QM philosophy talk
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This document discusses our current understanding of matter at the quantum scale based on developments in physics over the past century. It outlines how classical physics broke down in the face of experiments like blackbody radiation and the photoelectric effect. This led to the development of quantum mechanics, which describes reality in strange ways like wave-particle duality and quantum entanglement. While highly successful, quantum mechanics raises philosophical questions about determinism, observation, and the nature of reality that are still debated today. It also explores implications for understanding the mind and consciousness.
QM philosophy talk
- 1. How We See the Matter That Makes All Things Steven Spencer Applied Mathematician Philosophers Corner 2nd October 2012 1
- 2. Outline • The world of classical physics • Things don’t quite add up! • Enter the quantum • The mechanics and the quantum • Stranger and stranger • What does it mean? • Where is the mind in all this? • Are you sure? 2
- 3. The world of classical physics • Deterministic (Laplace 1749 - 1827) • External observer and isolated experimental systems • Particles (Newton 1642 -1727) • Waves (Hooke, Huygens, Young, Maxwell) 3 • Atomic theory (Dalton)
- 4. Things don’t quite add up • Black-body thermal radiation → colours • Stable atoms • Line emission spectra • Photoelectric effect 4
- 5. Enter the Quantum • The physics of atomic and sub-atomic scales? • Energy is emitted in ‘bits’ (quanta) (Planck, 1900) → tricky maths? • Energy in light is in ‘grainy bits’ (photons) which are particles with wave properties → photoelectric effect (Einstein, 1905) 5
- 6. Two views of EM radiation • Light is a wave! Light is a particle! 6
- 7. The Mechanics and the Quantum • Orbital atomic theory (Rutherford, 1911) • Quantised electron orbit atomic model (Bohr, 1913) → ‘flights and perchings’ • Particles are waves! (de Broglie, 1924) → orbiting electrons have integer wavelengths! • Matrix mechanics (Heisenberg, 1925) → unanschaulich atomic world! 7
- 8. • Wave mechanics (Schrodinger, 1926) → how the quantum state of a system evolves with time. Anschaulich atomic world? • Complementarity – wave-particle duality • Deterministic description for wave functions + Statistical description of matter and energy. • Uncertainty principle (Heisenberg, 1927) Momentum and position cannot be simultaneously measured with unlimited precision. 8
- 9. The observer and the system • The role of the classical observer (measurement) of a quantum system becomes central and hotly contested – “We are not only observers. We are participators. In some strange sense, this is a participatory universe.” – John A. Wheeler 9
- 10. The Quantum World? • Wave function evolution U(objective & deterministic) + measurement R(subjective) = confusion?!? 10
- 11. Electron Double Slit Experiment (Feynman) • Detector ‘D’ turned on or off by observer → affects pattern on screen by double slit. Observer affects outcome of experiment! 11
- 12. Stranger and stranger • Superposition of states → possible in quantum but not classical world (Schrodinger’s cat). • Quantum emtanglement → Many particle systems have a complicated combined wavefunction even at ‘large’ distances! • Einstein-Podolski-Rosen (EPR) effect – QM is either ‘non-local’ (faster than light influences) or is not a complete theory! 12 • Bell inequalities – QM wins again!
- 13. Schrodinger’s Cat Thought Experiment! • Quantum superposition affects the classical world? 13
- 14. ‘Spooky action at a distance’ (Einstein) • Before detection the electron wave is ‘everywhere’, at detection the wave function collapses throughout the universe! 14
- 15. • Single source of two photons – ‘spin’ observation method at one end affects observation at a distant point! Do particles communicate with one another or are they one entity ?!? 15
- 16. • Standard QM violates Bell’s theorem. Separated particles are connected (entanglement)!?! • Result confirmed by experiment (Aspect, 1982)!! 16
- 17. What does it mean? • Starting point – no experiment has ever been found that concludes against QM maths! • Whatever happened to determinism? “God does not play dice” – A. Einstein vs “A physical object has an ontologically undetermined component that is not due to the epistemological limitations of physicists’ understanding” – A. Eddington 17
- 18. • Ontologies (interpretations) – a) Copenhagen (Bohr, Heisenberg and Born, 1927) – Complementarity + uncertainty principle + measurement + correspondence principle. QM describes knowledge NOT reality! “There is no quantum world. There is only an abstract physical description.” - N. Bohr “The idea of intermediate kinds of reality was just the price one had to pay” – W. Heisenberg 18
- 19. b) Many-worlds / relative state (Everett, 1957) – universal wavefunction never collapses → multiverse c) Environmental decoherence – rapid disappearance of quantum superpositions by interaction with environment (useful for many interpretations). d) Ensemble (Einstein) – Minimalist, statistical – wavefunction for large numbers of particles only. e) Relational – different observers see different quantum states. 19
- 20. f) Pilot-wave (de Broglie, Bohm) – Particles guided by wavefunction. Non-local, holistic universe, hidden variables. g) Objective collapse (Penrose) – physical mechanism of collapse – extended QM. h) Conciousness collapse - subjective reduction (von Neumann/Wigner) & participatory anthropic principle (J.A. Wheeler) g) New theories (many!) – objective R wave function collapse / non-linear U function. 20
- 21. Where is the mind in all this? • What is a brain? • Dense network – more than 104 cell bodies and km of wiring per cubic mm! • Multiple cell types: spiking Q: Is the mind neurons (1011 cells) for info (consciousness) processing, analog neurons highly organised & ‘supporter’ cells . brain activity? 21
- 22. Neuronal Behaviour ⇒ 22
- 23. Quantum Theory of Mind • Non-algorithmic thought → cannot be modelled by a digital (Turing) computer. • Consciousness as a quantum mechanical phenomenon (Penrose & Hameroff) – Hypothesis: Neuron microtubules within neurons support quantum superpositions (non-computable behaviour) + macroscopic quantum entanglement across brain. • Highly controversial – decoherence counter-argument! • Physical collapse of quantum wavefunction of microtubules essential for consciousness (Orch-OR). 23
- 24. Complex Dynamical Behaviour Theory of Mind • Intrinsic non-linear dynamics of each individual neuron + network dynamics (attractors, bifurcations of behaviour, small changes in inputs lead to large changes in outputs). • ‘Simple’ non-linear models found for behaviour of individual spiking neurons → reproduce complex bursKng behaviour. • Apparently non-algorithmic behaviour (sometimes chaos) from algorithmic (deterministic) components. • Consciousness as an emergent phenomenon from a neural network complex dynamical system of the physical brain. 24
- 25. Are you sure? • An underlying level of reality? • Quantum state decoherence and gravitons? • Non-linear quantum theory • The classical-quantum divide - looking for decoherence • To be continued… 25
- 26. THANK YOU!!! 26