Understanding Quantum Mechanics
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- Опубликовано: 21 мар 2018
- This video is an simple introduction to quantum mechanics that explains why there is still so much controversy over the meaning of this scientific theory.
Thanks to Vlogbrothers for their sponsorship of this video! I really really appreciate it!
If you'd like to help transcribe this video into another language, that would be amazing: / timedtext_vide. .
Homework questions:
1. We talked about doing the double slit experiment with small things like electrons. But is there any reason in theory we can't do it with bigger things? If not, what would you need to do to make it work?
2.We didn't measure where the electron went in the middle of the experiment. But it is possible. If we measured each door to see if the electron went through it, what would we find? And what would happen to the pattern on the back wall?
3. There is another way to interpret the double slit experiment, which I think is really cool- it's called Pilot wave theory. I made a video about it. In that theory, the particle does go through just one door, even though our argument said that's not possible. Find the flaw in our argument. Also comment on why particles still act strange in Pilot wave theory.
Music: Thanks Falcxne for allowing me to use this song: / phas. . 
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I wanted to find a video about something over my head from someone with a nice voice so I could bore myself to sleep. I settled on this but now I'm about to start a series on "understanding" quantum mechanics. Super well made. Bravo.
Loving the improvements and the background music. Well done!
Very much a result of your advice :)! Thank you!
This channel is INSANELY GOOD! I just love these videos. Keep up the great work!
Thank you so much!!
wow insanely good, i bet that some how is actually really bad... i mean if you like something that was good, sounds pretty sane to me... But to absolutely be enamored with something undeniably awful.... I think we've reach insane territory....
Lets celebrate by not taking our drugs!! I feel ok.. I doubt I need them anymore anyways..
I love this channel!!!! So happy to see you active looking glass universe!
Thank you :D!!
Glad to see you are back! And I love the updated style/ elegant design of your video. I've watched all your other videos and this one flowed logically the best. Can't wait for the series to continue!
Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you Thank you
It means so much to me that you'd say this. I took a week off to write the script and it was so much pain.
So excited! Just subscribed a few weeks ago and so happy to see new stuff already!
omg I'm super hyped. what a great day to see a great channel updating again
Haha! Thank you! I’ll try be around more regularly!
YES, MY FAVOURITE RUclipsR IS BACK!!!
No way, that is way too much flattery!
but since you observed this, she has now collapsed into a state of not existing... well done...was it worth it? publish the paper and lets find out but not a very good one... I'm not very good at sciencing
I'm so glad you are back. What I like the most about your videos is the animations which are very useful, the subjects you choose, the way you are explaining it and your voice tone which is pretty pleasant to listen to. Anyway I can't wait for the video about quantum computing.
Thank you very very much :D!
Ecstatic to see you again!!!! I've learnt a lot watching your videos. Keep uploading more videos please
I discovered your channel with this video and fascinated about it. Thanks for your big efforts to make it understable
Awww man, I watched all your videos years ago and now am re-watching them With the same inspired awe. Wonder what awesome job/research you are up to. Great explanation 🙂
Thrilled to see a new upload from this channel!! I am eagerly looking forward to the new series. Hopefully, this will be the time I finally understand the basics of QM.
Hopefully I will too...
Thanks!
What a great video on the dual slit experiment and introduction to particle behaviour. Looking forward to the new series!!
Thank you!!
Very informative and funny video, love it! :) Another interesting (and important) point about the double slit experiment is the fact that you destroy the interference pattern if you measure which door each of the particles took over the course of the experiment.
This video is awesome! One of the best concise overviews of quantum mechanics I've seen. I'm totally completely psyched for the whole series. Keep it up! :-D
I'm going to give some probably incorrect answers to your questions:
1) I'm assuming to get the apple to behave in a quantum mechanically weird way you'd need to totally isolate it from all interaction with anything else. Shay Lempert below says that the wave-function of the apple is probably going to be smaller than the apple, but it seems intuitive to me that the longer the apple stays isolated from the outside world, the larger its wave-function will get. Eventually, given a crazy large setup and a crazy lengthy experiment, wouldn't it become larger than the apple itself? More importantly, if not, why not?
2) In the second example I happen to already know that if you measure which slit each electron goes through, the electrons form two clumps behind each door, much as you'd naively expect a particle to behave from the beginning. Measure the particle, and it assumes a definite position while passing through the slit. This still confuses me a bit... one might guess it's the interaction with the particle used to perform the measurement that causes this effect, but what if you create a system to measure only the particles going through the left slit, then observe the distribution of only the particles which went through the right slit? Do they fail to form an interference pattern because they would have been measured if they'd gone through the other slit? My science-enthusiast-level understanding of the matter says yes, they would fail to perform an interference pattern. In that case was it the potential but seemingly non actualized interaction that caused the difference? Very strange indeed.
3) Thirdly, in the case of pilot wave theory, the particle does have a definite position at all times... but that position is guided by the wave function, which is itself sort of a mathematical representation of all the different ways the particles could have gone, and how those ways interact with each other... including the particle going through the other slit. That last sentence was probably pretty philosophically extravagant, but I'm not a physicist or a philosopher of physics, so I don't have a reputation to lose :-)
Anyway, the fact that the particles are guided by a wave-function which itself, if my novice understanding is correct, is comprised of all the different ways the particle could have gone nicely explains why the trajectory of the particle is so insane.
😮 I’ve also been working on my first ever youtube video which is going to be about quantum computers explained. I got a lot of help from your old videos, sooo glad to see you back and excited for this new series!!
Oh nice! I wish you lots of luck with your channel!!
I'm so glad you're back! This has been one of my favourite channels in the past.
I kind of hope you do dig into the maths of various quantum videos like you have (to a certain extent) in the past - it my opinion, it helps to provide the video with more content and legitimacy, rather than the "Look how weird this thing in QM is! Isn't that spooky?" that you get from many more RUclips channels elsewhere.
Yes, that’s something I’d like to quite seriously do. Also because I want to teach you the maths so we can do quantum computing stuff too :)
Ph.d. In quantum computing? That sounds awesome! I would love to learn more about what's in progress for that. This is one of the best channels I watch and it's great to see you post again. Thank you
Yeah, it's really starting to happen in QC. I'll try summarise it in a video soon :)
I really enjoy your videos. You have an unique style and approach.
Quantum Mechanics in one sentence: Things get wavy when you aren't looking.
MORE. I love this channel and i just found it. Ive just started studing the quantum world and out of all the people i know that are very certified to talk about the matter this video made it so much simpler. I wish you posted this months ago.
Thank you very much! I'm glad it helps you :)
I really love your explanations to quantum mechanics. I saw all your videos and it's great how you are able to explain all these phenomenon of qunatum mechanics in context to the basic principles/laws, because I used to struggle to find the connection between these concepts.
I was wondering if you could make a video Quantization in quantum mechanics. How can it be explained with the basic principles or do we have to simply accept it aswell as a basic law?
Hmmm! Very good question. I just had an hour long conversation with my office mate and we didn't resolve anything. But that was fun, so thank you. I'll make a video if I understand it.
So happy these great videos are coming back!!! I love them so much :)
Yay! Thank you!
I couldn't have asked for a better approach to the subject, loved it.
Love the way how you explain this difficult subject matter to us novice in this field.
Thanks a lot- but I’m so happy that people want to come learn about Quantum mechanics
This is a great video, keep up with the series! I’m so excited!!
Thank you!!
Thank you very much for making this video series. This is really helpful.
Thank you again... from Bangladesh
Just like a thousand others, love your videos - the slow, measured pace of your voice.
Thank you :)!
This is a really well done video on the intro to QM, the one comment I would make is that the background music is a bit too loud and so it’s a bit distracting. Other than that though, it’s wonderful to see you remaking videos from the original series.
Thanks! Yes, I’ll work on improving the music level next time :)
Every video is better than the last. So amazing!
The explanation of “observation” of larger objects was very good, and to make the distinction with observation of subatomic phenomena where to detect such requires absorption of all of their energy, hence collapsing the “wave” function, was ideal.
Lovely animation + impressive EDU skills + mind blowing topic = A Looking Glass Universe Video. Loved it!!
Oh stop it you! For context, I met Tangerine Tries Stuff at Vidcon and she is wonderful. Go check her channel out!
Looking Glass Universe Your channel is awesome! It’s a fact! 😊 aww you so nice 💕
No, seriously, you are :)
I'm really glad that you are back. If I may suggest, the sound needs some improvement.
Thank you. Yes, I completely agree!
Best video on the topic I've found so far!
Glad you've truly returned! Great visuals, too!
HW:
1. So long as the object being tested doesn't interact with anything except itself, it may work. I know it's been done with carbon-spheres (including C70?), so it's definitely not limited to single particles, or even atomic scales. Problems might come with the size of the slits; if the slits are too large, it won't work. Too small, and things (generally) won't get through.
2. If we know where they pass, we know where they pass :)
3. The the assumption made in the explanation earlier is: objects a particle doesn't interact with don't affect the particle (and that it must go through both slits, in a sense, to make the pattern as a result of interacting with the two slits). I intuitively like Pilot Wave Theory, but it certainly has weirdness! But it's under-determined as a theory with respect to other interpretations and I'm in a completely different field (and apparently the math is dreadful), so I could hardly accept it.
Really interesting comments! And thanks a lot for doing the questions :)
You’re so fierce! I love this channel
The style is nice. :) It's crisp.
The old version have a nostalgic feeling, but these are good. It's also nice that you are doing the math(s) behind it. Thanks. :)
That’s a lot! I feel a bit nostalgic look back at the old style too- but I do like this a lot better :)
I'm so glad you're still making videos on this topic! Keep it up, looking forward to the set on quantum computing. And disregard the dislikes, it's impossible not to catch a few jerks on RUclips (:
Thanks so much! Lovely to hear from you. Don’t worry, I’m fine with any negativity. I tried a lot of new things this video editing etc wise, and so inevitably I did some things wrong. If i did nothing wrong it’d only be because I didn’t try improve- so I’m happy to just take on feedback and get better next time.
i`m glad you are back to your channel
She's back! Yay! I have waited for this for Soo long!
Thank you for waiting :D!
1) For larger objects, this experiment is impossible because all of the atoms that make up the object "observe" each other through the interactions of their bonds.
2) If we measure the electrons mid-experiment, they would appear to only go through one door and the resulting pattern would appear like we originally predicted with 2 distinct patches of electrons.
3) Even if the particle goes through only one door, it's wavefunction interacts with the slits and guides the particles in the interfering waves pattern we observe.
Awesome video! This definitely seems like a great starting point for diving into quantum mechanics. I really liked the art style as well (especially that moebius strip title card).
So excited to have you back! Took a modern physics class in undergrad a couple years back, and you helped a lot to explain things as simply as quantum can be expected to be explained. Cant wait to dive back in with you!
I’ll take a stab at the homework problems, leaving my pride at the door, as I might give some embarrassing answers.
1) Scaling things up by frequency and wavelength is familiar to me, but as far as I understand, a standard large object like an apple would be made up of countless smaller particles, all of which would be measuring each other, so that would not work. If a single subatomic particle were somehow scaled up and used, I don’t see why it would not work.
2) If we test which slit the electron is going through, we have measured it, and would see two lumps of hits.
3) I probably have an ignorant understanding of it, but pilot wave theory seems to just shift the blame, as it were, of the uncertainty that comes with quantum mechanics from the object itself to our understanding of the object. It says that the object does have a precise position and momentum, we just can’t measure it precisely, rather than saying that the object itself has uncertain position and momentum. If this is all wrong, then I will wait for your new pilot wave video, but if my understanding is correct, it seems that pilot wave is saying the same thing, just from a different standpoint.
Again, extremely excited to watch your new video series!
"I’ll take a stab at the homework problems, leaving my pride at the door, as I might give some embarrassing answers." Yes! This is exactly what I want people to do- because getting it wrong is how you learn. So thank you :)
1) Very good point- this is subtle so I'll cover it in a follow up video.
2) yup!
3) Hmm! Very interesting view. And I think you might be right on this one. Certainly the Pilot Wave thing shifts the role of the wavefunction so that statements like the uncertainty principle have very different meaning in this theory but still exist.
I really enjoyed the style of your previous series and I'm glad to see you kept the same style. The content and narration are great, as always. Hopefully you won't take this negatively, but I must say I find it more difficult to hear what you are saying with the music in the background. I don't recall background music in your previous series. Maybe it's because I have hearing loss, but it really does interfere with the narration for me. Nonetheless, looking forward to the rest of the new series!
Very sorry about that! It was too loud actually. I'll definitely try to make it better next time- but please let me know if it's an issue again.
Best voice in science tutorials.
im excited for to rest of the series nicely explained video ! :)
Thank you!
1. You can do it with bigger things, but you need to ensure that the constituent components share the same quantum state and don't interact with the environment (i.e. "be observed") so you'd have to use something like a BEC.
2. You'd see which door the electron goes through, but the interference pattern would disappear and you'd see two bands behind each door on the screen.
3. The point is that some part of the electron must be non-local (goes through both doors). In pilot wave theory the electron only goes through one door, but its pilot wave goes through both doors. Essentially the pilot wave takes care of the non-local bit of the problem allowing us to feel good about our intuitions that particles can only be in one place at a time.
Eric Patterson bucky balls... C60... Has been used in the double slit and it still shows up as a wave pattern.
AFAIK pilot wave theory is not compatible with special relativity. (QM isn't either, but QFT is.)
Ferdinand Kraft yet all fields contain pilot waves...
Awesome. I didn't realize that. Do you know of anything I could read that goes further on explaining the dividing line between stuff behaving like waves and stuff behaving like what we're used to? How did they have to prepare the buckyballs?
QFM still doesn't play well with relativity, that's why we don't have a ToE. I don't say that in defense of pilot wave theory, though, as I find myself falling into the category of folks that see the Everett interpretation as the most likely at the moment.
I love these videos. Thanks for them.
Now you asked several questions to test whether we, your audience, are getting the ideas you are trying to communicate. I'm not a good subject because I've read books on the subject, like for instance Richard Fenyman's "QED (Quantum Electrodynamics)." Thus my understanding, or lack thereof, is contaminated by many things.
There is something you said in the video that I've never heard so clearly stated before, but yet have long wondered about. It starts at about 1:20 in the video, where you talk about what measurement means.
This seems to me to be an obviously crucial issue, and yet many texts I have read seem oddly evasive on the subject. And then there are even some texts (many?) that imply that it's only measurements by people that matter.
If you are correct that any interaction between one particle and another is enough to collapse the wave function, then that has huge and far-reaching implications. I don't mean to say I have actually figured out what the implications are, but I know that if I think about it, I'll start seeing them.
And so for instance: What if it's not an electron being fired at the double-slits but a proton?
Well I assume, without having an actual experiment to point to, that we will see the same wave-particle duality. Thus when we aren't measuring which slit the proton goes through, we will see an interference pattern and when we are measuring we will see something different.
But here's the problem. The proton, unlike the electron, has sub-structure. It's made up of three quarks and they are interacting with each other. Wouldn't the interacting quarks 'measure' each other and therefore collapse the wave-function and hence we shouldn't ever see a proton interference pattern?
Now I'll use my intuition and guess the answer to this seeming paradox is that if you can draw a line (or surface) around any system of particles and nothing is crossing that line (or surface) then the system of particles behaves like a quantum mechanical particle with respect to the rest of the universe.
But though I can guess that this is probably part of the explanation I need to verify that and also to explore a bit how that all works.
Very nice point raised! This is an extremely subtle issue that I wanted to spend several videos explaining. I know I kind of implied that measurements are just interactions here. This is not true. It’s about the leaking of information, not the interaction. So, a thing could interact with another, but as long as it doesn’t carry away information about that thing, it wasn’t a measurement. There’s still more to it, but I’ll cover this soon!
1) Since bigger object consist of more particles it is hard not to make those interact and constantly "measure" one another; their wave fuctions are also too small to have a significant impact.
2) If we would measure through which door the particle went we would get a 50/50 split and two blobs behind the doors as the pattern
3) Although particle might only go through one door it can end up in the diffraction pattern due to the fact it's motion is defined by how many doors are open.
I love watching your videos, it's so much more fun watching your drawings than reading lengthy articles on the internet!
On to the homework then:
1. You mentioned that larger objects don't behave the same way as smaller particles, e.g. electrons, becuase they are being constantly measured by their surroundings - so all we'd have to do to see larger obejcts behave the same way as smaller ones do, is to isolate them from those measuring elements? I don't know how we'd do that exactly - perhaps have the obejct in a vacuum chamber, of some sort? Though you show the bigger obejct as being an apple, and I don't know how we'd be able to use THAT big an object in the current experiment setup - but larger molecules might be possible!
2. All I know of the double slit experiment and its interpretation is that the particle, when NOT measured, has wavelike functions - the particle is in a superposition (you taught me that word *thumbs up*) , which would mean that ANY measuring would force that superposition to collapse and therefore hindering the many-dotted pattern happening - because the moment you measure where the particle is, and you'll obviously be doing this when measuring which door the particle is going through, you're making sure the particle can't have wavelike functions, and only particlelike funtions... right? So you might as well have just kept one door closed.
3. I don't know how to answer this one but I hope to be able to soon!!
Thanks for a great lesson!
So great to see you post again :D
Just here to tell you that your videos are amazing.
Excellent presentation!
Glad you are back
My new favourite channel!
HOW HAVE I ONLY JUST FOUND THIS CHANNEL !
awesome.
The part about one 'bin' per door when each is closed does not match what we see in real experiments with either matter or light.
When one door is closed then the pattern that appears is still an 'interference' pattern and it still exactly matches a pattern predicted by QM. The beam widths of the single slit pattern, together with the form of its surrounding bars, is inversely proportional to the aperture dimensions in a way that cannot be explained by random scattering. These are also disturbed if you 'look' at the particle transiting the aperture(s).
For this reason, I think the depiction of the difference between single and double slit patterns shown in the video is very misleading. Especially the idea that the single slit pattern reverts to a single 'pile' behind each opening (like a simple shadow) - I really question the ethics of propagating this trope and then claiming to represent some form of authority on QM.
In particular:
a) The single slit pattern is a quantum phenomenon with exactly the same explanation as to the double. and
b) In order to be mathematically consistent with QM, the single slit pattern needs to fully overlap the region of the double-slit interference.
For all aperture patterns, (single, double, grating) the observed particle scattering patterns correspond exactly to particles/photons acquiring a transverse momentum from a probability distribution that is given by the square of the Fourier transform of the aperture pattern divided by Planck's constant. This is independent of the type of incident particle or wavelength.
For a bright line in the two-slit. sin(theta)=n*lambda/d, substitute de Broglie wavelength and p=n*h/d. In effect, the de Broglie/photon wavelength is eliminated from the calculation of the scattering pattern.
For a single slit, the beam width is also an exact function that depends on QM = first dark line p=h/w (w=slit width). Same deal, the pattern depends on QM and from a momentum perspective, is totally independent of the incident 'wavelength'.
In effect, the experiment is explained if, at the instant that the particle transits the slits, it experiences a discrete momentum transfer from a probability distribution that is given by a simple formula predicted by QM. (provided nothing interacts during the transit).
When the particle transits the slits it exchanges momentum if it is deflected. The spectrum of possible momentum exchanges can be calculated using QM by calculating the energy distribution of virtual photons that mediate the momentum transfer, this is a fixed pattern that depends on the aperture pattern and has nothing to do with some painful confabulation and waves that is adapted from classical wave propagation.
The semiclassical arguments about waves and interference, not-looking, and the tortured nonsense about particles becoming waves and interfering harks back to Bohr's attempts to create a semiclassical model. it is actually unnecessary provided one uses QM to model the momentum transfer between the slit and the screen as a discrete interaction.
Are you even interested in explaining QM to lay people or just criticizing the content creator? Your criticisms and explanations are inscrutable to this lay person.
1. Particles and objects with more mass have a shorter de Broglie wavelength, meaning that when they pass through a slit of some length, it will diffract less than than an object whose mass is lowerr because it has a longer de Broglie wavelength.
2. Measuring which door the electron goes through in the double slit experient causes the electron's wavefunction to collapse, causing it to act like it only goes through one slit or another.
3. The assumption made in the Copenhagen interpretation of QM is that only the four known fundamental forces can act on a given particle. Pilot Wave Theory introduces a new force whose field evolves via the Schrodinger equation, causing some given quantum particle to move in a nonintuitive, chaotic manner.
I look forward to watching your series of videos.
2 and 3 are good! I think 1 is more subtle than that- I talked about it in my video on the wave particle duality if you’re interested.
So you are doing video again. Awesome.
Great video! True to your style, but more refined. =)
One tiny criticism: The voiceover volume (+ freq. spectrum) varied quite a bit between sections. A more consistent distance to the mic could help? (Mitigating it in post manually with gain/EQ is a hassle, and (multi-band) compressors can be tricky to set up right...)
I liked the music, esp. in the pauses & didn't think it was too loud, but preferences vary. Some RUclipsrs release (unlisted?) no-music versions & put a link in the description?
I think the most drastic jump is after 4:26 - I'm guessing you were closer for the latter part, which also made it sound a bit boxed-in due to proximity effect? The former was maybe a bit quiet vs the music, but sounded way more natural, and it seems your room is dry enough to allow for a bit of distance (also makes it less sensitive to the angle, which can be a whole 'nother source of annoyance...).
I like to [consults dictionary]... cock a snook (?) (the thumb-nose-mocking gesture) at the mic/pop filter before takes whenever I'm unsure if I moved too much, esp. after recording breaks. Either one- or two-handed is usually a good distance.
/lengthy unsolicited audio engineering remote diagnosis, sry ^w^'
Good production overall, and great script & performance!
Thank youuuu! Honestly, I recorded and recorded this audio so many times because I hated how it sounded- I moved to a better, supposedly much better, set up and couldn't work out anything. Any more advice would honestly be so appreciated. You clearly know what you're doing. How come?
This is already way smoother than your first attempt at the series. It might just become my go-to resource to send people to if they're confused about quantum!
Yayyyy. Thank you. It really bothered me that the start of the old series was so bad.
Hi Mithuna,
Truly excellent work putting this video together. As a soon-to-be PhD physics student who has done quantum coursework extensively, I’m anxious to answer the questions for fear that they’ll expose how little I know or how misguided my thinking might be. So here it goes…
1) In principle, everything is a quantum object. Why wouldn’t an apple thrown in the middle of a double slit go through both?
In a double-slit experiment, the distance between visible peaks in the interference pattern is proportional to the wavelength of the object and the distance to the back screen and inversely proportional to the distance between the slits.
If you think of a thrown 70g apple as being one big quantum object, its wavelength (h/p) is on the order of 10^-33 m, or about a billionth of a yoctometer. The smallest width between slits we could currently create (a bit generously) is 10^-10m. So in one way of thinking about it, you couldn’t produce slits simultaneously big enough for the apple to pass through and small enough a distance between their centers.
And at a macroscopic distance to the back screen, the distance between the intensity peaks would be too small to resolve anyway - on the order of 10^-23m.
If you instead thought of the apple in terms of its constituent subatomic particles, and tried to run the experiment on an “electron-sized” double slit, the barrier with the double-slit isn’t the only potential to consider anymore. It is already in the presence of other subatomic particles pulling on it with various forces. The result on the back screen after you take into account the forces from the barrier and other particles would just be a splattered apple.
A couple questions came up in thinking about this:
What happens if you move the location of the electron emitter? I know it so often gets portrayed as being exactly in between the two slits, but how does the resulting pattern change as the emitter gets moved closer to (or past) a slit?
Also, how does changing the slit size affect the interference pattern?
2) So I’m not sure what the measuring device is doing, but my guess would be that if it stops the particle entirely then you would get the same result as the observed slit being closed with 50% particle detection from the detector. If the device detected and allowed the electron to pass through, you’d get the same 50% detection and I think the result becomes two piles behind the slits, as if you added the results of each of the “one door closed” scenarios together.
My suspicion has been that there’s something fundamental about measuring that causes this. My teachers hand-wavingly talked about “increasingly subtle” detection devices and that may be the reason my view is less nuanced.
3) I had an interest in Bohmian mechanics but never followed through, so this is a best guess - the particle is, as your illustration suggests, riding a wave. (What is that wave exactly? The fabric of the universe?) So when the double slit is encountered, the particle only goes through one slit but the wave goes through both and interferes with itself, affecting the travel pattern of electrons such that collections of them detected on a screen make an interference pattern.
Soon to be PhD? Dude. We teach in undergrad physics that a measurement in physics is an irreversible energy transfer. Somebody either wasn't paying attention or they are lying about themselves. ;-)
Love the graphics!
Really appreciate the effort !
Aww! I really appreciate the comment.
Thank you, I enjoy these videos. I'm not a physics literate, just interested. Now a few questions:
1st) if superposition supposes that both position and momentum are in an undetermined state, and thus potentially all states (I visualize this as kind of like a cloud, however I understand that any physical representation of an unknown may not be appropriate), and if we're firing multiple particles in series, which are also waves in series until measured, is it possible... here's the stupid part... that each particle resumes wave form post measurement, and then acts on the next particle being fired? This is kind of a hybrid pilot wave question, where other items in wave form are acting as pilot waves for the particle being measured. Another way of posing this question might be, is a particle dead after measurement, or is it still active post measurement?
2nd) Is measurement done as a single observation after the fact of a collective of results? If so, how would we be able to preclude any interim behavior between the first particle firing and the amalgam observation?
3rd) Is an act of measurement confined to each single particle? Are other wave-particles precluded from acting on the one being measured/observed? if so, how are they precluded from interacting?
4th) and most important... is that Schrodinger's cat in your illustrations? ;>)
Thank you for taking the time to read my questions.
Great video. I kept waiting for you to talk about Pilot Wave Theory because it makes all of these effects very intuitive and at the end, I smiled.
I'll take a crack at the three questions:
1) Yes, you could do it with MUCH bigger particles (although Copenhagen seems to suggest a lower quantum limit) as literally proven by the oil droplets in the Pilot Wave videos. In those cases, an oil droplet (particle) is sent through one of the doors while the guiding pilot wave(s) are going through both. The interference patterns of the waves affects the trajectory of the oil droplet and when sent through over time, they display the same interference effect as in the standard Young double slit experiment.
2) Measuring the particle affects the distribution of the particles (they go back to being dumped in piles as if they went through only one door). I believe this is due to the fact that the measuring device interferes with the particle's guiding wave and destroys the interference effect and so the particle just proceeds to which ever pile it would have if the other door was closed.
3) Pilot Wave theory allows for the particle to go through just the one door while the guiding wave goes through both. The wave when it recombines on the other side of the door interferes with itself and guides the particle regardless of which door it went through to one of the nodes just as standard QM would predict. If you "measure" the doors, you interfere with the guiding pilot waves and ruin the interference effect so the particle ends up always at a pile behind one door or the other as you measured them. No mystery at all - and no need for special observers, the moon can exist when we aren't looking at it and the poor cat dies the instant particle decayed and not when we opened the box. Also, there is no quandary when it comes to entangled particles. You already know when you measure one that the other one has to be the opposite as you defined that initially. No need for FTL travel at all. It does require non-local hidden variables (the state of the universe which affected the particle up to that point in time but that's no biggie as so does standard QM or any other theory that matches the results of QM - as proved by John Bell).
Very good!
But I’m going to play devils advocate- so we can both learn more. Bell’s theorem shows any good theory should be nonlocal. But in QM, that non locality only happens right at the end- when you measure. In BM it’s constant, at every point in time, the pilot wave of entangled things is nonlocal.
Great question... My initial thinking on this (and I'm going to ponder it a lot more) is that QM only generates non-locality at the end because that's when the wave function "collapses" (or reality emerges if you believe it) - it's impossible for it to emerge earlier because it can be in all possible states before then. In BM, the waves and particles exist all along so it follows that the pilot wave must nonlocal all the time for it to fit with Bell's theorem (which it does). This has interesting consequences but since the pilot wave exists in an N-dimensional configuration space outside of real space, it's nonlocal by definition.
Awesome, LGU. I love your videos, they really have been the most helpful to me of all in getting a better understanding of these ideas. Am I correct to surmise that if an object is large enough to interact with itself fairly constantly through its own bonds then it should 'resolve', or its wave function should collapse, fairly constantly? Does this mean that, say, atoms should pile up into two neat piles because the interactions of the nuclear forces mediated by the associated bosons already count as a 'measurement'? So the only quantum aspect of atoms would be radiation?
Thank you!
That's a really good point, but in fact it isn't true. The reasons are very subtle... and I'll go into them in lots of detail in the follow up video.
1 glad you're back
2 is there a difference between a measurement and an observation.
3 I want to know more about the other experiments that show strange behaviors.
1. Thanks :)
2. Yes! And I’ll talk about that.
3. Good idea. Another one is the spin thing- but I might cover some others
Great video; Keep it up. I think the single door case at 4:50 isn't right though. Narrow doors mean that the pattern on the screen will spread out. The two patterns from the individual doors should overlap significantly for the experiment with both doors open to work. Only where the two patterns overlap can they interfere with each other.
Nicely done. I've tried to explain QM to friends and family in the past but it is so hard. Partly because the maths describes behaviour but doesn't explain it. And you need the maths to even see why, for example, the uncertainty principle is a consequence of the wavelike aspects of matter. QM isn't kind to human intuition. Looking forward to more of your work.
Absolutely! I wrote and rewrote this script over days and weeks.. It's very hard to be correct while still being somewhat understandable- as I'm sure you found.
Your videos are among the best on RUclips regarding this topic.
1. Is "measure" the right word, or would "interact with" be the better term? Either way, larger massed objects interact too much with their local environment, which includes the insane amount of particles within the object itself, for them to behave as those with very low mass and physical dimensions. For those reasons, I don't think there is a way to make that work. I'm probably wrong or don't have the full answer, though.
2. To measure the electron as it passes the openings would be an interaction with it, thus changing its behaviour from a wave function (not sure if that's the correct term). The pattern would be two blobs of electrons instead of the interference pattern without any interaction/measurement.
Thank you for these videos. Please keep going with them.
Thanks a lot!
I very tactically used measure rather than interact, because actually, not all interactions are measurements (and vis versa!).
1. Yup, you're right!
2. Yes :)
Yay ! You back again welcome :)
Great having you back. Hope things are going well. The answer to question 2 (my guess) is the wave function collapses and the particles will gather near one spot.
Thank you :) yes that’s right!
Fantastic video!
A few questions remain:
An electron racing through space creates an electromagnetic field, right?
Electromagnetic fields are infinite in their spatial dimensions, right?
So a flying electron can`t avoid interference with “the universal electromagnetic field”.
So it is in fact constantly “measured”, even if we humans have no instrument to give us any readings of these very subtle changes in “the universal electromagnetic field”.
Our present technology of measuring is too clumsy not to interfere with delicate things like electrons - it is like playing the piano with a hammer.
By the way: Why do all experts seem to put the whole burden of explaining all the effects we can observe in the quantum world exclusively on the shoulders of particles?
What if space were not such a dull continuum (along with time) waiting to be twisted and tortured by matter? What if space instead were a very smart matrix consisting of “intelligent” units (e.g.space cubes) with a complex “software” interacting constantly with matter? What if space caused the interference pattern of the double slit experiment (“spatial facilitation”)? Does it not take a little while for the interference pattern to build up? Time enough to “program” the space cubes?
(Please be generous when responding to these silly questions. I have no background in mathematics or physics.)
Very good explained video. Based on the explanation in this video, could the answer to q1 be: use a device in perfect vacuum and of course perfectly dark to experiment the double slit with a big object ?
Hooray! Awesome job!
Thank you!
What nice little video. I love it.
Thank you!
Thanks for the videos. Physics professor John G Cramer's Transactual Interpretation of Quantum Mechanics would be a good topic for a video. I've seen it treated summarily but it was first published in a 1986 paper and he has a recent book. In I'm not a physicist but I like the way this interpretation follows the maths. One question is: does it successfully give qualitive predictions that are consistent with numerical and experimental results in situations where other interpretations struggle?
Answering #2:
From my understanding, we use the Schrodinger Eqn and probability distributions to describe the potential motions of a particle because there are fundamental uncertainties to our measurements. (Not from any technological limitations, there are fundamental limitations to knowing certain pairs of information we have to consider at this scale).When we fire the electrons, we know the position and momentum only so well, so we have to treat it as a distribution that covers all the possible results that we would get if the electron had a specific position and momentum.
So when the electron is observed in the middle of the experiment, we have more information. Some of the paths/outcomes previously thought to be possible we now know have to be ruled out, so in a sense, we “update” the wave function upon measurement, and then again the fundamental uncertainties help tell us how our new probability distribution has to evolve through time.
So if we know what door it went through, then we already know the possible outcomes: the results of the single slit.
Yup, that’s right!
To answer the homework questions:
1. The particles that make up the apple are interacting with (i.e. measuring) each other, so our assumption that nothing is measuring it is false. Instead, we'd have to model it as a whole lot of individual particles all clumped up together feeling some force holding them together, all while traveling through the double slits and hitting the apple detector. (I'm not actually too certain about my answer to this)
2. We would now know which door the particle went through, so it's as if we closed the other door; the pattern on the detector at the end would be all in one place or the other. Basically, if we repeat this over and over, we'd get our original prediction back.
3. I think you've explained this before (maybe in the video you linked to? I didn't rewatch it). The particle goes through one door, but then there's an invisible force that makes it not just travel in straight lines, but in some sort of chaotic pattern - that is, chaotic in the sense of exponentially amplified error, but there's still some structure to the chaos (that's what makes the particles clump up in the wave pattern we see on the experiment). This wave does not do the same thing when we close one door (or equivalently, measure the particle at the doors, as in question 2), which is why the particle acts differently when we measure it's going through one door vs. when we don't measure it (even if it does actually go through the door).
Really good answers! And it raised some points I want to go discuss more in a follow up video.
I have no clue about this but wouldn't the object that is being fired change direction while passing through the slits because of velocity and wind direction? Like, say the atom was a little closer to the top of the slit be impacted by the velocity and wind which would force it to go downward. Then you shoot another particle and as it passes through the slit at a different distance be knocked into a different direction? Is there a way to shoot the particle at the exact same speed and distance and make sure it passes in the same spot in the slit and see where it goes then? Would it still be random? or maybe my understanding of this is completely off?
Great video!
Where are you doing your phd?
Are those hand drawn???
Yes, they’re hand drawn :)
I’ll tell you more about myself etc later.
ABSOLUTELY AMAZING. 💯
Dankeschön. Du erzeugst eine wahre Freude.
This is very elegant. Thank you for this. My own notion, as a crank, is that electrons and photons have a different relationship to time than the objects we are used to thinking about (prehistorically: sticks, pieces of fruit, an occasional stone). Having our own relationship with time, we find it hard to imagine what is going on when objects spread part of their reality quite differently from how we-or a bus, or a sock-do. But we do have part of our nature similar to electrons and photons, without which we could not exist. So there’s a part of us that behaves in this manner. Whether it’s detectable or not is another matter. Anyway, I think time is the most complex and weird variable here. And that is where the mathematics needs to adapt.
Very good questions and doubts you arise.
Love the video looking forward to more
Thank you!
Thanks a lot for ur effort 😊
I love the title animation!
Thank you so much! That took so long...
I have a question: would two free electrons in an almost completely isolated system count as an observation? Or would that not matter since once they've repelled each other and caused their wavefunctions (assuming it is the case) to collapse, their wavefunctions would just evolve back to near normal after the time it would take to come into contact with another particle?
I think it depends on how "close" they get? Whatever closer means when the positions of the electrons are fundamentally undefined. Or, they might get entangled with each other, which is a thing that really makes the notion of observation unhelpful.
Really, I'm just commenting so the algorithm knows to rank your comment higher.
Do you draw the images in your videos? They look great!
Thank you so much!
Fabulous video.
In double slit experiment, when both doors are open, are we firing electrons one by one?
Regarding the outcome on the luminescent wall (where electron hits and emits light), do we have more particle emissions than the number of electrons emitted from gun? This part was not clear in the explanation
Yesss! Finally back!!
Sorry for the wait :)
Looking Glass Universe
Your videos are always high quality, so it's worth it.
1. A big Object such as an apple is very very very much likely to be observed by an other particle so it can almost be immposible for the apple to remain unobservable.
2. We will just find 2 dots on the wall .
Another beautiful video of yours, cannot thank you enough about it. One important point is often overlooked when talking about the double-slit experiment: how far apart can the slits be and how large the doors have to be in order to notice the effect.
There isn't a distance limit between the splits. However, there is for their width. It has to be equivalent to the wavelength of light.
@@jimsagubigula7337 This is something I find quite amazing ... Having the slits a few wavelengths away or 1m away should have some effect? Or is it only that if they are 1m away the effect is still there but the intensity on the wall is negligible?
@@christophealexandre1538 No, the intensity will be exactly the same. It will only affect the angles that the bright lines will be created. Think about it another way. When a light wave passes through a slit, it diffracts and spreads in all directions. So, the slits act as wave sources. A common day analog is throwing two rocks into the water. When the rocks hit the surface of the water, waves will be created and will spread in all directions. The rocks here are the analog of the slits and the water waves the analog of the light waves. Does it really matter how far away these rocks will fall into the water? They will both create waves, which will combine a few seconds later and create destructive and constructive interference. This will happen regardless of how far away from each other they will fall into the water.
@@jimsagubigula7337 You can do this with large slits just fine.
@@lepidoptera9337 Depends on the light's wavelength
Hello, I'm a 17yo student and I'm deciding what to study in university.
I'm super-intrested in quantum mechanics and particularly in quantum computing.
I couldn't belive my hears when you said that you're doing a Phd on it!
Can I ask you what should be my studying path if I want to research in quantum computing?
For now I'm studying IT in high-school but noone of the teachers could tell me where should I study for that.
On a sidenote: Thank you so much for these videos, they're making me intrested in this quite obscure field. I already suggested your channel to all my friends and physics teachers (even though we're not english so it can be quite hard to understand).
Homework (I watched all the other videos so it's not a local feedback on this video alone):
1) I think you couldn't make the experiment with bigger object as evert particle (quantum?) contained in the bigger object would interact with the others and measure it. If I understand it correctly it's not even possible to isolate the particles from each other because any force applied will measure the "particles" (because it's trasmitted by bosons).
2) Measuring the electron in the middle of the experiment will make the electron act as a particle so you find that the particle passed only in one of the holes (by probability) but the experiment changed trough the measurement so the result will be two piles of electrons.
3) You say in the video that the particles "must have gone trough one of the door", but with the pilot wave theory the wave generated by the electron goes trough both doors. This will change the wave function and will interact back with the particle making it change direction in a way that seems randomic but is in reality defined by complex mathematics.
Sorry for the missing terminology, I don't remember any :(
Hii! It's great to hear from you :)
That's awesome you're interesting in quantum computing!! Where do you live/ want to study?
If you want to study QC, there's basically two ways in. One is to do a purely physics and maths undergrad degree. The other is to do a purely computer science degree. (Ideally, you'd do a little of both.) Then after that, you'd specialise in a masters degree and a PhD (if you want). Most places don't do any QC in undergrad.
My advice is that you decide whether you like physics/maths better or IT. Because you'll have to do a whole degree in one of those- and if you really love that degree, you might not do QC at all and decide to do something in that instead (which is also awesome!).
Feel free to email me at looking.glass.universe@gmail.com if you'd like to discuss this further :) Good luck!
1. This is a great point! It's a bit subtle, so I'll explain in the follow up video!
2. Yes, you're right! Though, I don't think it's because it was acting like a wave and now it's acting like a particle. We just know this happens, because now the situation is the same as if it'd gone through one slit.
3. Yes, exactly :) Thank you for your answers!
I do like your videos.
I wonder if you have studied Quantum Field Theory where the wave particle duality is fully explained and one no longer refers to objects but rather creation and annihilation operators.
Would also love you to try to explain the stern gerlach experiment using pilot wave theory ( not sure it's possible ), or to describe the pilot wave associated with an apple.
I do know QFT, but I actually think it doesn’t solve the issues.
I actually talked about the Stern-Gerlach machine in BM in my contextuality video :)
That's was goooood.. Can u do quantum gravity??
This is very helpful and also hilarious