Shulou(Shulou.com)11/24 Report--

All really brilliant ideas have been thought thousands of times, but for them to really become our thoughts, we must honestly rethink them until they take root in our life experiences.

John Wolfgang von Goethe

Albert Einstein (1879-1955) was not only a physicist, but also a real innovator, a man who tore down the physics building with his own hands. His unique attitude towards science was determined by deep curiosity and imagination. He dared to question the basic laws of the universe, thus changing our understanding of reality.

Einstein's thought experiment (Gedankenexperimente in German) was the method he used to explore the most complex and abstract concepts and a key part of his method of developing the theory of relativity.

He is neither the first nor the last to conduct thought experiments in research, but at least in his time, no one can match his ability to use thinking to study areas that cannot be touched by practical experiments.

Unlike physical experiments, thought experiments do not produce new results, but they must be able to draw definite inferences based on the initial hypothetical reasoning.

Here are some of Einstein's iconic thought experiments that reflect some of his most groundbreaking discoveries.

Chasing the beam Einstein wrote in his biography:

... I discovered a paradox when I was 16. If I chased a beam of light at speed c (the speed of light in a vacuum), I should observe that the beam is a static electromagnetic field, even though it oscillates in space. However, no matter according to experience or according to Maxwell equations, there seems to be no such phenomenon. From the beginning, I saw clearly intuitively that from the point of view of such an observer, everything must be done according to the same law as the observer who is relatively stationary. So how does the first observer know or determine that he is moving at a fast and uniform speed? In this paradox, we see the sprout of special relativity.

In other words, Einstein's thought experiment considered the situation of moving at the speed of light and a beam of light. He reasoned that if this were possible, the beam would freeze in time, contradicting Maxwell's equations. However, Einstein finally concluded that the speed of light is constant, that light must travel at 300,000 kilometers per second, and that time, not the speed of light, must be changed.

For people who move with the beam, the rotation of the clock is normal. However, for observers outside the beam, the moving person's clock is much slower and may even stop completely.

Einstein's groundbreaking work on special relativity came from this thought experiment when he was 16.

The elevator experiment, a famous thought experiment, inspired Einstein to put forward his most beautiful theory of general relativity in 1915, which describes how matter and energy bend space-time and how the bending of space-time affects the motion of matter in the universe.

Suppose you find yourself in a windowless elevator suspended in space, he points out. If the elevator is stationary, you will feel the same gravity as standing on the ground, but if someone is pulling the elevator up with a rope to speed it up, you will feel as if you are being pushed down. So the question arises: is this feeling caused by gravity or by the acceleration of the elevator? It is clear that the two produce the same result, a question that led Einstein to conclude that gravity and acceleration are indeed equivalent.

This thought experiment helped Einstein establish the principle of equivalence, that is, the gravity effect and the acceleration effect are indistinguishable. This principle later became the basis of general relativity.

Einstein wrote in his personal memoirs in 1920:

In 1907, when I was busy writing a summary of my work on special relativity for the Jahrbuch der Radioaktivit ä t und Elektronik, I came up with the happiest idea of my life: the gravitational field exists only in a way similar to the electric field generated by electromagnetic induction. For example, for an observer who falls freely from the roof, there is no gravitational field during his fall, at least in a small area near him. In other words, if the observer releases any objects, they are still moving at rest or at a uniform speed relative to him, regardless of their special physical or chemical properties. So the observer has reason to interpret his state as "stillness".

EPR paradox Einstein was one of the founders of the old quantum mechanics, but he did not agree with some of the basic principles derived from this theory. He believes that the theory of quantum mechanics is incomplete and that there must be some potential physics that cannot be explained by the probability interpretation of quantum mechanics. He dislikes the principle of uncertainty, that is, a pair of physical quantities, such as coordinates and momentum, time and energy, cannot be accurately measured at the same time. The more accurate the measurement of one physical quantity, the greater the measurement error of the other. Einstein opposed the principle of uncertainty because he thought it meant a lack of determinism in the physical world.

Bohr and Einstein are both very clever people. Einstein tried to prove that quantum mechanics was self-contradictory, while Bohr kept trying to overturn his theory. But in Einstein's last counterattack, he pointed out some very profound, counterintuitive, confusing but at the same time exciting points that attracted another group of theoretical physicists at the beginning of the 21st century. Bohr's response to Einstein's last great discovery, entanglement, was to ignore it.

Leonard Suskind

EPR paradox is a thought experiment put forward by Albert Einstein (Albert Einstein), Boris Podolski (Boris Podolsky) and Nathan Rosen (1935). The purpose of this experiment is to clarify the problems in the author's interpretation of quantum mechanics.

The basic idea of the EPR paradox is that the state of one of the two entangled particles depends on the state of the other in the entangled pair, even if they are far apart. For example, if one particle is "spin up", then another particle is "spin down" or vice versa. But before the measurement, until the measurement is completed, we do not know the spin direction of any particle. This seems to violate the locality principle, that is, events can only be affected by their direct environment.

Einstein, Podolski and Rosen believe that this entanglement suggests that there must be some kind of instantaneous communication between particles ("ghostly super-distance interaction"), which to some extent violates the principle of relativity because it breaks the limit of the speed of light. They proposed this thought experiment to prove that quantum mechanics is incomplete and that there must be some hidden variables to determine the behavior of particles.

However, subsequent experiments show that the EPR paradox is incorrect and entanglement does not violate the principle of relativity.

Physicist John Stewart Bell (1928-1990) proposed a theory in 1964 to explain how entangled particles exchange information. This thought experiment was verified by experiments in the 1970s, and the results showed that Einstein's view of quantum entanglement was wrong.

Twin paradox one of Einstein's most interesting thought experiments is the twin paradox, which involves two twins, one staying on earth and the other traveling in space at a speed close to the speed of light.

According to the theory of relativity, time is relative to the observer's frame of reference, which means that the time experienced by a traveler in space is different from that experienced by his brother on Earth.

As a result, when the traveling twin came back, he was younger than the one left on earth. This thought experiment helps us to understand the effect of time inflation in a very intuitive way.

In a word, Einstein's thought experiment is a key part of his method of putting forward new ideas and theories in physics, and his thought experiment continues to be studied by scientists and scholars to this day.

Author: Areeba Merriam

Translator: Xiao Cong

Revision: Tibetan idiots

Original link: einstein's best-known thought experiments

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Areeba Merriam

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.