Physics
pontiff | February 8, 2009In a prior post I asked about the how the structure of fixed points of stochastic maps changes under composition of such maps. Robin provided an interesting comment about the setup, linking this question at least partially with zero error codes:
R has at least one fixed point. If it's unique, there need be no relationship between fixed points of P and R. (Q can project to a single vector, which becomes the unique fixed point of R.) If R has N > 1 fixed points, then things get more interesting. The fixed points are closed under linear combination, so they're a subspace (I'm actually…
rallain | February 7, 2009A couple of commenters expressed concern over the use of centrifugal force after my rant on the use of the word force. So, what is the deal with these two terms? Are they ok to use? Are they real forces?
First, are they real forces?
It depends on what you mean by real. What is a force? Here is a quick overview of what a force is. I previously talked about real vs. non-real forces. For me, I say that if the force is essentially one of the 4 fundamental forces then it is "real". With this definition, centripetal force would be real and centrifugal not real.
Centripetal Force
Centripetal…
drorzel | February 6, 2009There's a new paper from the PAMELA dark matter search out that's written up in Physics, including a link to a free version of the PDF. This paper is considerably less dramatic than one that appeared last year, leading Physics World to suggest that they're backing off the earlier claim.
What's the deal? Sean Carroll has you covered, with a detailed explanation of what's in both papers, and why the findings have been published and reported the way they have:
What happened is that the PAMELA collaboration submitted their second paper (anomalous positrons) to Nature, and their first paper (well-…
pontiff | February 5, 2009I've never made it to Benasque, and am always profoundly jealous of those who have gone:
Dear Colleague,
We are pleased to inform you that following a very successful editions of Benasque 1998, 2000, 2003, 2005, and 2007, we are organizing another workshop of the similar type in June 2009. This is to invite you to apply using the electronic form that you can find on the website specified below. We encourage you to apply as soon as possible and not later than the end of March 2009. The number of participants at the Benasque Centre at any given time is limited to about 50. We will do our best…
drorzel | February 5, 2009Having mentioned this a few times in course reports, I thought I'd throw out a link to my lecture notes (PDF) on complex numbers. This is the one-class whirlwind review of complex numbers from defining i to Euler's theorem about complex exponentials.
To answer a slightly incredulous question from a commenter, this is necessary because the math department does not teach about complex numbers exponentials (edited to correct an inadvertent slur against the math department) in the calculus sequence, and the only math prerequisites for the sophomore modern physics class I'm teaching are calculus…
drorzel | February 4, 2009I got the last round of line edits on the book-in-progress Monday night after work, but I haven't had a chance to do more than leaf through the pages. This is mostly because I had lab reports to grade-- the second written report is due Sunday, and I needed to get comments back to the students before they start on the next report.
(Yes, I know, as a practical matter, I could've waited until Saturday for that, but I hope for better.)
Grading labs is just about my least favorite part of the job (narrowly edging out committee meetings), and since this is turning into a blog primarily about…
drorzel | February 4, 2009In the last report from my modern physics course, we wrapped up Relativity, and started into quantum mechanics, talking about black-body radiation and Planck's quantum hypothesis. The next few classes continue the historical theme
Class 10: I make a point of noting that Planck himself never liked the idea of quantization of light, and in fact never applied the idea to light directly. His quantum model for black-body radiation was based on the idea of having "oscillators" in the object emitting the radiation. Einstein was the first to apply the idea of quantization to light directly, and take…
rallain | February 3, 2009People say I am picky. Ok, sometimes I am. But somebody has to stand up for what is right and just. Maybe I am that person.
Please stop using the word force if you don't know what it is.
There. I said it. You can attack me now.
It wasn't just one thing that got me fired up. It was two things. First, I read this article on physics and football (Physics of 'The Hit' from the NY Times). If it was just this article, I would have let it go and moved on. But no. One of my kids just happened to be watching MythBusters (We all love MythBusters) and there was a discussion that used the term…
drorzel | February 3, 2009The Arxiv blog highlights a post on John Scalzi's favorite science question: the Fermi Paradox:
We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?
The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations…
rallain | February 2, 2009I enjoyed the super bowl commercials for the most part. You have to be careful not to have too high of expectations, or you will set yourself up for a big letdown. Here is a quick analysis of one of the commercials. This is a Bud Light commercial where at the end they throw a guy out of an office window because he suggests they save money by not buying beer. Are there any actual office meetings that serve beer? (Sorry if I spoiled the ending for you)
I am going to analyze the motion of the guy going out the window. Just because.
At some point in the future, I am going to make a short…
rallain | January 30, 2009I said I would come back to this, and I am. I am a man of my word. Yesterday, I posted a link to a video of this really cool water rocket thingy.
How does this work? What is the physics going on here? I think this can be best explained with the momentum principle.
Let me start by pretending like I have some object that shoots out a piece of water (or really it could be anything). Also, let me pretend like this is in space ore something where there are no external forces.
Above is a before and after picture. Initially, there is something (the box) with water inside. Through some process…
drorzel | January 30, 2009This week's lab (well, half of it-- the class is so big that I have to run two experiments in parallel) is somewhat controversial, so I thought I would throw this out to my wise and worldly readers to see what you all think.
The problem is this: we have two different set-ups for doing a photoelectric effect experiment. One of these is a PASCO apparatus with the phototube wired to a circuit inside an actual black box. You shine light into the tube, press a button, and the output of the box rises to the stopping potential for that frequency in a more-or-less exponential manner. This gives very…
rallain | January 30, 2009Buzz Out Loud is one of my favorite tech podcasts. Unfortunately, I am a little behind in the episodes. However, in the episode 900 there was an email from a listener regarding LHC and black holes. The emailer claims that a massive black hole would mess up Earth's orbit. This is not quite true.
I was getting ready to make a lengthy post about how black holes work, but did a way more awesomer job than I could do. Stefan and Bee describe some very important points:
First, black holes created in the Large Hadron Collider are based on a theory that has not really been verified. So, it…
drorzel | January 30, 2009I'm not sure what the BBVA Foundation is, but they've awarded a Basic Science prize to Ignacio Cirac and Peter Zoller:
The Basic Sciences award in this inaugural edition of the BBVA Foundation Frontiers of Knowledge Awards has been shared by physicists Peter Zoller (Austria, 1952) and Ignacio Cirac (Manresa, 1965), "for their fundamental work on quantum information science", in the words of the jury chaired by Theodor W. Hänsch, Nobel Prize in Physics. Zoller and Cirac's research is opening up vital new avenues for the development of quantum computers, immensely more powerful than those we…
edyong | January 30, 2009On Tuesday, I wrote a short essay on the rightful place of science in our society. As part of it, I argued that scientific knowledge is distinct from the scientific method - the latter gives people the tools with which to acquire the former. I also briefly argued that modern science education (at least in the UK) focuses too much on the knowledge and too little on the method. It is so blindsided by checklists of facts that it fails to instil the inquisitiveness, scepticism, critical thinking and respect for evidence that good science entails. Simply inhaling pieces of information won't get…
rallain | January 29, 2009I saw this on Hack a Day, but I am sure it has been posted in other places also (seems like something that would be on Swans on Tea). Check it out.
Amazing New Water-Powered Jet Pack - Watch more free videos
Some pretty cool stuff. I am pondering the questions to be answered right now.
rallain | January 29, 2009I really didn't want to post this, but I am going to anyway. I used ScreenToaster.com to make a screen capture movie (with audio) of a tutorial on spreadsheets.
This should accompany my previous post on numerical calculations.
Free online screen recorder
drorzel | January 29, 2009Boskone, the Boston-area SF convention that Kate and I go to every year, is the weekend after next. Once again, I'll be doing a few panels and one talk. For those who might be attending, or who care about this for some reason, here's my preliminary schedule:
Saturday10am Physics: What We Don't Understand
Geoffrey A. Landis
Mark L. Olson
Chad Orzel
Karl Schroeder
Ian Tregillis
In 1999 John Cramer wrote a column in Analog describing seven big
unsolved problems in physics (including the nature of dark matter,
the origin of ultra-high…
drorzel | January 28, 2009Physics World's news aggregator had a story yesterday with the headline Chilly solution to neutrino mass problem, and the one-sentence teaser
Ultracold atoms could be used to measure the mass of the neutrino.
This creates a wonderful image of somehow turning a magneto-optical trap or a Bose-Einstein Condensate into a neutrino detector, which is a nice thought, but highly improbable. Even a BEC has a density a million times less than the density of air, and a volume that's way too small to catch any neutrinos.
So what's going on? The answer is cool in its own right, and the path from the…
drorzel | January 28, 2009The American Physical Society has sent out another of its email alerts encouraging people to write to Congress in support of more funding for science. Actually, they're urging people to send two messages: a thank-you to Speaker Pelosi for the generous science funding in the House stimulus bill, and a letter to your Senators asking for more funding.
The explanation from the message:
As you may be aware, the U.S. Congress is currently formulating a
stimulus package to help spur the recovery of our economy. In
addition to the tax cuts in the draft packages being discussed,
the packages include…