Human understanding of motion and space has evolved over many centuries. The ancient Greek philosopher Aristotle believed that the Earth was at the centre of the universe and that all motion sought a natural state of rest. Objects fell to the ground because that was their natural place, while celestial bodies moved in perfect circles around the Earth. Space and time, in his view, were absolute and unchanging.
This picture dominated Western science for nearly two thousand years until the 16th and 17th centuries, when thinkers like Copernicus, Galileo, and Newton challenged it. Copernicus placed the Sun at the centre of the solar system, and Galileo’s experiments with motion revealed that all objects fall at the same rate regardless of their mass. More importantly, Galileo realised that motion is relative – meaning that the laws of mechanics are the same for any observer moving at a constant speed in a straight line. A person on a smoothly sailing ship, for example, cannot tell by any internal experiment whether they are moving or at rest.
Isaac Newton later expanded on Galileo’s ideas to create the first comprehensive mathematical description of motion. In his Principia Mathematica (1687), Newton introduced three laws of motion and the universal law of gravitation. He described space as a vast, immovable framework within which all objects exist and move, and time as an independent, continuous flow that passes at the same rate for everyone. These concepts formed the foundation of classical mechanics and remained largely unchallenged for more than two centuries.
However, as physics progressed into the 19th century, experiments involving light and electromagnetism began to reveal inconsistencies with Newton’s framework. If motion is relative, how could light always travel at the same speed regardless of the observer’s motion? This puzzle suggested that Newton’s absolute space and time might not be fundamental after all. The stage was set for a profound transformation in our understanding of the universe – one that would eventually merge space and time into a single dynamic entity.