I Never Understood How Gravity Bends Light Even Without Mass… Until Now!

[@Mahesh_Shenoy]

Head to squarespace.com/floatheadphysics to save 10% off your first purchase of a website or domain using code FLOATHEADPHYSICS PS: There are quite a few comments about how gravity doesn’t bend light, but it bends spacetime and light just follows it. Well, If we didn’t know this already, how would we go from special relativity + Newtonian gravity to rediscover space time curvature (and in the process, gain a deeper insight into it)? That’s the question this video series is trying to answer! PPS: Yes, I should have used limit m->0. If not show it, at least mention it.

[@bofinkerketta9094]

If our sun is bending the light then it is accelerated upwards and light come from every direction so, if sun is accelerating upwards at every direction then why is it not expanding? Please clear it...

[@petervankas1352]

Absolute horse shit.

[@leonhardtkristensen4093]

@@petervankas1352 A good fertilizer then. Ha Ha. I kind of agree in that the earth can't go upwards in all directions.

[@doesntmatter5106]

There are more ads than teaching in your videos. I literally had to go through 4 ads in a 20 minute video(excluding your square space thing). I'm not saying that there must be no ads, in just saying don't make your videos "only ads". Have clarity in your mind whether you're here as a teacher or a businessman. Imagine how a teacher feels when he's fully involved in his teaching and someone for no reason disturbs the flow, how bad will be feel? You allowing ads on between the teaching is like admitting that the your work is not so important that you cannot put an advertisement in between!

[@leonhardtkristensen4093]

We have two formula's that involve mass and G. One is G = m(1)m(2)/rr and the other is F = ma (G and F is really the same if taken away from a planets surface in my opinion. Also remember G varies and reduces if we get inside the earth.) Assuming 2 masses are without any influence of anything else then if the two masses where equal then they would both pull equally at each other. F = ma tells us that a small mass gets accelerated much faster than a big mass. If light has no mass there is no reason that it should pull on the earth at all and also there is no reason that it should be pulled anywhere. In my opinion there are two possibilities. One is that light has mass. No two is that some thing else is doing the bending of a light beam and that could be bending of Space Time but maybe some thing else too. I don't believe that the earth is exploding.

[@jcole1679]

Gravity doesn't change light, it changes space, light travels in a straight line through space, if space is curved, the light curves with it. In a straight line.

[@Precis000]

Yes

[@spvillano]

I usually say it as, gravity doesn't bend light, it bends the universe and takes light on for the ride. One of the biggest problems in physics isn't a problem in physics, it's a problem in miseducation initially that gravity is a force.

[@spvillano]

@davidmudry5622the very description of a progressive collapse. Easily prevented by a spacetime straightener. ;) I guess that the easiest way to explain gravity is that mass loves to tell spacetime to get bent. I'll just get my coat...

[@kzelmer]

Exactly. The answer is geodesics. Mass curves spacetime and light traverses space in a straight line on a curved surface, which is basically a curved line because you cannot trace an straight line in a curved surface.

[@Reaction1s]

Wrong. DENSITY converts the amplitudes into propagation of mass or not.

[@rize2137]

Zooming out - there is another person on the other side of the planet, where ground accelerates "up" (which is other direction for our first elevator guy). So planet accelerates in all directions at once. And since it is "impossible" it means that it is not a planet moving in all direction but it's space moving into planet from all directions :D

[@jean-claudewallard9309]

The explanation with the ground going up has a limit and you are right. Except that spaceTIME is curved.The earth has a mass which is energy, big enough to curve the space. From all directions.

[@antman674]

Yes i think thats where he is going to take us in the next video :)

[@leonhardtkristensen4093]

The earth is exploding! The surface speed will very soon reach the speed of light so some thing is wrong. Space time bending may be able to explain it but I think there could be other explanations too. That is a good project for you to find out if you are a physicist.

[@amoghsod2212]

​@@leonhardtkristensen4093 Well no , see in general relativity we redefine what the acceleration means , in flat spacetime i.e no concentration of large amounts of energy/mass , the second derivative of your position is defined as acceleration but in curved spacetime things go a lot different the second derivative of position is now = acceleration- a new term which represents curvature in , this part of the equation is named the Ricci tensor , so if things go well the acceleration and the new term cancel leaving second derivative of position= 0

[@DJCaab]

yeeeeei finally someone who really underdstands gravity. bin waiting a long time for this moment. pleased to make you acquaintance

[@scienceisdope]

I finally understand the equivalence principle! I still have some questions but like you said, I'll wait till the next episode of dragon ba... I mean of float head physics...

[@MiyamotoMusashi21]

:(

[@manasyadav1993]

RIP Akira Toriyama 😢

[@tushargehlot4618]

work's done

[@anupamshukla6357]

Yeah when I saw it, I thought it was the old video but I saw that it was uploaded 1 hour ago

[@rize2137]

I was wondering why this video is not marked as watched since I have for sure seen it

[@tryesports9482]

Yes bro

[@allinory]

This is true

[@c.jishnu378]

Fax

[@elmaruchiha6641]

4:03 You can't just score throught both m from mg/m, if m equals 0, cause than you divide by 0. You have to take the limit for m approaching 0. For m→0: m≠0 a=lim F/m=lim m*g/m=g

[@Reaction1s]

Zero is a Logical NOT. It can be approached in mass, though never achieved by it. Once the"density" is enough mass is never achieved by light.

[@Yezpahr]

That rollover to the sponsor message... Infinite pricelessness achieved.

[@Dinoplank]

Please do a video where you show off all of your joke t-shirts and explain the jokes.

[@fieryweasel]

In this particular case, it looks like the shirt is schematic for a circuit with a diode in it, maybe. A diode only lets current flow one way (so only positive feedback). It may be something else, I can't get a clear look at it.

[@Dinoplank]

​​​@@fieryweasel this one is an operational amplifier (the triangle symbol) with a positive feedback reaction circuit that's why it has the text

[@thebusdriver_gaming]

@@fieryweasel in the way a circuit flows, electrons are sent from the ground (the negative plug) to the voltage (the posititve plug) so if there is a negative comment or phrase sent, it is recieved as positive.

[@jarredjenkins8054]

Yesss I wanna order some those are great

[@nitinpandey5753]

@@thebusdriver_gaming In ideal Op-Amp case there is nothing to do with -ve plug, because there is open circuit between + and - ones. So whatever singnal you are giving at positive side, will be given to the output side as feedback and you will see no input inverting blocks. Positive amplitude will increase and vice versa according to the i/p voltage at the + side.

[@raymondmeyers8983]

Gravity doesn't bend light. It bends space and time. Light simply follows that curvature.

[@30benasabu65]

Exactly

[@curio78]

Nope, that is a totally wrong interpretation. Space does not wrap. Time is not mutable or a dimension to play with. You are overthinking this, clue: the answer is way way simpler.

[@Josh_728]

@@curio78 You're wrong.

[@curio78]

@@Josh_728 Well let me prove you wrong. Explain why galaxies maintain its shape. contrary to all gravitational laws. I am sure your answer will be to run to exceptions to laws.

[@Josh_728]

@@curio78 You didn't prove me wrong. You're still wrong, but now you're also off-topic.

[@rodrigowettstein5655]

Yes, even medium to large molecules fall at 9.8 m/s. We have many experiments about it! Brilliant explanation!

[@db.1881]

When time accelerated, the distance is shortened When distance is expanding, the time is slowed When time and distance both accelerated and expanding, it will works as a treadmill... times keeps accelerating but space also keep expanding and that will cause no change in time and no change in space That statement came from E=MC2 when c2 is m2/s2 (meter square per secon square) m2/s2 is a distance that expanding per time that also accelerating So masses(M) that moves in m2/s2 is an energy (E) Energy is always accelerating but not in time only but also in a space that keeps expanding that will makes energy somewhat always in a equilibrilium state Energy is the real force, and what kind of force? Its something that makes times accel and makes space expand at the same time... with a masses on it ofcourse And massless photon always moves in the max speed which is a speed of light When photon decelerate then it gains mass and its not become photon anymore That mean even the masses is almost like a gravity force.. its an illusion What left behind is only time and space But photon does not feel time does not feel distance also.. Could that mean that time and space is also an illusion? Everything came from energy... mass, time and space Is that why einstein said that you cannot create energy nor destroy it.. Energy was like the source of everything And what i mean by time is a how fast object can move through a space

[@DrDeuteron]

So when you do Coriolis/Centrifugal forces in Newtonian mechanics, all that matters is inertial mass: there is no gravitational mass in the problem, its your choice of "moving" spatial coordinates... All of gravitation is the same...it's a choice of "moving" spacetime coordinates.

[@amoghsod2212]

Yes but don't mix Newtonian mechanics with Relativity things become too complicated with the math of General relativity of tensor

[@Reaction1s]

​ffs, there is no inertial mass. Mass is produced by inertia/EM waves without protonic mass.

[@Reaction1s]

SPACE/TIME was Einstein's way of dealing with the differentia of wavelength and wavecycle. C^2 is only relevant to dimensional analysis. It creates a holdable point.

[@amoghsod2212]

@@Reaction1s yeah in most in the cases we generally take c = 1

[@user-dialectic-scietist1]

Nobody is looking over the magnifician Cavendish' experiment that proves that gravity is only an interaction between masses!

[@sgiri2012]

Its like listening to the story. It does not seems like watching the educational videos. This is because of mahesh sir incredible talent. Who all agrees ?

[@David_Lee379]

I’ll second that. 👍

[@philippebaillargeon5204]

Indians always make the best educational content on KZbin. You have no idea how much I learned from Indian KZbinrs during my bachelor's degree in Computer science

[@tiborbogi7457]

I disagree, this one is confusing and misleading as he admit at the and of his video.

[@Tahazif_TheCool22]

He just wanted to show an intuitive way of thinking why light falls...

[@donutwindy]

Newton pours water into a glass. Einstein moves the glass up to meet the water.

[@mkpatel981]

😂good one

[@Mahesh_Shenoy]

Einstein *accelerates* the glass upwards, without moving it, in a curved space time to meet the inertial water.

[@donaldmonzon1774]

Seems like almost everyone has drunk the Kool aid ...drank ?

[@thetormentor07]

No crazy terminology, no textbook explanation…. Just comprehensive enough for a child to understand. The best so far

[@NanaNi-du5fg]

I don't understand it either. Is it legitimate to randomly replace objects and ground as the curve in the cone and hence they're accelerating upwards now. Huh?

[@markburgess276]

Thanks for mentioning at the end of the video about the paradox that the earth accelerates upwards but doesn’t expand. I never understood that so standing by for its resolution 😊

[@MrCmon113]

Well, I hope you're into maths, because that answer is general relativity.

[@SoulQuest-fy6fi]

Thank you Mahesh nobody has the explanatory power like you. Truly gifted teacher. Can't wait for the next episode to find out.

[@vyvianalcott1681]

I AM VERY EXCITED FOR YOUR EXPLANATION OF SPACETIME CURVATURE

[@M_1024]

Edit: My reasoning is wrong, and this comment isn't true. If you want to see why, go to replies. 6:05 The reason why inertial mass (in `F = ma`) and gravitational mass (in `F = mg`) are the same: ***This comment is edited, if you are confused by replies the orginal comment is at the bottom*** 0. Assume that gravity accelerates everything, but not necesary at the same rate. 1. Imagine an apple with mass `M` close to some source of gravity. 2. Becouse of assumption 0 apple has some accelaration `A`. 3. Now imagine we split the apple into `X` **identical** parts (this is not possibile with a real apple). 4. This is a theoretical split, not actual cutting, the apple is still whole, we just think of it as `X` parts. 5. All these parts will fall with the same acceleration `a` (because they are identical). 6. The apple doesn't care if we think of it as one part or `X` parts, and will still accelerates at the same rate `A`. 7. Therefore all parts should also accelerate at the same rate. 8. So `A` (acceleration of the apple) and `a` (acclereation of each part) are the same! (Let's call it `g`). 9. But `M` (mass of the apple) and `m` (mass of each part) are different! 10. From `F = ma` we get that `F ~ Mg` and `f ~ mg` (`F` is force acting on the apple, `f` is force acting on each part and ~ means "is directly proportional to") 11. As you can see `g` doesn't depend on the mass of an object (apple or it's part), but it may depend on other factors (distance from earth or earths mass). 12. `F ~ mg` is just a less specific version of `F = mg` or `F = GmM/r²`! 13. All the lowercase `m`s are the the same thing (inertial mass). 14. But lowecase `m`s in `F = mg` and `F = GmMr²` are gravitational mass! 15. Therefore inertial mass = gravitational mass! Capital `M` in `F = GmM/r²` is also inertial mass because of newtons 3rd law (if something is affected by force proportional to it's mass, then it should also inflict a force proportional to its mass). ***Orginal comment:*** Imagine an apple with mass 2. The apple is falling with some acceleration g. Now imagine we cut the apple in half. The mass off both halves is 1. The laws of physics don't care whenever the apple is whole or cut in half so both halves still fall with the same acceleration g. Therefore acceleration doesn't depend on mass and it's always g. From F = ma follows that gravitational force must be = mg.

[@The_Green_Man_OAP]

That's a special case. You could divide into unequal portions, then each mass will pull on the Earth slightly differently, as F=GMm/r². The larger mass will receive and give out slightly more force than the smaller mass. The gravity strength is g= ↓GM/r² for the Earth but it's g'= ↑Gm/r² for the apple 🍎 portions. Earth 🌎 will fall up↑ to the apple at |g'|(«g). The net relativistic effect is the apple falling to the Earth at g↓-g'↑=(G/r²)(M+m)↓ but as m«M, this is ~g↓ and g' can be ignored.

[@thedeemon]

Can't you apply the same logic to magnets or charges moving in horizontal direction? And if you can, then it's not about gravity, so it doesn't tell us anything about gravitational mass and its connection to inertial mass.

[@M_1024]

@@thedeemon there is an assumption that gravity works on everything, while electric force only works on things that have charge. If one half of an apple has charge, and the other doesn't, they will fall differently.

[@M_1024]

@@The_Green_Man_OAP i am not sure if I understand your comment, but my reasoning is true for unequal portions: laws of physics don't care if you considier an apple to be one object, two halves, or bilion atoms.

[@leonhardtkristensen4093]

If you go for F= GMm/rr I assume you mean M is mass1 and m is mass2. If you have those 2 masses as the only influencing masses then G should be a force between them I believe. If say mass1 is much bigger than mass 2 then wouldn't inertia decide which mass would move the fastest? Thinking about the earth and the apple wouldn't that mean that the apple should move towards the earth? Using this logic light with no mass should not bend towards the earth and why should the earth move towards the light? Bending of space time around any mass might explain it but my brain isn't good enough to see that. I think many explanations are made without thinking it all through.

[@TehAntiSpammer]

Honestly, this guy explains physics probably in the easiest ways to understand that i've seen on this platform. good job man.

[@karduar]

Gravity doesn't bend light. Gravity bends space. The light travels through the bent space in a straight line.

[@wunxue]

Why does gravity bend space?

[@karduar]

@wunxue gravity doesn't actually bend the space. Mass bends the space. I could have phrased that better.

[@thomascarey6687]

What and why is Pi? Space time is its own entity. Space time has mass. It is the dark matter they can't find. Mass warps / bends space time. You can't bend nothing. Gravity is a force. It is warped / bent space time trying to achieve equilibrium. Consequently, gravity induces rotation or spin. And the reason Pi is endless...we haven't stopped spinning.

[@JamesWhite-th5vk]

two questions: how can the ground be accelerating up in relation to people across the other side of the globe as it would require acceleration of one object (earth) in opposite directions? And is it not accurate to say that all objects with mass are accelerating towards each other in some small way, though the pull of the earth towards a feather would be negligible, it still exists?

[@TenshiNyako]

Mahesh is the only person in the world, who “speaks” with dead people and I’m sure he’s totally fine and adequate. I have no idea who is Mahesh (at least for now), but the way he shows us the theoretical conversations between him and greatest/smartest people from the past, and the way how such conversations are built, what questions are asked… personally for me - I feel like I’m participating in the science debates… Just amazing. I have no interest in science, but Mahesh, oh my lord, I can’t skip your videos in my suggestion tab. And I decided to subscribe. For me, an adult guy, the Mahesh is the perfect teacher. Instead of “that is a law, now remember it”, we have this brilliant theoretical “discussions”. For younger generations this is a perfect approach to build interests I believe. This approach should be patented and named as “Mahesh’s approach in teaching” or something like that. Can be applied to any science subject, even to astrophysics. Daaaamn, just imagine such conversations with still alive great people. For example discussing some topic with Mahesh, Neil DeGrasse Tyson and “Einstein” for example. It will be interesting, full of great questions, with a little touch of fun. Maybe that or similar things were done already… Great idea to check the whole channel! Thanks Mahesh ☺️

[@Mahesh_Shenoy]

Wow, that means a lot 🥲. Thanks for sharing thsi

[@maatwerkengineering3398]

I also had a discussion with Newton in my head when I learned about him in highschool: so you just multiplied kg’s by 10 and called it “Newtons” instead and got famous for that?? But also: how does a rock “know” how to fall down to earth? How does the earth communicate to the rock “iam this way over here”

[@Gavainavain]

He’s right, Mahesh… this is a wonderful Socratic dialogue way of investigating these thought experiments that pull the rug out from under our intuitive assumptions. You’re actually going to help people develop an embodied sense of the strangeness of what’s really going on with space-time…. That can have huge implications for our societal evolution!

[@tapashnandy3594]

The path will be curved even if the elevator is moving up with constant velocity, in which case there is no g. What am I missing?

[@vaibhavgarg1982]

@@tapashnandy3594I had the same question. Here is how I solved it. Imagine the setup where the speed of light is ‘c’, speed of elevator is ‘v’ and width of elevator is ‘d’. The amount of deviation x at a distance d comes out to be -vc/d. That is a straight line in x-d coordinates. Hence no curve. In case of acceleration, there is a curve.

[@ARES_HANTRIO]

Bro, I too think the same thing every day. What if I am in a static position because if I look, everything around me is moving, our planet Earth is moving, our entire solar system is moving and our entire galaxy is also moving... That's really mind-blowing, brother. Thanks for making these types of videos for us. And sorry for the bad English..😶😶

[@aperinich]

If you're in a static position (relative to what?) If it's the Earth that you're stationary relative to, then the Earth is not moving relative to you.

[@piyushpathak1186]

@4:12 a/a = 1 is only defined if a is not equal to 0 Limit m tends to 0 would be a better way I guess

[@lazetochekjaja7450]

Correct

[@goswinvonbrederlow6602]

And no, you can not just cross out the m at the top and bottom. That would be dividing by 0 twice. You need to actually do something else, like looking a the limit when m goes towards 0.

[@dpkastel]

@@goswinvonbrederlow6602 the limit when m-> 0 = 1

[@dominicestebanrice7460]

Soren Kierkegaard said, about Hegel's philosophy of history, that "if he had presented it as a thought experiment, it would be one of the great inventive creations of the human mind, but he didn't, and that just makes it hilarious". This was a damming put-down by the standards of the day from a professional philosopher, especially since Hegel was a titan in the domain. Listening to Mahesh's superb exposition, there is a perceptible 'essence-of-Hegel' in Einstein's work after he got bored/frustrated with quantization and dedicated himself to gravity & relativity.

[@Shadowless_Kick]

Einstein’s explanation is nice when we only focus on this small elevator, but the Earth is a sphere, so all objects on Earth are accelerating upward toward the sky as if the Earth were exploding? That is weird😅

[@thedeemon]

There is no frame of reference where Earth is accelerating in more than one direction. But there are many different frames, and relative to them Earth is accelerating in different directions, one direction per frame.

[@yourguard4]

In a centrifuge, all parts of the wall are accelerating inwards, but it is not shrinking :P

[@andrew3203]

Einstein is right, and can be proved with a simple accelerometer. Hold one in hand, and it shows you are accelerating up, even if you don't move at all.

[@dominicestebanrice7460]

@@yourguard4 Oh dear. Employing the physics of circular motion and centripetal acceleration as a retort to the OP takes some nerve! Just reflect on the physics of a centrifuge versus an elevator, in particular compare and contrast the centrifuge wall failing versus the elevator floor collapsing and visualize the trajectory of the contents after failure to just before in both cases.

[@balkeebalakrishnan493]

When I saw the grammatically incorrect title (“Why gravity bends light even without mass?”), I almost skipped this video. But then I thought - maybe the title was added by a person other than the presenter. Glad I watched - I really liked your style. I’ll admit I do not understand the whole elevator floor rushing up bit, but that’s on me. I need to watch it again. And again. And again. Why do you say Newton’s argument about light being affected by gravity “hand waving”? If you can accept that gravity affects infinitesimal mass, then by limit theory it should apply to zero mass also, cos how small does a body have to be to be suddenly unaffected by gravity? What is the crossing point between non zero and zero?

[@fairworld990]

Gravity bends space not light. So what we are observing is light traveling trough bended space

[@GS-oc6ve]

in a straight line

[@paulroos8517]

Your interpretation of the "Einstein model" doesn't take into account that 9,8 m/(ss) only applies to the earth, however, remember when it comes to a "black hole" with infinite gravity, light doesn't move. So what happens if light travels near a black hole? Your reasoning is mind-opening to the Newtonian postulate that light is both a particle (having mass) and an electromagnetic wave i.e. the duality of light. This affects all assumptions about distance and time calculations in space.

[@justinhageman1379]

In Newtonian physics, the force g is calculated using the formula M1*M2*G/R^2 so if the mass of light is zero shouldn’t g be 0?

[@thedeemon]

Yes, in Newtonian mechanics it should (the force should be 0).

[@shaktimangangadhar3638]

Yes that seems to be correct. But Newton's 2nd law also says that force is rate of change of momentum. Photons have momentum, and it does change due to gravity, which itself as we will see is due to curvature of space time.

[@hamidrezamoasyyebi6754]

hello I read something in Einstein's book that confused me. In the book of relativity, Einstein says the following about the deviation of the light of distant stars when passing the sun during the eclipse of 1919: For a ray of light which passes the sun at a distance of Δ sun-radii from its center, the angle of deflection (α) should amount to 1.7 seconds of arc/Δ. It may be added that, according to the theory, half of this deflection is produced by the Newtonian field of attraction of the sun, and the other half by the geometrical modification ("curvature") of space caused by the sun. Einstein talks about two things: Newtonian gravity field and spacetime distortion caused by the mass of the sun. Some people say that gravity is nothing but the curvature of spacetime. But Einstein distinguished between these two. what is the reason?

[@juliavixen176]

For everyone asking: The force you are currently feeling on the surface of Earth is the lithoststic pressure of 3000 miles of molten rock and metal. The human body is too small to directly feel the Earth's gravity directly. You "fall" through air and water on Earth, but not rocks unless you can apply more than 15000PSI to the rocks under your feet. You sink into mud because you can apply enough pressure to the mud, and you can sink in snow, but not ice for the same reason. The iron-nickel core of the Earth is at about 1,000,000PSI The "force of gravity" is what keeps all this rock pressurized. The surface of the Earth could freeze solid about four billion years ago after it reached an equilibrium between how much pressure makes it accelerate "up", and how much gravity shrinks it "down".

[@windwardpro]

But what is the movement of the crust- the acceleration? Some places it is very slowly sinking and some places it is very slowly rising, but overall it is not moving- it is not accelerating!

[@juliavixen176]

​@@windwardproGravity is shrinking the volume of space occupied by the Earth, which is what is pressurizing it. Like a compressed spring, it gets harder and harder to compress the material, because the force keeping the molecules of the material from occupying the same location in space will push them apart. That's what you feel on the surface of the Earth. The repulsive electrostatic force that is pushing molecules apart from each other at least as fast as gravity is pushing them together. If the rocky surface of the Earth was not pushing you up, you would fall down, through the center of the Earth, and probably go into orbit around the Earth's center of mass. You are actually in orbit around the center of the Earth right now, but the ground keeps pushing you up into a higher orbit, so you never get any closer to the Earth's center of mass. (Just like you are on a rocket continously accelerating away from Earth's center of mass at 9.8m/s² to maintain the same distance away from the Earth's center of mass. The geometry of spacetime itself is curved, and this just looks like motion in 3D space.) (Also, I looked it up, and the radius of the Earth is actually between 3,950 and 3,963 miles depending on latitude.)

[@juliavixen176]

​@@windwardproBasically, imagine holding a pumb bob, a weight on a string. The string will be pointing directly at the Earth's center of mass (assuming a perfectly spherical non-rotating homogeneous Earth). Nearby, use a plumb bob to draw a line that points directly at the center of mass of the Earth from that location. Now, to the naked eye, these vertical lines will appear to be perfectly parallel lines... but... when you extend these lines 4000 miles down into the Earth, these lines will intersect! They are not parallel, they are two sides of a very long thin triangle with one vertex located at the Earth's center of mass... These straight lines... *_ARE_* straight lines... it's _the space between the lines that shrinks_ the rocks below our feet are getting squished on the side closest to the Earth's center. If you imagine using four plumb bob lines to be the corners of a square, the area of the square will shrink as you go down towards the center of the Earth, and would shrink all the way to zero area at the Earth's center of mass if all of Earth's mass was concentrated there at a point. Because the Earth's mass is spread out over 260 billion cubic miles (one trillion cubic kilometers) the amount of gravity _decreases_ below the surface. Yes, you weigh less inside of a cave. The core of the Earth is experiencing weightlessness, and is floating in orbit around the Sun. The mass of all the rocks and metal and stuff in and on Earth is essentially "pulling up" evenly on the center of the Earth. The 4000 miles column of rock on one side of the core, pulls by the same amount as the 4000 miles column of rocks on the opposite side of the core, and the two sides cancel out to zero. (Repeat for every direction.) So, yeah, the Earth's core is incredibly pressurized, and mostly weightless. Gravity keeps it pressurized, gravity does not give it weight.

[@zaconeil3709]

​@@windwardpro plate tectonics and gravity are unrelated.

[@andrew3203]

Einstein is right, and can be proved with a simple accelerometer. Hold one in hand, and it shows you are accelerating up, even if you don't move at all.

[@Tom__L]

Nice start… was hoping you get to the bend space part that counter the acceleration, but I think that’s the topic of the next part… 😊 Your videos are great and some of the best explanations of complex topics made easy to understand. Keep up the good work. 👍

[@giannagiavelli5098]

Space does not bend what on earth are you talking about

[@barefootalien]

Nice technique in the open there... the "I used to think... but then I learned..." thing is a very nice way to open someone's mind to new information even if they currently have some misconceptions about it. Nicely done.

[@profane253]

I'm so happy I stumbled upon your channel. You do such a great job of explaining things in a way in which it's easily - about as easy as physics can be anyway :) - digestible. Great stuff, thanks! Edit: and entertaining!!

[@ashishgmath]

I smell calculus around that m/m cancellation. Maybe that's where a more satisfying justification lies. As always, great stuff Mahesh!

[@rajanvenkatesh]

I quite like the reference to good old Newtonian physics.. the mass or its absence not making a difference to gravitational fall is a good thought-provoking beginning to this video. I also recall another video of yours where it was the Newtonian concept of relativity (of uniform motion) that Einstein used to figure out the constancy of c (speed of light or causality). I was in college before computers were born.. I am slightly partial to things classical - physics, art or music!

[@natashashvetz405]

Replace mass with charges and you would really "thought provoke" Relativists. Maybe there's electric space time 😂 They seem to be obsessed with gravity only. Light gets bent by water. Refraction explains light bending.

[@user-dialectic-scietist1]

The limit of c is a philosophical dogma of Einstein that everything is energy and do not have a place in relativity of a world under unstopped motion!

[@MFrrFrr]

Funny riddle: if mass bends space, and bended space creates gravity (which "attracts"/"makes move in some direction" also and masless objects/particles and makes time act a little different- we assume, that everything is connected (mass also as a trigger to this procces) - so we should be talking not only about space-time continium, but about mass-space-time-speed-continium. General relativity talks only about 2 parts out of a 4 or 5 :/

[@narfwhals7843]

The relationship of mass and spacetime is given by Einstein's field equations. The influence of the curvature on the motion of objects is given by the geodesic equation. Both are part of general relativity.

[@varsha_1703]

Mahesh is not pregnant,but he never fails to deliver (his insights)😂

[@barefootalien]

\*epic facepalm*

[@kiraPh1234k]

Light isn't massless in the real world. It has energy, which is equivalent to mass. ( M = E/c^2 ) Also, it doesn't bend light. It is the bending of space, the light travels in a straight line still - even through curved space. For light to not experience effects like lensing, it would have to bend, specifically opposite the bending of space. Remember, gravity is not a force. It is a shape. When we fall, we are not accelerating, hence the feeling of weightlessness. It's once we are on the ground that we are accelerating at 9.8 meters per second per second, which is why we feel weighted.

[@lazetochekjaja7450]

Yes that's correct light or name it any radio wave don't bent just simply follow curvature of space. Radio waves are not piece of metal or plastic that you can band hahahahah

[@kylelochlann5053]

Sorry, but photons are massless particles. To say it has some energy equivalent to mass-energy of something else is absurd. Rubber bands have an energy 0.5k(Δx)^2, but you would't say light is made out of rubber bands just because you can an energy equivalence.

[@kiraPh1234k]

@@kylelochlann5053 You're definitely trying to pretend it's absurd... I said nothing about it being anything else. This comes from Einstein's theory of special relativity. It's also the reason that, in theory, you can create a black hole with photons. This mass is what bends spacetime, and photons do bend spacetime.

[@juliavixen176]

The energy of "light" is E=hf or kinematicly E=pc

[@kylelochlann5053]

@@kiraPh1234k You're not understanding. A single photon is massless, specifically, g(P,P)=0, where P is the photon 4-momentum and g defines the inner product on the tangent space. Two or more photons can have mass, g(P_1+P_2,P_1+P_2)= 2g_{mn} P^m_1 P^n_2. You cannot write down a single photon stress-energy tensor, but you can for a photon gas which then sources the curvature, even if every photon is massless.

[@uvuwuewuewueonyetueosas227]

whe i drink from a glass of water, my intestines are the ones going up to meet the water. :D

[@ankurgaur3620]

😂😂😂😂😂

[@parthkevdiya757]

in einstein theory if bird want to fly it has to move up faster than 9.8 m/s and birlds uses air to push themselves up but if ground is moving and we are rest and birds are also rest then they just have to jump once and open their wing and then as ground pushes up, it will also pushes up air and you know what happens when air hit the wings, i think the bird should float in the air without flapping their wings. am i missing something here?? you can imagine parachute or something like that too. edit : and sorry if i said anything stupid i am just new in this stuff.

[@swayamsahoo8565]

1:46 Sir, i am unable to find the links to the videos mentioned just before this timestamp.

[@Master-zf5um]

It is in discription

[@swayamsahoo8565]

​@@Master-zf5um hey ssup. Umm .. it initially wasn't

[@hasanshirazi9535]

Inertial mass of an object increases as its relative speed increases until it approaches infinity as it approaches the speed of light. However, gravitational mass does not increase no matter whatever the velocity of the object. Thus gravitational force will remain constant not matter whatever the speed of the object. So inertial mass and gravitational mass seem to be two different quantities which are equal at rest but diverge as speed increases.

[@nevinthomas3199]

Oh man that transition from independent prop to website add in between was good.

[@popquizzz]

Simply stated; Gravity warps Spacetime. Light made up of massless photons will move in a straight line unless acted upon. Light is just moving in that straight path of warped spacetime and from our frame of reference is perceived to be being bent around a large body or gravitational mass. We know Dark Matter can warp spacetime, but why doesn't Dark Energy? If mass and energy are basically the same, i.e., E=MC2m, why doesn't Dark Energy warp spacetime or does it? Is this the reason for the difference in measurements of the expansion rate of the Universe? The aptly named: Crisis in Cosmology?

[@zaconeil3709]

Mass and energy are not the same. One is mass, the other is energy. Einstein's equation is about mass energy conversion, not that they are the same thing. The extent to which dark energy and dark matter are related is simply by the word 'dark'. Each relates to different things.

[@experienceyoga4]

Are you the Khan Academy guy?

[@Cartermchick]

💀

[@MrPoornakumar]

Beautiful! It isn't the mass but momentum (p) that is the real hero. Even Newton said, force is the rate of change of momentum, by a constant (g) times. He was right but we got him wrong. Quantum theorists talk of momentum (p). A light ray has momentum = h/λ, since hν = (mc)c = pc.

[@JerryPenna]

Save yourself 17 minutes: gravity bends the fabric of space not light itself. You’re welcome! 😉

[@thomasshelby1922]

It’s not just about the destination but the journey.

[@Dragaan786]

Light follow the shortest path

[@Darksightkellar]

Imagine being this insufferably obnoxious and getting it wrong anyway.

[@pythondrink]

We care about the delivery of the video, not just the answer. So no tnx.

[@mohayminasif]

​@@thomasshelby1922 100%

[@clasherofclans1482]

Mahesh this explanation sounds valid but then how do we answer these questions - 1. If there is no gravity and it is mere acceleration then how come that acceleration is more for the heavier celestial bodies. For example moon is lighter than earth and that is why gravity is lesser there. But for sure both are accelerating at same pace else both would have separated long time ago. Same between earth and sun. 2. How does it describe black holes? Lights does not escape a black hole from beyond the event horizon. Also, why these black holes were created out of massive stars and not from some tiny planetary body?

[@MadeForAI]

You’re the best teacher ever 🔥🔥

[@stephenanderle5422]

Why can't people make a video without showing their face all the way through it?

[@daledadolphin]

more engaging with a face and will get more views

[@akumpawatjr]

I think it's fine. Don't like it? Don't watch😂

[@pythondrink]

What are you asking?

[@xinpingdonohoe3978]

Such a strange niggle and question.

[@khushpamani]

Please don't stop making such videos your videos are just amazing

[@dmitrykim3096]

Both Force and Energy are abstract constructs to make calculations easier

[@krishanand4530]

4:04 in maths you can only cancle them when assuming m≠0, but in case of light it is zero, so in Newtonian physics acceleration of light towards mass is just not defined

[@astronomers]

Wow one of if not the best explanation. Einstein would be so proud of you. Please don't change and become as complex as the other physicist

[@pujamathssolution9906]

Please start a quantum physics series and also explain that what is photoelectric effect of Einstein

[@TIFFandDRETV]

A more accurate title of this video should read “why does gravity appear to bend light even without mass. It’s all about appearance. The coolest property of light is that it follows the path of least time in the fabric of space time.

[@heinerradau]

about 4:27 suggestion for an intuitive explanation: light its accelerated downwards by gravity, but unlike the other mentioned objects, light is already moving very fast in one direction and thus its directory can only slightly be altered. but anyway, doesn't the fact that light moves very fast mean that it carries energy, and thus that is does have mass?

[@neluna19]

Actually, g=9.81 m/s² is at the sea level, in Europe. Our planet is not a perfect sphere, and g depends on the distance from the center of the Earth. The farther you are from the center of the Earth, the smaller the value of g gets. So, at the Equator g=9.78 m/s², and in the poles g=9.83 m/s². In fact, if you want to lose weight, forget about diets. Just weigh yourself in the spot where the value of g is smallest on the surface of our planet: the summit of the Huascarán Sur, in the Peruvian Andes, where g=9.76392 m/s². You may think, why not just bring a scale on your next flight, and use it while you are flying at cruise elevation? Because g at commercial airplanes is similar to at sea level. Why? Too many factors, but mostly because of you are on the air.

[@karmakamra]

If we are accelerating up, and its an acceleration we cannot perceive, does that mean we are accelerating through time? And if we consider the expanding universe, can we say that it is not space that is expanding, but time is accelerating in the areas where there is no matter to absorb this acceleration, which results in what we perceive as space expanding? Makes me want to ask a question that seems kind of nonsensical.... What is the speed of time? I don't know why, but I feel as if there should be some correlation between expanding space and the flow of time. Inside space occupied by matter this acceleration manifests as gravity, and outside it it manifests as expanding space.

[@tanmaygupta7778]

I have a doubt when light is falling down its already falling at the speed of light now if it accelerates wouldnt it just violate the fact that nothing can travel faster than light??

[@cesarjom]

3:30 This is not how you show that acceleration, a, on an object is equal to g. You know that the term g is just a value given to the acceleration due to gravity on surface of earth (9.8 m/s^2). The argument you must make is to demonstrate that inertial mass and gravitational mass must be the same for the acceleration a = g. This is done by using Newton's second law (F=ma, containing inertial mass) and his universal law of gravitation (F is the inverse square law containing gravitational mass). Setting both force equations equal, you find that a = (constant) * (gravitational mass / inertial mass). Here is where Newton and Einstein had reasons to argue that gravitational mass and inertial mass are the same property of matter. This then makes a = constant = g. Namely, you can now assign the value g to a.

[@katalyst4stem]

nice video but i have a counter argument to Einstein's argument if the feeling of weight is because of earth accelerating, then the feeling of weight will depend on the direction of earth's accleration so if earth is accelerating due north, then someone on the N pole will weight and someone on the South pole should not feel any weight and in fact should accelerate away from earth at 9.8 m/s2

[@juliavixen176]

The direction of acceleration at the Earth's surface due to gravity is towards the Earth's center of mass (about 3900 miles below your feet). I wrote several other comments on this video about this, just look at the other comments here on this video for the full explanation.

[@katalyst4stem]

@@juliavixen176 i completely agree with that and it is the classical newtonian explanation But in the einstein thought experiment (as i have interpreted it) the feeling of gravity is because of an upward push from the earth because earth is acclerating through space at 9.8 m/s2. But this cannot happen in all directions. So weight should be felt only in the direction of acceleration. i will check out your other replies. may be it willmake things clear.

[@jameskennedy7093]

I'm not a physicist, but... it seems like the problem with what you're saying is that it assumes light would bend with a y component of 9.8 m/s^2. And that's not so. Light only bends noticeably under extraordinarily high gravity, so using your model it's acceleration would be much smaller.

[@BradleyDWoods-pz8rv]

I've always pictured the reason that a hammer and feather fall at the same rate was due to inertia. The greater mass of the hammer simply takes longer to accelerate. I've also always thought it was weird that they just happened to be EXACTLY inverse, and cancel each other out. Great video, thanks!

[@dgsean9775]

Your wrong, a better way to think about it is what exactly is a photon? Is it truely a unique partical? Or is it just a electron spaced out in frequency wavelenth? Because electrons are affected by gravity, and if you shirnk a gamma ray and get electron, well, then what did we learn?

[@chicodroid]

The algebra of mg=ma -> g=a is invalid. It only holds when m!=0. Dividing by m to get m/m in the right side implicitly assumes m is not zero. As an example 0=0 5*0 = 0 7*0=0 5*0=7*0 5=7 The proper reasoning is ma=mg Ma-mg=0 M*(a-g)=0 M=0 and/or a-g=0 M=0 and/or a=g Therefore acceleration is guaranteed to be the same as the force of gravity only when mass is not zero.

[@roberttarquinio1288]

Gravitation is a manifestation of space time curvature The fabric of space and time pushes us down toward the surface of a body of mass such as the earth Space is a fluid; it flows Space is dynamic Space time curvature manifesting as gravitation causes spatial and temporal distortion effects which causes light, comprised of photons, to deflect

[@vasocreta]

I can comprehend about 1/3 of the things you share, but am jazzed by 100% of your enthusiasm.

[@theevermind]

I remember when I realized the difference between gravitational mass and inertial mass. I asked why they were equal, and hardly anyone understood the question much less could answer it. The best I got was "they have to be the same thing." My first thought was that mass wasn't actually the fundamental property causing gravity. Instead, I thought what if gravity acted on momentum, and mass was just the result of mathematical simplification. It certainly could explain why massless particles (light) are affected by gravity because they still have momentum. But then I actually learned about Newton & general relativity. I don't particularly like the description of space being curved. Yes, the math works--not arguing that. But the mechanism of curvature causing movement seems to be a problem for particles of zero size. With zero size, the curvature of space seems like it would have no effect on them because they have no size to interact with that curvature. Instead, I choose to think of space like a fluid. That fluid can move. It can expand or contract. Or, it can be thought of as graph paper that moves, expands/contracts like a fluid. The difference is that mass acts as a 'drain' for the fluid of space. Space flows into mass like water flowing down a drain. Instead of thinking of a 'gravity well' as a location where space has curvature causing light to bend because it's traveling in the a straight light in bent space, think of it as light being a boat moving in a straight line in a moving stream that pulls it 'off-course.' For a black hole, the space is flowing/accelerating into the drain faster than light can move through space to escape. Now, the elevator thought experiment is intuitive: - 'Inertial effects' occur whenever you accelerate with respect to space. You feel it as a force because to move where you are in space, a force is needed. - In deep space, you are accelerating through the fluid of space, and you feel the inertial effects. - In gravity, space accelerates through you, and you feel the inertial effects. - The delta-acceleration of you & space are identical, so all math, sensations, & physics are identical. - No, the ground is not accelerating up and pushing on you. Space is flowing through both you and the ground. You want to move with space (aka, free fall) but the ground stops you, hence you feel inertial effects. Also, the effect of gravity on particles of zero size is also intuitive. All particles, regardless of size move with space, or they require a force to have an acceleration with respect to space. The idea of space being a fluid could also explain the universe's expansion. Space itself could be self-replicating. Wherever there is space, it creates more of itself, meaning if you have two points on that graph paper that are adjacent at time = 0, then at time = 1, there are now points on the graph paper between the two initially adjacent points. How? Don't know, just like how space disappears down the drain caused by mass. Just go with it. In a volume like the solar system, there isn't enough empty space between the sun & planets to generate enough new space to throw off the balance, and it behaves what we could call 'normally.' But with enough empty space between masses, such as over an entire galaxy, then things don't act normally, which could eliminate the need for dark matter. Again, there is even more space between galaxies, and they accelerate apart, because as expected, the increase in space from its self-duplication would do that. It isn't that anything pushes them apart (dark energy), it's just that there's an ever increasing amount of space between them.

[@DanieleVergini]

the big question is: is gravity "just" a geometric property of spacetime? or is the behaviour of gravity an emergent property of something else we have yet to discover?

[@kylelochlann5053]

We measure the gravitational field to be spacetime and gravity to be the curvature of spacetime.

[@MikkoRantalainen]

6:20 Another way to think about this situation is that there's no gravitational force in reality any more than there's centrifugal force either. Instead you have only inertia and curved spacetime and nothing more. There's only constant inertia m×a when an object is on the surface of an object that curves the spacetime where the acceleration is definited by the amount of curvature.

[@hederahelix8332]

This ended my sleepless nights. And makes one ask new questions that make even more time dilated nights,

[@peterdugan596]

A photon (a packet of energy) travels from point A to point B in "time =0". Gravity warps time and space. That's why light appears to bend.

[@ArnabSutradhar-p1y]

Suppose we have a black hole and we insert sufficient amount of positive charge in it and put a proton on it's event horizon. The positive charge inserted is sufficient to counterbalance the gravitational pull of the black hole , then will the proton on the event horizon be pulled inside the black hole?? If no, then is it possible to continue this process and reach the centre of the black hole???

[@juliavixen176]

Good question! There are some _practical difficulties_ with accomplishing this... but let's pretend that we can overcome those difficulties. So.... Let's also assume that the black hole is not rotating, and your test charge is exactly lined up with the black hole's center of mass, so we don't need to worry about magnetic fields. Hmm... assuming a "Classical" Swarzschild eternal vacuum solution black hole without any messy QM stuff... Hmm... hmmm... what exactly do you mean by "put a proton on it's event horizon"? Because the answer depends on the exact details of this. Assuming that by "event horizon" you mean the location in space, a certain constant radius from the black hole's center of mass, where a very distant observer will never receive any escaping light (or anything else) originating from beyond that horizon. So... "no", but... there are a lot of details I skipped over. So, assume that this takes place in an otherwise empty universe with just you and your positive electric charges. Because, presumably you are charging up this black hole by dropping protons (or whatever stuff with intrinsic positive electric charge) into it... and as the black hole's positive electric charge increases, you are not going to be able to get new additional positive electric charges anywhere near your black hole. (In fact, if you have any neutral atoms anywhere near the black hole, just the electric charge will shreed the electrons from the atoms, repell the positive ions, and neutralize the electric charge of your black hole.) The strength of the electromagnetic force is orders of magnitude greater than the "force" of gravity. There will be a limit, some distance outside the black hole's event horizon, when you can't get a positive electric charge to "fall straight down" past the event horizon. If the falling proton can cross the event horizon, it's stuck forever, if it can't quite reach it, it's either going to be at equilibrium (and remain at a constant radius from the center of the black hole) or be repelled away from the black hole and escape to infinite distance. I forgot to mention, I'm treating the test charge "proton" in your question as though it is a microscopic classical sphere with mass and charge, and not an elementary particle with intrinsic magnetic moment and gluon binding energy. There's more... there's a lot more details to consider before I even get to using the EM tensor and tidal effects. So... classically, beyond the event horizon of a black hole, spacetime is still locally continuous. That "event horizon" only exists in the coordinate system of a _very distant observer_ . Like a mirage, you don't "see" that "event horizon" when you are actually there at that location. (You will see an event horizon in the direction of the center of the black hole, and you will never see yourself cross it.) Blah blah blah... you can build a pile of positively charged matter outside of the black hole's event horizon which will never fall in... but if you _could_ build such a structure within the black hole's "event horizon for a distant observer", you still can't escape from the black hole by climbing up it... because to climb up using the electromagnetic force... because atoms are held together and repelled with the electric force... you can't push yourself "up" faster than you can push something down... and the fastest that two electric charges can push on each other is the "speed of light" (litterally the definition of an electromagnetic wave). The _coordinate system_ of anything beyond the event horizon of a black hole is moving away from a distant observer faster than the speed of light (as they say). The "force" of electric charge propagates at the speed of light, and can't catch up with the difference in movement between a coordinate system "inside the event horizon of a black hole" and the coordinate system of a "very distant observer far away from the event horizon of the black hole". If you're familiar with how proper acceleration works in Special Relativity, you get a Rindler "event" horizon far behind you while you're experiencing proper acceleration, because light can't catch up with you as you're running away from it with enough head start. I hope KZbin doesn't loose this reply, I don't want to rewrite this. KZbin's comment system is broken on the back end. The comment database isn't replicating between all of Google's data centers.

[@AdmiralandHen]

I find it easier to (perhaps incorrectly) think of it this way: gravity doesn’t bend light. Mass bends space and light just goes in a straight line through curved space. Might also be easier to think that gravity isn’t a “pull” from another object but a “push” from space trying to straighten itself. I didn’t watch the video yet though the question and first 30 seconds and got more confused. 0:26

[@tomasmiller]

So, if the earth is pushing up, then how is it pushing up? If this principle is true then wouldn’t our bodies also be pushing up with respect to our mass? Obviously, “up” doesn’t exist within the context of infinite scale, so that means our mass is pushing outward in all directions under this principle. Now, when I think of everything pushing outward with respect to its own center (me, planet, star, etc.) I think of expansion. We know that the universe is expanding, at least that’s what we have been told, so if that expansion became neutral or a contraction wouldn’t the effect or perception of gravity cease to exist? Now, in a related idea, if we could stop the expansion or create contraction in a given area, wouldn’t that create an effect of anti-gravity (with a neutral state) or shrinking (during contraction). If this were true then everything would be relative to the expansion or contraction and our ability to identify the source of this would be the key to understanding how all of physics operates.

[@zaconeil3709]

The expansion of the universe and spacetime curvature in the presence of massive objects is unrelated. In general, the surface of the Earth exerts a force equal to that exerted by an object sat at the surface experiencing acceleration towards the Earth's centre of mass. They cancel out and the acceleration is 0. Our bodies do not 'push up', but were a cat sits on your lap, it does not fall through you, therefore your body js exerting a force equal that of the cat's mass accelerated downwards. If the universe stopped expanding and began to contract, there is no reason to think it would change how gravity presents in our stellar neighbourhood.

[@dalemcgregor405]

In the 1st example all of the objects would be at a "rest" mass, until allow3d to be accelerated by gravity. The photon then, being at a "rest" mass, would not be massless, and should fall at 9.8. The photon, theoretically, would have mass in that example because it would not be accelerated at the speed of causality. Would this be a correct assumption? If not, why not?

[@keoghanwhimsically2268]

Except… Newton’s Law of Gravitation does not say gravity is 9.8 m/s^2. It says that g = Gm1m2/s^2, that is, it is proportional to the product of the masses of the two objects divided by a square of their distance, then multiplied by the constant G. 9.8 m/s^2 is just an approximation of the gravitational acceleration of a human-scale object (not a celestial body) at sea level, where the mass of earth so overwhelms the mass of the object as to render the latter effectively irrelevant.

[@trna2h1c]

Light is both a wave (Young’s double slit experiment proved this) and a particle. It is self propagating because it has both a magnetic field and an electric field that expand and collapse opposite of the other. Gravity bends all things that affect magnetism and electrical systems. Light travels at its fastest in space. Bend space and bend light.

[@Study-g2k]

Nice video! I have a persistent question. In a vaccum, both ball and feather will fall at the same time. But isn't gravity (weight) mg? In the video, you had shown that a=g under free fall. But gravity will still act on the ball? And it is mg. It's somewhat confusing. Please clarify and explain. Thank you

[@rupertchappelle5303]

Use the Cavendish experiment to demonstrate the curvature of spacetime bending light. if it doesn't , then gravity is a force, not a curvature of spacetime. The force is from the difference of high pressure time vs. ;low pressure time. TIME VARIANCE, what provides the "pull.".

[@maxp3141]

Also inertial mass being the same as gravitational mass is no coincidence at all. There is a _scaling factor_ between the two things called the Gravitational Constant. If all particles had positive charge we would marvel the same thing about electromagnetic force.

[@colinnewton7020]

So what happens when two people on opposite sides of the Earth drop an apple? Does Earth bulge to hit both apples? It seems a model where the apples move towards the Earth only makes sense. It seems in a lot of the comments people are just mocking each other's understanding of physics and not trying to work together to increase understanding. I notice that the mathematical descriptions of physics rarely explains what we actually observe making me wonder about some of these "advances". String theory is a spectacular example.

[@bussinessmindset2450]

Hey, I have a question, its weird tho. If the gravity bends the space-time and creates like a hollow bended downwards space, like we see in Einstein's theory. Wouldn't be the object ultimately fall into its own bended space Time. And if the object doesn't fall, wouldn't be the poles of earth have a greater radius than the equator?

[@hiral_9]

I think I saw you with Aanand Srinivas sir, both of you are really a true master of physics..❤👑❤

[@ben_b_blake]

6:32 that's the point. Heavy mass and inertial mass are the same and not the same alike. And if something does not have inert mass, then it does not need force to be accelerated... But the true explanation is time dilatation. I'd say the effect is the same as why refraction is depending on frequency.

[@Zorro33313]

10:48 - it's not ridiculous at all! It's really simple! Mass twists spacetime in such a way the uniform linear movement trajectories there are pointing towards the mass until it gets in a way applying acceleration = mg to you to decelerate you.

[@Doctor_Raad]

Best physics show ever, i love your style when making imaginary conversatioms with Einstein and the others

[@stochastaecrez9868]

A video that left me on the edge of my seat the whole way through. And he ends it on a cliffhanger. Brilliant.

[@paulneelon8343]

4:30: a motionless photon will fall at 9.8 m/s - you can prove this by using a motionless photon. A tornado is approaching my house, I am frightened and leaning heavily against the force of the wind, then the tornado arrives and picks me up bodily, I am travelling at the same speed as the wind, I feel nothing - thank god, it is obvious now that the tornado never existed. I enter a passing elevator, which happens to contain a floating elephant. Now you understand that gravity is a downward force that makes the elephant shit upwards, while I lift him. I know this is not intuitive, but it makes more sense than phlogiston. I like to think that gravity sucks.

[@gastube22]

In the man + elephant scenario, in the left-hand (Newton) case, you said that when the lift and its contents are all accelerating downwards at the same rate towards the ground, they feel no force between them (and so feel weightless). Fair enough. But in the right-hand (Einstein) case, you said that after the upward-accelerating ground has reached the bottom of the lift and is now causing everything in it to accelerate upwards at the same rate, they now DO feel a force between them (though not called 'gravity' in this case), and they experience weight (as you would expect with the lift on the ground). This seems inconsistent - why the difference, when in both cases the lift and its contents are all accelerating together at the same rate? (Albeit downwards in the first case and upwards in the second.) I guess I must be missing something crucial here.

[@PreKGraduate]

Maybe I’m not understanding the logic behind this fully. But based on this explanation, objects (including massless particles) would ‘bend’ in opposite directions based on which side of the accelerating object they were on. If Earth’s “gravity” is due to it’s vector through space, you’d infer objects would ‘bend’ in opposite directions based on which side of the vector they’re on? Edit: I just watched your second video on this topic, and it did help make a lot more sense out of it! My brain is still trying to wrap itself around the concept of spacetime in general though 😅

[@TheSonshade]

Not a stientist here.Thanks for these, Brother. Love these deep dives made for designers like me. I have a feeling I'm going to learn more about the Higgs field and space-time just so I can understand mass and time. Down the rabbit hole we go. Cheers mate.

[@michaelmccoy1831]

Very conversational/easy to listen to. A few technical problems, including that Newton never cold have made any statement about how fast a BASKETBALL would fall...

[@sherakhela4044]

You win my subscription. Awesome explanation. Thanks

[@abberepair8288]

Photons don’t have mass but they DO have an electric charge. This charge would bend light all by itself! Like charges repel. Thats why light moves in the first place. It tries its best to create an equilibrium! It pushes itself into every place inertia will let it go

[@0ntropy0]

Light can accelerate through a change of direction only. Moving vertically downward it can only travel at ‘c’. How does that affect the basketball analogy?