Gravity Is Not a Force (And The Acceleration Is Upwards!)

when I was a kid I was told that gravity happens because the earth is like a magnet it took me decades to understand Einstein's modern explanation of gravity which I put into my award-winning video how gravity makes things fall but people still ask where the force of gravity comes from if something is accelerating that requires a force so gravity must be a force right it's not Isaac Newton described it as a force but today we say that when something Falls and accelerates no force is making it do that even more counterintuitive the acceleration of gravity is actually upward it's not downward first consider a situation where there is no gravity things moving with no forces being applied to them in physics this kind of motion is called inertial things are moving or not moving by way of their own inertia only if we're observing something while we ourselves are moving about inertially we say that we are in an inertial frame of reference objects moving inertially as measured in an inertial reference frame travel at a constant velocity nothing is accelerating this is captured in Newton's first law of motion there's no way to define what's moving and what isn't all motion is relative and if we want to say that an object is at rest we have to specify that it's at rest relative to some reference frame measured against a different reference frame that same object might be moving there's no such thing as absolute motion or absolute rest but now suppose that we fire up an engine and begin to accelerate in one direction from inside our spaceship now things have changed we can tell that we're no longer in an inertial reference frame if we release an object it begins to move as if a four acting on it it accelerates but no such force actually exists the object is just floating freely and the spaceship is speeding up around it the ship's walls are now constituting and accelerated or non inertial reference frame and in that reference frame inertial objects appear to accelerate in the opposite direction one of Einstein's brilliant realizations is that you cannot distinguish between being accelerated in one direction and being under the influence of gravity from inside an elevator car you couldn't tell whether it's sitting on the surface of the earth or in deep space and being accelerated in the direction of the ceiling by 9.8 meters per second squared in either case if you let go of an object it will accelerate toward the floor at that same rate but from the perspective of the object that is in its inertial reference frame the elevator car appears to be accelerating ceiling word Einstein realized that rather than gravity being a force acting at a distance that accelerates freely moving objects downward we have to say that instead gravity puts us in a non inertial accelerated reference frame and we have to say that the surface is what's being accelerated upward but why what's special about inertial reference frames it's because inertial reference frames are where the laws of mechanics take their simplest form no external influences need to be taken into account so when you are sitting in a chair you are quite literally being accelerated upward but you might be saying acceleration is a change in velocity and we aren't speeding up but speeding up along a straight line is only the most familiar form of acceleration if you swing a ball in a circular manner you're constantly accelerating it toward the center of the circle even if it isn't speeding up or going anywhere in particular if you let go the ball gets flung off and it begins traveling inertially when you remove that real force the ball goes from being accelerated to moving inertially similarly when we're standing on the earth the ground is pushing us up with a real force and if that force is removed our body goes from being accelerated to moving inertially and then in that now inertial reference frame we see the earth accelerating upwards whether it's speeding up along a straight line changing direction toward a center of rotation or being pushed upward by a massive planet any deviation from inertial motion is a real acceleration and real acceleration requires a real force in fact when you step on a scale you aren't directly measuring your mass you're measuring the force required to accelerate you out of your inertial path toward the center of the earth but thanks to another one of Newton's laws that force is proportional to your mass a scale wouldn't measure your weight in deep space unless your ship happens to be accelerating at 9.8 meters per second squared

Channel: EdwardCurrent

Views: 195,836

Keywords: general relativity, einstein, gravity, spacetime curvature, four dimensions, time, space, space and time, gravitation, acceleration, edward current, centripetal force, normal force

Id: nR9nE1TalZc

Length: 5min 56sec (356 seconds)

Published: Wed Jan 01 2020

Reddit Comments

[u/DAnSqueaker]

Fucking leave this planet...

[u/dave_baksh]

This is nonsense.

[u/BacnRL]

This is the dumbest thing I’ve watched in my existence

[u/shawster]

Why are you guys shitting on this, it’s not like he’s denying gravity. This is actually sound logic.