Until the end of the 19th century, it was assumed that ether as a hypothetical substance penetrated all matter and space. The propagation of electro-magnetic waves was also explained with the aid of the light-ether hypothesis. Theorists such as James Clerk Maxwell (1831-1879) were firmly convinced that ether occurs as a substance which is in a stat [..]

Speed which is always constant, irrespective of the reference system under which it is measured. Einstein made the absolute speed of light the basis for his Special Theory of Relativity. This made the idea of an "absolute rest" (rest regarded under every reference system) untenable.

A universal time measurement which is the same for all observers in the universe irrespective of their movement. In Newtonian Mechanics absolute time plays a decisive role – Einstein was the first person to demonstrate that time must also be understood relative to a point of reference.

Acceleration is the measurement of the change in speed: A freely moving body which experiences an effect of force shows an accelerated movement. Negative acceleration is also called deceleration (or slowing-down).

Precision clocks with a deviation of approximately one second in three to thirty million years. The atomic clocks made it possible to confirm by experiment the effects on time predicted by the Special Theory of Relativity. The first atomic clock was constructed in the USA in 1949 using technology developed by the American chemist and physicist Isid [..]

The scientific postulation, testing and discussion of principles of natural science, which does not have to be motivated by any practical application. Einstein's work was pure theoretical physics. His theories show best how basic research can become useful even if no practical application can be derived at first.

In 1827, the botanist Robert Brown observed an irregular motion of pollen under a microscope. At first, a comparison to the migration of spermatozoa seemed obvious. Then, however, he also noted the phenomenon in the smallest particles of inanimate matter. The cause of motion is therefore of a physical and not a biological nature and it is dependent [..]

Science of the movement of objects and the impact of forces on them. The basic laws of mechanics were developed by Galileo Galilei (1564-1642), Christiaan Huygens (1629-1695) and Isaac Newton (1643-1727). Until well into the 19th century, people believed that all physical phenomena originated from mechanical processes. Einstein's theory of rel [..]

The lightest electrically charged stable elementary particle. Electron (Greek) means amber because electricity was first observed in amber. The electron and its properties in electric and magnetic fields are important for the development of the theory of relativity.

The term "energy" designates the ability of a physical system to perform work. In this process, the generated energy can be transferred to other bodies. In 1905, Einstein was the first to show that mass and energy are the same in essence.