This is a simple quantum state … |➚> = α|↑> + β|↓> … built from an up |↑> state and a down state |↓>. α and β are complex numbers. The result |➚> is in the middle, oblique. The oblique state is a superposition or the up and down base states. Making a measurement, you…

# Tag: Quantum Mechanics

## Integrating the Delta Function (Again) – Dirac Version

The Delta Function is, roughly speaking, shaped like an infinitely tall and infinitely thin needle. It’s discovery – or invention – is commonly attributed to Paul Dirac[*]. Dirac needed a function like this to work with integrals that are common on quantum mechanics, a generalization of a matrix that has 1’s in the diagonal and…

## Poetry: Dynamical Variables and Observables

The lines of the following poem are phrases selected from consecutive pages of the second chapter of Paul Dirac’s Principles of Quantum Mechanics, Fourth Edition (Revised), Dynamical Variables and Observables. we may look upon the passage for the triple product We therefore make the general rule in spite of this fundamental difference which conforms with…

## Poetry: The Principle of Superposition

The lines of the following poem are phrases selected from consecutive pages of the first chapter of Paul Dirac’s Principles of Quantum Mechanics, Fourth Edition (Revised), The Principle of Superposition. ~ one would be inclined to think There must certainly be some internal motion from general philosophical grounds we cannot expect to find any causal…

## Entropy and Dimensions (Following Landau and Lifshitz)

Some time ago I wrote about volumes of spheres in multi-dimensional phase space – as needed in integrals in statistical mechanics. The post was primarily about the curious fact that the ‘bulk of the volume’ of such spheres is contained in a thin shell beneath their hyperspherical surfaces. The trick to calculate something reasonable is…

## Learning Physics, Metaphors, and Quantum Fields

In my series on Quantum Field Theory I wanted to document my own learning endeavors but it has turned into a meta-contemplation on the ‘explain-ability’ of theoretical physics. Initially I had been motivated by a comment David Tong made in his introductory lecture: Comparing different QFT books he states that Steven Weinberg‘s books are hard reads because at…

## On the Relation of Jurassic Park and Alien Jelly Flowing through Hyperspace

Yes, this is a serious physics post – no. 3 in my series on Quantum Field Theory. I promised to explain what Quantization is. I will also argue – again – that classical mechanics is unjustly associated with steampunk pictures of clocks and trains. It looks more like representations of time-lines in Back to the…

## May the Force Field Be with You: Primer on Quantum Mechanics and Why We Need Quantum Field Theory

As Feynman explains so eloquently – and yet in a refreshingly down-to-earth way – understanding and learning physics works like this: There are no true axioms, you can start from anywhere. Your physics knowledge is like a messy landscape, built from different interconnected islands of insights. You will not memorize them all, but you need…