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!
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.
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.
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.
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
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 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.
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.
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.
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.
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.
I am not a physicist, I am a programmer who likes physics but I think the most logical conclusion is MOND I don't understand why the scientific community favors the DM. maybe because DM gets more funding? I think that we calculate the mass of all solar objects wrong because we don't understand correctly how particles are created. What I found most fascinating is Quantum grvity theory. proposing that everything is an expression of positive and negative pressure.
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).
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.
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)
"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
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
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.
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.
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.
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.
Multiple infinities is a big problem, if you want to explain infinity you ask a mathematician not a physicist . As we know there are multiple infinities, I think that multiple infinities are all the same but different language . If there are 2 infinities there is a border, infinity can't have a border because it has an end
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
George Nipius Dark Matter No wonder dark matter is so hard to find, there isn’t any. The explanation is comparatively simple. You will have to work in reverse. First recognize the galaxies we see are in a stable condition. They have existed that way since their beginning, with small changes. What has caused the attention is the progressive increase of speed of the bodies in orbit, as the orbits go from center to perimeter. It is not what the astronomers have calculated. The first part of the problem is the speed of the orbital bodies. Which can be calculated knowing the strength of gravity of the masses within the orbit of that body. This gives a curve of speed vs distance that drops off with the square of the distance. (example the speed differences of the planets of the solar system) This is only part of the forces that explain the speed of the bodies in orbits. Consider the galaxy, with an infinite number of orbits, each corresponding to a isogravity line. A galaxy is not really homogenous since it consists of very large clumps of matter. (stars, black holes, pairs of stars asteroids) The big question has been that the orbital speed vs increases in radius, of the masses in the galaxy are. approaching a straight line, that is it is approaching constant speed, as the orbits progress from the center to the perimeter. Extra forces are required to supply the extra speed. With just the static gravity of masses within their orbits, the speed of bodies inward of the orbit will be faster than the bodies outward of the orbit. This speed difference is the source of forces, that produce the extra necessary speeds. As two masses(bodies) pass each other in adjacent orbits they produce an attractive force on each other, speeding up one and slowing up the other. Resulting in an increase of speed of outward orbital masses. Over time billions of these passes will supply more than enough forces, since they are all additive, to cause the speed vs radius curve to approach a straight line (constant speed). Note the speed difference of the outer orbital masses are self limiting since no additional forces are supplied when the two passing masses are traveling at same speed. There has to be some other force acting for them to go faster. Remember the faster outer orbital speeds has existed since the origin of that galaxy and only a limited amount of forces is necessary to maintain the condition if you are questioning if enough forces can be supplied. (The energy that supply’s the extra speed to the outer orbits are come from the kinetic energy of the rotating galaxy.) A documentary on the effect of moonlets in Saturn’s rings can supply an extra enlightening view of the transfer of forces of passing bodies. George Nipius
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" ?
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.
11.35 " Do not have enough cetripedal force to maintain them in orbit." In fact they have too much centripedal force and should fly off in to space; they do not have enough gravitational " force" to maintain their orbit.
Love it. Sent to this vid by a friend and fellow CGI artist as we debate the proper way to simulate a spiral galaxy (and figure out why mine was such a clusterfuck...) Keep up the greatness. CGI Dark Matter is a real bitch.
The problem of modern physics is they're trying to explain everything with particle physics and the physics is being cornered more and more to the dead end. To escape the dead end, they invent or design another imaginary particle in vain instead of trying to revise their way to approach to the problem. I agree to that idea that the interaction between mass and space must be explained with quantum mechanics. But that doesn't mean gravity is the QM phenomena. That's because gravity is not a force. Gravity is just a joint effect of the expansion of the Universe and the curvature of spacetime. Details are given below. Alternative Explanation of Dark Matter and Dark Energy - Newly proposed model of Universe can explain both of Dark Matter and Dark Energy Einstein’s theory of General Relativity states that spacetime is curved by the presence of mass. This curvature influences the motion other objects with mass and gives rise to gravitation. Thus, gravity is a result of geometric features in spacetime. However, we also observe gravitational effects - curvature of spacetime - in areas without any detectable mass. This has given rise to the concept of dark matter, which is matter that does not interact in any detectable way with normal matter, except through gravity. So, there is some large quantity of dark matter scattered throughout the universe, which curves spacetime and causes gravitational effects just like normal matter, but we cannot see or detect it with any known method. An alternative theory to the identity of dark matter is proposed - it is not matter at all, but rather an intrinsic curvature of spacetime. In other words, spacetime is not naturally flat. Even in the absence of matter, we observe some inherent curvature of spacetime. So, the question is now - why is spacetime naturally curved? Why is it not flat in the absence of mass? The universe is 4-dimensional, with 3 spatial dimensions and one dimension in time. Rather than consider time as a linear dimension, we can consider it as a radial one. Therefore, rather than describing the universe with a Cartesian coordinate system, we describe it with a 4-dimensional spherical coordinate system - 3 angular coordinates, φ1, φ2, φ3, and one radial coordinate in time, t. We live on the 3-dimensional surface of a 4-dimensional bubble which is expanding radially in time. Thus, the Big Bang represents t=0, the beginning of time. The crucial point is that the expansion of the universe is not homogeneous in all directions. The expansion rate at one point on the bubble’s surface may differ slightly from another point near it. The universe is only roughly spherical in 4 dimensions, the same way that the Earth is only roughly spherical in 3 dimensions. The same way we observe local mountains and valleys on the surface of Earth, we observe local “mountains” and “valleys” on the surface of the universe bubble. The inhomogeneity of the expansion of the universe has given rise to natural curvature of spacetime. This natural curvature causes the phenomenon of “dark matter”. “Valleys” in spacetime pull matter in, similarly to the warping of spacetime of massive objects. So “dark matter” is really “valleys” in spacetime that are expanding slower than the regions surrounding it. These valleys tend to pull matter in and create planets, stars, and galaxies - regions of space with higher-than-average densities of mass. Conversely, “mountains” in spacetime will repel matter away, an “anti-gravitational” effect, which gives rise to cosmic voids in space where we observe no matter. Each point on the surface of the universe bubble traces out a time arrow in 4-dimensional space, perpendicular to the surface. These time arrows are not parallel to each other since the universe is not flat. This causes points to have nonzero relative velocity away from each other. It is generally accepted that the universe is expanding faster than observable energy can explain, and this is expansion is believe to be still accelerating. The “missing” energy required to explain these observations has given rise to the theory of dark energy. The time dilation caused by non-parallel time arrows can be proposed as an explanation for dark energy. Alternatively, dark energy is real energy coming from potential energy gradients caused by non-parallel time arrows. As a sanity check, we can calculate the expansion rate of the universe based on the universe bubble model. Since the radius of the universe bubble is expanding at the speed of light in the time direction, it increases at 1 light second per second. Therefore, the “circumference” of the 3-dimensional surface increases by 2π light seconds per second, or about 1.88*10^6 km/s. This expansion is distributed equally across the 3-dimensional surface, so the actual observed expansion rate is proportional to the distance from the observer. At present, the age of the universe is estimated to be 13.8 billion years, so the radius of the universe bubble is 13.8 billion light years, or about 4233 megaparsecs (3.26 million light years to 1 Mpc). Thus, we can calculate the expansion rate of the universe, per megaparsec from the observer, as: Expansion rate = ((d(circumference))/dt)/radiusofuniverse=(1.88*〖10〗^6 km⁄s)/(2π*4233Mpc)=(1.88*〖10〗^6 km⁄s)/26598Mpc=70.82(km⁄s)/Mpc The popularly accepted empirical expansion rate is 73.5 +/- 2.5 km/s/Mpc, so our calculated value is close. There may be some additional source of expansion (or observed red shift) to make up for the discrepancy. For example, if two adjacent points have some gravitational gradient due to non-parallel time arrows, then light passing through these points will be red-shifted. - Cited from www.academia.edu/82481487/Title_Alternative_Explanation_of_Dark_Matter_and_Dark_Energy
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....
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
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 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
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.
Thought Experiment: Imagine at an amusement park.. we ride a carousel.. that large rotating disk spinning parallel to the ground.. now of course if we were sitting on one of the plastic horses while it was spinning and decide to get off the horse and see if we can stand on the edge of the disk.. we would probably get thrown off.. but now suppose that instead of being a person on the disk.. that we are a particular atom of that disk itself.. even the furthest atom experiences the same velocity as any other atom.. but none of the atoms are thrown off the disk (the galaxy).. perhaps the atoms have a vague awareness of being part of a larger object known as a disk.. and suppose there was one genius atom that realized that the atoms at the edge of the disk must be thrown off this strange disk.. unless the atoms invent imperceptible dark atoms.. we being larger and having a better view of things explain this apparent confusion by the electrostatic forces of "metallic bonding" or intermolecular forces.. so.. isn't it at least possible that there is no need to invent a magical dark matter to explain how distant stars remain within a galaxy or how the velocity of stars rotating around the galaxy is constant.. but that even from lightyears away the matter within the galaxy holds itself together with some kind of "star bonding" (spooky action at a distance) mediated by some force F? without further evidence or observations to go off on.. wouldn't this explanation be just as plausible as a dark matter explanation?
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!
So greatly explained...
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.
awesome lecture! - learned about Dark matter more than by listening to some ignorant people throughout my life...
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!
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!!!
I'd love to see the calculations for how we determine dark matter must be in a halo around a galaxy.
Fantastic ... again!
Very good! Congratulations for this video. Thank you teacher...Greetings from Brazil!
Viva, mais um buscando esse tipo de coisa!
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.
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....................
aaaaaaaaand subscribed.
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
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 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.
So clear explanation, thanks.
The acceleration refers to a change in direction not a change in speed.
Interesting well thought-out explanation ...
great video as always!
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.
Still absolutely brilliant! Many kind 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.
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.
BSc (physics) and PhD (nuclear physics)
DrPhysicsA FRS soon
Already CBE
Can''t wait to watch 'Black Holes-An Introduction'
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
Your voice makes me feel like I'm having courses from C3PO😂! Love it!!
Your videos are just awesome!
I love your lectures too much especially when you ( correct your mistakes) thanks very much sir 😚🌹❤️👍
I am here after 10 years. WOO HOO Anniversary !
Fascinating!
That was a great video
Your video was an enjoyable experience.
Would be a good idea talk about Inflation, Slow Roll and etc.
Btw nice videos i'm just loving.
You sir, are awesome
6:00 sir you are really a great man
great explanation even for a class 10 child like me
You could well be right. Who knows what might be revealed once Gravity/General Relativity and Quantum Theory are fully integrated.
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.
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.
I am not a physicist, I am a programmer who likes physics but I think the most logical conclusion is MOND I don't understand why the scientific community favors the DM. maybe because DM gets more funding? I think that we calculate the mass of all solar objects wrong because we don't understand correctly how particles are created. What I found most fascinating is Quantum grvity theory. proposing that everything is an expression of positive and negative pressure.
In other words: If dark matter were uniformly distributed, it would neither add or detract from the effect of the galactic M.
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).
its so awesome understanding all of this! Thanks
to my physics class!
Fabulous. Thank you.
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.
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)
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.
"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
I love your channel and all your videos! I'm only a grade 10 student, but this extremely fascinating.
Excellent. Thank you.
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
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.
by the way...great video!
there is another explanation but, I'm still working on it...
Well? Let’s hear 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.
At time 16, there is a velocity vector diagram, where one of the velocities is greater than the speed of light?
Hello! We found the equation of the paralell Universe you mention!
YOU are ROCK sir.....thanks for ur videos.........
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.
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.
Absolute Madlad
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.
Multiple infinities is a big problem, if you want to explain infinity you ask a mathematician not a physicist . As we know there are multiple infinities, I think that multiple infinities are all the same but different language . If there are 2 infinities there is a border, infinity can't have a border because it has an end
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
well in 25 minutes a high school student understood nearly everything about 25 percent of universe
im 52...lol
6:08 little thanks
George Nipius
Dark Matter
No wonder dark matter is so hard to find, there isn’t any.
The explanation is comparatively simple.
You will have to work in reverse.
First recognize the galaxies we see are in a stable condition.
They have existed that way since their beginning, with small changes.
What has caused the attention is the progressive increase of speed of the bodies in orbit, as the orbits go from center to perimeter.
It is not what the astronomers have calculated.
The first part of the problem is the speed of the orbital bodies.
Which can be calculated knowing the strength of gravity of the masses within the orbit of that body.
This gives a curve of speed vs distance that drops off with the square of the distance.
(example the speed differences of the planets of the solar system)
This is only part of the forces that explain the speed of the bodies in orbits.
Consider the galaxy, with an infinite number of orbits, each corresponding to a isogravity line.
A galaxy is not really homogenous since it consists of very large clumps of matter.
(stars, black holes, pairs of stars asteroids)
The big question has been that the orbital speed vs increases in radius, of the masses in the galaxy are.
approaching a straight line, that is it is approaching constant speed, as the orbits progress from the center to the perimeter.
Extra forces are required to supply the extra speed.
With just the static gravity of masses within their orbits, the speed of bodies inward of the orbit will be faster than the bodies outward of the orbit.
This speed difference is the source of forces, that produce the extra necessary speeds.
As two masses(bodies) pass each other in adjacent orbits they produce an attractive force on each other, speeding up one and slowing up the other. Resulting in an increase of speed of outward orbital masses. Over time billions of these passes will supply more than enough forces, since they are all additive, to cause the speed vs radius curve to approach a straight line (constant speed).
Note the speed difference of the outer orbital masses are self limiting since no additional forces are supplied when the two passing masses are traveling at same speed. There has to be some other force acting for them to go faster.
Remember the faster outer orbital speeds has existed since the origin of that galaxy and only a limited amount of forces is necessary to maintain the condition if you are questioning if enough forces can be supplied.
(The energy that supply’s the extra speed to the outer orbits are come from the kinetic energy of the rotating galaxy.)
A documentary on the effect of moonlets in Saturn’s rings can supply an extra enlightening view of the transfer of forces of passing bodies. George Nipius
Wow amazing. Upside down capital M by o(the universe) by small m upside down.
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" ?
I love you to the moon and back
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.
11.35 " Do not have enough cetripedal force to maintain them in orbit." In fact they have too much centripedal force and should fly off in to space; they do not have enough gravitational " force" to maintain their orbit.
Love it.
Sent to this vid by a friend and fellow CGI artist as we debate the proper way to simulate a spiral galaxy (and figure out why mine was such a clusterfuck...)
Keep up the greatness. CGI Dark Matter is a real bitch.
Thankyou
Can you please make a video on Kepler's Law
These are covered in my video on Gravitational Fields - A Level Physics.
The problem of modern physics is they're trying to explain everything with particle physics and the physics is being cornered more and more to the dead end. To escape the dead end, they invent or design another imaginary particle in vain instead of trying to revise their way to approach to the problem.
I agree to that idea that the interaction between mass and space must be explained with quantum mechanics.
But that doesn't mean gravity is the QM phenomena.
That's because gravity is not a force.
Gravity is just a joint effect of the expansion of the Universe and the curvature of spacetime.
Details are given below.
Alternative Explanation of Dark Matter and Dark Energy - Newly proposed model of Universe can explain both of Dark Matter and Dark Energy
Einstein’s theory of General Relativity states that spacetime is curved by the presence of mass.
This curvature influences the motion other objects with mass and gives rise to gravitation.
Thus, gravity is a result of geometric features in spacetime.
However, we also observe gravitational effects - curvature of spacetime - in areas without any detectable mass.
This has given rise to the concept of dark matter, which is matter that does not interact in any detectable way with normal matter, except through gravity.
So, there is some large quantity of dark matter scattered throughout the universe, which curves spacetime and causes gravitational effects just like normal matter, but we cannot see or detect it with any known method.
An alternative theory to the identity of dark matter is proposed - it is not matter at all, but rather an intrinsic curvature of spacetime.
In other words, spacetime is not naturally flat. Even in the absence of matter, we observe some inherent curvature of spacetime.
So, the question is now - why is spacetime naturally curved? Why is it not flat in the absence of mass?
The universe is 4-dimensional, with 3 spatial dimensions and one dimension in time.
Rather than consider time as a linear dimension, we can consider it as a radial one.
Therefore, rather than describing the universe with a Cartesian coordinate system, we describe it with a 4-dimensional spherical coordinate system - 3 angular coordinates, φ1, φ2, φ3, and one radial coordinate in time, t.
We live on the 3-dimensional surface of a 4-dimensional bubble which is expanding radially in time.
Thus, the Big Bang represents t=0, the beginning of time.
The crucial point is that the expansion of the universe is not homogeneous in all directions.
The expansion rate at one point on the bubble’s surface may differ slightly from another point near it.
The universe is only roughly spherical in 4 dimensions, the same way that the Earth is only roughly spherical in 3 dimensions.
The same way we observe local mountains and valleys on the surface of Earth, we observe local “mountains” and “valleys” on the surface of the universe bubble.
The inhomogeneity of the expansion of the universe has given rise to natural curvature of spacetime. This natural curvature causes the phenomenon of “dark matter”. “Valleys” in spacetime pull matter in, similarly to the warping of spacetime of massive objects.
So “dark matter” is really “valleys” in spacetime that are expanding slower than the regions surrounding it.
These valleys tend to pull matter in and create planets, stars, and galaxies - regions of space with higher-than-average densities of mass.
Conversely, “mountains” in spacetime will repel matter away, an “anti-gravitational” effect, which gives rise to cosmic voids in space where we observe no matter.
Each point on the surface of the universe bubble traces out a time arrow in 4-dimensional space, perpendicular to the surface.
These time arrows are not parallel to each other since the universe is not flat.
This causes points to have nonzero relative velocity away from each other.
It is generally accepted that the universe is expanding faster than observable energy can explain, and this is expansion is believe to be still accelerating.
The “missing” energy required to explain these observations has given rise to the theory of dark energy.
The time dilation caused by non-parallel time arrows can be proposed as an explanation for dark energy.
Alternatively, dark energy is real energy coming from potential energy gradients caused by non-parallel time arrows.
As a sanity check, we can calculate the expansion rate of the universe based on the universe bubble model.
Since the radius of the universe bubble is expanding at the speed of light in the time direction, it increases at 1 light second per second.
Therefore, the “circumference” of the 3-dimensional surface increases by 2π light seconds per second, or about 1.88*10^6 km/s.
This expansion is distributed equally across the 3-dimensional surface, so the actual observed expansion rate is proportional to the distance from the observer.
At present, the age of the universe is estimated to be 13.8 billion years, so the radius of the universe bubble is 13.8 billion light years, or about 4233 megaparsecs (3.26 million light years to 1 Mpc).
Thus, we can calculate the expansion rate of the universe, per megaparsec from the observer, as:
Expansion rate = ((d(circumference))/dt)/radiusofuniverse=(1.88*〖10〗^6 km⁄s)/(2π*4233Mpc)=(1.88*〖10〗^6 km⁄s)/26598Mpc=70.82(km⁄s)/Mpc
The popularly accepted empirical expansion rate is 73.5 +/- 2.5 km/s/Mpc, so our calculated value is close.
There may be some additional source of expansion (or observed red shift) to make up for the discrepancy. For example, if two adjacent points have some gravitational gradient due to non-parallel time arrows, then light passing through these points will be red-shifted.
- Cited from www.academia.edu/82481487/Title_Alternative_Explanation_of_Dark_Matter_and_Dark_Energy
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....
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
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
really good!
Well explained, the math made my head hurt. But I got the concept.
How would you calculate this for eclipses (RE: MV^2/r and V^2 proportional 1/r) ?
it means that the physical constants assumed to be uniform and consistent throughout the universe are actually not constant anywhere in the universe
Except for where we measure them, yes? Now that would be a coincidence.
am I the only one that s trying to roll up to see what is said before?
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 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
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 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
Thought Experiment: Imagine at an amusement park.. we ride a carousel.. that large rotating disk spinning parallel to the ground.. now of course if we were sitting on one of the plastic horses while it was spinning and decide to get off the horse and see if we can stand on the edge of the disk.. we would probably get thrown off.. but now suppose that instead of being a person on the disk.. that we are a particular atom of that disk itself.. even the furthest atom experiences the same velocity as any other atom.. but none of the atoms are thrown off the disk (the galaxy).. perhaps the atoms have a vague awareness of being part of a larger object known as a disk.. and suppose there was one genius atom that realized that the atoms at the edge of the disk must be thrown off this strange disk.. unless the atoms invent imperceptible dark atoms.. we being larger and having a better view of things explain this apparent confusion by the electrostatic forces of "metallic bonding" or intermolecular forces.. so.. isn't it at least possible that there is no need to invent a magical dark matter to explain how distant stars remain within a galaxy or how the velocity of stars rotating around the galaxy is constant.. but that even from lightyears away the matter within the galaxy holds itself together with some kind of "star bonding" (spooky action at a distance) mediated by some force F? without further evidence or observations to go off on.. wouldn't this explanation be just as plausible as a dark matter explanation?
The photon accelerates? What?
it was a helpful vedio....but i would be really thankful if you made a vedio describing tackyons, bradyons or bradyonic matter