How to prove that you are made of atoms?
Brownian motion explained...
A physicist is just an atom’s way of looking at itself - Neils Bohr
Greetings, fellow Bohron! (Special thanks to my friend Tejas for this beautiful new name.)
What is everything in this universe made up of? Today, we can answer this simply: atoms. Although the idea of the existence of atoms was popularized centuries ago, proving the physical significance of atoms remained a mystery for a long time.
If you have ever seen a light ray inside a dark room, you must have observed the randomly moving dust particles. But why just any direction? Why not up? Down? Left? Right?
The secret lies in the medium(air in this case) in which the dust particles float. A relatively heavy dust particle is bombarded from all directions by invisible and lighter air molecules every now and then. The net impact of numerous air molecules is enough to continually change the direction of the dust particle after every collision.
Kinetic Theory of Gases: An Overview
Einstein's derivation established a relationship between the random walk of a single particle and the scattering of many particles. Einstein was very realistic with the molecular kinetic theory of heat.
What was this theory about?
In liquid, extremely small-sized particles only visible through a microscope perform movements that we can effortlessly detect as a molecular motion of heat. This idea of Einstein was applied to the interaction between a fluid of Brownian particles and the fluid that has suspended particles.
Discovery
In 1827, one day botanist Robert Brown was observing pollen grains suspended in water, when he saw that they were dancing around randomly. He thought pollen grains were busy with their reproductive activity. For Robert's pollen grains, the medium consists of water molecules, but the reasoning is also the same.
“On the Motion of Small Particles Suspended in a Stationary Liquid, as Required by the Molecular Kinetic Theory of Heat“, (received May 11 and published July 18 in the journal Annalen der Physik) was the second paper by Einstein in 1905.
This paper indirectly proved the existence of atoms as physical particles and led to the subsequent development of the kinetic theory.
This random motion of particles suspended in a medium is known as Brownian motion.
This phenomenon is similar to the diffusion process, which is the movement of matter or energy from high to low-pressure regions. Einstein accurately predicted the exact trajectories of the particles through his knowledge of Statistical Mechanics and the Kinetic Theory of Gases. Similar predictions were also made by Polish physicist Marian Smoluchowski in 1906.
The same experiments were repeated with particles derived from dead plants and rocks, volcanic ashes, and meteorites. The results were the same.
Applications
Earth and Environmental Sciences
Life sciences
Dynamic processes(crucial for sustaining life).
Engineering and technology
Even after his paper was published, physicists like Ernst Mach and Wilhelm Ostwald didn't like the idea of the existence of atoms. In 1908, Einstein provided more experimental details regarding the Brownian motion. Finally, his ideas were proved to be true through the experiments of French physicist J.B. Perrin. For this consequential verification, Perrin was honoured with the Nobel Prize in Physics in 1926.
