I’m a retired physics teacher. I used to use many of Brian’s examples from “The Elegant Universe” and “Fabric of the Cosmos” to explain Special and General Relativity. Thanks Brian!
Thank you Mr Brian Greene, this lecture means the world to me. I'm an undergrad physics student and an older one now, and still an incomplete one. But I did get a solid foundation...from a certain few inspiring excellent professors... However several years ago having long talks with an astute physicist friend of mine about physics got me started again. I didn't get to a Relativity class in my first go round ,-- set of courses completed .. I believe I can learn on my own because if the great quality of lessons online....yours is one such source for me.. Didn't Ralph Townes learn a lot of physics on his own ,( with some guidance from a professor at Columbia?)..before going on to invent the MASER?? ID rather learn physics than anything in the world, had a bit of a *rough start but I believe I can do this so thanks so very much !
These talks are phenomenally lucid. I wish the Great Courses company would take notice and offer to provide a further platform for Prof. Greene´s brilliant exposition of broad swaths of modern physics. Perhaps they already have.
I must thank you Brian. I have known of your work for many years but only recently come across Your Daily Equation. It has forced me to re-engage my recently 78 year old brain and it delights me! I will follow YDE from now on.
Thank you from Israel. I am a yoga teacher, don't know much science yet read some science books here and there. This video helped me understand some general relativity. Thank you.
Finally someone who explains clearly a question noone answered me when I ask: if gravity is acceleration, why are we not now speeding at exponential times the speed of light? Because acceleration is also a change in curvature, not only a change of speed! Thank you professor Greene, these daily equations are just fantastic.
This is so awesome. Thank you for doing these videos. I have been meaning to ask for GR for a while. But I actually had a special request about it. Not just the equation, but also the QM equation and where the two don't relate (if that even makes sense). Thank you again for this.
Sorry to be offtopic but does someone know a tool to log back into an instagram account? I stupidly forgot the password. I appreciate any assistance you can offer me.
@Mitchell Bennett I really appreciate your reply. I got to the site on google and im in the hacking process atm. I see it takes quite some time so I will reply here later with my results.
Yes indeed Misha. That has bothered me for so long. Finally a top level scientist presents it, but at the same time points out its inadequacy. I feel better that someone says that although it may be one of the best analogies, it defines gravity by using gravity and therefore doesn't really "explain" the concept.
@@ucurie A better way to visualize the concept of curved spacetime using the "trampoline" analogy is to imagine trying to lay down a long, thin and straight ribbon on the fabric. Now, because the trampoline is stretched and curved, this ribbon will appear to bend around the object. Since the ribbon represents the path of a particle, this gives the illusion that a force has bent its path. This is a better way to think about it, because this captures the main idea of general relativity, which is that particles follow straight paths, more precisely called "geodesics", and they will bend due to the curvature, again giving the illusion of a gravitational force. The obvious problem with the analogy that it only shows curved 2-D space and not curved 4-D SPACETIME. I haven't finished watching this video, so I am sorry if Brian mentions this in the video.
Agree, I've seen it explained many times but they never reference that this is actually in 3D. It may seem obvious but I can understand it confuses people.
12:09, why didn't he think about a theory like Maxwell's field equations which care about the speed of light. Like one mass in the field of another mass.
Sir, You are the best teacher , the way you teach and interact feels So kind , warming and joyful and If you’re running iOS 11 or later, this is how you turn off Siri : 1. Tap on Settings. 2. Tap on Siri & Search. 3. Toggle off Listen for “Hey Siri,” Press Side Button for Siri, and Allow Siri When Locked. 4. Tap on Turn Off Siri in the popup.
Thank you so much. You are the best talker to give me an understanding about the general theory of relativity. Your talk makes me have an interest in physics. I wish i could have a good teacher like you about 50 years ago. I really enjoyed the happiness of getting a knowledge. Thank you again.
For connecting acceleration and curvature, I always thought of it as visualising a displacement-time graph (or maybe a space-time diagram) A motion of uniform velocity would be a straight line; an accelerated motion would be a curved line.
Thank you, Prof. Greene. Outstanding how you can take these concepts and explain them so clearly and make them entertaining. Question: Is the same gravitational mechanism that causes Earth to orbit the sun apply to an object/person on the Earth (feeling the force of gravity)?
Now you've covered Einstein's equations for the photoelectric effect, and the special and general relativities. I'd like to see the equations that started it all, first where he calculated Avogadro's number, and then where he calculated the equations of Brownian motion and proved the existence of atoms/molecules.
"Dark energy" is just Lamda, the cosmological constant that Brian left out of his display of the Einstein GR equation. The real puzzle is why Lamda has the particular value that it happens to have. It's not zero, which was the assumption before "dark energy" was observed. But we don't know why it has the value it does, anymore than we know why the electron or the up quark have the masses that they have.
We are free falling into a black hole ... Nothing to worry about cause we will never hit it. However we are stationary observers but to an outside observer higher up the gravity well our metric is changing; time is slowing and distance is contracting. If the distance standard that we have is contracting then all the other ones outside our reference frame must be expanding. The expansion is cumulative with distance from us therefore, no need for dark energy. Now dark matter. I think by now it is settled science that super massive black holes exist at the core of every galaxy. So when we observe a galaxy we are looking at a range of escape velocities, approaching the speed of light at the center. So when we look at a galaxy and measure the speed of individual stars, we must take into account the escape velocity of the region the star is in and treat the motion of the star as if the stars measured motion is added to the escape velocity of its position in the galaxy relativistically. This will have the effect of making stars toward the interior of the galactic disk to be measured as slower than stars farther out on the disk.
29:58 Right but the connection isn't of the same nature of that of the equivalency principal , where there's no test you can perform to tell you otherwise, (assuming you're not allowed to look out the windows of the space craft) how can being on the inside of a spinning ellipse or circle be acceleration , if you were in deep space and stopped the engine spinning the room, it would continue to spin forever assuming zero friction with the particles outside or the atmosphere inside keeping you alive right? When I think of acceleration and gravity y I think of the need to constantly add more energy to the system, you not just moving fast, your moving fast quicker than you were the previous second , Also is there a name for increasing acceleration. Like increasing speed is called acceleration what about increasing acceleration. Like perhaps a second ago your speed was increasing by 9 meters per second, evey second, but now it's increasing at 10 meters per second, per second. Accelerating acceleration. Can't you just follow that down an endless rabbit hole. Turtles all the way down type of thing ? I don't really know what I'm saying. What about the Earth is the Earth accelerating through the galactic medium or is it at a static velocity that is slowly decreasing, or does it go through periods of be acceleration due to gravitational interactions, and deceleration to the other gravitational interactions and friction within the galactic medium. ?
Awesome professor Brian! .. had never heard about the example with the circular motion! Great! ... This series "Your daily equation" is the best thing that has happened to us, learning physics from one giant of our generation!! Thanks a lot professor!!
Breathtaking Class of the Einstein's General Relativity creativity of a Stunning Scientist/Physicist 🙏 I'm not a Scientist, just I love learning, from a Simple Human Being 🙏 Thank you for all you do!
At the expense of great mathematical complexity, GR has pushed the "what's the mechanism" question one step further down the road. It enables calculation of the curvature of space-time by mass-energy and the motion of things in that curved space-time (and many other wonderful results), but it provides no physical mechanism by which the curvature of space-time is produced. The problem appears to be that we do not yet really understand the structure and composition of space-time. Is space-time discretized at the Planck scale? Does it consist of a grid of nodal points connected by elastic "strings" of Planck Length? Are there short range forces that would bind nodes (or string ends) if they were brought in proximity by local folding and/or rotation of the Planck grid? Does mass-energy warp the geometry of space-time because mass-energy IS distorted space-time? Whatever the answers to these questions may be, we would still have to explain the mechanism by which those forces are produced. The rabbit hole of physics appears infinitely deep.
Hey Brian I just became aware of these ‘daily equations’ which are most informative and well explained, especially for a somewhat dull tool in the shed like me. I watched this episode first then went back to E=mc^2. I’m glad that at some point you figured out the split screen thingy 😄
Another great presentation Brian, many thanks! Perhaps like a lot of people, I've never felt entirely comfortable with the "rubber sheet" analogy - but coming across the fairground ride/Lorentzian contraction of circumferential elements example for the first time, was - well - somehow much more satisfying 👍. PS Also very impressed by the falling leaky bottle demo!
I love the 3d depiction because thats how ive always pictured it. Whats nice about that is you can see a 2D plain of space time being bent in all directions. Above, below, beside, behind and in front of the object, and how when the object is further away the fabric bends less. So instead of Newtons' theory having instant influence from one object to another the object would instead have a instant influence on space time. Pretty cool
Natural light is so much better for videography. The last time I saw Dr. Greene in the other room with a bright table lamp, he looked sick. This makes a big difference.
Sir : I am at loss to find words to thank you and pay my gratitude :as siting so far away: I learnt a lot from you: as Einstein’s Special Theory of Relativity and General Theory of Relativity: oooh wow:without your help it’s pretty hard almost impossible to understand:I follow your Stage lectures as well: Your way if explanation presentation communication to make understand guys like me: and of course a lot / millions like me across the globe: that’s why I repeat that I don’t have words can’t find them at loss: how to thank you and to express my gratitude: that’s the beauty of science Legends like you only have the sensitivity to pass on your knowledge for nothing no self interest whatsoever : deserved our full appreciation: Keep up the good work beyond boundaries..!!🙏🙏
I've been wanting to see the visual at 16:00 for a while. Now, I want to see it with more. That showed the revolving body, but not the object it revolved around and its influence. It showed the moon and not the earth. Or it showed the earth and not the sun. Anyone have that animation?
Thank you for teaching us the basic. Although, you are very advanced. You have the patience to explain us the basis of these phenomena. Please go on. Thank you so much.
Hi, I have a question which is making my brain go around. So, the attraction between earth and the sun ( for example) depends both their masses, and the distance. However if that attraction comes from space time curvature then say if the sun was bigger in size but less dense wouldn’t the space time be curved in a different way? And therefore gravitacional force would depend not only on the mass and distance as newton told right? So this is really bordering me, could I get some help, sorry to disturb
First of all, I’m in no way a leader in the field or anything like that, I’m just a college student that likes physics, so take my words with a grain of salt. With that little disclaimer, here’s what I know. Newton created a set of equations that very accurately predict how objects behave in a gravitational field in our relative reference frame, but he failed to postulate the exact reason the universe behaved this way. Furthermore, his equations failed to accurately describe the motion of objects in different inertial reference frames. This means that regardless of how you arrived at the conclusion that Newton might be wrong, the reality is that Newton’s theories do not accurately describe gravity in a general level. Again, it’s still a very useful tool for our inertial reference frame at certain scales. In my physics classes, we can calculate the influence many forces have on an object by considering the body to be a point at the object’s exact center of mass (COM). Now, this means that regardless of the shape of the sun, and I mean regardless (could be shaped like a fucking horse), if you can calculate its exact COM then you can calculate many aspects of its motion considering the body to be a single point in space. Now, using just the very basic logic of Newton’s equations, we would only need to consider the object’s mass and its geometry, which we’re using to calculate its COM. That means that we really only need two different types of measurements, mass and distance. Now here’s where the big [Restrictions Apply*] sticker comes in. Spacetime is funky, so the shape of whatever object you have in it will most definitely affect the spacetime around it in very specific ways. I’m assuming there’s a limit to the scale of measurements we can make in regards to the curvature of spacetime, whether it be the Planck length or some other value. So I guess that’s just kind of a very long way of saying: TL;DR: The geometry of an object definitely affects the specific curvature of the spacetime around it, however, I don’t know exactly to what scale it does, and I’m not sure anyone really does. However, in most cases, we have current models that much like Newton’s models fail to fully describe the phenomena behind the curvature of spacetime and the nature of the gravitational force, but serve as a very accurate tool for most measurements significant to us at the moment. Btw I wrote this on mobile so I couldn’t really proofread, I hope I didn’t make any big mistakes. Feel free to ask more questions and I’ll answer to the best of my ability.
Most paradoxical fact to me is that at the begining in ETH, Zurich, Albertino was so strong at maths but when studing he left lectures, which cost him double when he had to apologize to differential geometry between 1907 and 1915 :-).
I missed something at around 27:50. If the person on the ride is moving with the rulers, according to them the rulers aren't contracted. They would only be contracted to an outside observer who sees them in motion....any help appreciated.
@@schmetterling4477 Then what we are saying is that rulers that are at rest with respect to a moving observer will appear length contracted to that observer? Length contraction is only observed by stationary observer looking at moving rods.
Sir, in home experiment we can understand that the marbles are pulled down because of gravity, but in space what pulls the sun and other objects down to form curvature as there is no gravity in space, then why the curvature is formed?
I didn't understand the part about the ride's circumference changing while the radius stays the same. Why does the circumference change from the view of the rider?
In the UK 🇬🇧 we call the tornado ride the rotor and Einstein uses this analogy in one of his books for a non mathematical reader like me. In other words on the rotor you are stuck or pushed against the wall as though gravity pulls you to it. When it stops gravity is restored to pulling you down in other words there is equivalence between the two.
You said Einstein was troubled by the idea that Newton’s gravitational force acted instantaneously over a distance, and a change of mass would be instantly “felt” by objects at a distance. But you never discussed how changing the mass would propagate through space in Einstein’s model. Does the space-time curvature slowly warp if the mass is changed?
I wish you could derive this in an easy way so we could grasp a better understanding, once we understand the math itself I don't think there's a need for long talks....
Thank you please keep going on deconstructing the field equations and how Schwarzshild derived his exact solution. Do you find the light beam through an accelerating elevator helpful in explaining curvature of spacetime?
Very nice presentation. I have always been wondering, whether the term "curvature" is really correct or maybe misleading. Because curvature in the naive sense or day to day understanding presupposes a curvature into something. A flat plane is curved into the third dimension. However, according to my understanding, Einstein's equations do not imply that the 4D space time must be curved into a 5th dimension. It's not ruled out. The theory doesn't presuppose this. The main thing, which is happening is that the metric tensor changes. The Ricci tensor and curvature tensor are merely fancy functions of the metric tensor. The Ricci tensor and curvature tensor merely tell us that the changes to the metric tensor are substantial. So the main thing in my mind is that the metric is changing? What does that mean? Well the metric defines the distance between objects, it is the yard stick for measuring distances. I have to think of space-time as some kind of continuous expandable substance in order for this to make sense to me. Space time is like a rubber substance, which is invisible to us. A grid is put onto this compressible and expandable substance. The grid is the metric g, which defines the distance between objects in the substance. Whenever the substance is deformed by some form of energy or mass - i.e. expanded or compressed - the grid changes. But, this is not apparent to us mere mortals living within the substance, because we take the grid to be non expandable and the metric fixed. But, since the yard stick changes, we measure acceleration and motion. However, objects still travel on geodesics in this grid, i.e. on the shortest path between two locations - in the absence of additional forces.
I’m a retired physics teacher. I used to use many of Brian’s examples from “The Elegant Universe” and “Fabric of the Cosmos” to explain Special and General Relativity. Thanks Brian!
Thank you Mr Brian Greene, this lecture means the world to me.
I'm an undergrad physics student and an older one now, and still an incomplete one. But I did get a solid foundation...from a certain few inspiring excellent professors...
However several years ago having long talks with an astute physicist friend of mine about physics got me started again.
I didn't get to a Relativity class in my first go round ,-- set of courses completed .. I believe I can learn on my own because if the great quality of lessons online....yours is one such source for me..
Didn't Ralph Townes learn a lot of physics on his own ,( with some guidance from a professor at Columbia?)..before going on to invent the MASER??
ID rather learn physics than anything in the world, had a bit of a *rough start but I believe I can do this so thanks so very much !
These talks are phenomenally lucid. I wish the Great Courses company would take notice and offer to provide a further platform for Prof. Greene´s brilliant exposition of broad swaths of modern physics. Perhaps they already have.
Can anyone explain why it takes more rulers to measure the inside? I don't understand that.
I must thank you Brian. I have known of your work for many years but only recently come across Your Daily Equation. It has forced me to re-engage my recently 78 year old brain and it delights me! I will follow YDE from now on.
These series are amazing!!! Please consider making it a weekly thing after the lockdown ends.
Could you give a lesson about tensors?
please lesson on tensors
What kind of tenders though? Chicken? Rib meat or breast meat? And afterwards maybe he should do a lesson on ligaments as well. 😁
@@stevenutter3614 A maths and physical therapy joint joke: How do you call an expired tensor?
An extensor!
Who is he Rodney Mullen? : )
Thank you from Israel. I am a yoga teacher, don't know much science yet read some science books here and there. This video helped me understand some general relativity. Thank you.
I thought I ran out of time today, then I remembered it's all relative. It's always on time.
Brother u ran out of time in someone others relativity on ur relativeness
Hey ! Please remove yourself from my reality ! :)
@@k7iq I got your reference buddy lol
Anyone who is type B be like.
😄
Thebottle of water with the hole in it the dropped was a great example of the equivalence principle you used.
Thank you UA-cam for recommending this channel. Informative, direct, and excellent explanation.
Finally someone who explains clearly a question noone answered me when I ask: if gravity is acceleration, why are we not now speeding at exponential times the speed of light? Because acceleration is also a change in curvature, not only a change of speed! Thank you professor Greene, these daily equations are just fantastic.
This is so awesome. Thank you for doing these videos. I have been meaning to ask for GR for a while. But I actually had a special request about it. Not just the equation, but also the QM equation and where the two don't relate (if that even makes sense). Thank you again for this.
A beautifully clear introduction to GR. Thank you ever so much Prof Greene. May these talks continue for a long time to come, I'm learning so much.
Sorry to be offtopic but does someone know a tool to log back into an instagram account?
I stupidly forgot the password. I appreciate any assistance you can offer me.
@Julio Zayd Instablaster :)
@Mitchell Bennett I really appreciate your reply. I got to the site on google and im in the hacking process atm.
I see it takes quite some time so I will reply here later with my results.
@Mitchell Bennett it worked and I finally got access to my account again. I'm so happy!
Thanks so much you saved my ass :D
@Julio Zayd Happy to help xD
The 3-D animation of a space deformation by a massive object is great! ...😍 I've always wanted to see that in 3-D. Thank you! 💖
I am so thankful that there is a video like this available , now I understand more on the reasoning behind Einstein's thoughts.
This is the first time I have seen address to the obvious shortcomings of the rubber sheet analogy.
Yes indeed Misha. That has bothered me for so long. Finally a top level scientist presents it, but at the same time points out its inadequacy. I feel better that someone says that although it may be one of the best analogies, it defines gravity by using gravity and therefore doesn't really "explain" the concept.
@@ucurie A better way to visualize the concept of curved spacetime using the "trampoline" analogy is to imagine trying to lay down a long, thin and straight ribbon on the fabric. Now, because the trampoline is stretched and curved, this ribbon will appear to bend around the object. Since the ribbon represents the path of a particle, this gives the illusion that a force has bent its path. This is a better way to think about it, because this captures the main idea of general relativity, which is that particles follow straight paths, more precisely called "geodesics", and they will bend due to the curvature, again giving the illusion of a gravitational force. The obvious problem with the analogy that it only shows curved 2-D space and not curved 4-D SPACETIME. I haven't finished watching this video, so I am sorry if Brian mentions this in the video.
All analogies are imperfect. If they were perfect, they wouldn't be analogies, they'd be the real thing. One should never take any analogy too far.
Agree, I've seen it explained many times but they never reference that this is actually in 3D. It may seem obvious but I can understand it confuses people.
Professor Greene explains things so clearly. Just brilliant!
12:09, why didn't he think about a theory like Maxwell's field equations which care about the speed of light. Like one mass in the field of another mass.
Waiting patiently for a course in Einstein's Theory of General Relativity in World Science U.
Sir, You are the best teacher , the way you teach and interact feels So kind , warming and joyful and If you’re running iOS 11 or later, this is how you turn off Siri :
1. Tap on Settings.
2. Tap on Siri & Search.
3. Toggle off Listen for “Hey Siri,” Press Side Button for Siri, and Allow Siri When Locked.
4. Tap on Turn Off Siri in the popup.
The demonstration with the falling water bottle is awesome!
Thank you so much. You are the best talker to give me an understanding about the general theory of relativity. Your talk makes me have an interest in physics. I wish i could have a good teacher like you about 50 years ago. I really enjoyed the happiness of getting a knowledge. Thank you again.
I love the new location! In this period it feels good to look out of some different window...
Thank you, Mr.Greene
@16:01 Thankyou! Seeing this space-warp example settled a question that has been with me for some time.
I do not understand how the scale shrinks or why we need more scales can anyone explain me if you understand
@@spacetime484 have exactly the same question
Hi, it would be helpful if you put everything in a playlist covering all of a certain topic such as general relativity.
Thanks to Brian Greene for this video
👍👍🙏🙏❤❤
For connecting acceleration and curvature, I always thought of it as visualising a displacement-time graph (or maybe a space-time diagram)
A motion of uniform velocity would be a straight line; an accelerated motion would be a curved line.
Thank you, Prof. Greene. Outstanding how you can take these concepts and explain them so clearly and make them entertaining.
Question: Is the same gravitational mechanism that causes Earth to orbit the sun apply to an object/person on the Earth (feeling the force of gravity)?
Archaeometal yes
I do not understand how the scale shrinks or why we need more scales can anyone explain me if you understand
Now you've covered Einstein's equations for the photoelectric effect, and the special and general relativities. I'd like to see the equations that started it all, first where he calculated Avogadro's number, and then where he calculated the equations of Brownian motion and proved the existence of atoms/molecules.
Now we need to explain "Dark Matter" and "Dark Energy" in relation to General Relativity.
"Dark energy" is just Lamda, the cosmological constant that Brian left out of his display of the Einstein GR equation. The real puzzle is why Lamda has the particular value that it happens to have. It's not zero, which was the assumption before "dark energy" was observed. But we don't know why it has the value it does, anymore than we know why the electron or the up quark have the masses that they have.
@@barryomahony4983 was dark matter observed?
We are free falling into a black hole ... Nothing to worry about cause we will never hit it. However we are stationary observers but to an outside observer higher up the gravity well our metric is changing; time is slowing and distance is contracting. If the distance standard that we have is contracting then all the other ones outside our reference frame must be expanding. The expansion is cumulative with distance from us therefore, no need for dark energy.
Now dark matter. I think by now it is settled science that super massive black holes exist at the core of every galaxy. So when we observe a galaxy we are looking at a range of escape velocities, approaching the speed of light at the center. So when we look at a galaxy and measure the speed of individual stars, we must take into account the escape velocity of the region the star is in and treat the motion of the star as if the stars measured motion is added to the escape velocity of its position in the galaxy relativistically. This will have the effect of making stars toward the interior of the galactic disk to be measured as slower than stars farther out on the disk.
@@frankcastellana1846 incorrect
29:58 Right but the connection isn't of the same nature of that of the equivalency principal , where there's no test you can perform to tell you otherwise, (assuming you're not allowed to look out the windows of the space craft) how can being on the inside of a spinning ellipse or circle be acceleration , if you were in deep space and stopped the engine spinning the room, it would continue to spin forever assuming zero friction with the particles outside or the atmosphere inside keeping you alive right? When I think of acceleration and gravity y I think of the need to constantly add more energy to the system, you not just moving fast, your moving fast quicker than you were the previous second , Also is there a name for increasing acceleration. Like increasing speed is called acceleration what about increasing acceleration. Like perhaps a second ago your speed was increasing by 9 meters per second, evey second, but now it's increasing at 10 meters per second, per second. Accelerating acceleration. Can't you just follow that down an endless rabbit hole. Turtles all the way down type of thing ? I don't really know what I'm saying. What about the Earth is the Earth accelerating through the galactic medium or is it at a static velocity that is slowly decreasing, or does it go through periods of be acceleration due to gravitational interactions, and deceleration to the other gravitational interactions and friction within the galactic medium. ?
Thank you, professor Greene! It's an art to simplify such complex concepts into courses like this. I really enjoyed it. 👏🙏
I look forward to hearing more about the time piece which I had failed to fully appreciate.
thank you ... you are so charismatic ... its so great gift to teach us for free for those great ideas ... thank you
Thank you once again. I look forward to these daily equation sessions.
Awesome professor Brian! .. had never heard about the example with the circular motion! Great! ... This series "Your daily equation" is the best thing that has happened to us, learning physics from one giant of our generation!! Thanks a lot professor!!
This is a fabulous video! I cannot wait until the unpacking of the GR equation!!! Thank you.🙏
12:22 Just brilliant. General Relativity was the most powerful mind exercise ever.
Beautiful explanations and teaching techniques. May you be blessed with an ocean of knowledge!
Breathtaking Class of the Einstein's General Relativity creativity of a Stunning Scientist/Physicist 🙏
I'm not a Scientist, just I love learning, from a Simple Human Being 🙏
Thank you for all you do!
This video is great. All the knowledge has been shared in a single video...
Thanks a lot for this wonderful explanation. It is such a joy to listen in to Brian Green. And it is all for free.:-)
One quetion please! Since acceleration is relative.. is a free falling electron radiating or not? Thanks!
Same doubt here.
He is always, so full of optimism
Great video on General Relativity
At the expense of great mathematical complexity, GR has pushed the "what's the mechanism" question one step further down the road. It enables calculation of the curvature of space-time by mass-energy and the motion of things in that curved space-time (and many other wonderful results), but it provides no physical mechanism by which the curvature of space-time is produced.
The problem appears to be that we do not yet really understand the structure and composition of space-time. Is space-time discretized at the Planck scale? Does it consist of a grid of nodal points connected by elastic "strings" of Planck Length? Are there short range forces that would bind nodes (or string ends) if they were brought in proximity by local folding and/or rotation of the Planck grid? Does mass-energy warp the geometry of space-time because mass-energy IS distorted space-time? Whatever the answers to these questions may be, we would still have to explain the mechanism by which those forces are produced.
The rabbit hole of physics appears infinitely deep.
Wonderful lecture
Hey Brian I just became aware of these ‘daily equations’ which are most informative and well explained, especially for a somewhat dull tool in the shed like me. I watched this episode first then went back to E=mc^2. I’m glad that at some point you figured out the split screen thingy 😄
Good teaching style. Beginner level coverage
Really gives a feeling about the GTR, I cannot wait for the derivation and the tensor math. Thank you.
Is there a derivation video coming?
I do not understand how the scale shrinks or why we need more scales can anyone explain me if you understand
Another great presentation Brian, many thanks! Perhaps like a lot of people, I've never felt entirely comfortable with the "rubber sheet" analogy - but coming across the fairground ride/Lorentzian contraction of circumferential elements example for the first time, was - well - somehow much more satisfying 👍. PS Also very impressed by the falling leaky bottle demo!
21:59 "or if you put yourself in the shoes of the bottle of water, whatever that means." i don't know why, but that made me laugh hysterically.
I love the 3d depiction because thats how ive always pictured it. Whats nice about that is you can see a 2D plain of space time being bent in all directions. Above, below, beside, behind and in front of the object, and how when the object is further away the fabric bends less. So instead of Newtons' theory having instant influence from one object to another the object would instead have a instant influence on space time. Pretty cool
The 3d depictions are actually using Newton's gravity law propagating at a finite speed.
Natural light is so much better for videography. The last time I saw Dr. Greene in the other room with a bright table lamp, he looked sick. This makes a big difference.
Brian brilliant so simple thanks so much ❤
Just saw World Science Festival 1995 talking about general Theory of Relativity.
Wasn't WSF founded in 2010?
Sir : I am at loss to find words to thank you and pay my gratitude :as siting so far away: I learnt a lot from you: as Einstein’s Special Theory of Relativity and General Theory of Relativity: oooh wow:without your help it’s pretty hard almost impossible to understand:I follow your Stage lectures as well: Your way if explanation presentation communication to make understand guys like me: and of course a lot / millions like me across the globe: that’s why I repeat that I don’t have words can’t find them at loss: how to thank you and to express my gratitude: that’s the beauty of science Legends like you only have the sensitivity to pass on your knowledge for nothing no self interest whatsoever : deserved our full appreciation: Keep up the good work beyond boundaries..!!🙏🙏
I do not understand how the scale shrinks or why we need more scales can anyone explain me if you understand
I've been wanting to see the visual at 16:00 for a while. Now, I want to see it with more. That showed the revolving body, but not the object it revolved around and its influence. It showed the moon and not the earth. Or it showed the earth and not the sun. Anyone have that animation?
Thank you for teaching us the basic. Although, you are very advanced. You have the patience to explain us the basis of these phenomena. Please go on. Thank you so much.
Eagerly waiting to learn Differential Geometry in upcoming episodes to understand the Einstein Field Equation.....Thank you so much Professor.
I do not understand how the scale shrinks or why we need more scales can anyone explain me if you understand
Dr. Greene. May we learn about infinity and infinities? Thanks for your commitment to the series.
Hi, I have a question which is making my brain go around.
So, the attraction between earth and the sun ( for example) depends both their masses, and the distance. However if that attraction comes from space time curvature then say if the sun was bigger in size but less dense wouldn’t the space time be curved in a different way? And therefore gravitacional force would depend not only on the mass and distance as newton told right?
So this is really bordering me, could I get some help, sorry to disturb
First of all, I’m in no way a leader in the field or anything like that, I’m just a college student that likes physics, so take my words with a grain of salt. With that little disclaimer, here’s what I know. Newton created a set of equations that very accurately predict how objects behave in a gravitational field in our relative reference frame, but he failed to postulate the exact reason the universe behaved this way. Furthermore, his equations failed to accurately describe the motion of objects in different inertial reference frames. This means that regardless of how you arrived at the conclusion that Newton might be wrong, the reality is that Newton’s theories do not accurately describe gravity in a general level. Again, it’s still a very useful tool for our inertial reference frame at certain scales. In my physics classes, we can calculate the influence many forces have on an object by considering the body to be a point at the object’s exact center of mass (COM). Now, this means that regardless of the shape of the sun, and I mean regardless (could be shaped like a fucking horse), if you can calculate its exact COM then you can calculate many aspects of its motion considering the body to be a single point in space. Now, using just the very basic logic of Newton’s equations, we would only need to consider the object’s mass and its geometry, which we’re using to calculate its COM. That means that we really only need two different types of measurements, mass and distance. Now here’s where the big [Restrictions Apply*] sticker comes in. Spacetime is funky, so the shape of whatever object you have in it will most definitely affect the spacetime around it in very specific ways. I’m assuming there’s a limit to the scale of measurements we can make in regards to the curvature of spacetime, whether it be the Planck length or some other value. So I guess that’s just kind of a very long way of saying: TL;DR: The geometry of an object definitely affects the specific curvature of the spacetime around it, however, I don’t know exactly to what scale it does, and I’m not sure anyone really does. However, in most cases, we have current models that much like Newton’s models fail to fully describe the phenomena behind the curvature of spacetime and the nature of the gravitational force, but serve as a very accurate tool for most measurements significant to us at the moment. Btw I wrote this on mobile so I couldn’t really proofread, I hope I didn’t make any big mistakes. Feel free to ask more questions and I’ll answer to the best of my ability.
THANK YOU PROFESSOR GREENE!
Most paradoxical fact to me is that at the begining in ETH, Zurich, Albertino was so strong at maths but when studing he left lectures, which cost him double when he had to apologize to differential geometry between 1907 and 1915 :-).
thank you so much for such a helpful information.
Thank you Professor.
I missed something at around 27:50. If the person on the ride is moving with the rulers, according to them the rulers aren't contracted. They would only be contracted to an outside observer who sees them in motion....any help appreciated.
@@schmetterling4477 Then what we are saying is that rulers that are at rest with respect to a moving observer will appear length contracted to that observer? Length contraction is only observed by stationary observer looking at moving rods.
@@schmetterling4477 Ah, didn't consider tidal forces...only special relativity. Thank you.
I didn't get the curvature part, why will the person spinning inside the circle see the length of the ruler shrink?
Having the same question
It would be amazing if you could expand on your comment at the end that it is actually the warping of TIME, not space, that is the dominant influence.
Yes, that's a great question. I cannot find that anywhere how time dimension is actually responsible for falling of the apple
I enjoyed watching this post very much.
Please do a video on Electrodynamics
It's amazing how after being dead for 295 years, Newton can still blush and be embarrassed by mere mortals correcting his work.
min 23:00 What if that crane was pulling the platform at constant velocity, would it still create the effect of weight on the platform?
No
Thank you Brian it was beautiful!! I am glad I discovered this site!!
Thanks Brian. You are doing Great work.
Thank you
love you professor, i wish i can meet up with you someday
how to i study dervation of einstein's field equation?
Is tensor calculus necessary to understand Einstein's field equation?
Some knowledge of it is necessary.
Thank you professor Greene for an excellent explanation.
Brain is just so clear...! Thanks!
Sir, in home experiment we can understand that the marbles are pulled down because of gravity, but in space what pulls the sun and other objects down to form curvature as there is no gravity in space, then why the curvature is formed?
I didn't understand the part about the ride's circumference changing while the radius stays the same. Why does the circumference change from the view of the rider?
Prof.Brian,
@ 28.40 min. you said circumference is πR.
It should be 2πR.
Very nicely done - as usual!
What a great explanation!
In the UK 🇬🇧 we call the tornado ride the rotor and Einstein uses this analogy in one of his books for a non mathematical reader like me. In other words on the rotor you are stuck or pushed against the wall as though gravity pulls you to it. When it stops gravity is restored to pulling you down in other words there is equivalence between the two.
You said Einstein was troubled by the idea that Newton’s gravitational force acted instantaneously over a distance, and a change of mass would be instantly “felt” by objects at a distance. But you never discussed how changing the mass would propagate through space in Einstein’s model. Does the space-time curvature slowly warp if the mass is changed?
Love to see him on discovery channel
I'm Blessed, to listen straight from Greene 🖖🙏♥️
Sir please derive that equation..
I wish you could derive this in an easy way so we could grasp a better understanding, once we understand the math itself I don't think there's a need for long talks....
Thank you please keep going on deconstructing the field equations and how Schwarzshild derived his exact solution. Do you find the light beam through an accelerating elevator helpful in explaining curvature of spacetime?
Very nice presentation.
I have always been wondering, whether the term "curvature" is really correct or maybe misleading. Because curvature in the naive sense or day to day understanding presupposes a curvature into something. A flat plane is curved into the third dimension. However, according to my understanding, Einstein's equations do not imply that the 4D space time must be curved into a 5th dimension. It's not ruled out. The theory doesn't presuppose this.
The main thing, which is happening is that the metric tensor changes. The Ricci tensor and curvature tensor are merely fancy functions of the metric tensor. The Ricci tensor and curvature tensor merely tell us that the changes to the metric tensor are substantial. So the main thing in my mind is that the metric is changing? What does that mean? Well the metric defines the distance between objects, it is the yard stick for measuring distances.
I have to think of space-time as some kind of continuous expandable substance in order for this to make sense to me. Space time is like a rubber substance, which is invisible to us. A grid is put onto this compressible and expandable substance. The grid is the metric g, which defines the distance between objects in the substance. Whenever the substance is deformed by some form of energy or mass - i.e. expanded or compressed - the grid changes. But, this is not apparent to us mere mortals living within the substance, because we take the grid to be non expandable and the metric fixed. But, since the yard stick changes, we measure acceleration and motion. However, objects still travel on geodesics in this grid, i.e. on the shortest path between two locations - in the absence of additional forces.
"It was always there" ... that is a monumental epistemological claim !
Loved it! Very explanatory and theoretical xx
Outstanding! Thank you.
Great video....3 cheers
Great 🙏thanks sir 🙂☀️