Wayne Myrvold: Einstein and the Atom

The speaker opens the final lecture of the year for the Department of Philosophy's library talks, a tradition spanning 15 years. Acknowledgments are given to key contributors, including Margaret, Greg, Debra Fox, and others from the Rotman Institute. Special mention is made of the co-sponsorship by the Rotman Institute in celebration of the 100th anniversary of Einstein's theory of relativity. An upcoming lecture by Chris Mink is also highlighted, along with the significance of the year 1915 in the context of Einstein's contributions to the acceptance of atomic theory.

This paragraph delves into the historical controversy surrounding atomic theory, from its roots in ancient Greek philosophy with Democritus to its eventual acceptance in the scientific community by the 20th century. The speaker discusses the skepticism of scientists like Lord Kelvin and the pivotal role of indirect evidence in establishing the reality of atoms, drawing parallels to Sherlock Holmes's investigative methods. The importance of scientific evidence based on observable phenomena is emphasized, despite the invisibility of atoms themselves.

The speaker explains Avogadro's law and its significance in providing indirect evidence for the existence of atoms. By observing the behavior of gases and their reactions in fixed ratios, scientists inferred the existence of indivisible units. John Dalton's work is highlighted for promoting this idea, and the speaker discusses the process of how scientific evidence, even in the absence of direct observation, can lead to the acceptance of theoretical concepts.

Einstein's work on Brownian motion is introduced, where he theorized that the erratic movement of small particles suspended in a fluid could be used as indirect evidence for the existence of molecules. The speaker explains Einstein's thought process and the formula he developed to estimate the number of molecules based on the observed movement of these particles. This paragraph also touches on the historical context of Einstein's work and the limitations of the data available to him at the time.

The speaker describes how experiments by Jean Perrin provided empirical evidence for Avogadro's number by observing the movement of suspended particles, as predicted by Einstein. Perrin's measurements offered a tangible estimate of Avogadro's number, bringing the concept of atoms from theory to tangible fact. The paragraph also mentions other methods of estimating Avogadro's number, such as through radioactive decay and the blue color of the sky due to Rayleigh scattering.

The speaker discusses the convergence of various lines of evidence that collectively reinforced the reality of atoms and molecules. Jean Perrin's work is again highlighted, as he compiled different methods of estimating Avogadro's number, all of which pointed to the same conclusion. The paragraph emphasizes the strength of scientific evidence when multiple independent methods yield consistent results, effectively confirming the existence of atoms beyond reasonable doubt.

The speaker reflects on how the confirmation of atoms' existence led to a deeper understanding of their structure and behavior, with a look forward to the advancements of the 20th century. The paragraph touches on the shift from viewing atoms as indivisible and eternal to recognizing their complexity and the new 'worlds' within them. It also connects the work on Brownian motion to broader concepts in statistical mechanics and quantum mechanics, including Einstein's later work on the photoelectric effect.

The speaker addresses questions about the Sun's energy production through fusion reactions and the source of Earth's internal heat. The paragraph explains the process of nuclear fusion in the Sun and the role of gravity in maintaining the reaction. It also touches on the difference between uncontrolled fusion reactions, like hydrogen bombs, and the goal of controlled fusion as a sustainable energy source. The discussion includes the historical context of地质学家（地质学家）and the debate over the age of the Earth.

The speaker delves into the difficulties of achieving controlled fusion on Earth compared to the Sun's natural fusion process. The paragraph discusses the balance of forces within the Sun that prevent it from exploding and the statistical probabilities of atomic collisions that sustain its reactions. The conversation also explores the concept of the Sun as a 'hydrogen bomb' that continues to react due to its immense size and the pressure at its core.

The speaker concludes with a discussion on the perpetual nature of light and the Sun's ability to sustain its reactions over eons. The paragraph addresses the question of why the Sun doesn't simply explode, explaining the role of gravity and the balance of forces at play within the star. It also touches on the concept of light not requiring energy to continue in a vacuum, contrasting it with the energy needs of physical objects in motion.