Question

Reading through Einstein's Brownian motion paper On the Movement of Small Particles Suspended in Stationary Liquids Required by the Molecular-Kinetic Theory of Heat, it seems the final argument is that he can calculate the Avogadro's constant by using data on the diffusion rates, particle size and fluid viscosity. But its hard to see the connection that ultimately atoms must exist. Can someone lay out a flowchart of step-by-step reasoning leading to that conclusion? I see all the math steps, but need a more philosophical type of breakdown. Also can't the random movement and diffusion law movement of the particles be just as well explained by fluctuations of pressure and density of continuous matter?

A) Observations of Brownian motion led to the formulation of diffusion laws, implying that the random movement of particles could be explained by fluctuations in pressure and density of continuous matter, negating the need for the existence of discrete atoms.

B) Einstein used empirical data on diffusion rates, particle size, and fluid viscosity to mathematically model Brownian motion. However, the ultimate connection between these observable phenomena and the existence of atoms remains elusive, as the interpretation of these phenomena varies.

C) By analyzing the statistical behavior of suspended particles undergoing Brownian motion, Einstein inferred the existence of discrete atoms, postulating their interaction with the particles and providing a mathematical framework to calculate Avogadro's constant.

D) The philosophical breakdown of Einstein's argument concerning Brownian motion does not definitively establish the existence of atoms but rather highlights the necessity for continuous revisions and reevaluation of scientific theories based on empirical observations and mathematical models.

Answer 1

Einstein's mathematical model of Brownian motion and subsequent experimental confirmation by Perrin provided direct evidence for the existence of atoms, allowing precise measurement of Avogadro's number.

Step-by-step explanation:

Einstein's work on Brownian motion has been critical in establishing the evidence for the existence of atoms. Through mathematical modeling, using empirical data on diffusion rates, particle sizes, and fluid viscosity, Einstein was able to predict the behavior of particle movement. These predictions matched the observed Brownian motion, suggesting that the particles were being jostled by individual atoms. Following up on Einstein's theory, Jean-Baptiste Perrin performed experiments that confirmed these predictions and calculated a precise value for Avogadro's number. Perrin's measurements of atomic and molecular sizes through Brownian motion provided the first truly direct evidence of atoms and led to him receiving the Nobel Prize for his work in 1926.

The philosophical breakdown of this evidence proceeds from the visible effects of invisible causes. While pressure and density fluctuations could explain the movement, Einstein's theory that molecular collisions were causing the observed motions provided a means to measure the unseen forces at work. This was a philosophical shift from concepts of continuous matter to those supporting the discrete nature of matter as comprised of atoms.