# What is spacetime? Connection of 3D and time

The concept of spacetime is a conceptual model that combines the three dimensions of space with the fourth dimension of time. The idea of spacetime explains the unusual relativistic effects created by traveling at the speed of light and the movement of massive objects in the universe.

At the cradle of the concept is the famous physicist Albert Einstein. He helped develop the idea of spacetime as part of his theory of relativity. Before his pioneering work, scientists had two different approaches to explain physical phenomena:

1. Isaac Newton’s laws of nature described the motion of massive objects

2. James Clerk Maxwell’s electromagnetic models explained the properties of light.

## What is spacetime?

In physics, spacetime is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional manifold. Scientists can use spacetime diagrams to visualize relativistic effects, such as why observers perceive different realities where and when events occur.

## The speed of light

When scientists experimented with light in the late nineteenth century, they discovered something special was going on. Measurements showed that light always travels at the same speed (186,000 mi/s or 299,792,458 m/s), regardless of conditions. In 1898, French physicist and mathematician Henri Poincaré speculated that nothing could surpass the speed of light. Around the same time, other researchers considered the possibility that objects changed in size and mass depending on their speed. These different facets come together in the concept of spacetime.

## Who was the inventor of spacetime?

The concept is part of Einstein’s theory of relativity. It explains the unusual effects of traveling at the speed of light, such as why different observers perceive a different reality where and when events occur (think of the double-slit experiment). The movement of massive objects in the universe is also part of the theory.

Einstein brought together various theories and findings of Isaac Newton, Henri Poincaré, and others in the 1905 theory of relativity, which stated that the speed of light was a constant.

## Minkowski space

German mathematician Hermann Minkowski developed a theory closely related to Einstein’s theories of special relativity and general relativity and is the most widely used mathematical structure on which special relativity was formulated.

While the individual components in Euclidean space and time may differ due to length contraction and time dilation, in Minkowski spacetime, all frames of reference will agree on the total distance in spacetime between events.

In current spacetime theories, Minkowski space still stands as a basis and serves as a background for calculations in the theory of relativity and quantum field theory. According to astrophysicist and science writer Ethan Siegel, the latter describes subatomic particles’ dynamics as fields.

## Spacetime: flexible as rubber

When developing his general theory of relativity, Einstein realized that gravity was the result of curves in the fabric. His statement that spacetime can be thought of as a piece of rubber has been widely adopted.

Massive objects – such as celestial bodies – create distortions in spacetime that cause them to bend. These curves, in turn, constrict the way everything in the universe moves because objects must follow paths along this curvature. Motion due to gravity is actually moving along the twists and turns of spacetime. This movement is explained in this video.