Quantum Wavefunction
ฝัง
- เผยแพร่เมื่อ 4 มิ.ย. 2016
- In this video David gives an introductory explanation of what the qauntum wavefunction is, how to use it, and where it comes from. Note: There is a missing square on Planck's constant in the left side of the Schrodinger equation written in the video. Sorry!
- แนวปฏิบัติและการใช้ชีวิต
![Quantum Theory Made Easy [1]](http://i.ytimg.com/vi/e5_V78SWGF0/mqdefault.jpg)
![เกิดใหม่ทั้งทีก็เป็นสไลม์ไปซะแล้ว ซีซั่น 3 - ตอนที่ 57 [ซับไทย]](http://i.ytimg.com/vi/pNhft3YZFRE/mqdefault.jpg)
I have watched dozens of these videos. You are the first one to explain all of this in way that it can actually be understood!
Fun fact, nobody understand it completely...
Thank for this video. I've gone through many this last hour and this is the first that addresses the problem of what's waving. It's also helpful to know that even Schrodinger wasn't clear about how to interpret it.
You guys beautifully expressed the complexeties of wave functions out of all the physics I know, wave functions and particle waves are one of the hardest to grasp.
Thank you David, great and simple explanation, high video quality, no noise. It was a pleasure listening to you. :)
Marco Polo so glad you liked it!
Wonderful, the explanation precisely follows what we think in our minds, and in the exact sequence. Very helpful to put wave function in a perspective.
Thank you for the explanation! It was a great help to understanding quantum mechanics and I hope you continue to help others through sharing your knowledge.
ur video is a great help....
pls keep on uploading videos like such.... ur the best person and have amazing knowledge
You really piece it together with your explenation. Thank you man.
What is waving? The aether. "Electrons" are like the cracking of a whip. Which is why a single electron can pass through a double slit and interfere with itself... It's actually the aether interfering with itself, but the "whip" only gets cracked at one point, giving the illusion of a particle
great explanation. thanks for sharing
Very good, the questions that count.
Sorry for my language
I saw several, but this is very good work.
simply explains the history
entschuldigung für meine Sprache
Ich sah mehrere, aber das hier ist sehr gute arbeit.
einfach erklärt auch die Geschichte
So finally here is a video that made sense !
Excellent lecture sir
I don't know if you still read comments on this video... but. I've been chasing what the wave function is for a couple of years. Not having taken calculus, or any higher maths, I do understand layman particle physics. This one video cleared up my confusion on two primary topics. One, what the wave function represents in terms of a single particle, and what it represents for a group of particles. Based on your explanation, I can now see the troubles a single particles probability of existence being creates in being defined by the function. What I still have issues with is why there are different functions to describe the probability density of particle systems. That is something now to chase for me.
Alexander Filatov Glad it helped. Good luck.
Once people started doing quantum field theory they pretty much stopped talking about single particle wave functions. Although interpreting the field there can be difficult as well.
Schrodinger was talking about what happens to the electron in areas that it can't be discovered in and why electrons exist, more so than why they accumulate in some areas more than others and what that means.
are you the guy who made some physics videos in khan academy? btw totally awesome video.
Wowwwwwwwww just simply awesome vedio. 10,000likes from my side👍
It's stolen from khan academy .... What like
Great video
Very well done, Trillion dollar question "What is the 'wave' function?
Yeah, I am. Glad you liked it :)
We Are Showboat you are what, Showboating?
whats the writing tool you've used???
This man is a synonym for the word clarity.
Maybe psi (x) is describing both a single electrons mass spread out through space and also a system of electrons
After 100 years, I think this debate is valid. What is the waving? There are two informations that we have nowadays: 1) the Quantum Vacuum fluctuation which interacts with the Electron field; 2) The Universe is accelerated expansion, showing us that on quantum level the wave function represents a piece of a frame that when it collapses, it represents a Frame in the PAST of a system in continuo movement. So...
I think what is waving it is the interaction of the Electron field with the quantum vacuum Fluctuations which causes a little open or a “dilution” of field of the electron when it is movement and what it defines the Charge density probability is the proportion of minimum state of energy of a electron in its position in electronic cloud of the Atom.
☝️😉... We are in high speed guys!
🤷🏻♂️... At least, this is my hypothesis!
Thank u!
Hard to understand... not helped by the fact that some sentences are badly written
Confused... What does the variable x represent specifically? I know it's position, but position of the electron relative to WHAT? What are the units? I understand the gist of the wave function, but there are so many gaps
Found the answer?
A moving electron, will have two waves. It has a magnetic wave because it has right handed mag field in direction of flow. The electro force is the EMF. So electrons and protons have the EM fields in common.
What tablet are you using?
Good job
Nice video, but how does the graph change with consecutive measurements wouldn't that mean the e‐ is moving?
There are no consecutive measurements in quantum mechanics at this level. Once the quantum has been measured, it has been removed from the system. At least that's the case for strong measurements in the naive theory that we are talking about here. We can extend this to weak measurements using the density matrix and then we get proper approximations of the quantum-classical transition, but that's on another level of the theory.
That's a great explanation. But, you didn't mention superposition. Doesn't QM posit that the electron exists at many positions simultaneously until measured? You seem to say that it is in only one position, and when we measure it, we find out where.
Well, what we're sure of is that the square of the wavefunction gives the probability density of finding the electron in that region. Whatever metaphysical story ("the electron exists at many positions simultaneously" before measurement or "takes all possible paths" or "branches off into different multiverses") we want to tell ourselves happens between measurements doesn't seem to matter much as long as you use the math properly. QM is truly in the results business. We as humans are in the story business.
@@WeAreShowboat , could you say how we are "sure that |Xi|^2 gives probability density of finding the electron in that region"? Did we experiment 1000s of times and indeed the histogram looked like that curve, even at points outside the 'peaks'?
@@rgudduu Good question. In some cases like electron crystallography diffraction we measure the position of the electron and build up a position probability histogram as was shown. But in most cases we measure something else like energy or momentum and build up a histogram of those values. You can represent the wave function in terms of position, or momentum, or energy, or any basis you want and the shape of the squared wave function in that basis will yield the histogram of those values.
@@WeAreShowboat , let me see if i got that correctly:
We find Psi(momentum) and Psi(energy) along with Psi(x).
We find electron's position x in a few experiments and their histogram matches |Psi(x)|^2. We find momentum in many experiments and their histogram matches |Psi(momentum)|^2. We find energy in many experiments and their histogram matches |Psi(energy)|^2.
Is it?
rgudduu Pretty much. But for any given experiment, if you know the wave function in any basis (position, momentum, etc) you can transform the wave function into any other basis without the need for experiment. But to check if your original wave function is right, you would need to measure something.
That's pretty good but really, that equation. That psi is a dependent variable right? I wanna see somebody really use that equation. It looks like a second order partial differential equation dependent on t and x. One physical dimension?
Comprehensiveboy Comprehensiveboy Yes this would be for one dimension. And yes psi depends on x and t here. Though you can generalize it to more dimensions pretty easily. It's a tough equation to solve in general so we usually try to write the solutions in terms of a time dependent part and space dependent part if possible.
The system of electrons might interfere with each other’s waves
I can't understand why the wave function is used to find energy when it is used to find probability density
Thank you.
the equation is incomplete. I think is ħ^2/2m not ħ/2m
Whoa, you're right. I forgot the square, thanks! I'll put a note in the video.
The square of the amplitude gives the probability of detecting the electron in that position.
No, it doesn't, but there are too many textbooks out there that claim that it does to correct them all. The proper understanding of the measurement process is through the Born rule, which inserts the detector's spectral response function between the wave function and its complex conjugate. The representation of the operator of an ideal position measurement device happens to be the unity operator, so it looks like as if the scalar product of the wave function with itself (i.e. its complex conjugate) represents the position of a particle. That's just a mathematical coincidence because we are usually doing this in a position representation. If we were using a momentum representation, then the position measurement operator would be a Fourier transformation (two, actually, if I am not mistaken). These kinds of shoddy treatments lead to a number of false claims about the meaning of the wave function. All by itself the wave function does not have any physical meaning. We ALWAYS have to define the measurement process with a projection operator, even if it happens to be the unity operator.
How can we derive uncertainty principle from this
Derivation of the uncertainty principle can be done by proving that any solution to Schrodinger's equation must have a product of standard deviation's in position and momentum that is greater than h bar over 2. There's a little more you need that I didn't talk about (like momentum operator definition, etc).
Where were you until today?
What program is used to show this?
Sketchbook Express to draw (along with a Wacom tablet), Camtasia to screencapture, and a desktop usb mic to record audio.
Thanks for the reply!
Super duper
Now i am happy because nobody on earth understands wave function
like me
the wave function is not a function, it is a section in a complex line bundle over the physical space. to really understand it requires deep knowledge in topology.
The stupid problem I don't get it is why electron but not other particle?
All particles are described by wave functions
@@WeAreShowboat Not really. This is just the naive non-relativistic theory.
Because electrons are the lightest fields for which non-relativistic QM works (somewhat). You can apply this approximation to any massive quantum field, if you like and it will, for simple physical scenarios, give some useful results. It won't work for photons because EM fields don't have a non-relativistic limit. In general you have to understand, though, that there are no "particles" in quantum mechanics. We are always talking about quanta of energy here.
@@lepidoptera9337 I wouldn’t call it naive, just the low energy approximation to quantum field theory.
@@WeAreShowboat The non-relativistic theory is naive. It's neither physical nor self-consistent. Part of its structure follows trivially from relativity, so it is definitely not "just" a low energy approximation. I would say that it's mostly a piece of rather unfortunate science history that we have to live with. Do I have a suggestion what to replace it with? No, not really. The gap to quantum field theory is just too large. Trying to use QFT for problems that have a reasonably well defined classical potential in them is, for all I can see, an even worse approach than the SE is.
Just waves..
spaceandmotion
There are no waves here. That's all just a misunderstanding.
The answers to your questions will never be known...even after a million years. You doubt that? Note how far other technologies have progressed given just 20-30 years. Compare that to the last 100 years!!! of QM. Flight...mastered. Computers...mastered. QM? We know about as much as Niels Bohr did all those years ago.
just an overview delivered pleasantly
no solved example or derivation
That's so wrong. Wavefunction is used to find the probabilities on position of the electron. And electron wavelength is a different thing. It is the wavy nature of its trajectory.
you copied a whole entore video in Khan academy
This *is* his video on Khan academy lolol
I learnt how to derive Schrodinger's equation....and ...I'm only 16....it's pretty easy. Try it out.
That's cool, very few have, so congrats. I've "derived" Schrodinger's equation, but technically you can't really derive Schrodinger's equation. You can motivate the equation from empirical information and previous concepts, but since it is a fundamentally new physics, it isn't strictly derivable (unless you already assume the postulates of QM in the first place which is just begging the question in a way)
@@WeAreShowboat Yes. It's true.It is fundamentally a new physics. But I didn't derived it without knowing the previous concepts of QM. Every one is thinking that Schrodinger's Equation and QM concepts are hard af.But that just used for finding the probability of an electron in space. It's like F=ma of Quantum world. All u need to know is 1. E= KE+PE
2. De broglie's relation
3.Some basics of wave mechanics
4.Basic calculus
5.Basic High school algebra.
And that's all. Schrodinger's equation is yours...😍...PS. Thanks for replying We are Showboat
This is just Khan Academy's video reuploaded...
No, he’s done videos for Khan Academy. This specific video is actually in Khan Academy’s QM playlist.
Do you think it is logical that if the future is unfolding relative to the atoms, if we look down at the individual atoms we will find probability? This is an invitation to see a theory on the nature of time! In this theory we have an emergent uncertain future continuously coming into existence relative to the spontaneous absorption and emission of photon energy. Within such a process the wave particle duality of light and matter in the form of electrons is forming a blank canvas that we can interact with forming the possible into the actual! The future is unfolding with each photon electron coupling or dipole moment relative to the atoms of the periodic table and the individual wavelengths of the electromagnetic spectrum. As part of a universal process of energy exchange that forms the ever changing world of our everyday life the ‘past’ has gone forever. At the smallest scale of this process the ‘past’ is represented by anti-matter annihilation with the symmetry between matter and anti-matter representing the symmetry between the future and the past as the future unfolds photon by photon. In such a theory the mathematics of quantum mechanics represents the physics of ‘time’ with the classical physics of Newton representing processes over a period of time, as in Newton’s differential equations. In my videos I explain how this process is relative to temperature and the phase changes of matter.
Schrödinger, not Schrodinger.