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Comment on Did the premise of an entity approaching you only when it's not being viewed originate with Doctor Who's Weeping Angels?

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DarkGamer@kbin.social ⁨4⁩ ⁨months⁩ ago

it’s still the act of measurement, not the act of a conscious person looking at that measurement, that causes the collapse of the wave function.

That's not the case here; when particles are measured but the information erased/nonrecoverable it remains a wave:

what makes this experiment possibly astonishing is that, unlike in the classic double-slit experiment, the choice of whether to preserve or erase the which-path information of the idler was not made until 8 ns after the position of the signal photon had already been measured by D0.

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hperrin@lemmy.world ⁨4⁩ ⁨months⁩ ago
That may not be the correct way of saying it. You can equally explain the data by phrasing it, “when the photon remains a wave, the which path information is nonrecoverable.”

Moreover, it’s observed that the apparent retroactive action vanishes if the effects of observations on the state of the entangledsignal and idler photons are considered in their historic order. Specifically, in the case when detection/deletion of which-way information happens before the detection on D0, the standard simplistic explanation says “The detector Di, at which the idler photon is detected, determines the probability distribution at D0 for the signal photon”. Similarly, in the case when D0 precedesdetection of the idler photon, the following description is just as accurate: “The position at D0 of the detected signal photon determines the probabilities for the idler photon to hit either of D1, D2, D3 or D4”. These are just equivalent ways of formulating the correlations of entangled photons’ observables in an intuitive causal way, so one may choose any of those (in particular, that one where the cause precedes the consequence and no retrograde action appears in the explanation).

The total pattern of signal photons at the primary detector never shows interference (see Fig. 5), so it is not possible to deduce what will happen to the idler photons by observing the signal photons alone. In a paper by Johannes Fankhauser, it is shown that the delayed choice quantum eraser experiment resembles a Bell-type scenario in which the paradox’s resolution is rather trivial, and so there really is no mystery. Moreover, it gives a detailed account of the experiment in the de Broglie-Bohm picture with definite trajectories arriving at the conclusion that there is no “backwards in time influence” present.[23] The delayed-choice quantum eraser does not communicate information in a retro-causal manner because it takes another signal, one which must arrive by a process that can go no faster than the speed of light, to sort the superimposed data in the signal photons into four streams that reflect the states of the idler photons at their four distinct detection screens.[note 2][note 3]

But more importantly, you will get the same results regardless of whether a human being is there to observe it. It’s the detection of the photon (by way of interacting with the photon detector) that matters, not whether there is a person there to observe the detection.

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