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Quantum MechanicsNatural Law or

Calculating Device?

Principia 1687, Opticks 1704

Particulate theory of light; Corpuscles

Newton’s theory of colors

Matter in motion, collisions, action at a distance

Causality and determinism

Electromagnetic theory –

combined electricity,

magnetism and optics into

unified theory

A Dynamical Theory of the

Electromagnetic Field, 1864

Light as an electromagnetic

wave

Continuous energy

spectrum

Kinetic theory of Gases

Daniel Bernoulli, 1740

Macro-properties of gases described in terms of motion of and collisions by particles

Cannot follow each particle instead use statistical averages to make simple, accurate predictions

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Gold backed currency

“The procedure of statistics corresponds to depositing the gold in the bank. Whenever you become uneasy with the statistics, you can always check. You only have to make the calculations, that is to claim the gold or any part of it.”

“I can tell you in a word what happened to physics when quantum mechanics came. Physics went off the gold standard! You still have the statistics, but it is no longer possible to go back into the bank and exchange the statistics for the concrete gold of reliable orbits. All we are left with is a systematicsof probabilities.”

Black body Radiation –radiation that is emitted by a warm body but is entirely absorbed again.

Cavity radiation

Ultraviolet catastrophe

Planck’s quantum of action 6.626068 × 10-34 m2 kg / s

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Heuristic Viewpoint Concerning the Production and Transformation of Light, 1905

Photoelectric effect

Energy exists in discrete packets or quanta

E = hν

Waves and Particles are different “Beasts”

Particles exist at specific points, follow linear trajectories: waves spread out in space, can “bend” (diffract) around obstacles

In classical physics something cannot be both a particle and a wave

Application of quantum theory to atomic structure

Bohr/Planetary model

Explanation of atomic spectrum

A mathematical trick?

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“There appears to me one grave difficulty in your hypothesis, which I have no doubt you fully realize, namely, how does an electron decide what frequency it is going to vibrate at when it passes from one stationary state to the other?” Rutherford

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A mathematical device that produces tantalizing agreement between theory and experiment

Inconsistencies between the quantum model and classical mechanics would require resolution

Matrix Mechanics Wave Mechanics

Wave/particle nature of matter

De Broglie equation

λ = h/ mv

Me = 9.10938188 10-31

kilograms

h = 6.626068 10-34 m2 kg / s

Atomic electrons essentially waves, free electrons had particle characteristics

“Wave Packets” localized wave phenomena

Wave harmonics explained the quantum leaps

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Thomas Young’s double slit experiment1803

If particles move through a single slit, we get a “particle” distribution: through double-slits, we get a “wave” distribution

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Concerned only with correlation of observable quantities rather than underlying physical explanation

Uncertainty principle

Causal or statistical?

You cannot know precisely both the position and momentum of any given particle. The more precisely one is known the less precisely the other is known

“As the statistical character of quantum theory is so closely linked to the inexactness of all perception, one might be lead to the presumption that behind the perceived statistical world there still hides a ‘real’ world in which causality holds. But such speculation seems to us, to say it explicitly, fruitless and senseless.”

“Physics ought to describe only the correlation of observation. One can express the true state of affairs better in this way: Because all experiments are subject to the laws of quantum mechanics …it follows that quantum mechanics establishes the final failure of causality.”

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“To believe this is logically possible without contradiction but, it is so very contrary to my scientific instinct that I cannot forego the search for a more complete conception.”

Nature is not fundamentally probabilistic

EPR argument

“God does not play dice.”

“Stop telling God what to do.”

Originally Instrumental

Became a new interpretation of what exactly counted as a theory

The statistical aspects of quantum mechanics are a feature of the world

Also dissatisfied with the Copenhagen interpretation of quantum mechanics

The wave function (Ψ)

Probability of finding a particular particle in a given space

Physical meaning

Schrödinger’s cat

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