Classical mechanics, as laid down by Isaac Newton, was once the undisputed framework for understanding the universe. But as time progressed, scientists began noticing flaws in the theories. Enter quantum theory, which solved many of those issues but at a cost. One significant problem it tackled was the photoelectric effect, where Einstein showed that light consists of photons—packets of energy—rather than pure waves, thus reshaping our understanding of light and energy.

Another major fix came with Niels Bohr’s model of the atom, explaining why electrons orbiting a nucleus don’t constantly emit photons. However, quantum theory introduced randomness and disrupted the deterministic views held by classical mechanics. While we don’t see this randomness in our daily lives, at the microscopic level, it’s ubiquitous.

Combining Einstein’s general relativity with quantum mechanics has been hard and, so far, unsuccessful. Yet, we’ve still made great strides in understanding the universe. For small scales and high-speed particles, special relativity applies, merging smoothly with quantum mechanics in a framework known as Quantum Electrodynamics (QED). This theory, developed with major contributions from Paul Dirac, takes the continuous fields of electromagnetism and translates them into discrete quantum terms.

Dirac’s 1928 equation married quantum mechanics with special relativity, predicting antimatter’s existence—a bold stance vindicated when the positron was discovered in 1932. Later, the efforts of Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga further cemented QED’s place in physics, earning them the 1965 Nobel Prize.

QED replaces the classical idea of continuous electromagnetic fields with the exchange of photons, explaining interactions like electron repulsion in terms of quantum electromechanics. Feynman diagrams make these complex interactions more intuitive by visually representing particle interactions. Each diagram corresponds to a detailed equation, breaking down the probability and mechanics behind subatomic events.

Quantum theory also allows for numerous outcomes beyond simple photon exchange, such as the temporary creation of matter/antimatter pairs. Despite the complexity, Feynman’s pictorial representation makes navigating the math more manageable. Solving these equations can require supercomputers, given the probability decreases with each new interaction vertex.

QED’s lessons extended to other quantum field theories, such as Quantum Chromodynamics (QCD) and the Electroweak theory. Despite requiring a shift in our intuitive understanding, QED offers an astoundingly accurate description of reality—accurate to within 12 decimal points.

In essence, quantum mechanics, and specifically QED, is the most precise language we’ve found for the universe. It might defy logic, but it’s as close to absolute certainty as science gets.