Gravity

Mechanics

Mechanically, gravity is a force of attraction which acts between all matter. Gravity is directly proportional to the mass of the objects and inversely proportional to the distance between those objects.

As seen in the above equation where

· G is the gravitational constant ( 6.6743 × 10-11 m3 kg-1 s-2 ).

· M is the mass of the objects.

· R is the radius or distance between the objects.

Dimensions

To further understand gravity, as the way Einstein described it, we need to understand “How higher dimensions affect lower dimensions.”

Let’s consider 2 friends in only 1 dimension, namely A and B. Let’s say they had a fight with each other and then went off in opposite directions alone. Soon, they met up, which although isn't possible in 1 dimension, is possible in 2. We can consider their world a circle within 2 dimensions. But then again, with information of only 1 dimension, they're unable to explain how.

Now assume that A and B were 2-dimensional beings. This time, A went north, and B went east. After a while, they met up again! This time, it was because they were on a sphere in the third dimension. As we know, any straight line on a sphere is known as a geodesic. Geodesics on the same sphere always meet at 2 points, the points where A and B cross their paths.

The third dimension, in which we live is also bounded by a higher dimension, time.

Spacetime

Spacetime is the 4-dimensional realm in which we live. You constantly move through spacetime at the speed “c”, roughly 300,000 km/s. To move faster through space, you must move slower through time, and vice versa. But while you are sitting still, reading this, why isn’t time passing faster? But remember, the Earth is moving, the solar system is moving, the galaxy is moving. So, you can’t stay still in space.

The universe is made of matter, in spacetime. Viewing in 2D, if we view spacetime as a trampoline, which is flat, anything placed on it presses it into the third dimension, height. The same goes for 3D matter in spacetime. Its mass pushes spacetime into the 4th dimension, which is why any object's trajectory changes into gravitational orbit, since trajectory measure of an object's path in time.

Time dilation

Let’s say you are travelling in a car in space at 90% the speed of C. You put a light clock (an instrument which uses photons bouncing back and forth to measure time) in the car and flick it on. Now, the photon inside the clock is bouncing back and forth while covering the distance travelled by car. To do this, the photon has to exceed C, which isn’t possible. So, time around the photon slows down as spacetime squishes so, the photon remains at the speed of light. To a person inside the car time will be perfectly normal, an accelerated frame of reference, unlike a person outside the car, who will see the car slow down. This is time dilation due to an accelerated frame of reference.

Gravity also causes time dilation. Due to Einstein’s equivalence principle, which states that gravity behaves the same way as acceleration, the more gravity, the more we accelerate. Since acceleration causes time dilation, inevitably gravity does too.