long as nothing has perturbed either particle in a random way in the meantime). So (absent perturbations) an instrument on the spaceship could measure the spin orientation of the particle it's carrying, and then it would know the orientation of the particle left behind on Earth. But the instrument on the spaceship cannot specify the orientation of its particle; it can only measure the orientation. So, no information can be transferred across time or space via the entanglement and measurement.


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