# Quantum Physics — A Notebook

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Category: Science
Slides: 13
Updated: 2026-05-17T20:55:47.367Z
Tags: catalog, science, quantum, physics

## Summary

Quantum Physics — A Notebook — from Planck (1900) to Entanglement Key sections include: Quantum Physics; 1900 · Planck; 1905 · Einstein; 1913 · Bohr; 1924 · de Broglie; 1926–27 · Schrödinger & Heisenberg; The Double-Slit Experiment; 1935 · EPR; 1964 · Bell's Theorem; Decoherence & Measurement.

## Slide Outline

1. Quantum Physics
2. 1900 · Planck
3. 1905 · Einstein
4. 1913 · Bohr
5. 1924 · de Broglie
6. 1926–27 · Schrödinger & Heisenberg
7. The Double-Slit Experiment
8. 1935 · EPR
9. 1964 · Bell's Theorem
10. Decoherence & Measurement
11. Quantum, in Your Pocket
12. What IS the Wavefunction?
13. Further Reading

## Slide Transcript

### Slide 1: Quantum Physics

- — A Notebook —
- from Planck (1900) to Entanglement
- Lab notebook of K. Ning · vol. III
- May 2026

### Slide 2: 1900 · Planck

- Energy comes in lumps.
- Studying blackbody radiation, Max Planck made a desperate ad-hoc fix: assume oscillators
- can only emit/absorb energy in discrete chunks —
- quanta
- E = h·ν
- h = 6.626 × 10⁻³⁴ J·s tiny!
- Planck himself thought it was just a math trick.
- It wasn't. The classical world cracked open.
- "An act of desperation," he later called it.
- slide 2 / 13

### Slide 3: 1905 · Einstein

- The photoelectric effect — light is granular too.
- Shine light on metal → electrons pop out.
- Classical theory predicted: brighter light = more energetic electrons.
- Wrong. What matters is frequency, not intensity.
- Below a threshold ν₀, nothing happens — no matter how bright.
- KE = hν − φ
- Light arrives in discrete packets — photons
- Won Einstein the 1921 Nobel (not relativity!).
- Wave-particle duality is now real.
- slide 3 / 13

### Slide 4: 1913 · Bohr

- Electrons live on discrete orbits.
- Hydrogen's spectrum had specific colors — not a smear.
- Bohr postulated electrons orbit only at quantized angular momentum:
- L = n·ℏ (n = 1, 2, 3, ...)
- Photons emitted when electrons jump down.
- Explained the Rydberg formula.
- Crude model — but a huge step.
- Sketch: Bohr atom (hydrogen)
- slide 4 / 13

### Slide 5: 1924 · de Broglie

- Matter has wave nature.
- Louis de Broglie (in his PhD thesis!): if light waves act like particles,
- why shouldn't particles act like waves?
- λ = h / p
- Every electron is also a wave
- Confirmed by Davisson–Germer (1927): electrons diffract through crystals.
- Even buckyballs (C₆₀) show interference. Even molecules of 2000+ atoms.
- slide 5 / 13

### Slide 6: 1926–27 · Schrödinger & Heisenberg

- The wavefunction. The uncertainty principle.
- Schrödinger wrote the equation that governs the wavefunction Ψ:
- iℏ ∂Ψ/∂t = Ĥ Ψ
- Almost simultaneously, Heisenberg showed you cannot pin down both position and momentum:
- Δx · Δp ≥ ℏ/2
- Not a measurement clumsiness — it's fundamental.
- |Ψ|² gives the probability of finding the particle (Born rule).
- The same physics, two formalisms — wave mechanics & matrix mechanics.
- slide 6 / 13

### Slide 7: The Double-Slit Experiment

- "All of quantum mechanics in one experiment." — Feynman
- Send one electron at a time → fringes still build up.
- Each particle goes through both slits
- as a wave — but lands as a single point.
- Try to peek at which slit, and the fringes vanish.
- slide 7 / 13

### Slide 8: 1935 · EPR

- "Spooky action at a distance."
- Einstein, Podolsky & Rosen wrote a paper attacking QM as incomplete.
- Their target: entanglement.
- Pair two particles so their spins are correlated. Send them light-years apart.
- Measure one — instantly the other's outcome is fixed.
- How? They must have carried the answer all along, said EPR.
- Reality must be locally pre-determined by hidden variables.
- Schrödinger coined "Verschränkung" — entanglement — that year.
- Einstein: "God does not play dice."
- Bohr: it's fine, you just can't talk about properties before measurement.
- For 30 years the debate seemed philosophical. Then Bell took up the pen.
- slide 8 / 13

### Slide 9: 1964 · Bell's Theorem

- Hidden variables — ruled out.
- John Bell derived an inequality that any local-hidden-variable theory must obey:
- |S| ≤ 2 (local realism)
- Quantum mechanics predicts |S| = 2√2 ≈ 2.83.
- Aspect (1982), Zeilinger, Clauser — experiment after experiment violates Bell.
- 2015: loophole-free tests in Delft, Vienna, NIST.
- 2022 Nobel Prize.
- Conclusion: no local hidden variables. Reality is non-local or non-real.
- Pick your poison.
- slide 9 / 13

### Slide 10: Decoherence & Measurement

- Why doesn't my coffee cup superpose?
- Quantum systems don't sit in a vacuum — they entangle with their environment
- (photons, air molecules, phonons) at femtosecond speed.
- This decoherence rapidly washes out interference for
- macroscopic objects. The cat is dead OR alive, in our local "branch."
- Decoherence ≠ collapse. It explains the appearance of classicality.
- Why we never see Schrödinger's cat suspended in superposition.
- Why quantum computers need millikelvin shielding.
- Schrödinger's cat — a thought experiment, not a how-to
- slide 10 / 13

### Slide 11: Quantum, in Your Pocket

- Modern applications.
- Lasers — stimulated emission (Einstein, 1917).
- From DVD players to LIDAR.
- Semiconductors — band theory is quantum mechanics.
- Every transistor in your phone.
- MRI — nuclear-spin precession, a direct quantum effect.
- GPS — atomic clocks tuned to a Cs hyperfine transition.
- Solar cells, LEDs — photoelectric effect & bandgaps.
- Quantum computers — superposition + entanglement as compute resources.
- Shor's algorithm, error-corrected qubits, NISQ era → fault tolerance.
- ~30% of US GDP touches quantum tech.
- slide 11 / 13

### Slide 12: What IS the Wavefunction?

- The unresolved question.
- The math works. But what is Ψ made of?
- Copenhagen (Bohr, Heisenberg) — Ψ is a tool for predicting
- measurements. Don't ask more. "Shut up and calculate."
- Many-Worlds (Everett, 1957) — Ψ never collapses; the universe
- branches. Every outcome happens, somewhere.
- QBism (Fuchs, Caves) — Ψ is an agent's belief, a
- subjective Bayesian wager.
- Pilot-wave (de Broglie–Bohm) — particles do have positions, guided
- by a non-local wave.
- Objective collapse (GRW, Penrose) — collapse is real and physical.
- All make the same predictions today. The pen, here, hesitates.
- pick one ☺
- slide 12 / 13

### Slide 13: Further Reading

- R. Feynman — QED: The Strange Theory of Light & Matter
- D. Griffiths — Introduction to Quantum Mechanics
- A. Becker — What Is Real? (interpretations & history)
- J.S. Bell — Speakable & Unspeakable in Quantum Mechanics
- S. Carroll — Something Deeply Hidden (Many-Worlds)
- YouTube
- Double-slit experiment — search
- Feynman quantum lectures — search
- — end of notebook —
- "I think I can safely say that nobody understands quantum mechanics." — R. Feynman
- slide 13 / 13


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