Double-slit experiment holds up when stripped to its quantum essentials
12 comments
·July 31, 2025habibur
Uehreka
I don’t have a source to hand at the moment, but when I looked into the famous Delayed Choice Quantum Erasure experiment the consensus seemed to be:
- The double slit experiment’s conclusions still hold, but:
- The particularly exciting and stark results of the Quantum Erasure experiment may have been misinterpreted or miscommunicated to the public, in particular:
- The presenter of PBS SpaceTime has said that he regrets certain things about how he worded his video on the Quantum Erasure experiment, and I think may have left a comment on the video to that effect.
Every time I look into QM, I keep coming back to the same fundamental axiom: “Quantum Mechanics’ weirdnesses can make otherwise straightforward things frustrating, but will never make interesting inventions possible.” Like how entanglement is able to break locality (which is frustrating) but without breaking causality (which would be interesting). If you hear about a quantum principle and think “Wow, I could use that to build X,” then it’s more likely that you’re not fully understanding the principle (not “you” specifically, I’ve fallen for this myself countless times).
The only exception seems to be Quantum Computing, but even that only arises out of a deep deep mathematical analysis (you can’t get to QC on your own from the things in popular science books) and is only applicable to really niche applications.
naasking
Entanglement doesn't violate locality, it's measurement that does that. And that's because we don't have a rigourous handle on what measurement actually is, and why we call it "the measurement problem"!
justonceokay
My understanding is that this “temporal fuckery” (I’m not a physicist) exists even in the basic math of light diffraction. When light passes from air to water, it somehow “knows” the right angle to diffract at to reach its destination as fast as possible, even though from a classical viewpoint the destination is not known until after the light has passed through the medium.
The short story “Story of your life” (that the movie Arrival is based on) uses this as a pseudo-argument for how the aliens could have a non-temporal understanding of reality.
Strilanc
The standard explanation for light "knowing" the angle of diffraction is that actually light just propagates in every direction and then constructive interference is stronger for paths near the shortest path because its length is more consistent when the path is perturbed (meaning the phases of the perturbed paths tend to agree more so they add up instead of cancelling). I don't think you even need quantum mechanics for this; it occurs in classical wave optics.
You can see Feynman explaining mirrors this way in recorded lectures [1]. There's also a recent Veritaseum video explaining why the shortest paths dominate [2].
tsimionescu
That only works with quantum mechanics - it's a consequence of the "path integral" idea of QM. In classical optics this wouldn't work, because you'd be able to detect light on the other paths if it really did take all paths.
naasking
I don't think this "standard explanation" is as standard as it has been portrayed:
renox
> I am more interested in its explanation, now that the theory has been proven correct again and again.
What do you call an explanation? An interpretation of QM? There are dozens but none are especially satisfying..
As for the 'delayed choices' IMHO it is a poor interpretation of the data: see https://www.youtube.com/watch?v=RQv5CVELG3U for example.
briffid
I don't get the point. The article says that if you "somewhat" measure, then you lose "somewhat" from the wavelike nature. So the photon is a wave by X%, and a particle by 100-X%?
moktonar
The simulation rolls back to match the constraints, easy
I am more interested in its explanation, now that the theory has been proven correct again and again.
Especially interested in "delayed choice quantum erasure experiment", where you decide to determine the "which path" after the photon has passed through the slits and hit the detector. And depending on your later decision the photon seems to rewrite history going back in time.