Quantum Decoherence and the Many Worlds Interpretation

Quantum Histories and Decoherence

• Quantum Scale vs. Classical Scale
  • Multiple histories observable on quantum scale, not on macroscopic scale.
  • Quantum decoherence proposed as the reason.

Measurement Problem

• Last episode discussed wavefunction collapse and conscious observation.
• Increasingly, physicists believe consciousness doesn't cause collapse.
• Wavefunction collapse itself may be an illusion.

Quantum Decoherence

• Wavefunction: Mathematical object defining distribution of possible outcomes.
• Schrodinger Equation: Describes wavefunction evolution over time.
• Feynman’s Path Integral Formulation: Summation of histories to calculate state transition probabilities.

Coherence and Decoherence

• Coherence: Matching frequency/shape and constant phase difference among waves.
• Double-Slit Experiment: Demonstrates coherence with photons.
  • Constructive interference (in-phase waves)
  • Destructive interference (out-of-phase waves)

Experiment Insights

• Coherence results in recognizable interference patterns.
• Decoherence: Losing phase information causes interference patterns to blur.
• Any measuring device introduces decoherence.

Practical Implications of Decoherence

• Observing a single history due to decoherence.
• Photon Example: Interaction with detecting device and environment causes decoherence.
• Macroscopic Scale: Realistic isolation of a coherent wavefunction is infeasible.

Theoretical Background

• H. Dieter Zeh (1970): Rigid mathematical framework for decoherence.
• Decoherence is increasingly accepted but not universal.

Connection to Many Worlds Interpretation

• Decoherence explains the loss of observable alternate histories.
• We only see the decohered branch of the wavefunction.
• Many Worlds Interpretation suggests wavefunction doesn't collapse, but histories decohere.