This blog post explores how Einstein’s theory transformed the concepts of time and space, and how it overcame the limitations of Newtonian mechanics.
How did people understand the relationship between time and space? From ancient times through the Middle Ages, time and space were regarded as immutable concepts associated with divine beings. Time was thought to have begun with the creation of the universe, and space was seen as a stage prepared by God. This perspective was also widespread among philosophers; thinkers like Descartes understood space as an absolute and independent entity. Until Einstein emerged, people regarded time and space as independent. They also believed that time and space would exist on their own, even if matter did not. Underpinning this perception was Newton’s classical mechanics. Newton introduced the concept of universal gravitation, positing that objects like the Earth attract other objects, generating gravity. The accuracy of Newton’s ideas was proven through observation and experimentation, establishing them as fundamental laws of physics for many years.
However, Einstein rejected Newton’s idea and instead argued that gravity is the ‘curvature of space’. Einstein’s concept was considered quite radical by the scientists of his time, but he developed this new perspective through deep exploration of the interaction between the speed of light and gravity. According to Newton’s classical mechanics, light propagates along a straight path within the range of gravitational influence (the gravitational field). Einstein, however, asserted that light bends within a gravitational field. He explained this by stating that light undergoes accelerated motion due to the gravitational force within the field. To explain this, he posited that any object occupying space causes the space it occupies to be curved.
Therefore, massive celestial bodies like the Sun or Earth would also warp the three-dimensional space around them due to their mass. This was not merely a theoretical assumption but a scientific prediction that could be verified through actual observation. Consequently, when light passes near these massive bodies, its otherwise straight path becomes slightly deflected. Einstein’s hypothesis was proven by an observatory led by the British astronomer Arthur Eddington. To observe the total solar eclipse occurring in the southern hemisphere on May 29, 1919, Eddington’s observatory team traveled to Suvral in Brazil and the island of Principe in West Africa. This eclipse observation was regarded as a highly significant event in the scientific community at the time and was seen as a decisive opportunity to verify Einstein’s theory. Through meticulous observation, the team confirmed that light from distant stars behind the Sun bent around it, and the degree of this bending matched Einstein’s prediction. This event caused a worldwide sensation and instantly made Einstein famous. It was the moment Newton’s law of gravity, which had held sway for over 200 years, began to crumble.
If gravity is viewed as ‘the curvature of space’ as Einstein proposed, time itself expands within a gravitational field. This follows naturally from the fact that space is curved. When identical light signals are emitted instantaneously, their paths differ between regions with and without gravitational fields. That is, an observer in the region without a gravitational field would see that light bends in the region with a gravitational field, taking longer to reach them. This is very different from our everyday concept of time. Especially in the universe beyond our solar system, the time delay becomes significantly greater.
Based on this fact, Einstein defined gravity as the ‘curvature of space and time’. This definition gave birth to a new paradigm called ‘spacetime,’ viewing time and space as a single unified concept. Our solar system has a weak gravitational field, so the curvature of space and time is extremely minimal. Therefore, within the range of our senses, it is difficult to find any noticeable theoretical gap between Einstein’s theory and Newtonian mechanics. However, unlike Newton’s theory, Einstein’s theory provided a powerful tool for explaining physical phenomena in situations with strong gravity. Yet, in the outer reaches of space beyond our solar system, where heavy matter like black holes exists, events occur that cannot be interpreted without Einstein’s theory. The intense gravitational field of a black hole warps space and time so severely that time appears to slow to a near standstill. Newtonian mechanics is useless there. It is precisely for this reason that we say Einstein expanded human perception and broadened the horizons of understanding.
