Gravity is one of the four fundamental forces of force and was discovered by one of the most revered scientists to have ever been born, Sir Isaac Newton, who, in his celebrated work the Principia Mathematica, described gravity as a force that pulls objects towards the ground and is also the same force that underlies the motion of planets and stars. For decades after Newton, gravity was thought to be only a force that attracts objects, and it remained so until Einstein stepped in and painted a strange and unintuitive picture. It wasn’t until Albert Einstein that finally, a new idea came along, a strange idea that clashed against Newton’s definition, completely revolutionizing the way gravity was thought to be up and until the moment in time.
According to Einstein, gravity was a static, unchanging force and fundamental structure of the universe that holds the universe together. Time goes faster the farther away you are from the earth’s surface compared to the time on the surface of the earth. This effect is known as “gravitational time dilation”. It is predicted by Einstein’s theory of General Relativity and has by verified multiple times by experiments. Gravitational time dilation occurs because objects with a lot of mass create a strong gravitational field. The gravitational field is really a curving of space and time. The stronger the gravity, the more spacetime curves, and the slower time itself proceeds. We should note here, however, that an observer in the strong gravity experiences his time as running normally. It is only relative to a reference frame with weaker gravity that his time runs slow. A person in strong gravity, therefore, sees his clock run normal and sees the clock in weak gravity run fast, while the person in weak gravity sees his clock run normal and the other clock run slow. There is nothing wrong with the clocks. Time itself is slowing down and speeding up because of the relativistic way in which mass warps space and time.
Gravitational time dilation occurs whenever there is a difference in the strength of gravity, no matter how small that difference is. The earth has lots of mass, and therefore lots of gravity, so it bends space and time enough to be measured. As a person gets farther away from the surface of the earth – even just a few meters – the gravitational force on that person gets weaker. We don’t notice it much as humans, but even going from the first floor of a building to the second floor of a building moves you away from the earth and therefore slightly weakens the gravitational force that you feel. The difference in gravity between that felt at three meters above the surface of the earth and that felt at four meters is too small to notice with our human senses, but the difference is large enough for sensitive machines to pick up.
Because the strength of gravity is weakening with every step you take up a flight of stairs, the rate at which time proceeds is also speeding up with every step. People who work on the bottom floor of a skyscraper are literally time-traveling into the future compared to the people who work on the top floor. But the effect is very small. So small, in fact, that you will never notice the time difference in everyday life. People who live and work farther away from the surface of the earth are only fractions of a nanosecond ahead per year compared to those close to the surface. Though small, the time rate difference between different altitudes is real and has been measured experimentally using very accurate atomic clocks. Atomic clocks measure the electromagnetic signal that electrons emit when it changes energy levels, which helps them calculate the difference in time rate.
Scientists are continuously developing on these theories provided, and developing it more and more as time progresses. To be honest, nobody knows if the direction we now move in is right or not, because just how Einstein defied Newton’s ideas, there may very well come a time when another scientist may disprove Einstein, and put forward a new, better theory than the ones proposed today, again maybe putting us at ground zero, making us start all over again. However, what we can do is keep moving forward, and keep developing, and keep putting forward new, better ideas than before.
