Making sense of quantum mechanics

Welcome to the Making sense of Quantum Mechanics research project, a subproject of the Theory of Everything Project.

Quantum Mechanics is the cornerstone of physical theories dealing with the most fundamental issues of nature. Its principles appear to be different from classical laws of nature. This research project aims to make sense of this arduous field, privileging multiple points of view and developing intuitive approaches and insights. It is hoped that putting Quantum Mechanics in such a perspective may facilitate comprehension of the laws governing the elementary constituents of nature.

Fundamental issues of Quantum Mechanics

Contribute to a fundamental issue below (eventually adding one) discussing it on the talk page and holding in mind the aim of this research project: Making sense of Quantum Mechanics. When it is sufficiently mature, add it to the lessons in the box above.

What are the first principles of Quantum Mechanics?

The four lowest energy states of a rotating arrow bouncing back and forth in a box

You may contribute or research on the first principles at Principles_of_Quantum_Mechanics.

In summary, we have the following principles:

First principle: A quantum system may be represented by a vector
Second principle: The orientation of the vector representing a quantum system evolves
Third principle: Kets are transformed into other kets by means of operations that reveal an observational property with example: Particle in a box
Fourth principle: In quantum measurements, the result is always undetermined
Fifth principle: Quantum probabilities involve interaction cross sections of both observed and observing particles

May the present postulates be deduced from these first principles?

Do elementary quantum systems behave really different from macroscopic ordinary systems?

Do Quantum Mechanics and Classical Mechanics address the same questions?

Least action in both frameworks

In classical mechanics, an elementary particle is represented by a point that follows a path of least action. Classical evolution laws describe the evolution of the location of the point.

In quantum mechanics, an elementary particle is represented by a vector whose most probable path is that of least action. Quantum evolution laws describe the evolution of the orientation of the vector.

In classical mechanics, an elementary particle is represented by a point that follows a path of least action

In quantum mechanics, an elementary particle is represented by a vector whose most probable path is that of least action

Uniform motion in CM and QM

In Classical Mechanics, we have Newton's first law: Every body continues in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it.

An analogous quantum "first law" would be: Every arrow-like body continues in its state of rest, or of uniform spinning motion, unless it is compelled to change that state by forces impressed upon it.

In classical mechanics, an object without forces impressed on it continues to move at a constant velocity

In quantum mechanics, an arrow without forces impressed on it continues to spin at a constant angular velocity

Practical applications

Photon

Electron

3D view of needle spinning about its symmetry axis that precesses half as fast about the z-axis. The angle between symmetry axis and precession axis is 45°

Sense-making quotes

…and you will find someday that, after all, it isn’t as horrible as it looks. Richard P. Feynman, Feynman's Epilogue in The Feynman Lectures on Physics, Vol. III, 1965.

You will have to brace yourselves for this - not because it is difficult to understand, but because it is absolutely ridiculous: All we do is draw little arrows on a piece of paper - that’s all! Richard P. Feynman, QED: The Strange Theory of Light and Matter (Princeton Science Library), 1985.

The laws of motion and the quantum conditions are deduced simultaneously from one simple Hamiltonian principle. Schrödinger, 1926.

Readings

A. Einstein, B. Podolsky, and N. Rosen, Can quantum-mechanical description of physical reality be considered complete? Phys. Rev. 47 777 (1935).
Herbert, "Quantum Reality" (1985).
Paul Quincey, Why Quantum Mechanics Is Not So Weird after All, Skeptical Inquirer magazine, July 2006.

Active participants

Active participants in this Learning Group