What is Gravity? The Illusion of Force by a Curved Dimension

one of the first things we learn about shapes and geometry is the concept of parallel lines two lines that both travel in the same direction and their paths never cross well let me tell you reality is a lot more complex all our lives we've been told we live in a three-dimensional space or the third dimension those dimensions being height width and depth now this is superficially correct and thinking any different won't change your life but the reality is we exist within a four dimensional realm called space-time we have freedom of movement within three of these dimensions space but the fourth time is restricted this means I can move in any direction within space at any speed or any acceleration my only constraint is the energy needed to change my momentum but in the fourth dimension time I can only go one direction at one speed for that reason we are considered three dimensional beings we don't possess the ability to comprehend the fourth dimension but that doesn't mean it doesn't exist and believe it or not it's why things are attracted to each other by what we call gravity in order to comprehend space-time and how the fourth dimension creates gravity we need to be able to comprehend how higher dimensions affect lower dimensions so to begin let's pretend we have a pair of one-dimensional friends friend a and B and these friends they get in a fight and decide I'm done with you and they start walking away from one another in opposite directions then after a while all of a sudden friend B pops up out of nowhere and both of them lose their minds how is it possible there's no conceivable notion other than teleportation of how these two friends could possibly meet up again they're one-dimensional minds are just unable to comprehend what is happening because their world is actually a circle within two dimensions however without information from the second dimension it's impossible to know the true direction of their path or any path for that matter therefore the one-dimensional friends are bounded by the second dimension the same thing happens for those living in two dimensions these friends walk away from each other turn 90 degrees to their north keep walking in parallel lines and yet somehow they run into each other that is because they actually exist upon a sphere again without information on the third dimension it's impossible for them to conceive the true nature of the paths they taking that brings us to our world the third dimension and yes we too are bounded by a higher the fourth dimension just like our friends in the previous two examples there's no way for us to conceive exactly how we can travel in straight parallel lines and meet up again but we can understand that our plane of existence is curved in the next higher dimension what does that mean we have no idea just like our friends from before but that doesn't mean we can't understand the consequences of it this curvature in the fourth dimension is what we experience as gravity and just like how everything in the lower dimensions that travel in straight parallel lines eventually meet up the same thing happens here in the third dimension however here things differ a little from our friends before unlike our lower dimensional friends we don't have the freedom to choose how fast to move through our four-dimensional space-time whether you are running sitting or falling you are moving through space time at the notorious speed C roughly 300,000 kilometers a second this is of course the same C from the famous e equals mc-squared postulated by Einstein and it is equally distributed between space and time so if you decide to move faster through space you must move slower through time and if you were to somehow slow down in space you'd move faster through time now you may be thinking well I'm just sitting here why isn't time passing faster but remember the planet's surface is moving the earth is moving the solar system is moving in the galaxy is moving it's impossible to stop moving through space plus your changes in velocity are so small compared to C the difference is imperceptible even Rockets that travel at eight kilometers a second are only moving to ten thousandths of a percent of the speed of light so we are constantly moving through space-time at a constant speed and since space-time is curved just like the previous examples are perceived straight paths appear to attract or converge with one another if this still isn't making sense don't get discouraged we are talking about a very complex concept normally outside our realm of comprehension but bear with me we're gonna start visualizing this and I think you'll have the same Eureka moment I had okay let's start visualizing this to begin we'll start with the most common visualization of gravity but it's not my favorite will visualize the fabric of space-time as a trampoline now normally empty space-time just looks like a trampoline but of course space-time is not empty is filled with matter normal and dark alike and this matter has a very strange effect on space-time now although they exist within space-time the elementary particles that make up all matter are not made up of space-time themselves they are for lack of a better term and as far as we know today pure energy and this pure energy occupies volume within space time or disturbs it but this volume that should be space time doesn't simply disappear because energy or matter is occupying it it is displaced so the more energy or mass that exists the greater a disturbance and displacement it has on the surrounding space-time so planets and stars and all energy within them warp space-time around them that means space-time is curved by matter which is very important because straight lines on curves have unique behaviors a straight line along a curve is called a geodesic and an easy way to identify geodesics on spheres is that they always pass through the point on the exact opposite side of the sphere the only reason it wouldn't is if some force was applied to it along its path but then it would no longer be a straight line now two geodesics no matter where you put them on a sphere will cross each other's paths now whether objects following those paths hit each other is a matter of timing and relative velocities but they are constantly moving to intercept the other's path so just like how moving along a curve in the third dimension can be viewed as moving along a straight path in the second dimension moving along this now curve fourth dimension means it still feels like we are moving in a straight line through the third dimension and just like how two dimensional beings moving in parallel lines eventually meet one another along the surface of a sphere us moving in straight parallel lines in space means we still end up meeting each other or crossing ones path within space-time think about how crazy that is if we suspend a ball above the Earth's surface it's moving in the same direction as the earth through space let's even freeze the rotation of Earth so we don't have to worry about the angular velocity affecting our balls moving now when we look at the ball on the earth they are both clearly moving along two parallel paths through three dimensional space so there's no reason for them to cross each other's paths but when I let go as they travel through space-time just like how we saw with the friends walking on the sphere because they're traveling along a curve in a higher dimension the ball on the earth end up running into each other despite traveling parallel with each other this is the fundamental concept of gravity this becomes abundantly clear if we change our perspective if you look at our two friends walking along in two dimensions it looks like they walk into each other however if we remove any reference to their velocity because they are walking the same speed it simply looks like they are gravitating towards each other for no reason the same thing applies to our ball and earth as they both whiz past it's clear that okay they're moving along a curve on the fourth dimension and thus converge we can see both of their horizontal and vertical movements but to someone standing on the earth the ball appears motionless as if it's not moving through space at all the only difference is that the balls path through space-time converges with the Earth's path and even though it appears as if the ball is motionless on the ground since both the earth and the ball are still moving through space time they're still constantly colliding finally let's go back to our trampoline example and I want to explain my original confusion with this model in case anyone else had or has it as we roll a ball around our space-time it's clear that we see the curve of orbits and we see that oh yeah things fall down the well as it's called but why does it need to if gravity isn't a tangible force why if I place a motionless ball here on the trampoline does it have to roll towards our planet and this is where my mistake was you see before when we talked about lower dimensional beings moving about there's nothing stopping them from stopping themselves or just deciding to sit down but remember everything is always moving through space-time so the ball placed on the trampoline has to move because everything is space-time moves and our planet in the middle of the trampoline isn't motionless either it's also moving through space-time at the same speed as the ball and once you see the trampoline like this well I hope it clicks and it makes sense why something would just fall as we perceive it straight down so remember if it feels like you're stuck in a rut or not making any progress the universe is always there behind you moving and pushing you forward [Music] you

Channel: But Why?

Views: 605,921

Rating: 4.8370991 out of 5

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Id: jhpKUapI3cY

Length: 8min 41sec (521 seconds)

Published: Tue Oct 01 2019

Reddit Comments

[u/ClankCapital]

This video made me feel like a 1 dimensional being

[u/blindnarcissus]

I still don’t get it. Goddamnit.

[u/half-assHipster]

Wow! this was the most i think ive understood gravity thus far! great video, im gonna be on a physics kick for week now

[u/CurtisAurelius]

Honestly best visualization and common speak of space time. Kudos.

[u/iHeartBats8]

Can I copy someone’s notes?

[u/justapassingguy]

That was very well explained and I was actually surprised to see something more in depth than the usual "gravity is like a fabric" and the guy even explained WHY it's like a fabric.

Looks like I'm going to binge this channel for a bit.

[u/Wtkeith]

Is this going to be on the quiz?

[u/pincheperroloco]

THIS IS INCREDIBLE!

[u/Mclevius-Donaldson]

So if it bends space time like a ball on a blanket... then what force is pulling the ball down the blanket and closer to the massive object