**People love to drop Albert Einstein’s theory of relativity into conversation, whether they’re discussing the latest Hollywood blockbuster or just trying to look smart. But what is the theory of relativity? You may know that it involves gravity pulling objects and some possible time dilation, but probably don’t know that it is a whole new way of describing reality itself. You may take for granted that you have to meet a friend for breakfast at your favorite place at ten in the morning, but without the forces outlined in the general theory of relativity you would meet at a completely different place at a different time.**

**First published in 1915, Einstein’s theory of relativity managed to solve problems physicists and astronomers had been grappling with for centuries. It’s revealed secrets about black holes, planetary orbits, and space travel. And as you learn more facts about the theory of relativity and spacetime, you’ll discover just how mind-blowing it is.**

##### It Was Born From Einstein’s Theory Of Special Relativity

In 1905, Einstein published his theory of special relativity, which proved to be a pretty big deal in the mathematics and physics communities. The basic theory states that the laws of physics are exactly the same between objects moving at the same speed. The key is that those objects can’t be accelerating – they have to be at a constant speed. It also states that despite your acceleration or speed, the speed of light in a vacuum is the same for everyone.

##### The General Theory Of Relativity Adds In Acceleration

For ten years after creating the theory of special relativity, Einstein worked to add acceleration into the mix. He had determined that the laws of physics (as in, space and time) were the same for two people moving at the same constant speed. The minute one starts accelerating, however, then you run into problems. The faster you accelerate, the more of a time difference you’ll have when observing occurrences with others at different speeds.

##### Spacetime Is The Fourth Dimension

In order for all these theories to work, the Universe has to be measured in a different way. Standard X and Y coordinates describe a position in a two-dimensional plane, but because the Universe is a three-dimensional space, a Z coordinate is needed as well. But there’s actually a fourth dimension at play in reality: time. “Spacetime” refers to this fusing of time and three dimensional space, and it gave physicists a whole new perspective on understanding the Universe.

##### Gravity Affects Space-Time

When it became apparent to Einstein that gravity could disrupt spacetime, it changed the constants that he was working with. When acceleration (and thus gravity) is constant or non-existent, spacetime is also constant. But when gravity changes, then you need to be prepared to change all the variables.

##### Yes, You Have An Effect On Spacetime

Just because you have a small gravitational pull doesn’t mean you don’t have an impact on the Universe. Everything with mass has a gravitational pull, which means that while the Earth is pulling you, you’re pulling it right back. But because the Earth has much more mass, it tends to win those tugs of war and keep you firmly planted on the ground.

However, everything with mass in the Universe has an impact on the other objects in it. The Moon’s pull creates the tides, for instance, and the Sun’s gravity pulls all the planets into elliptical orbits.