[halfcat]

> unlikely to make a meaningful difference at distances measured less than how far light travels in that time

PBS Space Time did an episode that posed the question as a delayed choice quantum eraser experiment where the “long” leg is farther away, like on the moon, and we somehow reflect a particle back and forth to delay the observation indefinitely. I also wonder if they can do something like this at CERN.

Their conclusion was, it would be possible theoretically, but you wouldn’t be able to read the result.

The sci-fi enjoyer part of me likes to believe CERN is a big delayed choice quantum eraser experiment used to receive messages from the future.

[elcritch]

I'm reading (well listening to) a sci-fi novel based on that premise called "Quantum Radio". Pretty classic techno-thriller, complete with shadowy organizations. I really enjoyed the premise and setup of CERN data being used as a quantum radio reading messages from the future, or perhaps parallel universes.

[pmontra]

This one? [1]

Beware, it's a review so there are possible spoilers.

[1] https://sfbook.com/quantum-radio.htm

[elcritch]

Yep, that’s it.

[dheerajvs]

Hasn't the supposed weirdness of the delayed choice quantum eraser experiment been debunked? Can someone in the field please confirm? I find contradictory videos on YouTube.

[nyssos]

Depends on what you mean by "weirdness". Whether you see interference really does depend on which axis you choose to measure along, but it's not because you're sending signals backwards in time. The electron was in a superposition of interfering and not interfering all along: the delayed choice is just choosing which component of that superposed state you want to measure.

[tobiasSoftware]

The delayed choice quantum eraser is misunderstood (even by PBS Spacetime) to invoke time travel/retrocausality. The truth is that the pattern seen on the screen is the same whichever set of detectors you send it to, and as such, there is no evidence of time travel.

The more plausible explanation behind the delayed choice quantum eraser involves Heisenberg's Uncertainty Principle, which states that you cannot obtain position and momentum to a high degree of accuracy at the same time. Einstein's EPR paradox "proved" quantum physics incorrect by setting the Uncertainty Principle against Entanglement. He did this by a thought experiment that entangled two particles, and measuring the position of one and the momentum of the other to thwart the Uncertainty Principle.

The delayed quantum choice eraser is a realization of Einstein's thought experiment. However, what Einstein didn't realize was that while the standard double slit experiment produces a pattern at the screen that gives you the momentum information, entangling two particles creates a different pattern at the screen that causes the particles by themselves to give neither momentum nor position information. The delayed quantum choice eraser initially recovers the position information by combining information from both particles, but by choosing the other set of detectors you can "give up" that information to gain the momentum information. Either way, you are still unable to obtain both pieces of information at the same time.

Source: I am writing a book on Quantum Physics and have spent months doing research and finding out that even many quantum physics Youtubers routinely say misinformation. By far the worst is the incorrect idea that a which-way detector on the double slit experiment will produce two bands as if the particles are marble-like. It doesn't, it destroys the interference pattern, producing a single slit pattern. This sounds like a minor detail, but it contains the realization that quantum physics particles ALWAYS act like waves, even after a measurement, and wave-particle duality is a misnomer.

[mjan22640]

Have a look at time double slit, a spot in a material being made transparent twice in a quick succession. A photon travels through both and interferes, ie the future interfes with the past, and the Feynman path integral encompasses also paths through time.

[nyssos]

> The more plausible explanation behind the delayed choice quantum eraser involves Heisenberg's Uncertainty Principle, which states that you cannot obtain position and momentum to a high degree of accuracy at the same time.

This is not what's going on: uncertainty principles are a generic feature of wave mechanics, quantum or classical. Delayed choice quantum eraser experiments are just an ordinary case of entanglement.

> I am writing a book on Quantum Physics and have spent months doing research and finding out that even many quantum physics Youtubers routinely say misinformation.

I strongly suggest you work through a quantum physics textbook first. Griffiths is a standard choice: the interpretational aspects leave a lot to be desired, but that's unfortunately unavoidable in introductory texts. You're right that physics youtubers have no idea what they're talking about - but frankly if that surprises you then you're really not ready to filter out the garbage on your own.