Rise of the Quantum: How Quantum Mechanics Actually Works
Book: Quantum Supremacy: How the Quantum Computer Revolution Will Change Everything Author: Michio Kaku ISBN: 978-0385548366
Chapter 3 of Quantum Supremacy is where Kaku gets into the actual physics. After two chapters about digital computing and its limits, he goes back to the early 1900s and walks through how quantum mechanics was born. It’s a surprisingly good summary for a popular science book. Not too dumbed down, not too dense. Right in that sweet spot for engineers who want to understand what is actually happening inside a quantum computer.
It All Started with a Broken Formula
In 1900, physicists thought they had everything figured out. Newton explained motion. Maxwell explained light. Done. One annoying problem though: when they tried to calculate the energy emitted by a hot object, the math gave them infinity. Obviously wrong. This was called the Rayleigh-Jeans catastrophe.
Max Planck, a very conservative German physicist, tried a different approach for his class. He assumed energy comes in tiny discrete packets, not as a continuous flow. It was supposed to be just a math trick. The formula worked perfectly though. This was the birth of quantum theory, and Planck introduced his constant h (6.62 x 10^-34 joule-seconds), which is incredibly small. So small that we never notice quantum effects in everyday life.
Kaku makes a nice connection here: if you set h to zero, you get back to Newton’s classical world. If you let h grow, quantum effects appear. Same thing with computers. Set h to zero and you have a classical Turing machine. Let it grow and you get a quantum computer.
Einstein, the Patent Clerk
Then came Einstein. Not the famous professor, but a broke patent clerk who could not get a teaching job. He used Planck’s idea to explain the photoelectric effect: light hits metal, electrons fly out. Einstein said light comes in packets too (photons), and that is what knocks the electrons loose. This is how solar panels work, by the way.
Einstein also introduced duality: light can act as both a wave and a particle. Then in 1924, a grad student named Louis de Broglie asked: if light can be both, why not matter? The double-slit experiment proved him right. When you shoot electrons through two slits, you get a wave interference pattern, not two clean lines. Electrons behave like waves.
Schrodinger’s Equation: One Formula to Rule Them All
Austrian physicist Erwin Schrodinger asked the obvious next question: if electrons are waves, what equation do they follow? He found it during a weekend in the Alps with one of his girlfriends. Historians actually call her “the muse of the quantum revolution.” Physicists are interesting people.
The equation itself was spectacular though. Before Schrodinger, the atom was just a vague “tiny solar system” picture. His wave equation showed that electrons form wave resonances around the nucleus, like how certain notes resonate in a shower or a trumpet. Different resonances give you different elements.
Kaku uses a hotel analogy from the book that works well for engineers. The atom is like a hotel. Each floor has rooms (orbitals). Each room fits two electrons. You fill rooms from the ground floor up. First floor: one room (1S), fits hydrogen and helium. Second floor: more rooms (2S, 2P), fits lithium through neon. When rooms have unpaired electrons, atoms can share them with neighbors, and that creates chemical bonds and molecules.
One equation explains the entire periodic table. Paul Dirac said the laws of chemistry are now completely known, the only difficulty is that the equations are too complex to solve. This matters for engineers because this complexity is exactly why quantum computers exist. Classical computers cannot solve these equations for large molecules. Quantum computers can.
Waves of Probability and the Measurement Problem
What is actually waving in these electron waves though? Max Born proposed: the electron is a particle, but the probability of finding it is given by a wave. This split the physics community in two.
The practical rules are:
- An electron is described by a wave function.
- Put it into Schrodinger’s equation to find all possible states.
- Before measurement, the electron exists as a sum (superposition) of ALL possible states simultaneously.
- When you measure it, the wave “collapses” to one state.
Rules 3 and 4 are exactly what makes quantum computers work. A classical bit is 0 or 1. A qubit exists as a superposition of states between 0 and 1. That is where the computational power comes from.
Einstein hated this. “God does not play dice with the universe,” he said. Bohr reportedly fired back: “Stop telling God what to do.”
Schrodinger’s Cat
Schrodinger himself hated the probability interpretation of his own equation. To show how absurd it was, he proposed his famous cat thought experiment. A cat in a sealed box with poison triggered by radioactive decay. Before you open the box, quantum mechanics says the cat is both dead and alive simultaneously as a superposition of two states. Only when you observe it does the wave collapse to one state.
For us practical people, this sounds insane. Electrons actually do this though. They exist in multiple states, tunnel through barriers, take all possible paths at once. We just do not see it at our scale because we are made of trillions of atoms and quantum effects average out, and because h is so incredibly small.
Entanglement: The “Spooky” Part
Einstein tried his final attack on quantum mechanics with the EPR paper in 1935. Take two electrons with total spin zero. Separate them across the galaxy. Measure one spinning clockwise, and you instantly know the other spins counterclockwise. Information traveling faster than light? That violates relativity, Einstein argued.
Experiments proved quantum mechanics right though. The catch is that the information transmitted is random, so you cannot send useful messages faster than light. Einstein gets the last laugh on that point.
For quantum computers, entanglement is critical. Kaku uses a good analogy: a classical computer is like accountants working independently in an office, each doing their own calculation. A quantum computer is like accountants who can communicate with each other while computing. They solve problems coherently, together, through entanglement.
Engineering Takeaway
Kaku ends the chapter with the tragedy of World War II and how it scattered the quantum physicists across the world. The key takeaway for engineers though: quantum mechanics is not just weird philosophy. It is the actual physics that makes transistors, lasers, and computers work. The same properties that seem absurd (superposition, entanglement, wave-particle duality) are exactly what give quantum computers their power.
If you want to understand why quantum computing is fundamentally different, this chapter gives you the physics foundation. Not the simplified “cat in a box” version, but the actual progression from Planck to Schrodinger to entanglement.
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