Quantum Wavefunction | Quantum physics | Physics | Khan Academy

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In this video David gives an introductory explanation of what the quantum wavefunction is, how to use it, and where it comes from.
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Physics on Khan Academy: Physics is the study of the basic principles that govern the physical world around us. We'll start by looking at motion itself. Then, we'll learn about forces, momentum, energy, and other concepts in lots of different physical situations. To get the most out of physics, you'll need a solid understanding of algebra and a basic understanding of trigonometry.
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[@1articoli]

So far, the clearest explanation I've seen.

[@poibnm2341]

Yes yes yes. I totally agree. I don't have any words to describe the quality of his explanation

[@lourdesmary4909]

Amazing explanation Best explanation Thank you so much sir

[@parkerwebster2571]

how many words did you speak, before you learned how to speak? Cous, you def. no how 2 speak. Tu 4 ^^^

[@AdeshBenipal]

So true

[@sunnynegi722]

I agree

[@lokeshs2632]

It was hard to listen while Schrodinger was staring at us

[@mariaorsic9763]

that means you are thinking!

[@Gavin-cu7ti]

*Schrödinger

[@vaishnav_mallya]

Schrodinger : Ayy, you learning my equation

[@Ra-thesunking]

Lol

[@Quwucuqin]

💀

[@mrpickles1]

My favorite is how he automatically knew what common questions people would have about this. Like, guys this is just the way it is, don't worry about the equation, just accept that psi squared is density probability. period.

[@AlexHunter2525]

I've been looking for this explanation for months. Makes much more sense now

[@younessidbakkasse9742]

He is a legend

[@josephjmurphy1718]

'Nah' - Max Born

[@ankitaaarya]

😂😂👍

[@sunilnamdeo1971]

😂😂👍

[@darpanaswal9291]

😂😂👍

[@ZzSlumberzZ]

😂😂👍

[@mistercraftpiggy]

😂😂👍

[@blackpink5937]

So the lecture started with the very question which kept me depressed and from really trying to understand the quantum mechanics...so thank you so much for clearing my doubts.

[@leosteinman3057]

Me understanding it: oh that’s cool I’m pretty satisfied Kahn: if I were you I wouldn’t be satisfied Me: yea Fr I ain’t satisfied at all yet

[@peacekipu3720]

so I wasn't all alone after all

[@Pokemonzeldabro]

My exact thought process haha

[@saleemshaikh4904]

Schrodinger couldn't interpret the equation, then Max was born.*wave intensifies*

[@Lucas-zd8hl]

Max was born

[@legendarylightyagamiimmanu1821]

Nothing happened actually ehem

[@Gavin-cu7ti]

*Schrödinger

[@vers8278]

@@Gavin-cu7ti no one minds being it without the two dots, you don't need to reply that to every comment

[@Gavin-cu7ti]

@@vers82781) I do mind 2) it's how his name is actually written 3) if it doesn't disturb you, why did you reply to my comment

[@mozorellastick2583]

This is like one of the best videos I've ever seen. Better than my university lecturers. Thank you so much

[@snehashukla5545]

At least he made it clear that we're not the only ones who don't get it Thanks man!

[@chimedemon]

Schrodinger: so uhhh... yes... I will tell you how I interpenetrate this equatio- do you wanna explain your own way of interpenetrating this? Max Born: is this a test? Schrodinger: ............. yep...

[@Gavin-cu7ti]

*Schrödinger

[@udith]

*interpret

[@yankoshbadal]

Fun fact :- a single electron is present in every possible points within the probability amplitude until it is observed ... See double slit experiment ...

[@mozorellastick2583]

It’s not actually present, it’s got a single location, we just don’t know where it’s location is so we have a probability of the space the electron could occupy. When it’s observed it then shows it’s single position, but we had no way of calculating where it was until we saw it

[@pgong415]

I’ve just begun reading a book on quantum physics! Your demonstration about the wave function is clear and sensible ! My take away is that the thing that is waving is the amplitude of probability wave!

[@tedunguent156]

Yes. Either the amplitude of the probability wave/magnetic field or of the conversion of matter to energy or energy to matter. Or both. OR, of the motion of the particle/wave moving forward or backward in space/time.

[@mozorellastick2583]

Could it be the motion of the "particle" in the electron field? We know that particles are disturbances in each fundemental particles field, so does this wave mean the motion of this disturbance? The particle can't have a definite position but it can have a definite path/trajectory right? Or have I gotten it wrong? I'd love some insight

[@pgong415]

@@mozorellastick2583 Definitely it is not about the motion of quantum, but truly on the whereabouts of them, scientists are crazy on matters location and speed! So far we humans failed to pin down quantum , instead, we could only tell how probably them can be, which is their probability. And the value of the probabilities are sort of waving along ! Interesting!

[@duvallroberts9926]

I find great joy in these physics videos. They help my interests in quantum mechanics grow.

[@hairyaries1]

Hey Khan academy. I had a thought. Maybe you can say yay or nay to it. If the wave function can happen with particles and atoms (with mass), could this account for all the extra mass they calculated needs to be in the universe? If electrons and atoms are reacting (interfering) with all their other possible realities, then is it possible that their mass is duplicated, if only temporarily? It's hard to imagine that a probability of something would be real enough to have mass, but on the other hand, it's definitely real enough to interfere with itself and all its probable twin buddies, so why not? Thanks

[@WilliamGerot]

To bring you up to speed on dark matter (The universe's missing mass) it is not that we don't know what causes it, the problem is only that we can't get a good look at it, as it seems that it doesn't interact with the electromagnetic spectrum (Our most versatile and common source of information in astronomy). We know that it is a different thing than matter because you have effects such as gravitational lensing (Google it if you are unaware) which can occur regardless of dark matter's proximity to other matter. Besides all this, probability density is not equal to real density. Wavefunctions do not increase the mass of a particle, a great proof being how accurate Einstein's General Relativity is without his knowledge of quantum physics. In fact, Einstein famously hated wave functions and the unknowability inherent to quantum mechanics. To conclude, nay.

[@danielkmchow1185]

Addressing questions that an amateur like me want to ask and explaining it clearly. Well done!

[@sksnawaz1064]

I feel this is an iconic explaination

[@peshnjugush4496]

Wow that is amazing proffesor Dave... it's true you understand concepts in minutes of which have been taught for a couple of hours in lectures in vain of understanding

[@peacekipu3720]

He's the same guy in "prof. Dave explains" vids?

[@samovarmaker9673]

Jesus Christ it's Max Born

[@vaishnav_mallya]

Lol

[@sadovniksocratus1375]

Psi (Ψ) - in the light of quantum behavior. The Problem with Quantum Measurements - Psi (Ψ) The '' measurement problem'' / ''wave-particle collapse'' About one wave measurement of one quantum particle. # There isn't electric wave without quantum particle. The wave-function is result of a real work of quantum particle (h) The wave-function Psi (Ψ) is derivate form of quantum particle. The wave-particle collapse problem could be contemplated as boundary changes of wave and particle simultaneously. # When the wave collapses, the pure electric particle (E=h*f) changes its parameters into negative potential state - Dirac's virtual / antiparticles (-E=Mc^2) and "disappears " in Zero Vacuum T=0K. =====

[@LuisAldamiz]

What do we mean by "finding the electron"? We detect something that looks like a dot but what is it? We've grown accustomed by analogies (bad analogies) to think of particles as tiny balls or even dots ("point particle") but particle itself only means "small part" (Lat. particula) what can be actually anything: a "ball" or a "string" or a "spring" or whatever else. My (probably shallow) take is that it is some sort of vibration of spacetime itself and what we experience as "dot" is an effect of it, not it, that the particle is a vibration of spacetime itself or maybe a "pressure density" but something of spacetime as "substance".

[@timrodriguez9532]

The election isn’t a point particle. It’s an electron field. We don’t think of the magnetic field as point particles.

[@LuisAldamiz]

@@timrodriguez9532 - The "election"? That's a funny Freudian slip! ;p

[@LuisAldamiz]

@@timrodriguez9532 - A lot of people, including physicists present it as point particle. Famously Feyman claimed that in one of his much referenced lectures. I agree with you but there is this contradiction of concepts that physics, notably quantum mechanics, has been dragging on since the "particle-wave" duality was established (by Einstein in 1905 if I'm correct). My point was (I believe because seven months have passed since then) just to emphasize that "particle" only means "small part" (literally) and that the nature of such "small part" is sometimes confusing.

[@qualquan]

The equation is not derived but Psi (x) discussed Psi (x) or "wave function" (WF) or "probability wave" (PW) is not the matter wave of the particle. Psi is the amplitude of the WF whose square gives probability of finding particle along (x). On landing the WF collapses since there is no position uncertainty left. The matter wave of photon also collapses since photon at rest ceases to exist passing its energy to the acceptor body in a non elastic collision.

[@whiteboardanimatorhamna]

Thank you soooo much for making it much easier to understand...

[@FaithNoMore223]

The same thing comes up with a deck of cards. When a deck is being shuffled everything is a probability but once a card is pulled the probabilities collapse to be 100% chance of that card being the one pulled.

[@jaybee1299]

Because the past is set in stone. The future is undetermined.

[@PaPaScorp1on]

man we need this to e linked in a playlist to study it please!!!!

[@user-lm7yx7wj5l]

You have a mistake!!! In the schrödinger equation, at the left side you wrote, it is supposed to be ĥ² (h-bar squared )...

[@ankitaaarya]

I guess we can forgive him for what hes doing for all of us

[@Ghost-vg6iq]

Knurdddd

[@jrsolomon5960]

the way he explains, even secondary school students can understand it, compared to my physics lecturer at university.

[@schmetterling4477]

That's the problem... he tells you a bunch of baloney. Yes, you can understand it, but you are walking away with the wrong mental model. This is not how it works.

[@jamesruscheinski8602]

When the quantum wave function is measured, the energy level at the present moment in time is given?

[@chiramana_]

Woa, very well explained 😁🌱

[@igormichetti]

This is actual proof for why you should learn the subject before memorizing the formulas

[@ajtepal8596]

I liked the bad news you said in the last two minutes... It made more interested to know more about the quantum mechanics

[@nishatiwari9212]

Very elegant explanation. 😎

[@drakbar3809]

Best explanation I've ever had!

[@sumanpandey397]

Very Clear & nicely explained, Thank U Sir.

[@tonyyu5002]

Dudes be like: "wave check" *Shrödingers equation intensifies*

[@Forever._.curious..]

Here , I like bad news over good news ☺️

[@sdutta8]

Best description of the present state of the “understanding” about wave-particle duality, or non-understanding depending on your position on the interpretation question.

[@lepidoptera9337]

There is no such thing as wave-particle duality. There are only people who don't understand physics. In this case it's high school physics. :-)

[@wulphstein]

In the Expanding Graviton model, gravitons are (1) the carriers of the physics constants AND (2) gravitons are what wave functions are describing. Therefore, what is waving is/are the carriers of the physics constants.

[@alabiadewale8734]

I really understand this now. Thanks sir. I'm ahead of the class now.

[@erikadelgaldo1079]

Hello everyone, I would like to ask a question. How do you proceed, in a typical experiment, to confirm whether the wave function has collapsed or not? Let me explain. Let's take an overlapping electron of states and let it pass through a "channel"; I want to know if it has remained consistent up to a certain point. But doesn't the act of checking coherence cause us to lose it? In a nutshell, how do we verify collapse if the act of measurement itself causes it? Thank you

[@erikadelgaldo1079]

@Ensrick thanks

[@sebastianback]

A little clarification for the video: the h with a line crossing the top of it is Dirac's constant, not Plancks constant h.

[@julsius]

And the difference?

[@Michiel_de_Jong]

@@julsius toopeye

[@rakhibhuyan7460]

This is the best explanation of wave function in KZbin. But we don't find such clear explanation on every topic that we come across, so can you refer a book on QM which we should follow to be conceptually clear?

[@schmetterling4477]

That's cool. especially since this explanation is wrong. ;-)

[@helloworld-hv9oy]

learning a concept :Schrodinger Applying it in real life:Max Born Both are legends !!

[@nc8002]

Wave function: useless Square of wave function: usefull 🗿

[@kryt7955]

But how can we describe the position of a particle by only a single value i.e. the X-axis?

[@luqman_alifio8075]

we can't. the actual wave equation usually is in 3 dimension (unless there are some constraint). however, with 3 dimensional equation (3 unknown x,y,z) the equation will be very complicated that's why the existing explanation usually use 1 dimensional wave equation. simply... if they can explain the concept without short circuiting our brain, why wouldn't they?

[@mariob7791]

Nice explanation! Many thanks! First I found I could understand! Regarding probability of finding a particle: - exactly WHERE? In the atom? In the LHC? In a specific point in time and space? Or any of these alternatives? Weird.....seems more a way to circumvent lack of more specific math or even worse - lack of deeper understanding of particle physycs - for the subatomic world. Could it be that all these Nobel Prizes fooled us for so many decades? I suppose it is necessary to work this out or Science will resemble more a religion. In fact I heard Sean Carroll talking about this fundamental problem without having a minimal rational of the wave function, but now, after this video, I suppose I am starting to understand the message he was trying to pass through.

[@proffoctopus66yearsago22]

Hey the wave function gives you the probability of finding an electron at a particular time and point in your QUantum state. What exactly is a quantum state? basically the tiny particle system you're studying The wave function probably helps in giving you the probability of finding an electron in a p sub shell or an s-shell. Hope this helps! :)

[@TheBinaryUniverse]

The wave function is a function of the way the electron moves through time ! (Faster or slower) This is because time is a wave of energy, varying in energy over duration. Read "The Binary Universe" (2nd Edition 2018)

[@legendarylightyagamiimmanu1821]

How is time a wave of energy ?

[@rejanibps2120]

A greattttttttt teacher, No words... Speechless .....thank you veryyyyyyy much.... 😘

[@andruss2001]

Good explanation, thanks!

[@michaelgonzalez9058]

Eletro magnetizm,wave function

[@soumyasrivastava5648]

What about the question - what is waving?

[@ducatista_squid]

you.....are.......awesome. tysm

[@crescent4033]

Very well explained sir

[@adrianbiber5340]

But *where* is the electron? Floating in space, held by what? And why is it a 2D plane? Is that the distance from a nucleus?

[@thegeebees5695]

How can there be 0 probability of finding the electron at the end of each wave? Wouldn't that mean that electrons traveling at a line somehow skip points in spacetime as if it disappeared then reappeared?

[@AxanLderE]

The way I see it, that point cannot be defined as there is no such thing as an infinitely small unit of space. The probability approaches 0 as you get closer and closer to that point, but saying it ever reaches 0 might not translate to the real world. Also, I'm not sure that's the way physicists interpret an electron. Instead of thinking of it as existing along a path, think about it as existing everywhere with some distributed probability of being measured at any point within spacetime. Note I am not a physicist, so I could be completely off.

[@User-ei2kw]

Its only true for non-relativistic theory.In relativity, its always nonzero

[@blaze-pn6fk]

This opens up one electron universe theory lol

[@manishbhatter60]

You used the same graph for psi as well as the probability density. Secondly, since you used the time dependent equation, psi is a function of both x and t.

[@blackpink5937]

Can you tell me what's 'x' here

[@ronitmajee4235]

Thank you

[@srb20012001]

Very well explained.

[@goldibollocks]

What I don't understand is: Where do you measure the electrons that are shown in the last diagram? There is an x axis that is distance from some origin, I suppose? And the wave function shows you at which points in space you're most likely to find the electron when measuring, right? But, what kind of stuff is measured here? Are there single electrons being shot out of x=0 in the direction of x=infinity and the wave function goes on forever and incorporates time and shows you where you're most likely to find the electron in space after any amount of time? Or does x loop at the right end of the graph and begins again at x=0 and time is not even relevant for the graph? Also, how would this graph look when describing an electron that 'belongs' to an atom? Where in space would be the nucleus of the atom in this graph? Is the graph extending into 3 dimensions for describing an electron in an atom?

[@schmetterling4477]

An electron is simply a bit of energy. What we call measurement is a transfer of energy from one part of the system to another. The wave function is not a physical object. Ontologically it's very similar to a probability distribution. You don't attach a physical probability to a pair of dice, do you? If you don't, then there is no reason to do it to a wave function, either. If you don't call a throw of a pair of dice "a collapse of a probability function", then there is no need to use that terminology on a wave function. People have simply been confusing themselves with these things for a century because Einstein and a few others said a few very foolish things during the early years which have hung around because they were repeated by people who know more about saint veneration than they know about physics.

[@thebeast5215]

Jesus what a well made, well explained video. I am truly fascinated by this topic.

[@roxybadass5262]

so WHAT IS A WAVE FUNCTION? why noone can tell that? is it a number? an expression? where do I get it from? what shall I plug into Shoiedinger equation instead of Psi to solve for partial derivatives etc???

[@vectorclassic6403]

Beautiful mathematics

[@eyosiyasgtachew5540]

you have been so helpfull

[@toanhien494]

Thank you from the bottom of my heart

[@TechsScience]

If you were teacher in my masters I would have became a great scientist

[@schmetterling4477]

If you were a great scientist, then you would know that he is not a great teacher. :-)

[@jamesruscheinski8602]

Does the quantum wave function give you energy levels (amplitudes) and how often (frequency) of energy level in the future?

[@ConnecttoSoul]

😇 Say thanks to you for the interesting video, it certainly is greatly appreciated and I really value your hard work !👍

[@legendarylightyagamiimmanu1821]

Connect to Soul the glory for hard work should be given to G-d that gave physicists like Schrödinger ideas

[@aelobalthrop1413]

Basically, the "Cheat code" way of thinking in this "Human panpticon"

[@michaelgonzalez9058]

The Darwin method is now complete

[@scottsobon9256]

I think the electron is shrinking and expanding at the same time giving the wave and particle probability and once measured because of the size we see a sliver of the wave or ie particle. Which gives it’s a superposition moving through the curve of space

[@kurshidulalamlaskar8744]

Thanks .. indeed the best video I have got to watch

[@jamesruscheinski8602]

what can make up probability(s)? is there greater probability of a particle because there is more energy at location, or something else? does a particle form when there is enough energy?

[@soldiergar5725]

Thank you 👍

[@Ra-thesunking]

Thank you David!!! This is what I needed ✨💖🙏

[@szjozsi]

the wave function is not a function, it is a section in a complex line bundle over the physical space. if you really want to understand what the wave 'function' is, a deep understanding in topology is required. this video is way oversimplified but understandable as it was made for the public. but anyone who watch this do not think you really understand it well. it is like you learn velocity is distance divided by time but witout any idea about what a derivative is.

[@nimrodboshilevine9685]

I think it is quite important to acknowledge that it is a density function and not a discrete probability functiom

[@prithviprasad5648]

Density?

[@hifellow]

This was and excellent explanation of Schrodinger's equation. Very good speaker and a clear explanation. Wished he could have addressed what are the dimensions or units of "x".

[@l.h.308]

In the 1-dimensional case, x is distance, with dimension m (meter); in the 3-dim. m^3. For psi it is m^(-1) and m^(-3), since probability itself is a pure number with no unit.

[@tedunguent156]

I always thought that what was "waving" was a magnetic field. As the particle collapses its mass becomes a magnetic field. Then as the field collapses its energy becomes matter. So on and so forth. Each time this happens the electron "moves" backward or forward through space-time. Each time "searching" for the path of least resistance. That path being affected by the other fields around it. I thought Feynman wrote about that in one of his books.

[@paulm5376]

there is an arror in the equation, it should be h-bar² !!! This is because k² is defined as k²=2mE/(h-bar)² and not h-bar be careful

[@MichaelAdamsStory]

Great video! The Everettian Multiverse explanation of the wave function seems to be the *only* explanation that is actually an explanation - and its an explanation with deep and testable implications for understanding our universe and information theory. The instrumental philosophy of 'shut up and calculate' is simply bad philosophy - it blocks progress.

[@schmetterling4477]

Cool, except that when you read Everett's thesis (which you clearly didn't), then you will find that he made a major mistake in his second sentence from which he never recovered. ;-)

[@IqbalHamid]

@08:00 you will never answer these questions UNTIL you analyse where dBroglie wave equation comes from (lambda = h cross/p)

[@stevebutrimas9972]

Finally someone tells it like it is

[@sadashivtodakar6019]

Very helpful

[@kunraiyan]

3:10 how can the charge of an electron be distributed in different places?

[@ReactIonGlobal]

If the electron weren't thought of as a point charge...

[@borington4317]

I lapsed for a moment at 9:22, when I looked back that x! really confused me :D

[@mercury6284]

Thank you so much this help a lot

[@En-of5oh]

Very good minutes of quantum wave function.

[@AliAhmed-fi1oj]

Thanks ! what a neat and understandable explaination.

[@techspace1797]

God bless Khan Academy

[@sitaramar13]

have a doubt sir. In wave propagation water or sound , how individual particle vibrations are transmitted from particle to particle in the direction of wave propagation? There are gaps between particles in solids, liquids and gases. Is this not against principle of locality?

[@mrcool9837]

Can anyone help me with this question: Na atoms move at a speed of 500.0000 m / s upstream towards a laser beam with a wavelength of 588.9950 nm. a) Calculate the wavelength of the photons that hit the atoms, seen from the perspective of the atoms? b) Estimate the velocity change ∆v of the atom for each photon the atom absorbs. c) Estimate how many times an atom needs to absorb a photon to slow down to a speed v ≈ 0.

[@TjipzPK]

Thank you! Quantum mechanics are beautiful.

[@minkymoo5773]

Nice video! I do have a question though. Assuming a complex wavefunction, how are we graphing the wavefunction on a linear axis (rather than the complex plane)?

[@ashokjangidchemistryguru8071]

Excellent👍👍

[@ShopperPlug]

That was a great explanation.

[@jeffreyluciana8711]

I understand what you are saying about the probability of psi squared. I thought the act of measuring an electron changed the momentum? Won't that change the electron? Are you talking about numerous electrons with the same wave function? Is this like firing photons at a double slit?

[@kavishchauhan1955]

Tysm 😭

[@thecomprehensionhub4612]

Wasnt this explained by Quantum Field Theory? That basically electrons are projections of many layers of quantum fields, so I would assume the Shrodinger Equation gives you the wave function of a particular wave in space, which at the quantum level is waving like the ocean.

[@rohanthapa1154]

What level students are supposed to study this equation? High schoolers or even above?