Einstein’s revolutionary notion that gravity is a curvature of space overturned Newton’s classical understanding of time and space and provided a new paradigm for an integrated view of space and time.
How have people understood the relationship between time and space? From ancient times to the Middle Ages, time and space were considered immutable concepts associated with divine beings. Time began with the creation of the universe, and space was thought to be the stage set by God. This view was also prevalent among philosophers, such as Descartes, who understood space as an absolute, independent entity. Until Einstein came along, people thought of time and space as independent, and that even if matter didn’t exist, time and space would exist on their own. Newton’s classical mechanics is at the root of this perception. Newton introduced the concept of universal gravitation, which states that objects like the Earth attract other objects, creating gravity. Newton’s ideas were proven to be accurate through observation and experimentation, and became the fundamental laws of physics for many years.
However, Einstein did not accept Newton’s idea and argued that gravity is a “bending of space. Einstein’s ideas were considered quite radical by scientists of his time, but he formed this new perspective as he delved deeper into 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 gravity’s influence (the gravitational field). However, Einstein argued that light bends within a gravitational field. This is because within a gravitational field, light is subjected to accelerated motion under the force of gravity. To explain this, he postulated that when any object exists in space, the space it occupies is curved.
If so, then heavy planets like the Sun and Earth would also warp the three-dimensional space around them because of their weight. This wasn’t just a theoretical assumption, but a scientific prediction that could be verified by actual observations. As a result, light traveling near these planets would deviate slightly from its straight path. Einstein’s hypothesis was confirmed by an observatory led by the British astronomer Eddington. On May 29, 1919, Eddington’s group traveled to Subral, Brazil, and an island in West Africa called Principe to observe a total solar eclipse in the southern hemisphere. The observation of the eclipse was a major event in the scientific community at the time and was seen as a crucial opportunity to verify Einstein’s theories. Through careful observation, the observers confirmed that light from a distant place behind the sun bent around the sun, and that the bending was consistent with Einstein’s predictions. This event caused a global sensation and catapulted Einstein’s name to instant fame. It was the downfall of Newton’s law of gravity, which had stood for more than 200 years.
If gravity is viewed as a “curvature of space,” as Einstein believed, then time is also dilated in a gravitational field. This can be naturally deduced from the fact that space is curved. Given the same instantaneous light signal, the path of the light will be different in a region without a gravitational field and in a region with a gravitational field, i.e., an observer in the region without a gravitational field will see that the light will bend and take longer to arrive in the region with a gravitational field. This is very different from our everyday experience of time. Especially in space beyond our solar system, the time delay is even greater.
Based on these facts, Einstein defined gravity as “the bending of space and time”. This definition gave birth to a new paradigm called “spacetime,” which views time and space as a unified concept. In our solar system, the gravitational field is weak, so the bending of space and time is very small. So, as far as our senses are concerned, there is no noticeable theoretical gap between Einstein’s theory and Newtonian mechanics. However, Einstein’s theory, unlike Newton’s, provided a powerful tool to explain physical phenomena in the presence of strong gravity. In contrast, in space outside our solar system, where there is heavy matter like black holes, things happen that cannot be interpreted without Einstein’s theory. The powerful gravitational field of a black hole distorts space and time to such an extreme degree that the passage of time appears to almost stop. Newtonian mechanics is useless there. This is why Einstein is said to have expanded our senses and expanded our horizons of perception.
