Quantum Randomness
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- Опубликовано: 6 июн 2024
- How is quantum randomness anymore mysterious than the randomness of a coin flip?
You'll see.
The homework questions and extra readings are below:
The questions:
1. What if there are three slits and you only have a detector at one. What does the wavefunction of a particle that goes through look like before and after?
2. The second question is about what counts as a measurement. I kind of implied that interactions with air and light count as measurements. Do you think all interactions count?
3. What about if a machine does a measurement and then, without storing it in memory, prints the result, and burns it. Is the wavefunction still collapsed?
4. And finally one about interpretations. What do you think of quantum randomness? Do you understand why physicists had problems with it? As you may know, there are hidden variable alternatives to Quantum mechanics that don’t have true randomness does this make them more appealing? Are there any issues with hidden variables?
Citations and extra reading!
-Check out this remarkable video on the 'randomness' of coin flips: • How random is a coin t...
-Also check out this great videos by Veritasium and Vsauce on this exact issue of apparent randomness (versus true randomness): • What is NOT Random? and • What is Random?
-If you want to know how to do really sophisticated stuff with the ideas touched on in the video, I highly recommend Ch 3 of Vol III of the Feynman Lectures. www.feynmanlectures.caltech.edu/
-Einstein's quote in full is: "As I have said so many times, God doesn't play dice with the world." .... At least according to wikiquote: en.wikiquote.org/wiki/Albert_E...
I was expecting this video to be about all possible things, but by the time I played it, other viewers had collapsed it's wave function. So now it's just about quantum randomness.
How dare they! I'm sorry about that.
It's okay. I'm used to it. The other day I was going to eat all possible sandwiches, and that quickly collapsed into a turkey/bacon club, even though I was hoping for a ruben.
Patrick Melody lol
Patrick Melody
@@LookingGlassUniverse you should take more responsibility and prevent this!
I don’t understand how something can have a probability of happening, but still not be driven by something. Something that can be measured and calculated given an advanced enough understanding
I think thats the point, that we dont have a strong enough understanding. Until we do, its random.
@@bubbleteakun that’s what I was thinking before, but I thought they said they proved it to be random (but I can’t watch it again rn)
No, when particles are a wave, they are truly a wave of possibilities. Meaning they are in a state of statistical possibility. This is TRUE randomness. It's difficult for our brains to comprehend something happening without a driving force but logically things of this nature must exist.
For instance, how did the universe begin?
You could say the universe, space, and time started with the big bang, in that case it must be a reaction without an action as there were no laws of physics to govern its inception.
Or if you believe that the universe is somehow eternal and has no beginning or end and we just live in a bubble of that eternity, then you're still left with the same problem. For something to have no beginning it must exist without an action to set it into motion.
Therefore, logically, there must exist phenomena in the universe that just are, without it being nescessary to include a driving force.
These videos are didactically brilliant. Very intuitive and yet the narration is _precise_ (no flawed analogies, no hand waving). Bravo !
First, this is a FABULOUS series on Quantum Physics--so clear! Thank you!
I also want to mention that I've read a different explanation for why macroscopic objects don't create interference patterns even though they are made of quantum particles so should have "matter waves." The explanation you gave is that their wave functions quickly collapse due to interactions with other particles. That makes sense. However, in addition, macroscopic objects have a lot more energy than quantum objects. The higher the energy, the shorter the wavelength. Short wavelengths don't experience diffraction when traveling through slits that are much bigger than themselves (true in classical physics, too). No diffraction pattern results in no interference pattern.
Late answers without having read the posts below...
1) I would expect a triple-slit experiment to mathematically act the same as a double-slit experiment. The number of slits would not affect the basic reality of the quantum wave/particle duality.
2) Yes. Any method of measurement that interacts with a "particle" will collapse that particle's quantum waveform.
3) No. There are certain experimental circumstances (like the delayed-quantum eraser) whereby which-path information can be first ascertained and then "erased"... whereupon the particle resumes acting in a wave-like manner.
4) How do I feel about quantum randomness?
Excited! To quote Neil DeGrasse Tyson: "The universe told me." Hard to ignore...
The demonstrably WEIRD nature of Quantum Mechanics proves we're missing something important in our modern understanding of physics. For me, the deepest mystery of QM today is entanglement. The double-slit experiment is kinda the "kindergarten-artwork-on-the-fridge."
OTOH - I'm really excited about the unfathomable experimental results of all the "entanglement" explorations going on today. Apparently, information is INSTANTANEOUSLY propagated, across ANY distance, between specifically and deliberately paired sub-atomic particles - Regardless how large that distance is!
I'm ECSTATIC that we have more to learn, and that we might find some answers during MY lifetime! What a GREAT time t be alive!!!!!!
It's open and creative explanations like these that inspire new perspectives and new breakthroughs in human understanding. Great work!
I love your videos! Unlike many other videos, you explain things really well and also discuss the deep questions! Also your drawing and animations are very cool!
you just BLEW MY MIND!!!
I actually feel like I understand why we don't see quantum stuff in the macro-scale. It just... wow
This is absolutely amazing! You've taught me so much- I'm truly grateful.
You're great at explaining things. I've understood everything so far! (I think) Keep it up! Can't wait to learn more :)
True randomness really bugs me. It probably has something to do with me being a programmer and being used to think in terms of deterministic systems. If you're playing, say, Monopoly on a computer, when it's time to roll the dice, if you take a snapshot of all of your computer's memory, you can positively determine what "random" number on the dice is going to land - as is the case IRL with classical physics. You simulate, because from one state you can only get to a single possible next state, there's no real randomness to it. I get that, and I feel comfortable thinking in those terms. But this "true" randomness in quantum mechanics... I just can't help but feel there's more to it, that there's something we're missing, another bunch of hidden variables that determine the outcomes, just this time at a much lower level.
But then again, if the entire universe is deterministic, you could simulate it. Of course, it would be impossible to measure everything in the entire universe all at once and use it for simulation, that could then essentially predict the entire future, forever. But what if that could be done on a smaller scale? There's an idea that bewilders me - what if you could simulate yourself and enough of your surroundings? That simulation would contain your thoughts about it and your reactions to seeing your thoughts - about seeing your thoughts. I can't help but wonder what that would look and feel like. Similarly, if someone created a prefect copy of yourself in split second in front of you - what would you say to each other? Would you just start saying exact same things in unison, because your brains started from the same state and are functioning in the exact same way? I guess non-determinism of the universe would at least nullify such concerns. But then again, I love sci-fi and sometimes think too much...
(edit: I'm aware that my "local simulation" has a bunch of problems, including the recursive nature of it (such a simulating machine would have to simulate itself for it to work), but I'm still guessing even with limited recursion and limited area and whatever else needs to be limited, it could at least theoretically be accurate enough for you to be profoundly perplexed for at least a few seconds)
I understand your pain! I only do basic programming, but I have a similar training in a way: because of my classical physics training, I view Newton's laws as this iterative process. You put in initial conditions at each time step and then update them using a linear approximation. In fact that was one of the first things I learnt to code. That way of thinking had such a profound impact on me- and I think it has on you too.
I love your thought experiment about programming a copy of yourself! I wonder whether the behaviour necessarily converges or if it blows up at some point! Self reference is fascinating, so feel free to spew crazy ideas whenever :P Oh! Do you have any good sci-fi book recommendations?
The edit is awesome :P
Sorry, I'll have to dissapoint in that regard - never been much for reading. My sci-fi mostly comes from movies, TV and games. Shameful, I know.
Looking Glass Universe My guess is that you would start out saying the same thing, but because each copy of yourself is getting different context cues, and different photons are coming into each of your pair of eyes, the electrical brain activity would be altered, so you would have different behavior.
Leslie Colton Yeah, that sounds about right, I was thinking the same thing. Soo... pure white sensory deprivation room for maximum effect! :)
I see true randomness a bit like a perfect circle. No one can ever see it, yet it makes sense to talk about it. We have a whole set of geometric theorems etc. that lead to some very practical results, derived from some properties we can only think about. In the same way, we can only think about true randomness, but nothing in our abilities can generate it, because it is such a fundamental concept. What we're observing here might just be another case of hidden variables, but where would that lead? Is there an infinite series of underlying causes? When you get to the underlying variables, what determines them? And those rules that shape everything, where do they come from? There are some theories about other universes with different physical constants and rules... So I wonder if we'll ever hit a real boundary, and what that would mean for science.
Interesting, concise, and brilliant as always. Keep up the great videos. Thank you so much!
Thank you so much for such a sweet comment :)!
Absolutely love your videos. I like the questions at the end, which brings me to a request. I would love to see a video about weak measurements and the attributes we can get from a particle in a superposition state without collapsing the wave function. IE: add enegy to a particle send it off and measure the photons it spins off rather than the particle itself.
I really, really love this channel. Last night I watched everything in row (yup, that's how I spent my late friday night. I know I'm sad, you don't have to tell me :D) and ended up falling asleep in couch with the video still playing :D So today I tried again and actually took some notes (like I often do when watching my favorite channels. Again, I'm a sad person) and here are my answers:
1. I think we would see an interference pattern for two unmeasured doors (not slits, 'cause I'm not THAT boring after all) and one extra hole with "normal" stack of...apples? Not sure how that would work out as an equation but I'm lost in math anyways. Superposition for unmeasured doors plus one 1/3 change to go in measured door?
2. Mostly yes, but I've heard about "weak measurement" that doesn't effect the outcome like the normal measurement but still tells us something about the particle, what's that?
3. I think you just explained that once wave function is gone, it's gone? So yes it would collapse it.
4. I love it. Like a cat I'd like to think that we're all mad here and some strangeness and truly random things contrary to deterministic nature of most sciences. Random do play role in many things, say evolution, but I understand that's just random due to ignorance? However, I think Veritasium or MinutePhysics talked about some experiments that seem to prove that there is no hidden information and encounters are truly random. I should seek the video I'm thinking...
Great video, it answered the question about “does the measurement collapse the wave function even if you don’t look at the results” question I’ve had for a long time. Thanks!
First of all thanks for the new video, it was brilliant as usual :)
Question 1:
I would say that before it looks like |Y> = a|door 1> + b|door 2> + c|door 3> before
If it goes through door 1 (the one with the detector) |Y> = |door 1>
If it goes through another door |Y> = d|door 2> + e|door 3>
so the interference pattern will look like a normal one but with a higher concentration of particles behind the first door.
Question 2:
I think not, as when you change the polarization of light the wave function doesn't always collapse. That is one example but there are probably other interactions that won't modify the wave function but only ones that would not allow you to know which door it went through.
Question 3:
Yes, because it is the act of measuring and not the act of storing the data that collapses it.
Question 4:
I personally love the idea that there are some aspects that can never be predicted. I find it very interesting even though I can see why it was (and still is) discomforting for some people and scientists.
Disclaimer : these are all personal answers to the questions that I came up with on the spot. I did not do research to find them so they may be (and probably are) incorrect.
Thank you, that's really lovely (and a bit of a relief!)
1) Perfect!!
2) Such a great example! Might use that one actually in the follow up video to this one.
3) I agree... but I want to convince you that the information part is still important.
4) I think your personal opinions are great and I'm very happy that you didn't research them. It's a brave and worth while thing to be prepared to be wrong sometimes :P
Is quantum randomness truly random, or do we just not know how to calculate how the wave function will collapse? Perhaps we just don't have the math to calculate wave function collapsiness and can only guess at its probability.
No, some sets of quantum experiments had showed that such thing don't exists. It the fundamental nature of reality to behave that way. It will be more clear if go check out the bells theorem.
@@ankittiwari1647 It can still be deterministic. Bell's inequalities just mean hidden variables interpretations can't keep locality, but the universe can still be deterministic.
@@orlandomoreno6168 yes I agree but your answer is applicable in only broader sense.
If you would dig deep enough universe is nondeterministic. I don't believe it though
@@orlandomoreno6168 Yes but how? And why is there no videos (or literature, for that matter) about this whatsoever?
Rupesh Sahu I wonder the same thing. Also, if it’s random, how can there be a predictable probability distribution?
Finally I understood what the wave function is . Thank you.
Thanks for the nice vedio. Your ideas are flowing smoothly to our brains :)
For the 3 slit experiment, the particle will go through the monitored door one third of the times and hence its wave function will collapse after passing the detector (no interference). Two thurds of the times, the particle will be in a superposition for both of the un-monitored doors and interference pattern similar to double slit experiment should appear.
For the apple example, I believe there will be no interference pattern because of the size and distances of the two doors compairing to the huge size of the apple.
regarding the other question, I have no clue and wonder if there are experiments in this matter.
Thanks again for your kindness.
In relation with question 2 , experiments were done that show quite conclusively that deleting the detector results *before* checking the result on the screen (X-ray sensitive film) always results in interference pattern. That sort of supports the idea that the detection information must be available not merely performed by a machine.
Great videos! You really have a talent for explaining very complicated things simply. Thanks! Keep it up :-)
Ill take a whack at it...
1. If the particle is measured (at the top door) the wavefunction collapses. If it is not measured, then it is still in superposition between the middle and lower doors.
2. Interaction only collapses the wavefunction if what it is interacting with is a collapsed wavefunction
3. The wavefunction was collapsed at the point it was measured. That is its startingpoint and a new wavefunction would need to be calcuted based on that time zero.
4. randomness from chaos makes more intuitive sense, but quantum randomness is a mindtwister but QM has extremely good predictive power so should be accepted. People typically have difficulty with comprehension of physical laws and theories that are outside their sensory experience with things that scale with us and our natural environment. The TL;DR... our brains didn't evolve in a microscopic or an immensely macroscopic (eg planetary) scale. And we surely never even pondered the Planck scale until last century.
1. Yes!
2. ohh, that's a really cool idea!
3. Yup :)
4. Great points, that's very true that we aren't made for and used to things at that level!
Well done!
Looking Glass Universe ty :D
Looking Glass Universe how come you never say, well done, to me
2) correct me if I´m wrong but isn´t it possible to describe all particles (electron neutrons.................) with wavefunctions how then should the first collapsed wavefunctrion have been created. (if it only collapses by interaction with other collapsed wavefunctions).
ps. i really like the idea. just instantly came up with this maby a little bit philosophical "where did it all start" kind of question.
Great video, it really helped me understand the double slit experiment, thanks!
Stephenn Bmoremiriiij So happy to hear it :)
Cool! I loved it! Good luck in making more videos! All the best!
Thank you so much for your videos. You make this subject very interesting to learn about. I do have a question, I'm wondering why there are square roots in the coefficients for the wave function?
Truely good as always
hey great videos!!! I do want to know the answer of your homework in this video, do you have a video to explain that? Thanks
If you have a double slit with detectors at both slits, and then behind that grating, have another grating with double slits but without any detectors, would it just form another double slit interference pattern on the observing screen or just 2 lumps?
As for the apples not creating an interference pattern:
For waves to interfere with each other, the slits must be about the same size as the wavelength. Our everyday word seems deterministic because the wavelengths of these large objects are too small in comparison to the size of the object. This is why larger molecules like C60 can exhibit wavelike properties, but we can't perceive the dual nature of an apple. It has nothing to do with other things like light and particularly air collapsing the wave function. If this were the case, the wave functions of electrons or atoms or molecules would always or almost always be collapsed as well due to their interactions with photons.
For question 1 would it go through the other ones as a super position and ignoring the 1st door/slit as if it is being watched
1. I suppose you'd see particle-like behaviour from the particles that went through the slit with the detector and a wave-like interference pattern from the ones that went through the other slits.
2. I don't know. The fundamental forces are always affecting a particle, just not always very much depending on the distance, so those can't really count as interactions that "must" collapse the wave-function.
3. That particular wave-function stays collapsed, but does it really collapse into just a single point with 100% probability, or does it just collapse into a simpler wave-function? If I understand Heisenberg's uncertainty principle correctly, the latter seems more likely to be the case.
4. I honestly prefer the alternatives with true randomness. This is more for philosophical reason: if everything is deterministic, what becomes of free will?
2. Yes! I grinned so hard when I read that. Exactly!
3. The heisenberg uncertainty principle doesn't actually prevent us from collapsing the wavefunction fully in this case- it would if I was measuring position or momentum so it's a really good point to bring up, but in this case its fine :) I'll explain it in a video soon- but basically its because the complimentary variable in this case does now have maximum uncertainty.
4. Ah! So glad you brought this up. I've been really keen to discuss this with more people. I don't think quantum randomness saves free will. Say there are two different versions of Alice, A1 and A2, in two types of universes. One is deterministic, the other has randomness due to quantumness. They are presented with a choice. A1's action is determined. Howevever, A2's is not... her choice will, completely randomly, be influenced by quantum mechanics. How is that in anyway her will? She didn't choose the outcome any more than A1, surely? She can't influence what quantum mechanics decides for her.
Looking Glass Universe Free will discussions often skip an important part which is definition of self. If self is purely physical and free will is something not influenced by the physical then it ends right there, you don't have free will. If however you argue that there is something metaphysical about the self then you raise all kinds of questions like: Could you ever (and how) measure that? What makes the connection and could it be established artificially?, and so on. This goes for QM effects too if the argument is that they do something that is not just random.
To me it makes much more sense that our brain is made so that it constructs an appearance of its agency, than the other options. However it still has its will determined by the surroundings and its individual history, and I don't see why it shouldn't be like that.
Really interesting. I don't think lack of true randomness in our physical environment, even on the quantum level, means there is no free will. The laws of gravity dictate that if you jump out of a plane, you're going to fall back towards the Earth. You don't randomly fall up some of the time or even fall at different speeds. If you jump out of a plane, someone with better math skills than me :) would probably be able to work out where you would land if they knew the height of plane, your mass, body position, wind speeds, etc. But whether or not you jump, exactly when you jump, how you jump, or whether or not you even get on that plane to begin with is all up to you. Those are all your choices that you make with your own free will. The laws of nature ensure a kind of consistency of experience, but we're all making choices to set things in motion, I think.
SerenityChaser Oo well the choices you make are the product of interactions in your brain right? You thinking is really just an array of neurons firing a certain way. If you decide to jump it's because your mind, your physical brain is in such an orientation that is it set for you to jump. If I could know what every particle that would ever interact with you would do and how it would effect every particle you are made of I could no if you would jump or not. Your decisions could be traced back to the big bang essentially. With quantum that is not the case because it is nondeterministic. The quantum randomness messes with my ability to know. To predict.
@@LookingGlassUniverse exactly. No one can predict how she will chose, but it's not her choosing, but rather the god of dice.
Great video!!!!
i hope you make videos answering all the question time questions
I should.... (that was the original plan)... but it will depend on my laziness :P
[edit]- rewrote part 2 to be more pedagogical. It's been a while since I thought about this stuff so it's good practice for me. I'm used to just blindly doing calculations. Sorry for spamming the comments section with walls of text but I'm glad to see outreach projects like your video series being undertaken. They're important.
Ok, so I thought I'd say a little about wavefunction collapse and the ambiguity that often surrounds it.
At 3:34, the video discusses the a two-slit + detector experiment, and describes one observer objectively collapsing the wavefunction for another. There are certainly interpretations that attempt to describe quantum phenomena in these terms, but it is not part of the standard interpretation of QM. I'll try to describe the standard quantum interpretation.
It's important to disentangle (no pun intended) two procedures that often fall under the umbrella term "wavefunction collapse".
1) The observer accounting for all degrees of freedom of the experiment correctly.
2) An observer updating their information, based on some new observation.
1) Degrees of freedom: First, we must clarify what is meant by "the particle's wavefunction". The wavefunction is not just a description of a quantum particle. It is a description of what we can observe of the particle, in the context of a particular experiment. This contextuality is vital for understanding the wavefunction as described by standard QM. So, even before any observation is made, or any experiment is run, the wavefunction for the slits-with-detector experiment will look very different from the slits-without-detector experiment.
For the slits-without-detector experiment, the wavefunction will look like (ignoring normalisation terms like square root of 1/2)
|ψ(x)> = a(x)|particle goes through slit 1> + b(x)|particle goes through slit 2>
For the slits-with-detector experiment, the wavefunction will look like
|ψ'(x)> = a(x)|particle goes through slit 1>|detector goes off> + b(x)|particle goes through slit 2>|detector doesn't go off>
Notice that |ψ'(x)> has some extra kets. These extra kets are what destroy the interference pattern in the experiment. They represent a correlation between the detector and the particles. So, even before an experiment is carried out by either Alice or Bob, they can both use the correct wavefunction to predict what pattern will appear on the screen, depending on what experiment they carry out. This is why Alice knows the particles will form a clumped pattern on the back screen even if Bob does not tell her whether or not the detector went off. She knows it even before the experiment starts.
2) An observer updating their knowledge: With the previous point in mind, I can now show that Bob's observation of which slit the particle went through does not collapse the wavefunction Alice uses, even though neither of them see an interference pattern.
The setup: As the particle passes through the experiment, Bob observes the detector result, and so updates his knowledge of which slit the detector went through, while Alice doesn't. We'll look at the sequence of events in three steps.
i) The particle before it passes through the slits.
ii) The particle passing through the slits+detector
iii) The particle striking the screen
i) Before the particle reaches the detector, both Alice and Bob know as much as each other, so they will be using the same wavefunction |ψ> = a(x)|slit 1> + b(x)|slit 2>
ii) Bob looks at the detector result, and therefore updates his knowledge. His wavefunction is now, for example,
|ψ> = a(x)|slit 1>|detector goes off>
It has "collapsed". Alice, however, does not look at the particle detector result. Her wavefunction does not collapse, and is now
|ψ> = a(x)|slit 1>|detector goes off> + b(x)|slit 2>|detector doesn't go off>
Note that, even though she doesn't look at the detector result, she must still include the fact that the detector is now entangled with the particle. If she doesn't she will be describing the wrong experiment with her wavefunction. This entanglement is why Alice knows there will be no interference pattern, even though she has not personally observed the detector.
iii) Bob's wavefunction now predicts the particle will strike the screen at position x with a probability |a(x)|^2, while Alice's predicts a probability of |a(x)|^2 + |b(x)|^2. The difference in their wavefunction reflect their different knowledge, but neither is wrong. Bob just knows more than Alice. If the experiment is repeated multiple times, both Alice's and Bob's procedures will predict the correct pattern on the screen.
Awesome :D
This both cleared and obscured stuff a bit...
It seems to me that there are many preconditions the humans have made about the quantum theory, in order to make it make sense...
Your videos definitely get me thinking. I'm wondering, could it be that measuring what door the particle goes through "redefines" the wave function at that location, instead of "converting" the system into a particle for the duration of the experiment? The particle pattern would still occur while maintaining that the particle always exists in it's wave form when not being observed (by a force). Or does the system actually stay a particle after it's been collapsed?
To answer your questions:
1) I'm guessing you'd see the type of interference pattern you'd expect from 3 waves? Since you're asking the question i'm guessing that's not the case.
2) I'm glad you bring this up because it seems like no matter how hard you try, a system will always have some external forces acting on it. Whether it be gravity, the "launch" of a particle itself, or even the idea that the superposition of every other "particle" in the universe must, in some sense, occupy that space as well, i'm very curious as to what kind of interactions cause the wave function to "collapse", because there is a clearly a distinction between what does and doesn't collapse the system. Tbh though i'm still pretty confused with the concept of "measurement" or "observation" itself, given that what's collapsing the wave function is also a wave function itself.
3) Going back to what i was saying before, i think the main question here is after the wave function is collapsed, does it stay collapsed forever? Or does it "uncollapse" after there ceases to be a suitable interaction with the system?
4) Is there a reason why most think that QM is a matter of true randomness, as opposed to apparent randomness? Clearly many physicists feel this way for a reason so i'm guessing they've ruled out more sensible possibilities like extra information that we can't detect or the system as a whole (which could very well be our entire universe + even other universes) being so arbitrarily complex we can't even begin to fathom calculations and predictions.
I think true randomness is nonsensical. Maybe it's my deterministic nature speaking but i just don't see how something can happen for no particular reason. The idea that wave function probabilities so strictly adhere to the predictions that QM makes is in some sense deterministic itself. Clearly the consensus is in favor of true randomness, i'm just curious as to why we're so quick to jump to conclusions when we're still relatively ignorant to the complete truth of reality. Not to go too far off the deep end but at the end of the day all we have are descriptions and equations that fit with out observations of reality. I don't think anyone can tell you what matter, energy, gravity, etc. actually are. The more i think about things like entanglement, wave functions, Higgs boson, time dilation, dark matter/energy, etc. the more i feel like there's something going on at a grander scale that we've yet to discover.
/ramble
> I'm wondering, could it be that measuring what door the particle goes through "redefines" the wave function at that location, instead of "converting" the system into a particle
Yes! This is exactly what happens. QM doesn't try to define what a particle is. It only instructs us on what we will observe of it. Trying to figure out what a particle is is a matter of interpretation.
A typical wavefunction for the experiment without detectors will be
|Ψ> = |slit 1> + |slit 2>
but if detectors that correlate with the passing particles are placed in front of the slits (or behind, it doesn't matter provided they can correlate with the particles) the wavefunction becomes
|Ψ> = |slit 1>|detected slit 1> + |slit 2>|detected slit 2>
The extra bits are how physicists describe the correlation between the detectors and the particles (in quantum mechanics, correlation is often called "entanglement"). They are the bits that, when you do the math, are responsible for the destroyed interference pattern.
Hello! In your quantum mechanics playlist, it says that 3 videos are unavailable. Should this be the case?
Love your videos!
My responses to your questions:
1: I'm not sure where to go with this, to be honest. Is there such a thing as a partially collapsed wave function?
2: I think any interaction which reveals information about the particle will act to collapse the wave function. I think that's why it's said that measurement is what causes the collapse - what I described is a measurement.
3: Yes, the wave function remains collapsed, because the machine measured the particle. It's the same situation with Alice and Bob; the machine "forgetting" the result of the measurement is the same as the machine performing the measurement and then not telling anyone.
4: I don't really know how I feel about quantum randomness. For me it always felt wrong, this idea that the quantum world is indeterminate, in the same way that it superposition feels wrong to me. But then, just because it's counterintuitive doesn't mean it can't be correct. Either way, this is more a philosophical question, I think, than a scientific one. Science is about building working models, and if the model works, the science is pretty much done. Not that philosophy isn't equally important. =P
For the past few weeks I have been theorizing and trying to find ways to prove that randomness does not exist. Because of this I developed a VERY deterministic mindset and felt lost. Like a bead falling down a string, I felt like I could not deviate from my destined future. After watching this video and admittedly losing sleep as I stay up and research quantum mechanics, I actually teared up. Maybe randomness does exist after all :)
Hey mate. just checking on you. How are you holding up after one year. What do you think now about randomness and how does it affect your approach to life?
i could propose a theory that says that randomness is the same thing as freedom of choice.
personaly i believe in free will cause i dont think god is a tyrant.
i dont think god plays dice, but i do think that god allows his creation to play dice.
cause thats our choice.
also your destiny is partly up to you, since you have freedom of choice.
The problem with Laplacian determinism is that it is intrinsically bound up with the notion of _locality._ If you believe that it is possible, in the sense of Laplace, that we can predict the future accurately from knowing its past states, this tacitly assumes it is possible to isolate systems in order to reduce them down to their essential causes (reductionism). Isolation of systems, in turn, tacitly assumes _locality,_ as systems are isolated by physically placing distance between them and the environment, which would not be possible in a universe with nonlocality.
This was why Einstein actually did not like nonlocality. For him, it implies the isolation of systems is impossible, reducing things down to things-in-themselves which can have their autonomous behavior predicted with certainty would be entirely unfeasible. The physicist Dmitry Blokhintsev had heavily criticized Einstein for this, because he came from a philosophical school of thought known as dialectical materialism where things-in-themselves are typically denied as being coherent at all, and so for Blokhintsev, locality and essentialist causality were merely approximations anyways and in practice the universe is irreducibly random due to the impossibility of isolating systems.
The distinction between locality and nonlocality is somewhat of a misnomer as it really is a distinction between metaphysics and anti-metaphysics. The term "metaphysics" is sometimes used in philosophy to refer to certain schools of thought which uphold the existence of autonomous metaphysical objects, either existing in the mind or in the world as things-in-themselves, that can be conceived of as independent and separate from the rest of the universe. Anti-metaphysical philosophies instead reject the notion of autonomous objects and argue in favor of variations of relationalism, that things only exist in relation to other things and do not have autonomous existence in themselves.
Locality is really just a belief in metaphysics, a belief that objects can be in principle fully isolated and conceived of entirely in themselves, while nonlocality is really just a belief in anti-metaphysics, that systems cannot be isolated even in principle because if they were, they would cease to even exist or make any coherent philosophical sense. A universe with fundamental inseparability would not be a reductionist universe, certain causes would not appear reducible down to an essential cause innate to the particle being studied, i.e. it would random.
Philosophies that are anti-metaphysical thus have had actually no difficulty in coping with quantum mechanics without positing a measurement problem nor positing a multiverse or pilot waves or anything of the sort. Dmitry Blokhintsev variation of the ensemble interpretation from the dialectical materialist school of philosophy (Marx, Engels), Carlo Rovelli's relational interpretation from the empiriomonist school of philosophy (Mach, Bogdanov) and Francois-Igor Pris' contextual interpretation (Wittgenstein, Benoit) all come from anti-metaphysical schools of philosophy which find quantum theory easy to cope with without positing anything bizarre.
1:30 I love the arrow accusing the particle of being there for "no reason." I can't think of any clearer way than that to demonstrate how unsatisfying an explanation "randomness" truly is.
thanks for your effort!
I know i'm a bit late to the party here but i just found these very interesting videos and i have a question about these wave funtions, they look a lot like an expectation operator of a discrete random variable (most likely since you are using a finite number of states in the example) and the collapse of the function looks a lot like a change of probablility measure used for the expectation (to a conditional probability given the "information" provided by a measurement). My questions are: Is the wave function an expectation operator of a certain random variable with state space the same as the states of the particle with an approriate probability measure? if not, what are differences? Also, is the collapse of the wave function a change in the probability measure used or is there more to it?, tks in advance and great videos!
Does anyone know the answer to #2? I’m a bit stuck on that. I have my guess below but if anyone knows for sure I’d really appreciate an explanation.
My guesses to the questions:
1) With 3 slits and a detector at 1 slit, the particles would behave as if there was a detector at every slit. Because a superposition would mean the particle behaves as if it is taking each possible path, meaning a particle in a superposition would would always register as passing through each door if it could be measured while in a superposition. That means that if the detector in the 3 slit experiment wasn’t effecting the wave function, it’d always observe the particle. However the observation would thus collapse the superposition and wave function.
2) Yes, all forms of interaction will affect the particle’s behavior. A particle isn’t sentient, they don’t act shy. If it’s having it’s behavior changed by observation that’s because the interaction of that observation affects it. It’s the interaction, not the measurement, that matters.
3) Yes, it’d stay collapsed. The interaction has already happened and it’s the interaction, not the knowledge, that’s influencing behavior. There may not have been a sound, but the tree is still fallen.
4) My feelings towards quantum randomness is that it’s really fucking weird and ultra confusing. That said, it also offers a good explanation of the universe. I don’t think it’s wrong just because, on the surface, it’s counterintuitive. The universe generally doesn’t care whether or not we understand it.
Just a question about changing the polarisation of a photon after it has gone through the double slit and how it changes the interference pattern.
From what I understand if you change the polarisation after the double slit and if you can't determine what slit the photon went through then an interference pattern will be observed.
On the other hand if you have 2 different screens after the double slit that polarise in different directions depending on what slit the photon went through then you will not see an interference pattern.
In the first case the changing in polarisation had not caused the wave function to collapse but in the second case the change in polarisation caused the wave function to collapse just by having 2 screens that polarise the photon in different directions depending on what slit they went through.
From this it seems that changing polarisation of a photon does not cause the wave function to collapse but the act of being able to measure which slit the photon went through causes the wave function to collapse. Is this correct?
I konw I'm kinda really late, but i have a question about #1. If 3 slits are open, according to the superposition principle (as far as i understand), wouldn't the particle go through all slits at the same time, then the detector would detect it going through the top slit, so the 2 other wave functions would collapse, and the particle would be measure as always going through the top slit. I read a few other people's answers and i seem to be getting at a whole different idea here. Why?
how does the size and the location of the two slits affect the interference?
Love this channel
I don't know if someone already said this- there are too many comments to check all of them- but for 3 there is a great Wikipedia article on decoherence theory that gives criteria for effect of the environment (measuring apparatus) on a quantum system. It does not come down to a philosophical matter of what constitutes a measurement but instead there are maths that explain the change from quantum behavior to classical when measured. It's quite interesting.
Keep up! =) Your videos are so nice and interesting! I've never thought i could learn quantum mechanics having so much fun! =D
In 5:12 you say that particles can stay in a fragile superposition state when they do not interact with much in a very controlled environments. Could you elaborate on that? How to avoid collapse? What are the conditions that need to be provided so as to allow for such 'separation' of a particle from the 'outside world'?
Another question, If we calculate the probability by knowing exactly what a particle is interacting with, and make an accurate assumption of the conclusion which should by all means be true, without the true story of the particle not yet measured, would it still account for randomness? I mean, is "conciousness" a requisite for a wavefunction collapse to be true? (since the particle is interacting with light, sound and everything that isn't consious) And also, would the wavefunction collapse, then?
I think that before it goes through, there's 1/3 chance for all slits. Afterward, when the partial is measured in the slit with the detector it only goes through that slit. You get a big clump behind that slit. When it is not measured in the slit with the detector, it interferes with itself in the other 2 and you get an interference pattern behind the 2 without detectors.
so if u throw the apple in vaccum( where it doesn't interact with other things) the wave function shouldn't collapse right?
So, the wave function of a particular particle confines the "randomness" of each of its properties? For instance, the wave function of the position of a particular electron is collapsed by a photon and the exact position will be unpredictable or random, but only within the probability of the wave function, correct? If we collapse the wave function of an electron somewhere on Earth its subsequent position will not be somewhere on Mars.
Also, when the wave function of an electron, atom, etc is collapsed it's position though more well-defined is still not exactly precise, correct? The wave of probability never becomes zero, right? Sorry my response is so large. I just want to know if my comprehension is accurate.
in the future, would it be possible to get the debate questions in the video description as well so we don't have to pause the video? minor nitpick, I know, but would be nice. on the questions...
1) I was actually wondering this myself watching the video, and had been planning to ask. my guess, and it's just a guess, would be that you'd see a third of the particles wind up in a pile behind the detected door, while the other two thirds form an interference pattern from the other two doors, because those two times they haven't been measured and thus you don't know which of the two they went through, but given that we're talking about quantum events I would not be surprised if it was something weirder.
2) my recollection is yes, interacting with anything forces the particle to choose where it actually wants to be. whether that technically counts as a "measurement" depends on how you define the term, but I believe it collapses the wave function, which is close enough.
3) yes. measurements aren't about anyone or anything knowing the results, it's just about physical interactions forcing the particle to choose a consistent location.
4) I'm not really sure anymore. it's weird, certainly, but I'm just so used to the idea now that it doesn't bother me anymore. it'd be nice if everything behaved the way it seems to on classical, Newtonian scales, but if they don't then they don't.
Great suggestion! I've just written them for this video and I'll do it in the future too :)
1) You're exactly right :)!
2) & 3) Interesting :)... I'll try convince you that maybe there is more to measurement than just interactions in a follow up video.
4) Yeah, I feel like I've gotten used to it too... then sometimes (very occasionally) I think about what it means and I have a little crisis.
For number one I think it will go to what we will think that will happen then singnal the other particles to know that there being watched ( I totally got this wrong but hey the more you know) for number 2 I think yes. If you sort each interaction into categories and mark it each time the particle touches it the final product will be the measurements for each category. For number 3 yes. No matter what the wavelength stays collapsed. And for number 4 I don't really have any emotions on what I think.
Could a small Bob *partially* collapse the wave function, causing a change in the probabilities for Alice, but not totally determining the result?
Is there a experiment done on question 3?
Usually when one says something chooses to act (as these particles do) then one means that it causes its own actions. It what sense, then, do the actions of the particle moving through the slit have no cause?
Why does the wave function of the double slit experiment collapse so that the pattern looks like it was influenced by classical mechanics? Am I missing something?
what happens if you only shoot one particle through the double slits and then measure, well you would know the out come of just a single electron so then shoot another one through. you know the outcome. do that alot of times, when do you get to the point where the wave funtion applies?
I would think that the particle
would have collapsed for both Bob and Alice, as the pile at the wall would
demonstrate.
As for your written questions: (1)
I don’t know what would happen if there were three slits. What happens to the
wave function of a particle that goes through look like before and after? I
guess it must (partially) collapse. Which raises a further question: since the
particle is moving (through one or two doors), that suggests it retains a wave
function along its trajectory. How else would movement be possible? In other
words, something moves, whether it’s as small as a particle or large as a
planet by being in several positions at the same time: here most likely, a bit
further on too but less probably, and very unlikely down the road. As the
likelihood of the object being in a place moves, so does the object (most
likely).
A question: if further along there
were another two doors, would the “collapsed” particle recover a new
superposition and pass through both?
(4) Randomness follows rules of
probability, or else there wouldn’t be any wave function, so I can’t see why
anyone should have an issue with it. I don’t think there are hidden variables
After reading the comments section for one and a half hour I now think this:
As people pointed out, the "non-collapsing measurement" is only when the "waveicle" "collides" only with another "thing" that itself is in the state of superposition. I hope I wrote it that you can understand. Now let me imagine three slots with detector at each of them and shooting particles one at a time. The apparatus will show that the particle was detected either at A or B but not C, or was detected at B or C but not A, or was detected at C or A but not B. Now this is what I imagine to be a "weak measurement". Since it is being made by "colliding" one superposition state with another superposition state, it should not collapse any wavefunction and you should still see the "modulated" interference pattern (actually after I googled it I found out it was a bit different than I had imagined, but close enough). The measurement is in fact not giving any answer about which one of the three slots the particle went through, but rather which one slot of the three it did not. I am sure such an experiment was already carried out, but I am too lazy/incompetent to search for it. I assume that such a "weak measurement" would not affect the interference pattern at all. If anybody knows more I would appreciate your comments. Question: Can there be a quantum Monty Hall problem? Three slots, information about that the particle did not go through one of them. Changing "doors" will not help at all in QM as there is still another wavefunction. Am I correct? (I know that I am not, that this example is nuts, but for the sake of argument, think about it (or don't)).
I remember that a few days ago the Royal Institution uploaded a nice public lecture about quantum biology which pointed out a few questions that I was thinking about myself (but rather for the wrong reasons, or from the wrong viewpoint). Yet at the end of the video I was left with more questions than answers... What struck me is that even relatively "big" particles behave in the weird quantum way - even some small molecules. Now that idea I find very interesting. I ask myself if the transition from quantum mechanics to classical is a smooth one where there is a certain chance of the "waveicle" to interact with itself in a double slit, so the wave function does not always collapse but the two places behind the slots have a higher intensity or if there is rather an abrupt and strong line that is between these worlds. If it is true that not just subatomic particles, but small atoms and molecules can be described by a wave function, this would be a nice thing to research. I can imagine ways how to put this to the test. According to my internal thought processes I see rather a strong division between the quantum and macroscopic world. My "argument" so far is that the function that describes the chance of the "waveicle" colliding with itself is a probability "distribution", so one wavefunction "interacts" with another wavefunction. If and only if the probability of "interacting with itself" gets to 0 we will observe the "classical" outcome - two "hotspots" behind the slits. Does anybody see the fallacy here? I would love to read your argument.
Also, people mentioned that randomness itself might not be really random, but at the same time a lot of them have problems with it. :-) So, according to MWI it is not random at all, but everything happens. Even if that is true, due to the unpredictable behavior of the "collapsing itself" in "our" reality, it still remains chaotic on the big scale. I guess we should clarify the differences between the meanings for words random, unpredictable, chaotic, what are the differences between the "prior conditions" and "effects after" of each of these words/meanings (also we should define what we mean by apparent/true randomness). My understanding and definition: unpredictable is for the quantum world, chaotic for the “relativity” world (our, based on QM) and the word random is just plain false in itself, such as “free will”. Maybe finding ONE specific answer is impossible and all our attempts are vain and doomed to fail as they try to give ONE answer to a possibility of MANY outcomes. Maybe the truth (note to self: define truth) is that ALL possible answers are correct, no matter how crazy they are. Now that is a nice example of how my stream of thoughts that formed this is wrong and I start to feel I do not know what I wrote anymore. Remember the modified Stoll/Zappa quote I wrote last time? Maybe that is what happens if you try to find a question to an answer which in itself cannot be asked since it cannot be defined. Actually this paragraph is probably the worst I ever wrote. I wonder why I am not deleting it and keep on writing.
About information. If information cannot be destroyed, can it be created? Let me assume that information=energy as energy cannot be destroyed either. Now the interesting (maybe not) part. Since the measurements in QM are non-commutative, it means that when we measure value A, then value B and then again value A, we will see that A is different than before. So the original information about value A was "destroyed"? No it was not. It was only converted to a new value A of the same thing. So conversation of energy in principle. Still the disorder might be increasing (at the cost of other disorder being converted into new disorder). The same like energy, you can convert it any way you want, but you will not destroy it. Now, I argued previously that the amount of "information" in the universe must be rising in order for the concept of time to make sense (maybe I am wrong). Now I see that this might not be true. Maybe the amount of information is constant and actually the whole information of the whole universe (or multiverse) is zero. How come? Because if conservation of energy = conservation of information and the whole energy of all there is zero, then the change of information must be zero, it just gets constantly mixed up in a chaotic and unpredictable way. Would the 2nd law for thermodynamics still work? Why and how? Why is not time mixed up, but rather seems (in our "relativistic" scale) as a one-dimensional "property" with only one direction? Now another thought: What if that what we call gravity actually moves energy/information from one universe to another? Could there be such a mechanism that one universe (our) is expanding at the cost of some other universe shrinking? The "medium" that "transfers" stuff being "gravity"? Or another explanation: Information and energy are being constantly exchanged between various multiverses at the quantum level. It is not that I intend to write and argument for MWI, such an explanation would give me no information whatsoever about "my" universe. Oh no, not the third paragraph again! I did not want to end up with that. Addition: What if our very own thought processes (as a result of quantum biology) are the "carriers" of energy/information from one universe to another. The more we know/think about our world/universe, the faster it is expanding. I mean literally expanding. No, this is stupid, but sounds good. :-)
One "interesting" point: What if the struggle to come to an answer other than probability distribution is like the struggle to count to infinity? QM describes the limit that at which the universe works when it approaches infinity. But we will simply NEVER be able to come up with anything more. I mean, this questions are one hundred years old now and the answers get even more complicated and confusing with time. Now the question (if I missed a great fallacy in my thinking please excuse me): Can we apply this to relativity as well, just in the opposite direction? That it describes how the universe "works" when approaching the other "infinity"? And both are like two half-circles on a flat plane, joined by ends. Yet without the possibility to know of each other near one point where they meet. OK, now that is crazy even by my standards.
If anybody got this far I would like to know your opinions about what I wrote. Maybe you can recommend me a good psychiatrist, seeing this as a mental illness. :-) Wow, wasted 2 hours of my life reading the comments section and writing all this nonsense. A lot of disorder has been put to the world because of that. Maybe if you read it and will find something that "orders" your mind you can counteract. But I imagine the dear reader will be now even more puzzled and confused than before reading this post. Sorry, it was not intended. Also, I used modern spellcheck to fix typos and errors, but too bad that they did not invent a spellcheck for reason. :-D Wow, it is so late already? Good night!
with the apple example you said even if your not watching plenty of other things are ie. air, light, etc. that collapses the wave function.. my question is why doesnt the door itself or the material its made from collapse it? is that not a variable?
You collapse a wave function by forcing an object to make a choice. The doors force the object to go through either doorway to get to the other side, but they do not make it choose which doorway to go through. Thus a superposition between both doorways is formed.
+didles123 ok, more simply, would the material these "doors" are made if be a variable?
I really liked your explanation of why quantum randomness doesn't usually happen in everyday life, i don't think i had heard it explained that way. Usually its just said that it's really unlikely, and that it. :)
Thanks heaps! I'm so glad you liked it. It was this question I had for such a long time and I'd hear that sort of answer too and it never clicked. Plus I'd heard that answer about the de Broglie wavelength of big objects being too small as well- which I disagreed was the reason.
Looking Glass Universe Where did you hear it? Do you have any extra reading about it? :)
Looking Glass Universe
Why don't you think that's the reason?
JohnAJ An awesome book I'm reading about it is called 'Decoherence and the Quantum to Classical transition'. It's a textbook, but it's not too too technical. Plus the first couple of chapters are almost equation free. Really nice read. It's based on this guy's (Zurek) work, arxiv.org/pdf/quant-ph/0306072v1.pdf, but I don't really like how he writes... But you can see if you like it!
Michael Sommers
Ok, I'm going to have a little rant about why I hate how some people portray quantum mechanics :P I'm sorry- I have a lot of pent up emotions about it.
It's simply wrong to say that every object is a wave and has a wavelength given by the de Broglie formula. The reality is that that formula only applies to the wavefunction of 'free particles' (not in a potential, not interacting with anything). This is very very different from the case with a large object that is constantly interacting with other objects. So it is invalid to even apply the formula. However, if you do, you still don't get all the answers. People hand wavingly say stuff like, if the waves of different particles don't overlap then they act classically. But this is so vague and evades the really difficult question about where the quantum to classical transition comes from. It basically envisions objects as 'really just classical objects with these wave-like skirts'. No where in the maths of quantum mechanics is this suggested. Things are not 'really just classical' with these quantum features sometimes. They are quantum. What needs to be explained it the *classical* behaviour. It's just so convenient to use that language to 'explain' things without actually explaining anything. I think an honest explanation has to actually go down to the axioms of quantum mechanics and explain it from there. On the other hand, some people realise they can use pretty mental images to make people feel like they've given them an explanation, when really they've just given a nice story that they haven't justified and is not the correct, currently agreed upon answer by actual quantum physicists.
i think the moment(i mean a small interval of time where delta tends to zero.) a force carrier interacts with a matter wave, the matter wave becomes a particle,provided the force carrier(here photon) has enough energy to excite the matter wave enough to make it behave as a particle this is what i believe.
great video! I truly enjoy them :) Is there a way to angle multiple mirrors to observe the double slit experiment without the detector and project the results somewhere else? I know they are subatomic but its a way of observing without directly observing---
And now you're in great company, because you're asking the kinds of questions Einstein did. These are very tricky to resolve, but with a lot of careful reasoning you can see that if you detect the particle's slit, it does collapse the wavefunction. If you're interested in why, check out the Einstein/ Bohr debates.
Thanks heaps :D
You are the best and thank you!!!! you have answered 2 of my questions in depth and in a timely manner :) Don't forget to Remember me, I'm Anthony, I'm going to contribute something to this field-You are hands down intelligent and an awesome girl, your little side notes on the videos are funny lol ;) NeW JerSey USA
OK Anthony, I would love to see you contribute to this field. Make sure you tell me about it when you start :)!!
Thanks a lot!
1 question: wave function before=a|w>+b|w>+c|w>...it can pass from any of the slit..but when we set up a detector the wave function collapses...maybe i wrong..if i m plz correct me..
2. donot collapse till results..
3.yes all interactions are measurements as they can collapse wave functions
4.i think randomness is like magic..or at least for me it is magic.
Some people already touched on this but I want to add my 2 cents.
The whole "true randomness" vs "deterministic" debate always seems to come down to semantics/definitions. People tend to think that true randomness means there is just simply an inherent randomness built into the universe. I believe it's most likely that the "random" behaviour we observe at the quantum level is just an UNPREDICTABILITY by fundamental nature, in the same way that uncertainty defines a limitation on what we can know (i.e that "certainty" would be a mathematical/logical/physical impossibility). Either that or there are factors beyond our measurable reality (possibly things outside of our universe) that affect things at the quantum level. Either way, it would mean that quantum randomness just means "impossible to predict", but the results we observe are still DETERMINED by some causal process (and not some inherent randomness, or perhaps what I've described IS our inherent randomness, it's all semantics).
In this sense Einstein and QM are both correct, they probably just didn't agree on what it meant for the universe to be considered "random" or "deterministic".
what your talking about would still be considered deterministic. True randomness really means true randomness.
Did you hear that from "this place"? Just asking.
Bell tried to prove that hidden variables exist,it's the thing you talked about,he failed and in the process proved the contrary,in other words if there are some kind of hidden variables,they woukd exist only in another universe or something like that
I don't fully understand the dual split experiment, regarding to the observer effect. My question: how does the act of measuring make the wave form collapse? Do the physical/chemical properties of a particle change after being measured?
Rafi Chai Great question!! In fact that's the biggest unanswered question in quantum mechanics: it's called the Measurement Problem. It's something I have and will make a lot of videos about.
"Measurement" is a less fancy way of referring to an interaction; to measure something is to observe how it interacts with something else. A detector can use different things for this purpose, such as magnetic fields or, in most cases, light - photons. The act of measuring, i.e. sending a photon to interact with an electron does exactly alter the state of that electron, and that, somehow, causes it to collapse and "choose" a physical state. This is why the universe doesn't need a conscious being to do the measurement... or does it? We know that if the particle is measured, but then the information is lost, the particle resumes its state of superposition. In other words, if a detector measures what slit the electron went through but nobody is there to read the information, does it still collapse the wavefunction? If a tree falls in the woods and nobody is there to hear, does it make a sound?
The detectors used causes the wave function to collapse by a thermodynamically irreversible manner. Any randomness in quantum mechanics is due to hidden variables that are not accounted for, a paradigm shift in the near future and an increase in precision with technology and techniques will yield more predictable and accountable results.
Amazing video
This cant be real. There must be something we don't know.
+wuuspigs There´s lots of things we don´t know:)
+wuuspigs Hahahaha, there is no rule binding the universe to be logical. Just because you think it's not real doesn't make it less real. Just because it disagrees with our macro experience doesn't mean it can't exist. We developed our classical theories in a macro world, there is no reason why the same theories had to hold when we move into the micro. In science, observation trumps everything. When our predictions clashes with our observations, something has to give. And that something will always be our theories
+Pak Huide I agree. I meant what i typed in a more " I'm baffled and blown away" kind of way. That being said, i don't know who this Lookinglass person is and how factual her claims are. She sounds credible enough but would i get the same answer from every physicist? Is this science fact? Because something happening without a cause is a pretty big deal.
***** It is our observation. That's all I can say. Your theory could also be true. For all we know, it could be caused by something immeasurable, it could be caused by something from another dimension for all we know. But yeah, this is the observation, we can make what we want of it. ,
*****
We definately wouldn´t get the same answer from every physicist. A lot of it is still "just" theoretical physics. And even the empirical physics are creating often "just" pragmatic models to live by.
I can only answer the 4 th question:
to me , superposition is a five dimensional point , as we visualize it , it will look like a cone (i think) , actually is the condensed possible space time line , the height of the cone might be time ( very very small period of time) , and I think somehow in this space size will be related to the amount of possibility , each line will then split up into another bunch of lines .
after doing this assumption , I will do another , assume that those lines will somehow collide and exchanged with each other , making the space time "random" , as more dense the lines are , more chance of colliding.
As apple is big enough , it's possibility lines will not have much chances of colliding , so it remain the same ; or we can say , because that small period of time cannot support big changes , so even is changed , we cannot obserf it as it's too little for us to understand.
but for photons and electrons are different , they move faster , and they are very small , and they have more chances of exchanging space time line with the other possibilities, so that they can be told as random .
those are just my imaginations , I don't even know it is true or not XD
Time and time again, we seem to underestimate the power of "bias" in our "observations" of Natural phenomena.
I would argue that randomness is nothing more than what we conclude when our bias has been repeatedly defeated.
It's not about not having enough elements/data/figures or not knowing the "variables". Rather, it is that as we tailor our experiments to answer specific questions, we ignore other questions and their possible conclusions.
This is something that is pervasive in the way we experience the world. To me, this says something crucial about Human nature and the Human brain, regardless of whether we are talking science, philosophy, psychology or even languages.
Our capacity for understanding is limited by our inability to reach omniconsciousness.
Lake Ishikawa For some reason I can't reply to your comment so I'll do it like this.
Yes there have been double-slit experiments done with buckyballs which contain 60 atoms and the reason that it works is that they are basically entangled and described with one wave function just like an electron would be. When you learn about bonds in chemistry, most of the time the talk about quantum effects as the basis is avoided even though it's exactly what describes them with great accuracy.
There are also recent experiments observing quantum properties in structures made out of billions of atoms.
1. Three slits - still collapsed because measuring one of three should be the same as measuring only one slit in the double slit experiment.
2. Not all interactions. because a particle is self-interacting :D
3. Yes, it stays collapsed because it was measured, you said in one of the previous videos that one that is doing the measurement doesn't have to be conscious mind.
4. I think that the particle is at the same time in different dimensions, so when its measured, it reveals itself as it is in one of these universes. when its not measured, it interacts with itself from other dimensions.
If we could see or experience in some way those different dimensions, it would all make sense. What I haven't decided yet is whether the particle is in spacial or time dimensions, or both of them.
Do I get some kind of diploma if I've answered first three questions correctly? I know I'll get a Nobel prize if I've done so for the fourth question :D
Anyway, I like quantum physics, but often I think that eventually we'll discover some new solution to all of this and that we won't need quantum physics. Its just to illogical to comprehend. But, whatever the case might be, I just hope laws of physics will allow us to travel the universe :)
Hi,
Amazingly clear, LGU, once again. Thank you !
How about that, that I think of about the wavefunction collapse and the measurement: the wavefunction is not the position of the particle, but the space in which it is allowed to spread; and the incoming photon is not collapsing the electron but the space in which the electron spread, forcing it to appear in a point which position is defined by the photon, but energy defined by the electron (only certain wavelength of photons "work").
My assumption here is, that in the absence of photons, matter would spread evenly in the space in which it is allowed to spread, and that the energy of the electron defines the energy that will react to it but not the position, which would be brought by measurement.
Is there a link, a proportionnality, between the "size" of the observed particle and the energy brought by the measurement?
Hello from Belgium!
Aw, thank you. That's really really kind.
That's a really cool idea! It's like a new interpretation for the wavefunction I haven't seen before :) I'll have to think some more about it.
Looking Glass Universe Thank you for you answer ! I'm glad you've never seen it before, i'm writing a book about some stuffs around that idea :D If i can spare you some time, i'd be glad to read myself about it but I don't know a lot of trustworthy sources about this topic.
Since any interaction with a quantum particle results in its collapse, I am curious about the odds it would interact with a virtual particle in the vacuum of space. I would expect this number to be extremely low, but this would potentially collapse any entangled particles given enough time. Hmm, sounds something similar to the half-life of a radioisotope.
I also favor Bohmian Mechanics with the Pilot Theory and such. I can't accept the fact that there is true randomness on the quantum level. The fact that we claim randomness tells us we are looking at a black box that spits out numbers, not knowing why or how. I would love to take a look inside that black box someday and see how it works.
That's a really cool point about virtual particles- hadn't thought about that but yes, there must be interactions! However, not all interactions are actually measurements so in fact, those probably don't collapse the wavefunction.
I think this is the point that gets me about randomness as well: there's no reason for it :/
The statement at 1:20 - I feel like that should have an explanation. How do we know that there is no additional information?
What if we place a detector but let it remain switched off during the entire experiment? Will the wave function collapse in this case?
I love your techniques of learning from Bengal in INDIA.
Your voice sounds like somethings always moderately amusing.
What would happen if you put one electron through the wall and it was observed entering door 1 and you retrieved the same electron and shot it again? Would it necessarily behave the same way it did at first? (Assuming the same electron can be retrieved.) -- Ari, almost 7 yrs old.
These are wonderful videos. Thank you to Alice through the Looking Glass.
The empirical evidence which starts our journey into bizarre realm of superposition, the fundamental measurement problem and postulation of more than one Universe - all seem to emerge from the double slit experiment performed on single particles - which was first performed many years after Schrodinger came down the mountain with his new equation... (please correct me here if this is not where the strange road starts). Before taking a journey into the unknown - where reality plays hide and seek with our measurement equipment - I would tend to ask more about this critical experiment. How do we know - for sure - that just one particle/entity has been fired at the two slits? Can we be sure it is just see one particle emanating from the source? Could it be two particles/entities - or maybe multiple entities. Any pointers here - much appreciated. Thank you.
As an aside …... the word Universe is of interest here in relation to the many worlds interpretation.
The origin of the word Universe - is from the Latin "Uni- One" -"Versus-Against" ... which demands the question "one versus what ? "
yay you're back !!!!
Yeah, sorry for being away :'(
no no no i understand
thanks for being
This wave function is a bit sloppy and does it tell the all possible outcomes or it just tells that this will be the outcome
Particle move the path of least resistance.
The thing shows with the doors would only be 50/50 if the particles came straight on.
But being distance perfect for that outcome is the same lackness of balancing a pencil on its tip.
If the particle is coming from the left it's momentum will pull it to the right door.
It stopping perfectly in the medium seems insanely unlikely.
Isn't any acceleration gonna cause gravitational waves. Wouldn't that collapse the wave function.
Hi, could I do a random act by saying if a particle decays or not I will lift my hand in the air? Will using the 50/50 chance of a particle decaying as a coin flip allow me to do true random actions?
Yes! And if you did it this way, Many Worlds interpretation would say you did both. (Which wouldn't be the case if you just tossed a normal coin instead)
+Looking Glass Universe Thanks for the quick reply, going to make this computer a quantum number generator now and use it to create different universes now.
Forgive me if I missed something, but in the double slit experiment, why don't the air molecules interact with the particle and collapse the wave function?
Well, if the electron hits an air molecule it's either going to be absorbed or deflected, same as if it hits the wall instead of going through the slits. The electrons reaching the screen are generally the ones that don't interact with anything on their trip. The apple interacts macroscopically with ALL of the air around it, which provides information on its location.
But that's actually not a complete description. Because even if you threw a bunch of apples in a perfect vacuum chamber with no light or particles of any sort, you still wouldn't get an interference pattern. It's because of how diffraction works. The electron's wavefunction spreads out from each slit as a function of the width of the slit and its DeBroglie wavelength (which is related to its momentum). The wider the slit and the shorter the wavelength, the less the wavefunction spreads out. A macroscopic object like an apple has a HUGE amount of momentum compared to an electron, therefore its wavelength is much shorter, and it requires a much wider slit because of its size. So the wavefunction of the apple is always going to be a straight line with no "spread" at the slits, and so it can never interfere with itself like the electrons do.
Thanks for the response. There's still one thing I don't quite understand. If the gun that shoots the particles is 100% accurate in shooting straight, it seems as if every particle would hit the space in between the slits, meaning that any particles that went through a slit would do so because the slightly inaccurate gun fired it a little bit sideways. Wouldn't this mean that the particles go through the slits because of a slight difference in how the gun shot it as opposed to a true chance?
Right, there's always a spread to the beam, whether it's electrons or photons or bullets, etc. To perform the double-slit experiment you have to make the slits so they fit inside that spread.
In the case of bullets from a gun, you're right that there's a macroscopic randomness to it. If you know all the variables about the barrel and the primer, etc., then you can theoretically predict the path of each bullet. Quantum particles are a little trickier. You can certainly set up some detectors to precisely track each particle's path to the slits, but that's going to destroy the interference pattern at the screen. Because you just measured each particle and determined what slit each one is going through.
Oh, so if I interpreted it right you are saying that the atoms before they are detected don't really exist in the same way bullets do, so there is no way to predict where the atoms go by taking all the variables of the atom gun.
You actually cleared a while bunch of doubts I had regarding the measurement and wavefunction collapse. THANK YOU.
Also, does the WAY of measurement affect the wavefunction? Meaning if I change the way a particle is measured, would it still collapse into one of rhe many possible situations, given that the quantum system isn't influencing the particle at all?
Yes, the kind of measurement directly affects what the resulting wavefunction will be. When you measure a particular mechanical observable, you get a state that has a definite value for that observable. For example, if you measure the position of a particle then the wavefunction after measurement will be highly localised around some point at the time of measurement. However, this same state may not have other well-defined features. For example, when you have a state of definite position, then that state cannot also be one of definite momentum. Another basic example is angular momentum; if you measure the spin of the particle along some axis you cannot gain any information about the component of the spin in the two transverse directions.
Ooooh. So basically the wave function collapse depends on the intensity of the way of meaurement. Lol, I said intensity because I can't find any other explanatory word. So a constant position will differ if the way of measurement is different and hence the possible variable position comes into account, but one feature in either of the situation(Given that there are only two possibilities) is defined and isn't influenced by other features enough to be enlightened or collapsed.
I got it. Thanks :)
The theory does not predict outcomes of individual experiments, it only yields statistical information. A measurement of position (or some function of position only) will always yield a definite position (which is limited by the resolution of the detector only). However, the, say, momentum of the particle as it is measured (which can be calculated) will not be as well-localised.
Yes. I got it now, perfectly. Thanks!!
The bit that gets me is, imagine the double slit experiment with a detector at slit A. Now, in this thought exp against all odds all the particles pass through slit B and form the "clump" on the detector right behind slit B. Yet, the detector at slit A doesn't even know the exp even started, it never saw anything. Yet, doing nothing what so ever it still collapses the wave function. This just makes me think Pilot Wave Theory holds more sense to my limited "educashun".
Lol, I'm also struggling with addition. Multiplication feels much easier)
About the questions:
1 - I guess, it should collapse to 50/50 wave function.
2 - Cloud chamber would be measurement.
I think, set of experiments with different to each other vacuum densities might give an answer.
3 - I think, it collapses when chance to be 'detected' is bigger then 'n'. And, burning the results as they're printed is certainly bigger than that 'n'. Maybe, there are some traces left behind on the ram?
4 - Bohmian mechanics FTW :P
Quantum mechanics feels like the lazy way of doing things. "This works, let's just use it!".
am I the only one who loves her voice?
no im here lol
istván fodor she should know.
+Farid Jefry You are not alone
she doesn't care. at least in the way you would like it. :D
+MrDoboz being a little presumptive I think
Now to my answers:
1: The wave function looks like |X> = sqrt(1/3)|sli_1> + sqrt(2/3)|slits_2&3> The pattern would be similar to the 2-slit experiment but because of the 1/3 chance of going through the top slit instead of the 1/2 chance, the actually pattern will be changed accordingly (exactly how I do not know).
2: All interactions do count as measurements. Looking at something is interaction by way of the photons that the subject is emitting while running into something or bouncing of something is measuring its position and/or velocity.
3: The wave function does remain collapsed because destroying the recording of the information doesn't actually destroy the information/event from the timeline.
4: Not entirely sure. It partially infuriates me because it seems like there has to be an underlying cause to quantum phenomena but I've been told by my professors that this is merely my classical understanding trying to go somewhere where it is not able to go. So I am personally more inclined towards the pilot-wave interpretation/other deterministic interpretations.
would the difference between quantum and classical randomness mean that there is necessarily no causality in quantum randomness?
Last time I did not answer the questions properly, but today I am going to write it (actually it is a nice distraction from work):
1. My guess on "Three Slits": There would be a wave patter within a wave pattern. Something similar to amplitude modulation maybe? I know this is oversimplified, but for the sake of having something to imagine in my head I wrote this. If you measure one slit, then one of the wave "collapses" and you end up with an "unmodulated carrier wave" with a "hotspot" behind the measured slit? Hmm. Maybe I wrote something totally stupid, but at least I am honest with you here. I will google "Three Slits" after I post this.
2. There are some so called "soft measurements", they do not count as they tell us only that out of let us say 100 measurements, 20 went through this slot, but we cannot tell which 20 of the 100. At least that would be my understanding of it without having studied it any deeper. I hope I did not write total BS now. Will google it also.
3. Yes, it stays collapsed. We discussed it already. :-)
4. I have no problem with the randomness. Actually it makes sense to me from a (pseudo-)philosophical point - as I wrote earlier, the deterministic "macroscopic" behavior had to break down at some point in order to have true randomness (out of chaos). If we could measure everything absolutely precisely (so there would not be any more digits left), the universe would be a deterministic "machine". But it is not and that might give us the illusion of free will (more pseudophilosophy). But I see that there is something not quite right with this view, but it would be a longer discussion where I point out why it might be a fallacy, no time for that now. I guess some physicists had/have problems with it as they interpret it differently, have their own reasons to believe one way or another or see other interpretations as a threat to their own views. It is a psychological matter, like the preferences between colors.
Thank you for the really honest replies. I really really appreciate that you wrote this reply first, and then googled it. I think it is the best way to learn.
As for your ideas, they're not stupid at all!
1. Awesome work
2. Ahh, that's a cool way to approach this question! I like it!
3. Yup :)
4. "It is a psychological matter, like the preferences between colors." Lovely way to put it :)
I'll make a follow up video to this about the questions, in case you want more information :)
3 It won't stay collapsed, the "collapse" is just epistemology. The quantum eraser experiment for example allows the reconstruction of the interference pattern.
When you say that when we look away, and particles are not being observed that they act irrationally, why do they return to a constant place so that when we view them again they are in the same place?
When the electron hits the detector "behind" the slit, why doesn't the wave function collapse then? What the special about the detectors in the middle?
Niloy Mondal
The detectors in the middle let you deduce which slit it went though, collapsing the superposition before it can interact with itself. The detector behind the slits does not let us deduce which slit it went though, so the superposition collapses after having time to interact with itself.
I hope I understood your question properly.
+didles123 yes, thanks, makes sense
What if you put a detector in between the slits and don't tell the particles? Would the particles strike the slit detectors and the wall detector equally? Would the wall detector measure the amount of indecisive particles? These are serious questions.