Scienceblogs: Physical Science
Arriving Home in a Hurricane? [Living the Scientific Life (Scientist, Interrupted)]
YIKES! I am arriving home tomorrow early afternoon, in the middle of a dying hurricane. If my flight manages to land without problems (unlikely), I still have to rely on the train to get home and NYC subways tend to flood when the rain gets heavy, as is predicted for Sunday, especially the subway line I need to ride home. The thought that I might end up trapped at the airport or worse, on a stopped train underground is not comforting.
Data paparazzi. [Adventures in Ethics and Science]
In a comment on another post, Blatnoi asks for my take on a recent news item in Nature:
An Italian-led research group's closely held data have been outed by paparazzi physicists, who photographed conference slides and then used the data in their own publications.For weeks, the physics community has been buzzing with the latest results on 'dark matter' from a European satellite mission known as PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics). Team members have talked about their latest results at several recent conferences ... but beyond a quick flash of a slide, the collaboration has not shared the data. Many high-profile journals, including Nature, have strict rules about authors publicizing data before publication.
It now seems that some physicists have taken matters into their own hands. At least two papers recently appeared on the preprint server arXiv.org showing representations of PAMELA's latest findings (M. Cirelli et al. http://arxiv.org/abs/0808.3867; 2008, and L. Bergstrom et al. http://arxiv.org/abs/0808.3725; 2008). Both have recreated data from photos taken of a PAMELA presentation on 20 August at the Identification of Dark Matter conference in Stockholm, Sweden.
I'd say this is a situation that bears closer examination.
Read the rest of this post... | Read the comments on this post...No matter what happens, it is probably going to rain a lot in Florida [Greg Laden's Blog]
It is raining cats and dogs in Florida, thanks to Tropical Storm Hanna. Ike remains a real threat. Josephine is a giant question mark. Details below the fold.
Curently Reading: Just Add Exploding Spaceship Edition [Science After Sunclipse]
Cepheid variables are a type of star whose brightness fluctuates over time. They played a major part in the discovery of the Universe's true scale, since the time it takes a Cepheid to go through its cycle of bright-and-dim is related to its intrinsic luminosity, the average brightness you'd measure if you examined the star from a standard reference distance away. If you know how bright a star would be at, say, ten parsecs away, and you know how bright it appears in your telescope, then you can compare those intensities to figure out how far away the star has to be to appear the strength it does. Thus it was found that Andromeda is a separate galaxy far outside our own, not just a patch of nearby gas, and the Milky Way shrank to a sand grain, with ourselves a subatomic particle inside it.
Recently, four scientists have suggested that a sufficiently advanced civilization could use Cepheid variables as a method of very-long-range communication. In an arXiv preprint, Learned, Kudritzki, Pakvasa and Zee propose that a jolt of extra energy could influence a Cepheid's oscillation, provoking an outburst earlier than normal. A Cepheid builds up ionized helium gas in its outer layers, and this ionized gas blocks the starlight radiating out from the stellar core, making the star go dim. Eventually, the Cepheid's atmosphere expands and the helium ions pick up electrons, neutralizing themselves and making the atmosphere go transparent. Thus, the star goes through a "sawtooth" oscillation, slowly dimming before quickly brightening and then gradually dimming again. This curve, measured for the star δ Cephei (the prototype after which the class is named) shows the pattern:
(Image shamelessly filched from HyperPhysics.)
So, our hypothetical Sufficiently Advanced Aliens could send a beam of neutrinos into a handy Cepheid variable. Neutrinos pass through matter remarkably well, so they could easily reach the star's core; however, they do have a chance of interacting with atoms they pass through, so the beam will deposit a portion of its energy within the star, and pumping extra energy into an unstable system is always a recipe for fun.
Unfortunately, the kind of effect such perturbations might have on Cepheid oscillations wouldn't be immediately obvious. Learned, Kudritzki, Pakvasa and Zee argue that the normal Fourier transforms and whatnot through which variable-star observations are traditionally stuffed would miss the tell-tale effects of Cepheid Streaming Video modulation, and they propose another technique (looking at phase residuals) which might let us observe the green-skinned space teenagers singing into webcams on Andromeda.
John G. Learned, R-P. Kudritzki, Sandip Pakvasa, A. Zee, "The Cepheid Galactic Internet" (arXiv:0809.0339).
We propose that a sufficiently advanced civilization may employ Cepheid variable stars as beacons to transmit all-call information throughout the galaxy and beyond. One can construct many scenarios wherein it would be desirable for such a civilization of star ticklers to transmit data to anyone else within viewing range. The beauty of employing Cepheids is that these stars can be seen from afar (we monitor them out through the Virgo cluster), and any developing technological society would seem to be likely to closely observe them as distance markers. Records exist of Cepheids for well over one hundred years. We propose that these (and other regularly variable types of stars) be searched for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional signaling.Read the comments on this post...
Homeric Epicycles [Dynamics of Cats]
Epicycles can be thought of as correlated 2-D Fourier sums.
As such, they are complete.
Any connected, delimited, periodic curve in the plane can be reconstructed to arbitary precision with high enough order epicycles and requisite deferents.
Below is an illustration of this. It is impressive.
Doh!
Charging the Earth [Built on Facts]
Teaching Physics 201 has me digging out some of my old favorite concept-y problems. Nothing dramatic in the mathematics, but at the 201 level you can't even assume knowledge of derivatives. But you can try to catch their minds with interesting examples. Here's a classic one:
You've got the earth and the moon. They have mass and so they attract each other with gravity. Both the earth and the moon are pretty large, and so the attraction is considerable. On the scale of earthbound undergraduate lab equipment however, gravity from anything but the earth is pretty hard to measure. Pretty much impossible, in fact. We can do a little better with electrical forces. You can charge a glass rod by rubbing it with fur, and observe the effect of the charge on little sheets of foil or similar. These electrical forces are very, very tiny. But even so we're able to see them, which is more than we can say for gravity.
So, if you sprinkled some extra electrons on the earth and the same number of electrons on the moon, how much charge would you have to add in order to completely cancel the gravitational attraction? Let's figure it out. Call the charge q, and we'll put the gravitational force on the right and the electrical force on the left
Of course Me of the mass of the earth, and similarly for the moon. The q2 really is the product of the charge on the earth and the charge on the moon, but we'll assume they're equal for conceptual convenience. Nicely, the distance r will cancel and solving for q we get:
Plug in the appropriate numbers to find the required charge on each body. I find that the answer is 5.71 x 1013 coulombs. That's a pretty huge amount of charge in total. But for the earth it's only about 10-11 coulombs per kilogram. And that itself is only sixty million or so excess electrons per kilogram. And considering each kilogram of earth contains trillions of trillions of electrons, only an absolutely tiny percentage of the total atoms in the earth would actually need to be ionized.
We often think about gravity being the strongest force in our daily experience. It isn't. Electrical forces just have the decency to cancel themselves out to very high precision. Gravity builds up on itself without limit. Which in the final analysis is a pretty lucky thing for us - it's nice having these solid planets which hold themselves together and solar systems which stay mostly stable over quite long time periods.
Still, next time lint clings to your shirt think about how amazing it is that electrical charge can produce forces strong enough to have visible effects from something so small. Gravity couldn't hold lint to your shirt in a million years.
Read the comments on this post...Ike: Yikes!!! [Greg Laden's Blog]
Ike is now a Category Four Hurricane, and quite a nice looking one at that.
Hurricanes are giant engines made of air that are driven by the transfer of heat from the sea surface to the top of the troposphere. The greater the difference in SST (sea surface temperature) and higher altitude temperature, the more power in the engine. But, there are some very strong wind currents in the atmosphere above the troposphere, and that matters as well.
When you fly in a commercial air liner over a long distance, sometimes (depending on the airline) they display a chart that shows current location, speed, etc. as well as outside temperature and sometimes windspeed. You see some pretty remarkable numbers up that high, above the Ozone Layer. If the sea surface temperature is 27 degrees C and the at 8 km t is close to -40 C, that is a lot of temperature differential across the area covered by a hurricane.
However, high winds in the upper atmosphere will interfere with this process. This is why hurricanes don't really form farther north (in the northern hemisphere) than they do. Too much upper level wind activity. This 'wind shear' causes the beautiful turning engine that drives itself pumping heat upward and outward to get all messed up.
Right now, Ike is experiencing some wind shear and will weaken over the next several hours. However, that will go away and other factors will contribute to a re-strengthening.
But where is Ike going to go? Where will it make landfall?
Read the rest of this post... | Read the comments on this post...I Don't Like Ike [The Intersection]
Tropical Storm Ike intensified into a hurricane today, and then rapidly intensified into a sudden Category 3 storm, our third major hurricane of the year. And instead of recurving northward, as hurricanes at its location tend to do, Ike is forecast to plow straight towards Cuba and Hispaniola, and possibly threaten the United States.
All of which is so not cool....but just more proof that this hurricane season is far, far from over.
To that end, my latest Science Progress column is an attempt to seize the moment to direct attention beyond Anderson Cooper dodging flying billboards on CNN, and towards critical matters of hurricane policy: research funding, insurance policy reform, global warming adaptation, and the protection of our most vulnerable major cities. You can read the hurricane policy agenda here.
Read the comments on this post...Wisely Using Your Advantage [The Quantum Pontiff]
Velocity dispersions in a cluster of stars [Dynamics of Cats]
Hrmph.
The real issue is the exact proper motion, not the dispersion about the mean.
Although I suppose outliers can be interesting, even in small N groups.
The other Arctic sea ice loss [A Few Things Ill Considered]
There has been lots of discussion of this year's arctic sea ice extent. Last year was a shocking 23% lower record breaker. That's 23% lower than the previous record, for which one had to go all the way back to....2005! That's not 23% below the 1979-2001 average, but 23% below the lowest previous measurement! 2005, aside from being the previous record, was also remarkable for being the fourth consecutive year that fell below the trend line. (With a steady decline in noisy data one would expect equal probablities of data points falling above the trend line as below.)
Here is a graph made at that time (2005). 2007's record breaking minmum falls well off that chart, where 4 would have been on the x-axis if it had gone that low:
So, as the discussions discuss, here comes 2008, hot on 2007's smokey trail...
Read the rest of this post... | Read the comments on this post...Two Happenings in Physics [Built on Facts]
Physics is a continuous thing, progressing steadily forward with only rare dramatic leaps. This is not the kind of style that makes for flashy news stories in the popular press. When there are interesting things being reported, they're usually wrong. "Faster than light" laser pulses, quantum teleportation, invisibility cloaks... if it's in the popular press it's probably not anything remotely resembling what they tell you it is. It's like asking me to report on avant-garde fashion.
But every once in a while some interesting things pop up. Today two things did. The first is the sun.
The sun is currently in one of the minimums of its 11-year sunspot cycle. Very unusually it's gone a month with no sunspots at all, and the last few months have had a much smaller number of sunspots than normal even for the low end of the cycle. Why? I have no idea. I'm not an astronomer and I'm pretty sure even the astronomers aren't sure in this case. The sun is very complicated. It's a fairly constant star as far as stars go (and it has to be in order to support life), but it's interesting to remember that in fact we live around a variable star. Not a very variable one, but a variable one nonetheless.
As far as I know no one anticipates this quiet period causing any problems. Past minimums have been associated with freezes and famines, but from looking at the graph this minimum doesn't seem to be nearly as small or as long as the old damaging minimums. Either way, unlike in science fiction even if it did cause problems humanity is not quite capable of adjusting the output of the sun just yet. It's interesting to watch nonetheless.
The other story is the demise of Bell Labs. Bell Labs was of course the research arm of the Bell telephone monopoly, and was responsible for an unbelievable number of advances and discoveries. It has something of a legendary reputation in the golden age of physics; they collected Nobel prizes by the fistfull.
Long story short, the breakup of the Bell monopoly meant that Bell had increasingly little money to spend on fundamental research. Bell Labs was split off the company into Lucent and lasted for another decade or so before finally calling it quits. Overall the increased competition in the telecommunications industry is probably a good thing for the country at large, but the loss of Bell Labs is a bitter price to pay. Cross your fingers that someday another huge company will take an interest in fundamental physics and create their own new institutes. Gates? Jobs? Heck, Carlos Slim? I've got a proposal for y'all...
Read the comments on this post...Boneyard Is Up! [Deep Sea News]
Zach at When Pigs Fly Returns has the latest edition of the paleo-carnival, The Boneyard! Keep an eye out for preserved naughty bits...
Read the comments on this post...Past decade is warmest in at least 1,300 years [A Few Things Ill Considered]
Mann et al. has a new paper out that again reconfirms that the MWP was not as pronounced or as high a warming period as today's climate changes are bringing.
This is no longer surprising and is in close agreement with all other NH reconstructions that have been done, and all global reconstructions as well.
Read the rest of this post... | Read the comments on this post...The Large Hadron Rap [Pharyngula]
Am I allowed to mention physics here? How about if it's a rap video?
Read the comments on this post...Life Science, Physical Science and Environment Weekly Channel Highlights [Page 3.14]
In this post: the large versions of the Life Science, Physical Science and Environment channel photos, comments from readers, and the best posts of the week.
Read the rest of this post... | Read the comments on this post...
Large Hadron Rap [Pure Pedantry]
In honor of the opening of the Large Hadron Collider at CERN, Michigan State University graduate student Kate McAlpine has an LHC rap on YouTube. The best part: the science is dead on.
Read the rest of this post... | Read the comments on this post...Still a Lot to Do [The Quantum Pontiff]
Over hyped press releases are a standard for quantum computing research and a stable of what makes me sound like a grumpy old man. Really I'm not that grumpy (really! reall!), but I always forget to post the stuff which isn't over hyped. For example, today I stumbled upon an article about a recent experimental implementation of a code for overcoming qubit loss done in China. In this article I find a graduate student whose was able to get a reasonable quote into the article:
While optimistic critics are acclaiming the newly achieved progress, the team, however, is cautiously calm. "There are still a lot to do before we can build a practically workable quantum computer. Qubit loss is not the only problem for QC; other types of decoherence are to be overcome," remarks LU Chaoyang, a PhD student with the team. "But good news is, the loss-tolerant quantum codes demonstrated in our work can be further concatenated with other quantum error correction codes or decoherence-free space to tackle multiple decoherence, and may become a useful part for future implementations of quantum algorithms."Ah, that makes me happy. Read the comments on this post...
Walking the Plank [Built on Facts]
In honor of Physics 201 which I'm teaching this semester, I present a very elementary statics problem.
Here we have a board of uniform composition and weight W. It has length l and the supports are separated by a distance s. What are the two forces (call them A and B) on the boards?
The board isn't moving. It's just sitting there, and so if there's no acceleration there's no net forces. That gives us
Hmm. That's two unknown quantities with one equation. Not enough. Fortunately there's another equation we can use involving the torque. Torque is the angular equivalent of force. Get a wrench and turn a bolt, and you're applying a force at a distance from the bolt. That distance times the force is the torque about the bolt. If there's no angular acceleration (it's not spinning at all here), there's no net torque. There's no bolt either, but fortunately it turns out that you can measure the toque about any convenient point - some might make the problem easier than others. Here's let's pick point A as the point to measure the torque about, and we'll write down each force times its distance from A. They'll have to add to zero since there's no angular acceleration and thus no torque.
That factor of (l/2) represents the torque from the weight of the board. Since the board is uniform we can just pretend all the mass is at the center point. So now we can solve the second equation for B, and use that to find A in the first equation. I get
and
Easy, huh? Everyone has to start somewhere though, and this is a pretty good place to start for statics.
Exit question (easy): If s is too small, the board will fall over. What is the smallest value of s that will allow the board to balance in the picture and how do we know this from the equations?
Exit question (medium): If the board is not uniform but instead has a weight per length (x increasing toward the right) given by
The constants are of course picked so that the total weight is still W. What is the minimum s that allows for stability? Sadly there are no prizes other than fame in the comments, but I'm sure the thrill of success will be reward in itself!
Read the comments on this post...