The Stern experiment is the experimental substantiation of the molecular-kinetic theory

In the second half of the nineteenth century, the study of Brownian (chaotic) motion of molecules was of great interest to many theoretical physicists of the time. The theory of the molecular-kinetic structure of matter, developed by the Scottish scientist James Maxwell , although it was universally recognized in European scientific circles, existed only in a hypothetical form. There was no practical confirmation of it then. The movement of molecules remained inaccessible to direct observation, and the measurement of their speed seemed simply an unsolvable scientific problem.

That is why experiments that are able in practice to prove the very fact of the molecular structure of matter and determine the speed of movement of its invisible particles were initially perceived as fundamental. The decisive significance of such experiments for physical science was obvious, since it allowed us to obtain a practical justification and proof of the validity of one of the most progressive theories of the time-the molecular-kinetic theory.

By the beginning of the twentieth century, the world science had reached a sufficient level of development for the appearance of real possibilities for experimental verification of Maxwell's theory. German physicist Otto Stern in 1920, using the method of molecular beams, which was invented by the Frenchman Louis Dunoyer in 1911, was able to measure the velocity of the gas molecules of silver. The Stern experiment irrefutably proved the validity of the Maxwell distribution law. The results of this experiment confirmed the correctness of estimating the average velocities of the atoms, which resulted from the hypothetical assumptions made by Maxwell. True, Stern's experiment was able to give only very approximate information about the nature of the rapid gradation. More detailed information science had to wait another nine years.

With greater accuracy, the law of distribution was verified by Lammert in 1929, which somewhat improved the Stern experiment by passing a molecular beam through a pair of rotating disks having radial holes and displaced relative to each other by a certain angle. Changing the speed of rotation of the unit and the angle between the holes, Lammert was able to separate the individual molecules from the beam, which have different speed indicators. But it was the Stern experiment that initiated the experimental research in the field of molecular-kinetic theory.

In 1920, the first experimental setup was created, which is necessary for carrying out experiments of this kind. It consisted of a pair of cylinders, designed personally by Stern. Inside the device was placed a thin platinum rod with a silver coating, which evaporated when the axis was heated by electricity. Under vacuum conditions that were created inside the installation, a narrow beam of silver atoms passed through a longitudinal slot cut on the surface of the cylinders and settled on a special external screen. Of course, the unit was in motion, and during the time when the atoms reached the surface, it managed to turn to some angle. In this way Stern determined the speed of their movement.

But this is not the only scientific achievement of Otto Stern. A year later, together with Walter Gerlach, he conducted an experiment that confirmed the presence of spin in the atoms and proved the fact of their spatial quantization. The Stern-Gerlach experiment required the creation of a special experimental setup with a powerful permanent magnet in its base. Under the influence of the magnetic field generated by this powerful component, the elementary particles were deflected according to the orientation of their own magnetic spin.