Why a theory of everything is so hard to find - physicist explains | Don Lincoln and Lex Fridman

Don Lincoln and Lex Fridman explore the history of physics through the lens of unification — the recurring pattern where phenomena once thought unrelated are discovered to be governed by the same underlying principles. Lincoln begins with Newton, who in the mid-1600s unified terrestrial gravity (objects falling on Earth) and celestial gravity (the motion of planets and moons) into a single universal law of gravitation. The word 'universal' in Newton's law, Lincoln notes, was deliberately chosen to signal this unification.

Lincoln then traces the next major unification to the 1800s, when James Clerk Maxwell synthesized decades of experimental work on electricity and magnetism into a unified set of equations — electromagnetism. Maxwell's equations revealed that electricity and magnetism are two sides of the same phenomenon, and as a further consequence, applying calculus to them yields a wave equation whose solution travels at the speed of light, effectively proving that light itself is an electromagnetic wave. This also underlies much of chemistry, since atoms are held together by electromagnetic forces.

The broader goal Lincoln describes is a 'theory of everything' — a single framework that would explain all matter, energy, space, and time. He draws an analogy to Lego bricks: knowing the smallest building blocks of nature is not enough; you also need to understand how they interact, which is why forces are studied alongside particles. Lincoln positions particle physics and cosmology as the disciplines most directly aimed at this reductionist bottom-up understanding of reality.

Lincoln makes a strong case for the practical value of fundamental research, citing how basic studies of electricity and magnetism led to the entire modern technological society, and how nuclear physics — once purely theoretical — now offers humanity a powerful energy source in the form of nuclear fission and potentially fusion. He extends this argument speculatively to unsolved mysteries like antimatter and dark energy, suggesting breakthroughs there could unlock future energy sources and even propulsion systems for space travel.

The conversation acknowledges the dual-edged nature of scientific power — that the same discoveries enabling nuclear energy also enabled nuclear weapons — and argues that while scientists can discover how the world works, society as a whole must decide how to apply those discoveries. The discussion closes on a celebratory note about the intrinsically human impulse to understand the universe, describing science as collective curiosity that, over time, transforms civilization.