scientist with beakers
Matter waves, also called de Broglie waves, are the wave nature of all matter, including the atoms that make up your body. One of the first and most important discoveries in quantum physics is that electrons have a dual wave-particle nature. It soon became clear that all matter has this dual nature, but since conventional matter has a large momentum with respect to electrons, the wavelength of matter waves is very small, and in most cases, barely noticeable. For example, the wavelength of the matter that makes up a person is on the order of 10 to 35 meters, much shorter than can be observed using current measurement technologies.
The concept of matter waves was first clarified by the French physicist Louis de Broglie, who was expanding on the early theories proposed by Albert Einstein, Max Planck, and Neils Bohr. Bohr primarily studied the quantum behavior of hydrogen atoms, while de Broglie attempted to extend these ideas to determine a wavelength equation for all matter. De Broglie devised a theory and presented it in his 1924 doctoral thesis, for which he received the Nobel Prize in Physics in 1929. This was the first case in which the Nobel Prize was awarded for a doctoral thesis.
Equations known as de Broglie relations describe the dual wave-particle nature of all matter. These relationships state that a particle’s wavelength is inversely proportional to its momentum (mass times velocity) and its frequency is proportional to its kinetic energy, which is a frame-dependent (relative) value. Therefore, particles with low momentum, such as electrons at room temperature, have a de Broglie wavelength of about 8 nanometers. Particles with even lower momentum, such as helium atoms at temperatures of a few nanoKelvins, can have matter waves with wavelengths down to a few microns. Under such unusual conditions, the realities of the quantum world are almost pushed into the realm of the macroscale.
De Broglie’s theories about matter waves were confirmed in 1927, when Bell Labs scientists Lester Germer and Clinton Davisson fired slow electrons at a crystalline nickel target. The resulting diffraction pattern demonstrated the wave characteristics of electrons, similar to those exhibited by photons such as X-rays. Matter waves could only be observed in this case because the electrons used to produce them had very low momentum. Since 1927, the wave nature of other elementary particles has been empirically demonstrated.