The Story of Physics ft. Edward Witten

The script begins by tracing the origins of relativity back to 19th-century works on electromagnetism by Maxwell, Faraday, and others. It highlights how Maxwell's equations unexpectedly described light waves and predicted their constant speed, regardless of the source, which contradicted traditional Newtonian physics. The Michelson-Morley experiment later confirmed this constant speed of light. The script then describes the emergence of quantum theory due to the discovery of the electron and the inability of classical physics to explain its behavior around atomic nuclei. It mentions Niels Bohr's model of the atom and the development of quantum mechanics in the 1920s, which treated electrons as both particles and waves.

The script discusses the efforts to reconcile quantum mechanics with Einstein's theories of relativity. It details the successful unification of quantum mechanics with special relativity, leading to the prediction of antimatter by Paul Dirac. The script then addresses the challenges faced in combining quantum mechanics with general relativity, Einstein's theory of gravity, which resulted in inconsistencies and contradictions. This led to the exploration of string theory as a potential framework for a unified theory that could encompass all fundamental forces and particles.

The script narrates the evolution of string theory from its initial conception to explain the strong nuclear force to its role as a candidate for a theory of everything. It describes the Veneziano amplitude and the subsequent realization that string theory could potentially describe all particles and forces, including gravity. The discovery of supersymmetry within string theory is highlighted as a key development, predicting new particles and offering a new perspective on the fundamental structure of the universe.

The script explains how string theory requires extra dimensions beyond the familiar three dimensions of space and one of time for consistency. It also discusses the theory's prediction of massless particles, which initially seemed at odds with the goal of describing the strong nuclear force. However, these massless particles were later reinterpreted as necessary components for a quantum theory of gravity, aligning with the need to describe gravitational waves as predicted by Einstein's general relativity.

The script outlines the shift in perspective that led to the reinterpretation of string theory as a theory of quantum gravity rather than just a theory for strong interactions. It discusses the work of physicists like Michael Green and John Schwarz, who showed that string theory could incorporate supersymmetry in a way that was not initially apparent. The script also mentions the discovery that the five known string theories were actually different limits of a single, more comprehensive theory, later referred to as M-Theory.

The script highlights the importance of parity violation in particle physics and how string theory initially struggled to account for this asymmetry between left and right. The breakthrough work of Green and Schwarz in 1984, which introduced the concept of anomaly cancellation, is discussed as a significant milestone that allowed string theory to accurately model the weak interactions and address the issue of parity violation.

The script delves into the implications of string theory for cosmology, particularly the idea of a multiverse with different regions having different physical properties. It discusses the discovery of the accelerating expansion of the universe and the concept of dark energy, which suggests that the vacuum energy of empty space might not be zero. This has led to speculation about the nature of the universe before the Big Bang and the potential for diverse physical laws in different cosmic regions.

The script anticipates the potential discoveries at the Large Hadron Collider (LHC) at CERN, focusing on the search for supersymmetry. It explains that the discovery of supersymmetric particles would confirm predictions of string theory and revolutionize our understanding of fundamental particles. The script also touches on the personal connection of the speaker to supersymmetry and its significance in advancing the field of theoretical physics.

The script uses the analogy of musical harmony to explain the concept of strings vibrating in different ways to produce the variety of particles and forces observed in the universe. It describes how string theory attempts to unify all phenomena in nature within a single field theory, combining quantum mechanics and general relativity. The script also discusses the historical development of string theory and its evolution into M-Theory as the candidate for a super unified theory of nature.

The script reflects on the importance of intuition in theoretical physics, drawing a comparison to Einstein's ability to make great leaps in understanding. It discusses the process of discovery in physics as more incremental and collaborative, involving the synthesis of ideas within a framework. The speaker shares personal anecdotes about their journey into physics, the role of curiosity, and the joy of exploring the unknown.

The script concludes with a discussion on the ambitious nature of string theory and the challenge of testing such a comprehensive framework. It acknowledges the difficulty of proving the theory but points to historical precedents where once seemingly untestable ideas have been confirmed. The speaker also shares thoughts on the legacy of great scientists and the pressure to contribute meaningfully to the field, emphasizing the importance of enjoying the process of scientific discovery.