Spacetime and the Theory of Relativity

Spacetime and the Theory of Relativity

The universe, as we see, exists in 3 dimensions. But in reality, it exists in four- length, width, depth, and time. Earlier it was believed that the universe had only three dimensions and time been a separate thing, but then Albert Einstein gave the Theory of Relativity which had the idea of combination of three-dimensional space and time, called spacetime. Spacetime is a physics model in which space and time are combined as a continuum called Minkowski continuum.

The idea of spacetime helped scientists study the universe in a whole different way. It led to the study of motion of massive celestial objects, effects of travelling at or near the speed of light and the working of time. 

Working of gravity

According to the theory of relativity and the concept of spacetime, gravity occurs due to the bending of spacetime due to the presence of matter, regardless of the magnitude of mass present. Even your body, or the gadget you are holding right now, bends the spacetime fabric because of the presence of matter in it. The magnitude of gravity depends on the mass of the two objects and their distance from each other.

If the mass of the object is larger in magnitude, there will be more distortion of spacetime, thus attracting the other object with a greater magnitude of force. But that is not the only situation, if the distance is large too, it will take more time to get pulled towards it.

Bending of spacetime by different celestial bodies (Source: Wikimedia Commons)

The working of gravity can be explained by the following experiment:                                                Take a bedsheet or a trampoline. Place a ball A somewhere on it, then place another ball B. Both the balls will bend the surface just like matter bends spacetime and both the balls will get attracted towards each other due to the bend in the surface of the sheet or trampoline.

Working of time

Time is a primary property of the universe which comes from every particle present and has no definite direction of flow. Earlier it was believed that the time is constant throughout the universe and even Sir Isaac Newton believed it. But Einstein proved that time is variable and can be changed by the speed of the observer.

An object travelling at high speed would experience slower time as compared to a stationary object or another moving object but with slower speed. Theoretically, traveling at light speed stops the time.

Time dilation due to the motion of an object is called ‘Velocity time dilation’ and the time dilation due to the effect of gravity is called ‘Gravitational time dilation’.

Time is present everywhere, even within the fabric of spacetime. That means bending of spacetime would lead to the bending of time. So of course, if a person is on a planet or near any other celestial body, he would experience time slower than the observer floating in free space.