The Einstein Podolsky Rosen (EPR) Paradox - A simple explanation
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- Опубліковано 6 кві 2012
- This video responds to a question about the EPR Paradox. It is explained in simple terms (no maths) but requires knowledge of some of the basics of Quantum Mechanics in my other videos. Too simple for experts!
- Наука та технологія
The rules of debate on my channel are that we keep it civilised. Otherwise I delete comments and block the users.
oh yeah well try to block me then?
+Iva Boss The axis of spin can be in any direction. What we measure is the component of that spin in either the x, y or z directions.
+Iva Boss Spin is almost certainly not what we think of in the classical sense. But spin up (along z axis) does mean as you say. x and y spin coordinates equate to left and right and in and out. As fas as Alice and Bob are concerned, if Alice measures the x coordinate the wave function then collapses and Bob ends up measuring the collapsed wave function not the original one.
I wanna be a quantum physicist but im 30 already :(
+marck hoffmann I was 37 when I started! I know 59 years old PhD student. Its never late
"Experts will probably be cringing"
I spent a good amount of time during my Ph.D with quantum -- I think you were fantastically lucid and appropriately simple.
+PhysicsMathMan not to mention that he did influence non-experts like me to study further physics. His channel helped me a lot in my bachelors and now I'm about to start my masters in physics.
PS: What subject did you study for your PhD?
+PhysicsMathMan I don't know bud, I think he pretty much laid a fundamental outline of the issue. I'm curious to know what doesn't check out.
PhysicsMathMan Yes. What's an expert anyway? He gives a tactful disclaimer
Physics specifically optics. Good luck with the Ph.D!
Is this speaking to or from a quantum life matters perspective? Because this is 4 years after.
I am from West Africa, thank you Professor. Your explanation in English is very clear. I am going to teach this when I go back home. I will teach it in all the languages I speak. This is my way of learning physics. I WILL TELL MY FRIENDS ABOUT THIS GOOD FOOD FOR THE BRAIN.
That's beautiful!
Top man. I actually feel I'm able to understand some of this stuff after I've listened to your videos, which is quite an achievement on your part.
Your simple explanation just shows me how quantum mechanics are amazing and difficult at the same time, really thank you
the problem with college these days is that they spend just 1 class attempting to give you a mental understanding and be able to mentally visually exactly what your trying prove on paper, but then every other class is just the mathematics involved... if you cant visually what your trying to prove, your just poking in the dark, unsure at every turn... thank you! I hope physics professors everywhere include these explanations much more often...
Thank you. Your lectures are great for introduction to complex ideas.
You, sir, got yourself a new subscriber. Congrats on a very simple explanation. I am going to check your other videos as well. Keep up the good work!
Excellent explanation ! For us who are not experts in the subject, this way of explaining things is awesome. Thanks you very much DrPhysicsA !
This is an Eyeopener...very good explanation for beginers.
Bravo !!!
That was the best explanation of EPR paradox I have seen so far. Many thanks!
Great overview video. Found it after Aspect, Clauser and Zellinger won the 2022 Nobel Prize in Physics demonstrating practical uses of entanglement in quantum computing and telecommunication
Many thanks for what I believe was a very helpful as stated simple explanation on a confusing state of affairs. I look forward to watching many more of your videos.
Your presentations/explanations are the best!
Absolutely astonishing lecture! Thank you very much!
That was indeed a brilliant introduction. Thanks!
Thank you so much for this clear, easy to understand explanation of the EPR Paradox. It is refreshing to see a video where you have the rule of keeping things civilized in the comment section. I have been studying quantum mechanics for about four years now and can say that I do understand quite a bit about the subject, but there is still ALOT that myself (as just an interested person) has yet to learn, and sometimes when I will post a question on other video's, I get no help, only a string of comments about my being a dumbass, or people telling me that my question was fucking stupid or the such. I am going to watch your other video's on the subject and I will post questions if I have them. I am truly thankfull for your video, it helped me to understand the EPR paradox more clearly than I had before.
There's nothing like physics being explained with a British accent! :-) Very instructive videos, thank you very much!
Thank you DrPhysicsA, your lectures are clear and interesting.
As always great video DrE
It seems that a hint of an explanation for both of these issues (EPR and Pauli) is rooted in idea of particles as waves. If the electron and the positron are thought of as two “nodes” of a shared wave function then entanglement would be inevitable. Once the spin of the electron is measured the wave function for not just one, but both particles collapses and if you are measuring an attribute of the wave function for the positron it already collapsed.
Similarly it’s hard to think of every discrete particle in the universe being connected to every other particle but easy to imagine how waves in a medium would be influenced by one another (and adjust accordingly). Just as if you throw a pebble into a pond, watch the waves and then throw another pebble in it will effect (and be effected by) the waves from the previous pebble. The only snag here is the idea that the wave needs to propagate to infinity... instantly.
Just a thought
DrPhysicsA,
This was a great video that explained clearly, and simply, a part of quantum physics that is difficult, I guess it's all difficult, in such a way I could understand it retain it enough to talk about it, and understand easier any further research that I will do, and I'm sure there will be plenty. Now if I would only watch a video about run-on sentences.
Thank you very much. I will, of course, be returning to this and many other of your videos for understanding of the very thing I want to work with for the remaining time I have left alive. At least this is part of it. I will have to understand, mathematically, all of Einstein and Rosen's work.
I look forward to more.
Hey thank you so much.. you made me understand the syllabus of 11th and 12th standard CBSE physics (India) in one go...
That’s my entire life thinking what the fuck did I study in my high school..
You made me connect the dots. Hail Quantum Mechanics 👏🏼
Thank-you very much for taking the time to make this video. Much appreciated and enjoyed. (^-^)
Thank You DrPhysicsA, good talk. Enjoyed your insight!
Thank You Sir, I finally get it ! I will now watch all of Your videos. Thank you, Thank You, Thank You.
This is a very helpful and beautiful video. Thank you.
An incredibly clear explanation. Very easy to follow. Must have taken some effort to put it together in such fashion.
Thank you. I thoroughly enjoyed your explanation. It would be interesting to see the reactions of those in a positions to decide where research funding is allocated. Humanity has such a long way to go to understand the Universe... if only they stopped trying to blow each other up first.
Your lectures are very useful. THANK YOU!!!
I think that still assumes that there would be information hidden in that additional dimension.
Can’t we consider the mechanics of the wave function as a hidden variable? That’s whats determining the probability of each observable like position, momentum, spin - it’s non-local - what’s the problem with that?
Thank you - a good lay-explanation of the EPR Paradox and a nice link to the Pauli Exclusion Principle
Very good and clear explanation that can help most people to understand. Thank you! Subbed!
I’m here because of the 2022 Nobel Prize in Physics. These videos are the clearest explanations on UA-cam IMHO.
wow you're really good at explaining things, thank you!
Excellent videos from you,keep going and simply they are great even for mid physics knowledge and more important about quantum physics,thank you
Well done Sir., I am pleased to say the simple terms were just the key. Thanks
Excellent intro sir, very well explained indeed.
This is awesome mind blowing stuff. Thank you.
Fantastic content. I feel like an expert and I am not even good at maths. Only at the end a possibility of total entanglement through all the universe was mentioned but not in detail, Id be interested in that hypothesis. Thanks!
Thanks for this nice video! :)
What about thinking about the information is being exchanged in another dimension, where the distance between the entangled particles is still zero, even if they are are removed far from each other in the three space and the time dimension. This would explain why the exchange of the information happens immediately.
Does this make sense to you?
I will deal with this in the 4th part of my current series on Quantum Mechanics concepts. In essence, Alice's measurement changes the wave function of the entangled pair which means that Bob will not be measuring the spin of the original particle but the wave function of its collapsed state.
John doesn't have to know the result at exactly the same time. It is perfectly possible for Alice to shout across the laboratory. The key point is that if Alice measures the X component of the spin and John measures the Y component of the spin of the entangled particle then John will be aware of both the X and Y components of the spin of his particle which violates Heisenberg's uncertainty principle.
the pauli exclusion story regarding each electron mysteriously assuming a unique energy level is pretty spooky !
Suppose Alice now takes her entangled photon and passes it through and up-and-down polariser. Both entangled photons will be polarised in the up-and-down direction. If Bob tries to pass his photon through a side to side polariser it won't go through. So in a similar way, when Alice measures the x component of the spin of a particle the entire wave function for the entangled particles collapses to the x component.
I love these videos, man!
Well kind of. You can get further info in my 2nd video in my atomic physics playlist. Essentially its to do with an electron's wave particle duality. The wave function also describes the probability of finding the electron at a particular point. The electron cloud is the probability distribution.
hey dr physics i really liked your video on space time and the twins paradox . physics does make sense after i watched your videos
You totally caught me off-guard w/ the Pauli Exclusion Principle. For years, I thought that only applied to particles within the same atom. I had no idea that it applies to ALL particles at the same time in all places! Thank you for the education!
It does only apply to each orbital in an atom. He is wrong in his description.
@@dynapb OK, I'm totally confused. How do I verify what the right answer is?
@@BTC_DNA Here is a good link with a diagram and description that only 2 electrons can be in any given orbital (1S, 2S, 2Px, etc). It also mentions molecules where one electron from each atom (2 electrons total) are sharing one orbital in both atoms. It definitely does not apply to a whole mass of copper or all electrons in the universe.
chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Electronic_Structure_of_Atoms_and_Molecules/Electronic_Configurations/Pauli_Exclusion_Principle#:~:text=The%20Pauli%20Exclusion%20Principle%20states,electrons%20must%20have%20opposing%20spins.
@@dynapb Thank you!
Oh ok I think I'm starting to understand, thank you! Your videos are great by the way
Excellent video. Insightful.
Thank you for the conceptual clarification.
Wonder if electrons obey the Pauli exclusion principal, in a band, not by differiencing energy levels, but by differiencing time.
Every electron must have floating time spin.
Time should be an intrinsic attribute of particles.
Astonishing, Thank you for this video. Could you make a video on heisenberg's uncertainty principle about energy and time aswell as momentum and position
This is a really good video. Thanks for uploading it was explained very well. I've subscribed :D
Brilliant, i understood finally! Thank you
Simply brilliant. Many thanks
Brilliant, thank you. I'm at last feeling less excluded, in principle ;)
Just a small point that I got stuck for a while and I need to clarify. The Pauli exclusion principle example given is good only to back the argument that it isn't strange for a particle to "know" how all the other particles of the system behave, that's what happen with electrons (in general, fermions), BUT it is not a explanation for why measuring state of one entangled particle, will guarantee we know the state of the other. Not only mathematically, it wouldn't be correct, but also because bosons can also be entangled and they suffer no Pauli exclusion principle.
Again, nothing wrong with the video, which was great, by the way. I simply got confused with that detail for a moment and I thought a public explanation would be nice, in case someone had fallen in the same trap as I did.
Ingenious. I suspect the answer is that the mechanism employed to keep the particles in the labs would affect the spin etc that would eventually be measured.
That's a very good question. It appears to be the case that no two electrons can have the same quantum state anywhere in the universe. This means that every time an electron gains or gives off energy and moves to a different energy level it had to take account of the energy states of every other electron in the universe in order to determine precisely the energy state it can occupy. That of course appears impossible but it is just one of many features of the quantum world that appear odd.
Your videos are really fantastic
Sir,
I was going to put forward a question at 9:40 when you jist answered it. I thought maybe by quantum entanglement , we can violate Heisenberg's uncertainty principle. Love to see your videos and it is my earnest request to you to upload more videos on the difference between black holes, neutron stars and white dwarfs
U r really Amazing sir thank so much enjoyed a lot😍
Great explanation, thank you!
way better than other videos on the internet.
1. It is a bit misleading to say that Bob can not measure the X spin, he can, it is just that the entanglement will be broken.
2. I have always had the theory that entanglement is just that in a higher dimension the particles are in the same "place" or not suffering from the separation of distance in our 3 spatial dimensions, therefore, there is no "traveling" of the information between them, does this make any sense?
Armando Maynez I had the exact same idea. I think space itself should be redifined in quantum physics.
I also agree with this theory. In 2D space, like a piece of paper, you can draw an electron on one end and positron on the other. They are separated by a large distance of the paper. Then when you curl the paper in the third dimension and place them on top of one another, the distance is very short. So in 2D they are far apart but in 3D (or hyperspace, as it were), they are literally on top of each other. Can't prove it but good enough for me.
Like that theory! I just read about ER = EPR which as I understand basically states that entangled particles form little wormholes. Seems similar to your theory :)
If I were to code this in a simulation, I would just have a pointer field in each particle that refers to its entanglement partner. Essentially instantaneous access to the state of the other particle without searching through arrays of "space" data or propagating any boson.
@AgentFriday Sounds like an Einstein hidden algebra hack :)
Thanks for this video, but thanks even more for your comment responses. I was already familiar with the content of the video but wanted to know about experimental verification. In Aspect's experiments (which I have to pay for a full version in order to get), is this the result? Does he just get no polarization data at 90 degrees for the entangled photons recieved on "Bob's" end?
Excellent explanation. In my A- Level class my teacher did not give this type of clear picture.
Great video but hold on: you might be confusing people when you mentioned the Uncertainty Principle when measuring the two spins on the respective particles. There is important experimental data that shows for each individual particle, when the measurement is done in the X direction and find up, then the Z direction and find up, we will find that, should we once more test the X direction, it has become "scrambled": the X direction could once again be 50/50 up or down. It seems that measuring in the other direction has "lost" the information about the first direction, which might seem spooky, but could just be that the second measurement has had a physical effect on the particle.
So, when Alice measures her particle in the X direction and sees it is positive, we do indeed know that Bob's X measurement is negative. HOWEVER: by measuring the X direction, the Z direction has become "scrambled" for Alice. As in - the coordination between her and Bob's particles is no more. Now, Bob will still find his particle to be perfectly correlated with Alice's findings in the X direction: his is indeed negative, but again by doing so he has scrambled the information in the Z direction. Both Alice and Bob, by measuring the X direction, have destroyed the correlation in the Z direction. This is what is meant by a wavefunction "collapse". It is not some magical thing, but actually really intuitive. It means the probabilities are "reset", that the correlation between the two is no more. The physical act of measuring is significant, and while this has been deeply philosophically disturbing for many and has made people think the role of the Observer is vital for reality, this isn't really the case: measuring a particle is a physical process, and it makes sense that imposing a physical process on a particle would have consequences.
So, if Bob tests the Z direction while Alice tests the X direction, what they are essentially doing is destroying the correlation between the pairs. Alice tests X, which destroys the correlation between her and Bob's particle in the Z, and Bobs tests in the Z, which destroys the correlation in the X. It is not true that by knowing Alice has X spin up and Bob has Z spin down we can "put the two together" - the other half of the information has been lost as their correlations have been terminated in the non-measured direction.
It's not that Bob "can't" measure in the X direction if Alice measured in the Z direction : it's that the information Bob gathered is not a meaningful correlation any longer. Alice tests in X direction and finds positive (Bob's should therefore be negative), however, by now testing her X direction, she has now "reset" her particle into a 50/50 probability of having either Z direction. So when Bob tests in the Z direction and finds positive (while knowing Alice is X positive), he cannot "know" that Alice's must be negative - for she has tested in the X direction, which has scrambled her Z direction. The correlation no longer exists.
Mind...blown.... Want...to..know...more.. AAaaaahhh. Dam you, Physics. Dam your addictive nature! (OK, just kidding) Seriously, I just came across your collection of videos and LOVE them. Keep them coming. We have a serious shortage of educators with your talent. They make me really miss my academic years, and help me enjoy a little more of my professional ones. Signed - a very entertained Engineer.
A good video.
If of any use, a good explanation - in more detail but not requiring a huge jump in understanding - can be found in Brian Green’s book The Fabric Of The Cosmos.
Thank you, very informative.
thanks, that is a good and easy video to understand the EPR paradox
thanks for posting the interesting video.
Electrons are particles (which could be thought to be at a single location) but also waves which have no single location. Pauli's principle certainly applied to an energy states within a single atom. It clearly applies to energy states in a crystal/ chunk of material (eg copper) because that's how we get valence and conduction bands (see other videos). Opinion is divided on whether it means no two electrons can have same state anywhere in universe.
Thanks for the great vid. I have a question. On 13:05 you say that "the electron needs to know that its entangled partner no longer exists" which leads to those 2 possible scenarios, of either hidden variables or information travelling faster than speed of light. But why does the electron need to know that its entangled partner no longer exists? Does it really matter? Is the electron's behaviour dependet upon if its entangled partner still exists or not?
Good question. As always with quantum mechanics the answer is less clear cut. Some argue (eg Prof Brian Cox) that when electrons in one atom change energy this has an impact on every other electron in the universe which have to readjust. That is certainly true in a collection of, say, Copper atoms. Its the way we get valence and conduction bands (see my 3 videos on Atomic Physics in the playlist of that name.
DrPhysicsA thanks a lot . i learned lot from you thank you again. i just got few questions needed to ask.how can we show all the fermions in the whole universe are in different states using maths ? can we also show that in a equation as those states are relevant to position ? which means atoms in two objects in two different locations cannot be 100 same ?
what is your idea about delayed quantum eraser experiment ? Thank you .
There is a very simple solution to the paradox, that fits neatly with my interpretation of QM (I am a phys graduate): The entire concept of "Colapse" and "Locations" and "Events" in the universe is the consequence of subdivision of the universe based on the "Observer", the observer can be anything at all, a human can function as one, same being a rock of sufficient size. An observer's "Point of view", the ensemble of their existance in a universe that otherwise renders everything since the very big bang as a super position of all possibilities, is what gives arise to the Existance of Events and wave function collapse.
It's an artificial point of view of the universe that is in itself the observer's exitance. Given that ensemble there is no wonder any 2 elecrons we take can communicate in a distance, at least seamingly so: It is US that have done the measurment that now contain the information needed to "Communicate" this state to the other electron, in other words measuring an electron spin changes the Observer such that it now slices the superpositional Universe so that the other electron will now be measured to go in the oposite spin. BTW measuring a spin in X erases it's spin in the Y direction, for a reason that can easily be understood given the above ensemble.
That's really Impressive Sir.
How would you related Higgs field with this entanglement of electron and positron.
Thanks for the explanation! I was struggling with the topic and this video and the one on Bell's inequality really helped me out a lot.
I'm sure this has been mooted before but an explanation of total entanglement of all particles in the Universe could be explained by the fact that originally all particles in the Universe were perfectly entangled inside the so called Singularity that gave rise to the big bang. In essence since all particles come from this original source they are all in perfect entanglement at all times.
Is it possible that there is a non-quantifiable property
in the manifold itself which allows particles to jump around
filling in for the new "available" spots thus occupying unique energy levels?
Excellent explanation. Thank you Dr.
I found a simple explanation of the EPR paradox in the following work "Proper present interpretation of quantum mechanics". It's really simple and amazing!!!!
Great explanation, I really like it.
That's a very good question. The answer must be that when Alice measures the x component of one particle then the equipment which Bob is using to measure the y component of the entangled particle will not give an answer for that particular particle.
Hello Dr. P'A, and thank you for all your informative videos. I have some serious questions about this subject;-
- When we talk about taking measurements, are we referring to the actual taking of measurements or just to what we predict from theory would be the results?
- Hypothetically or not, when taking the two measurements in each separate laboratory, must they be taken at precisely the same instant as each other? (I guess so).
- When the positron of the entangled pair gets annihilated, what happens to the electron and has this been experimentally verified?
Thank you for your answers.
still waiting for an answer?...i hope you sat down.
Actually, I fell over.
@@victoraraoz75
Thanx for the excellent explanation. I wanted to know how do we know which pair of properties would be present in quantum entanglement. like momentum and position, or spin in various axis etc, thanx
We are not saying that a particle can spin in multiple directions. What we are saying is that whatever direction represents the axis of the spin then that axis can be resolved into the three spatial components, X, Y and Z. The uncertainty principle says that you cannot measure any two of these components at the same time.
Very clear presentation.
Hi again,
One more question regards the two ground state hydrogen atoms. First you indicate every particle or atom in the universe might "know" its place relative to all other particles and that this might be the mechanism which ensures no two have the same energy levels. But, then you go on to say that "As the two atoms approach each other....." implying that this is the time when the energy levels become different, not before.
I would like to know which it is, or even if both ideas might be possible?
Thanks again for your answers.
I think you are right. Remember that the paradox was set up by EPR essentially to challenge the concepts of quantum mechanics. Einstein did not like the probabilistic nature of quantum mechanics. He thought that things were only probabilistic because there was some information that we do not yet know. He may, of course, yet be proved to be right. But at present quantum mechanics is fundamentally based on the principle that outcomes are probabilistic not deterministic.
I haven't read the comments below, so maybe these have already been asked, but:
How does the inability to measure the x manifest itself when Bob tries to measure it? Does no data register in the instrument, is the data unreadable, does Bob suddenly decide he doesn't REALLY want to do the experiment anymore (ahem jedi)?
Does the electron anihilate itself when the positron anhialites itself?
When Alice measures along the x axis the wave function collapses which means Bob will get a 50% chance of measuring up or down along the y axis.
Thank you for your replies.
I see then. So does this just mean that (as someone suggested below) the act of gathering information from the electron causes it to align along the dimension it is being "read"? A combing effect of sorts?
Alternatively, if you could gather the data with only partial combing, and if you could deduce how great of a combing you caused, could you then know both to a significant certainty?
If Alice measured the Y spin and got a value then Bob measured the X spin then Y spin which would be a different value to what Alice got would this mean that the particles or no long entangled? What if Alice measured the Y spin again? Would she get the same value as Bob did (so the particles are still entangled) or would they be different?
Actually, Bob explodes! (ahem!)
Till now, I thought the Pauli exclusion principle applied to 'single' atoms. I didn't know it applied (or is believed to apply) to 'every' atom/electron in the universe. That's mind blowing.
Thanks for comment. The answer is that there would be no y cmpt measurement. A probably too simplistic explanation goes like this. Consider a neutral pion decaying to 2 entangled photons. Photon A goes to Alice. Photon B goes to Bob. Alice passes her photon thro a polariser which polarises in the x direction and subsequently measures whether the spin is up or down. Bob attempts to use a y direction polariser and measure whether spin is left or right. But when Alice passes her photon thro....
Me too. Ph.D. physics. You made a great summary.
Very interesting. It's what I think about "in vacant or in pensive mood" instead of the golden host of daffodils. (The Daffodils, William Wordsworth). ...from Ireland.
Hi DrPhysics, I have a question. Back in 1927 or so, did Heisenberg know about entanglement? Has there ever been an experiment to predict the location of an electron using entanglement. Does this have anything to do with the Carl Jung double slit experiment.
Wonderful explanation 👍
Couldn't there be a third possibility explaining unique electron energy levels aside from (1) information traveling faster than the speed of light and (2) pre-programmed electrons with tons of information.
Could it be that a "collision" where two electrons have the same energy state is just a very low probability event even across the entire universe ? Since the change in state can be very slight as you said this seems feasible to me.
Very good... Two thumps up..))