PBS Space Time explains the quantum eraser experiment, in which erasing which-path information appears to reverse causality in a double-slit setup. It discusses what this means for quantum mechanics.
Why Hacker News points people here: HN recommends it as a quick introduction to the quantum eraser and delayed choice weirdness, though one commenter notes later corrections to its framing.
“a quick video from space time for those being first introduced”HN comment, 2019
“if you'd like to know more about this experiment and why it has ridiculous implications, check this PBS clip”
Explains the quantum eraser experiment and its implications.
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One of the more head exploding experiments I've seen regarding entanglement is this one: link By all apparences, it seems to violate causality. It's one of those things that make you suddenly stop and bemusedly wonder if maybe we've finally found a kludge in the Universe's code. edit BTW, if you'd like to know more about this experiment and why it has ridiculous implications, check this PBS clip: this video
RecommendscomboyMar 2019
“Also not directly related video if you like your mind being blown”
Mind-blowing video about quantum weirdness.
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Here's a dumbed down version: link Also not directly related video if you like your mind being blown: this video Especially given how our understanding of the world changed during the last 200 years, I would say we are still very much clueless. I find that exciting. Btw, no idea why did researchers get "freedom of choice" involved.
RecommendsmitchtyOct 2019
“a quick video from space time for those being first introduced”
Quick introduction to the quantum eraser for newcomers
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Indeed, a quick video from space time for those being first introduced. It’ll likely make you even more confused to the double slit experiment. this video
RecommendsmbellFeb 2020
“See the Delayed Choice Quantum Eraser experiment for even more weirdness, a good video on it”
Good explanation of the delayed choice quantum eraser experiment
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If you place a detector in front of (or behind!) the slits the wave function collapses and there is no interference pattern. This is all part of the mystery of it, as soon as you 'observe' a particle, in any way, it stops acting like a wave. See the Delayed Choice Quantum Eraser experiment for even more weirdness, a good video on it: this video
Cites itcomboySep 2019
“we still seem to have a lot to learn about how time and causality works”
Shows we still have much to learn about time and causality.
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Not sure if it's the first time, we still seem to have a lot to learn about how time and causality works: this video
Cites itSchoolmeisterOct 2019
“as demonstrated by e.g. the quantum eraser experiment [1][2].”
Quantum eraser cited as showing one thing after another is abstraction.
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> Exactly. I don't know why Haskell fanboys insist on abstracting us so far from the machine. I believe it is because abstractions are the way we have always made progress. Is the C code that's so close to the machine not just an abstraction of the underlying assembly, which is an abstraction of the micro operations of your particular processor, which in turn is an abstraction of the gate operations? The abstractions allow us to offload a significant part of mental task. Imagine trying to write an HTML web page in C. Sure it's doable with a lot of effort, but is it as simple as writing it using abstractions such as the DOM? > We live in a mutable physical universe that corresponds to a procedural program. One thing happens after another according to the laws of physics (which are the procedural program for our universe). You just proved why abstractions are useful. "One thing happens after another" is simply our abstraction of what actually happens, as demonstrated by e.g. the quantum eraser experiment [1][2]. [1] link [2] this video
Cites itelcritchMar 2024
“The quantum erasure experiment is to my mind the best example of the spooky action at a distance.”
Cited as the best example of spooky action at a distance
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> One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. > I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. The quantum erasure experiment is to my mind the best example of the spooky action at a distance. The outcome of the particle pairs is measured after the entanglement occurs implying not just "spooky action at a distance" but also in time. this video
CriticalcalnyFeb 2025
“PBS Spacetime did an interesting video on DCQE, but it tripped me up trying to fully understand what was happening”
Video's rewriting-the-past claim was later debunked and retracted by host
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PBS Spacetime did an interesting video on DCQE, but it tripped me up trying to fully understand what was happening: this video ... Later Sabine Hossenfelder did a video debunking the proposition that DCQE somehow showed that the past was being rewritten. link And Matt from PBS Spacetime acknowledged she was right in this respectful comment: > Sabine, this is amazing. You are, as usual, 100% right. The delayed choice quantum eraser is a prime example of over-mystification of quantum mechanics, even WITHIN the field of quantum mechanics! I (Matt) was guilty of embracing the quantum woo in that episode 5 years ago. Since then I've obsessed over this family of experiments and my thinking shifted quite a bit.
