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Showing posts from June, 2013

### Rindler's Just Flat Out Pretty Derivation of the Special Relativistic Time Dilation Factor Gamma

Rindler demonstrates[2] the best way ever to derive the relativistic Lorentz contraction/time dilation factor, gamma, (of twin paradox fame), from four velocity!  I've been working through Rindler's paper on hyperbolic motion as a result of constant acceleration[1] lately. Starting from the constancy of the speed of light, Einstein's theory of special relativity posited, and Minkowski refined the idea that the universe is actually four dimensional with space and time sitting on an equal footing.  Starting from here, we can write an expression for the distance squared along an infinitesimal line element in four dimensions, (think Pythagorean theorem)... Brian Greene popularized the idea of four velocity[3] in one of his books and although it isn't mentioned as much as some of the other aspects of special rel, it's a simple idea.  Everything is moving at the speed of light.  Something might have more of it's velocity pointed into either the space dime

The ongoing series of posts on cool places related to STEM: Today.. Hyderabad! I was called to Hyderabad, India a few years back in my alternate guise as an electrical engineer.  I'd just spent a week making presentations in Nice, France, (more on that later), and my boss called to ask if I could make it to Hyderabad in two days.  I hustled up to Paris and spent the day outside the Indian consulate trying to get a visa.  After a few meetings, I was able to get ahold of one and off I went. Hyderabad is the fourth biggest city in India and plays host to Advanced Micro Devices, ATI, and Xilinx among other semiconductor companies.  It's a huge and vibrant city with a bit of a traffic problem. but not to worry, everyone here ride shares. In case you missed anything, there are four people on the motorcycle.  I haven't been allowed to try this with Jr. yet, despite my assurances that it's perfectly safe. I was able to sneak away via auto-rickshaw one afternoon

### Radio Direction Finding and Sense Antennas... Oh and the Equivalence Principle

For what's going on with research, scroll down.  But first, another study topic for the amateur radio extra class exam.  One of the questions asks what the purpose of a sense antenna is.  The correct answer is that "It modifies the the pattern of a DF antenna array to provide a null in one direction."  Whatever that means.  The DF referred to in the answer is direction finding.  Small loop antennas, like the one shown in the picture to the left (picture 1), can be used to find the direction that radio signals are transmitted from.  By rotating the loop until the received signal becomes the weakest, you can locate the direction.  There's only one problem, you can't tell whether the signal is coming from in front of, or behind the loop.  This is where the small vertical antenna in the picture comes in.  That's the 'sense antenna' or 'sense aerial'.  Its signal is added to the signal of the loop antenna and the net result is that it provides a u

### The Sodium Chlorate Challenge

As the third week of the short summer session for freshman electromagnetism opens, the minds of young professors everywhere run towards cool polarized light demonstrations.  In helping track some of these down, I remembered that there was an awesome experiment involving sodium chlorate in a book titled "Crystals and Crystal Growing" by Alan Holden, Phylis Morrison.  It turns out that sodium chlorate crystals pass polarized light at different angles depending on the wavelength of the light.  In short, if you place a sodium chlorate crystal between two Polaroid sheets, and then rotate one while keeping the other still, you will see the color of light passed though the crystal change, (picture1)[1]. Detail of the Experiment Since I don't have time to grow a crystal, I thought it should be easy enough to find a video of the experiment  on the internet.  So far, I've searched to no avail though.  So, here's the challenge... Can anyone provide a video of th

### Physics on Father's Day

Happy Fathers Day everybody!!! In honor of Fathers' Day, here are a few physicists who had kids that went on to become scientists themselves.  I know there are far more examples than I've listed here.  Feel free to add your favorites to the comments below! William Fairbank and William Fairbank Jr. William Fairbank Sr. performed one of the first two experiments that verified the existence of quantized magnetic flux[6].  He was also one of the architects of the Gravity Probe B experiment.  His son, William Fairbank Jr. is a physicists at Colorado State University who works on the detection of single atoms via photon burst mass spectroscopy (PBMS)[7]. Another one of William Fairbank's sons, Richard Fairbank, founded Capital One Bank which provided the last bit of funding so that work on Gravity Probe B could be completed after NASA quit funding it in 2008. Sydney and Persis Drell Sydney Drell proposed the Drell-Yan hadron scattering process in 1970.  The   proc

### A Very Brief History of Time Paradoxes

I've been reading up on the twin paradox for the last year or so.  This is the paradox where one twin flies away from another at relativistic speeds and when they get back, they find that they're younger than their sibling who stayed home.   It amounts to time travel into the future. Last night when I got too tired to do anything productive I made a histogram, (shown in picture 2 below), using Google Scholar data of the number of citations containing the phrase 'twin paradox' over the years.  The first reference I found to the twin paradox was in 1956.  Prior to that it seems to have gone by the moniker of "Clock Paradox".  As I perused through the references, (there were a total of 2,393 between 1956 and 2013 by the way), one caught my eye because it was published by the U.S. Naval Research Laboratory in 1959[3].  As I've mentioned before, their was a push for anti-gravity in the late '50s and early '60s[8]. The document turned out to be

### How I Became Interested in Physics

We're planning an outreach event with Google at the G+  STEM on Google+ Community  where scientists, engineers, and mathematicians will answer questions via video like "Why do the STEM fields matter to you?"  Keep an eye on the community as this ought to be pretty fun and interesting, and it should kick off next Monday.  For the fun of it  here's my answer. References: 1.  STEM on Google+ Community https://plus.google.com/communities/110555615319066448343

### Machine Shop!!!

So, in physics graduate school, you have your quantum mechanics, and your EM, and your statistical mechanics, and classical mechanics, and so on, and all of this is very well and good.  And then, if you're very, very lucky, there's machine shop class and it's awesome!!!  Obstensibly, the class is to teach you to be a better communicator with machine shops, but you still get to learn how to use the tools!  You actually get to learn how to build scientific instruments.  It's not for everyone though.  Heisenberg for example almost didn't get his PhD because of issues with his experimental lab grades. Machine shop started for me today after missing the first two meetings for an engineering conference last week.  Today we started in with the tools.  If you'd told me last week that an hour long lecture on saws would be interesting, I might have rolled my eyes, but not anymore!  We learned about a few different kinds of saws.  Then, we learned that with the vast ma

### Wolfgang Rindler and the Rod vs. Hole Lorentz Contraction Paradox

If a Lorentz contracted rod travels over a hole smaller than it's un-contracted length, does it fall in?  Wolfgang Rindler, (picture 1), pointed out the answer in 1961.  Dr. Rindler is my new favorite author for the week.  His papers are paragons of clarity.  Rather than immediately bogging down in formulas or complicated jargon, he spends a significant amount of space in every paper explaining the problem and its solution in everyday terms.  Then, almost as an afterthought, he lays out the math that describes the situation.  Sometimes though, you have to read into his math and then read in a little more.  If anyone has a more clear explanation of the rod and hole contradiction, it would be great to hear. Dr. Rindler has done interesting work on special relativity, general relativity, and cosmology.  He moved to the Southwest Center for Advanced Studies in the mid '60s, and he's still there.  The institute now bears a different name however: the University of Texas at D

### Lab Outtakes: The 25 kHz AC Magnetic Field Superconductor Levitation Run

Not Very Educational, Just Pretty I'm a little crunched for time since today's a travel day, so to get things started back off, here's a question.  What do the two pictures below have to do with each other? Maglev trains like the one announced this week by Japan, (shown on the left), use pairs of superconductors and magnets to levitate.  Testing has to be done to ensure that the levitation won't become unstable because of mechanical vibrations or stray magnetic fields.  The picture on the right is a capture from the lab outtake video shown below.  The video is from a playday, but the apparatus was used in an experiment[1] that characterized the levitation of a superconductor by an alternating current magnetic field. As quantitative data, the video is fairly useless because I'm changing way to many variables at once.  It's fun for me at least to see all the things going on.  Oh yeah, please excuse my super-classy super-scientific use of the phrase 'cr

### A Graphical Note on Beta Decay and Parity Violation

After writing about parity violating beta decay a few days I discussed it with a professor here at A&M and he pointed out that the whole thing isn't that odd at all if you look at the correct part of the following diagram based on Cottingham and Greenwood [1]. At first glance, it seemed odd to me that that magnetic field represented by the thick orange-ish arrows above didn't reflect in the mirror.  My professor pointed out, however, that the source of the magnetic field, the small circular current, reflected exactly as you'd expect a directed circle to reflect in a mirror.  Consequently, everything is simple and exactly as it should be if you look at the reflection of the cause rather than the effect. References: 1.  An Introduction to Nuclear Physics http://dx.doi.org/10.1017%2FCBO9781139164405 Cottingham W.N. & Greenwood D.A. An Introduction to Nuclear Physics,  DOI:  10.1017/CBO9781139164405