@@lecturesbywalterlewin.they9259 I have this question. It has been troubling me for a while. The electron in a box has a wave function. If we square the wave function we get the probability amplitude. Does that mean that the Electron randomly changes its position with accordance to the probability amplitude ? That is most of the time it will be in the place where there is the hills & valleys and never in the nodes? Or does the probability density mean that, the electron is in all the places where there is a non zero probability at the same time ? I would be really thankful if you can help me out with me. Thank you.
@@lecturesbywalterlewin.they9259 I had a doubt that if we take that the slit to be made of 2 different opaque sheets and if we remove one of them , then will the spreading of light be stopped?
watching this from a remote village from Sri Lanka after 5 years I have a strange feeling as even though there is a great space and time variation,i still enjoyed this lecture from a MIT professor , where I will never be able to see physically,let alone USA. I am a medical doctor but still enjoyed this as it refreshed my college physics. Thank you sir!
One of the most heart touching physics class that one can hear from a great teacher in his whole life! what a fantastic, amazing person you are!!! You are going to live forever! 💖
Hello sir ....I am saying this from my heart that you made quantum so easy for me ... really before this lecture i found quantum was so boring but you make it easy to me ...as I am from in india I like only person who teach physics so well which is alakh pandey sir ( physics wallah) and now today I watch your lecture .. really it is so good experience to watch your lecture....hats off to you sir ..❤️😊
I feel really fortunate to have have come across this vedio and got to hear this amazing topic by a great physicsist like you whom i may never be able to even see. Sitting here in india , preparing for neet ,i 'm privileged to learn from a MIT professor from USA
I think he says "orbit" during the lecture which was later corrected to "energy level", as evidenced by the voiceover and frame change each time the word comes up.
I love that presentation. Especially with the Physics book. The energy it takes to understand the content is much higher than the Gravitational energy that can be changed in potential energy. It's the other way round with Poem books. A poem book generates energy.
Dear Professor. Your lectures are way more than awesome. I'm a huge fan of yours! I'm subscribed to your TH-cam Channel, I have got your book, I have got an autographed picture of yours. Thanks a lot for everything you've been doing for all of us!!! We can't thank you enough!!! Regards from Brazil/Canada!!!
Hello Prof Lewin. We know that stars are made mostly of hydrogen with other elements present in small fraction. The spectrum of hydrogen gas has discrete wavelengths. For example in the visible region we have 4 wavelengths in Balmer series. Then why we approximate the radiation coming from the stars as blackbody radiation and use weins law to calculate their surface temperature. At the same time the spectrum of stars also contain some missing lines like the case of discovery of helium element from the spectrum of Sun.
You are correct, the spectrum of stars is not a perfect Planck spectrum. Thank god it's not... if it were, then we couldn't identify the chemical composition of stars from far away! Temperature is, as you are most likely aware of, a thermodynamic equilibrium quantity. Stars are not in exact thermodynamic equilibrium and therefor their surface temperature is an approximation.
In the original video he said "orbits" instead of "energy levels" or "energy states." I assume he changed it to be more accurate as electrons do not move in traditional orbits but instead exist in a probability field based on how much energy they have. Also, Walter Lewin is a bit of a perfectionist so minor things like that bother him until he actually goes and fixes it.
Professor, please take a class on Thermodynamics. It's okay if it is not in MIT, because all I want is you to teach Thermodynamics. MIT or your home, doesn't matter, sir. Please.
I love how every word moves the lecture forward! No digressions or filler words. But I have two concerns regarding the content. It's not as simple that e.g. electrons are sometimes particles and sometimes waves. The probability distribution for the properties of the particle is wave-like, what you actually measure is *always* particle. That's two different levels of abstraction. Secondly, the uncertainty principle is about repeated experiments. If you measure the momentum of the billiard ball many times within the triangle, you will have a large variance in your set of measurements. The principle does not apply to one and the same particle.
That is a common mistake in most introductory classes to quantum mechanics. You didn't get it right either, though. We never measure particles. We can only measure quanta, i.e. small amounts of energy that quantum systems transfer between each other. Quanta do not have coordinates and hence they do not have particle-like behavior. Einstein got this wrong in his 1905 paper on the photoeffect and his mistake has stuck around for 116 years... time to end it.
Great lectures, unbelievable that I can just watch them for free. Can I ask what you said in the room when you’ve edited in you saying “energy levels” or “from a higher to a lower energy level” in the video? E.g 7:30
Mr. Lewin. Thanks for this lecture. We can not enter the world of particles therefore their behavior does not come to us intuitively. The laws of physics are working, and god does not need the dice for it.
Sir, its so great to talk easily to an expert like u ... can u plz say how can i cover maths required for general relativity myself parallely with my academics at UG level ? best books covering entire maths required for GR ...
i don"t have any knowledge for GR , i asked quora but many people are saying different things , i just want to start some maths required for GR in free time now before college , so wanted advice for how to cover some maths from u sir
At 41:35 u said the spreading of the light was already explained earlier.....by that did u mean the wave nature of light and the experiments done by young?
yes the double slit interference in 1801 by Young was Proof at the time that lights are waves, This was before QM. We now know that light is BOTH particles (photons) and waves. A concept that does not belong in Classical Physics - a concept that neither you nor I can understand but it's the way the world ticks. Watch Feynman’s double slit lecture th-cam.com/video/2mIk3wBJDgE/w-d-xo.html
It would be amazing to watch a series of lectures given by Prof Lewin on Modern physics, his approach to QM ,General Relativity, supersymmetry or multiverse, and how gravitatonal waves recent finding can impact.
I retired from lecturing courses at MIT in 2009. My legacy are my 3 MIT course lectures, Help Sessions, colloquia and special talks. They are being viewed daily by about 30k people.
Lectures by Walter Lewin. They will make you ♥ Physics. Your legacy is bigger than you can imagine, you aré a source of inspiration for young minds all over the world, a few people can say that they reach every corner on the planet sharing and spreading love for physics. Respect and love from south america Prof.
So for Heisenberg principle We can say that it is only applicable in microscopic world and it is negligible in macroscopic world and hence not applicable.Right? 29:09
At 0:46 , When you talked about how many atoms put to form one inch , shouldn’t we consider the size of the atom as well? Cause some have one layer or some have two or even more layers
atoms have no layers. **Size: **Atoms have an average radius of about 0.1 nm. About 5 million hydrogen atoms could fit into a pin head. The nucleus of an atom is 10,000 times smaller than the atom. If an atom was the size of Wembley Stadium, then the nucleus would be the size of a garden pea.
Hello Sir, I truly enjoyed this classical mechanics series , I am now going to start part 2 , thank you putting it on here , also If I start learning quantum mechanics which lectures/ books would you recommend?
Sir, Suppose I send a polarized beam of light from an infinite distance away from a thin slit, whose thickness is slightly higher than the diameter of the photons in that polarized beam, then as the light passes trough that slit, we have an idea of the photon's position at the time it passes through the slit, and since the light was sent from infinite distance so, the vertical momentum is zero as well as the horizontal momentum is arguably constant( assuming it doesn't collide with other particles in the medium) till the time it passes trough the slit, so at time 't' when it passes trough the slit we know precisely what the position of photons are and the momentum at the same time 't'.
When your light passes through the slit, you know the position in the direction perpendicular to the slit very well. Thus according to HUP the momentum in that direction will be very uncertain and if you look at the screen behind the slit you will SEE THE SPREAD of light in that direction. There is NO way to by-pass HUP. Any Newtonian way of thinking is not valid.
it's a corner stone of QM. In QM particles and waves are IDENTICAL. You cannot think of them as separate. In Newtonian physics we think of them as separate. To apply QM to a base ball would not be very useful.
Hii sir I'm from Kashmir and i am your a big fan and our teacher is also a fan of yours sir even he shows us your experiments in class and always say that i have learn this from prof walter @physics with Nasir hajni
So it is possible to drive electricity on an element in 80 ways because of QM. Sparks take different directions though electricity is in a single direction. So quantum probability is one by eighty. Or 84×2 root 168. Or 163 and R constant.
professor i am a student of class 11... i was searching for the topic atomic structure but i found ur channel and started watching it ... it made me think positive against classical mechanics thank u sir.... kindly make more videos on this topic
Exactly at 40:22....why are we seeing this funny shape and after this time where does the green spot, which is going outwards, where has it gone because we can't see it now? Also some part is separating from the spot around 40:22?
the video is badly out of focus. I suggest you watch this lecture. th-cam.com/video/MeK0DV329mU/w-d-xo.html It's well in focus there. Watch 57:15 and threafter.
yup . to be more precise it's the mc laurin expansion . when you substitute angles whose values are closer to zero you get almost the same result if you had substituted zero .
around 10 min in video you made a energy level diagram of an electron and you said that an electron in higher energy state would come to lower energy state by releasing a photon, so here I want to know that how an electron could produce a photon in higher energy state and releases it to come to lower energy state .i.e. how an electron can produce a photon??
When an amount of energy E is available according to QM EM as well as particles can be produced. In the case of EM (visible light or X-ray or gamma ray) It's even possible to draw a parallel with classical physics. The electron does NOT disappear. In class ph any accelerated charge will create EM radiation.
If electrons can exist only in specific or discrete energy levels, how does an electron move from lower to higher energy levels? Would that electron not move through all space in between including area that do not include the allowed energy levels?
Prof Levin, I know that this question has nothing to do with this video but I didn't find any of your videos about this subject, My doubt is: gravity is the curve of space-time or is a force with graviton as a force exchanging particle? If it is curved space-time why an quantum theory of gravity is necessary and not a quantized space-time? If is a force and the graviton is the force exchanging particle like photon is for electromagnetic force, then why a strong magnetic field does not causes time dilatation like a gravity field do? I study physics and every professor I make this question and every book I read answers it different according to their point of view.
If you could attach a clock to a photon ,''somehow'', then the clock will show no reading, that's what is meant by ''time stops at the speed of light''. That's the ultimate time dilation. I suggest you consult cosmologists regarding most of your questions. I highly recommend Professors Scott Hughes sahughes@mit.edu, Ed Bertschinger edbert@mit.edu and Alan Guth guth@mit.edu all at MIT.
Thank you for answering me. I understand how photons don't experience time. But my doubt is if a strong enough magnetic field would cause time dilation in particles inside this field. (else the photons itself causing the magnetic field). Why only gravity curves space-time and not all fundamental forces? Another doubt I have (now in context with the lecture) What if the photon is a wave, only a wave, and the device trying to measure it in the double slit experiment changes the phase of the wave changing the pattern in the detector causing us to believe it is a particle? The photon/electron being only a wave would solve most problems of non locality and collapse of the wave function... And again, thank you for your patience and all your amazing videos.
Quantum mechanics is hard to think.As everything is nothing,and absolute nothingness can not be imagined.The absence of matter is referred to as vacuum.But even field like gravity acts there.The universe is not bound by the limits and what is beyond that beyond that often blows my mind up.But you have given me an exemplary effigy what I was supposed to learn.
With due respect sir , I am from India and I love Quantum Physics and Nuclear Physics from the core of my heart . Kindly suggest me the ways so that i can make my career in these two great fields . Thank you sir .
after high school go to the very best college that will accept you consistent with your highschool grades. Get a bachelor's degree in Physics. After that apply to the very best Universities that may accept you and get a PhD in QM & Nuclear Physics. Take it from there. 3 yr college + 6 yr for your PhD adds up to about 9 years. I was 29 yr old when I got my PhD in nuclear physics.
I think that Heisenberg Uncertainty Principle is one of the strongest arguments, that we are living in simulated reality. Therefore at small scales everything is inconsistent. It seems like introducing too large value of (dt) in terms of iterating and integrating diferential equations. Sometimes you can observe glitches in games, when object has to large velocity and just fly by wall (tunneling), because (dt) taken for calculations isn't small enough to detect collisions. Sometimes object rotating with very large velocity (bug in games), appears on screen like just jittering and shaking randomly. The same problem: (dt) in calculations. It seems, creators of our simulation (universe), just have not enough powerfull computers. What do You think? :)
They are called "diffraction gratings". If you live in the US or Europe I'll send you 2. I have sent over the years several to India and Pakistan they never arrived; they were stolen!
Hi Prof. Lewin Do buckyballs also display the interference pattern in the two-slit experiment? If 'yes', how is it possible since buckyballs are much bigger than electrons, photons. (My answer is 'yes' but would like to double check with my concept.)
+Lectures by Walter Lewin. They will make you ♥ Physics. en.m.wikipedia.org/wiki/Double-slit_experiment In the paragraph 4 & under the 'Variations of the experiment' stated that buckyballs do display this interference pattern.
Sir wave means there is motion of disturbance in a space Like a em wave. Sir in em wave , the electric field and magnetic is oscillating in space. If Electron is a particle then how it can oscillate in space in various point
Professor, if electron can jump between two energy levels, but can't exist between them, shouldn't it be the most fundamental unit of universe? If yes, shouldn't it be considered as a fundamental unit?
@@lecturesbywalterlewin.they9259 But professor, can't we measure the energy difference between two adjecent orbitals or energy levels, quantize it as fundamental there after use it to define other fundamental units?
@@lecturesbywalterlewin.they9259 Sorry the question is moot now (or was moot just I didn't realised). I just read that the standard platinum mass kg was redefined by an equation keeping Planck's constant fixed in equation E=hf=mc^2 few years back😅. So indirectly they have defined mass based on energy difference between electron orbitals which is more fundamental than that prototype. Earlier I meant to use that energy difference as fundamental but potato pathato they are same principle.
Perhaps I'm missing something, but the Uncertainty Principle doesn't seem all that counter-intuitive. Imagine a crowded sports area. At the end of the event, people start filing out a wide exit door in a very orderly way. For some reason, the door slowly begins to close so people are forced to exit through a continually narrower space. At a certain point, panic ensues and, now individuals are squeezed together at the exit, and some can pass or are pushed through the door in a disorderly sequence and in unpredictable directions. Same thing happens with an adjustable nozzle on a garden hose! Why not photons?
Heisenberg's UP is QM. All QM, including HUP is counter intuitive as we all think classical phyisics (newtonian). *Objects at position P in space can stand still*
@@lecturesbywalterlewin.they9259 So, QM is counter-intuitive with respect to classical physics exclusively and perhaps not with respect to "particle" behavior in other domains such as animal behavior. Granted; but for me being a non-scientist, (but comfortable with the mathematics), thinking of possible analogies is helpful in grasping the ideas. I loved 801 and will be continuing with 802 and 803. Bless you so much for making these available.
What does it mean for the uncertainty of the momentum to be greater or equal to hbar/Δx, is there no upper bound? Does that mean that if i'm walking in my room I might all of a sudden reach the speed of light and die? How can a particle have a higher speed and the same energy as another particle?(meaning where do I get the energy to have a higher speed?)
But at school they taught us that atoms have some layers with different energy levels which can hold a limited number of electrons according to the formula 2n^2 and I meant that the one with more layers has to have more volume .
I have a slight doubt Professor. When an electron is transiting from one energy state to other during that time at any instany won't it occupy an intermediate position just like a ball in gravitational field does. If not , why ?
Dear Prof. Lewin Heisenberg Uncertainty Principle & Third Law of Thermodynamics seem to contradict each other. Thought experiment: Say, imagine at 0K, S=0, the motions of the particles (atoms, molecules) cease i.e. static, in a very orderly fashion, these particles will have a well-defined position. Now, we try to probe the exact position or momentum. However, in virtue of the Heisenberg Uncertainty Principle, one can never pinpoint the exact position or momentum of a particle, even at 0K I reckon. Therefore, is there a contradiction between Heisenberg Uncertainty Principle & Third Law of Thermodynamics? Please enlighten. Thank you.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thanks for your prompt reply. Can we say that modern physics is superior than classical physics? It offers new perspectives & holistic approach to our understanding of nature itself? Although it depends on the context that we are dealing with. Classical physics is easier to handle.
+Lectures by Walter Lewin. They will make you ♥ Physics. In the field of physics/science, can we use a theory/law/principle to defeat another theory/law/principle? It is more like a crash course whereby putting 2 concepts head-to-head, like the above case.
>>>Can we say that modern physics is superior than classical physics?>>> NO!. Classical Physics is EXCELLENT as long as you work in its domain. You cannot use QM to solve classical problems (e.g., resonance frequencies of strings and cavities, explanation of a rainbow . . . . .). QM is EXCELLENT as long as you work in its domain. You cannot use classical physics to explain the behavior of atoms,
the uncertainty principle is a strong argument against the idea of teleportation since the information of each particle can never be completely determined, is this correct? If it is impossible,why it is still speculating?
correct - that is also an issue with Schrodinger's cat and with an "object" tunneling through a barrier. It lacks the *coherence* for that to happen. Alpha particles can tunnel through a barrier but not a tennis ball.
Is photon separate able? How do we know if one photon is one photon , not a group of mass when we shoot ONE photon every day and to observe the landing on the screen, , can we really measure that accurately?
Sir, can we use entanglement to clone humans or particular part of our body as we can use it for teleportation(maybe a lot latter in the future)? And if yes, then there must be some way to cure diseases like cancer by taking information of each and every particle and then exchange the information of defected organ by the information of a healthy organ and then use entanglement to send this information to some other set of particles to constitute the body back in the way it was.
I m slightly off from the topic.....I went through principle of least action today( hamilton' s varriational principle) it says particle will take a path such that some integral is minimum.....can there be more than one paths for which the integral is stationary??
Light always behaves like a wave. What seems to behave like particles, if you don't look carefully, are quanta. What is a quantum? A quantum is a bit of energy. All we mean by "a light source emitting a photon" is that the source transfers a little bit of energy into the electromagnetic field. That field propagates in a wavelike fashion, but we can't localize the energy that we put into it. Eventually the field transfers a little bit of energy, a quantum of energy ("a photon" but not "the same photon") to the detector. Because of energy conservation the amount of energy that the source put into the field has to be the same as the amount of energy that the detector takes out (at least if the two are stationary relative to each other, otherwise we are getting a Doppler shift!), it LOOKS LIKE AS IF we got the same photon out that we put in. That, however, is a logical mistake on our part. One can't write "Photon 2356" on a photon, i.e. the idea that a specific photon propagates like a particle trough the vacuum is not backed up by any observation. We are merely observing energy conservation at the quantum level.
That bizarre feeling when you discover yourself applauding alone at your bedroom after the final speech. Thank you Walter, see you in 8.02.
very cool
@@lecturesbywalterlewin.they9259 I have this question. It has been troubling me for a while. The electron in a box has a wave function. If we square the wave function we get the probability amplitude. Does that mean that the Electron randomly changes its position with accordance to the probability amplitude ? That is most of the time it will be in the place where there is the hills & valleys and never in the nodes? Or does the probability density mean that, the electron is in all the places where there is a non zero probability at the same time ?
I would be really thankful if you can help me out with me.
Thank you.
@@soutrikchakraborty5211 this is covered in every QM course. Both QM 1 and QM 2 are on my channel
@@lecturesbywalterlewin.they9259
I had a doubt that if we take that the slit to be made of 2 different opaque sheets and if we remove one of them , then will the spreading of light be stopped?
@@lecturesbywalterlewin.they9259 I cant find the quantum mechanics lectures can you please provide the link for it..it would be really helpful.
I know this is MIT and students should expect the best but the professor should have been given a standing ovation.
The best possible explanation over the internet.
watching this from a remote village from Sri Lanka after 5 years
I have a strange feeling as even though there is a great space and time variation,i still enjoyed this lecture from a MIT professor , where I will never be able to see physically,let alone USA.
I am a medical doctor but still enjoyed this as it refreshed my college physics.
Thank you sir!
thanks for your kind words
Love from srilanka
@@lecturesbywalterlewin.they9259 Accept Islam, you will go to heaven.
excellent lecture!
many thanks from a Greek physicist from California!!!
my pleasure
Professor, I would like to thank you for uploading this wonderful resource to the Internet, I have very much enjoyed "taking" 8.01
:)
One of the most heart touching physics class that one can hear from a great teacher in his whole life! what a fantastic, amazing person you are!!! You are going to live forever! 💖
Wow, thank you!
Very important lecture explaining Heisenberg principle with great clarity. Fantastic.
:)
An excellent lecture, thank you for taking the time to make this publicly available
You're very welcome!
Hello sir ....I am saying this from my heart that you made quantum so easy for me ... really before this lecture i found quantum was so boring but you make it easy to me ...as I am from in india I like only person who teach physics so well which is alakh pandey sir ( physics wallah) and now today I watch your lecture .. really it is so good experience to watch your lecture....hats off to you sir ..❤️😊
It's my pleasure
I feel really fortunate to have have come across this vedio and got to hear this amazing topic by a great physicsist like you whom i may never be able to even see.
Sitting here in india , preparing for neet ,i 'm privileged to learn from a MIT professor from USA
Glad you enjoyed it!
I think he says "orbit" during the lecture which was later corrected to "energy level", as evidenced by the voiceover and frame change each time the word comes up.
I love that presentation. Especially with the Physics book. The energy it takes to understand the content is much higher than the Gravitational energy that can be changed in potential energy. It's the other way round with Poem books. A poem book generates energy.
Dear Professor. Your lectures are way more than awesome. I'm a huge fan of yours! I'm subscribed to your TH-cam Channel, I have got your book, I have got an autographed picture of yours.
Thanks a lot for everything you've been doing for all of us!!! We can't thank you enough!!!
Regards from Brazil/Canada!!!
Many thanks!
Its always a pleasure watching your dynamic lectures.
No words to say just incredible thank you
Hello Prof Lewin.
We know that stars are made mostly of hydrogen with other elements present in small fraction. The spectrum of hydrogen gas has discrete wavelengths. For example in the visible region we have 4 wavelengths in Balmer series.
Then why we approximate the radiation coming from the stars as blackbody radiation and use weins law to calculate their surface temperature. At the same time the spectrum of stars also contain some missing lines like the case of discovery of helium element from the spectrum of Sun.
You are correct, the spectrum of stars is not a perfect Planck spectrum. Thank god it's not... if it were, then we couldn't identify the chemical composition of stars from far away! Temperature is, as you are most likely aware of, a thermodynamic equilibrium quantity. Stars are not in exact thermodynamic equilibrium and therefor their surface temperature is an approximation.
I have no words to express how much I liked this conference. Thank you Professor Walter Lewin :')
Our pleasure!
Why is the video and sound edited whenever you refer to "energy levels" or "energy states"?
In the original video he said "orbits" instead of "energy levels" or "energy states." I assume he changed it to be more accurate as electrons do not move in traditional orbits but instead exist in a probability field based on how much energy they have.
Also, Walter Lewin is a bit of a perfectionist so minor things like that bother him until he actually goes and fixes it.
Using the term “orbits” can give you the wrong idea of what is going on, so he changed it to “energy levels”
Professor, please take a class on Thermodynamics. It's okay if it is not in MIT, because all I want is you to teach Thermodynamics. MIT or your home, doesn't matter, sir. Please.
I would never have understood it so easily before----thanks for this video
I love how every word moves the lecture forward! No digressions or filler words. But I have two concerns regarding the content. It's not as simple that e.g. electrons are sometimes particles and sometimes waves. The probability distribution for the properties of the particle is wave-like, what you actually measure is *always* particle. That's two different levels of abstraction. Secondly, the uncertainty principle is about repeated experiments. If you measure the momentum of the billiard ball many times within the triangle, you will have a large variance in your set of measurements. The principle does not apply to one and the same particle.
That is a common mistake in most introductory classes to quantum mechanics. You didn't get it right either, though. We never measure particles. We can only measure quanta, i.e. small amounts of energy that quantum systems transfer between each other. Quanta do not have coordinates and hence they do not have particle-like behavior. Einstein got this wrong in his 1905 paper on the photoeffect and his mistake has stuck around for 116 years... time to end it.
And yet radio waves are never treated as particles, they always treated as waves even though they are still photons.
Great lectures, unbelievable that I can just watch them for free. Can I ask what you said in the room when you’ve edited in you saying “energy levels” or “from a higher to a lower energy level” in the video? E.g 7:30
Amazing explanation sir
Hats off to you sir
Mr. Lewin. Thanks for this lecture.
We can not enter the world of particles therefore their behavior does not come to us intuitively. The laws of physics are working, and god does not need the dice for it.
Such a great teacher . I never be see such type teacher
Thank you for your great way of teaching... Makes physics fun and enjoyable... 🙏🙏🙏🙏🙏
:)
Sir, its so great to talk easily to an expert like u ... can u plz say how can i cover maths required for general relativity myself parallely with my academics at UG level ? best books covering entire maths required for GR ...
No I cannot
take a course in GR and decide on your own
i don"t have any knowledge for GR , i asked quora but many people are saying different things , i just want to start some maths required for GR in free time now before college , so wanted advice for how to cover some maths from u sir
Best physicist in the whole world.🙏🙏🙏🙏🙏
At 41:35 u said the spreading of the light was already explained earlier.....by that did u mean the wave nature of light and the experiments done by young?
yes the double slit interference in 1801 by Young was Proof at the time that lights are waves,
This was before QM. We now know that light is BOTH particles (photons) and waves. A concept that does not belong in Classical Physics - a concept that neither you nor I can understand but it's the way the world ticks. Watch Feynman’s double slit lecture th-cam.com/video/2mIk3wBJDgE/w-d-xo.html
It would be amazing to watch a series of lectures given by Prof Lewin on Modern physics, his approach to QM ,General Relativity, supersymmetry or multiverse, and how gravitatonal waves recent finding can impact.
I retired from lecturing courses at MIT in 2009. My legacy are my 3 MIT course lectures, Help Sessions, colloquia and special talks. They are being viewed daily by about 30k people.
Lectures by Walter Lewin. They will make you ♥ Physics. Your legacy is bigger than you can imagine, you aré a source of inspiration for young minds all over the world, a few people can say that they reach every corner on the planet sharing and spreading love for physics. Respect and love from south america Prof.
thanks for your kind words
I do not solve problems for viewers. I teach Physics. Watch my 8.02 lectures.
So for Heisenberg principle
We can say that it is only applicable in microscopic world and it is negligible in macroscopic world and hence not applicable.Right?
29:09
No, that is completely wrong. The uncertainty principle is just as valid for sound waves, water waves, classical electromagnetic waves etc..
At 0:46 , When you talked about how many atoms put to form one inch , shouldn’t we consider the size of the atom as well? Cause some have one layer or some have two or even more layers
atoms have no layers. **Size: **Atoms have an average radius of about 0.1 nm. About 5 million hydrogen atoms could fit into a pin head. The nucleus of an atom is 10,000 times smaller than the atom. If an atom was the size of Wembley Stadium, then the nucleus would be the size of a garden pea.
Thank you very much dear Professor Lewin.
Welcome!
What a wonderful professor
Hello Sir, I truly enjoyed this classical mechanics series , I am now going to start part 2 , thank you putting it on here , also If I start learning quantum mechanics which lectures/ books would you recommend?
any college physics book will do
use the web
thanks a lot, love the way
professor explains physics
You are welcome!
Sir, Suppose I send a polarized beam of light from an infinite distance away from a thin slit, whose thickness is slightly higher than the diameter of the photons in that polarized beam, then as the light passes trough that slit, we have an idea of the photon's position at the time it passes through the slit, and since the light was sent from infinite distance so, the vertical momentum is zero as well as the horizontal momentum is arguably constant( assuming it doesn't collide with other particles in the medium) till the time it passes trough the slit, so at time 't' when it passes trough the slit we know precisely what the position of photons are and the momentum at the same time 't'.
When your light passes through the slit, you know the position in the direction perpendicular to the slit very well. Thus according to HUP the momentum in that direction will be very uncertain and if you look at the screen behind the slit you will SEE THE SPREAD of light in that direction. There is NO way to by-pass HUP. Any Newtonian way of thinking is not valid.
Ok ,Thank you so much for replying! I was just wondering is HUP a fundamental law of nature? or Is it just because of the wave nature of particles?
it's a corner stone of QM. In QM particles and waves are IDENTICAL. You cannot think of them as separate. In Newtonian physics we think of them as separate. To apply QM to a base ball would not be very useful.
calculate the wavelength of a baseball going 80 mph using De Broglie!
Hii sir I'm from Kashmir and i am your a big fan and our teacher is also a fan of yours sir even he shows us your experiments in class and always say that i have learn this from prof walter @physics with Nasir hajni
So nice of you
So it is possible to drive electricity on an element in 80 ways because of QM. Sparks take different directions though electricity is in a single direction. So quantum probability is one by eighty. Or 84×2 root 168. Or 163 and R constant.
Super duper professor, you are amazing at explaining.
professor i am a student of class 11... i was searching for the topic atomic structure but i found ur channel and started watching it ... it made me think positive against classical mechanics
thank u sir.... kindly make more videos on this topic
if u can please reply me sir.... regards ur student from india
You are most welcome
46:36 best applause ever...
a great teacher a great person
Dr. Lewin,
Just a great teaching style.
Sadly, in the era of publish or perish, most professors dont teach as good.
Best,
Joe
Exactly at 40:22....why are we seeing this funny shape and after this time where does the green spot, which is going outwards, where has it gone because we can't see it now?
Also some part is separating from the spot around 40:22?
the video is badly out of focus. I suggest you watch this lecture.
th-cam.com/video/MeK0DV329mU/w-d-xo.html
It's well in focus there. Watch 57:15 and threafter.
37:16 Is that because of the Taylor expansion of the sine?
yup . to be more precise it's the mc laurin expansion . when you substitute angles whose values are closer to zero you get almost the same result if you had substituted zero .
What does a proton do if sitting at rest in an experiment as the moon passes over? Will it react? And how?
the proton becomes a lunatic
@@lecturesbywalterlewin.they9259 god i love you xD
around 10 min in video you made a energy level diagram of an electron and you said that an electron in higher energy state would come to lower energy state by releasing a photon, so here I want to know that how an electron could produce a photon in higher energy state and releases it to come to lower energy state .i.e. how an electron can produce a photon??
When an amount of energy E is available according to QM EM as well as particles can be produced. In the case of EM (visible light or X-ray or gamma ray) It's even possible to draw a parallel with classical physics. The electron does NOT disappear. In class ph any accelerated charge will create EM radiation.
If electrons can exist only in specific or discrete energy levels, how does an electron move from lower to higher energy levels? Would that electron not move through all space in between including area that do not include the allowed energy levels?
you think Newtonian - QM has it own rules. The question how did the electron move from quantum level E1 to E2 is an illegal question in QM.
@@lecturesbywalterlewin.they9259 Thank you very much sir
Thank you professor, god bless you
11:20 Where can I find those gratings?
Thank you sir for this wonderful lecture 😊. You make physics so easy .
It's my pleasure
Thanks sir your explanation is such awesome
There is no video on tunnel effect 1-d box and other?
First time quantum mechanics feel having sense,it never convinced me before
Prof Levin, I know that this question has nothing to do with this video but I didn't find any of your videos about this subject, My doubt is: gravity is the curve of space-time or is a force with graviton as a force exchanging particle? If it is curved space-time why an quantum theory of gravity is necessary and not a quantized space-time? If is a force and the graviton is the force exchanging particle like photon is for electromagnetic force, then why a strong magnetic field does not causes time dilatation like a gravity field do?
I study physics and every professor I make this question and every book I read answers it different according to their point of view.
If you could attach a clock to a photon ,''somehow'', then the clock will show no reading, that's what is meant by ''time stops at the speed of light''. That's the ultimate time dilation. I suggest you consult cosmologists regarding most of your questions. I highly recommend Professors Scott Hughes sahughes@mit.edu, Ed Bertschinger edbert@mit.edu and Alan Guth guth@mit.edu all at MIT.
Thank you for answering me. I understand how photons don't experience time. But my doubt is if a strong enough magnetic field would cause time dilation in particles inside this field. (else the photons itself causing the magnetic field). Why only gravity curves space-time and not all fundamental forces?
Another doubt I have (now in context with the lecture) What if the photon is a wave, only a wave, and the device trying to measure it in the double slit experiment changes the phase of the wave changing the pattern in the detector causing us to believe it is a particle? The photon/electron being only a wave would solve most problems of non locality and collapse of the wave function...
And again, thank you for your patience and all your amazing videos.
I suggest you contact any of the people I suggested in an earlier msg. You can also consider Professor Max Tegmark of MIT. tegmark@mit.edu
Quantum mechanics is hard to think.As everything is nothing,and absolute nothingness can not be imagined.The absence of matter is referred to as vacuum.But even field like gravity acts there.The universe is not bound by the limits and what is beyond that beyond that often blows my mind up.But you have given me an exemplary effigy what I was supposed to learn.
With due respect sir , I am from India and I love Quantum Physics and Nuclear Physics from the core of my heart . Kindly suggest me the ways so that i can make my career in these two great fields . Thank you sir .
after high school go to the very best college that will accept you consistent with your highschool grades. Get a bachelor's degree in Physics. After that apply to the very best Universities that may accept you and get a PhD in QM & Nuclear Physics. Take it from there. 3 yr college + 6 yr for your PhD adds up to about 9 years. I was 29 yr old when I got my PhD in nuclear physics.
Thanks professor for explain such hard topics in intersting way
You are most welcome
why do the lines on the spectra have any thickness at all?
THINKKKKKKK
@@lecturesbywalterlewin.they9259 I know this is late but is it due to the thickness of the light source?
amazing question . did you find the answer . if so please explain
I think that Heisenberg Uncertainty Principle is one of the strongest arguments, that we are living in simulated reality. Therefore at small scales everything is inconsistent. It seems like introducing too large value of (dt) in terms of iterating and integrating diferential equations.
Sometimes you can observe glitches in games, when object has to large velocity and just fly by wall (tunneling), because (dt) taken for calculations isn't small enough to detect collisions. Sometimes object rotating with very large velocity (bug in games), appears on screen like just jittering and shaking randomly. The same problem: (dt) in calculations.
It seems, creators of our simulation (universe), just have not enough powerfull computers.
What do You think? :)
The universe itself is the computer running the simulation. And just like our computers, there is an ultimate limit to the precision that is possible.
No
Dear Prof. Lewin where can I get those gratings used in this lecture?
use google
Thanks for your reply. But Prof can you tell me a specific name of those gratings or a particular online store where I can find them.
They are called "diffraction gratings". If you live in the US or Europe I'll send you 2. I have sent over the years several to India and Pakistan they never arrived; they were stolen!
I understand that. I live in Indian and I will find them. Thanks a lot for even thinking of sending them 😊
+Devansh Parikh transmission grating amazon , something like that
Whether the quantum nature is due to Planck constant, h or quantum number, n? E=nhf
*E=nhf*
Mr. Walter, Classic Physics may fade away but Classic Walter would not!
Hi Prof. Lewin
Do buckyballs also display the interference pattern in the two-slit experiment? If 'yes', how is it possible since buckyballs are much bigger than electrons, photons.
(My answer is 'yes' but would like to double check with my concept.)
no, neither do tennis balls and base balls
+Lectures by Walter Lewin. They will make you ♥ Physics. en.m.wikipedia.org/wiki/Double-slit_experiment
In the paragraph 4 & under the 'Variations of the experiment' stated that buckyballs do display this interference pattern.
Yes I now remember. The balls must have been super small. Read this
en.wikipedia.org/wiki/Double-slit_experiment
Amazing. Thanks for posting
Sir wave means there is motion of disturbance in a space Like a em wave. Sir in em wave , the electric field and magnetic is oscillating in space.
If Electron is a particle then how it can oscillate in space in various point
use google
Dr. Lewin, what is the name of the double slit experiment you illustrated in this course? Please let me know; thanks!
use google
Excellent lecture Sir. Thanks 🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏
Most welcome
How many factors are involved in collision of test probe on an sub atomic particle?
use google
Professor, if electron can jump between two energy levels, but can't exist between them, shouldn't it be the most fundamental unit of universe? If yes, shouldn't it be considered as a fundamental unit?
free electrons can exist at any energy.
@@lecturesbywalterlewin.they9259 But professor, can't we measure the energy difference between two adjecent orbitals or energy levels, quantize it as fundamental there after use it to define other fundamental units?
@@lecturesbywalterlewin.they9259 Sorry the question is moot now (or was moot just I didn't realised). I just read that the standard platinum mass kg was redefined by an equation keeping Planck's constant fixed in equation E=hf=mc^2 few years back😅. So indirectly they have defined mass based on energy difference between electron orbitals which is more fundamental than that prototype. Earlier I meant to use that energy difference as fundamental but potato pathato they are same principle.
Perhaps I'm missing something, but the Uncertainty Principle doesn't seem all that counter-intuitive. Imagine a crowded sports area. At the end of the event, people start filing out a wide exit door in a very orderly way. For some reason, the door slowly begins to close so people are forced to exit through a continually narrower space. At a certain point, panic ensues and, now individuals are squeezed together at the exit, and some can pass or are pushed through the door in a disorderly sequence and in unpredictable directions. Same thing happens with an adjustable nozzle on a garden hose! Why not photons?
Heisenberg's UP is QM. All QM, including HUP is counter intuitive as we all think classical phyisics (newtonian). *Objects at position P in space can stand still*
@@lecturesbywalterlewin.they9259 So, QM is counter-intuitive with respect to classical physics exclusively and perhaps not with respect to "particle" behavior in other domains such as animal behavior. Granted; but for me being a non-scientist, (but comfortable with the mathematics), thinking of possible analogies is helpful in grasping the ideas. I loved 801 and will be continuing with 802 and 803. Bless you so much for making these available.
sir i think the wavelength of the ball is 0.132*10^-34
What does it mean for the uncertainty of the momentum to be greater or equal to hbar/Δx, is there no upper bound? Does that mean that if i'm walking in my room I might all of a sudden reach the speed of light and die? How can a particle have a higher speed and the same energy as another particle?(meaning where do I get the energy to have a higher speed?)
google Heisenberg's Uncertainty Principle
But at school they taught us that atoms have some layers with different energy levels which can hold a limited number of electrons according to the formula 2n^2 and I meant that the one with more layers has to have more volume .
The Bohr Model is a simplification. Electrons in artoms have discrete energies but not discrete positions. In QM nothing has dicrete positions.
what is difference between shells, sub shells and orbits or orbitals in accordance with physics?
I have no clue, use google
@@lecturesbywalterlewin.they9259 thank u sir, but is not available on google ..thank u so much
Professor, why angular displacement, a. Velocity, a. Acciliratit are directed toward axis of rotation
question ill-defined
Sir so can we say that heating objects emits light as the heat energy sends electrons to higher orbitals and then they go back down to release light
those account only for emission lines, not for the black body radiation. 99% of the Sun's radiation is due to black body radiation. use google
I have a slight doubt Professor. When an electron is transiting from one energy state to other during that time at any instany won't it occupy an intermediate position just like a ball in gravitational field does. If not , why ?
QM is the way the world ticks
Professor Lewin, do you have any courses in quantum mechanics?
no
superb explanation 👍
Dear Prof. Lewin
Heisenberg Uncertainty Principle & Third Law of Thermodynamics seem to contradict each other.
Thought experiment:
Say, imagine at 0K, S=0, the motions of the particles (atoms, molecules) cease i.e. static, in a very orderly fashion, these particles will have a well-defined position. Now, we try to probe the exact position or momentum. However, in virtue of the Heisenberg Uncertainty Principle, one can never pinpoint the exact position or momentum of a particle, even at 0K I reckon.
Therefore, is there a contradiction between Heisenberg Uncertainty Principle & Third Law of Thermodynamics? Please enlighten.
Thank you.
Thermodynamics is classical physics, HUP is QM. They obey very different rules.
+Lectures by Walter Lewin. They will make you ♥ Physics. Thanks for your prompt reply. Can we say that modern physics is superior than classical physics? It offers new perspectives & holistic approach to our understanding of nature itself? Although it depends on the context that we are dealing with. Classical physics is easier to handle.
+Lectures by Walter Lewin. They will make you ♥ Physics. In the field of physics/science, can we use a theory/law/principle to defeat another theory/law/principle? It is more like a crash course whereby putting 2 concepts head-to-head, like the above case.
>>>Can we say that modern physics is superior than classical physics?>>>
NO!. Classical Physics is EXCELLENT as long as you work in its domain. You cannot use QM to solve classical problems (e.g., resonance frequencies of strings and cavities, explanation of a rainbow . . . . .). QM is EXCELLENT as long as you work in its domain. You cannot use classical physics to explain the behavior of atoms,
If theories are not (or no longer) consistent with observations they will have to be changed.
Professor do you have similar lecture series for thermodynamics/ quantum physics/ cosmology? or perhaps any suggestions for similar lecture series?
MIT 8.04 QM 1 and MIT 8.05 QM 2 are on my channel
@@lecturesbywalterlewin.they9259 thank you so much! Is there anything for thermodynamics?
the uncertainty principle is a strong argument against the idea of teleportation since the information of each particle can never be completely determined, is this correct? If it is impossible,why it is still speculating?
correct - that is also an issue with Schrodinger's cat and with an "object" tunneling through a barrier. It lacks the *coherence* for that to happen. Alpha particles can tunnel through a barrier but not a tennis ball.
Is photon separate able? How do we know if one photon is one photon , not a group of mass when we shoot ONE photon every day and to observe the landing on the screen, , can we really measure that accurately?
read up on Photo-electric effect for which Einstein received the Nobel Prize.
Sir, can we use entanglement to clone humans or particular part of our body as we can use it for teleportation(maybe a lot latter in the future)? And if yes, then there must be some way to cure diseases like cancer by taking information of each and every particle and then exchange the information of defected organ by the information of a healthy organ and then use entanglement to send this information to some other set of particles to constitute the body back in the way it was.
ask a physician
Lectures by Walter Lewin. They will make you ♥ Physics. Thanks for replying, sir.
Does uncertainty principle and Quantum leaps in quantum physics contradict each other?
no Heisenberg is also dE * dt = hbar/2pi use google
Full depth explanation...
Sir light when passes through the slit. It can also be explained through diffraction. Sir than why need QM for this
HUP always applies. It's there also in diffraction
Love you sir ❤️❤️ FROM NEPAL
sir, what is the size of one photon? OR WHEN i CAN SAY, IT IS ONE PHOTON
photons have no mass but they have energy and momentum. As far as their size is concerned I suggest you use google.
I m slightly off from the topic.....I went through principle of least action today( hamilton' s varriational principle) it says particle will take a path such that some integral is minimum.....can there be more than one paths for which the integral is stationary??
Sir can light behave as wave and particle at a time. If not why sir??
Light always behaves like a wave. What seems to behave like particles, if you don't look carefully, are quanta. What is a quantum? A quantum is a bit of energy. All we mean by "a light source emitting a photon" is that the source transfers a little bit of energy into the electromagnetic field. That field propagates in a wavelike fashion, but we can't localize the energy that we put into it. Eventually the field transfers a little bit of energy, a quantum of energy ("a photon" but not "the same photon") to the detector. Because of energy conservation the amount of energy that the source put into the field has to be the same as the amount of energy that the detector takes out (at least if the two are stationary relative to each other, otherwise we are getting a Doppler shift!), it LOOKS LIKE AS IF we got the same photon out that we put in. That, however, is a logical mistake on our part. One can't write "Photon 2356" on a photon, i.e. the idea that a specific photon propagates like a particle trough the vacuum is not backed up by any observation. We are merely observing energy conservation at the quantum level.
Great content. Regards
If we know the history of an event, can the test probe be used to know the position and change the course of the event?
question unclear
sir since Bohr model has many drawbacks then why still its theory of quantisation is still used as a pillar of quantum mechanics?
google "quantization in QM"
Sir if particle collide and vanish, will it be converted into energy?
Energy is always conserved
what the amazing lecture, love it
Glad you enjoyed it!
Does the students where sitting on the left side have the same order of light colors as students sitting on the right side??