Yaffa asked: How does quantum mechanics influence practical science? What led to the foundation of this theory, and how does it influence humanity 

Hello Yaffa,

Towards the end of the 19th century, some new phenomena were discovered that could not be explained by known physics of that time. This led to the development of quantum theory in the early 20th century. Among the most noteworthy phenomena, were black-body radiationhydrogen spectral series and the photoelectric effect.

In 1900, the German physicist Max Planck proposed an explanation for black-body radiation; assuming that light is made up of discrete quantities of energy (quanta) and that the amount of energy in each quantum is proportional to the frequency of light. Previous calculations of black-body radiation energy yielded the irrational result that the body supposedly emits an infinite amount of energy (also called the ultraviolet catastrophe).Planck’s revolutionary idea, a simple physical assumption, went on to explain black-body radiation spectrum for the first time. He received the Nobel Prize in 1918 for this research.

Afterwards, Albert Einstein used Planck’s assumptions to explain the photoelectric effect. And Niels Bohr utilized the same ideas in order to explain the hydrogen spectral series. Over the next fifty years, quantum theory has developed remarkably, and today it remains one of the building blocks of physics. Every physicist knows its fundamentals, and nowadays most active research is developed from its theories

Pictured: A photo from the Solvay Conference in 1927 including many of the physicists who developed the fundamentals of quantum theory.

In most physical phenomena we encounter in our everyday lives, we do not see these discrete amounts of energy; the quantum properties of particles are hidden from our eyes. Nevertheless, quantum theory is essential for the way we understand the world. Without it we could not properly explain the colors of the sun and the sky, basic properties of materials, nor the periodic table of elements.

On the more practical side, basic technologies that we use every day are based upon quantum theory: for instance transistors (the basic components of computers, calculators and cellphones of all kinds), lasers, LED and fluorescent lamps, solar cells, MRI machines in hospitals, magnets etc.

Boomerang – Question Back at You
What cat is famous in the context of quantum theory and what basic principle in the theory does it demonstrate?

Hagai Edri
Department of Physics of Complex Systems
Weizmann Institute of Science

Article translated from Hebrew by Elee Shimshoni, PhD student at the Weizmann Institute of Science.

A note to the readers
If you find the explanations unclear or have further questions, please drop us a line on the forum. We welcome your comments, suggestions and feedback.