The theory of relativity is one of the most important and influential scientific theories of the 20th century. Developed by Albert Einstein, the theory has revolutionized our understanding of space, time, and the nature of the universe. However, the theory is often seen as complex and difficult to understand. In this article, we will attempt to explain the theory of relativity in simple terms.To mention the principle of relativity, we have to move the story line forward a long time, because it is quite related to the famous “Earth Sun” dispute in history. As early as in ancient Greece, when people looked at the stars and the moon, they subconsciously believed that the earth they lived on was the center of the universe, and all the stars revolved around them; After long-term observation, a complex cosmological model established by Ptolemy, the Geocentric Model, can better explain some astronomical phenomena observed at that time. Presumably, high school students have some understanding of these histories, but the textbooks have devoted a lot of space to introducing them. This self centered view of the universe was very popular with the church at that time, so under the official platform, geocentrism was able to rule for a long time. In fact, despite factors other than politics, there were also ideas of heliocentrism before geocentrism, but heliocentrism could not answer what seemed to be a difficult problem at the time: Since the earth revolves around the sun, why do we jump up and fall back into place without being thrown out? Now, junior high school students will disdain to say four words: due to inertia. But you should know that the concept of inertia was something that only existed after Galileo Newton! You put it in ancient times, it’s not difficult! Even if the later Copernicus solemnly proposed the heliocentric theory, which not only greatly simplified the model of celestial motion, but also turned the explanation of the retrograde phenomenon of Mars into an obvious and achievable result, without the divine assistance of Galileo, Copernicus’s view would be as unstable as its predecessors. The core problem Galileo wanted to solve was: If the earth was rotating, why couldn’t I feel it? His insights on this issue have been brilliantly described in his masterpiece “A Dialogue between the Two World Systems of Copernicus and Ptolemy.”. Galileo envisioned a scenario in which you were thrown into a cabin that could not be seen outside. Can you determine whether the ship is stationary or in uniform linear motion by observing the conditions in the cabin? Galileo’s answer was: No! Whether you are doing a jump experiment, observing the falling point of a water droplet, or observing the water surface in a water tank, these phenomena cannot help you distinguish whether a ship is stationary or in constant linear motion. Today, you can completely repeat this experiment in a closed vertical elevator. As long as this elevator is quiet enough to run without looking at the floor indicator, you will definitely not feel the difference between the two situations when the elevator is stationary and running at a constant speed! To elevate these facts to a theoretical level, we simply cannot distinguish whether the ship is in a static state or in a uniform linear motion through mechanical experiments! Of course, you can change your boat into an elevator, a train, or even the planet we live on! When they are in a static state or a state of uniform linear motion, there is no difference in the various mechanical phenomena that occur on them! This is the well-known Galileo principle of relativity. With such a profound understanding, Copernicus’s heliocentric theory completely established itself. “Since you cannot prove whether the earth is moving through jumping experiments, isn’t the biggest obstacle to the heliocentric theory unassailable?”? Now let’s jump out of the “Earth Sun” debate and examine Galileo’s principle of relativity. There are more cognitions waiting for you to discover. We all know that when describing the motion of an object, it is necessary to select a reference object. The reference object can be arbitrarily selected, and it can be dynamic or static. Although selecting different reference objects can lead to different results in the description of the motion of the object, when the reference object is in a stationary state or a uniform linear motion state, even if the motion of the object has different descriptions, its mechanical characteristics must be the same. This is the essence of Galileo’s principle of relativity!
First let’s see the history of relativity. In the early 19th century, scientists began to study the behavior of light. They discovered that the speed of light was constant, regardless of the motion of the observer or the light source. This led to the development of the concept of the ether, a hypothetical substance that was thought to fill all of space and serve as a medium for the propagation of light.However, experiments in the late 19th century, such as the Michelson-Morley experiment, failed to detect the presence of the ether. This led to a crisis in physics and the realization that the laws of physics might not be the same for all observers.In 1905, Albert Einstein published his theory of special relativity. Einstein’s theory showed that time is relative, and that time can appear to pass differently for different observers, depending on their relative motion. This theory also led to the famous equation E=mc^2, which relates energy to mass and the speed of light. In 1915, Einstein published his theory of general relativity. This theory was based on the idea that gravity is not a force, but rather a curvature of spacetime. According to general relativity, massive objects like planets and stars warp the fabric of spacetime around them. This curvature causes other objects to move in a curved path, which we perceive as the force of gravity.General relativity has been confirmed by a wide range of experimental evidence, including the observation of gravitational waves in 2015.
What is relativity?
Relativity is a theory that explains how the laws of physics apply to objects that are moving at different speeds. It is based on two main principles:The laws of physics are the same for all observers, regardless of their motion relative to each other.The speed of light is always constant, regardless of the motion of the observer or the light source.
These principles may seem counterintuitive, but they are supported by a vast amount of experimental evidence.
Special relativity.Special relativity is the first part of Einstein’s theory of relativity. It deals with the behavior of objects that are moving at constant speeds relative to each other. One of the key ideas of special relativity is that time is relative. This means that time can appear to pass differently for different observers, depending on their relative motion.
The most famous equation in special relativity is E=mc^2, which relates energy (E) to mass (m) and the speed of light (c). This equation shows that mass and energy are interchangeable, and that even a small amount of mass can be converted into a large amount of energy.
General relativity.General relativity is the second part of Einstein’s theory of relativity. It deals with the behavior of objects that are accelerating or in a gravitational field. One of the key ideas of general relativity is that gravity is not a force, but rather a curvature of spacetime.
According to general relativity, massive objects like planets and stars warp the fabric of spacetime around them. This curvature causes other objects to move in a curved path, which we perceive as the force of gravity.
The theory of relativity has been confirmed by a wide range of experimental evidence, including the famous Michelson-Morley experiment and the observation of gravitational waves. It has also led to a number of important technological innovations, such as GPS and nuclear power.
In conclusion, the theory of relativity is a complex and challenging subject, but it is also one of the most fascinating and important scientific theories ever developed. By understanding the basic principles of relativity, we can gain a deeper appreciation of the nature of the universe and our place in it.
