The Einstein Podolsky Rosen (EPR) Paradox - A simple explanation
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- เผยแพร่เมื่อ 7 ต.ค. 2024
- 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!
- วิทยาศาสตร์และเทคโนโลยี
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!
"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.
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
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.
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
Excellent explanation ! For us who are not experts in the subject, this way of explaining things is awesome. Thanks you very much DrPhysicsA !
I’m here because of the 2022 Nobel Prize in Physics. These videos are the clearest explanations on TH-cam IMHO.
This is an Eyeopener...very good explanation for beginers.
Bravo !!!
I think that still assumes that there would be information hidden in that additional dimension.
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.
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 👏🏼
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
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.
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.
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.
Thank you DrPhysicsA, your lectures are clear and interesting.
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!
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.
That was the best explanation of EPR paradox I have seen so far. Many thanks!
the pauli exclusion story regarding each electron mysteriously assuming a unique energy level is pretty spooky !
Thank You DrPhysicsA, good talk. Enjoyed your insight!
There's nothing like physics being explained with a British accent! :-) Very instructive videos, thank you very much!
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.
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.
Absolutely astonishing lecture! Thank you very much!
Thank you - a good lay-explanation of the EPR Paradox and a nice link to the Pauli Exclusion Principle
Your presentations/explanations are the best!
hey dr physics i really liked your video on space time and the twins paradox . physics does make sense after i watched your videos
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.
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.
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.
You are right that Bob can make a measurement. Its just that he wont get an answer. Its like trying to measure the left/right polarisation of a light wave after it has passed thro a vertical polariser.
An incredibly clear explanation. Very easy to follow. Must have taken some effort to put it together in such fashion.
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.
Simply brilliant. Many thanks
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.
That was indeed a brilliant introduction. Thanks!
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.
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.
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.
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.
Heisenberg's UP usually says you can't precisely measure the position and momentum of a particle (eg an electron) at the same time. But there are a range of factors which can't be measured at the same time eg the x and y components of spin. EPR say that if Alice knows the x cmpt of her spin then Bob's will be known to be the opposite. If he were successfully to measure his y cmpt he would know both - and he can't. It's not just a thought expt. It can be done in lab. And you don't get an answer.
This is a very helpful and beautiful video. 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!
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.
I suppose the easiest way to think of this is to consider the position of photons. Photons in a beam of light may be polarised in any direction. But once you pass them through a polariser they will all be polarised in the direction of the polariser. Let us suppose that that is up and down. There will therefore be no side to side oscillation. If you try to pass the up-and-down polarised photons through a side to side polariser, none will get through.
Yes. Alice and Bob can be at opposite sides of a lab. They can agree in advance how they will define the axes and who will measure what.
if you search Google for "stern gerlach experiment hyperphysics" you should find a useful hyperphysics page describing the Stern Gerlach experiment. Basically you send a stream of electrons through an inhomogeneous magnetic field which splits the electrons into two beams (those with spin up and those with spin down)
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.
Thank You Sir, I finally get it ! I will now watch all of Your videos. Thank you, Thank You, Thank You.
thanks, that is a good and easy video to understand the EPR paradox
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!
The question then is, if two electrons can have the same state - how far apart do they have to be. But you are right. Every atom must have a massive number of energy states in order for every electron to have a unique one.
Thank-you very much for taking the time to make this video. Much appreciated and enjoyed. (^-^)
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.
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 :)
Agree, in essence.
At a METASPACE level distance is not the same.
It's not a matter of more DIMENSIONS.
It's more kind of caleidoscopic quantum energy soup, whose vibrations give raise to reality, as a hologram.
Yes, we are talking about very bizarre reality behavour.
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.
Well done Sir., I am pleased to say the simple terms were just the key. Thanks
Great explanation, I really like it.
I don't think you can for electrons. That is why it is a thought experiment. But it appears you can do so for photons. I'm not sure exactly how. A neutral pion decays to two entangled photons. Alain Aspect et al did this experiment in 1981/82. You can search on the web for "EPR - Alain Aspect" for more details.
That was what EPR argued. They said that either the entanglement meant that information was communicated instantaneously or that the particles each contained a hidden DNA which controlled their every move. Neither appears to be right. EPR does not mean we can communicate instantaneously because no useful info is transmitted. If Bob were 1 light year away from Alice and measured the x cmpt of his particle he instantly knows that the x compt is of Alice's. But no useful info has been communicated.
U r really Amazing sir thank so much enjoyed a lot😍
As one other comment suggested, there may be only one particle. It is assumed that there are two and that a split actually occurred. As was stated, at the subatomic level, things behave differently than what we can perceive at our macroscopic level.
Here's a very crude analogy:
On a piece of tracing paper, draw a source dot (particle). At 180 degrees apart draw lines spanning one inch from the source dot and place another dot (daughter particles) at the end of each line. Draw a semi circle around each daughter with an arrow indicating opposite spin direction. Now it appears as though there are two daughter particles with opposite spins.
If at the subatomic level, the space / time relationship is not what we perceive it to be at our macroscopic level, we can view this a bit differently. Fold the paper such that the crease bisects the parent dot and superimposes the daughter dots on top of one another. Note as perceived from either side of the paper, the spins are identical. They are just viewed from a different perspective. This is just like viewing the hands of a clock from the front and the back. The hands have the same rotation, but depending on perspective, one is clockwise and the other is counter clockwise.
So at this subatomic level, has space been transcended?
I should say that this is not a view which is shared by everyone. It is a bit difficult to think that whenever any electron changes its energy state every single other electron in the entire universe has to make an adjustment. But clearly the Pauli principle extends beyond just one atom because that is the way, the example, that valence and conduction bands are formed in metals.
That is the perversity of quantum mechanics. It's not about limitations on experimental technique. It's just a fundamental point about the behaviour of elementary particles. Your point is precisely what puzzled E P and R. They couldn't believe it either. They thought there had to be something deterministic, that we didn't know about yet (the so called hidden variables) but that doesn't seem to be the case.
Excellent explanation. In my A- Level class my teacher did not give this type of clear picture.
Contrary to what the video says at 10:34, Bob can always measure any coordinate, no matter what Alice does.
This is really a thought experiment. But it has been tried with particles which don't decay so they can be measured. In practice, Bob's equipment will not give a result in the circumstances you described.
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.
I like the statement at 17:21 'there has to be a reason why this happens'. Leibniz' principle of sufficient reason is still with us.
Use a spectrograph to measuere the ×@y function,and using a block intercept to see the outcome
Such an easy introduction indeed =p
I'm glad I've heard Richard Feynman's quote: "If you think you understand quantum mechanics, you don't understand quantum mechanics."
"In other words, instead of treating a woman like a sexual service provider to be purchased with alcohol, the master suggested that a man “disrespects” a woman by being honest and asking for sexual consent. Feynman takes his advice, and consequently trains himself to think of women as “bitches”:
Well, someone only has to give me the principle, and I get the idea. All during the next day I built up my psychology differently: I adopted the attitude that those bar girls are all bitches, that they aren’t worth anything, and all they’re in there for is to get you to buy them a drink, and they’re not going to give you a goddamn thing; I’m not going to be a gentleman to such worthless bitches, and so on. I learned it till it was automatic."
restructure.wordpress.com/2009/08/07/sexist-feynman-called-a-woman-worse-than-a-whore/
Feynman was a fucking boss dude
Brilliant, thank you. I'm at last feeling less excluded, in principle ;)
You've got me there I'm afraid. I wonder if instead of teleporting you might just create a clone. But of course you'd have to find a way of doing what you propose. Not easy!
"there will be no maths"
>pulls out the lambda
yeah, even worse--Greek!
(joke)
Great video, thanks for doing your best to explain what is far beyond us laymen.
her x polariser the wave function of the entangled system (ie one wave function covers both photons since they are entangled) will collapse to a x polarised state (even tho Bob's photon has not been thro an x polariser). So Bob's photon will no longer have a y component of spin. So he will get no result when he tries to measure it. Ie the result will be that it is neither up nor down.
Brilliant, i understood finally! Thank you
This is awesome mind blowing stuff. Thank you.
This gentleman treats the subjects within the integrity of proven scientific formalism...
* In fact, both Alice and Bob are bound to measure the spin of the entangled electron-positron pair zero since the fermions can always be found in singled states, so no paradox...
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....
There is a further possibility and that is that the entangled pairs are connected via another dimension and represent different aspects of the same particle or wave.
congratulation.. Your intuition is true ... I have a mathematical proof - unpublished - for this talk .. Actually, the entanglement does not happen in the same dimension
This explanation sounds nice, but I believe it's functionally the same as hidden variables- at least that's what I've been told.
Your lectures are very useful. THANK YOU!!!
When Bob tries to measure the y component, there will not be one because the collapsed version of the wave function now contains only an x component of the spin.
Not quite. Where you have two entangled particles, then if Alice makes no measurement Bob can measure the x (ie the x component of his particle's spin) or y (but not both simultaneously). But if Alice measures x of her particle, Bob can measure his x, but not his y
way better than other videos on the internet.
As normal matter moves towards the speed of light time from an outsider's perspective time slows down. For objects travelling near the speed of light, time appears frozen. However, time is not frozen from within the fast moving object (it merely takes must less time to travel although external matter is aging very rapidly). Energy travels exactly at the speed of light (in a vacuum) where time essentially completely stops from an outsider's perspective looking inward (the internal state appears completely frozen in time) despite the external perspective's of time passing. Thus light (or electrons) are completely frozen in time from the time they leave a source to the time they arrive at a destination from an outsider's perspective. In the case of entangled pairs, it's possible that the e- and e+ left a source point is exactly the same time frame it arrives at the destination (thus appearing to be instantaneous from e- and e+ perspective). Thus two e- and e+ travelling away from each other are essentially leaving and arriving at the same moment in time. Measuring one state of e- or e+ at the destination could affect the other instantaneously at the source point because the e- and e+ leave and arrive at the same moment from their perspective (without breaking relativity). In other words, measuring the state at the destination is like measuring the state at the source point as they both e- and e+ are effectively at both places at once (i.e. source and destination) even though time is happening around e- and e+.
+ardana1973 I think you genuinely just solved the paradox.
+iFokshe Pah I'm just glad someone else was able to understand my confusing explanation!
Modern physicists and mathematicians are insanely narrow minded. It's sad that so much information doesn't get the proper respect it deserves. You are answering a very difficult question that will baffle these narrow minded 'intellects' for another 100's years until they somehow think of it themselves.
Superstring theory has gained knowledge of time and distance distortion when speed is introduced. The faster an object travels the shorter the distance. An object travelling near the speed of light has no distance. Since we are stationary we observe distance but it is an illusion.
+ardana1973 It happens also below the speed of light. Sadly.
Very good... Two thumps up..))
Very good and clear explanation that can help most people to understand. Thank you! Subbed!
Your videos are really fantastic
wow you're really good at explaining things, thank you!
Thanks for a very clear, simple explanation of this whole topic.
Personally, I just find it very hard to believe in many of the theories scientists today proclaim as facts, more or less, such as quantum mechanics. If things behave as both particles and waves, clearly it's a very different phenomena than we currently understand. Electrons can't be in the same state from our old models, but clearly they can. There is much in many of the theories that makes it quite obvious that they are temporary guesses at best, such as "strange" quarks. Things are only strange as long as they're not understood. The ideas that particles also "communicate" is ludicrous. Heisenberg's uncertainty principle only describe a problem in measuring or observing a phenomenon, it's not an explanation of reality. You cannot measure anything without spending time on it, for instance, so when the observation has been done, the world has already changed. I've been saying these are all models which are useful tools, but not even close to the truth, and for once, someone else actually managed to make that a point. We don't have the answer yet. We don't know why things are like they are.
+Vermilicious Agreed. But the Heisenberg uncertainty principle really goes much, much deeper than a measurement problem alone. I think we need to think about elementary "particles" as manifestations of one underlying system we have no clue of what it is. Well, we call it by the name of "the universe". That is as far as I got. Not very far....
The Einstein-Podolsky-Rosen paradox or the EPR paradox of 1935 is a thought experiment in quantum mechanics with which Albert Einstein and his colleagues Boris Podolsky and Nathan Rosen (EPR) claimed to demonstrate that the wave function does not provide a complete description of physical reality, and hence that the ...
I greatly appreciate DrPhysicsA for his videos and knowledge, but as a chemist I have always understood/learned the Pauli exclusion principle as no two electrons " in a covalent bond" can have the same spin. All covalent bonds (orbitals) have two electrons therefore one has to be up and the other down +1/2 and -1/2. It doesn't mean that no two electrons "in the universe" can have the same quantum number.
Not sure how. If Bob and Alice are on different stars and Bob wants to know whether a football team has won with an understanding that 0 = win and 1 = loss Alice cannot do the expt till the result is known and Bob will have to wait till the entangled particle reaches him (at less than or equal to the speed of light) before seeing if the measurement can be made.
There is an interesting debate on this. Not everyone supports the idea that Pauli's exclusion principle prevents any two electrons anywhere in the universe from having precisely the same state. But that is certainly the case eg for a block of copper. That's how we get valence and conduction bands (see my video: "Atomic Structure - A Level Physics").
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.
10:29 in original EPR, A measures position and B decides measure momentum! The IMPORTANT is that B knows con certainty the position AND has mesure the momentum. The argument is similar changing to A-momentum and B-position
Dynamism does not require some form of "knowing." Electrons don't just move, they give off and absorb photons. This is entirely dynamical and could very easily explain how electrons and other particles adjust so that they don't violate the Pauli exclusion principle. There's doesn't need to be some "spooky" communication in order to accommodate this. Particles react through their forces / interactions with force carriers. But there do seem to be certain conserved qualities even when particles react and interact. Direction of spin, apparently, is one of them. This does not require some "hidden variable" if these qualities are conserved.