These videos are really great. I'm an engineer with great interest in physics - watching Susskind lectures in my free time, reading Feynman, and taking online courses - what I like most about these videos is that they are perfectly clear and while watching them some complicated concepts seem pretty simple and clear. This is something I really appreciate - being able to pass on knowledge in such a way - so to sum up, thank you and keep up the good work!
That's a lovely comment! It's really great that people keep on learning even after engaging in a professional career that doesn't directly require them to keep doing so.
I absolutely LOVE your channel. Being able to understand some cosmology, astrophysics, quantum mechanics, relativity, etc. with at least the basic math behind them is GREAT. I've watched about 20 or so of your videos and I just can't get enough. Unfortunately, I'm a bit too old (35) to become a physicist, but I enjoy your channel immensely. Thanks!
Thanks. Yes you are right. The example is a simplistic to give a general impression of how it works. And of course the photon must always travel only at the speed of light as you say.
Thank you!! I've been struggling to understand dark matter for a while now, and thanks to this video, I've finally understood it 2 days before my A2 exam! Many thanks :)
Thank you so much! You are advancing humanity with your giving of education. Thank you a million times over. If there is anything I can do to help you, please let me know.
I am hooked. I will be good like him one day. Chapeau Professor. It is good good ... it is crazy, I can visualize his explanations. You pointed me out to that DM. Thank you Prof.
Is there a video where the "Shell theorem" or "Newton's theorem" is derived? Many thanks for all these lessons, they are very inspirational and helpful.
Well done. To reduce my typing time and reduce your reading time, everything you do and have done is excellent up until the time I can prove beyond a doubt, via a post, that you have blundered in a magnificent way.
Yes it does and it can't therefore accelerate in the sense of going faster or slower than the speed of light (unless it goes thro another medium where the speed of light is different). But it can be subject to change in direction which is an acceleration.
The curious thing about space expanding is that it doesn't expand into anything. It just expands. The density of dark matter in the universe suggests it tends to be found where there is also ordinary matter. But the reason for this is unknown since we dont yet know what dark matter consists of.
Certainly true that the velocity inside the Schwarzchild radius will look different, but once you get significantly beyond it (say twice the radius) no reason for the orbital velocities to change.
With a limited understanding I have question on this topic. Could you please reply back? Isn’t the Stars edge of a galaxy is bound gravitational field from other stars? They are more closely packed when compared to solar system, where orbits are less affected by other planets. I always thought arms of galaxy more like ceiling fans blades. They rotate along with other stars and doesn’t have individual orbits. Thus having more or less Same angular rotation with respect to the stars closer to the center. Please point out where my understanding is wrong. Thank you
I think I'm right in saying that this was first detected during a solar eclipse. It was known that there were stars which should have been immediately behind the Sun and therefore not visible during the eclipse. And yet they appeared just slightly to the side of the eclipse. It could be concluded therefore that the light from those stars was being bent as it passed the sun.
What i believe isn't taken enough into account is the increase in density which means increase in gravity which makes the center effectively less viscous. The large scale rotational energy becomes small scale turbulence. Plasma binding, gravitational densification
What if the expansion of the universe actually slowed down photons. Be that as it may, ever so slightly as to be undetectable to our instruments because we would need to measure such speeds throughout enormous distances. A photon slowing down would give it an ever so minuscule mass (hence it can move as a particle & a wave). With so many photons flying around any given Galaxy, wouldn't that account for dark matter? My background is chemE so my math is not that good. But I would love to see someone calculate how much a photon would need to slow down in order for them to account as dark matter (just a a silly hypothesis).
How would you do the calculation of the deviation of light in the classical approach with Newton gravity but not making the simplification that the delta v happens only over a length 2R equal to the diameter of the sun (or other heavy body). You show with GR the angle would double, but what would be the exact scaling?
You'd have to develop the theoretical side of this idea and see if it accorded with the experimental observations. I guess people have tried it (tho I've not seen it) to see if quantum fluctuations might account for it.
Thinking further... wouldn't it make more sense to think of the galaxy away from the center as mesh of finite masses where the attraction of neighboring mass is stronger than that of the galactic center? That would explain the uniform velocity and why stars stick around that "shouldn't".
Your comment is very similar to my thoughts on the subject. The spiral arms should be an indicator as to the nature of the physics involved with rotational speeds of galaxies. It seems that it should be possible with our current computing power to set up a model with strings of large mass objects bound gravitationally to each other and to the center of a massive object. It could be viewed similarly as strings of balls on rubber bands attached to a drill head and then spun. If most galaxies were comprised of rings rather than spiral arms one could see a point of concern if the speed of the objects within multiple rings were the same throughout the subject galaxies. We know that the probability of having perfectly consistent rings where the gravitational effects between all objects within the rings are consistent would be absurdly low. I find the lack of intuition on this matter by so many individuals a little disturbing. In any of the videos similar to this one there is no real accountancy for the gravitational effects between all objects of mass which we know exists.
My thoughts exactly. I did a spreadsheet today assuming central black hole region is one third of total mass, but the rest is evenly spread, and the net inwards pull on a star of any outer orbit is pretty flat. The stars is further out orbits cancel out gravity of some in inner orbits.
Triangle for determining alpha, does it mean the outcoming light speed is greater than C (speed of light supposed to be constant)? Or its energy increases (blueshift)?
Is there a case of a single galaxy observed in which the rotation curve and the gravitational lensing arrive at the same or similar values for the galaxy's mass?
Another possible explanation - what if we measure speeds incorrectly? What if there is a problem with how we interpret doppler effect - i.e. the photons coming to us over long distances are red shifting not because of negative acceleration but because of say photons getting "tired" when flying through matter / space / ..., among other explanations
I haven't considered it before, correct me if I am wrong: the parallel universe explanation of dark matter implies that gravity interacts in a space of a higher dimension than 4-space. So, does this assumption fall naturally from General Relativity or is this an artefact of the dark matter explanation?
noob question, but shouldn't the center of the galaxy be moving slower through time due to having more gravity and velocity than the outside arms? the center should be younger than the outer, right? Thus it would appear to spin like a record
There are a couple of alternative gravity hypotheses, such as MOG (STVG) and MOND. STVG in particular apparently explains things like galactic motion well. What I like about it is that there's no need to invoke dark matter and energy which so far have poor explanations.
"Yes it does and it can't therefore accelerate in the sense of going faster or slower than the speed of light (unless it goes thro another medium where the speed of light is different). But it can be subject to change in direction which is an acceleration." I understand that and suggest something outside the box: If speed of light can go faster than C through "another medium", then I'm thinking perhaps a planar wave front of light could also be brought into classical rotation (spin) by a binding energy that gradually tends toward entropy as spinning wave particles interact and impart their spin on others (a bit of tug of war). Thus time (spin) slows down and rotating waves spread away from each other. Thus there is no center of the expansion. I suspect the binding energy relates to the perceived dark energy. The halos of dark matter might also be another aspect of that. Of course this reverts back to pre-relativistic physics and explains relativity in an alternate classically rotating wave mechanics perspective. I don't see a problem with that. One can think of it as just another perspective. Bill Christie
Yes exactIy! I've been studying the wave structure of matter and our universe now for at least five years.. . .There is only two combinations of these spherical sine-wave's they have opposite vectors, and spin forming the positron input+0/1-output electron. Antimatter is relative to every observable radius of infinity solves infinity problem. The negative sine-wave's strength of the gravitational field, is inversely proportional to the square of the distance from the source of the light sphere.
My question concerns, I believe, a rather technical issue. How does one know what is the size of the alpha angle (of divergence)? In other words - how do we know what was the initial photon's trajectory? Thank you in advance.
With the second hypothesis..that neutrinos have miniscule mass,machines which could detect it would be the equivalent of creating the LIGO machines which can detect miniscule gravitional waves.
Could you please arrange in videos in order . I would like to go through them.in chronological order. Was a science student 35 years earlier. Time to revisit . I find your videos upto mark. Tks for your efforts.
What would happen if you assume the inertial frame of the galaxy was rotating so that kepler curve illustrates the rotation relative to the rotating inertial frame?
Is there any reason to assume that the dark matter is a single thing? Perhaps a combination of the hypotheses you mention is the solution? Or some other phenomenon that provides the missing gravity.
since we don't know what dark matter is there is no reason to suppose that it is a single entity. Some people think that it can be accounted for by supersymmetry, which requires more fundamental particles but much heavier.
Can u pls give me the mathmatical expression or derivation of the graph wich is actually obserbe that velocity is constant throughout the galxy because i m not able to findout it how scientists concluded that it must be constant thre must be some calculation which is contradicting neutonian eqn....
When I did physics A-level (a long time ago!) I always found mention of a centripetal force very confusing. There is after all only one real force on the Earth; the gravitational pull of the sun. Newton's 2nd law equates this force to mass * acceleration and this acceleration can be calculated to be v**2/r, a purely mathematical property of moving in circles - nothing whatever to do with forces or indeed physics. Trying to pretend that there is some extra force seems to me to be distinctly misleading.
i think it's just a mistake in the law of gravitation as you said firstly ... because in electric forces they found r^2 is not accurate but it's r^2+x where x approaches(3*10^-16) ... and i think the electric and gravitational forces have the same law because they are the same force indeed , but we cannot figure out what this force is
13:40 ~ 16:50 : Shouldn't delta v be considered more precisely as the curve integral of the y-component of the gravitational force over the photon instead of simply a constant over the distance 2R? This would for sure yield a greater angle, maybe not exactly double but for sure bigger than 2MG/Rc² while still using Newtonian mechanics, which would theoretically make it more precise.
I think the acceleration only refer to the delta v or 'sideways' acceleration it is subjected to by the gravitational pull. The speed of c of course remains constant.
I have 2 questions: 1 - As I understood the big key here is the comparison between the mass of a star and the mass of the galaxy (using the same formula - alpha=4MG/Rc^2). But the galaxy it's different from a star, cause it does have spaces between objects and the star has isotropical mass distribution. Can it be equivalent (just because we consider the mass within)? 2 - Can the law for the galaxy be different from the one that we know (Newtonian Mechanics -> v prop to r^(-1/2) )? Thanks
João Sousa The answer to your questions is explained by "Gauss's Law" check it out. That law is in electricity but same concept holds here. If you were to think about it, you would say F is not simply equal to G.M.m/r^2 because we don't have point forces in here, instead you have many stars, every star attracts you to a different direction, so you should count all the forces of all the stars in the galaxy then you have to do vector analysis and integration then you get another law for the system but Gauss's Law tells you that after doing all that hard stuff you're gonna get the same answer, so you have to use the original law where M is the mass enclosed without any further to do.
How is it that a massless particle is effected by gravity? I don't get how a photon and gravity can interact. To calculate how much gravity effects an object you need the mass of M and m, correct? So, in the case of a photon m would equal 0, right?
That makes a lot more sense. Gravity and photons aren't acting on each other, gravity just distorts the space that the photon travels through. In the case of a black hole spacetime beyond the event horizon only points inward. The photon's only path is deeper within the black hole. Does that mean gravity really isnt a force at all? Its just a property of mass. Would it be possible then to distort space time without mass? Makes me think of the possibilities of what dark matter could be.
According to this, in order to achieve the uniform mass distribution necessary to maintain (and explain) uniform rotational V irrespective of R, dark matter would have to be distributed throughout the galaxy in inverse ratio from zero at the galactic center to progressively more as the orbital distance from the center increases. And which would mean that at some (varying) distance, the factors would be in perfect equilibrium Which should petty much kill that theory unless all of intergalactic space is filled with progressively more or less dark matter as its proximity to observable matter increases or decreases. How much do magnetic fields influence spiral arm formation and is there such a thing as, "magnetic drag." How would that affect the velocity of a star v. the velocity of the arm its being swept along in. Do you think?
Wow. and this is A-level? Damn. I took A-level physics in 1989 and it was hard enough without any of this cosmology stuff. I definitely need a refresher or better yet an update. I salute the kids taking it, but hey they have youtube to help them. In may day not a single computer in sight. Ha ha ha. We used log tables back then to do our calculations. I wonder if they still use them or study them today. But A-level physics was worth the effort. I stood on its shoulders to go all the way to a PhD in engineering in the United States. Good stuff.
gwho oh yeah. great stuff. very informative, and very rigorous. I have been watching the videos and re-educating myself. good stuff. I will be watching more.
gwho ha ha ha ha. wow. lucky bastards. ha ha ha ha. interestingly enough, when I was using log tables, my dad used to say "...you guys are lucky, in my time we used slide rule..." I guess a future generation will say "...you idiots, you only got use computers?..." I guess progress marches on.
Surely the clustering of the stars in the arms of the galaxy has a large effect on the velocity for the outer stars. When compared to a galaxy which does not have spiral arm clustering, we must logically and mathematically expect is much different velocity ( all other issues being compatible)
Sir, in the vector diagram part, doesn't that mean that the photon's speed would exceed the speed of light!? As the hypotenuse represents the photon's speed. Another question, concerning the gravitational lensing proof, at first you removed the small (m) with the other one in the other side..isn't photon's mass equals zero, which would make few mathematical problems. Thanks a lot in advance, you have no idea how your work is useful and how it brighten our minds :)
in quantum electrodynamics you talk about mass being "borrowed out of nothing" but for a very brief moment, what if there is many of these borrowings happening constantly, couldn't that "borrowed mass" account for the "dark matter" ?
23:33 ooh 🤔😔 Hot Dark matter theory . why didn't you Explained that Little bit !!!! can Relativistic mass of an object, effect on its mass & gravity ??????
These videos are really great. I'm an engineer with great interest in physics - watching Susskind lectures in my free time, reading Feynman, and taking online courses - what I like most about these videos is that they are perfectly clear and while watching them some complicated concepts seem pretty simple and clear. This is something I really appreciate - being able to pass on knowledge in such a way - so to sum up, thank you and keep up the good work!
thats a comment i would write….cheers
That's a lovely comment! It's really great that people keep on learning even after engaging in a professional career that doesn't directly require them to keep doing so.
In vector terms you can have an acceleration without a change in speed. A change in direction represents an acceleration.
30 minutes of equation > 10 hours of documentary
@@ansems3136 I'm probably late but one answer: library genesis
I absolutely LOVE your channel. Being able to understand some cosmology, astrophysics, quantum mechanics, relativity, etc. with at least the basic math behind them is GREAT. I've watched about 20 or so of your videos and I just can't get enough. Unfortunately, I'm a bit too old (35) to become a physicist, but I enjoy your channel immensely. Thanks!
I suspect I was simply drawing a galaxy representation without thinking too much about which way the arms should spiral.
It goes the opposite direction in the southern sky.
Well done. Inspirational. Thank you.
What a lovely speaking voice. I think the microphone set up here is fantastic! Well done!
Thanks. Yes you are right. The example is a simplistic to give a general impression of how it works. And of course the photon must always travel only at the speed of light as you say.
Amazing set of videos, i will rtn to digest these, thank you for sharing!
Thank you!! I've been struggling to understand dark matter for a while now, and thanks to this video, I've finally understood it 2 days before my A2 exam! Many thanks :)
Thanks. I hope the exam went well.
Thank you so much! You are advancing humanity with your giving of education.
Thank you a million times over. If there is anything I can do to help you, please let me know.
I am hooked. I will be good like him one day. Chapeau Professor. It is good good ... it is crazy, I can visualize his explanations. You pointed me out to that DM. Thank you Prof.
same feeling here!!!
Is there a video where the "Shell theorem" or "Newton's theorem" is derived? Many thanks for all these lessons, they are very inspirational and helpful.
Well done. To reduce my typing time and reduce your reading time, everything you do and have done is excellent up until the time I can prove beyond a doubt, via a post, that you have blundered in a magnificent way.
The acceleration refers to a change in direction not a change in speed.
So greatly explained...
Yes it does and it can't therefore accelerate in the sense of going faster or slower than the speed of light (unless it goes thro another medium where the speed of light is different). But it can be subject to change in direction which is an acceleration.
I'd love to see the calculations for how we determine dark matter must be in a halo around a galaxy.
Very good! Congratulations for this video. Thank you teacher...Greetings from Brazil!
Viva, mais um buscando esse tipo de coisa!
The curious thing about space expanding is that it doesn't expand into anything. It just expands. The density of dark matter in the universe suggests it tends to be found where there is also ordinary matter. But the reason for this is unknown since we dont yet know what dark matter consists of.
awesome lecture! - learned about Dark matter more than by listening to some ignorant people throughout my life...
Still absolutely brilliant! Many kind thanks!
aaaaaaaaand subscribed.
Certainly true that the velocity inside the Schwarzchild radius will look different, but once you get significantly beyond it (say twice the radius) no reason for the orbital velocities to change.
Man, that was an awesome video. You really explained it very well.
Thank You Very Much
I am eager to your video on dark energy....................
With a limited understanding I have question on this topic. Could you please reply back?
Isn’t the Stars edge of a galaxy is bound gravitational field from other stars? They are more closely packed when compared to solar system, where orbits are less affected by other planets. I always thought arms of galaxy more like ceiling fans blades. They rotate along with other stars and doesn’t have individual orbits. Thus having more or less Same angular rotation with respect to the stars closer to the center.
Please point out where my understanding is wrong.
Thank you
So clear explanation, thanks.
I think I'm right in saying that this was first detected during a solar eclipse. It was known that there were stars which should have been immediately behind the Sun and therefore not visible during the eclipse. And yet they appeared just slightly to the side of the eclipse. It could be concluded therefore that the light from those stars was being bent as it passed the sun.
Your voice makes me feel like I'm having courses from C3PO😂! Love it!!
Fantastic ... again!
How at 16:16 we got the value of alpha , is it a rule of vector calculation that I am currently unaware of?
tan(alpha)=alpha for very small alpha.
Your video was an enjoyable experience.
At time 16, there is a velocity vector diagram, where one of the velocities is greater than the speed of light?
What i believe isn't taken enough into account is the increase in density which means increase in gravity which makes the center effectively less viscous. The large scale rotational energy becomes small scale turbulence. Plasma binding, gravitational densification
Would be a good idea talk about Inflation, Slow Roll and etc.
Btw nice videos i'm just loving.
hey I love all ur vids could u go into more detail about the meaning of the symbols and why certain equations equal others thnks
How would you calculate this for eclipses (RE: MV^2/r and V^2 proportional 1/r) ?
May I know what are those principles of general relativity at 17:10 that led to doubling alpha?
good question
do you know something i dont....acording to the question...lol
Your videos are just awesome!
Interesting well thought-out explanation ...
I love your lectures too much especially when you ( correct your mistakes) thanks very much sir 😚🌹❤️👍
What if the expansion of the universe actually slowed down photons. Be that as it may, ever so slightly as to be undetectable to our instruments because we would need to measure such speeds throughout enormous distances.
A photon slowing down would give it an ever so minuscule mass (hence it can move as a particle & a wave).
With so many photons flying around any given Galaxy, wouldn't that account for dark matter?
My background is chemE so my math is not that good. But I would love to see someone calculate how much a photon would need to slow down in order for them to account as dark matter (just a a silly hypothesis).
How would you do the calculation of the deviation of light in the classical approach with Newton gravity but not making the simplification that the delta v happens only over a length 2R equal to the diameter of the sun (or other heavy body). You show with GR the angle would double, but what would be the exact scaling?
BSc (physics) and PhD (nuclear physics)
DrPhysicsA FRS soon
Already CBE
You could well be right. Who knows what might be revealed once Gravity/General Relativity and Quantum Theory are fully integrated.
I stand to be corrected but I think most of the multiverse/ parallel universe ideas now stem from string theory with its multi dimension requirement.
You'd have to develop the theoretical side of this idea and see if it accorded with the experimental observations. I guess people have tried it (tho I've not seen it) to see if quantum fluctuations might account for it.
6:00 sir you are really a great man
great video as always!
its so awesome understanding all of this! Thanks
to my physics class!
Excellent. Thank you.
Thinking further... wouldn't it make more sense to think of the galaxy away from the center as mesh of finite masses where the attraction of neighboring mass is stronger than that of the galactic center? That would explain the uniform velocity and why stars stick around that "shouldn't".
Your comment is very similar to my thoughts on the subject. The spiral arms should be an indicator as to the nature of the physics involved with rotational speeds of galaxies. It seems that it should be possible with our current computing power to set up a model with strings of large mass objects bound gravitationally to each other and to the center of a massive object. It could be viewed similarly as strings of balls on rubber bands attached to a drill head and then spun. If most galaxies were comprised of rings rather than spiral arms one could see a point of concern if the speed of the objects within multiple rings were the same throughout the subject galaxies. We know that the probability of having perfectly consistent rings where the gravitational effects between all objects within the rings are consistent would be absurdly low.
I find the lack of intuition on this matter by so many individuals a little disturbing. In any of the videos similar to this one there is no real accountancy for the gravitational effects between all objects of mass which we know exists.
My thoughts exactly. I did a spreadsheet today assuming central black hole region is one third of total mass, but the rest is evenly spread, and the net inwards pull on a star of any outer orbit is pretty flat. The stars is further out orbits cancel out gravity of some in inner orbits.
Can''t wait to watch 'Black Holes-An Introduction'
Triangle for determining alpha, does it mean the outcoming light speed is greater than C (speed of light supposed to be constant)? Or its energy increases (blueshift)?
Fabulous. Thank you.
Is there a case of a single galaxy observed in which the rotation curve and the gravitational lensing arrive at the same or similar values for the galaxy's mass?
Another possible explanation - what if we measure speeds incorrectly? What if there is a problem with how we interpret doppler effect - i.e. the photons coming to us over long distances are red shifting not because of negative acceleration but because of say photons getting "tired" when flying through matter / space / ..., among other explanations
I haven't considered it before, correct me if I am wrong: the parallel universe explanation of dark matter implies that gravity interacts in a space of a higher dimension than 4-space. So, does this assumption fall naturally from General Relativity or is this an artefact of the dark matter explanation?
noob question, but shouldn't the center of the galaxy be moving slower through time due to having more gravity and velocity than the outside arms? the center should be younger than the outer, right? Thus it would appear to spin like a record
There are a couple of alternative gravity hypotheses, such as MOG (STVG) and MOND. STVG in particular apparently explains things like galactic motion well. What I like about it is that there's no need to invoke dark matter and energy which so far have poor explanations.
You sir, are awesome
"Yes it does and it can't therefore accelerate in the sense of going faster or slower than the speed of light (unless it goes thro another medium where the speed of light is different). But it can be subject to change in direction which is an acceleration."
I understand that and suggest something outside the box:
If speed of light can go faster than C through "another medium", then I'm thinking perhaps a planar wave front of light could also be brought into classical rotation (spin) by a binding energy that gradually tends toward entropy as spinning wave particles interact and impart their spin on others (a bit of tug of war). Thus time (spin) slows down and rotating waves spread away from each other. Thus there is no center of the expansion. I suspect the binding energy relates to the perceived dark energy. The halos of dark matter might also be another aspect of that.
Of course this reverts back to pre-relativistic physics and explains relativity in an alternate classically rotating wave mechanics perspective. I don't see a problem with that. One can think of it as just another perspective.
Bill Christie
by the way...great video!
Fascinating!
Yes exactIy!
I've been studying the wave structure of matter and our universe now for at least five years.. . .There is only two combinations of these spherical sine-wave's they have opposite vectors, and spin forming the positron input+0/1-output electron.
Antimatter is relative to every observable radius of infinity solves infinity problem.
The negative sine-wave's strength of the gravitational field, is inversely proportional to the square of the distance from the source of the light sphere.
My question concerns, I believe, a rather technical issue. How does one know what is the size of the alpha angle (of divergence)? In other words - how do we know what was the initial photon's trajectory? Thank you in advance.
With the second hypothesis..that neutrinos have miniscule mass,machines which could detect it would be the equivalent of creating the LIGO machines which can detect miniscule gravitional waves.
how heavy and wide milky way should be if we skip dark matter consept ? i read milky way is much wider than we see.. even 500 AU
Could you please arrange in videos in order . I would like to go through them.in chronological order. Was a science student 35 years earlier. Time to revisit . I find your videos upto mark. Tks for your efforts.
S Mishra thanks. within each playlist the videos are in the order I would recommend watching.
What would happen if you assume the inertial frame of the galaxy was rotating so that kepler curve illustrates the rotation relative to the rotating inertial frame?
YOU are ROCK sir.....thanks for ur videos.........
Is there any reason to assume that the dark matter is a single thing? Perhaps a combination of the hypotheses you mention is the solution? Or some other phenomenon that provides the missing gravity.
since we don't know what dark matter is there is no reason to suppose that it is a single entity. Some people think that it can be accounted for by supersymmetry, which requires more fundamental particles but much heavier.
I love your channel and all your videos! I'm only a grade 10 student, but this extremely fascinating.
Can u pls give me the mathmatical expression or derivation of the graph wich is actually obserbe that velocity is constant throughout the galxy because i m not able to findout it how scientists concluded that it must be constant thre must be some calculation which is contradicting neutonian eqn....
Thanks alot dr .may you explain what m v^2 represent
When I did physics A-level (a long time ago!) I always found mention of a centripetal force very confusing. There is after all only one real force on the Earth; the gravitational pull of the sun. Newton's 2nd law equates this force to mass * acceleration and this acceleration can be calculated to be v**2/r, a purely mathematical property of moving in circles - nothing whatever to do with forces or indeed physics. Trying to pretend that there is some extra force seems to me to be distinctly misleading.
i think it's just a mistake in the law of gravitation as you said firstly ... because in electric forces they found r^2 is not accurate but it's r^2+x where x approaches(3*10^-16) ... and i think the electric and gravitational forces have the same law because they are the same force indeed , but we cannot figure out what this force is
13:40 ~ 16:50 : Shouldn't delta v be considered more precisely as the curve integral of the y-component of the gravitational force over the photon instead of simply a constant over the distance 2R? This would for sure yield a greater angle, maybe not exactly double but for sure bigger than 2MG/Rc² while still using Newtonian mechanics, which would theoretically make it more precise.
I think the acceleration only refer to the delta v or 'sideways' acceleration it is subjected to by the gravitational pull. The speed of c of course remains constant.
Great video. But why do galaxies spint to begin with? How did everything end up with angular velocity?
good question...but i think it is as simple as an ice skater rotating pulling arms(mass) closer to the body
Can I get the proof of 4GM/RC^2 somewhere??
I have 2 questions:
1 - As I understood the big key here is the comparison between the mass of a star and the mass of the galaxy (using the same formula - alpha=4MG/Rc^2). But the galaxy it's different from a star, cause it does have spaces between objects and the star has isotropical mass distribution. Can it be equivalent (just because we consider the mass within)?
2 - Can the law for the galaxy be different from the one that we know (Newtonian Mechanics -> v prop to r^(-1/2) )?
Thanks
João Sousa The answer to your questions is explained by "Gauss's Law" check it out. That law is in electricity but same concept holds here. If you were to think about it, you would say F is not simply equal to G.M.m/r^2 because we don't have point forces in here, instead you have many stars, every star attracts you to a different direction, so you should count all the forces of all the stars in the galaxy then you have to do vector analysis and integration then you get another law for the system but Gauss's Law tells you that after doing all that hard stuff you're gonna get the same answer, so you have to use the original law where M is the mass enclosed without any further to do.
Can you please make a video on Kepler's Law
These are covered in my video on Gravitational Fields - A Level Physics.
I am here after 10 years. WOO HOO Anniversary !
DrPhysicsA do you mean angular velocity or just velocity?
That was a great video
How is it that a massless particle is effected by gravity? I don't get how a photon and gravity can interact. To calculate how much gravity effects an object you need the mass of M and m, correct? So, in the case of a photon m would equal 0, right?
That makes a lot more sense. Gravity and photons aren't acting on each other, gravity just distorts the space that the photon travels through. In the case of a black hole spacetime beyond the event horizon only points inward. The photon's only path is deeper within the black hole. Does that mean gravity really isnt a force at all? Its just a property of mass. Would it be possible then to distort space time without mass? Makes me think of the possibilities of what dark matter could be.
According to this, in order to achieve the uniform mass distribution necessary to maintain (and explain) uniform rotational V irrespective of R, dark matter would have to be distributed throughout the galaxy in inverse ratio from zero at the galactic center to progressively more as the orbital distance from the center increases. And which would mean that at some (varying) distance, the factors would be in perfect equilibrium Which should petty much kill that theory unless all of intergalactic space is filled with progressively more or less dark matter as its proximity to observable matter increases or decreases. How much do magnetic fields influence spiral arm formation and is there such a thing as, "magnetic drag." How would that affect the velocity of a star v. the velocity of the arm its being swept along in. Do you think?
Wow. and this is A-level? Damn. I took A-level physics in 1989 and it was hard enough without any of this cosmology stuff. I definitely need a refresher or better yet an update. I salute the kids taking it, but hey they have youtube to help them. In may day not a single computer in sight. Ha ha ha. We used log tables back then to do our calculations. I wonder if they still use them or study them today.
But A-level physics was worth the effort. I stood on its shoulders to go all the way to a PhD in engineering in the United States. Good stuff.
lol. A small price to pay for such exquisite new knowledge of the universe, wouldn't you say? =]
No log tables, no trig tables. I started university a few years after the turn of the millennium.
gwho oh yeah. great stuff. very informative, and very rigorous. I have been watching the videos and re-educating myself. good stuff. I will be watching more.
gwho ha ha ha ha. wow. lucky bastards. ha ha ha ha. interestingly enough, when I was using log tables, my dad used to say "...you guys are lucky, in my time we used slide rule..." I guess a future generation will say "...you idiots, you only got use computers?..." I guess progress marches on.
Hello! We found the equation of the paralell Universe you mention!
Absolute Madlad
Surely the clustering of the stars in the arms of the galaxy has a large effect on the velocity for the outer stars.
When compared to a galaxy which does not have spiral arm clustering, we must logically and mathematically expect is much different velocity ( all other issues being compatible)
You are a legend, what is your field of study?
Q.1) If we are at end of the space and we produced energy then there will formation of space ?
Q.2) Is dark matter found more towards Gravatiy ?
A little confused, why would the velocity decrease inside the star, object would be more likely to fall in?
The "governor" like properties of the supermassive black hole Saggittarius A. The event horizon acts like a buffer at times.
it was a helpful vedio....but i would be really thankful if you made a vedio describing tackyons, bradyons or bradyonic matter
Sir, in the vector diagram part, doesn't that mean that the photon's speed would exceed the speed of light!? As the hypotenuse represents the photon's speed.
Another question, concerning the gravitational lensing proof, at first you removed the small (m) with the other one in the other side..isn't photon's mass equals zero, which would make few mathematical problems.
Thanks a lot in advance, you have no idea how your work is useful and how it brighten our minds :)
in quantum electrodynamics you talk about mass being "borrowed out of nothing" but for a very brief moment, what if there is many of these borrowings happening constantly, couldn't that "borrowed mass" account for the "dark matter" ?
great explanation even for a class 10 child like me
23:33 ooh 🤔😔 Hot Dark matter theory . why didn't you Explained that Little bit !!!! can Relativistic mass of an object, effect on its mass & gravity ??????