### “The Stars are Too High” and Gravity Waves

Rumor has it that LIGO is finally going to announce the discovery of gravity waves on Thursday!  The author of “The Stars are Too High”, Agnew Hunter Bahnson Jr. helped to fund one of the first general relativity conferences where the existence of gravity waves was discussed.  In 1957 at the Chapel Hill conference.  Not all the physicists present considered gravity waves to be a possible physical reality.  Details were hashed out outside of conference sessions, and the physicists, while not reaching a consensus, were able to easily share ideas  by the simple expediency of being in the same location.

All of this was made possible by Bahnson.  Reaching out Bryce DeWitt after reading his Gravitation Research Foundations prize-winning essay, Bahnson proposed that DeWitt head up an academic institute for the study of gravitation.  Bryce was at first inclined to decline, but accepted after speaking with his mentor John Archibald Wheeler, (originator of the term Black Hole), who implored him to “Take the money!”. Shortly thereafter, using his own money, as well as funds from the military and other private industrialists, the Institute for Field Physics was born.  A few years later after Hunter’s untimely death in a plane crash, funding to the Institute would be cut by his family, but in the intervening time, it played host to early gravity wave discussions, as well as some of the work of visiting scholar, Peter Higgs, (yes, THAT, Higgs!)

### Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

### Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…

### Unschooling Math Jams: Squaring Numbers in their own Base

Some of the most fun I have working on math with seven year-old No. 1 is discovering new things about math myself.  Last week, we discovered that square of any number in its own base is 100!  Pretty cool!  As usual we figured it out by talking rather than by writing things down, and as usual it was sheer happenstance that we figured it out at all.  Here’s how it went.

I've really been looking forward to working through multiplication ala binary numbers with seven year-old No. 1.  She kind of beat me to the punch though: in the last few weeks she's been learning her multiplication tables in base 10 on her own.  This became apparent when five year-old No. 2 decided he wanted to do some 'schoolwork' a few days back.

"I can sing that song... about the letters? all by myself now!"  2 meant the alphabet song.  His attitude towards academics is the ultimate in not retaining unnecessary facts, not even the name of the song :)

After 2 had worked his way through the so…