Quantum Physics

The Mind-Bending Story

12 min readAug 5, 2023
Image by Bamdad Norouzian

Exploring the Curious Beginnings

In the bustling streets of Berlin, circa 1890, a new era of industrialization was underway. The German Empire, fresh in its unity, embarked on a journey of innovation and progress. Among the marvels of modern technology, the light bulb emerged as a symbol of this advancement. However, little did anyone anticipate that this humble invention would be the catalyst for a scientific revolution that would reshape our understanding of the universe.

The Illuminating Puzzle: Color and Heat

The early 1900s saw engineers grappling with a perplexing challenge related to the light bulb. They noticed that as they heated the bulb’s filament, not only did its brightness increase, but its color changed as well. The relationship between temperature and the resulting color of light remained a baffling mystery. To solve this conundrum, the German government established the Technical Research Institute in Berlin and enlisted the help of a meticulous scientist named Max Planck.

The Birth of Quantum Mechanics

Planck’s task seemed deceptively simple: explain the connection between temperature and the color of light emitted by a heated object. To do so, he meticulously studied a device called a blackbody radiator, capable of producing light at precise temperatures. Through experimentation, Planck made a groundbreaking discovery — he established a mathematical link between the frequency of light, its color, and its energy. However, this revelation was just the tip of the iceberg.

Planck’s Quantum Theory — Black Body Radiation, Planck’s Constant

The Ultraviolet Catastrophe: A Challenge to Common Sense

Scientists of the late 19th century encountered an inexplicable phenomenon that defied the prevailing understanding of light as a wave. When investigating radio waves, they stumbled upon an unexpected link between light and electricity. Shining a powerful light on metal spheres made sparks jump across them more easily, a behavior that remained unexplained by the wave theory of light.

The Photoelectric Effect

The conundrum deepened with the discovery of the photoelectric effect. This phenomenon revealed that ultraviolet light could remove the static electric charge from metal leaves with remarkable efficiency, while other types of light, including red light, failed to produce the same effect. This puzzling behavior challenged the conventional notion of light as a wave and prompted physicists to question their fundamental understanding.

Photoelectric effect

The Collapse of the Wave Theory

The prevailing wave theory of light, which had provided elegant explanations for phenomena like shadows and colorful soap bubbles, began to crumble in the face of these anomalies. While water waves exhibit predictable behaviors, the light was demonstrating behaviors that could not be reconciled with wave-like characteristics.

The Quantum Leap of 1905

Amid this scientific turmoil, a revolutionary leap was taken. In the year 1905, a physicist by the name of Albert Einstein introduced a radical idea: light could behave as discrete packets of energy, which he called “quanta” or “photons.” This daring proposition marked the birth of quantum theory and laid the foundation for a new era in physics.

Albert Einstein’s Quantum Breakthrough

While his theory of relativity is perhaps his most renowned achievement, it was another groundbreaking idea that earned him the Nobel Prize. In the year 1905, Einstein presented a revolutionary concept that challenged the established norms of physics and forever changed our understanding of light.

A Monument to Discovery: The Arnholt Sternbach Observatory

Nestled in the heart of Berlin, the Arnholt Sternbach Observatory stands as a testament to scientific exploration. Its colossal telescope, a feat of iron and steel engineering from 1896, captivated the public’s imagination with celestial wonders. It was here that Albert Einstein delivered a seminal lecture on his theory of relativity, captivating audiences and laying the groundwork for the future.


A Heretical Proposition

Einstein boldly suggested that we should discard the notion of light as a wave and envision it instead as a stream of minuscule, energy-packed particles — quanta. In this vision, each quantum carried a tiny parcel of energy, and despite its seemingly counterintuitive nature, this notion would become the key to unlocking the mysteries of light.

Quantum light

Light’s Particle Nature Unveiled

Einstein’s audacious proposal paved the way for a simple yet elegant explanation of the photoelectric effect. To illustrate, consider an analogy involving different types of balls representing quanta of light. In the original experiments, it was observed that only ultraviolet light could dislodge electrons from metal surfaces, while red light, with its lower frequency, remained ineffective. Einstein’s breakthrough held the key to resolving the long-standing mystery of the ultraviolet catastrophe. The scarcity of ultraviolet quanta compared to red ones could be attributed to their significantly higher energy requirements. This understanding shed light on the unbalanced distribution of colors emitted by heated objects, such as the filament in a light bulb. It became clear that the energy carried by each quantum dictated its ability to influence electrons.

The Birth of Modern Physics

Einstein’s theory heralded a true revolution in physics. It shattered conventional thinking and demanded a complete paradigm shift. The year 1905 marked the birth of modern physics, forever altering the trajectory of scientific exploration. Yet, this transformation was only the beginning.

A Paradox Deepens: Wave-Particle Duality

As the scientific community grappled with Einstein’s groundbreaking theory, a perplexing paradox emerged. Light once understood as a wave, now displayed particle-like behavior. This duality introduced a new battleground in the quest for understanding reality itself.

The Great Battle: Einstein vs. Bohr

The early 20th century was a time of sweeping change across the world. Amid social, cultural, and political upheaval, a titanic clash was brewing in the world of physics. On one side stood Niels Bohr, a trailblazing Danish physicist, and his cohort of modernist scientists. On the other side, a resolute Albert Einstein, armed with reason and brilliance. Their battleground was not a physical arena, but rather the realm of ideas, theories, and experiments.

An Experiment Unveils Uncertainty

The turning point came in the mid-1920s at Bell Laboratories in New Jersey. An experiment involving electrons and crystal scattering revealed a shocking revelation. Electrons once thought to be solid particles akin to miniature billiard balls, exhibited a behavior that defied conventional wisdom.

Unveiling the Wave-Particle Duality

To grasp the perplexing nature of quantum mechanics, let’s embark on a journey into the world of waves and particles. Imagine a simple experiment involving water waves, which can provide insights into the wave-like behavior of light. By setting up a water ripple tank and projecting its image onto a screen, we can observe interference patterns — alternating bands of light and dark — that characterize wave-like phenomena.

Ripple tank

A Surprising Parallel with Light: The Double-Slit Experiment

Remarkably, a similar pattern emerged when electrons, initially thought to be solid particles, were fired through two narrow gaps onto a screen. This astonishing discovery at Bell Laboratories mirrored the interference patterns observed with water waves. Even more astonishingly, the wave-like pattern emerged even when individual electrons were fired one at a time. This baffling result challenged the very foundations of classical physics and demanded a new perspective.

Double-slit experiment

A Breathtaking Revelation: Quantum Mechanics Emerges

This perplexing behavior of electrons laid the groundwork for the birth of quantum mechanics. Niels Bohr and his colleagues embraced this enigmatic duality of particles and waves, constructing a theory that defied all conventional understanding. In this strange new realm, particles like electrons ceased to be solid entities with fixed positions; instead, they became probability waves, existing in a state of potentiality until observed.

A Peculiar Dance of Probability: The Copenhagen Interpretation

Imagine a coin spinning in the air, its outcome uncertain until it is caught and its fate determined. Bohr’s Copenhagen Interpretation likened this to the behavior of quantum particles. Just as the spinning coin exists in a blurred state of possibility, so too do quantum particles exist in a realm of probability until observed. This interpretation suggested that the act of observation conjured a specific reality into existence.

The Quantum Conundrum: Einstein’s Dissent

Not everyone was willing to embrace this radical departure from classical physics. Albert Einstein, a towering figure in science, vehemently opposed the Copenhagen Interpretation. He questioned whether reality truly ceased to exist without observation. He famously queried, “Does the moon cease to exist when I don’t look at it?” Einstein’s skepticism laid the groundwork for a profound scientific debate.

The Entanglement Problem: Einstein’s Gambit

Einstein’s quest to challenge the Copenhagen Interpretation led him to a concept known as entanglement. Imagine two spinning coins, separated but entangled in such a way that when one’s state is determined, the other’s fate is simultaneously revealed. Einstein proposed that this entanglement defied the idea that particles’ properties are undetermined until observed.

Quantum Entanglement?

The Communication Across Space and Time

Einstein’s insight into entanglement hinted at a mysterious connection between entangled particles that transcended space and time. When one particle’s state was measured, the other particle’s state was instantaneously influenced, as if they communicated faster than light. This notion challenged the very fabric of our understanding of the universe.

Einstein’s Quest for a Deeper Reality

Einstein, dissatisfied with the implications of entanglement and the Copenhagen Interpretation, sought a more comprehensive theory that would preserve a sense of objective reality. He believed that hidden variables might explain the apparent randomness of quantum mechanics, allowing particles’ states to be determined even before observation.

The Bell Test: Resolving the Quantum Paradox

Einstein’s skepticism about the spooky action at a distance and his belief in an objective reality hidden behind the quantum curtain faced a formidable challenge in the form of the Bell test. A group of unconventional physicists, often associated with the counterculture movement of the 1960s, took an interest in the enigmatic world of quantum mechanics. These physicists sometimes referred to as “hippy physicists,” were intrigued by the parallels between quantum concepts and their own spiritual beliefs.

Putting Bell’s Equation to the Test

John Bell’s groundbreaking equation, formulated in 1964, held the key to resolving the decades-long debate between Einstein and Bohr. The Bell test aimed to experimentally test the predictions of quantum mechanics and decide whether particles could communicate their properties instantaneously across space, as Bohr suggested. The experiment involved entangled particles, which would reveal correlations in their properties when measured, reflecting the mysterious link between them.

The Quantum Coin Game: Experimental Setup

The Bell test experiment was ingeniously designed using entangled photons, akin to the spinning coins in the analogy. These entangled particles were split and sent through detectors, with settings similar to the rules in the coin game. Measurements of polarization and other properties were made, and the results were compared against Bell’s equation.

The Earthshattering Result

Upon analyzing the experimental data, it was discovered that the correlations between the entangled particles violated the limits imposed by Einstein’s view of objective reality. The measured results exceeded the threshold specified by Bell’s equation, indicating that the universe does indeed follow the principles of quantum mechanics as described by Bohr.

Quantum Mechanics Triumphs: A Paradigm Shift

The outcome of the Bell test had profound implications. It unequivocally supported the ideas put forth by Bohr and quantum mechanics, which suggested that particles exist in a state of probability until observed. The concept of entanglement, though counterintuitive, was experimentally confirmed, providing strong evidence against Einstein’s hopes for a hidden variable theory. The experimental result showcased the deep and puzzling nature of the quantum world, where entanglement defies our classical understanding of space and time.

A Definitive Answer to the Quantum Debate

The Bell test was a pivotal moment in the history of physics, settling a long-standing dispute and establishing the dominance of the quantum mechanical view of reality. It showcased the inherent weirdness of the quantum realm, where particles seemed to communicate instantaneously, challenging our everyday notions of causality and separability. The test’s success reaffirmed that the universe operates on principles that are fundamentally different from our classical intuitions, paving the way for further exploration into the fascinating and perplexing realm of quantum mechanics.

Reflections on the Quantum World: A Journey Continues

The exploration into the quantum world reveals a reality that defies common sense and challenges our understanding of the universe. The profound mysteries of quantum mechanics, as demonstrated by the Bell test and other experiments, have led to a deeper appreciation of the complexities inherent in the nature of reality.

Einstein’s Quest and the Persistence of Mystery

Einstein’s lifelong quest to understand the fundamental nature of light quanta illustrates the enduring mystery of quantum mechanics. Despite his brilliance, Einstein was unable to provide a satisfying common-sense explanation for the behavior of particles at the quantum level. The very essence of the quantum world, where photons only become real upon observation, continues to defy human intuition and logical reasoning.

The Unresolved Debate: Bohr vs. Einstein

The debate between Niels Bohr and Albert Einstein epitomizes the clash between classical and quantum understandings of reality. While Bohr championed the idea of a probabilistic, observer-dependent universe, Einstein clung to the hope of an objective, hidden-variable theory. The Bell test, a groundbreaking experiment, ultimately confirmed the predictions of quantum mechanics and underscored the mysterious interconnectedness of particles, disproving Einstein’s viewpoint.

Quantum Mechanics’ Continuing Legacy

The diamond light source and other cutting-edge scientific facilities exemplify the enduring quest to unlock the secrets of the quantum world. Scientists harness the power of quantum mechanics to probe new materials, develop advanced electronics, and push the boundaries of technological innovation. Quantum entanglement, once a source of Einstein’s frustration, now fuels developments in secure communication, computing, and beyond.


The resolution of the quantum world has been a journey of astonishing revelations and perplexing Puzzles. From the glow of a simple light bulb to the intricate experiments of modern laboratories, the nature of reality has been laid bare, challenging our understanding and reshaping the very fabric of physics. Einstein’s quest for a comprehensible reality met with both triumph and disappointment. While his theories transformed our understanding of space, time, and gravity, the realm of quantum mechanics remained a realm of uncertainty and paradox. His resistance to the probabilistic nature of quantum mechanics, as championed by Niels Bohr, exemplified the struggle between classical intuition and the counterintuitive world of particles and waves. The Bell test emerged as a battleground where theories clashed and where the very essence of reality was put to the test. In the end, the results spoke louder than words, revealing that the universe dances to a tune that defies our conventional notions of causality and separability. The victory of quantum mechanics over Einstein’s hidden variables demonstrated the profound interconnectedness of particles, a phenomenon both baffling and awe-inspiring. As we stand on the precipice of quantum advancements, the legacy of these pioneers lives on. Laboratories around the world continue to push the boundaries of our knowledge, harnessing the peculiarities of the quantum realm to revolutionize communication, computation, and technology. The once-disputed concept of entanglement now fuels the development of unbreakable encryption and quantum computers, promising a future that once seemed unimaginable. Yet, the quantum world remains a realm of mystery, inviting us to question, explore, and expand our understanding. Just as Einstein’s inquiries led to groundbreaking insights, future generations are poised to dive even deeper into the riddle of quantum mechanics. With every discovery, we inch closer to unlocking the universe’s most guarded secrets. In this ceaseless pursuit, we come to realize that the quantum world, with all its strangeness and uncertainty, is a reflection of the vast and intricate tapestry that is our cosmos. It beckons us to embrace the unknown, marvel at the complexity that lies beneath the surface, and humbly acknowledge that there is still much to learn. As we continue our journey into the quantum world, let us do so with open minds and a spirit of wonder, ready to confront the challenges and revelations that lie ahead. For in the heart of this mysterious realm, where particles entangle and reality defies our grasp, we find the essence of scientific exploration itself — an unending quest to understand the universe and our place within it.