Table of Contents

Overview
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Quantum mechanics revolutionized our understanding of the physical world. This timeline covers the key discoveries and scientists who shaped modern quantum theory.

Timeline of Major Developments
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1900 - Max Planck
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Blackbody Radiation and Energy Quantization

Planck introduced the concept of energy quanta to solve the ultraviolet catastrophe:

$$ E = nh\nu $$

Where:

  • \(h\): Planck’s constant (\(6.626 \times 10^{-34}\) J·s)
  • \(\nu\): Frequency
  • \(n\): Integer quantum number

This marked the birth of quantum theory.

1905 - Albert Einstein
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Photoelectric Effect

Einstein explained the photoelectric effect using light quanta (photons):

$$ E_{photon} = h\nu = \phi + KE_{max} $$

Where \(\phi\) is the work function. This demonstrated the particle nature of light.

1913 - Niels Bohr
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Bohr Model of the Atom

Bohr proposed quantized electron orbits:

$$ L = n\hbar = n\frac{h}{2\pi} $$

Energy levels:

$$ E_n = -\frac{13.6 \text{ eV}}{n^2} $$

Explained hydrogen spectral lines.

1924 - Wolfgang Pauli
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Exclusion Principle

No two fermions can occupy the same quantum state:

$$ \Psi(x_1, x_2) = -\Psi(x_2, x_1) $$

Explains electron shell structure and periodic table.

1924 - Louis de Broglie
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Wave-Particle Duality

Matter exhibits wave-like properties:

$$ \lambda = \frac{h}{p} = \frac{h}{mv} $$

All particles have an associated wavelength.

1925 - Werner Heisenberg
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Matrix Mechanics

Formulated quantum mechanics using matrices. Observable quantities are represented by matrices.

1926 - Erwin Schrödinger
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Wave Mechanics

The Schrödinger equation describes quantum system evolution:

Time-dependent:

$$ i\hbar\frac{\partial}{\partial t}\Psi = \hat{H}\Psi $$

Time-independent:

$$ \hat{H}\Psi = E\Psi $$

1927 - Heisenberg Uncertainty Principle
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Fundamental limits on measurement precision:

$$ \Delta x \cdot \Delta p \geq \frac{\hbar}{2} $$$$ \Delta E \cdot \Delta t \geq \frac{\hbar}{2} $$

1928 - Paul Dirac
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Dirac Equation

Relativistic quantum mechanics:

$$ (i\gamma^\mu\partial_\mu - m)\psi = 0 $$

Predicted antimatter (positron).

Key Concepts Summary
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YearScientistContribution
1900PlanckEnergy quantization
1905EinsteinPhoton concept
1913BohrAtomic model
1924de BroglieMatter waves
1924PauliExclusion principle
1925HeisenbergMatrix mechanics
1926SchrödingerWave equation
1927HeisenbergUncertainty principle
1928DiracRelativistic QM

The Copenhagen Interpretation
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Developed primarily by Bohr and Heisenberg:

  1. Wave function describes probability
  2. Measurement causes wave function collapse
  3. Complementarity principle
  4. Observer-dependent reality

Modern Developments
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  • 1935: EPR paradox, quantum entanglement
  • 1964: Bell’s inequalities
  • 1980s: Quantum computing foundations
  • 2000s: Quantum information, cryptography
  • 2020s: Quantum supremacy demonstrations