# What are simultaneous events in physics

## Physics compact basic knowledge 8, textbook

Relativity of simultaneity 21.3 RG 8.1 and G 8.1 Theory of relativity 7 This sentence turned the entire classical physics on its head. The principle of relativity was given up in favor of absolute space in order to combine electro-magnetism with classical mechanics within the framework of an ether theory. In classical physics, the speed of light in a vacuum only assumes the value c 0 in a system that is at rest in absolute space. The absolute space is thereby distinguished from all moving frames of reference, and the principle of relativity is therefore violated. In his special theory of relativity, Albert Einstein renounced the concept of absolute space and thus the ether. He showed that if the principle of relativity is maintained, Newton's mechanics must be corrected because the assumptions about space and time within the theory of relativity differ from our everyday experiences. The formalism of Maxwell’s theory of electromagnetism could be incorporated unchanged into the special theory of relativity. However, the formulas had to be reinterpreted. The speed of light in a vacuum, regardless of the state of motion of the source and observer, always has the same value c 0. Regardless of the state of motion of the source and the observer, the speed of light always has the same value c 0 in vacuum. According to the definition of the meter, the following applies since 1983: c 0 = 299 792 458 m / s Fig. 7.1 Three observers show different speeds with regard to the light source. Nevertheless, both measure the same value for the vacuum speed of light c 0. A1 Explain the outcome of Michelson and Morley's experiment using the principle of the constancy of the speed of light! The two principles of the special theory of relativity appear at first glance to be not very radical and do not suggest any dramatic effects. In fact, the following unexpected and far-reaching consequences arise, for example: Principle of the constancy of the speed of light W1 1. Whether two events take place at the same time depends on the state of motion of the observer. 2. The following applies to observers at rest: Moving clocks go slower, moving scales are shorter and moving masses are more sluggish. 3. The vacuum speed of light cannot be exceeded by particles. 4. Space and time cannot be viewed independently of one another. Relativity of simultaneity A2 Indicate when one speaks of simultaneous events in everyday life! In everyday life, the term “simultaneity of events” is used without the meaning of this term being precisely defined. Fig. 7.2 We look into the past. The light impressions that reach our eyes at the same time come from events that by no means have to have taken place at the same time. A3 Interpret Fig. 7.2 on the right and explain how it can be determined that two events take place at the same time! Two events are simultaneous if they could be started by the same light signal from a light source located in the middle between the locations of the events. Two events are simultaneous, if they could be started by a light source located midway between the locations of events by the same light signal. Fig. 7.3 The arrival of the first photons at those points which are a distance I from the light source corresponds to the events E 1 and E 2. Both events take place for observer B at the same time. A4 Is the declaration of simultaneity you have given compatible with the above definition? 21.3 E1 E2 l l E 1 E 2 B De˜nition of simultaneity S1 For testing purposes only n - Property of the publisher öbv