The non-quantum delayed choice eraser

A classical analogue of the delayed choice quantum eraser sheds light on common misconceptions about the experiment.

References:

(0:00) Introduction
(1:28) Key elements of experiment
(3:42) Step by step breakdown
(5:44) The missing element
(7:34) Conclusion

[francescoromano]

Best explanation, even better than Sabine's, and that is really something!

[robwood]

The problem that I have with this explanatory video is that, first, you provided an analogous classical demonstration to show how an analogous 'interference pattern' can be produced with coins and a dice. All well and good, and it makes sense and is well explained. Unfortunately, you then move on to the quantum experiment, spend minimal time on it and basically just say "it works like the dice and the coin". Surely here you should spend twice as much time to explain how the entanglement is paralleled in your classical explanation, how the causality violation is an illusion, and so on. I'm not denying that all that information is implicit, but if you want to convince then you need to put more time into the second section of your video. It may be obvious to you, but not necessarily to your audience.

[cstuart]

An appropriate analogy would be shooting two bullets from one gun, one bullet hits a target first, the second bullet hits a deflector that has a 50% probability of letting the bullet continue to hit a target in a straight line OR deflect the bullet at an angle to another target, yet the first bullet always hits one specific point on the first target when the second bullet goes straight and always hits a different specific point on the first target when the second bullet is deflected BEFORE the second bullet even reaches the deflector; this correlation is impossible in physics and has been experimentally proven countless times in quantum mechanics.
The fact that a point in a pattern for a single detector hits the screen BEFORE the entangled pair particle has reached any detector, while it still has a probability of hitting EITHER a detector that indicates which slot it went through (particle pattern) OR hitting a detector that erases the information of which slot it went through (wave pattern of particle interfering with itself), which means that either it was predetermined which detector it would hit before it actually hit it OR that after it hit a detector it influenced the point on the screen backward in time; there are no other options or explanations how the point on the screen is formed before the entangled pair particle hits a detector and it's always at the corresponding point on the screen for the detector that it eventually hits.

[EspritBerlin]

Thanks for the video! Just saw Sabine H's video about this topic. Good explanation, thanks for demystifying.

[fischX]

The biggest problem with your video is that you actually did not understand how the experiment works and at what point you change the measurement. So you try to explain a experiment you don't understand and talk about something different. It's not oversimplified it just plain wrong.

[rickhewitt]

Just was answering some questions about this video to some other people. I would say that although I definitely see what you're saying and I'm not saying you're wrong, I will say that the "filtering" of data that you suggest here might imply (to some) that wave-particle duality isn't a thing and muddy the concept a bit. This is of course more of a before/after probabilistic look, but some nuance there might help. Your conclusions are obviously correct though, and should at least communicate the key results to viewers.

[loriwan]

Thank you! I read 2 articles and watched 3 videos trying to explain this experiment in a non-retrocasality way, this is the only one that made me understand!

[alexritchie]

If the Universe had retro-causality, surely it would never actually reach the point of being able to do anything? Every discrete action, observed or not, would be constantly altering its outcome of varying probabilites in the past, and so no discrete events would happen, meaning the Universe would remain static and 'timeless'. Am I correct or just spitballing?

[harliethomas]

Brilliant, I am going to need to ponder this much much more.

[davidsansom]

Great video well explained classically and quantumly useful correlated for wave and useless garbage for no wave depending on how data is filtered after.

[johnshillsburg]

Wow thanks so much for this video. I knew there was a problem fan Bois on the internet must be overlooking and that classical example with the dice and coin explains it perfectly

[toomanydonuts]

This guy knows nothing about quantum mechanics. BS

[bakshiavijit]

Despite a good attempt, the video does not explain away the central mystery of quantum delayed choice eraser experiment, . Suppose we have detector-screen D0 at the writers end where, for certain subsets of 1st twin photons, we either see ripply, or see smooth pattern. A light year long arm away we have the "choosers end" where we actually have 4 people - Riley and Ron who always see Ripply pattern formed, and Sam and Saloni who always see a Smooth pattern form. For the subset of all 2nd twin photons that reach Riley (or Ron), the correlated subset of 1st photons at D0 always show a ripply pattern (imprinted a year ago). Likewise for the subset of all 2nd twins reaching Sam (or Saloni), the correlated 1st twins make a smooth pattern at D0. The mystery remains, what is it about the 2nd twin photons ontology, that a year later it somehow knows where to go: either to Riley/ Ron OR to Sam/Saloni, in a perfect correlation with patterns at d0 that were imprinted a year earlier. How do 2nd photons know whether to go to Ripplers or to Smoothers? What property or variable is making it choose? Retro-causality may not be the explanation, I agree, but the mystery remains and no one surely understands what else explains the mystery. Anyone claiming they explained away the mystery in delayed choice eraser experiments, actually don't understand it yet.

[KharBrons]

I believe you have your results flipped concerning the "shake" and what results were being recorded. In the Kim et al paper, by "shaking", or mixing the photons from Slit A and Slit B back into the same detectors (D3 / D4), they were recording an interference pattern (ripply group). When they didn't "shake" the data and kept Slit A and Slit B information separate (D1 / D2), they were recording a diffraction pattern (smooth group). Detectors 1-4 were positioned using 2.5m of additional fiber cable than the control detector (D0), so D0 was recording its initial mixed signals 8 nanoseconds prior to D1-4 receiving signals.

With the data and charts shown in the Kim et al (1999) paper, looking at the homogenized data of D3 and D4 would show peaks and troughs indicative of a wave interference. In your video you describe this as "missing data", even though its comprised of all data points from both slits. I suppose the best way I could describe it using your analogy would be if you were to shake the coin box and only ever get heads, resulting in a ripply sample.

I'm assuming you're likening Slit A to odd dice rolls and Slit B to even dice rolls, where D3 / D4 are both giving all total dice rolls, D1 is giving Slit A's rolls and D2 is giving Slit B's rolls. This can be simplified by just looking at D1 (Slit A) and D3 (Both Slits). In the Kim et al experiment, D3 (both even and odd results) would be presenting only even or odd dice rolls, but not both, and D1 (odd rolls) was presenting both odd and even results combined. Hopefully you can see both how the analogy breaks down and the results are counterintuitive when you look at the actual results of the paper.

[god_damn]

the most funny thing is: most of the channels you mention above nobody from them performed the experiment!!!
most of the vids about quantum eraser experiment (like most of other vids on YT) are from second, third and four hand

Sabine Hossenfelder has a video debunking the experiment!!!🤘

[MikeBUSA]

I'm sure the entire physics community has missed a video with 357 views that invalidated the works of Wheeler and Kim. A few more views and should you get a wing built at MIT in your name. Here's your mistake - Bob always writes down his data and keeps it. It never gets thrown out. EVER. Bob is getting the signal photon and the signal photon gets recorded 100% of the time and saved.

What you are missing is the other dice roll, the idler photon, which I guess Fred writes down. Now when Charlie tosses the coin, that decides whether Fred saves the idler photon result - not Bob's signal photon. One half of the entangled pair will go to Bob 100% of the time no matter which slit it goes through. But that detector has no idea which slit it came from because one half of each pair will always go to Bob no matter what. The idler photon contains the path information. It can either tell us which slit it came from with 100% certainty or not at all. The entire point of this experiment is that we can know which path the idler photon took, erase it, and create an interference pattern in Bob's results even after it's already been recorded. Or we can know which path the idler photon took, keep it, and create a clump pattern in Bob's results. This has been reproduced countless times by physicists all over the world and it's 100% reproducible. Your example is throwing out results from the wrong place and leaving out the place where you do throw out the results.

[itsajin]

Isn't the part where Charles (in the future) telling Bob (in the past) what to "record" the very definition of retro-causality?

[ivankontra]

if the experiment is as you describe it simply looks pointless, I remember there were 4 different scenarios in the pbs video, not 2

[Razor-pwxn]

Sorry, I don't agree. In my view this explanation does not physically explain the results of the experiment. _ "Correlation does not mean causation" _. Sure not, but it can mean it, right? I don't see the physical explanation for that. It is simply mentioned that the results are filtered and grouped once the experiment is finished. Of course, it is that without filtering and grouping in subsets, no assessable result is obtained. My question is taking into account the scheme of Kim et al (most famous quantum eraser experiment), if the signal-foton is a cause and the idler-foton is an effect and the cause precedes the effect in time, why is the signal-foton sometimes hits D0 in the interference aligned position and sometimes in the non-interference aligned position? (Taking into account the subsets separately).

[erinm]

One other nitpick. The rippliness of the classical experiment is an artifact of the specific way that the correlations were designed, with odds being heads and evens being tails. If you instead said values =< 3 are heads, and values >= 4 are tails, then you would end up with a smooth pattern, not a rippling one.