A Century of Quantum

 

Copyright: Sanjay Basu

From Planck’s Quanta to Tomorrow’s Mysteries

The Crack in the Wall

At the turn of the twentieth century, physics seemed nearly complete. Newton’s mechanics, Maxwell’s equations, and thermodynamics had sewn together a picture of the universe so tight you could almost hear the hum of certainty. The textbooks promised that all that was left were refinements. Decimal places to be filled in, equations to be polished.

And then came the crack. A problem with radiation, of all things. A dull problem, more bookkeeping than revelation. Why did heated objects glow the way they did? Classical theory predicted a catastrophe, an infinite flood of energy in the ultraviolet. Experiments said otherwise.

Into that crack stepped Max Planck in 1900. His solution was both desperate and audacious: energy, he suggested, came in tiny, indivisible packets. Quanta. He didn’t much believe it himself at first. It felt like a trick. Yet that idea split physics open, and out poured a century of wonder and confusion.

A Centennial Worth Pausing For

Here we are in 2025, marking a hundred years since Werner Heisenberg scribbled out the first true form of quantum mechanics on a lonely island in the North Sea. The UN has declared it the International Year of Quantum Science and Technology. It’s a centennial not of a finished theory, but of a revolution still unfolding.

Quantum mechanics has given us semiconductors, lasers, MRI machines, GPS, and perhaps soon quantum computers and sensors that will change how we live. But it has also given us headaches, paradoxes, and late-night debates about whether the moon exists when no one is looking.

A century in, the quantum story is as much about people as it is about equations. Some names are famous. Einstein, Schrödinger, Feynman. Others are almost forgotten. Lucy Mensing, Maria Goeppert Mayer, Deborah Jin. And still others are personal, like my own great uncle Satyendra Nath Bose, whose quiet letter to Einstein shaped a whole new state of matter.

Let’s walk through this century not as a dry chronology, but as a narrative, decade by decade, stopping at the moments that mattered, listening for the voices that often got drowned out.

1900–1910: Sparks of the Quantum

It begins with Planck’s quanta in 1900, an act of reluctant genius. Five years later, Albert Einstein sharpened the blade. In 1905, while working as a patent clerk in Bern, he showed that light itself could behave as particles, Photons, explaining the photoelectric effect. The Nobel Prize would eventually come for this, not relativity.

In 1911, the first Solvay Conference gathered Einstein, Curie, Lorentz, and a handful of others in Brussels. They debated radiation and quanta with more confusion than clarity. But a new world was brewing.

By 1913, Niels Bohr proposed his planetary atom. Electrons were circling the nucleus in quantized orbits. It explained hydrogen spectra, but left an itch: why should nature care about orbits like rungs on a ladder?

The 1910s also saw the Stern–Gerlach experiment fling silver atoms through a magnetic field and discover they split cleanly into two beams. Spin, a new quantum property, entered the stage. The old smooth world of classical physics was crumbling into steps, jumps, and probabilities.

1920s: Quantum Is Born

In the 1920s, the dam burst.

In 1923, Arthur Compton scattered X-rays off electrons, showing light acted like a billiard ball, carrying momentum. In 1924, Louis de Broglie, a French prince turned physicist, proposed that if light could be both wave and particle, so could electrons. His doctoral thesis suggested all matter had a wavelength. A year later, Davisson and Germer would prove him right.

More on the seminal paper, accompanied by a letter, later, from my great uncle to Einstein on June 4, 1924.

Then came 1925. Werner Heisenberg, plagued by hay fever, retreated to the island of Heligoland and reimagined physics not in terms of orbits but in terms of matrices. Strange arrays of numbers that could predict spectral lines but defied visualization. Together with Max Born and Pascual Jordan, he hammered this into matrix mechanics, the true birth certificate of modern quantum mechanics.

Erwin Schrödinger, in 1926, offered a different but equivalent picture. Wave Mechanics. His equation described electrons as rippling waves of probability. Suddenly, electrons weren’t tiny planets. They were smeared-out clouds, existing everywhere until you looked.

And then Heisenberg added his infamous 1927 uncertainty principle. You can never know both position and momentum exactly. Certainty itself had been outlawed.

That same year, the fifth Solvay Conference in Brussels became legendary. Einstein argued, “God does not play dice.” Bohr countered, “Stop telling God what to do.” Physics had become philosophy by other means.

1930s: Expanding the Quantum Zoo

The 1930s saw quantum mechanics extend its reach. Paul Dirac merged relativity and quantum theory, predicting the existence of antimatter. Carl Anderson soon found the positron in cosmic rays. The quantum world was getting crowded.

Hidden figures began to shape this era too. Lucy Mensing, one of the first women to apply quantum mechanics to molecules in the late 1920s, laid groundwork for spectroscopy that chemists would use for decades. Her name is rarely mentioned, but her fingerprints are everywhere in molecular theory.

By 1935, Einstein, Podolsky, and Rosen published their EPR paradox, arguing that quantum mechanics was incomplete. Schrödinger responded with his infamous cat, both alive and dead until observed. The philosophical discomfort was palpable.

Yet even in discomfort, progress. Quantum mechanics became the language of chemistry, of nuclear physics, of the entire microscopic world.

1940s–1950s: From Chalkboard to Cold War

The mid-century decades hardened quantum into a tool, sometimes terrifyingly so. Quantum mechanics underpinned the Manhattan Project. The splitting of atoms, the binding of nucleons, the chain reactions of fission. All of it was written in quantum ink.

But beyond the bomb, subtler experiments refined the theory. In 1947, Willis Lamb and Robert Retherford discovered the Lamb shift. A tiny discrepancy in hydrogen’s energy levels. Theorists like Feynman, Schwinger, and Tomonaga used it to build quantum electrodynamics (QED), the most precise theory physics has ever known.

In 1956, Chien-Shiung Wu performed her cobalt-60 experiment, showing that the weak nuclear force violates parity. Nature, it turned out, could tell left from right. Lee and Yang won the Nobel; Wu did not, though her experiment made their theory real. Man!

And in 1955, Clyde Cowan and Frederick Reines finally detected the elusive neutrino, a particle Pauli had once called a “desperate remedy.”

This was also the era of transistors, invented in 1947 at Bell Labs, translating quantum tunneling into the foundation of the digital world.

A Family Connection: S. N. Bose

Amid this mid-century ferment, I pause to honor a personal figure. Prof. Satyendra Nath Bose, my great uncle. In 1924, he sent Einstein a paper on photon statistics, so elegant that Einstein translated it into German himself. Together, they developed the theory of what would be called the Bose–Einstein condensate: a state where particles pile into the same quantum state, marching in perfect lockstep as a single wave.

At the time, it was theoretical fantasy; there was no way to cool atoms enough. But in 1995, scientists finally achieved it in the lab. Today, Bose–Einstein condensates are playgrounds for probing quantum behavior. Every time atoms condense into one giant wavefunction, it’s Bose’s insight made flesh.

Boson has immortalized Bose. The general term “boson” is named after him, Bose, to commemorate his contributions to the statistical description of such particles.

1960s: Quantum Becomes Practical

By the 1960s, quantum mechanics was no longer young rebellion. It was infrastructure. The first working laser was built in 1960 by Theodore Maiman, turning Einstein’s theory of stimulated emission into an object that would transform communications, medicine, even entertainment.

Maria Goeppert Mayer received the Nobel in 1963 for her nuclear shell model, a triumph achieved after years of unpaid academic work. She showed how protons and neutrons arrange themselves in shells, much like electrons in atoms, cracking open the logic of nuclear stability.

Meanwhile, Murray Gell-Mann introduced quarks in 1964, at first as a mathematical trick. They soon became the building blocks of matter.

Quantum had slipped out of ivory towers and into every household, embedded in transistors, televisions, and radios.

1970s: Symmetry and Unification

The 1970s were about unification. Sheldon Glashow, Steven Weinberg, and Abdus Salam built the electroweak theory, merging electromagnetism with the weak nuclear force. Salam, a Pakistani physicist, became the first Nobel laureate from his country, though his achievements were muted at home because of religious discrimination. His story is one of brilliance entangled with politics.

More on a brief encounter with Prof. Salam, when I was eleven, in a later article.

At the same time, quantum chromodynamics emerged as the theory of quarks bound by gluons. The Standard Model, still our best description of particles, came into focus.

And in the practical world, semiconductor physics surged ahead, setting the stage for the personal computer revolution. Quantum was no longer philosophy; it was industry.

1980s: Precision and Paradoxes

The 1980s brought both breathtaking precision and renewed philosophical strangeness.

In 1980, Klaus von Klitzing discovered the quantum Hall effect, so precise it became a new standard for resistance.

In 1982, Alain Aspect’s experiments confirmed Bell’s theorem. Entanglement was real, local realism was dead.

Meanwhile, Mildred Dresselhaus, the “Queen of Carbon,” pioneered the physics of low-dimensional systems, laying groundwork for nanotechnology decades before the buzzword existed.

And in 1981, Richard Feynman proposed using quantum systems to simulate nature. He was sketching the blueprint for quantum computing. His provocation: “Nature isn’t classical, dammit, and if you want to make a simulation of nature, you’d better make it quantum mechanical.”

1990s: Information Becomes Quantum

The 1990s shifted focus from particles to information itself. Peter Shor’s algorithm in 1994 showed that a quantum computer could crack encryption schemes underpinning the digital world. Security suddenly seemed fragile.

In 1997, Anton Zeilinger’s team achieved quantum teleportation, transmitting a photon’s state without moving the particle itself. The word “teleportation” grabbed headlines, but the deeper truth was subtler: entanglement could transmit information beyond classical limits.

Quantum cryptography also emerged, with Bennett and Brassard’s key distribution scheme proving secure against eavesdroppers. The field of quantum information science was born.

2000s: From Ghosts to Tools

In the 2000s, the ability to trap and manipulate single atoms and photons matured. Serge Haroche and David Wineland built laboratories where quantum states could be tickled and measured at will.

In 2003, Deborah Jin created the first Fermi condensate, extending Bose’s dream into the fermionic world. Her work remains central to ultracold physics, though her name is rarely mentioned outside the field.

The idea of quantum computers went from chalkboard fantasy to experimental roadmaps. The first qubits. Trapped ions and superconducting circuits entered the stage.

2010s: The Quantum Race

The 2010s made quantum geopolitical. China launched the Micius satellite, distributing entanglement across thousands of kilometers. The EU invested a billion euros in quantum technologies. The U.S. passed the National Quantum Initiative Act in 2018.

In 2019, Google claimed quantum supremacy with its Sycamore chip, performing a task in minutes that would take classical computers millennia. Critics argued over definitions, but the point was made: the race was real.

Researchers like Rainer Blatt and Jian-Wei Pan quietly achieved extraordinary control over ions and photons. Their work, though less flashy, laid the real foundations for the field’s future.

2020s: Quantum in the Public Mind

In the 2020s, quantum became mainstream conversation. Venture capital flowed. Startups promised machines that could revolutionize drug discovery, finance, cryptography. Some of this was hype; some was real.

Quantum sensing emerged as a practical game-changer, with interferometers that could navigate without GPS and magnetometers that could read the brain’s activity without electrodes.

And in 2022, the Nobel Prize went to Aspect, Clauser, and Zeilinger. A belated recognition for decades spent turning entanglement from philosophy into physics.

We are now in 2025, one hundred years since quantum mechanics became a discipline. And still, the questions linger: What collapses the wavefunction? Does observation shape reality? Are probabilities fundamental, or just placeholders for ignorance?

The Unfinished Symphony

Quantum mechanics is a century old, but it feels like a book half-written. It has given us everything from semiconductors to satellites, yet it still leaves us groping at questions of reality itself.

It is a story of giants. Planck, Einstein, Schrödinger, and also of those history overlooked, Lucy Mensing, Maria Goeppert Mayer, Chien-Shiung Wu, Mildred Dresselhaus, Deborah Jin, Abdus Salam. And, of course, Prof. S. N. Bose, whose quiet collaboration with Einstein still shapes laboratories today.

One hundred years in, quantum mechanics is not done. It is an unfinished symphony, humming its strange tune, waiting for the next movement.

And perhaps that’s the real gift. Not answers, but the questions that keep us awake at night.