How it works: Relativity theory

By Giorgia Sanna

Image courtesy of Flickr

Many of us may have heard of the term “relativity”, Albert Einstein’s theory which completely revolutionised the world of physics in 1915. But how many of us are actually familiar with what it means, and with how it changed the way we look at physics?

The term “relativity” refers to how things change depending on where the observer is standing. For example, a racing car appears to be faster if we were looking at it from a stationary point, than if we were moving at the same speed as the car. This principle is what Einstein’s theory is all about, but instead of racing cars, about time.

Just like the racing car, Einstein claimed that time changes depending on where the observer is standing. In order to understand this concept, we need to visualise time as something tangible but most importantly, we need to combine it with space. One way to understand how the two things are related, is by considering that every type of movement requires space: even the smallest particles, like human cells, wouldn’t be able to grow and regenerate without space, therefore nothing would evolve without space, meaning that time wouldn’t exist.

After understanding the concept of space-time, it’s easier to comprehend and visualise Einstein’s relativity theory. All you have to do is to think of space as a flat, 2-dimensional surface which can be bent and distorted by the masses of the celestial bodies such as stars and planets. Just like a rubber surface, space would extend under the pressure applied by a heavy mass, but since we are not considering space on its own, but we are now talking about space-time, it means that heavy masses can distort time as well. Einstein therefore claimed that the greater the gravitational force exerted by a body in space, the slower the time passes.

Theoretically, if we put a man on Jupiter, whose mass is over 300 times bigger than the Earth’s, he would age more slowly compared to anyone on our planet. This is because the gravitational force exerted by Jupiter is larger than the one exerted by Earth, and the space-time underneath it would stretch by a more significant amount.

Einstein completely revolutionised the concept of time, and his theory allowed science to make great improvements and discoveries, leading to more complex arguments and assumptions about the nature of the universe.