Physics
drorzel | December 4, 2008There's a kind of tradition in theoretical physics of wacky "what if" papers. The whole "wormhole" thing is an example of this in action-- somebody noticed that the structure of General Relativity would allow you to make tunnel-like structures between points in space, and then asked what you would need to make such a structure. The answer turns out to include "a negative energy density," which is impossible, as far as we know, but that hasn't stopped people from creating an entire cottage industry around papers about wormholes.
(I don't know if other sciences do this-- are there biologists…
oracknows | December 4, 2008I've long had an interest in World War II history. Ever since I was around 11 or 12 years old, a major portion of my reading diet has consisted of books and articles about World War II. Back when I was young, my interest was, as you might expect, primarily the battles. The military history of World War II fascinated me, and I build many, many models of World War II fighter aircraft and warships when I was in my early teens. (No cracks about how the airplane glue obviously affected me, although it is true that back then it was real airplane glue, chock full of toluene and lots of other organic…
rallain | December 4, 2008Ok - I like Alabama football (sorry, but it's true). There is a clip on youtube of the end of the Alabama-Auburn game where the fans sing the traditional "Rammer Jammer". If you don't know what that is, don't worry. I am not sure I completely approve of the cheer, but it is a tradition. If you are curious, here it is:
So, what is cool about this? Notice that the entire crowd is yelling the same thing, but they are out of sync. Can this be used to estimate the size of the stadium?
I made an audio file from that youtube clip and looked at it with Audacity. Although I am completely…
rallain | December 1, 2008This is something I have thought about for some time. It is also something I (as a father of 4) have a lot of experience with. The problem is these infant car carriers. In the car they are not a problem. The problem is out of the car. Not sure what I am talking about? Here is a picture:
I don't mean to attack the infant carrier industry. I am sure some people really like these things. For me, there is only two situations that are good for taking the seat out of the car.
In a restaurant. The infant seat works well with those toddler high chairs. Most of the current infant seat…
pontiff | December 1, 2008The blackberry hole (aka the Perimeter Institute) has swallowed another person. Most fittingly, however, this time the observer will exist both inside and outside of the Perimeter Institute, thus giving us an answer to the black hole information paradox:
WATERLOO, Ontario, Canada, November, 2008 - Dr. Neil Turok, Director of Canada's Perimeter Institute for Theoretical Physics (PI), is pleased to announce the appointment of internationally regarded scientist Prof. Stephen Hawking to the position of PI Distinguished Research Chair.
Prof. Hawking will conduct regular stays at PI in coming…
drorzel | December 1, 2008I got email last week from the Institute of Physics pointing me to a pair of video interviews with Anton Zeilinger of the University of Vienna. Zeilinger has built an impressive career out of doing fundamental tests of quantum mechanics-- he's not only got the accent and the hair to be a brilliant physicist, he's got a long list of amazing experimental papers to back it up.
They've gone the Locus route, and not included any of the questions he was responding to, which is always a little weird. Zeilinger provides enough context that everything makes sense, though, and he says some really…
rallain | November 25, 2008You see this all the time in textbooks:
This is often described as "the acceleration due to gravity". Is this really the best thing to call this? No. A better name would be "the local gravitational field" and list it in units of:
Where does g come from? The usual source is from the weight, or gravitational force:
This is the best way to write it (in vector notation) but you will often see it written as:
which looses the vector nature. In the vector notion, the vector g is a vector pointing towards the center of the Earth.
Why not acceleration due to gravity?
Take the following case…
amillikan | November 24, 2008Last week, scientists positively identified the bones of Nicolaus Copernicus, the astronomer credited with scientifically formulating the idea that the universe is heliocentric and prompting the 16th century scientific revolution. To be sure that the bones were actually those of Copernicus, the scientists compared DNA from the unmarked remains found in a grave beneath Frombork Cathedral with DNA collected from the pages of one of Copernicus' books and found them to be identical. Using computer modeling software, his face has been virtually reconstructed.
rallain | November 24, 2008This is an old video, but still interesting. In this video clip, Kobe Bryant jumps over a pool of snakes.
You are probably thinking what I thought when I see that - this doesn't look real. Really, it must be fake. Why would Kobe jump over a pool of snakes? Isn't that dangerous (even if there were no snakes in there he could hurt himself). Video analysis is needed. Is this fake or is it real?
Start with my favorite video analysis tool (tracker). Use this to get position time data.
Step 1: Get the movie. I used Mpeg Streamclip to get the movie in quicktime format from the flash video…
rallain | November 23, 2008One of my favorite podcasts to listen to while driving or mowing the lawn is [Buzz Out Loud](http://bol.cnet.com). Buzz Out Loud (BOL) is basically just a tech-based podcast, but very entertaining. Anyway, as part of my attention seeking disorder, I try to get mentioned on the show. I succeeded once when I posted my [Optimal Commuting Speed Calculator](http://www.dotphys.net/page1/page10/efficiency/calculator.html). When I heard Tom and Rafe talking about orbital speeds, I realized this was my chance. Find any tiny flaw in their reasoning and I could perhaps come up with a comment worthy…
rallain | November 22, 2008One of things I like to think about in science is "how do we know that?" It is interesting how one thing builds on another. This is a story of how the Greeks estimated the distance from the Earth to the Sun (an important idea in the development of the model of the solar system). I like this story because it is not too complicated. In fact, one could easily reproduce these measurements themselves. So, here is what I will talk about:
Measuring the size of the Earth.
Determining the distance from the Earth to the moon and the size of the moon.
Calculating the distance (and size) to the Sun…
rallain | November 20, 2008Georgia Tech is playing Miami (not the real Miami, the other one Miami Florida). Right after a commercial, the camera shows this sign from a student (or just person) at the game:
(Sorry if the image isn't that great.) I had to pause the game and take a closer look at this sign. I am not sure I get it. In case you can't see, the sign shows two players and the trajectory of a ball (clearly labeled x and y axes). The equations are:
![Gtequ 1](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/11/…
drorzel | November 20, 2008I seem to have been sucked into a universe in which I'm talking about the Many-Worlds Interpretation all the time, and Neil B keeps dropping subtle hints, so let me return to the whole question of decoherence and Many-Worlds. The following explanation is a recap of the argument of Chapter 4 of the book-in-progress, which will cover the same ground, with cute dog dialogue added.
The central question here is what sorts of things count as producing a "new universe" in Many-Worlds. The scare quotes are because I've come around to the opinion that the whole "parallel universe" language does more…
drorzel | November 19, 2008A little while back, when I complained about the treatment of the multiverse in Anathem, a number of people commented to say that it wasn't all that bad. And, indeed, they were right. Compared to last night's History Channel program on "Parallel Universes," Stephenson's book is a miracle of subtle nuance, teasing out the crucial distinctions between different theories, and making them clear to the reader.
Yeesh. That was so actively irritating that I don't know where to start. So I won't-- you can read what I wrote in the earlier post, and apply it to the History Channel, ten times over.…
rallain | November 19, 2008Rarely am I up late enough to watch the Colbert Report, but by chance I saw it last night. I know Stephen Colbert is a big fan of Dot Physics, and so this is a message to him. Stevie, good job. Here is what he said during his show on the "The Word" segment. Just to give you the context, he was making some point about how if you say anything while talking like a hippie, you make what you said untrue:
Colbert: "Net force of the object equals mass times acceleration, MAN. There. I completely invalidated Newton's second law of motion."
First, the good. He said "net force". How many…
rallain | November 18, 2008Big trucks are not as popular as they used to be, but gas prices are going down so maybe this commercial for the ford F-150 will start showing up again:
They say its a real demonstration, but it has seemed odd to me. (they also say this is a professional driver on a closed course and don't try this at home - damn! I was SO going to do that this weekend). Here is my analysis:
Here is the important data I have gathered from the Internets.
The truck (a Ford F-150) stops a plane C-123 Provider
The curb weight of the F-150 is around 5,000 lbs - depending on options and stuff.
The empty weight…
drorzel | November 18, 2008The History Channel ran a two-hour program on Einstein last night. I had meant to plug this in advance, but got distracted by the Screamy Baby Fun-Time Hour yesterday, and didn't have time to post.
The show restricted itself more or less to the period from 1900, just before his "miracle year" in 1905, to 1922 or so, when Einstein received his Nobel Prize. This was his most fertile period, scientifically, and they did a fairly comprehensive job of covering his life during this time, including his struggles for acceptance and his complicated personal life.
There were, of course, some…
drorzel | November 17, 2008Nobody reading blogs, anyway. Doug Natelson asked for comments on a recent workshop on iron arsenide superconductors yesterday, and the count of comments still stands at zero.
The under-representation of condensed matter physicists among bloggers and blog readers, relative to their abundance in the general population, really is amazing.
rallain | November 17, 2008Atwood's machine is the name of a device that looks like this:
Also known as "two masses on a pulley". Surprisingly, this simple device comes up a lot in intro physics texts. It also brings up some interesting issues. I will go over the basic way to solve a problem like this (as an example) and then talk about the other interesting issues it brings up.
Problem: A small, low mass, pulley has a light string over it connected to two masses, m1 and m2. If released from rest, what is the acceleration of the two masses.
Where to start? This is actually a very difficult question for…
drorzel | November 17, 2008There's a link in today's links dump to a post from Pictures of Numbers, a rarely-updated blog on the visual presentation of data (via Swans On Tea, I think). There's some really good stuff there about how to make graphs that are easy to read and interpret.
I would like to dissent mildly from one of their points, in the Better Axes post, specifically the advice about not starting at zero. In many cases, this is good advice, but like most rules of thumb, it shouldn't be followed too closely.
Take, for example, this post from one of my metastable xenon papers:
A strict application of the…