Category Archives: Physics

NY Times Article About Emmy Noether

The New York Times published a short but good article about Emmy Noether yesterday.The New York Times

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Einstein’s Happiest Thought…Doomed?

arXiv logoWhen Albert Einstein first realized that gravitational mass and inertial mass were the same thing, the resulting thoughts led him to expand the theory of special relativity into general relativity. He called this equivalence of gravitational mass and inertial mass the “Equivalence Principle”, and called it his “happiest thought”. Recent calculations posted in a paper on the arXiv, assert that this is not true at the quantum scale. The most important aspect of this research is that it should be experimentally verifiable. At least that is what the author of the Physics ArXiv Blog thinks.

Books: “Particle Physics A Very Short Introduction” by Frank Close

Particle Physics book cover
I found this book in the library the other day and found it to be a very good introduction to the basics of particle physics. I liked the fact that it explains the basics of the experimental side of particle physics as well as introducing the three families of leptons and quarks. Too often, popular science books explain the various subatomic particles with out giving you any idea of how we actually know of their existence. Because of this, I think disbelief tends to creep in. But Close does an excellent job of explaining the basics of how accelerators operate and also the basics of how detectors work. And he does all this in only 129 pages! Very short indeed, and highly recommended.

Iterated Function Systems and Fractals

This code generates fractals based upon an iterated function system (IFS). Several input files and a Makefile are included. The code is written in C++, and distributed as a tarball. I did this for a class at the University of Utah, but it is based upon a homework assignment for a computer graphics class at MIT (6.837).

Below is the famous Barnsley fern which was generated by an IFS with just four transforms!
Barnsley Fern

Dark Matter and Particle Physics

Michael Peskin recently posted an article to the arxiv entitled “Dark Matter and Particle Physics”. The article is an almost layman’s guide to how the WIMP model of dark matter might soon be partially validated experimentally at the LHC.

In the article he outlines the reasons why most matter in the universe is dark or in other words does not emit light or radiation, and thus is normally only detected via its gravitational effects. He then goes on to describe the WIMP model for dark matter and its predictions. Next he talks about how the LHC might detect WIMPs:

The discovery of events at the LHC with apparent unbalanced momentum will signal that this accelerator is producing weakly interacting massive particles. However, it would be far from clear that this particle is the same one that is the dominant form of matter in the universe. To demonstrate this, we would need to correlate properties of the WIMP that we observe at the LHC with astrophysical observations.

There are two possible ways to observe WIMPs outside of the LHC. First is the direct approach of observing the scattering of a WIMP from a nucleus in an extremely sensitive detector located deep underground in a mine to minimize noise. The second method is to observe gamma rays emitted from pairs of WIMPS annihilating each other. These gamma rays should have a characteristic spectrum and be most commonly found coming from parts of our galaxy where the concentration of dark matter is highest, namely near the center of the Milky Way.

If the mass of the WIMP seen at the LHC is the same as the mass from astrophysical detection experiments, this will provide strong evidence that the LHC is producing the true particle of dark matter.

Thanks to Hwasung “Mars” Lee for pointing out this article in his blog.