Manufacturing the present in Relativity theory
  • Ben St Clair
    2
    According to QM the moment one entangled particle is measured the other's orientation or measured properties are determined by the measurement of the other, instantaneously.

    According to Relativity there is no present moment because there are only different frames of reference in which time can run slower or faster relative to each other.

    The scenario:

    Imagine a rocket ship departing earth. on earth there is one entangled particle, on the ship there is another. If one hour passes after departure on earth and we measure the earth entangled particle (eep) then since time is slower on the moving rocket ship only half an hour has passed there in the earth frame of reference. Does this mean that the ship entangled particle (sep) has its properties determined half an hour earlier than the eep. If not then it seems that the determination of the sep's properties is not instantaneous in one frame of reference as QM states it should be.

    On the other hand if we consider ourselves correct in that the sep is determined half an hour early so it is instantaneous in the earth frame of reference then there are problems when we swtch to the ship's frame of reference. according to the ship the sep is determined when only 15 mins has passed on earth!

    How do we resolve this seemingly paradoxical situation? how can two events be said to be instantaneous in QM when relativity states there is no universal present moment?

    I'm not a student. just someone interested in the science.

    Thank you in advance for your answers I'll answer as many of you as I can.
    Ben St Clair Options
  • noAxioms
    1.5k
    According to QM the moment one entangled particle is measured the other's orientation or measured properties are determined by the measurement of the other, instantaneously. — Ben St Clair
    QM says nothing of the sort. QM simply predicts that the two measurements will correlate when compared at a later time.

    Anyway, yes, relativity denies the arbitrary simultaneity and simply says that the ordering of the two measurement events (assuming both are measured) is ambiguous if the events are outside each other's light cone. Other experiments blatantly appear to 'change' the past based on a future decision, altering measurements taken unabiguously in the past of some decision event.
    noAxioms Options
  • SophistiCat
    2.2k
    According to Relativity there is no present moment because there are only different frames of reference in which time can run slower or faster relative to each other. — Ben St Clair

    And to add to what @noAxioms said, you seem to be confusing eternalism, which the theory of Relativity does not assert, with relativity of simultaneity, which it does. But for your question, relativity of simultaneity is what you actually need, so no harm done.
    SophistiCat Options
  • Ben St Clair
    2
    QM says nothing of the sort. QM simply predicts that the two measurements will correlate when compared at a later time. — noAxioms

    I was under the impression that Bell's inequalities showed that the indeterminacy of the particles properties was a real aspect of nature and that the measurement of one effects the measurement of the other. These measurements can take place within an interval of time in which light is not fast enough to travel between them in order to relay the information.

    What you appear to be saying is that we cannot speak of one measurement 'causing' the other measurement to be a certain way. At least that is what I infer from what you've said. But isn't it implicative in what you said that some real event takes place by which the measurement of one entangled particle affects the measurement of the other at some point, or across some very minute interval, of time? This is an assumption that you seem to be avoiding and yet would logically be expected.

    After doing a bit of research there's this experiment wherein retrocausation appears to occur and is why, I suspect, there's a reluctance to use causation in relation with entanglement - the delayed choice quantum eraser experiment. This happens without any input from relativity. It's interesting because in some way the state of the particle's superposition is itself in a state of superposition with non-superposition of the particle. The problem might be resolved if you think of the particle hitting the screen as the measurement that decides the path of the other entangled photon?

    And to add to what noAxioms said, you seem to be confusing eternalism, which the theory of Relativity does not assert, with relativity of simultaneity, which it does. But for your question, relativity of simultaneity is what you actually need, so no harm done — SophistiCat

    Sorry, I meant to say no universally present moment.
    Ben St Clair Options
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