What is Gravity?

When going off a jump, whether it's skiing, snowboarding, or biking, gravity pulls you down to the landing. Have you ever thought of why this is? Newton believed that gravity was a mysterious attractive force, whereas Einstein developed the theory of general relativity explaining gravitational effects. Believe it or not, Einstein's theory first started when he saw a window washer on a step ladder and wondered what would happen if he fell. Einstein figured that if there were no air resistance the man would feel weightless, before he hit the ground of course. This theory became more developed over eight years and is now how we know how gravity and the relativity of time work.

To understand gravity you have to understand time. When I think about time, my thoughts have something to do with how long I have to complete a task, or when I need to be somewhere. If you dive in, time is much more complicated than that. Everyone has a concept of what time is, but when you get to how it works things get mushy. There is a past, present and future, and time is described as being the advancement of events. Time is ongoing. This is easy enough to understand.

The next thing to understand is kinematic time dilation, meaning moving things experience time slower. Einstein theorised this by imagining a photon clock made of two mirrors bouncing a photon back and forth like a bouncy ball. In theory, you could count how many times it bounced in a period. If you had two of these clocks, one moving and one stationary, the moving one would tick slower. This would happen because as the clock moved, the photon would have a longer distance to travel to catch up with it. If you were moving with this clock it would appear as if it was stationary and you wouldn’t notice the photon travelling the longer distance. The only way you’d be able to tell that the moving clock was experiencing time slower was if you counted how many times each photon bounced. The clock with the moving photon would have fewer “ticks”. This theory has been proven to be true, so we can conclude that time is relative.

It can get more complex when you understand that time passes faster as you move away from the mass of Earth; this difference in the speed of time is called gravitational time dilation. The incremental difference is minuscule and can only be measured by incredibly precise timepieces. These timepieces run slightly slower the closer they are to Earth, and slightly faster as they move away. Why is this? Massive objects warp space-time causing time to move slower the closer you are to them.

This space-time warp is gravity. You can picture space-time as a piece of fabric. An object on the fabric will cause it to dip down and bend. If you were to put a smaller object on this fabric it would fall towards the larger one. Another, more accurate way to visualise this, is by picturing an object travelling past the earth; the portion of the object closer to the earth moves through time slower and the portion farther away moves faster. Because of this, the object will be pulled toward Earth. The object accelerates through space and decelerates through time and is pulled into the surface of the Earth.

Is any of this information useful in our day-to-day lives? Probably not, but it’s fun to think about. Maybe just avoid thinking about it when going off a jump and worry about sticking the landing.