qm philosophy talk

How We See the

Matter That Makes

All Things

Steven Spencer

Applied Mathematician

Philosophers Corner

2nd October 2012 1

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

The world of classical physics

• Deterministic (Laplace 1749 - 1827)

• External observer and isolated experimental

systems

• Particles (Newton 1642 -1727)

• Waves (Hooke, Huygens, Young, Maxwell)

• Atomic theory (Dalton)3

Things don’t quite add up

• Black-body thermal radiation → colours

• Stable atoms

• Line emission spectra

• Photoelectric effect

4

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

Two views of EM radiation

• Light is a wave! Light is a particle!

6

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

• 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

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

The Quantum World?

• Wave function evolution U(objective &

deterministic) + measurement R(subjective) =

confusion?!?

10

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

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!

• Bell inequalities – QM wins again!

12

Schrodinger’s Cat Thought Experiment!

• Quantum

superposition

affects the

classical

world?

13

• Before detection the electron wave is

‘everywhere’, at detection the wave function

collapses throughout the universe!

‘Spooky action at a distance’ (Einstein)

14

• 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

• Standard QM violates Bell’s theorem. Separated particles are connected (entanglement)!?!

• Result confirmed by experiment (Aspect, 1982)!!16

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

• 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. Heisenberg18

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

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

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

neurons (1011 cells) for info

processing, analog neurons

& ‘supporter’ cells .

Q: Is the mind (consciousness) highly organised brain activity?

21

Neuronal Behaviour

⇒

22

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

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

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

THANK YOU!!!26