Proven in Quantum Physics when two particles become entangled, the spin of one directly correlates with the spin of the other. Is this possible on a larger scale with the spin of planets? Could earth be entangled with another planet?

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    "Spin is a solely quantum-mechanical phenomenon; it does not have a counterpart in classical mechanics (despite the term spin being reminiscent of classical phenomena such as a planet spinning on its axis)." (See Wikipedia.) – user3164 May 20 '13 at 7:12
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    This question is better suited to Physics.SE, though I don't think it will be a popular question there. – Niel de Beaudrap May 20 '13 at 11:06
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    This is a physics question, but not suited to Physics.SE. Just read a Scientific American article about entanglement. They cover stuff like this every year or so. – Rex Kerr May 20 '13 at 14:38

This more on the lines of an extended comment than an answer.

You should ask it in Physics.SE, they're not likely to appreciate how you've put it though. It's definitely a good question. It was after all, historically speaking, the spin of planets and of any macroscopic object that inspired the idea of QM Spin.

But you can reverse the question and ask whether there is an aggregate QM Spin of particles in the same way say you can add together the angular momentum of particles - not spin itself. You may want to confirm at least this on Physics.SE. I expect it is - since it will probably be subject to some conservation law.

Entanglement has been demonstrated practically on very small macroscopic scales. But the question is would it scale to planetary distances and planetary sizes. I expect theoretically yes. In that the similar mathematical reasoning will go through. But I expect it physically not - due to the meaning of infinite precision. That is there are likely to be some extremely small numbers entering the calculation - and one has to be careful as to the physical meaning of them.

Philosophically its a subtle question as it directly includes the interpretation of QM. What would entanglement mean in the instance the observer was on one of the planets?

  • That last paragraph is, IMO, plainly false. I suggest sticking with your comment (already there!) and removing this "answer". :) – user3164 May 20 '13 at 16:37
  • @Gugg: You care to say why its false? – Mozibur Ullah May 20 '13 at 16:48
  • @Gugg Indeed it is complete nonsense. If something is understood to be physically not possible, then any in theory which says it is possible is wrong and would be discarded. It's a cognitive dissonance to have both simultaneously. (By the way, entanglement has been clearly observed on macroscopic scales in a variety of experiments.) – David H May 20 '13 at 16:48
  • @MoziburUllah Google "macroscopic entanglement". But really, we shouldn't have this discussion here. – user3164 May 20 '13 at 16:51
  • @Gugg: I don't see how that contradicts what I've said. I've have altered what I said to be more careful about the difference between small macroscopic and large macroscopic. – Mozibur Ullah May 20 '13 at 17:08

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