Archive for the ‘Physics’ Category
Friday, May 22nd, 2009
As physicists, we learn that the Poincaré algebra has two Casimirs, [tex]p_\mu p^\mu[/tex] and [tex]W_\mu W^\mu[/tex], together describing the mass and spin of a particle. A standard question is then, "why does the algebra have two Casimirs?" and the standard answer is, "because it is a rank 2 algebra, for ...
Posted in Mathematics, Physics | 1 Comment »
Sunday, January 18th, 2009
Google Reader has an annoying problem when viewing arXiv.org feeds: The author names get mixed up with some HTML code and become unreadable.
I tried using Yahoo! Pipes to solve the problem, but Pipes somehow messed up the whole feed, even when it wasn't supposed to do anything.
Anyway, to ...
Posted in Physics | 2 Comments »
Saturday, January 5th, 2008
The Legendre transform is a simple and useful tool in some branches of physics such as Thermodynamics and Mechanics. In my experience though, this transform is usually explained in a very confusing way.
I want to give my own derivation, which I hope is clear and straightforward. If you're already ...
Posted in Mathematics, Physics | 2 Comments »
Saturday, November 10th, 2007
I recently needed to find the energy levels of hydrogen-like atoms (i.e. atoms with a single electron), taking into account relativistic effects. These effects become important for atoms with a large number of protons.
I only had a couple of days to do this, and I figured the easiest thing would ...
Posted in Physics | No Comments »
Friday, September 21st, 2007
If you're familiar with the twin paradox, you can skip straight to the Closed Universe section.
Suppose you're sitting in a car heading east at 100 km/h, while another car passes you by heading west at 100 km/h. According to special relativity, if you compare your clock with the clock of ...
Posted in Physics | 2 Comments »
Monday, September 17th, 2007
Last time I described the first pitfall I encountered when solving a PDE -- an inherent instability in the partial derivatives. This time I'll talk about the second pitfall, which is simpler conceptually, but has wider implications for programming in general.
In my first implementation of the solution I used a ...
Posted in Mathematics, Physics | No Comments »
Tuesday, May 1st, 2007
I just finished working on a numerical simulation of a set of partial differential equations (PDE). I developed these equations for a physics research project I'm involved in. The equations did not seem to be solvable analytically, so I had to do it numerically. This was my first attempt at ...
Posted in Mathematics, Physics, Uncategorized | 1 Comment »
Tuesday, January 9th, 2007
This BoingBoing article raises the following question: (see the link for a nice illustration)
If a can of compressed air is punctured and the escaping air blows to the right, the can will move to the left in a rocket-like fashion.
Now consider a vacuum can that is punctured. The air ...
Posted in Physics | No Comments »
Wednesday, December 6th, 2006
One of the hot research topics in theoretical physics today is quantum gravity. While physicists already figured out how to treat the rest of the basic forces in nature quantum mechanically, gravity is proving to be more difficult in this respect. One may ask, why bother? Why can't we just ...
Posted in Physics | No Comments »
Thursday, November 16th, 2006
Just found this nice list of Fermi questions. According to this Science Olympics site, A "Fermi question" is a question in physics which seeks a fast, rough estimate of quantity which is either difficult or impossible to measure directly.
Here's a nice question from the list:
If the mass of one teaspoon ...
Posted in Physics | No Comments »
Subscribe by email