The Delayed Choice Quantum Eraser, Debunked
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- Опубліковано 23 тра 2024
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The delayed choice quantum eraser is one of the weirdest, if not THE weirdest, experiments in quantum mechanics. It supposedly rewrites the past because the choice of a measurement changes what happened in another measurement earlier. In this video I explain why this is not what's happening. The quantum eraser isn't remotely as weird as you may have heard.
Sean Carroll's blogpost is here: www.preposterousuniverse.com/...
Technical remark: You can find a lot of webpages saying that the envelope of the double-slit interference pattern is that of the single-slit diffraction pattern. Note that this is is only approximately correct.
You can support our channel on Patreon: / sabine
0:00 Intro
1:45 The Double Slit
4:17 Entanglement
4:53 The Quantum Eraser
9:03 What they didn't tell you
11:45 Sponsor Message
#physics #quantum - Наука та технологія
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. And then I procrastinated on filming the retraction! Thanks for laying it out more clearly than I could have. I have some thoughts to share that might add one more nail to the coffin ... coming to a video real soon!
This is the kind of mutual respect that real scientists have for each other!
Congrats for your response Matt, others would be "insulted"
I learned to trust my intuition from QE. If the particulars of the experiment design confuse me too much, there must be something off.
Huge respect for your honesty. I am looking forward to your extra info on the topic!
In the spirit of Space Time videos without the comment checks: "The 2nd part of Matt's response was quantum erased and will have been restored in some past comment."
I’m glad you recognized the most important thing here: You can never have enough videos of kittens in boxes.
The prime rule of the internet.
✊🏻❤️🔥 Love wins! Unleash your kitties!
As long as they're not Schrödinger's experiments.
She should make one!
So the combined photons detected by D3 + D4 produce a non-interference pattern. But why, when viewed separately, do they each produce an interference pattern at all? Why not just a random subset of photons from the combined pattern (since the detections at D3 and D4 are randomly determined by a beam-splitter)?
Yes, I would love to have Sabine explain that. As far as I can tell it is a big hole in the explanation given in this video. Surely if Sabines logic is correct both measurements should result in similar blobs (that just take twice as many photons to produce as 50% are excluded).
Exactly what I was thinking, D3s pattern would just be the same pattern as D4 except with half the photons removed. If it’s an interference pattern, combining both D3 and D4 would be the same pattern just twice as strong.
@sgalas1 - I had the same question!! But I think I have it now... I don't know much about beam splitters, but most things can not make "random" choices. She says "the interference pattern really comes from selectively disregarding some of the particles". I think she is referring to the beam splitter causing the pattern...
I thought the same thing. Needs clarification!
"The non-quantum delayed choice eraser" by craig gidney might help
"You can find any pattern you want if you're willing to ignore enough data." -Matt Parker
Wonderful explanation of this experiment and eye opening to me.
And so do many keep on ignoring God within us for as long as they want. 😐
3:24 you lost me, the difference between getting a wave function from the double slit expirment and getting direct hits is when you measure it going through the split and if you unplug the sensor than you will get a huge wave function, you still get a slight wave function with the sensor turned on because there's space between the split and the photoelectric sheet where you observe the proton which means that it's gets turned back into a wave once it passes the sensor but because there's no two slits after the sensor so it's less random and won't be as spread apart but every once and a while an atom or particle will shoot off to one of the sides more than most particles ,but it's just not as probable, you try to rationalize it by combining the two blobs using math but that just illogical because ofcourse most of the locations are gonna average in the middle because that's just the more probable outcome, and based on our current equations to model the collapse of the wave function this is true, so explain to me how you can rationalize that, the whole premise of your argument is wrong lmfao. Literally if you send particles through one at a time they will end up in different location each time it's just more probable for the to be in the middle but when there's two slits the probabilities collide with each to create a more random outcome lmfao so when you collapse the wave function before the split it's less random because there's less probable outcomes lmfao. Like I seriously don't know what this bitch is on. She still doesn't confront the fact that our observation cause the wave function to collapse which is pretty much what the double split and quantum eraser prove.
@@theoldleafybeard ik right thank God another based person in this comment section
*****HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!*******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
@@randommans3407 This is doable by a 1$ red laser and 2 human hairs on an scotch tape. 2 hairs makes a nice spaced interference pattern, 1 hair makes just a diffraction pattern, which is exactly like a double hair interference pattern just much much wider, as if the two slits were closer (because they are).
"Ackchyually", upon returning to point A, the captain can be any age 46 or above, as we do not know the length of the voyage.
The voyage is 100 km, you didn't pay attention!
What we really need to know is how close is his birthday.
Also need to know his speed, that wasn't specified. Could have taken him 2 years to go 100km. I'm sure that's not the case, but it is a possibility.
@@K9Megahertz a container ship will typically go at about 10 knots at their minimal cruising speed, so it will do 100 km in just a few hours. Unloading can take a few days depending on circumstances, so the speed is not significant.
@@K9Megahertz You are still trying to parse all of the irrelevant information. The only thing of relevance is the stated age of the captain. It says the captain is 46 years old, not was.
@@jamiegagnon6390 Thanks. I used to teach my clients how to think. I’d give everyone in the group a double-sided page of questions. At the top of the first page was the instruction: read through all of the questions before proceeding to write answers. The last line of the the list stated: “do not answer any of the questions. Just write your name at the top of the page and sit quietly for a few minutes.”
Finally someone actually explains it instead of pretending to explain it while mystifying it further.
These people rely on the youtube algorithm for money, not being truthful to science.
Shrödingers cat has done absolutely nothing for the betterment of understanding in popular knowledge either. Some things should not be simplified down. If someone doesnt contain the requisit capacity to undersand you shouldn't try to teach them. You just end up with confused people who spread false information.
Goes to show that even most physicists don't understand the concepts they talk about, they merely parrot what they've heard others say.
@@adrianflo6481 I really hate that especially those who present their interpretations and metaphors and then say "the math is correct" so what they are saying should also be true. What a B.S! The math maybe correct but your interpretation is wrong. There is only one type of interpretation which is useful and that science should trust: a geometric interpretation. If you have a mathematical formula, interpret it using geometry to communicate it to the public. And then, make those who are interested to learn more and know its application by teaching them how to do your math. Other than that is how we get multiverses and holograms that don't even make scientific sense. Where is Popper's science now?
@@adrianflo6481 wow, now you are bringing the irreducible complexity. Btw, there are a lot of PhDs in photos that didn't grok the quantum eraser experiment. Or at least not many demonstrated a good comprehension
@@trucid2 there was a joke about maths or physics professors explaining a topic and asking the students is they did understand everything. After they said yes, he looks at the board and says :and I after 20 years still don't fully. understand it....
I’ve watched a dozen hours of your content. SO amazing. I got curious about double slit expt after coming across a Short from another channel. And then searched for double slit content and found your channel. You had the most accurate and precise explanation of things - the other videos were approximating some of the details and were therefore confusing me. Awesome channel, love it.
I am shocked. I feel like I could as likely won the lottery today without playing. As a quantum casual I feel somewhat betrayed by the simple explanation being disregarded. I today find myself more cynical than ever and appreciate people like you. I have neglected your channel over others and realized after the past few episodes that I have been wrong to do so.
Even though Sadine has offered an interesting perspective, there are still many lose ends between the wave-like behaviour, and entanglement. Entanglement is still a controversial subject, and we don't know for sure how information is being shared. There's no clear evidence of a linear relationship. Until a paper has been published and scrutinized, supported by experimental data, the controversial" Delayed Choice Quantum Eraser" is still on the table.
Sabine's explanation is incomplete, though. She does not explain why D3 and D4 individually would see an interference pattern at all - she says that for those detectors, scientists were "simply ignoring" 50% of the data, but that would just lead to D3 seeing a blob with half the count and D4 seeing a blob with half the count, but not in a certain pattern. Big flaw in the argument.
@@argfasdfgadfgasdfgsdfgsdfg6351 you have misunderstood the video
@@psiphisapiens It's strikingly clear that instead of giving us insight on how exactly we are wrong, you chose to criticize us without any factual substance, which is a strong sign of a lack of understanding from your side.
@@psiphisapiens That's high school physics and it doesn't even explain what I mentioned.
"I think they are all wrong.." You've got to love Sabine. I believe the number of friends she has decays as fast as Fr-87.
Maybe, but the ones that are still there, will last forever.
The thing about science is that disagreements are commonly friendly. What looks like an attack on someone is nothing more than a challenge to an idea.
@@sjzara Imagine if Nature allowed video submissions for the correspondence in "Matters Arising"...
@@sjzara I am only joking....But, some people are weird, and some do not like to hear things like "you are wrong". Some take offense, specially Physics PhDs who have been working on a particular field for many decades. By the way, I've seem mature scientists at each other's throats because of scientific disagreements. This behavior is becoming more common.
friends are passing, truth and integrity is forever
Would love to see someone film the actual experiment rather than just seeing it animated. Thank you for the clear explanation
I've seen the exact experiment, and I personally think the animation does more justice to explanation than the actual video. Personally I think animation works very well for College or even early PhD level students to get a better sense of what's going on. Of course, people working on this domain may want to know more about the set-up.
SHHHH. If you talk about that out loud ''THEY'' might hear you.
ᶜᴾᵁ > ᴳᴾᵁ > ᵀᴴᴱ ᴰᴿᴱᴬᴰᴱᴰ ˢˢᴰ ᴬᴿᴱ ᴬᴸᴸ ᴬᴺᴵᴹᴬᵀᴱᴰ. [ᴮᴱᵂᴬᴿᴱ ᵂᴬᵀᶜᴴᴵᴺᴳ], ᴴᴼᵂ ᴬ ˢˢᴰ ᵂᴼᴿᴷˢˀ ʸᴼᵁ ᶜᴬᴺ'ᵀ ᶠᴵᴺᴰ ᴬᴸᴵᴱᴺˢ ᴮᴱᶜᴬᵁˢᴱ ᴬᴸᴵᴱᴺˢ ᴬᴿᴱ ᴺᴬᴺᴼᵎ
''ᵀᴴᴱ ᶠᴵᴸᴱˢ!''
ua-cam.com/video/L_o_O7v1ews/v-deo.html
TheActionLab did one recently
i would like to see "globe from space,not cgi ed
I know this is super late but it’s actually possible to do at home, you just need a laser pointer as the only thing you might not already have, and you can get those for like 5 bucks.
“I did this by taking a piece of glass and holding it over a candle to get a nice thick layer of black soot on it, then holding two x-acto knife blades parallel to each other and scraping two nice thin lines right next to each other in the soot.”
You can probably do this with razor blades or anything similar to it, and you can even use aluminum foil instead of the glass (but be aware that the foil will tear super easily)
thank you so much for the work you do!! i've been interested in quantum mechanics since i was a teenager and your channel has been the perfect next step in expanding that interest 💙
I love this video. I couldn't find another one that explained it so well. concrete and simple. Excellent, it shows that you know what you are talking about. please do not stop making these jewels!
I still dont understand why D3 and D4 have complementary patterns that look like interference instead of complementary patterns that look like normal distribbution.
Me too. Since the half mirror randomises the photons that go to D3 and D4 why do those randomly selected groups of photons each produce an interference pattern.
Below is the very same post as I used in the reply to a very similar question elsewhere. It is not a satisfactory answer.
The reference is to equation 10 in arXiv:quant-ph/9903047v1 (figures 3 and 4 in the same).
Note: in the article the eraser path has D1 and D2, which is opposite to the notation in the video. The setup is in figure 2.
I would lie if I told You that I can really follow through the derivation.
What I can sum up:
the conclusion is that there is a phase shift between the two patterns in (10), one with cos^2( x pi d / lambda f) the other with sin^2([same]), so that when we sum the two patterns these two terms sum to one and only sinc^2(x pi a / lambda f) remains (which looks as a blob with no interference-like bands);
in turn, this comes from eq. 4, where "the different sign between the two amplitudes [...] is caused by the transmission-reflection unitary transformation of the beamsplitter BS [ref. to rig. 1 and 2]".
I think this is also to be considered in combination with the computations after eq. 4, which include the paths' lengths.
If I understand it correctly, it is a matter of different path lengths combined with the different effects on the phase of transmission-reflection at the beam splitter that causes the shift between the patters, but I might be wrong.
@@ThePinkus thanks for answer! So, if you are right, this interference pattern has nothing to do with wave functions, it is just Optics.
@@PSG_Mobile Current optics is done by wavefunctions, in fact the computation we find in the article derives the results as a "standard quantum mechanical calculation" (pg.2 just before eq. 1), and the equations are not classical wave optics, but quantum field theory.
So, correct, it is optics, hence, of course, it has everything to do with wavefunctions.
Best regards!
@@ThePinkus thanks!
Sabine calling out the YT physics boys. You gotta love it.
Sabine adding Joe among the UA-cam physics guys. That's an acknowledgement!
@@andrearaimondi882 Joe is not a phisicist so I don't really expect him to have that level of knowledge but if you're a phD physicist you really should know better!
@@isonlynameleft and that’s the thing. So many physicists don’t really understand what they are teaching. They’ve gone through the school, and passed the classes, but they fail to achieve Sabine’s level of understanding.
If you're any good at physics, you probably have better things to do than sensationalize video content on the web. 👍
@@alphagt62 This!
I would very much appreciate clarification on the nature of a particle detector in reference to the double slit experiment. It is frequently implied that observation itself is the cause of wave function collapse, rather than any force imparted by the measurement device. This can be pretty frustrating when trying to understand the why behind these things.
Relax. No need to be frustrated. Because "wave function collapse" does not exist. You don't need to worry about what causes it.
When the particle hits the detector, its wave function becomes entangled with the detector, resulting in a whole continuum of detectors in parallel universes, each registering a "hit" in a different spot. And the effects propagate until there is a continuum of multiple copies of YOU, each seeing a "hit" in a different spot. Nothing collapses.
Yes, I know that I sound insane here, but I'm simply telling you exactly what the Wave Function says. This was clarified by Everett many years ago.
And once you get used to the "many worlds" interpretation, you become the thing that Feynman didn't believe in : a person who understands quantum mechanics.
@@DavidByrden1 lol wut?
collapse is an illusion, it is an artifact of perception. it only appears to happen given one’s limited appearance of reality
Everyone: The delayed choice quantum eraser is impossible to understand.
Sabine: Hold my Bier
More like "Hold my beer, I'll present Sean Carroll's explanation."
@@jirijelinek2038 Fair enough 😂
Not fair. The didactic value here is higher.
@@jirijelinek2038 Richard Feynman says that Sean Carroll's explanation is crap so forget it.
Listen at 0.75 speed and it'll be clearer.
I've already given up to understand this topic after watching all those videos several times. Finally, today I got satisfaction, even though I still need to rewatch this several more times. Thank you so much!
I also have to rewatch the video. Still don't understand why the detectors can change the interference pattern.
@@lubricustheslippery5028 In the regular double slit you mean?
@@lubricustheslippery5028 It doesn't change the Interference pattern .
It will help if I explain how the sector works . The detector , when on blocks the light , but when it is off allows the light to pass through , it is literally that simple.
Next , inorder to create a interference pattern two beam of light need to over lap with each other and undergoes , destructive and constructive interference .
Now I want you take another look at the experiment .
You will see that the detector was on ,which prevents the second beam of light to interfere with the first beam of light , thus there is no interference pattern .
Now move the detector further back than the screen . The dector being on doesn't affect the light pattern in the future .
The light beam simply does what It would normally do when there is no other light to interfere with .
At this point you should realize the word trick that was being played on you.
I don't only disagree with the idea that causality is broken , I also disagree that the direction of the beams of light are erased , because as you can see the light is slit into two when the detector is off , so if I put a screen their I see light . It is literally that simple.
@@lubricustheslippery5028 We are enjoying to understand what we don't yet know😊 It's ok that I don't understand all the details, as these science experiment and math are not hands-on for me anyway.
But I've just wanted a rational explanation for this fascinating topic.
@@lubricustheslippery5028 Don't over complicate it. On detectors D3 and D4 each detector receives two beams of photons. One of the beams goes through a beam splitter, the other beam does not. The splitter reflects 50% of the wave basically cutting a sine wave in half. The patterns that show up are the gaps in the data from the reflected portion of the wave. It seems to be a test set up to see if you can predict one photon by measuring it's entangled counter part that got misconstrued.
Mam, I saw your video and I am a fan. For the last 10+ years I've been trying to understand how at once, when observed the interface pattern turns into two neatly separated points. You are literally the first person to call that out and call BS on these other "so called physics" channels. Thank you so much ! Maybe, could you also do a video on your views on the single slit experiment. e.g. Why you think it might be happening?
This is an amazing addition and quite fundamental to understanding what is actually going on. Thanks Sabine!
I've looked on several occasions for a video like this to describe what is actually going on but all I could find was videos of people saying the particles act differently based on if you observed them or not which just always frustrated me to hear. finally now I have a video that I don't completely understand but at least can point to when people bring this topic up.
If you're still struggling to understand, this video is also really good: ua-cam.com/video/iyN27R7UDnI/v-deo.html
I always point my mates to "Glitches and tricks in Half Life 2" when I need to explain quantum weirdness.
@@_whatthefacts_ The unexplainable disappearance of the wavelike interference pattern of the single particle double slit experiment when the which-way info is detected has been cited as proof of "simulation theory" (the theory that reality is a computer simulation). It's claimed this otherwise unexplainable phenomena can easily be explained/understood as a more detailed rendering. The wavelike interference pattern is explained as a less detailed rendering which appears when you aren't looking at which slit the particle went through. It's like a crappy rendering engine with noticeable "glitches".
DeSinc, Sabine doesnt question that the particles act differently based on if you observed them or not, thats a fact and she confirms it in this video.
@@pflaffik That's not what I got at all here... The particles didn't behave differently , we just observed them differently. I could be wrong but it seems she was saying that we observed the particles without the which way information. Don't murder me on here, I'm obviously not a quantum physicist and it's possible (if not likely) I misunderstood this video.
Where have you been all these years, Sabine? You are truly the only scientist capable of translating/adapting/simplifying/whatever the problem of grasping things that others deliberately romanticise.
She has been working and studying quite hard …
S. Hossenfelder is not a superhero. In science some perform experiments and try to give an interpretation, others (rightly) raise criticisms. This is how it works. At the end of the 19th century, almost all physicists thought that light must necessarily propagate through an ether.
There are so many great science communicators beyond your youtube algorithm
"deliberately romanticize" how can that be romanization if it is perfectly consistent with time not being experienced by a photon?. Wouldn't that be the expected result?.
What it is a romanization it is to think that this experiment not appearing conclusive to reiterate the result that time is not real as we perceive it, and that it would mean things still have a chance to evolve unexpectedly.
People who romanticize having free will have more interest in this experiment being not being conclusive than the other branch that see it as a result perfectly consistent with Relativity
She's one of my favorites because of how she tends towards skepticism and isn't afraid to call bs when she sees it even despite how doing so risks creating animosity with others in science and physics. Also she's really good at explaining physics in a practical, straightforward, and understandable way without dumbing it down too much
This amazing video is a perfect example why I am a subscriber to your channel. You have inspired me to start my own theoretical physics channel. I intend to cultivate discourse to create progress. Thanks Sabine!
I was deciding on which video should pop my q-eraser Cherry and selected yours first. I LAUGHED when you referred to all of the others. I chose well!
Sabine, love your channel, but I think some clarification is needed here. Yes, I think I understand the explanation being offered here that retro-causality need not be invoked to explain the outcome of the delayed choice quantum eraser experiment. And yes, I read Sean Carroll's article that offers essentially the same explanation that you do here. After all, "we can trust Sean with the quantum stuff" as you so aptly put it. But, Sean Carroll's explanation (and by extension yours) invokes the Everettian "Many Worlds" interpretation to explain away the need for retro-causality. The wave function doesn't "collapse" as it would in the Copenhagen interpretation, but rather there was a decoherence that branched the multiverse along all possible paths.
But, the Many Worlds interpretation of quantum mechanics has been something that you've been very highly and very publicly critical of here in the past. If we can really trust Sean Carroll with the quantum stuff, and his explanation invokes Many Worlds to explain the delayed choice quantum eraser, then does it not follow that we should trust Sean Carroll's opinion of the Everettian "Many Worlds" multiverse upon which it depends?
"There’s no need to invoke retro-causality to explain the delayed-choice experiment. To an Everettian, the result makes perfect sense without anything traveling backwards in time." - Sean Caroll, "The Notorious Delayed-Choice Quantum Eraser", Sep 21, 2019
My understanding is that one can subscribe to the "many-worlds interpretation", while considering the other universes as just a tool for the explanation, not implying they are "real" in any sense.
Wikipedia has this quote from Stephen Hawking: "But, look: All that one does, really, is to calculate conditional probabilities-in other words, the probability of A happening, given B. I think that that's all the many-worlds interpretation is. Some people overlay it with a lot of mysticism about the wave function splitting into different parts. But all that you're calculating is conditional probabilities."
@@martir.7653 Here is a video about multiple time dimensions: ua-cam.com/video/igDnqZG0-vs/v-deo.html
This improves on the "many-worlds interpretation" in some ways
There's no need to invoke the many worlds interpretation to explain the result. This delayed choice quantum eraser can be shown to be the same as Wheeler's delayed choice experiment. In that case, the detections at D0 just provide an alternative visual output for the experiment, which is nice, but nothing different.
@@markfernee3842 One can always "shut up and calculate" and perhaps this is even one of those times. But, the whole point of having an interpretation is to try to understand what the math is telling us. Yes, different "visual outputs" at D0 is empirically observed, but that alone is just ignoring the most profound aspect of the results. That is that the different outputs seem dependent on the presence, or absence, or arrangement of detectors that are further downstream in the experiment (and therefore reached at a later point in time).
Sabine here is accepting Sean Carroll's explanation for the most part and then stopping short at the point where Sean actually brings the argument home that under Many Worlds this doesn't necessitate retro-causality. Sabine is trying to have her cake and not eat it too (to belabor an analogy).
Even Sean Carroll in his article on the same topic acknowledges that if you subscribe to other interpretations of quantum mechanics where wave functions are considered to actually collapse then it would be understandable to invoke retro-causality to explain the outcome (though he ultimately disagrees on this point). But Sabine here seems to want to invoke all the math that Sean does, but not the interpretation that Sean does to bring it all home. In essence, Sabine just talks around the point without actually addressing it.
Again, from Sean's article cited in Sabine's video:
"But alas, not everyone is an Everettian. In some other versions of quantum mechanics, wave functions really do collapse, not just the apparent collapse that decoherence provides us with in Many-Worlds. In a true collapse theory like GRW [...] you can convince yourself that retrocausality needs to be part of the story.
Or you can accept the smooth evolution of the wave function, with branching rather than collapses, and maintain time-symmetry of the underlying equations without requiring backwards-propagating signals or electrons that can’t make up their mind."
Sean Carroll, "The Notorious Delayed-Choice Quantum Eraser"
@@blawrence42 the problem is that this experiment purports to be a proof of retro-causality. Retro-causality in quantum theory is an interpretational aspect that can be applied to a range of experiments. It's not just shut-up and calculate that shows no retro-causality in this experiment. One can just run through the detection chain logic without to see this. The photon pair generated in the crystal are momentum-entangled. When D0 is detected, that detection is compatible with the photon having a certain momentum. However, there is more momentum information available from the entangled partner. We just have to wait for it to be detected. Once it is detected, the particular detector, D1-D4, will determine the additional momentum information that is provided. So after the second detection, we can say more about the momentum of the first detection at D0 because we have updated out information. Where is that retro-causal?
One of the main problems with how people interpret this experiment is the complete disregard for the SPDC crystal and the effect it has on the interference pattern. It completely washes out the possibility of observing an interference pattern. That's due to the finite thickness (0.3 mm) of the crystal, the wavelength dispersion in the crystal, and the random point of down conversion within the crystal. These effects were included in the Scully's calculations in the paper, but otherwise not mentioned. However, these effects are well known to anyone who works with SPDC crystals in optical circuits. From that aspect, I find this experiment somewhat disingenuous. Furthermore, the paper didn't explain the origin of the two complementary interference patterns. There should only be one Young's double slit interference pattern, not two. This is should be red flag when interpreting this experiment. It is telling use that it is not working they way we expect it does.
Finally, one can actually see that this experiment is actually a rather unique version of Wheeler's delayed choice experiment by identifying the interferometer circuit. There is no "eraser", just the delayed choice outcomes as already described by Wheeler. This is rather profound, but already known. I could easily rewrite this experiment titled as, "Wheeler's delayed choice experiment with entangled photons".
Thank you SO much for this video. My favorite on your channel so far. I had read about the double slit experiment years ago and had been confused, but your explanation at 3:03 is a complete game changer and cleared up all my confusion about how this supposed paradox works. Again THANK YOU!
I did find a debunking of this problem on youtube a few years ago, but I couldn't find it again when I wanted a refresher and found your video instead! thanks a lot!
I should have known your exposition on this experiment would be unique, enlightening, really helpful and different from even the better ones on the topic.
Finally! The fact that you are not afraid to debunk the videos of your colleagues speaks volumes of how much integrity you have as a Scientist. That's what science is about! Science is not about friendship, It's about the truth. Congrats Sabine!
IKR. Sabine Rocks!
That's what I love about her
*****HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!*******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement.
All three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
***HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
She's all fine and good until it's her theories that are on the line. You'll see a different side of her when that happens
As usual, Sabine presents her deep insight in a conceptual context that is easier to grasp, just pay attention. A gifted communicator the likes of which are quite rare. These concepts make the math and statistical probabilities easier to grasp and interpret from the bigger picture. A delight for the young pup and old dog alike.
SABINE NONSENSE IS DEBUNKED BY NOBEL PRIZE 2022 WHICH PROVES ENTANGLEMENT IS REAL!
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement.
All three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
Thank you for the awesome explanation in video format. When those videos you mentioned were published, I spent days on the internet reading various forums to find the same anwer you presented. If only this video would have been available at the time. Subscribed.
SABINE NONSENSE IS DEBUNKED BY NOBEL PRIZE 2022 WHICH PROVES ENTANGLEMENT IS REAL!
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement.
All three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
Omg, ever since I watched the PBS ST video 5 years ago this been bothering me, it just didn’t sit right. I have been googling the experiment ever so often (hence how I found this video) and finally someone put it a way that both made sense and let me understand what the experiment really does/what it means. Thank you so much!!!
3:07 Joe’s face in that screenshot of his delayed choice quantum eraser video. 😂 Gotta love him. Love this video, too! I’ve heard about how the quantum eraser experiment doesn’t actually rewrite the past; however, I love the way you explained it in this video in that it was much easier to follow.
That’s because her experiment is nothing like the one done by skulls Kim et al
*****HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!*******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement.
All three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
***HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
You are the first one on youtube that I have seen to take the magic out with a fuller explanation. Thank you.
I'm just happy the kitten was alive
The one that turned fuller explanation into working clickbait (I definitely clicked). Others are fine by using magic in their videos to get views and sponsors.
not true: ua-cam.com/video/GFrS0Rv6OTE/v-deo.html
@@DrSharoyko Never saw that one thanks.
Check Science Asylum video on this. I think he was the first to demystify the situation
THANK YOU! I've always wondered when reading about these experiments how they leaped to these conclusions and always thought there was something I was missing. Thought I'd been taking crazy pills.
Danke, vielen Dank! Ich kehre immer wieder hierher zurück, wenn ich verwirrt bin. Super Präsentation. Klar und einleuchtend. Und die Didaktik im Video - einfach genial 🙏🏻
After reading Carroll's explanation, my understanding is that the error in the other videos is this: they show a stripe pattern appearing on the detector screen, but in actuality it doesn't. You can create a visualization after-the-fact, showing which parts of the blob pattern correspond to which measurements, and this way create an interference pattern.
Would you please give the reference to the book or article by Carroll you're quoting? Thanks
@@ggg148g The link to his blog post is in the video's description. It's apparently a section of his book that he had to edit out.
Just FYI in the two PBS Spacetime videos after the one mentioned here they do talk more about how the two interference patterns combine to form the single blobby image you get from the which-way detectors. In particular he talks about how the interference patterns are actually partitions of the original set of photons based on the characteristics being measured by the combined detectors C or D at the end. So there's no way to know in advance which photon is going to be in which interference pattern until you actually get the measurements from those two detectors.
He uses this as an example of why you can't build a "time machine" that sends morse code signals by placing or removing the mirrors at the which-way detectors to send a message back in time based on seeing or not seeing an interference pattern. The image you see is always the same, it's just whether you're categorizing the photons as two combined interference patterns or one blob and you can't know details about the interference patterns embedded in the image until you get the measurements.
Indeed! Matt even made a competition our of it if I remember correctly!
People may get too caught up in the time aspect and fail to realise how mind blowing it is that just by measuring the data is collapsed which is the best part
But why does the separation of photons into those two groups even create a pattern which looks like as if there was interference?
Why is it so that those photon-pairs that end up in one of the "after erasure" detectors can not hit certain locations on the screen?
And the other half - in opposite - hits these bands on the screen, so the second pattern is shifted exactly to match the "negative" of the first: except - if I understood correctly from a real published study and not some interpretations - the two patterns are almost the same just shifted...
@@Littleprinceleon As far as I understand it, it's like releasing rabbits towards a carrot and a lettuce pile. Later you measure the color of their poop and realize all green poop rabbits interfered with lettuce pile and orange poop rabbits with carrot pile. It's not like measuring their poop caused them to retroactively choose a certain pile. :D
@@janPeja but why did half of them choose one pile at all?
The paths to the "erasure" detectors are symmetric: only difference is that the photons leave the BBQ crystal at two different sites depending on the slit they "went through".
That's what Sabine emphasizes: the which way information is "detected" and transferred by the crystal (absorption, reemission).
That in the end we combine the information doesn't seem to "erase" anything. We only obscure the direct info on the path for ourselves.
So another relevant Q: are the particles distributed in the same two patterns on the "screen" if we detect their entangled pairs at the earlier "which way" detectors?
And we just cannot obtain the right information with this setup of the detectors?
Is the result random and the pattern emerges because of some property (phase? polarization?) of the photons? Just like with coins: two possible outcomes inherent to the object, evoked by random influences...
Is this property dependent on their path ? Even if, why are there discrete bands?
The "bomb experiment" implies that whenever the photon has a choice, eg. at the semitransparent mirror (beam splitter) in reality it goes through both ways: even interferes with itself... But in the case of the DCQE this happens to that part of the entangled pair detected by the "erasure" sensors. Does the entanglement influence all the information contained in the wavefunction?
How big/long can be one quantum of electromagnetic wave?
It seems that amongst chlorophyll molecules a photon takes many, many different paths until it "finds" the energy center.
Great video and a great explanation, @Sabine. Keep up the good work, and thank you for sharing!
Matt, Kyle, John and Joe. I like this dynamic, Sabine. I think they do too. I am stuck quantum rewinding instead of quantum erasing. Sean Carroll is amazing.
“How many videos do you need of…”
A lot more! This is a complicated subject, and it helps a lot by hearing multiple explanations, because all of these have a different angle. They complement each other, and I often understand it only after 3 or 4 such videos.
Agreed. even many available, admittedly this is one of the first to demystify it.
Actually i have seen one "not so prominent" physicist explain this story before, but being ignored and overlooked by many as nonsense.
A "Quantum Eraser" erases nothing! by Jeffrey H. Boyd MD
Well, he is a MD afterall.
@@boo6237 To be fair, many other videos get to the same conclusion, that it doesn’t actually touch the past or anything like that. But they do it in such a complicated way that it is harder to understand.
She has really cut the unnecessary information and made it simple.
*****HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!*******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement.
All three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
Thank You Sabine. I love you. I have been puzzling about this for years and can give my brain a rest and stop worrying about a patent application for long distance instant communication.
I might have to watch this one again! Or maybe five times. The funny thing is... throughout the video I kept thinking to myself, "these unintuitive paradoxes in quantum mechanics always seem to melt away when you think in Everettian terms..." - and then at the end, you recommended Sean Carroll's explanation :D I will definitely go and read his article too. I find it quite frustrating that I don't have the detailed physics knowledge to really explore these ideas, and yet I do have this intuitive conviction that all of the "weirdness" of quantum mechanics will one day turn out to be merely the confusion caused by our own quantum nature.
woww....so many great videos and explanations! I've watched PBS + Fermilab video of the quantum eraser + studied quantum mechanics at the university as an engineer but I've never got the essence of the quantum eraser in PBS + Fermilab....it led always to confusions. Now I know why....This explanation was really helpful! Danke schön for you and the team for this additional video..
The essence of all of these videos is bullshit. ;-)
@@schmetterling4477 hm. It is not clear what YT channels you are referring to. Do you mean PBS or Fermilab or Sabine's channel? I think however "bullshit" is too strong ...All of these channels are put a lot of effort in quality content creations and how to try to explain physics to a broad audience who have no background of high level math (eg high school students) .....
How does this disprove the mysterious aspect? The first particles are still landing on the screen seemingly dependent on the future randomly chosen destination of their pair particles..?
it breaks the mysterious aspect because you have causality backwards. In reality, The particles are landing on the screen, and latter they are at either detector d3 or d4. But whether they land at d3 or d4 is already determined by where they land on the screen. This effect, while weird, is just a normal quantum entanglement effect. So, your choice of using detector d3 and d4 vs d1 and d2 is not retroactively changing where the particle lands on the screen, it is only changing whether or not you apparently see an interference pattern for that grouping of particles. Does that make sense?
@@Lestertails2 Yes, the fact that the second particles "decide" whether to land on a detector with or without which-way-informatoon depending on where the first particle landed is the mystery, right? So I am not sure I get the point of the video.
@@williambenckert917 No not exactly. The apparent mystery is that you could change whether an interference pattern is observed after the first particle lands at the screen by changing between measuring with detector d1/d2 vs d3/d4. Because it is possible to make the choice of d1/d2 vs d3/d4 (hence the "delayed choice experiment") some people wrongly interpret this to mean that quantum information is sent backwards in time (spooky). Sabine points out that this is not the case. At the screen, there is no interference pattern, regardless of d1/d2 vs d3/d4. The interference pattern only apparently appears when using detector d3/d4 to match where a particle in the past landed on the detector screen. Thus where particle 1 landed on the screen will determine which detector (D3/D4) its entangled partner lands at, to make the apparent interference. This is an interesting property of quantum entanglement (and yes, quite mysterious), but it isn't "sending information back in time" mysterious.
@@Lestertails2 Uhm, either the first particles are looking into the future or the second particles are looking into the past (apparently). This video doesn't debunk anything.
@@Lestertails2 D3 or D4 both correspond to an erasure state. Summing the total of both is nonsense. Would you attribute a coin that landed heads today to a coin that landed tails yesterday and say that it was completely determined and dependent ?
This why I am much more interestes in having the crystal *BEFORE* the double slit.
A beam of individual photons is split into entangled pairs, entangled photon 1 goes into the double slit, number 2 goes in a different direction and travels further to preserve it longer. Number 2 then hits a beam splitter that either sends it to be measured, or a place where we don't measure it at all.
If number 2 is measured, the entangled pair collapses. And no longer acting like a wave, no interference can happen.
Please correct my understanding if I am wrong.
1 goes into a YDSE and interferes. How are 2's two paths supposed to change that?
@@DrDeuteron Because the photons are entangeled, you reveal information about photon 1 when you measure photon 2.
See it like this, if write 1 on a sheet of paper, and 2 on an identical piece of paper. Ask someone to shuffle them. Then light one on fire. You will still know which number was set on fire when you flip over the other one.
Whenever you observe (gain information) about a photon it collapses and acts like a particle. And a particle cannot interfere with itself.
And as this information reveals something about the past, and the outcome of the past is dependent on the information you have. It would seem like what happens in the future is able to interact with the past.
Now this doesn't nessecary mean you are able to change the course of time. Maybe it was always bound to happen anyway?
@@beanieteamie7435 I think you missed the point of the video. It's always a wave.
What you need to focus on is all the ways to get from the initial state to the final state. If there is more than 1, you need to add up the amplitudes FIRST, and the ||x||^2 them to get a probability.
That's it, all quantum woo is contained therein.
Really?
***HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
What now Sabine?
Most of the experiments that I have seen show 2 distinct vertical lines on the film plate when the "which way" information is measured. The way you are showing this is that there is one big horizontal blur when the which way information is measured. This seems to be the big disconnect in information that needs to be established more than anything else.
The thing I don't understand about Sabine's explanation, is that supposedly the fact that you can't see an interference pattern until you separate them by the path of their untangled pair, supposedly demystifies anything.
They do result in an interference pattern when correlated with either of the paths that send the beams down a path that makes it impossible to determine which slit the photons took.
it deserves more explanation as to how the merged 'interference' detections perfectly merge to a indiscernible pattern.
Sabine has stated that she thinks determinism solves these things in a more recent video. That explanation makes sense to me, and would resolve this also, essentially arguing that 'Determinism' is the 'hidden variable' all along.. that wave functions take future measurements into account.
***HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
What now?
Hi Sabine, I am relieved to watch this video as I too was unconvinced about any actual erasing. As many I was blown away by what has been inferred, but on analysing the original (Kim, Kulik & Shih) paper I saw that this is just a correlation after the fact. You have given me confidence.
I would actually go further than your presentation. The interesting thing is the differing phase relationship of the correlated interference patterns (seen in Figures 3 & 4 of K, K & S’s paper); I am assuming that these correspond to the phases of the entangled wave function as they provide the probability of arriving at one or other of the mixed detectors. If this be true then there is no mystery at all; the probability of recombination at a particular detector (and therefore a detection event) is dependent on the phase relationship at the point of entanglement, which also relates to the interference pattern.
It does, however, pose many new questions… Why is the phase of the entangled photons reset randomly (is it?)? Why does the generation of entangled pairs destroy the original phase relationship (no interference pattern seen directly on the screen)? Is the phase relationship to each entangled pair (as mixed in the beam splitter) related to the interference pattern? Indeed, is the original phase relationship (given by path differences) at the separate slits no longer important; or is the correlated pattern on the screen simply the superposition of these phases?
Most of all; the conclusion is that interference (or phase correlation) is taking place in circumstances requiring two coincident paths. I guess this is not at odds with either the Copenhagen interpretation nor the Pilot Wave but it does require both pairs to be present. Locality is clearly non-existent, but with no violation of causality with reference to proper time whatsoever.
"Hi Sabine, I am relieved to watch this video as I too was unconvinced about any actual erasing. As many I was blown away by what has been inferred, but on analysing the original (Kim, Kulik & Shih) paper I saw that this is just a correlation after the fact. You have given me confidence."
Then you truly misunderstood the experiment. I doubt that you read the data because if you have then you wouldnt be asking about random phase smh
The photon pairs are generated within a special crystal. One photon goes in; two come out.
The two that come out have the same phase.
The point at which the splitting occurs, is somewhat random - it's somewhere inside the crystal.
But now, add the slits to this setup. The original photon follows two paths (the blue and yellow beams of the video).
The points at which they split are somewhat random within the crystal. Therefore there's a COMPLETELY RANDOM PHASE SHIFT between blue and yellow. There is no HOPE of getting an interference pattern....
...unless you add the mirror, which actually sorts the photon pairs into 2 groups, because it introduces a 180 phase shift if Blue gets reflected. Not yellow.
Here is how I understand the weirdness of this experiment, which is in my view a little bit understated in this video:
Assuming a single photon is emitted from the source travelling through the double slit. Then, following Sabine, either the blue path or the yellow path is taken, whereby these paths are decoherent. Now the wave function of the upper photon will look like a one slit diffraction pattern and hits the screen with the according probability at which point a second decoherence is taking place: Either the photon hits a crest of the "interference" pattern of D3 or of D4. This information is via "Einsteins spooky action at a distance" transferred to the second photon still travelling.
Now the weird part: This means the second photon does not hit D3 and D4 with the same probability as the setup implies, instead it hits D3 with a greater probability if the photon was detected at a D3 crest and vice versa. If this is how the experiment actually works (I can't explain it otherwise), I would be greatly interested which state the second photon takes, such that the probability hitting the detector D3/D4 is no longer 50/50.
Way late to this comment, but this is the same question I walked away with. Sabine simply stating that you can select a sample, just like picking pennies from a pile, doesn't explain how/why detectors 3 and 4 show this bias. This point can't be trivialized if the argument is meant to trivialize the "sending information back in time" perspective.
And I'm there later still, and find myself with the same question. Does someone has found some ressource that could clarify that, or is it beyond layman explanation?
I explained this in a separate comment. But, to summarise it here: the mirror (that selects between D3 and D4) causes a 180 phase shift in the blue beam but not the yellow beam. That's just how mirrors work. So, you get 2 groups of photons with a 180 difference in how Blue relates to Yellow. Naturally they produce interference patterns that are 180 different.
@DavidByrden1 thank you for your answer, I am having the same question... Could you please refrence a more detail explanation on this mechanism?
Late to the party! But this drove me so nuts myself, that I thought you might want an answer! The answer is that both entangled photons are in a superposition of two beams (one from left slit, and one from right slit), but as soon as the first photon hits the D0 screen the relative offset of the phases of those two photons becomes set. The relative offset correlates to locations on the D0 screen in a way that cycles from 0 to 180 degrees and back to 0, repeatedly as you move across the screen horizontally. Hence anything that is correlated with values for the relative phase differential of the superposition will take on that stripey pattern.
The beam splitter does exactly that. It sorts photons based on wave amplitude, which is random for an ordinary photon, but which is nonrandom for a beam with a superposition of two phases with a *set* relative phase offset. Waves with certain relative offsets will have higher probabilities of going to D3 (and correspond with entangled photon twins that landed on certain stripes on the D0 screen), and waves with the other offsets will have higher probabilities of going to D4 (and correspond with the inverse stripes on the D0 screen, created by entangled twins).
It's all explained beautifully in a new video on the delayed choice quantum eraser by a youtuber called Diego Emilio.
If there is one thing I love about your channel it's the statement "It's not as weird as you think".
Because it always turns out not to be as weird as I've been told before.
@@dextermorgan4490
Because that is nonsense.
It's not "observed" and it doesn't change.
Instead the particle, the measurement device and you all synchronize, such that all possible you's see corresponding particles.
I remember we did the double slit eraser experiment in Highschool and I was so incredibly confused by this setup. thank you for explaining it so well!
To study the experiment at high school is amazing, which country are you in?
@@dosealas this was in Germany right before graduating, one of the last things we did in our intro to quantum mechanics.
@@fabiantombers4966Germany has a great history of physics. Einstein, Planck, and of course, Sabine Hossenfelder. I wish the same classes were offered in American high schools!!
Wow, thank you so much! Validating a clear discrepancy for me. I could only discern that just half of the recombined information is being measured at either detector, however the revelation comes when you put the two patterns up and immediately it is noticeable.. Wow. Superb rationale.
Craig Gidney's video on the DCQE experiment actually does clear up the misconceptions you covered here too!
Wow, he really did!
****HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
@Sabine Hossenfelder, I am afraid you didn’t get it right this time. What you say is partially correct: indeed you can select subsets of dots on the screen arbitrarily in order to create whatever pattern you want.
However, in this case, the subsets of dots that give rise to the interference pattern (as opposed to those that create a smoothed-out distribution) are not selected with the purpose of creating that pattern. Rather it’s exactly the way around. The subsets of dots are not selected arbitrarily to show target patterns: on the contrary, dots are grouped based on physical properties (photons with and without the which-path info), and only then it’s shown that from certain properties (photons with which-path info resolved) some patterns do emerge and from other properties (photons with which-path still unresolved) other patterns emerge.
It’s the coincidence counter in the experimental apparatus that makes the selection of the dots, grouping them based on what detector was hit by the entangled photons and thus distinguishing between dots originated by photons that have the which-path info and photons that don’t. Then it's just shown that an interference pattern emerges from the dots originated by photons without the which-path info.
Therefore, I believe you are wrong in minimizing the meaning of the experiment. On the contrary, I believe that the experiment really shows what is claimed in the main descriptions that can be found in the literature (and on UA-cam) that, instead, you contest:
• The dots originated by photons that were subjected to a which-path measurement formed a smoothed-out distribution on the screen regardless of the fact that at the time they hit the screen they could still skip the which-path measurement.
• The dots originated by photons that were not subjected to a which-path measurement formed an interference pattern on the screen regardless of the fact that at the time they hit the screen they could still undergo a which-path measurement.
In other words, it's like if at the time they hit the screen they had already incorporated in the dynamic properties the info on an event that indeed would have happened later (i.e. undergoing or not a measurement of the which-path info),
What this means then it’s another story.
On the other hand, since we know that space and time are so tightly bound and that non-locality is a core feature of QM, it seems to me that this just a manifestation of non-locality in spacetime rather than just in space. Then you can even call it retro-causality to let it fit better into the categories of our perception (and our classical mindsets).
It's amazing that so many creators are willing to chat in the comments... Except for skeptic scientists. They never address good rebuttals like this... Because you're right.
@@Azrael1486 thanks. Not sure I am right but I think at least that my argument is well grounded upon logics.
This shows, information from unknown UA-cam bloggers is not reliable. Thanks Sabine!
OK, I have a question - what are the separate patterns from photons hitting D1 and D2 - before they are combined? Another question - beam separator at the end that lets 50% of photos pass and reflects another 50% is it like round robin thing 1 pass 1 reflect or is it random thing that over time makes up to 50% pass 50% reflect? I think you've also omitted some of the details.
Correct, there is no explanation as to why any pattern appears at all. Sure, half the photons are excluded, but why are the not excluded totally randomly? why are they excluded such that an interference pattern appears?
Thank you Sabine. This experiment always confused me and I finally understand. You make it seem so effortless! Science educators on UA-cam more and more chase the clickbait as opposed to actually trying to bring understanding. I never miss one of your videos and I always come away more enriched.
Yes, Peter is 46 years old, but that is at the start of the puzzle. How long did his voyages take and the loading and unloading of the ship? Especially now, with container ships waiting offshore for their turn and canals sometimes getting blocked. At the end of the puzzle we are asked how old is the captain, not how old he was.
Where did she say 'At the start of the voyage Peter is 46 years old' There's no implication of an actual timeline in the two bits of information - Peter's age with his job, and what happened on some unspecified voyage at some unspecified time. Peter *IS* 46 years old is the only concrete information in terms of a when, which is 'currently' the rest is just noise (unless you're in logistics, then it might be of interest)
@@rog2224 Of course there is an implication of time between the 2 points unless of course you think the ship arrived instantaneously, therefore, Peter's age IS different from the start of the voyage then to its end, even if extremely slightly. "Noise" is simply someone's avoidance of measuring or determining a very very small subset of data that would be crucial to determine an outcome, otherwise the outcome would be flawed.
Summary: If the quantum eraser actually erased which way the photons went through, then D3 + D4 combined must be an interference pattern. But actually this isn't the case which means the quantum eraser didn't erase the information which way the photon went through. i.e., The quantum eraser didn't make the collapsed wave function return back to the superposition state.
thankyou a lot . I always wanted a perfect description about the Delayed Choice Quantum Eraser experiment but I always found different description in different places including websites like Wikipedia. TBH , I thought probably there's something fishy and that is what I found . All those UA-cam videos and blogs were really misleading. As I studied more about it I kind of assumed that there's lack of communication in this description and also tried to email to some of the scientists but never got a reply haha . But , I'm really thankful to you.
This video erased my previous misconceptions.
"Entangled particles are like a pair of brand-new socks. When you put a sock on your left foot, the other sock, no matter how far away will become the RIGHT sock!"
- The analogies physicists use to explain entanglement without hidden variables :)
As long as You don't use incompatible observables You won't see a difference between entanglement and classical correlations (in measurements on separated systems).
In fact, fixing the observable is equivalent to fixing a "slice" of classical logic within quantum logic.
It is important to understand what is the same in quantum logic and classical logic, as much as it is important to understand what is different.
That is why EPR and Bell use incompatible observables.
Sort of but not necessarily, let’s say that on the inside of the sock is an L or an R to denote which foot it goes on, you don’t know which is which until you check and when you see it is marked L, you know the other has to be marked right
@@matthewcahill4475 Your example, however literally has hidden variables.
@@HSMAdvisor well a simplified analogy will always lose detail it’s just a stepping stone to understanding, I just had to add the detail that you can’t choose the quantum state upon measurement you just know the other one when you do
What are the hidden variables? Where are the hidden variables? It is amazing how far mainstream scientisits will go to try and explain something which doesn't fit in with the mainstream (funny about Bohm though, he went well out of the mainstream, and believed in hidden variables).
Thank you ever so much Sabine. Your insights and instruction is invaluable!
I don't think you are debunking anything with this video. You make it sound like it's trivial because the path of the photons are decided by some hidden variable that also decides which detector they land on. But in the real experiment you choose whether the which path information should be destroyed or not by sending the photon to D1/D2 or D3/D4 after the initial detection on D0. When photons collide on D0 they decide if they should be part of an "interference group" or the "blob group" based on your future choice on where to send the particle. In fact you can separate the D0 detection and the other choice so they don't even happen in overlapping light cones and still see the same result. But the experiment is not more weird than e.g. the bell experiment. It just illustrates apparent non-local causality better without needing to understand correlation math. And it's true that it doesn't show any "rewriting of history", but it does show that quantum measurements are a function of all measurements on the system, including future ones. Even ones in another light-cone region of space.
I think this sums up the problems with Sabine’s presentation of the DCQE better than all the other zillion comments (including mine) on this video.
@@robertbutsch1802 Well, check this one:
ua-cam.com/video/RQv5CVELG3U/v-deo.html&lc=Ugy20HjnW0g2NEknvmJ4AaABAg
@@channel4me434 Yes your original comment does also point out some of the shortcomings of the video.
👏👏👏
Sabine, I think your reasoning misses the core idea of the original experiment done by Kim, Kulik, Shih and Scully in 1999. I see some principal differences:
1. you discuss the use of D1&D2 and D3&D4 separately, but the experiment is based on the combination of both.
2. you focus on what D0 (upper left) shows.(indeed a blurry blob, not surprizing when you combine 4 different patterns) rather than the flow of the photons.
The original experiment shows that when a photon arrives at D0, it should decide whether it contributes to the interference pattern (wave) or to the two-bars pattern (particle). This depends on whether its counterpart photon is detected by D3/D4 or D1/D2 respectively, which happens 8 nsec later. This is done with the use of the coincidence counter (which you don't mention). And that's the baffling part: how does the first photon know in advance?
You address the detector part of the experiment as total irrelevant, and indeed that goes for what is shown at D0 (your focus) but not for the puzzling result that the first photon acts 8 nsec earlier based on whether its counterpart releases their which-path information or not.
Good points, but isn't that curiosity inherent of any entanglement experiment, not unique to the "delayed-choice eraser" setup?
sabines point is you will never get a intereferrence pattern on the screen because of the BBO crystal.
You could now afterwards split you photons into two parts. Using D1 and D2 you will not get so much information. But with D3 and D4 which are detectors which are dependent on the interferrence of the photons (position where they where emmitted at the crystal) you will get enough information two split it into two parts where their equivalent created an interferrence pattern.
I think that was her idea. Its not contradicting what you said i guess
I am not sure if I get you right but the whole point of photon "deciding" is based on its wave function isn't it? If it's being detected by D1/D2 the counterpart at D0 is governed by a different wave function that when it's detected by D3/D4. It exactly the same as simple two slit pattern and selfinterference. How does a photon know whether it should interfere with itself and which wave function it's governed by? I think, currently it's accepted that it's given by the experiment setup, because how a single particle going through two slits at the same time would communicate if it's being detected or not at the other path. The act of detection in QM has it's problems with speed of light limits. How fast does the wave function change propagates? Isn't this the real problem here?
Entanglement also has it's problems with light speed, spooky action at a distance is pretty well test, so to me it isn't surprising at all that if you combine into an experiment you'll get weird effects in that regard.
@@WWLinkMasterX It is unique to the "delayed-choice eraser" because only in this experiment time is involved. It suggests that a photon has to predict what will happen in the near future.
Every other entanglement experiment is more about that as long as both entangled electrons are not interacting with something (e.g. a detector), they are in superposition which means that spin (and other properties) are not determined. As soon as one of the electrons is detected/measured, both electrons are forces to decide what the spin of each one is. This itself is weird enough when they are far away from each other: if the electron being measured decides to have spin left, the other electron must take spin left instantaneity, even if it is a billion km away. That's what Einstein calls "Spooky action at a distance".
@@folepi7995 If you put it that way you are right: our points of view doesn't conflict. But then I don't understand why Sabine calls her video ""Debunked", she does not refute the fact that the experiment suggest that photons caught by D0 must know in advance what the route is of their counterparts. And precisely that is the baffling part of the experiment and is not debunked.
This is why I watch Sabine's channel.
Sabine, thank you for being the voice of reason and keeping us grounded in logic and common sense
This is such a calm and easy to understand explanation. Outstanding.
Sabine always finds a way to debunk the mystical and add wonder. Science without the bull. Love it.
Mysticism is positing theres a physical reality outside of your conscious experiences - a reality you never have direct access to and one which breaks down in both quantum mechanics and general relativity - and of course the physicalist abstraction never accounts for the mind experienceing it
@@maecentric Through the use of ritual one can access this realm. The opposition of mysticism and science is a false dichotomy that is perpetuated by both in the current age.
Quantum mechanics is way worse than the mystical.
No matter which way you put it, something people considered obviously true has to give.
Thank you for this video. I always couldn’t understand what was meant to be so strange about the quantum eraser experiment- it seemed obvious what would happen and thought it was just me that was missing something. Your explanation makes complete sense :-)
Maybe, but important to point out we’re still nine of the wiser on the double slit experiment itself. The video was debunking quantum eraser experiment.
What part of the experiment setup determines which of the two non-overlapping interference patterns related to D3 and D4 end up shifted more to the left or to the right? Can we change the experiment in order to change how the patterns overlap? These might be minor points, but I'll register here my doubts anyway so I can think about this later
You can change the experiment any which way you like, but that won't change that you are really just chasing your own tail. The problems are not with the experiments, it's with how you are trying to describe the world. The world simply doesn't work that way.
why can't I see the answer to this question?
Thank you, I came from one of the other videos and I didn't make sense to me, I got stuck.
This make sense, thank you for that beautiful explanation. Thank you.
Imagine a "car detector." We want to know which gate the car goes through, so we build a "detector." The detector works like this: it contains a wrecking ball that smashes anything that passes through the gate. We can tell if the car went through the gate because any car that we "measure" with our "detector" no longer runs.
So weird. The act of measuring which gate the car went through, changes the car's behavior.
Incredible!
it is weird, since no one has and probably never will explain what actually happens at the point of measurement. For your analogy to be complete, the chance that the car is hit when you launch the wrecking ball is only 50%, meaning when you inspect the wrecking ball, 50% of the time there's damage on it and by extension the car. But if you don't measure the damage on the ball post launch, somehow 100% of the time the car is undamaged.
@@Google_Censored_Commenter That's a bit of an exaggeration but I do wish folks would spend more time explaining what, exactly, is involved when we "measure" and "detect" and "look at" a photon or electron, etc. And I think this should be stated up front: "we cannot look at, measure, or detect a subatomic particle without physically interacting with it and these interactions fundamentally change some of the properties and behaviors of the object." That's just a fact, and seems to be the sum of what the two slit experiment shows. But when stated plainly, it seems a lot less weird. A photon behaves differently after we physically interact with it. If you replace the word "measure" with "interact" it just seems to make more sense. The willful choice to keep using the word, "measure" in this context seems to be an intentional attempt to make the whole thing seem stranger than it needs to be. Which is the opposite of what an explanation is supposed to do. Where the audience seeks clarity, the presenter offers obfuscation. Bad form, folks. Bad form.
@ช่องน้องจิมมี่ Not quite. Let's make sure we're talking about the same experiments because different issues can come up that we can discuss. In the traditional two slit experiment a single particle goes through the slit. Then another. Then another. Until a pattern emerges. Now we redo this experiment by adding a detector. We send one particle. Then another. Until a pattern emerges. Interestingly, the pattern is different. The detector changed the behavior of the particles because there is no such thing as "detecting" the particle without interacting with it.
@ช่องน้องจิมมี่ my original response was highlighting the fact that if the author of the video really wants to get rid of the gobbledygook, she should stop using terms like "detect" without explaining that to "detect" a particle, we have to "interact" with it. When I first learned that "looking at" a particle changed it's behavior, I started asking questions like whether it mattered if I had my glasses on or not? What if I couldn't "see" it when I "looked" at it? Turns out, what was meant by this phrase, "looking at" was something more like "bombarding with a laser" or crashing the particle through a polarizing filter. But it took me decades of chasing my tail watching videos like this and reading books about this "mysterious" thing that was happening. It was very hard for me to find an explanation of what it meant "to look at" or to "detect" the particle. Once I did learn what physicists meant by these terms, I realized they meant something completely different than what a normal person would understand these terms to mean. Once I realized this, things became much, much easier to understand.
@ช่องน้องจิมมี่ you're correct that I am making a general point about communication. Such critiques do not require a degree in physics.
Secondly, arguments should live or die on their merits, not on the credentials of the person making the argument. Otherwise we fall victim to the argument from authority fallacy.
Yes, my critique here is a pet peeves and marginal to the content, but the channel brands itself on getting rid of gobbledygook and I am all for that. A good place to start with regard to that mission statement is with the heart of the confusion about interference patterns and the the things we do to make them come and go in these experiments.
Joe Scott shitting his pants about being called "always amazing" by the always amazing Sabine Hossenfelder... well done!
I do not think in this case it was a real compliment. Sloppy Joe.
"Emiliano non tradisce, gringo!"
Really? Mindset is what you were hearing. Disposition unwilling to accept truth.
***HOSSENFELDER HAS BEEN DEBUNKED****NOBEL PRIZE 2022 PROVES NON LOCALITY IS REAL!******
The trio’s experiments proved that connections between quantum particles were not down to local ‘hidden variables’, unknown factors that invisibly tie the two outcomes together. Instead, the phenomenon comes from a genuine association in which manipulating one quantum object affects another far away. German physicist Albert Einstein famously called the phenomenon ‘spooky action at a distance’ - it is now known as quantum entanglement. The
The three winners are pioneers of the fields of quantum information and quantum communications, says Pan Jianwei, a physicist at the University of Science and Technology of China in Hefei who participated in some of Zeilinger’s landmark experiments as a graduate student in the 1990s. The recognition was long overdue, Pan says. “We have been waiting for this for a very, very long time.”
What now Sabine?
The delayed choice quantum eraser experiment was done in 1999 by Yoon-Ho Kim, R. Yu, S.P. Kulik, Y.H. Shih, and Marlan O. Scully. Scully himself has clarified the interpretation of the experiment and addressed common misconceptions about its implications, particularly regarding retroactive causation and rewriting the past.
Nobody with any serious physics chops cared. None of this quantum mysticism makes any difference to real physics.
Brilliant! I've been looking for someone to clear this up for some time. Thank you!
Great video Sabine (as always). Delighted to see this strange experiment explained correctly, finally. And I am loving the mutual respect between Matt from PBS and yourself. Science communciation working as it should!
My thoughts for long time on the Delayed Choice Quantum Eraser experiment have been like this "Sounds too much like magic, can't be true or we are doing something wrong". And I hate that everyone jumps on the opportunity to make it sound like magic, everyone makes the "Look" vs "No look" sound like magic as well.
I had the same thoughts. Another thing that made no sense to me is this: Extrapolating from the double slit experiment that our consciousness somehow determines reality, because when you "look" at a foton the interacting wave pattern disappears.....but you cannot just 'look' at a foton. It literally has to hit you it the eye for you to register it. At quantum sizes everything that is measured is interacted with. (Influenced or even stopped dead in its tracks) As far as I understand this rule also applies to the censors used in these experiments. So the foton censors interact with the fotons that they measure. This does not sound like the magic of consciousness to me, but more like physically bumping into waves/particles.
@@ThingsYoudontwanttohear waves become particle or particles become waves, doesn't it sounds more magic to you?
@@freshbakedclips4659 If you put like that, then yes indeed, that sounds like magic too.
The result of the experiment is still influenced by the future. It is still magical.
@@frozen_eclipse The screen is merely a fifth detector. It detecting(interacting) with photons before the labelled detectors do the entangled ones just means it's the bit collapsing the wave function/entanglement.
Just have to love these explanations! Thanks you Sabine!
Sabine, thank you so much for this. I deeply appreciate your genius, especially when you demonstrate that so many people in the world are wrong. Thank you for showing us simplicity in good logic and sensibility with such important topics.
@@dextermorgan4490 I am not qualified to give an opinion in this field, so I can only share my experience as a learner. I don't see the double slit experiment as something that needs explaining; it is logically fine. There are a subset of people who paint a supernatural picture of the experiment and have made videos that spread their fantastical take on the experiment; be aware of such. Nova seems to be the only longstanding company that gets things right. Try this: Start by watching all of Brian Green full length videos, but don't make conclusions at this point. Important next step, watch all pbs spacetime videos in order, this will help you understand how things work. At this point, make tentative conclusions. Lastly, watch all of Sabina's videos, this will correct misinterpretations that you might have. After that venture into long lecture series of prominent physicists. In lass than a year's time, you are likely to feel a big change in your understanding. I hope this is helpful.
@@dextermorgan4490 You are welcomed. Happy to help.
Haha, I actually remember how long I read the Wikipedia to understand these details and came to the same conclusion. Such a good feeling to be on the same page with Sabine :)
Same here!
Sure you did.
🧢
Then you read it wrong...there's no reason to deduct that graphs at d3/d4 actually overlaps....if you go over the mechanical description, the screen at D0 has a step motor that moves the screen only in one direction across the x axis....also there's no such thing as "being selective" the coincidence counter tells exactly how to pair the photons absorbed at d0 with those absorbed at d1d2d3d4
@@AlexTorres-qv3hv To confirm, are you saying Sabine's video is correct or incorrect?
Wonderful video! This healed my mind of a very troubling particles/photons-moving-backwards-in-time phenomena that the videos she mentioned had given me. Thanks, Sabine.
The version of the experiment you present wasn’t the original one done in 1999 it’s a almost completely different experiment
Imagine an experiment with momentum-entangled photons A and B. (Actually the procedure is repeated many times, so that an interference pattern may emerge even if one is only measuring a single photon at a time). The observer measures the position of photon B just before A passes the double slit. Photon A then shows single slit interference only. Another scientist, Observer II, passes by. He is traveling very fast indeed. Because simultaneity is relative, he finds that Observer I measures the position of photon B after A passed the double slit, and even after photon A was measured on the backplate. What about observer II, will he observe that the pattern resulting from the A photons on the backplate shows double-slit-interference or single-slit-interference?
You're creating a delay through "relativity of simultaneity", such that the delay exists for one observer and yet does not exist for another observer, all at once.
That's interesting.
The result, however, is rather boring. There will be only a single-slit interference pattern. Because the which-way information DOES get collected, and it doesn't matter if it's before or after A transits the slits. Remember also that A is a single particle and it will generate a single point on the detector, NOT an interference pattern.
@@DavidByrden1 Thank you :)
I actually thought some of these videos that you mention already made this clear. Maybe I'm not understanding what it is they got wrong, but I remember them saying that you need the information in the present to know which particles to disregard and create the interference pattern in the past.
@@dextermorgan4490 the issue is that in order to observe something you actually have to interact with it, so when you add an instrument to detect which slit a photon goes through, you interact with the photon at the slit and cause the wavefunction to collapse. Exactly why and how wavefunctions collapse is still not well understood (as far as I know).
If I remember correctly, Matt from PBS actually comes to the same conclusion, and explains the particular detector correlation in the followup video about the "winning the lottery with the quantum eraser" question. ua-cam.com/video/2Uzytrooz44/v-deo.html
It sounds like a debunk, but it is NOT that simple. Because you do NOT change how you measure the "interfering - non-interfering" photons as it is done in the classical double slit...
Nope! You change how you measure their entangled TWINS. If that measurement happens MUCH later, then the "interfering - non-interfering" measurement, than the conclusion is true that the effect of a decision seemingly propagates back in time.
The fact that the 2 patterns can be combined into a non-interfering blob does not nullify the experience that the result of one measurement DO CHANGE based on the method of another measurement done LATER in time.
If both detectors are working, the non-interfering blob can be seen, but the separate interference patterns can be "reconstructed" after post-correlating the measurement with the delayed measurement.
This implies 2 things:
1. The entangled particles DO act in unison, which is very WEIRD
2. Einstein can rest in peace: information do not travel back in time, because the pattern can be restored by correlating the results of the 2 measurements.
(this would mean that the entanglement is FTL, but the actual quantum information still obeys causality)
@@meleardil I love finding a real physicist in the comments. Good job 👍
I guess he did not reach quite same conclusion because of the nature of his comment on this same video: ua-cam.com/video/RQv5CVELG3U/v-deo.html&lc=UgzX3BUTGug1AR1pabp4AaABAg
See above where Matt actually admits he was wrong and says he is working on a video to fix it.
@@meleardil I'm very confused because these explanations are all so different from the traditional explanation, but if measurements do change based on another measurement later, it creates a paradox. You could create an ultra-delayed quantum eraser where you see the screen AND control whether to erase the which-way information later. Now, the system would either magically force your choice, or you could choose to get an impossible result (get interference pattern while also measuring which-way information). Another possibility would be that the mere possibility of this happening would create a clump pattern, which would all kinds of weird implications, it would become a reality predictor of "is it possible to press this button fast enough to enable collection of which-way information".
Also another technical detail for the simple single photon/electron DS experiment. When you measure the which way, by positioning the appropriate apparatus just behind the two slits then of course you see nothing on the far away positioned detection screen (a detail that is usually omitted) . Clearly showing that the interference pattern is due to the stochastic interaction of the photon particle with its immediate environment and given experiment apparatus configuration each time (detector positioned close or far away from the two slits) that consists of a collection of radiated waves, obstacles for our humble photon. The particle which has a wave part and also a concentrated point part similar to a vortex smoke ring thus a wave-particle, interferes statistically randomly with the EM waves noise field and quantum foam of its environment and is guided to the the final interference pattern integrated over time we see on the far positioned detector screen. It is similar to a boat left randomly drifting on a sea to get across and reach a long shore ahead. Accumulate different arriving of the boat along the length of the shore and you will have your interference pattern.
Finally someone to shed some photons on a much-abused quantum space! Thank you, Sabine! Please, never stop!
Only just like everyone else, no actual demonstration. Just drawings and animations.
@@MadScientist267 Yeh, while i love that she does not peddle the bs of other science quacks, a live demo would go a long way.
@@TheDJRiffin Engaging in game of Semantics is not helping you. In order for the Nature of the sub-atomic Particle to be known, all the results have to be obtained. In order for all the results to be obtained, both the sub-atomic particle and the observer has to 'know' what those results are. If the observer is not aware of all the results, how do we know if the nature of that sub-atomic was changed in the past or not ? If the observer is aware of all the results, how do we know the results are or are not from a particle being influenced in the Past ? As John Wheeler has postulated, wether a photon leaving a Star is a particle or a wave, depends on wether an observer from billions of years in the future observes it as a particle or a wave. Thats even though that particular Star still even exists when it is observed in the far far future.
@@augustadawber4378 John Wheeler sounds like a dreamer. Light is most likely the vibration of electrons. The energy passed from one electron to the next is what we currently call a photon. Let me know how this ages.
Physics need more people like you, Dr. Hossenfelder! :D
Agreed
Global warming needs more people like Sabine
Don't put her in a pedestal. Science communicators have to over-simplify and mystify anyway. Being a researcher herself, she's just able to find out other's gap and make a nice niche for her UA-cam presence.
Understatement! She is gold. Academic community needs help!
There's only one Sabine
The old 'Obfuscated Science'
A good way to sound brilliant while republishing someone else's work.
I just read Your article, with Bracken and Hance, "The Quantum Eraser paradox", and I want to congratulate You for the publication.
It is very clear in the presentation of the experiments.
It also makes it very clear that the "paradoxes" are not about what QM says, but about its interpretations: when we approach QM trying to interpret it in a specific way, we might have certain problems, paradoxes and even inconsistencies that the adherent narration of the formalism just doesn't have.
It is in fact interesting to review the different classes of problems that the various approaches present.
This is important in both the evaluation of different interpretations but also in relation to divulgation, that all too often ascribes the issues to QM itself forgetting to mention that they are instead dependent on the specific interpretation. This is of course the case for "delayed choice" (sic) experiments.
It is very intriguing that You, Bracken and Hance have devised a set up that could experimentally discriminate between QM itself and a retro-causation approach to it, I hope someone will do the experiment.
Good comment. See the paper "Taming the Delayed Choice Quantum Eraser" by Johannes Fankhauser , University of Oxford, July 25, 2017 for a simple explanation based on the deterministic Bohm theory of quantum mechanics. Dr. Hossenfelder is mostly correct, she just doesn't as yet have a firm understanding of how simple explanations based on the Bohm theory really are.
@@david203 Thank You! I'll look into the article for sure! Best regards.
Stimulated by the article, I made some consideration on the topic.
The theoretical context is that of establishing the possibility of various kind of HVTs to match QM statistics (or, otherwise, determine how they would experimentally differ), given results such as Bell's inequalities. In particular, this topic is addressed respect to the classification given by the three assumptions that lead to Bell's inequalities themselves -- locality, no-retrocausation, statistical independency.
Note: Bell's inequalities were developed to address the possibility to match QM statistics of those HVTs that satisfy EPR's requirement, with a negative conclusion. They do not imply that other type of HVT couldn't match QM. The three hypothesis might not be a good classification of HVT that could match QM, as this was not their aim by design.
Understanding what "matching QM statistics" means requires an understanding of how those statistics are produced by QM.
The probabilities of QM are used as expectations about observable physical quantities, and they are produced (by Born's rule) with a very specific probability algebra, that is what constitutes quantum logic.
The distinction between quantum and classical logic is effective and physical: if the observable physical quantities used in QM are confronted with classical counterparts, they would give different results, and the latter don't match experimental results. That is why classical physical quantities must be HV respect to the physical quantities of QM (conceding that this "hidden" adjective does not imply in principle that they cannot, eventually, be observed, it does mean that the HVs cannot be the physical quantities of QM).
On the other hand, it is not always explicit for HVTs what logic-mechanics they should follow, namely, if they are classical, quantum, or some other type. But this is an essential point in determining the statistical matching between QM and HVTs, and should be most definitely addressed.
There is, though, another way of stating that a physical theory (a mechanics) is classical, and that is by saying that is deterministic (I will not address this here, as this is already too long).
As a consequence of how we use QM and its logic, states of QM encodes more than just "what is (determined)", as they also encodes for counterfactual alternatives and holistic correlations (holistic refers to the fact that the information on the combination of systems is encoded in a way that is not separable between the systems, which is the EPR basic observation). This yields as an input for the computation executed by the mechanics information on alternatives, as a direct effect of the superposition property which is a core characterization of the logic and the most basic distinction between quantum logic and classical logic. This is not an abstract property, as it is physically effective, as shown in the EV bomb experiment -- since the QM evolves computing over alternatives, in the specific sense that it does so as an expression of the requirement to maintain overall consistency of the correlations over all alternatives, when we test correlated results we obtain statistics that are consistent beyond the mere determination of facts. This is an expression of wave-mechanics (superposition property) applied to probabilities, rather than factual waves as those of classical mechanics.
I mention this to emphasize how difficult it is to match quantum statistics for classical, or otherwise limited HVTs -- QM "works", "computes" considering information that is accessed, brought into the computation, by alternatives (why quantum computing is a powerful thing? this is why). A classical theory cannot have that information available -- determinism does not support modal logic, it trivializes to actuality, where modal logic opens up potency, namely, consideration of alternatives (this is a reason why objective and subjective probabilities are distinct by their logic, which is often unrecognized in the debate on that topic). These are the kind of limitations that needs to be addressed by the discussion on the possibility of HVTs to match QM, and they are essentially about which information is available to the mechanics (of the HVs) to determine (discriminate between) the results.
That said, onto the article.
My main doubt is if it employs a fair representation of retro-causality, where the latter is applied as a feed-back loop, the inconsistency of which is then used to argue for the exclusion of a set of results which are expected according to QM. If the argument is correct, this would yield a physical (experimental) discrimination between this RC-HVs model and QM.
I think though, that this is not entirely fair to RC, and thus not sufficient to make the conclusion for RC in general.
Given my bloated premise above, to consider Local+RC HVTs in general we need to deduce the limitations that the assumptions imply for the class of theories.
HVs work as an ancillary notebook adding information to the physical quantities, so that results on the physical quantities of QM can be discriminated according to the complete set of information.
The limitations of the different kind of HV are on how we are allowed to feed information into the notebook, and how we can organize and elaborate it.
Locality (of the mechanics) means that we only add to the system the information that the environment (= the rest of the whole) offers locally (there is also a locality which is a consequence of trivial correlations, i.e., non-holistic correlations, which equates to the separability of the encoded information among the systems, note: QL is holistic, CL is trivial).
Forward-only causation implies that the information is accessible only after it is acquired. This is an effective limitation in the sense that when systems interact they can exchange information, and then other results can be discriminated accounting for this shared information. If causation is forward-only, the discrimination of results can only be affected on successive events. But if instead we concede retro-causation, we concede that the information of an interaction can be exploited also in previous events, which in turn can be interaction events, occurred in the past of the one we started from, with other systems. At this point we can follow the other system forward in time, and see that retro-causation thus renders available into the hidden notebook information on spatially-separated results.
This illustrates, I think, that retro-causation shows itself not as the logical deduction of the exclusion of inconsistent time-loops, but rather as a specified form of super-determinism, one that can exploit the histories of systems to share and synchronize the hidden information. This is why I think the argument in the article is not entirely fair to RC.
But, the very same article shows that this form of local-RC-HVTs might not suffice to match QM. This is deduced by the consideration of the EV bomb setup, where the presence of D1 along one of the paths to D3 and D4 can be detected in the coincidence statistics of QM for the correlations of U3, U4 with D3, D4.
IF we assume that the information in the hidden notebooks of the couple of photons was not already seeded with the information on the setup of the apparatus, then while retro-causation can synchronize the correlations of actual results across the whole apparatus, it still cannot be fed with information from parts of the apparatus that are not reached by the photons, and this is limited by the assumption that the HVs determines the paths of the photons. This is where QM can exploit the fact that it elaborates over alternatives -- it "explores" all the possible paths, and only later actual results, consistent over all alternatives, are produced. Our class of local-RC-HVTs cannot do that, and thus cannot distinguish the presence of D1 by the correlation in the statistics of only U3, U4 and D3, D4. We see, and this is typical, that the issue is not to discriminate the results that QM does not determine, but to distinguish those that QM actually discriminates!
We already know that QM does this kind of distinction, and that this is experimentally tested.
Therefore, we have already excluded this class of local-RC-HVTs, IF the information on the apparatus was NOT already fed into the HVs of the photons (e.g. if retro-causation is applied back to the big-bang, and assuming this means no separation between all existent systems, RC can account for the different setups of the apparatuses).
Thus, other forms of super-determinism / retro-causation are not excluded.
Stefano, I tried to read your reply but kept getting lost. It is likely that your knowledge of QM greatly exceeds mine, such that I cannot follow your discussion. One problem for me is "determinism does not support modal logic, it trivializes to actuality", which makes no sense to me since "actuality" is very different in the very tiny domain as compared to our macroscopic statistical domain, and since you did not define "modal logic". I did not understand the non-standard terms "holistic correlations" and "counterfactual alternatives", which you did not define. As to your in-depth discussion of HVTs, I understand them to relate to experiments with simple radial symmetry (such as in atomic orbitals), which the double-slit experiment does not have. In short, you appeared to have either ignored or misunderstood the simple basic premise of the Bohm theory, which in short is that (for the double-slit) individual particle trajectories are determined by their initial position relative to the width of the slit and the Schrödinger equation (which describes the complete nonlocal experimental geometry), which determines the trajectory shapes.
@@david203 It is more likely the combination of my writing being intrinsically confusing and the irreducible conflict between what I'd like to write about and YT limiting posts to a certain number of characters (something around 10000)! ;)
Bohmian mechanics was not addressed at all in my post since I was trying to comment on the article by Sabine (I have not yet managed to read the one You referred to!!! My opening was quite misleading on this point!!!) in respect to its aims, and it considers retrocausation together with locality in a sense that does not apply to Bohmian mechanics (e.g. in the sense of the non locality You referred to).
A foreword before I try to address those definitions, the issue of how we should intend quantum logic is valid irrespective of hidden variable theories because it is the logic of the physical quantities that we deal with. The issue of HVTs is how to deduce QM from them, but it is still the QM of physical quantities that we are dealing with (at least, today and as long as it is not falsified or integrated by other physical quantities). I state this because the notions I am using are meant to address the understanding of QM in itself, before any reference to possible HVTs. Indeed, I do not think that HVTs shifts the issue of understanding QM in itself.
In a broad sense, modal logic accounts for the qualification of "is", e.g. "is actual", "is necessary", "is possible", etc.
In its ontologically-styled narration, modal logic deals with different qualities of the modus essendi (the modality of existence), which can be exploited for a suggestive distinction of subjective and objective probabilities once we recall the old discussion of actuality and potency. Suggestions might be misleading, but there is a merit in these distinctions when establishing the significance of the various part of the theory as it is established by their different relation with physis (what is given to experience and comprehended by mean of the theory). For an example of a modal approach to QM see Bas van Fraassen "QM - An empiricist view".
Now, I use "trivial" not in a negative sense, but just in the sense that it simplifies to the extent that it makes certain distinctions irrelevant. E.g. if our theory is entirely, or at least in its fundamental formulation, about actuality, then I would comment that modal logic is trivialized in the sense that we can discuss the theory without its terminology.
This is the case for determinism already in the sense that it equates to getting rid of the probabilistic formulation of physics.
Note that determinism is always about the fundamental (and ideal/metaphysical) level, whereas determination (with reference to limitations such as resolution of the determination) can be addressed at different scales.
At perhaps a more significant level, the statement "determinism does not support modal logic, it trivializes to actuality" needs to go through the links between determinism, classical logic, and subjective-epistemic probabilities. Determination and subjective probabilities are dual: it is a subjective probability if and only if it is subjective uncertainty about an objective (possibly relational) determination. Uncertainty indicates determination.
The identification of determinism and (fundamental) classical logic is due to the atomization property of the logic -- by having a unique atomization with always compatible observables, CL legitimizes the idealization of the indefinite removal of uncertainty which is what yields the deterministic formulation of classical physics. QM disallows such a formulation for its physical quantities because their QL does not have a unique atomization limit, the limits of atomization corresponds to incompatible observable and thus to their indeterminacy relations. Which is why they are called "indeterminacy", rather than "uncertainty", relations.
Within fundamental CL, i.e., once we have warranted determinism, the talk about possibilities is "merely" epistemic, subjective, trivial (in the sense of the previous terms being entirely valid), and thus modal logic is trivialized in the sense that the fundamental physics is warranted to be deterministic and thus entirely actual.
The sense in which QL, instead, "opens up" to potency is the extent in which it prescribes indetermination in the effective function of objective probabilities for the physical quantities (irrespective of HVTs, as long as they remain H, and then it's another physics).
For the previous post, the relevance of "opening up" to potency, is the possibility for QM of having information about alternatives available within the state and thus to the mechanics yielding the results. These alternatives are not available to a fundamentally deterministic theory, in fact for the very reason that being fundamentally entirely actual it cannot consider alternatives to the one realization that it is following, so that such a theory has to have other means to yield the results that QM prescribes as experimentally discriminable as a result of its consideration of alternatives. Then, the general analysis goes, these other means might have to be constrained by the other assumptions that we might like to add, until the capacity of such class of HVTs is no longer capable to match QM, indicating that either we need to change our assumptions, or we set out to experiment which one is the right theory, if we don't know the results already.
Note that, in the modal logic parlance, QM processes alternatives (of course in the sense of the superposition property) precisely in the sense that these are NOT actual -- there is one unique state and it can be represented as sums over alternatives, depending on the arbitrary choice of basis-alternatives.
PS: as soon as we consider objective probabilities, we have to address their relation to subjective probabilities, because the latter establish the physical semantic of the theory. This is another topic, but within this perspective it is entirely the emergence of classical logic within quantum logic, which also happens to be the measurement problem.
I use the term "holistic correlations" to state the that a logic, as an "algebraic" structure of probabilities, encodes the information about the combination of systems in a way that is not separable between the systems, thus it is (a name for) an analytical property of the logic. "Trivial correlations" are, in contrast, those of a logic that allows their separation. Entanglement is not separable (which is why it got its name, referring to the fact that entangled systems are not representable as separate pure states), and it expresses this not only in correlations but also as joint observables. Arguably, this might put statistical physics on a better footing than if it had a classical foundation.
Classical correlations are instead trivial, the deterministic limit of classical logic implies that the correlations are always warranted by the deterministic separate state of the system, which is always given in the theory.
"Counterfactual alternatives" is a bit emphatic, since the mere consideration of alternatives requires at least some form of counter-factuality. There is also the consideration that these "alternatives" are not actual/factual in QM, and this equates to the sense in which QM considers them, as mentioned above.
Sabine, would you consider doing a video on the box-pair experiment? I read about it a long time ago in a book called The Quantum Enigma, by Bruce Rosenblum and Fred Kuttner. I always wanted to know if anyone had repeated the experiment but with additional semi-transparent mirrors, if that were even possible. Seems to me that with the additional mirrors, if there were some physical component to the wave function of light, then the probability of collapse would decrease the further away from the intial mirror. But, if there truly is no physical property associated with the wave function, then the furthest box would have the exact same probability of collapse as the first one. The other explanation is that I don't know what I'm talking about. If I understand Occam's razor, then that's the most likely explanation.
“Yes, you can trust Sean with the quantum stuff.” Haha is that some subtle shade on his cosmology
My experience is that with Carroll, safe themes are Newton, Einstein and QM; when he begins to talk about Entropy and Time, beware!!
i have no idea who sean carroll is so can anyone please educate me
@@mayabartolabac have heard of something called….THE INTERNET?
@@mayabartolabac He is a famous physicist who has written books about theories Sabine often criticizes, like the multiverse. But since quantum mechanics is considered elementary physics for these guys, you can trust him with that.
@@cipaisone yes, and i'm using it right now
Wow, this was very interesting to me. I too looked into videos about the delayed choice quantum eraser experiment a year or two back, and I too came to the realization that the results were all expected according to QM, no retrocausality needed, so long as you were careful with the quantum states of the photons, and what happened with those states once a photon had been detected at the screen. My thinking was heavily inspired by Sean Carroll's blog post that you mentioned in the video, and I was always confused about why seemingly nobody else was explaining this as well, especially PBS spacetime, who usually produce top-notch content. I think I was left assuming that I had misunderstood something, and I pretty much forgot about it. Now I am more sure of myself that I actually got it right.
Sabine, you are brilliant and entertaining. Keep up the great work.
This was really eye-opening. I'm a layman when it comes to physics, but I do have a background in programming and a bit of a sense for logical inconsistencies. Ever since hearing the delayed choice quantum eraser described in the way that you criticized, I'd been racking my brain over how the findings seemed to necessarily require actual, functional faster-than-light communication. If manipulating the measurement at one end did really create or destroy the interference pattern on a far-away screen simultaneously, that seems like it would break a lot of fundamental assumptions about how the universe works. This explanation seems to make a whole lot more sense.
“Manipulating the measurement at one end” (D1 - D4) does not “create or destroy the interference pattern on a far-away screen” (D0). What happens at D1 - D4 happens after the signal photons have been registered at D0, and we never see information already recorded mysteriously change before our eyes after the fact. The only thing that ever gets created at D0 is a non-interference pattern. But if the experimenter chooses to destroy which path information via the idler photons at D3 and D4 and the beam splitter then signal photon strikes at D0 can be picked out that correspond to entangled idler photon partners at D3 and D4 and interference patterns can be seen at D0 residing within that non-interference pattern.
@@robertbutsch1802 Yes, I watched the video. I was explaining why the (misleading) explanations that she criticized originally confused me. If the experiment had actually worked the way those other videos described (or at least implied), then full duplex, faster-than-light communication would have to be possible, at least in principle. If you can transmit one bit, you can transmit a billion.
I’m so thankful for Sabine - she takes the stress out of physics for me. This is the only physics channel I’ll watch, because she’s the one I trust.
Edit: I don’t think that initial part was nit-picking - it actually let me finally understand (and fully believe) the double slit experiment after years of low key distress about it - thank you so much, Sabine!
The same thing happens to me. In the past I was subscribed to several channels on physics but little by little I was decanting them and now this is the only one that remains in my list.
She’s a clueless skeptic.
@@hanniffydinn6019 why clueless?
@@illogicmath she doesn’t understand quantum physics. She can’t accept the hard facts.
@@hanniffydinn6019 well she's a PhD theoretical physicist working on quantum gravity. Do you think she doesn't understand QM?
Thank you for this explanation, Sabine! I’ve struggled to make sense of this experiment for years and it’s honestly been driving me nuts. I feel like my sanity has just been restored!
Pretty much: "The sun is not bright enough to show me the world....unless i take off my 5 polarized glasses"
I am the /ˈrīdər/ you manifested earlier this year with your hypothetical comment about the starting state of the verse, and I approve of this message. Once again you have corrected yet another misunderstood then mystificated measurement and corrected mass conceptualization of it's contextual implications. Your work is noted. Thank you so much.
You neglected to mention a reason for the apparent "pattern". I heard it is from phase shifts introduced photon entangler. (Or electron entangler). You end up with 180 degrees out of phase photons or spin-up and spin-down electrons. Is that right? So when you select just one going through a single slit you get a diffraction pattern that looks sort of like it an interference pattern but it's not. Is that right?
Thank you, Sabina! These experiments and explanations were driving me crazy. Quantum physics has enough weirdness even without past-changing phenomena