Physics posts
- November 24, 2010
- 10:56 AM
- 1,646 views
This “Week” in the Universe: November 9th – November 22nd
by S.C. Kavassalis in The Language of Bad Physics
Astrophysics and Gravitation:
Fundamental constants: Big G revisited
Davis, R. (2010). Fundamental constants: Big G revisited Nature, 468 (7321), 181-183 DOI: 10.1038/468181b
Credit: Nature. a, A spherical 'source mass' (ms) is brought near a pendulum's spherical bob (the 'test mass', mt) and causes the bob to move a small distance z from its usual resting position (grey). The gravitational force between the two masses (left side of equation), which depends on Newton's constant (G), can be obtained from a measurement of z provided that k is known (see b). b, The value of k is found by measuring the period (P) of the freely swinging pendulum. To compute the value of G, we need measurements of L, z, ms and P (but not mt). Parks and Faller's experiment was based on four cylindrical source masses of 100 kilograms each, two pendulums and many other refinements.
From the abstract:
Measuring Newton’s constant of gravitation is a difficult task, because gravity is the weakest of all the fundamental forces. An experiment involving two simple pendulums provides a seemingly accurate but surprising value.
For more, see Fundamental constants: Big G revisted.
Galaxy Zoo Supernovae
Galaxy Zoo (2010). Galaxy Zoo Supernovae arXiv arXiv: 1011.2199v2
This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae which, with 2500 volunteers, has categorized almost 14,000 supernovae candidates.
For more, see Galaxy Zoo paper goes supernova.
“Youngest” Nearby Black Hole
Credits: X-ray: NASA/CXC/SAO/D.Patnaude et al, Optical: ESO/VLT, Infrared: NASA/JPL/Caltech
From the Press Release:
This composite image shows a supernova within the galaxy M100 that may contain the youngest known black hole in our cosmic neighborhood. In this image, Chandra’s X-rays are colored gold, while optical data from ESO’s Very Large Telescope are shown in red, green, and blue, and infrared data from Spitzer are red. The location of the supernova, known as SN 1979C, is labeled… This approximately 30-year age, plus its relatively close distance, makes SN 1979C the nearest example where the birth of a black hole has been observed, if the interpretation by the scientists is correct.
Sure, black holes can have finite age, that seems perfectly reasonable… well no, not really. The “age” of a black hole is an exceptionally complicated, verging on philosophical, matter that I’ll have to write about.
For more, see Black Hole Baby Spotted Being Born, Youngest nearby black hole found, Youngest Nearby Black Hole.
High Energy Physics and Particles:
Trapped Antihydrogen
Andresen, G., & et al. (2010). Trapped antihydrogen Nature DOI: 10.1038/nature09610
From the abstract:
Antihydrogen, the bound state of an antiproton and a positron, has been produced2, 3 at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature’s fundamental symmetries. … Here we demonstrate trapping of antihydrogen atoms. …This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.
For more, see Antiatoms Bottled for First Time, Antimatter atoms held captive by physicists.
General Relativity, Quantum Gravity, et al.:
Pre-Big-Bang Penrose
V. G. Gurzadyan, & R. Penrose (2010). Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity arXiv arXiv: ... Read more »
Davis, R. (2010) Fundamental constants: Big G revisited. Nature, 468(7321), 181-183. DOI: 10.1038/468181b
Galaxy Zoo. (2010) Galaxy Zoo Supernovae. arXiv. arXiv: 1011.2199v2
Andresen, G., & et al. (2010) Trapped antihydrogen. Nature. DOI: 10.1038/nature09610
V. G. Gurzadyan, & R. Penrose. (2010) Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity. arXiv. arXiv: 1011.3706v1
Belgiorno, F., Cacciatori, S., Clerici, M., Gorini, V., Ortenzi, G., Rizzi, L., Rubino, E., Sala, V., & Faccio, D. (2010) Hawking Radiation from Ultrashort Laser Pulse Filaments. Physical Review Letters, 105(20). DOI: 10.1103/PhysRevLett.105.203901
Alberto S. Cattaneo, & Florian Schaetz. (2010) Introduction to supergeometry. arXiv. arXiv: 1011.3401v1
Benjamin Bahr, Bianca Dittrich, & Song He. (2010) Coarse graining theories with gauge symmetries. arXiv. arXiv: 1011.3667v1
Veronika E. Hubeny. (2010) The Fluid/Gravity Correspondence: a new perspective on the Membrane Paradigm. arXiv. arXiv: 1011.4948v1
- November 23, 2010
- 08:00 AM
- 558 views
Reconcile Einstein and Schroedinger by ditching Al
by David Bradley in SciScoop Science Forum
SciScoop contact Nykolai Bilaniuk brought an intriguing paper to our attention recently, that at first glance looks like a typical cracked conjecture of the kind SciScoop has reported in the past, but, says Bilaniuk, this one has a certain credibility. The idea is that of UC Berkeley’s Petr Horava, Bilaniuk tells us, and it’s one [...]Reconcile Einstein and Schroedinger by ditching Al is a post from: SciScoop Science News
... Read more »
Hořava, P. (2009) Quantum gravity at a Lifshitz point. Physical Review D, 79(8). DOI: 10.1103/PhysRevD.79.084008
- November 23, 2010
- 08:00 AM
- 441 views
Reconciling Einstein and Schroedinger
by David Bradley in SciScoop Science Forum
SciScoop contact Nykolai Bilaniuk brought an intriguing paper to our attention recently, that at first glance looks like a typical cracked conjecture of the kind SciScoop has reported in the past, but, says Bilaniuk, this one has a certain credibility. The idea is that of UC Berkeley’s Petr Horava, Bilaniuk tells us, and it’s one [...]Reconciling Einstein and Schroedinger is a post from: SciScoop Science News
... Read more »
Hořava, P. (2009) Quantum gravity at a Lifshitz point. Physical Review D, 79(8). DOI: 10.1103/PhysRevD.79.084008
- November 22, 2010
- 10:46 AM
- 834 views
Research – The World’s Smallest Water Bottle (Literally)
by Paul Vallett in Electron Cafe
How small is the world’s smallest water bottle? Well, imagine a water bottle that can only hold a single water molecule. As ridiculous as it sounds that’s what a group in Beijing has been able to achieve. They were able to use a modified carbon cage, commonly known as a buckyball, as the bottle to [...]... Read more »
Zhang, Q., Pankewitz, T., Liu, S., Klopper, W., & Gan, L. (2010) Switchable Open-Cage Fullerene for Water Encapsulation. Angewandte Chemie International Edition. DOI: 10.1002/anie.201004879
- November 22, 2010
- 09:27 AM
- 1,269 views
roger penrose hunts for traces of other big bangs
by Greg Fish in weird things
Inflationary cosmology, which is the current model of how physics sees space and time, gets pretty tangled in how it describes the Big Bang and its immediate after-effects. All sorts of odd quantum states, asymmetries, and exotic particles had to come into existence after a violent event that carved out an ever-expanding bubble of space, [...]... Read more »
V. G. Gurzadyan, & R. Penrose. (2010) Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity. n/a. arXiv: 1011.3706v1
- November 20, 2010
- 09:10 PM
- 442 views
Einstein, tea leaves, meandering rivers, and beer
by Zoltan Sylvester in Hindered Settling
If you make your tea the old-fashioned way, ending up with a few tea leaves at the bottom of the teacup, and you start stirring the tea, you would expect the leaves to move outward, due to the push of the centrifugal force. Instead the leaves follow a spiral trajectory toward the center the cup. The physical processes that result in this 'tea leaf paradox' are essentially the same as the ones responsible for building point bars in meandering rivers. It turns out that the first scientist to make this connection and analogy was none other than Albert Einstein.In a paper published in 1926 (English translation here), Einstein first explains how the velocity of the fluid tea flow is smaller at the bottom of the cup than higher up, due to friction at the wall. [The velocity has to decrease to zero at the wall, a constraint called 'no-slip condition' in fluid mechanics.] To Einstein it is obvious that "the result of this will be a circular movement of the liquid" in the vertical plane, with the liquid moving toward the center at the bottom of the cup and outward at the surface (see the figure below). For us, it is probably useful to think things out in a bit more detail.Einstein's illustration of secondary flow in a teacupA smaller velocity at the bottom means a reduced centrifugal force as well. But overall, the tea is being pushed toward the sidewalls of the cup, and this results in the water surface being higher at the sidewalls than at the center. The pressure gradient that is created this way is constant throughout the whole water tea column, and overall it balances the centrifugal force (unless you stir so hard that the tea spills over the lips). This means that the centrifugal force wins at the top, creating a velocity component that points outward, but loses at the bottom, creating a so-called secondary flow that is pointing inward. The overall movement of the liquid has a helical pattern; in fact, those components of the velocity that act in a direction perpendicular to the main rotational direction are usually an order of magnitude smaller than the primary flow.Einstein goes on to suggest that the "same sort of thing happens with a curving stream". He also points out that, even if the river is straight, the strength of the Coriolis force resulting from the rotation of the Earth will be different at the bottom and at the surface, and this induces a helical flow pattern similar to that observed in meandering rivers. [This force and its effects on sedimentation and erosion are much smaller than the 'normal' helical flow in rivers.] In addition, the largest velocities will develop toward the outer bank of the river, where "erosion is necessarily stronger" than on the inner bank.Secondary flow in a river, the result of reduced centrifugal forces at the bottomI find the tea-leaf analogy an excellent way to explain the development of river meanders and point bars; just like tea leaves gather in the middle of the cup, sand grains are most likely to be left behind on the inner bank of a river bend. Yet Einstein's paper is usually not mentioned in papers discussing river meandering -- an interesting omission since a reference to Einstein always lends more weight and importance to one's paper (or blog post).A recent and very interesting exception is a paper published in Sedimentology. It is titled "Fluvial and submarine morphodynamics of laminar and near-laminar flows: a synthesis" and points out how laminar flows can generate a wide range of depositional forms and structures, like channels, ripples, dunes, antidunes, alternate bars, multiple-row bars, meandering and braiding, forms that are often considered unequivocal signs of turbulent flow. As they start discussing meandering rivers and point bars, Lajeunesse et al. suggest that Einstein's teacup is extremely different dynamically from the Mississippi River, yet it can teach us about how point bars form:A flow in a teacup with a Reynolds number of the order of 102 cannot possibly satisfy Reynolds similarity with the flow in the bend of, for example, the Mississippi River, for which the Reynolds number is of the order of 107. Can teacups then be used to infer river morpho- dynamics? The answer is affirmative. When dynamical similarity is rigorously satisfied, the physics of the two flows are identical. However, even when dynamical similarity is not satisfied, it is possible for a pair of flows to be simply two different manifestations of the same phenomenon, both of which are described by a shared physical framework. Any given analogy must not be overplayed because the lack of complete dynamic similarity implies that different features of a phenomenon may be manifested with different relative strengths. This shared framework nevertheless allows laminar-flow morphodynamics to shed useful light on turbulent-flow analogues.Apart from helping understand river meandering, the tea leaf paradox has inspired a gadget that separates red blood cells from blood plasma; and helps getting rid of trub (sediment remaining after fermentation) from beer.That explains the 'beer' part of the title. And it is time to have one.ReferencesEinstein, A. (1926). Die Ursache der Meanderbildung der Flusslaufe und des sogenannten Baerschen Gesetzes Die Naturwissenschaften, 14 (11), 223-224 DOI: 10.1007/BF01510300Lajeunesse, E., Malverti, L., Lancien, P., Armstrong, L., Metivier, F., Coleman, S., Smith, C., Davies, T., Cantelli, A., & Parker, G. (2010). Fluvial and submarine morphodynamics of laminar and near-laminar flows: a synthesis Sedimentology, 57 (1), 1-26 DOI: 10.1111/j.1365-3091.2009.01109.x... Read more »
Einstein, A. (1926) Die Ursache der M�anderbildung der Flu�l�ufe und des sogenannten Baerschen Gesetzes. Die Naturwissenschaften, 14(11), 223-224. DOI: 10.1007/BF01510300
LAJEUNESSE, E., MALVERTI, L., LANCIEN, P., ARMSTRONG, L., MÃTIVIER, F., COLEMAN, S., SMITH, C., DAVIES, T., CANTELLI, A., & PARKER, G. (2010) Fluvial and submarine morphodynamics of laminar and near-laminar flows: a synthesis. Sedimentology, 57(1), 1-26. DOI: 10.1111/j.1365-3091.2009.01109.x
- November 19, 2010
- 10:38 AM
- 1,378 views
Interference of Independent Photon Beams: The Pfleegor-Mandel Experiment
by Chad Orzel in Uncertain Principles
Earlier this week, I talked about the technical requirements for taking a picture of an interference pattern from two independent lasers, and mentioned in passing that a 1967 experiment by Pfleegor and Mandel had already shown the interference effect. Their experiment was clever enough to deserve the ResearchBlogging Q&A treatment, though, so here we go:
OK, so why is this really old experiment worth talking about? What did they do? They demonstrated interference between two completely independent lasers, showing that when they overlapped the beams, the overlap region contained a pattern of bright and dark spots characteristic of interference.
How did they do that in 1967? What did they use, photographic plates? No, they used photomultiplier tubes, that produce an electrical pulse when a single photon falls on them.
But a PMT only detects photons in a single position. How did they make a picture out of that? They didn't, because they found a clever way to arrange it so they didn't need to. Here's a schematic of their apparatus:
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Pfleegor, R., & Mandel, L. (1967) Interference of Independent Photon Beams. Physical Review, 159(5), 1084-1088. DOI: 10.1103/PhysRev.159.1084
- November 18, 2010
- 05:39 AM
- 993 views
Fractals in clouds – why clouds appear ‘cloudlike’
by Croor Singh in Learning to be Terse
Clouds have distinctive shapes. Or they seem to have distinctive shapes. It turns out that is likely due to the fractal nature of clouds. The fractal nature of clouds was first shown in this paper in Science, from 1982.... Read more »
LOVEJOY, S. (1982) Area-Perimeter Relation for Rain and Cloud Areas. Science, 216(4542), 185-187. DOI: 10.1126/science.216.4542.185
- November 18, 2010
- 05:35 AM
- 767 views
Fractals in clouds
by Croor Singh in Learning to be Terse
Clouds have distinctive shapes. Or they seem to have distinctive shapes. It turns out that is likely due to the fractal nature of clouds. The fractal nature of clouds was first shown in this paper in Science, from 1982.... Read more »
LOVEJOY, S. (1982) Area-Perimeter Relation for Rain and Cloud Areas. Science, 216(4542), 185-187. DOI: 10.1126/science.216.4542.185
- November 17, 2010
- 03:48 PM
- 1,305 views
Trapped Antihydrogen
by Chad Orzel in Uncertain Principles
The big physics-y news story of the moment is the trapping of antihydrogen by the ALPHA collaboration at CERN. The article itself is paywalled, because this is Nature, but one of the press offices at one of the institutions involved was kind enough to send me an advance version of the article. This seems like something that deserves the ResearchBlogging Q&A treatment, so here we go:
OK, what's the deal with this paper? Well, the ALPHA collaboration is announcing that they have created antihydrogen atoms-- that is, a single antiproton orbited by a single positron-- at low temperatures, and confined them in a magnetic trap for something like 172 ms.
Awesome! When can we blow up the Vatican? Settle down. We're not talking huge quantities of antimatter, here. In 335 runs with their apparatus, they detected all of 38 atoms of antihydrogen. You're not going to be blowing anything up soon.
What's the point of making antimatter if you can't use it to blow stuff up? The point is to understand the laws of physics better. If you can do spectroscopy of anti-atoms, it will tell us a lot about whether antimatter obeys the same laws as ordinary matter, which might provide a clue as to why everything we see seems to be made of ordinary matter. You could also use it to test how antimatter interacts with gravity, which is something we don't currently have any way to test.
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Andresen, G., Ashkezari, M., Baquero-Ruiz, M., Bertsche, W., Bowe, P., Butler, E., Cesar, C., Chapman, S., Charlton, M., Deller, A.... (2010) Trapped antihydrogen. Nature. DOI: 10.1038/nature09610
- November 17, 2010
- 12:40 PM
- 623 views
To see the world in a grain of sand - movement from a turtle hatchling's perspective
by Alistair Dove in Deep Type Flow
(with apologies to William Blake). A grain of sand represents many things to a baby turtle. While still within the egg, sand represents a roof over your head, protection from the desiccating sun and from predators, and a blanket to keep you warm and level until its your turn to break free of the nest and do that mad nocturnal dash down the beach to the safety (yeah, right!) of the sea. From the moment of hatching, however, sand presents a range of obstacles to a baby turtle, and believe it or not, the way they overcome those obstacles tells scientists a lot about how things can and should move through and across granular substrates, and maybe offers a few solutions to human problems of this kind too. That’s because, while they look like little clockwork toys ceaselessly flapping their way to some unseen destination, they’re actually engaging in several different types of locomotion, and adapting them on the fly to best suit the substrate they happen to be on. Discovered by Nicole Mazouchova and Nick Gravish from Daniel Goldman’s biomechanics lab at Georgia Tech, these adaptations show us that baby turtles are much cleverer than perhaps we gave them credit for, and they may even explain to some degree why turtles nest on some beaches and not others.
Immediately after hatching a foot or more below the surface of the beach, a baby turtle must get to the surface to draw breath and begin its journey down to the water. That high up a beach, the sand is usually dry and loosely packed. Governed by the laws of physics, sand of this type can act either as a liquid or as a solid, depending on the force applied to it. (if you ever want to see what I mean, add a little water to some corn starch in the palm of your hand until its like whipping cream, and then rub the surface with your other finger. If you rub slowly, your finger will wet, but if you rub fast, the surface will appear dry and your finger will slide right across). To move across this kind of sand, the turtle reaches forward with its front flipper and places it flat on the sand, then digs the leading edge down until the flipper is perpendicular to the surface and mostly buried. By pushing back with just the right amount of force, the sand behind the flipper doesn’t yield, but solidifies like the corn starch in your hand, providing a solid point of leverage against which the turtle can gain traction and push further forward. It then repeats the process on the other side, lurching forward one push at a time with alternating strokes, rather like a rock climber makes progress up a wall. The key thing is that if the turtle pushes too hard or fast, the sand will fluidise and the flipper will pass through it like a liquid, producing no traction; they have to push just the right amount for the physics of the sand to work in their favour. Nick, Nicole and Dr. Goldman observed this in wild loggerhead hatchlings, then showed why this is mathematically, and then created robot turtles that recreated exactly the scenario in the lab to confirm their mathematical model (what, you mean you don’t have a robot turtle hatchling in your lab?). You might think that this kind of motion is pretty inefficient since you effectively stop after each push, but it works well for the hatchlings; they can move three body-lengths per second or more across the sandy surface. That’s the equivalent of a human running at a full sprint, and they’re doing it on dry sand. Good luck matching that effort!
Farther down the beach, the turtle meets a different kind of sand. Wetted and a sorted by the tide, this sand is flat and compacted and the hatchling would be unable to dig its flipper in, so it changes strategy. Instead of digging in and pushing against a block of solidified sand, it jams just the claw on the leading edge of its flipper into the surface like a spike and (with some help from the back flippers) pushes off it, rotating around the point as a pivot, to jam the next point in a little further ahead, just like a skier planting their stocks in the snow as the pivot point for turns.
Farther still, the turtle meets the water. At this critical point, the game changes completely. Instead of moving across a granular surface, the hatchling is now supported by a liquid medium that will never solidify or allow them to gain traction like thy did on the beach. That’s OK, though, because now the turtle gets the benefit of “inertial movement”. That is, it can build up momentum from repeated strokes, unlike on the sand, where as soon as you stop pushing, you stop moving. Movement through this sort of medium requires a totally different motion, so the turtle switches again, this time to the familiar symmetrical flapping that it will use for the rest of its life, creating lift and thrust with every stroke of the paired front flippers.
These biomechanical adaptations to different substrates may have a role to play in why turtles nest on some beaches and not others. That’s because not every sand behaves so predictably. Sands where all the grains are of similar size behave differently from those where the grains vary; and well sorted sands behave differently from poorly sorted sands. You know this is you’ve ever walked on a “squeaky” beach - those sounds come from the friction of sand grains all being the same size (try squeezing a bag of marbles and you’ll see what I mean). Taken together, these adaptations show a remarkable flexibility of locomotion for an animal just in its first hours of life. It must be working well for them, though, because the sea turtle lineage has been doing just fine on this planet for over 200 million years. To borrow from Blake once more:
Every night and every mornSome to misery are born,Every morn and every nightSome are born to sweet delight.
Mazouchova, N., Gravish, N., Savu, A., & Goldman, D. (2010). Utilization of granular solidification during terrestrial locomotion of hatchling sea turtles Biology Letters, 6 (3), 398-401 DOI: 10.1098/rsbl.2009.1041
... Read more »
Mazouchova, N., Gravish, N., Savu, A., & Goldman, D. (2010) Utilization of granular solidification during terrestrial locomotion of hatchling sea turtles. Biology Letters, 6(3), 398-401. DOI: 10.1098/rsbl.2009.1041
- November 17, 2010
- 12:31 PM
- 670 views
Excited State Control
by Paul Vallett in Electron Cafe
In depth explanation of control over excited state lifetimes that was achieved through simple modification of a donor-acceptor metal complex.... Read more »
Meylemans, H., Hewitt, J., Abdelhaq, M., Vallett, P., & Damrauer, N. (2010) Exploiting Conformational Dynamics To Facilitate Formation and Trapping of Electron-Transfer Photoproducts in Metal Complexes. Journal of the American Chemical Society, 132(33), 11464-11466. DOI: 10.1021/ja1055559
- November 17, 2010
- 09:30 AM
- 670 views
Unification: The Metaphysics of Physics
by Jörg Friedrich in Reading Nature
One of the great metaphysical ideas of theoretical physics is the conviction that the forces that act between the things must be described somehow uniform. But just the force that we experience in everyday life and feel completely without the use of measurement devices or even small tools, the gravitational force, will simply not be forced into a single model. Nevertheless, the theorist can not stop to seek a unified description of all forces.... Read more »
Toms DJ. (2010) Quantum gravitational contributions to quantum electrodynamics. Nature, 468(7320), 56-9. PMID: 21048760
David J. Toms. (2010) Quantum gravitational contributions to quantum electrodynamics. Nature 468:56-59,2010. arXiv: 1010.0793v1
Amelino-Camelia G. (2010) Fundamental physics: Gravity's weight on unification. Nature, 468(7320), 40-1. PMID: 21048752
- November 14, 2010
- 01:48 PM
- 1,294 views
The demon is out of the bottle
by Joerg Heber in All That Matters
Your desk at work, is it chaotic as mine, or clean and ordered? If the latter, I salute you, because it takes work to keep a desk tidy. Otherwise, chaos will soon reign. And while I admit that I should keep my desk cleaner (and no, I won’t share photos here), I have an excellent [...]... Read more »
Toyabe, S., Sagawa, T., Ueda, M., Muneyuki, E., & Sano, M. (2010) Experimental demonstration of information-to-energy conversion and validation of the generalized Jarzynski equality. Nature Physics. DOI: 10.1038/nphys1821
Van den Broeck, C. (2010) Thermodynamics of information: Bits for less or more for bits?. Nature Physics. DOI: 10.1038/nphys1834
- November 12, 2010
- 12:51 PM
- 1,498 views
Relativity on a Human Scale: "Optical Clocks and Relativity"
by Chad Orzel in Uncertain Principles
As mentioned in yesterday's post on ion trapping, a month or so back Dave Wineland's group at NIST published a paper in Science on using ultra-precise atomic clocks to measure relativistic effects. If you don't have a subscription to Science, you can get the paper for free from the Time and Frequency Division database, because you can't copyright work done for the US government.
This paper generated quite a bit of interest when it came out, because it demonstrates the time-slowing effects of relativity without any need for exotic objects like black holes or particle accelerators-- they deal with objects moving small distances at low speeds, and the results agree very nicely with the predictions of relativity.
I'm a little late for the buzz, but it's a cool enough experiment that it's worth unpacking a little in the usual Q&A format for ResearchBlogging:
OK, what's the deal with this? Well, they used a pair of identical atomic clocks of exceptional precision to measure relativistic effects at everyday scales. Their clocks are good enough to be able to detect shifts on the order of a few parts in 1016, which means they can see the slowing of time due to motion at a walking pace, and due to elevation changes of less than a meter.
Back up a bit-- what's this "atomic clock" business? Well, as I explained a few years ago, an atomic clock measures time by making use of quantum physics. Atoms will only absorb light of certain very specific frequencies, so you can use an atom as a perfect frequency reference to determine the frequency of a light source-- if it absorbs the light, you're at the right frequency, and if it doesn't, you can correct the frequency until it does. If you keep comparing your light to the atoms, and correcting the frequency, you can make a light source whose frequency can be used as a reference to mark the passage of time.
And this lets you test relativity? If your clock is good enough, yes.
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Chou, C., Hume, D., Rosenband, T., & Wineland, D. (2010) Optical Clocks and Relativity. Science, 329(5999), 1630-1633. DOI: 10.1126/science.1192720
Schmidt, P. (2005) Spectroscopy Using Quantum Logic. Science, 309(5735), 749-752. DOI: 10.1126/science.1114375
- November 10, 2010
- 10:30 AM
- 1,276 views
This Week in the Universe: November 2nd – November 8th
by S.C. Kavassalis in The Language of Bad Physics
Hot topics in astrophysics, gravitation, high energy, and quantum gravity for the week.... Read more »
Negrello, M., & et al. (2010) The Detection of a Population of Submillimeter-Bright, Strongly Lensed Galaxies. Science, 330(6005), 800-804. DOI: 10.1126/science.1193420
Aguilar-Arevalo, A., & et al. (2010) Event Excess in the MiniBooNE Search for ν[over ¯]_{μ}→ν[over ¯]_{e} Oscillations. Physical Review Letters, 105(18). DOI: 10.1103/PhysRevLett.105.181801
David J. Toms. (2010) Quantum gravitational contributions to quantum electrodynamics. Nature 468:56-59,2010. arXiv: 1010.0793v1
- November 10, 2010
- 12:12 AM
- 739 views
CV Raman on drums
by Croor Singh in Learning to be Terse
A paper from 1920 that describes why a class of Indian percussion musical instrument can produce harmonic overtones.... Read more »
RAMAN, C., & KUMAR, S. (1920) Musical Drums with Harmonic Overtones. Nature, 104(2620), 500-500. DOI: 10.1038/104500a0
- November 8, 2010
- 04:21 AM
- 532 views
The Secret Loves of Trees
by Torah Kachur in Science in Seconds
Falling in love is so romantic, so blissful, so cherished in our lives. Most people will fall in love more than once, first with the 'wait until we're married' sterilizer, then with the 'jealous defender' and finally you hit an age where want to settle down and find the 'practical answer'. And then, after imminent divorce you find yourself with some gold digger who just can't wait for you to die and leave him or her everything.
That darling of a fairy tale also applies to trees.
Trees don't have life partners, lovers, spouses or mistresses, but they do have important partnerships with ants throughout their lives. This is what evolutionary biologists call mutualism - the cooperation of two species for mutual benefit. New research conducted by the Pringle group at Stanford University found that lifelong monogamy for plants, just like for humans, is not the best idea. The common African acacia tree is a bit of a slut as it partners with up to 4 different species of ants through its lifetime. In fact, the slutty trees that had different ant partners were much better off than those that stayed loyal to only one ant.
Just like humans, young plants were found to partner with the chaste Crematogaster nigriceps species of ant first. These ants were found mostly on small colonies of trees and also sterilized the trees. Alas, the virginal ant made the tree wait until they were older and mature enough to consummate their partnership. So, what's in it for the tree? While the ant is keeping the tree honest, the acacia tree has time to mature because C. nigriceps aggressively defends the trees from herbivores. But, like all horny (or thorny) young trees, being sterile sucks and so the tree changes partners to an aggressive non-sterilizer ant - C. mimosae. Despite constantly being drunk, C. mimosae defends the tree and finally allows it to reproduce.
But the 'jealous defender' stage is only cute for a while. Depending on the size of the tree colony, some trees then shift to Tetraponera penzigi - the most 'suitable' partner for the tree. T. penzigi is loyal and treats the tree with respect while tree puts a roof over the ants' head - a match made in heaven. This phase of the trees life is the "any ant is better than no ant" stage. The tree is very fecund at this stage producing many progeny, but - like all vanilla relationships - the tree gets bored.
Yes, just like humans, the most successful of the species later in life find themselves surrounded by parasitic partners. In the trees' case, these gold-digging ants are called C. sjostedti. These ants aren't satisfied with a roof over their heads, instead they allow their beetle buddies to move in and mooch off the tree. Not surprisingly, these parasites and their beetle friends cause an increase in death rates for trees. This partnership should not occur in nature because evolution should select against such a negative partnership. Except, just like Anna Nicole Smith, the ants get one last contribution to the world from their partner - a final spreading of their wealth and seed before they die. So, the opportunisitc ants actually do benefit the ecosystem and provide an evolutionary purpose, at least in trees.
After all of these attempts at love, the poor plant never found the one ant that could complete it. sigh
Palmer TM, Doak DF, Stanton ML, Bronstein JL, Kiers ET, Young TP, Goheen JR, & Pringle RM (2010). Synergy of multiple partners, including freeloaders, increases host fitness in a multispecies mutualism. Proceedings of the National Academy of Sciences of the United States of America, 107 (40), 17234-9 PMID: 20855614
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Palmer TM, Doak DF, Stanton ML, Bronstein JL, Kiers ET, Young TP, Goheen JR, & Pringle RM. (2010) Synergy of multiple partners, including freeloaders, increases host fitness in a multispecies mutualism. Proceedings of the National Academy of Sciences of the United States of America, 107(40), 17234-9. PMID: 20855614
- November 7, 2010
- 11:08 AM
- 1,114 views
Where does desert sand come from?
by Vivienne in Outdoor Science
Sand is a great traveller. Go to the seaside for the day and it’ll ride home on your shoes or sneak into your picnic sandwiches. You may wonder, as you shake sand from your bag on the beach: ‘where did all this sand come from and how long’s it been here?’ Dr Pieter Vermeesch and colleagues had the same question about the sand in the Namib Sand Sea – one of …... Read more »
Vermeesch, P., Fenton, C., Kober, F., Wiggs, G., Bristow, C., & Xu, S. (2010) Sand residence times of one million years in the Namib Sand Sea from cosmogenic nuclides. Nature Geoscience. DOI: 10.1038/NGEO985
- November 7, 2010
- 02:56 AM
- 1,088 views
Rolling and Slipping of Euler’s Disk – Spin a coin and watch it roll!
by Croor Singh in Learning to be Terse
An experimental study of the motion of Euler's disk. It is shown that the major energy dissipation mechanism in the problem is the friction from the surface and not viscous drag.... Read more »
Caps, H., Dorbolo, S., Ponte, S., Croisier, H., & Vandewalle, N. (2004) Rolling and slipping motion of Euler’s disk. Physical Review E, 69(5). DOI: 10.1103/PhysRevE.69.056610
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