Category Archives: Physics

Kaliope Now Includes Gravitational Potentials

I’ve added a C++ class that handles gravitational potentials to my Kaliope project. Below is a picture of a binary cluster orbiting around a logarithmic potential well. A logarithmic potential is the simplest kind of potential well. It corresponds to an inverse distance radial force field.


Here is a slightly different simulation, with each body given its own color, so it is easier to see individual paths:



I’ve been a big fan of Dilbert for years now, but I recently found a great webcomic that I’ve started reading daily called XKCD. The tagline is: A webcomic of romance, sarcasm, math, and language. The drawings are simple stick figures, but it is the situations and ideas that are interesting and funny.

ADS Digital Library

While googling for information on the Virial Theorem, I ran across a really cool page hosted at the Harvard ADS system. ADS stands for Astrophysics Data System, and it is primarily an abstract search engine that helps you locate journal articles mostly in the realm of Astronomy and Astrophysics, but they also have a small virtual library of books that you can freely download.

Here are the titles I found interesting:

If you want to concatenate all the separate PDF chapters, I recommend using the texexec method oulined in this web page by Matthew Skala.

Command Line Unit Conversion Utility

I found a handy tool for figuring out unit conversions quickly, and yes I am aware that Google does this, but sometimes the command line is more convenient. Here are some examples of how to use it:

$ units lightyear parsec
       * 0.30660139
        / 3.2615638

$ units inches feet
        * 0.08333333
        / 12

$ units 2m cm
        * 200
        / 0.005

So the first line tells you what value to multiply the second unit by to make the conversion. And the second line is the inverse operation, that is, what you divide the second unit by to obtain the same value in the first unit.

To install this on a Debian/Ubuntu system, just run the following command:

$ sudo apt-get install units

Video: Feynman QED Lectures

I found a link via Marcus Woo’s blog to a superb set of videotaped lectures by Richard Feynman on Quantum Electrodynamics or QED. He masterfully describes the basics of quantum mechanics at the layman’s level. I’ve only watched the first video completely through, but I was very impressed with the clarity with which he explained the subject. The video requires the Real Player.

Book Review: The Trouble with Physics

The Trouble with Physics book coverThis book is Lee Smolin’s attempt to diagnose the physics community. Smolin entered graduate school in 1976, at the end of arguably the most fruitful era ever known to physics. However, since the 1980s no new fundamental challenges to the canon of physical theory have succeeded in reshaping how we view our universe. Although this fact troubles and frustrates Smolin, it is not this lack of substantial progress that he cites as the problem with physics. The problem as he sees it is that the majority of theoretical physicists are barking up the wrong tree, namely string theory. He argues very convincingly that string theory fails as a unifying theory. In the introduction he cites Nobel laureate Gerard ‘t Hooft as saying,

“I would not even be prepared to call string theory a ‘theory,’ rather a ‘model,’ or not even that: just a hunch. After all, a theory should come with instructions on how to deal with it to identify the things one wishes to describe, in our case the elementary particles, and one should, at least in principle, be able to formulate the rules for calculating the properties of these particles, and how to make new predictions from them. Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon. Whatever I did give you, can I still call it a chair?”

Smolin sees the widespread adoption of string theory as a continuation of the “shut up and calculate” mentality of the particle physics era that was so successful. He also argues that this follow the leader attitude is hurting diversity, especially the young physicists with bold new ideas. Not becoming part of an established research group and striking out on one’s own research path is tantamount to career suicide in theoretical physics, at least for those without established reputations. The notable exception of course is Einstein, but people like him are rare.

He divides his argument into four parts. In the first section, he sets the stage by giving a brief overview of the five great problems in theoretical physics, and the early attempts at unification. I especially liked how he described his set of heuristics for judging the promise of a new theory.

In the second section he gives a whirlwind history of string theory up to current times. This part of the book will be difficult for someone not familiar with the jargon of string theory. I recommend reading Brian Green’s “The Elegant Universe” before tackling this book, as it is a good introduction to string theory.

The third section examines some alternatives such as Smolin’s own research in loop quantum gravity as well as other programs such as Alain Conne’s non-commutative geometry research.

The final section looks at the physics community from a sociological perspective, attempting to understand how its internal power structure strongly encourages certain behaviors and punishes others. As a soon-to-be graduate student, I found this section to be very informative.

I strongly recommend this book. I however admit, that with only a bachelor of science degree in physics, I’m not yet qualified to judge string theory let alone even the Standard Model, but I can say that the book is well-written and I found it very interesting.