RSS

Tag Archives: quantum mechanis

When is a Wave not a Wave?

When it’s a perpetuated misunderstanding.

I’ve recently read (and watched on YouTube) Richard Feynman’s lectures on Quantum Electrodynamics (QED), the theory that accurately describes the physics of electrons, light and the interactions between them (including the effects of special relativity). It represents one of the most accurate physical theories we have to date, having been tested to incredibly high precision against the results of experiment. Though the lectures were given in 1979 they shed light on an issue that has been presented as a problem throughout all of my scientific education: the issue of wave particle duality.

The gist of the problem behind the wave particle duality is that electrons and photons can behave as particles or waves depending on how an experiment is performed. When they hit a detector they appear as single point particles; however when they come through the apparatus they can show wave-like behaviour such as interference, reflection, diffraction etc. that is apparently impossible to explain with particles. This causes an issue with the idea of what a photon (or electron for that matter) actually is at the fundamental level. It is only after listening to, and reading, Feynman’s lectures that I find that there is no problem of a wave particle duality, electrons and photons are definitely particles and in no way waves, and it is only through misrepresentation that this “problem” exists. Read the rest of this entry »

 
Leave a comment

Posted by on May 9, 2013 in Blog

 

Tags: , , , ,

Why The Universe Isn’t Soup

My friend Pete Hague recently answered a question on his blog regarding whether you can touch dark matter. He gave a good, basic explanation using coulomb’s law and then directed people towards me for a fuller solution. So here it is.

As Pete quite rightly explained, the coulomb repulsion of electrons stops atoms from getting too close to each other thus giving the feeling of solidness to objects, but before you even consider bringing atoms together you run into a problem bringing their constituents together.

Quantisation

If you want to build hydrogen you need a proton and an electron. The negative electron orbits the positive proton and you have an atom. The problem is that everyday experience tells us that the positive-negative attraction would just pull them together until they were touching, leaving no stable structure to the universe. But the experience we have turn out to be just a large scale effect, and at the quantum level things work differently.

In the quantum mechanics of atoms the energies that the bound electrons can have can only take certain values in an analogous way to the strings in a piano only being able to play certain notes. Theses energies in a basic atom are given roughly by

E_{n} = \frac{-Z^{2}e^{4}m_{e}}{32\pi^{2}\epsilon_{0}^{2}\hbar^{2}n^{2}} = -13.6\frac{Z^{2}}{n^{2}} \text{ eV},

Read the rest of this entry »

 
Leave a comment

Posted by on January 8, 2013 in Blog

 

Tags: , , ,