Physics
rallain | July 16, 2009Yesterday, I uploaded a post from my old site about slowing down time to make videos look like they were on the moon. If you haven't read that, the short story is that it doesn't look right when speed Apollo videos up so that the acceleration is -9.8 m/s2.
What started that whole thing was an even earlier post. Here is an example of using video analysis (Tracker Video Analysis) to measure the acceleration of a jumping astronaut on the moon. In this case, it is the famous "jump salute" from Apollo 16 astronaut John Young.
First, thanks John (or whoever videoed it). This is a good video for…
pontiff | July 16, 2009Via @mattleiffer, viXra.org:
In part viXra.org is a parody of arXiv.org to highlight Cornell University's unacceptable censorship policy. It is also an experiment to see what kind of scientific work is being excluded by the arXiv. But most of all it is a serious and permanent e-print archive for scientific work. Unlike arXiv.org tt [sic] is truly open to scientists from all walks of life.
Maybe I should submit one of my papers with all of the text reversed (yeah, yeah, it would still be incomprehensible.)
rallain | July 15, 2009Note: This is a repost from my old site. Time to move it over.
First, what is different about motion on the moon and on Earth? Since the moon has a smaller mass in spite of its smaller size*, the moon has a smaller gravitational field. The gravitational field on the surface of the moon is 1/6th the field on the surface of the Earth. This means that the acceleration of a free falling on the object would be 1/6th the acceleration on Earth. So the question is: how would you change the time scale of a movie so that it looks like its acceleration is 1/6th of 9.8 m/s2?
*If you make the size of…
pontiff | July 15, 2009Microsoft Research's Project Tuva website is up. Project Tuva is a collection of seven searchable Feynman lectures aimed at a popular audience (with extras coming online in the future.) The rights to these lectures were obtained by Bill Gates after he was entranced by them over twenty years ago. Well worth watching, especially if you're about to give a popular science talk (I've always been fascinated by how Feynman uses his hands in describing physics.)
Even more interesting, in my egocentric universe, are the comments by Mr. Gates himself about Feynman:
Someone who can make science…
drorzel | July 15, 2009I've sometimes seen it said that in order to have a productive discussion, people on both sides need to be willing to change their minds. I think that's probably slightly overdetermined-- you can find examples of cases in which neither side was going to change, but they managed to sustain a mutually beneficial dialogue all the same. The physics example that comes to mind is Bohr and Einstein, who spent decades arguing with each other over the philosophical basis of quantum theory, but were nonetheless good friends. They pushed each other, forcing each of them to refine their arguments and…
drorzel | July 15, 2009Yesterday's Michelson Interferometer quiz was surprisingly popular-- as of 8:30 pm Tuesday (when I'm writing this), just under 1500 people have voted in the poll, three and a half times as many as in the next most popular poll I've done. Who says there's no audience for physics?
So, what's the right answer, you ask?
The correct answer finished a distant second (as of 8:30 it has 21% of the votes, to 52% for the leading wrong answer). The answer is that the light goes back where it came from. Bob Hawkins and MattXIV have the right explanation: on the return trip, half of each beam goes to the…
rallain | July 14, 2009This has been on my list for quite some time. Really, it must be since i posted about measuring acceleration in free fall with an iphone. So, this post will be all about accelerometers.
How does an accelerometer work? Really, an accelerometer measures force some way on a known mass. Let me show an extremely simple accelerometer - a mass on a spring.
(image from Science Buddies where they have instructions on building such a device)
Suppose I put this accelerometer in a stationary and non-accelerating elevator. Let me draw a free body diagram for the mass on the end.
No magic here,…
drorzel | July 14, 2009Inspired by one of yesterday's easy questions, a pop quiz for you. The figure below shows a Michelson Interferometer:
A laser falls on a beamsplitter, which allows half of the light to pass straight through, and reflects the other half downward. Each of those beams then hits a mirror that reflects it directly back where it come from. The beams are recombined at the beamsplitter, and then fall on the viewing screen at the top of the figure.
When we add together the light from the two paths, we find that if the lengths of the two arms (that is, the distance from beamsplitter to mirror) are…
esiegel | July 13, 2009
The coolest things about science are often at the frontiers. We love to press the limits of nature: to cool things down as close as possible to absolute zero, to raise energies as high as possible, and to speed them up as fast as possible. But when it comes to speed, there's an absolute limit: the speed of light in vacuum.
Relativity tells us why this is the absolute limit: the faster you want to go, the more energy it takes. But, as you get close to the speed of light, you effectively increase the mass of your speedy particle, which makes it ever harder to accelerate it. In fact, it would…
pontiff | July 13, 2009Over at the optimizer's blog, quantum computing's younger clown discusses some pointers for giving funny talks. I can still vividly remember the joke I told in my very first scientific talk. I spent the summer of 1995 in Boston at the Smithsonian Astrophysical Observatory (photo of us interns) working on disproving a theory about the diffuse interstellar absorption bands by calculating various two photon cross sections in H2 and H2+ (which was rather challenging considering I'd only taken one quarter of intro to quantum mechanics at the time!) At the end of the summer all the interns gave…
rallain | July 11, 2009My friend J sent me a link to this gyrobike (http://www.thegyrobike.com/index.php). From what I can tell, it's a flywheel that you put in the front wheel of a bike. The site claims that this will help kids learn how to ride a bike.
So, what do I think? Clearly, this is a real product, but I am not so sure how effective it would be. As I mentioned in a previous post, it's not really about angular momentum that prevents you from falling over. Well, actually I didn't really say that. I referred to an excellent article on the physics of bicycles, David E. H. Jones and published in Physics…
pontiff | July 9, 2009The report from the Workshop on Quantum Information Science has now been posted. Color commentary soon :)
drorzel | July 9, 2009I'm sitting here finding new and inventive ways to not write the pedagogical paper I'm working on at the moment. This seems like a good excuse for a poll!
The hardest part of writing a paper is:(survey)
As you can tell from the list of elements, I have scientific papers in mind, here, but other sorts of scholarly work are also fair game. The question is really what you find to be the absolute worst part to write when you're working on some sort of scholarly publication.
I'm talking specifically about the writing of the text, here. There are a whole host of headaches associated with…
pontiff | July 8, 2009The arXiv is a game changer for how large portions of physics (and increasingly other fields) are done. Paul Ginsparg won a MacArthur award for his vision and stewardship of the arXiv (something other institutions might want to note when they decide that someone trying to change how science is done isn't really doing work that will impact them.) So...Given: The arXiv is great. But there is something that's always bothered me a bit about the arXiv: transparency.
(Note: those of you who wish to complain about the fact that you can't get endorsed on the arXiv, this article is not for you.…
rallain | July 8, 2009What do you see when you are in a completely dark room with no lights?
That is a great question to ask. It can bring out some interesting ideas. Anyway, here is an easy demo to show the color black. The basic idea is to build a box that has a small opening. Here is what it looks like from the outside:
As you can see, just a basic box. I have a door on the top, and I put a paper towel tube for a window. To make it look pretty, I covered it with black paper (so you couldn't tell where I stole the box from).
To demo this to students, I first go around and let everyone look inside. I ask…
pontiff | July 8, 2009Has the arXiv been hacked or is it offline? When I connect to arxiv.org it shoots me to mirror sites which haven't been updated since Oct 08. Via @MartinQuantum. Also nanoscale views reports the arXiv down.
Since this is a blog we can easily spread rumors by including a link to an article today about cyberattacks going on right now possibly originating from North Korea.
Update 9:03 am PST: At lanl.arxiv.org you can now get papers greater than October 2008 by searching, but the "recents" and "new" isn't working. Also the RSS feed seems to only have yesterdays posts. A comment on Secret…
drorzel | July 8, 2009I've got a couple more things to say about Unscientific America, probably, but I opted for some more David Foster Wallace last night, and don't feel like typing them up now, so I'll give you all a break. Anyway, what you're really here for is the baby and dog stuff, so here's another poll question from Emmy:
Cats are(survey)
(I think you should be able to choose multiple answers to this one, but I'm not 100% sure I set it up right.)
drorzel | July 8, 2009There's a press release dated a week or two ago from Leiden University headlined "Physical reality of string theory demonstrated," in an apparent bid to make Peter Woit's head explode. The release itself is really pretty awful, with poorly explained and irrelevant pictures, and a really confusing description of what this is really about (in part because English was not the first language of the person writing it, I suspect). You have to go down to the third paragraph to find a sort-of explanation of what this is about:
Electrons can form a special kind of state, a so-called quantum critical…
drorzel | July 7, 2009It's been a while since we've had any good, solid physics content here, and I feel a little guilty about that. So here's some high-quality (I hope) physics blogging, dealing with two recent(ish) papers from Chris Monroe's group at the University of Maryland. The first is titled "Bell Inequality Violation with Two Remote Atomic Qubits" (and a free version can be found on the Arxiv); the second is "Quantum Teleportation Between Distant Matter Qubits" (and isn't available on the arxiv because it's in Science, but you can get it from their web site). Both of these deal with the physics of…
drorzel | July 6, 2009Having repeatedly called for more popular-audience discussion of condensed matter physics (which is not my own field, but is the largest single division within the American Physical Society), I would be remiss if I failed to note a couple of really good efforts in this direction.
The first is last week's NOVA ScienceNOW segment on artificial diamonds and their technological potential. It's really cool to see time-lapse video of honkin' big diamonds being grown through chemical vapor deposition techniques.
The second is this New York Times piece on glass and the science of its use as a…