Gravity, It's Not What You Think It Is [UPDATED]

Gravity is NOT a force.

Gravity is not a force pulling you down, up, or sideways. Why not, because gravity is NOT a force.

Gravity used to be thought of as a force, invented (😉) and mathematically worked out by Sir Isaac Newton. For a tonne of maths it can be considered a force and it's no biggie, but it is NOT a force, even though you were taught that it was, it's not.

"Jeez, I hear you Mike. So what are you thinking a force is, coz gravity definitely feels like one?"

A force is an influence that can cause an object to change its velocity unless counterbalanced by other forces. The concept of force makes the everyday notion of pushing or pulling mathematically precise. Because the magnitude and direction of a force are both important, force is a vector quantity. 

"Ok, so what is gravity?"

In physics, gravity (from Latin gravitas 'weight') is a fundamental interaction primarily observed as mutual attraction between all things that have mass. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light.

It's an interaction, it is something that can be seen to make a difference on things, it interacts with things and makes them change.

Take a look at this image, the light is being affected by gravity, the gravity caused by something massive (it's called gravitational lensing and can give rise to an Einstein Ring)

By Lensshoe_hubble.jpg: ESA/Hubble & NASA derivative work: Bulwersator (talk) - Lensshoe_hubble.jpg, Public Domain, Link

"But if, Mike, you are so adamant that it is not a force and yet it affects things then what the hell is it?"
Um, prepare yourself, it doesn't actually exist ... nope. As far as being a force of any sort is concerned it's just NOT that.

Right, we gonna need some diagrams and definitely a video. But let's try some words first.

So, it all comes down to the General Theory Of Relativity, the geometric theory of gravitation published by Albert Einstein in 1915, the current description of gravitation in modern physics - all tests of general relativity have been shown to be in agreement with the theory. 

The basic idea is that instead of being an invisible force that attracts objects to one another, gravity is a curving or warping of spacetime. The more massive an object, the more it warps the spacetime around it. As everything is travelling in a straight line through spacetime (the four dimensions, up/down, left/right, forward/backward, (collectively "space") and time) then the shortest route with a curve is to follow it around.

Instead of an empty, blank, 3D grid, putting a mass down causes what would have been 'straight' lines to instead become curved by a specific amount. In General Relativity, we treat space and time as continuous, but all forms of energy, including but not limited to mass, contribute to spacetime curvature.

So, everything is travelling along on it's straight line but that line is bent by mass (a form of energy), all things bend spacetime, you and I are doing it right now but of course it's infinitesimally small compared to the Earth, or our Sun, or the biggest mass things in the known Universe, black holes. Black holes bend spacetime so much that we have no idea what's going on in there, light itself can't get past without falling into the "hole" created by the bending, eek.

So, gravity is NOT a force.

It is an interaction of spacetime and the mass of objects, causing bending/warping that means our straight line movement becomes curved and we experience and have historically explained it as a "force".

Easy really ... 

[UPDATED 16-Sept-2024] The following video gave me greater clarity and insight into the nature of gravity. Of course seeing that we don't know what time actually is we may end up in a circular argument, LOL.