and the Bad Language of Physics: From Failure to Foundations
September 1, 2010 2 Comments
You may have noticed the last of “This Week in the Universe” post this past week - that’s because The Langauge of Bad Physics is moving/has moved to the new PLoS Blogging network. Update your rss feeds/links to the new location, http://blogs.plos.org/badphysics/ and the RSS.
August 24, 2010 10 Comments
Lo Curto, G., Mayor, M., Benz, W., Bouchy, F., Lovis, C., Moutou, C., Naef, D., Pepe, F., Queloz, D., Santos, N., Segransan, D., & Udry, S. (2010). The HARPS search for southern extra-solar planets XXVII. Astronomy and Astrophysics manuscript no. HD10180
Image Credit: ESO Exo-Planet Press Kit 2010
Not exactly astrophysics, but the observations couldn’t exist without it. ESO’s HARPS instrument has its latest exoplanet find in the form of at least five planets orbiting the sun-like star, HD 10180, in the Milky Way. There are also two other possible candidates in the HD 10180 system taking the planet count up to a possible seven, including the lightest possible candidate exoplanet to date. This is the first time that we’ve been able to observe a solar system so similar to our own. It’s exciting because it helps confirm much of what we thought about solar system formation (that for a star like ours, the system should look pretty similar to our own).
For more, see ‘Seven planets’ in new solar system, ScienceShot: Neighboring Solar System Resembles Ours, Richest Planetary System Discovered (Press Release), ESO Exoplanet Press Kid [pdf].
D. J. Champion, G. B. Hobbs, R. N. Manchester, R. T. Edwards, D. C. Backer, M. Bailes, N. D. R. Bhat, S. Burke-Spolaor, W. Coles, P. B. Demorest, R. D. Ferdman, W. M. Folkner, A. W. Hotan, M. Kramer, A. N. Lommen, D. J. Nice, M. B. Purver, J. M. Sarkissian, I. H. Stairs, W. van Straten, J. P. W. Verbiest, & D. R. B. Yardley (2010). Measuring the mass of solar system planets using pulsar timing Astrophysical Journal arXiv: 1008.3607v1
From the introduction:
The technique of pulsar timing can provide precise measurements of the rotational, astrometric, and orbital parameters of a pulsar by modeling the observed pulse times of arrival (TOAs). The basic timing analysis provides a fittable parametric model of delays associated with variations in the Euclidean distance between the pulsar and the Earth (resulting from Earth’s orbital motion, the proper motion of the pulsar, and its binary motion), dispersive delays in the interstellar medium, and general relativistic time dilation of clocks in the observatory and pulsar frames and along the propagation path.
Basically, signals from pulsars can be used to measure a variety of properties. Charles Horowitz of Indiana University, Bloomington:
[Using pulsar-timing data,] you don’t even have to see the object, or even know it is there, to feel its gravitational effects.
For more, see Pulsar Signals Could Reveal Solar System Secrets.
Berné O, Marcelino N, & Cernicharo J (2010). Waves on the surface of the Orion molecular cloud. Nature, 466 (7309), 947-9 PMID: 20725034
A paper in Nature this week reports the presence of ‘waves’ (Kelvin–Helmholtz instabilities) at the surface of the Orion molecular cloud, where massive stars are forming. A pretty video of this is made.
For more, see Video: Surf’s Up for Massive Stars.
B. W. Ritchie, J. S. Clark, I. Negueruela, & N. Langer (2010). A VLT/FLAMES survey for massive binaries in Westerlund 1: II. Dynamical constraints on magnetar progenitor masses from the eclipsing binary W13 Astronomy & Astrophysics arXiv: 1008.2840v1
More from the ESO, astronomers are wondering why a once super massive star in the constellation Ara never became a black hole after exploding as a supernova. The star in question, believed to once 40 times as massive as our sun is now a magnetar, despite prevailing theory predicting it should have become a black hole. This is strongly suggestive of the fact that the current theory of gravitational collapse in astrophysics is not quite correct. This is certainly not the only piece of evidence to suggest this, as there is still no good explanation for why we should see matter collapse into a black hole, in finite time, at all.
For more, see The Mystery of the Absent Black Hole.
Credit: X-ray (NASA/CXC/KIPAC/N. Werner, E. Million et al); Radio (NRAO/AUI/NSF/F. Owen)
This image shows the eruption of a galactic “super-volcano” in the massive galaxy M87, as witnessed by NASA’s Chandra X-ray Observatory and NSF’s Very Large Array (VLA).
NASA’s Chandra X-ray Observatory and NSF’s Very Large Array have observed highly energetic jets coming from, what is assumed to be, the black hole inside Messier 87.
From the Press Release:
In the analogy with Eyjafjallajokull, the energetic particles produced in the vicinity of the black hole rise through the X-ray emitting atmosphere of the cluster, lifting up the coolest gas near the center of M87 in their wake, much like the hot volcanic gases drag up the clouds of dark ash. And just like the volcano here on Earth, shockwaves can be seen when the black hole pumps energetic particles into the cluster gas.
Aurora Simionescu of the Kavli Institute:
This analogy shows that even though astronomical phenomena can occur in exotic settings and over vast scales, the physics can be very similar to events on Earth.
Perhaps more importantly, it makes for a pretty picture.
For more, see Galactic Super-volcano in Action.
Ephraim Fischbach,, Peter A. Sturrock,, Jere H. Jenkins,, Daniel Javorsek II,, John B. Buncher,, & John T. Gruenwald (2010). Evidence for Solar Influences on Nuclear Decay Rates Fifth Meeting on CPT and Lorentz Symmetry : 1007.3318
In a series of rather surprising finds, Jenkins, Fischbach et al. have shown that there appears to be a relationship between solar flare activity and radioactive decay rates for certain elements. Back in 2006, while observing the decay of Manganese-54, Jenkins’ team noticed that the decay rate dropped during a solar flare, corresponding to an increase in solar neutrinos hitting the detector. These results are now no longer believed to just be due to some apparatus error or environmental factors in the detection system, but actually somehow connected to solar flare activity from the sun. Neutrinos are the most likely candidate, since we know that they are actually there, but we also know that they don’t really interact with much. There is nothing in the Standard Model to suggest that neutrinos should effect radioactive elements in a way that could influence decay rates. There is also talk of some yet unknown particle that may also be produced in the sun that is interacting in these systems, but there is nothing within conventional particle physics to suggest what this may be. There is still obviously a chance that neutrinos (or something else) are just interfering with the detection mechanism (although the authors feel they have ruled this out), but there is also an interesting chance that there is some new neutrino physics being observed here. This is something to keep an eye on.
For more, see The strange case of solar flares and radioactive elements, The strange case of solar flares and radioactive elements (Press Release).
P. E. Koehler, F. Bečvář, M. Krtička, J. A. Harvey, & K. H. Guber (2010). Anomalous fluctuations of s-wave reduced neutron widths of $^{192,194}$Pt resonances Phys. Rev. Lett. , 105 (7) arXiv: 1007.3675v1
By using neutron beams to measure the strength of neutron resonances, Koehler’s group notes that random matrix theory does not seem to be applicable to neutron structure (with a 99.997% confidence level), noting that the nucleons seem to move in “a coordinated fashion”.
Paul Koehler:
There’s no viable model of nuclear structure that could explain this.
Basically, this is yet again another example of a currently accepted model in particle/nuclear physics not being sufficient to describe the full scope of physical reality. This is exciting stuff.
For more, see Nuclear theory nudged.
Palenzuela, C., Lehner, L., & Liebling, S. (2010). Dual Jets from Binary Black Holes Science, 329 (5994), 927-930 DOI: 10.1126/science.1191766
The abstract:
The coalescence of supermassive black holes—a natural outcome when galaxies merge—should produce gravitational waves and would likely be associated with energetic electromagnetic events. We have studied the coalescence of such binary black holes within an external magnetic field produced by the expected circumbinary disk surrounding them. Solving the Einstein equations to describe black holes interacting with surrounding plasma, we present numerical evidence for possible jets driven by these systems. Extending the process described by Blandford and Znajek for a single, spinning black hole, the picture that emerges suggests that the electromagnetic field extracts energy from the orbiting black holes, which ultimately merge and settle into the standard Blandford-Znajek scenario. Emissions along these jets could potentially be observable at large distances.
Generally, I would relegate an article on black holes to astrophysics, but this one warrants actually being listed under general relativity. That is because, if you noticed in the abstract, the authors are actually solving the Einstein equations, which is actually a rarity in work on black hole jets (strange, I know). This is probably one of the most realistic treatments of black hole mergers done to date (and I swear, me saying that has nothing to do with the fact that it was done by UofT and Perimeter people).
Supporting Material
Snapshots illustrating the Poynting flux structure prior/after the merger takes place: Electromagnetic energy fluxes at times −5.6hrs and 2.3hrs (before/after merger). As the black holes orbit they induce a collimation which is evident by the tubes emanating from the central region. As the merger takes place, these tubes join and the orbiting behavior leaves its imprint in the twisting observed in the tubes.
For more, see A Tale of Two Jets.
At the International Congress of Mathematicians in India this week, the 2010 Fields Medallists were announced, along with the Nevanlinna, Gauss, and Chern Prize winners. Like in previous years, these awards, which are considered to be some of the highest honours a mathematician can receive, acknowledged some great achievements in mathematical physics.
For more, see Prize Winners 2010, Fields Medals, Other Top Math Prizes, Awarded, Four mathematicians reap Fields Medals, What is the Langlands Programme?.
August 16, 2010 2 Comments
This is just a very brief note to acknowledge that a key player in high energy physics, Nicola Cabibbo, has passed away today [ref]. It was just this week that he was awarded ICTP’s Dirac Medal and Prize for 2010 for his contributions to the understanding of the weak interaction, a well deserved prize. I imagine there will be a great deal of talk this week about how he was robbed of the 2008 Nobel Prize (see Peter Coles’s discussion from 2008), but instead of focusing on what he never was awarded, I say we focus on what he gave the world.
Humanity that disavows science risks falling into the hands of superstition. – Nicola Cabibbo
August 16, 2010 1 Comment
Sorry for the unsubstantial post this week.
Credit: ESA-Hubble/NASA
August 12th, 2010: Oli Usher, Junior Hubble/ESA Public Information Officer:
Looking at NGC 4696 in the optical and near-infrared wavelengths seen by Hubble gives a beautiful and dramatic view of the galaxy. But in fact, much of its inner turmoil is still hidden from view in this picture. At the heart of the galaxy, a supermassive black hole is blowing out jets of matter at nearly the speed of light. When looked at in X-ray wavelengths, such as those visible from NASA’s Chandra X-ray Observatory, huge voids within the galaxy become visible, telltale signs of these jets’ enormous power.
New observations suggest NGC 4696 is somewhat unusual (unlike all the totally regular galaxies out there) and that perhaps its strange shape is due to a past collision with another galaxy.
For more, see ScienceShot : Odd Galaxy Raises Many Questions, Press Release: NGC 4696: a cosmic question mark, from 2006 NGC 4696: Black Holes Found To Be Green By NASA’s Chandra.
Assef, R., Kochanek, C., Brodwin, M., Cool, R., Forman, W., Gonzalez, A., Hickox, R., Jones, C., Le Floc’h, E., Moustakas, J., Murray, S., & Stern, D. (2010). LOW-RESOLUTION SPECTRAL TEMPLATES FOR ACTIVE GALACTIC NUCLEI AND GALAXIES FROM 0.03 TO 30 μm The Astrophysical Journal, 713 (2), 970-985 DOI: 10.1088/0004-637X/713/2/970
Albert P. Linnell, Paula Szkody, Richard M. Plotkin, Jon Holtzman, Mark Seibert, Thomas E. Harrison, & Steve B. Howell (2010). GALEX and Optical Light Curves of WX LMi, SDSSJ103100.5+202832.2 and
SDSSJ121209.31+013627.7 The Astrophysical Journal arXiv: 1003.2564v1
Credit: NASA/ESA /JPL-Caltech/STScI /UCLA
August 11th, NASA/ESA/JPL-Caltech/STScI/UCLA:
Observations from NASA’s Galaxy Evolution Explorer (GALEX) picked out 30 elliptical and lens-shaped “early-type” galaxies with puzzlingly strong ultraviolet emissions but no signs of visible star formation. Early-type galaxies, so the scientists’ thinking goes, have already made their stars and now lack the cold gas necessary to build new ones.
Ie. More space stuff looks different than expected.
For more, see ScienceShot: Mystery Rings Spied Around Elderly Galaxies, Giant Ultraviolet Rings Found in Resurrected Galaxies, PIA13318: Ultraviolet Ring Around the Galaxies.
Kjær, K., Leibundgut, B., Fransson, C., Jerkstrand, A., & Spyromilio, J. (2010). The 3-D structure of SN 1987A’s inner ejecta Astronomy and Astrophysics, 517 DOI: 10.1051/0004-6361/201014538
The inner ejecta are spatially resolved in a North-South direction and are clearly asymmetric. Like the ring emission, the northern parts of the ejecta are blueshifted, while the material projected to the South of the supernova centre is moving away from us. We argue that the bulk of the ejecta is situated in the same plane as defined by the equatorial ring and does not form a bipolar structure as has been suggested. The exact shape of the ejecta is modelled and we find that an elongated triaxial ellipsoid fits the observations best.
The inner workings of SN1987A have been modelled and it appears to be a turbulent and asymmetrical place.
For more, see Supernova ejects material asymmetrically.
Knispel, B., Allen, B., Cordes, J., Deneva, J., Anderson, D., Aulbert, C., Bhat, N., Bock, O., Bogdanov, S., Brazier, A., Camilo, F., Champion, D., Chatterjee, S., Crawford, F., Demorest, P., Fehrmann, H., Freire, P., Gonzalez, M., Hammer, D., Hessels, J., Jenet, F., Kasian, L., Kaspi, V., Kramer, M., Lazarus, P., van Leeuwen, J., Lorimer, D., Lyne, A., Machenschalk, B., McLaughlin, M., Messenger, C., Nice, D., Papa, M., Pletsch, H., Prix, R., Ransom, S., Siemens, X., Stairs, I., Stappers, B., Stovall, K., & Venkataraman, A. (2010). Pulsar Discovery by Global Volunteer Computing Science DOI: 10.1126/science.1195253
Published this week in Science, the Einstein@Home volunteer computing project has released its first results: the discovery of a rare isolated pulsar with a very low magnetic field. Congratulations to the whole team!
For more, see Home computer finds rare pulsar, Donated Computer Time Discovers New Star.
Hansen, S., Juncher, D., & Sparre, M. (2010). AN ATTRACTOR FOR DARK MATTER STRUCTURES The Astrophysical Journal, 718 (2) DOI: 10.1088/2041-8205/718/2/L68
Credit: University of Copenhagen
The ordinary hot X-ray emitting gas can be observed in galaxy clusters. From this you can determine that the dark matter is densest in the inner part and slowly becomes diluted in the outer parts. The researchers hope in the future to be able to test the detected dark matter attractor through precise measurements of the ordinary hot gas.
Steen Hansen: “We have for the first time, through computer simulations, shown that dark matter halos have an attractor. We have found a very special relationship between the state of the temperature and the density of the dark matter from the inner part of the halo to the outer part”.
It appears to be an interesting and new approach to figuring out the dark matter mystery.
For more, see Dark matter is held together by ‘attractors’, Dark matter is held together by ‘attractors’.
V. M. Abazov et al. (D0 Collaboration) (2010). Evidence for an Anomalous Like-Sign Dimuon Charge Asymmetry Phys. Rev. Lett. , 105 (8) : 10.1103/PhysRevLett.105.081801
V. M. Abazov et al. (D0 Collaboration) (2010). Evidence for an anomalous like-sign dimuon charge asymmetry Phys. Rev. D, 82 (3) : 10.1103/PhysRevD.82.032001
D0 is still at it! The anomalous results that wouldn’t go away are still there, and D0 is running with them for now with simultaneous papers in Phys. Rev. Letters and Phys. Rev. D. Are these anomalies really signs of a new source of CP violation and new physics or are they just some experimental artifact? The jury is till out, but it seems that more support is building for “new physics”.
For more, see Experiments offer tantalizing clues as to why matter prevails in the universe, A new source of CP violation?.
August 9, 2010 14 Comments
I swear I tried to find something interesting happening in astrophysics/high energy this week; I really did!
Apparently Arizona has a big telescope: Arizona Telescope’s Wide Angle Images Rival Hubble’s.
Unrelated to any new results, “Physicists get political over Higgs” (there will only so much Nobel Prize to go around, after all).
Faulkner, T., Iqbal, N., Liu, H., McGreevy, J., & Vegh, D. (2010). Strange Metal Transport Realized by Gauge/Gravity Duality Science DOI: 10.1126/science.1189134
Gauge/gravity duality is a surprising and fun way for making calculations easier, by, bizarrely, making mathematical connections between certain aspects of quantum gravity and regular everyday gauge theory uses (for some lower number of dimensions). Usually, we think of using our friendly gauge theory techniques to help us in our search for answers in quantum gravity and not the other way around, but dualities aren’t one sided. Applying this duality correctly, we can make strong couplings into weak couplings, and thus can make difficult calculations a whole lot simpler.
From the abstract:
We employ the anti de-Sitter/Conformal Field Theory correspondence to identify a class of non-Fermi liquids; their low-energy behavior is found to be governed by a nontrivial infrared fixed point which exhibits nonanalytic scaling behavior only in the time direction. For some representatives of this class, the resistivity has a linear temperature dependence, as is the case for strange metals.
So basically, using gauge/gravity duality applied to non-Fermi liquids, by stepping up in dimension, they were able to end up with a believable metal phase. So, the duality still seems pretty solid (and is edging closer and closer to being useful for practical calculations – who said black hole horizons weren’t going to be applicable to your everyday life?).
For more, see Physicists use offshoot of string theory to describe puzzling behavior of superconductors, Offshoot of string theory used to describe behavior of superconductors, “Gauge/gravity duality” by Horowitz and Polchinski (arXiv).
Smolyaninov, I., & Narimanov, E. (2010). Metric Signature Transitions in Optical Metamaterials Physical Review Letters, 105 (6) DOI: 10.1103/PhysRevLett.105.067402
Using special metamaterials that allow for a high level of control over the propagation of light, Smolyaninov and Narimanov, have shown that these materials can have an effective metric signature (–++). Because these materials are designed to be so controllable, one is able to vary this effective metric; a metric signature change (transition) can then make them mathematically equivalent to a 4-dimensional spacetime (and we live in one of those now). This, as the authors point out, means that metamaterials might prove to be an interesting and useful analogy when trying to understand how our spacetime would have behaved during periods of metric/metric signature change. Is this exact? No, because any material will be fundamentally different than a spacetime in at least a few ways, but it still could be quite useful.
For more, see Metamaterials Probe Changes in Spacetime Structure.
Balachandran, A., Joseph, A., & Padmanabhan, P. (2010). Non-Pauli Transitions from Spacetime Noncommutativity Physical Review Letters, 105 (5) DOI: 10.1103/PhysRevLett.105.051601
A team from Syracuse has suggested a partial model, to replace the current quantum theory, that allows for violations of the Pauli exclusion principle in order give some insight into how matter could behave in/around black holes. I’m honestly not sure what to think about this paper yet; frankly, it is a little bit weird.
From the abstract:
We argue that the Earth’s rotation and movements in the cosmos are “sudden” events to Pauli-forbidden processes.
There are just too many questions to be answered at this point as to the consistency of the theory and agreement with current observations if one was to remove the Pauli exclusion principle. Perhaps shedding some insight into black hole physics is nice, but it might mean throwing out much of chemistry to do so.
For more, see Physicists develop model that pushes limits of quantum theory, relativity.
P ≠ NP by Vinay Deolalikar, HP Research Labs, Palo Alto, August 6th, 2010, scribd link.
This is farther outside my field than I usually travel, but if it is true, it’s significant enough that everyone should be at least a little excited. Vinay Deolalikar, a well known researcher in networks and complexity theory from HP Labs, has produced a 102 page (in 12pt font) paper that claims to prove P does not equal NP. Like all Millennium Prize Problems, a solution to the P versus NP problem would mean huge things, as it is considered by many to be the most important outstanding problem in theoretical computer science.
Wikipedia summarizes the problem quite well:
The question P = NP? asks: if ‘yes’-answers to a ‘yes’-or-’no’-question can be verified “quickly” can the answers themselves also be computed “quickly”?
While the P versus NP problem doesn’t seem to have much interest for relativists, it is still quite important for theoretical physics, specifically for quantum computing (see Scott Aaronson’s lecture “P, NP, and Friends”). If Deolalikar really has a formal proof that P ≠ NP, it can allow us to know when a problem just cannot be solved efficiently (so we should move on to a different problem or aim for a partial solution). If P = NP, however, it would mean that efficient solutions were possible for extremely difficult problems (which, one could imagine, would be very unsettling for cryptography).
Millennium Problems always attract a huge number of attempted solutions, some less credible, some more credible (see “An Argument for P=NP” [pdf] for a credible, but incorrect attempt), thus any paper claiming to have solved one should always be viewed very cautiously (as it is almost surely flawed). However, Deolalikar, who has published solid work on the infinite versions of the P = NP problem in the past, is being taken more seriously than most, by those in the field. One of the fathers of complexity theory, the University of Toronto‘s Stephen Cook (who is a real authority here) said (according to Greg Baker):
This appears to be a relatively serious claim to have solved P vs NP.
While it is quite outside of my field, has yet to undergo peer review (which will take a very long time), and 99% of these turn out to be wrong anyway, this paper might still be worth getting a little (cautiously) excited over.
For more, see The Quantum Pontiff: P <> NP ?, Gödel’s Lost Letter and P=NP: A Proof That P Is Not Equal To NP?, Greg Baker’s Blog: P ≠ NP, OR-Exchange: Best explanation of P=NP problem for a layman?.
Update: Putting my money where my mouth isn’t
Scott Aaronson ups the intrigue a little:
If Vinay Deolalikar is awarded the $1,000,000 Clay Millennium Prize for his proof of P≠NP, then I, Scott Aaronson, will personally supplement his prize by the amount of $200,000.
August 2, 2010 7 Comments
A. Kappes for the IceCube Collaboration (2010). IceCube: Neutrino Messages from GRBs Proceedings: Deciphering the Ancient Universe with Gamma-Ray Bursts arXiv: 1007.4629v1
The under-construction IceCube Neutrino Observatory in the Antarctic has produced some exciting results already (despite being roughly a year away from officially starting). IceCube has confirmed what had been previously suspected: That cosmic rays don’t appear to come equally from all directions in space. Why there seems to be an asymmetric number of cosmic rays coming from certain parts of the sky is still a complete mystery, however.
For more, see Antarctica Experiment Discovers Puzzling Space Ray Pattern, IceCube spies unexplained pattern of cosmic rays, IceCube drillers train for final Antarctic season, ScienceShot: Neutrino Observatory Picks Up Cosmic Rays.
Adam Moss, James P. Zibin, & Douglas Scott (2010). Precision Cosmology Defeats Void Models for Acceleration arXiv arXiv: 1007.3725v1
[W]e note that two of the most important assumptions in cosmology are those of the cosmological and Copernican principles. Therefore, in confronting void models, which blatantly violate both of these principles, with observations, we do more than just examine an unusual approach to the mystery of acceleration. We put the foundations of modern cosmology themselves to the test.
Moss, Zibin, and Scott compared the currently, somewhat, popular void model (a cosmological model based on the assumptions that our galaxy exists in a privileged position in the universe near the centre of a large, nonlinear, spherical void that was designed to help escape us from needing dark energy) to current cosmological data and found that the void model comes up lacking. While it does not require dark energy, it also does not fit with observations of matter fluctuations, primordial power spectrum, or red shift data, making it an unreasonable cosmological candidate.
For more, see Are you the center of the Universe?, Hubble Bubble.
Wun-Yi Shu (2010). Cosmological Models with No Big Bang arXiv arXiv: 1007.1750v1
I’ve already said my piece on this one.
For more, see TLoBP: “Cosmological Models with No Big Bang” by Wun-Yi Shu.
Hiyama, E., Kamimura, M., Yamamoto, Y., & Motoba, T. (2010). Five-Body Cluster Structure of the Double-Λ Hypernucleus _{ΛΛ}^{11}Be Physical Review Letters, 104 (21) DOI: 10.1103/PhysRevLett.104.212502
In 2009, KEK and J-PARC were attempting to study the creation of hypernuclei (specifically the Beryllium-Xi hypernucleus – made up of protons, neutrons, and hyperons) to see if they could play a role in neutron star physics. Now, Emiko Hiyama and colleagues have put forth the first model to explain and predict the interactions between regular nuclei and hyperons within the hypernucleus. If these strange quark containing atoms do form in relation to neutron stars, being able to understand their internucleus interactions should be quite important.
For more, see Nuclear physics incorporates a ‘strange’ flavor.
Press release from the Oakridge National Laboratory:
For more than a half century, scientists have assumed that highly excited states in intermediate- to heavy-mass nuclides are chaotic, and that data support this assumption. However, new data from the Oak Ridge Electron Linear Accelerator strongly disagree. The new results suggest that the roughly 200 nucleons inside the platinum nuclei studied act in unison to exhibit regular rather than chaotic properties. Given the relatively high energy and large number of nucleons involved, such collective behavior is totally unexpected and unexplained. A possible explanation is that an even more fundamental tenet of theory–something known as form invariance–is violated.
Interesting, but preliminary, results suggest that we need to reevaluate our models for heavy-mass nuclides.
For more, see Surprising nucleon behavior.
Peter Sorensen (2010). A coherent understanding of low-energy nuclear recoils in liquid xenon arXiv arXiv: 1007.3549v2
At IDM2010 this week, Peter Sorensen gave a talk suggesting that the detection sensitivity of experiments like XENON10 and XENON100 could be increased to rule our/address the possible light dark matter candidates that the CoGeNT collaboration was excited about in the spring. It appears that xenon-based detectors may be much more promising tools in the hunt for light dark matter than other detectors. Actually ruling out the CoGeNT dark matter results is still to come (but it should be feasible).
For more, see CoGeNT dark matter excluded.
Stephen D. H. Hsu (2010). White holes and eternal black holes arXiv arXiv: 1007.2934v1
A curious paper by Stephen Hsu has been making the rounds this week. Hsu presents isolated white holes as the time-reversal of isolated black holes, except that since white holes can not preform a process that is the reverse of Hawking radiation in black holes, he concludes that they must explode instead. This explosion of Hsu’s isn’t based in general relativity proper but is modified by the quantum/thermodynamical aspects of white holes/black holes (see new link). Avoiding a time-reversed-Hawking-radiation-mechanism seems like a must, to stay in agreement with thermodynamics, but it is unclear why this “explosion” would be more satisfactory.
For more, see Stephen Hsu’s confusion about white holes, Why Space Isn’t Filled with White Holes, White holes and eternal black holes (Stephen Hsu’s blog).
EDIT: Stephen Hsu has written some clarifying remarks to which Lubos has already responded in the comments.
*Sorry.
July 28, 2010 65 Comments
I received several emails from people asking me about this paper this past week (and honestly, the type-setting was so off-putting I wouldn’t have considered reading it otherwise), so I’ve prepared some remarks as to why I think it isn’t worth suffering through the type-setting.
Relax, that doesn’t relegate this to nonsense status. For some reason, a lot of people see attacks on “the Big Bang” (the term) as an affront to science, and that simply isn’t the case. While the Big Bang is part of the prevailing cosmological model, it doesn’t mean that the term “Big Bang” actually describes the same thing in all situations. The original Big Bang theory, proposed by Georges Lemaître in 1927, was an incredibly simplified version of what many cosmologists refer to as the Big Bang today, without out any explaining mechanism other than, “it happened”. So, in some sense, almost all cosmologist don’t really accept the Big Bang, because they don’t accept Lemaître’s version of it. There are also other models meant to help explain the origin of the universe like the Big Bounce (part of a cyclic model of cosmology). Some people refer to the Big Bounce as totally distinct from the Big Bang, and other people label it as an interpretation of the Big Bang. Unfortunately, there is not an agreed upon list of “What is a ‘Big Bang’ theory’ within the field – to some, it is any theory that tries to explain the formation of the early universe and to others it is an incredibly rigid consequence of FLRW cosmology (which frankly, we know can’t be true). Even if we want to imagine a universe with no beginning (no Big Bang type theory), it wouldn’t anything new or exciting (even if it is objectionable); just remember Einstein’s static universe.
Now, we can get to some real objections. I’m going to start by stepping through the abstract to set the mood, if you will, for what this paper is all about.
In the late 1990s, observations of Type Ia supernovae led to the astounding discovery that the universe is expanding at an accelerating rate. The explanation of this anomalous acceleration has been one of the great problems in physics since that discovery.
In 1998 and 1999, Riess [1] and Perlmutter [2] published results in The Astronomical Journal that put forth an explanation for the somewhat anomalous observations of Type Ia supernovae: The expansion of the universe must be accelerating (something that, when Edwin Hubble first made note of the apparent expansion of the universe in the 1920s [3], we were not able to detect). We should be still be totally happy with this paper at this point.
In this article we propose cosmological models that can explain the cosmic acceleration without introducing a cosmological constant into the standard Einstein field equation, negating the necessity for the existence of dark energy.
The third sentence of the abstract is where the trouble begins. Yes, the addition of the cosmological constant to the Einstein Field Equations (EFEs) has been an issue of debate (for mathematicians, physicists, philosophers, and historians of science) for quite some time, but it is a necessary addition for modern physics. The cosmological constant has nothing to do with dark energy, a priori. Its original introduction, to provide Einstein with the Static Universe that he had always dreamt about, started 
I think Eugenio Bianchi and Carlo Rovelli wrote it best:
Λ is not an appendage to Einstein’s theory added to account for observations: it is an integral and natural part of it. Its nature and scale are no more or less mysterious than any of the several other constants in our fundamental theories. [4]
Wun-Yi Shu’s desire to “not add” the cosmological constant to the EFEs is a little like me saying “I don’t want to introduce the 
There are four distinguishing features of these models: 1) the speed of light and the gravitational “constant” are not constant, but vary with the evolution of the universe, 2) time has no beginning and no end, 3) the spatial section of the universe is a 3-sphere, and 4) the universe experiences phases of both acceleration and deceleration.
Point 1 is a little frightening (we should all be very excited to see how he has completely re-written Einstein’s relativity though). Point 2 fits with his “no bang” approach. Point 3 is familiar from trivial FLRW cosmologies (which have a big bang, and where the idea of spacetime having a beginning came from), and point 4 could mean almost anything at this point.
One of these models is selected and tested against current cosmological observations of Type Ia supernovae, and is found to fit the redshift-luminosity distance data quite well.
Bring it on.
From the first paragraph:
The current mainstream explanation of the accelerating expansion of the universe is to introduce a mysterious form of energy—the so called dark energy that opposes the self-attraction of matter. Two proposed forms for dark energy are the cosmological constant, which can be viewed physically as the vacuum energy, and scalar fields, sometimes called quintessence, whose cosmic expectation values evolve with time.
Nope. Now, dark energy is the most popular way of “explaining” the observation of the acceleration of our universe’s expansion, but as I said above, the cosmological constant doesn’t have anything, a priori, to do with dark energy (ie. it is not a “form” of dark energy, no matter what the Wikipedia article that this sentence was copied from says). Particle physicists often interpret the cosmological constant to be a measure of the vacuum energy of the universe, but even that interpretation doesn’t imply anything about dark energy [5]. Dark energy steps in here when people realise that what we measure in terms of vacuum energy doesn’t match up with what we think
Now, this section, for some reason, starts off with a walk through of the FLRW-metric. Sure, it might seem a little unnecessary for a paper that is apparently about general relativity, but that’s because things are about to get wild. After the author has written down the line elements for the FLRW-metric in his chosen coordinates, we behold:
We view the speed of light as simply a conversion factor between time and space in spacetime. It is simply one of the properties of the spacetime geometry. Since the universe is expanding, we speculate that the conversion factor somehow varies in accordance with the evolution of the universe, hence the speed of light varies with cosmic time.
I hope most people read that sequence of sentences and found themselves saying, “huh?”. While I may not want to phrase it like that, the speed of light (I’d rather call it 
Why the author feels this is justified after writing out the line-elements, I am not quite sure. Straight out of Wald, the line-element for the FLRW-metric is written in this paper as,
where 
It is clear from the derivation of the line element (easy introduction to FRW cosmology here [pdf]) that 
I could actually stop right here in explaining why this paper is not to be taken seriously, but I won’t.
Shu begins this section by writing down the EFE (without
And then says,
In a cosmology with a varying
and varying
, one needs a new field equation for attaining consistency. Noting that
is the conversion factor that translates a unit of mass into a unit of length, we postulate that
vary in such a way that
must be absolutely constant with respect to the cosmic time t . We can make
by choosing proper units of mass and length.
The author is correct, that if you vary 
So, yes, 
However, using numerology, the author arrives at his new field equations,
Which are clearly much better.
While I’m not interested in chasing these equations through the appendices where the modified EFEs are solved, we’ll still keep going through the body of the paper for a little longer.
To obtain predictions for the dynamical evolution, we substitute metric (2.2) into the field equation (2.4) and solve for a(t) and c(t) .
Equation (2.2) is a line element, not a metric. Anyway,
There are two unknown functions,
and
, to be determined. To solve [our] equations we need a further postulate on the relationship between
and
.
Now Shu wants to relate his variable speed of light to the cosmic scale factor, which, from FLRW cosmology, relates comoving distances for an expanding universe with the distances at some other point in time. In actual general relativity, we determine the dynamics of
When converting the magnitude of increment in time,
, into that in length, Nature needs a universal standard to refer to.
Some people use
Noting that the concept of time arises from the observation that the distribution of mass-energy contained in the universe is dynamic and the rate of change,
, of the cosmological density is the very quantity that manifests the dynamicity of a homogeneous universe, we postulate that
, the concept of time would have no meaning. The cosmological density plays the role of ultimate clock in a homogeneous universe.
This should be met with another overwhelming, “huh?”. I’m not honestly sure where to begin with this. “[T]he concept of time arises from the observation that the distribution of mass-energy”? Does it? This is really not based on anything, other than casual philosophical musings by some people. The “
This strange notion of what mass density means for time is continued through the rest of the paper to “solve” the created field equations and arrive at the evolution of our scale factor,
![c(t) = \frac{8M/3 \sigma}{[1 + (t/ \sigma)^{4/3}]^2(|t|/ \sigma)^{1/3}}](http://s0.wp.com/latex.php?latex=c%28t%29+%3D+%5Cfrac%7B8M%2F3+%5Csigma%7D%7B%5B1+%2B+%28t%2F+%5Csigma%29%5E%7B4%2F3%7D%5D%5E2%28%7Ct%7C%2F+%5Csigma%29%5E%7B1%2F3%7D%7D+&bg=f0f0f0&fg=555555&s=0 "c(t) = \frac{8M/3 \sigma}{[1 + (t/ \sigma)^{4/3}]^2(|t|/ \sigma)^{1/3}}")
Where, 
![\kappa^{-2}\left[\frac{\dot a(t)}{a^2(t)} \right]^4 = \frac{2M}{a(t) - 1}](http://s0.wp.com/latex.php?latex=%5Ckappa%5E%7B-2%7D%5Cleft%5B%5Cfrac%7B%5Cdot+a%28t%29%7D%7Ba%5E2%28t%29%7D+%5Cright%5D%5E4+%3D+%5Cfrac%7B2M%7D%7Ba%28t%29+-+1%7D&bg=f0f0f0&fg=555555&s=0 "\kappa^{-2}\left[\frac{\dot a(t)}{a^2(t)} \right]^4 = \frac{2M}{a(t) - 1}")
We assume that a varying
[wavelength] with
[frequency] kept constant.
Interpreting the equation for 
At the “time origin” (
When 
What is fun about this is, if we recall 
So 
Basically, the dynamics of this model are nonsensical.
What is interesting about this section is that the author is basically saying “physics is normal, here are some weird equations”, clearly forgetting that changing the nature of spacetime means something a lot more profound than just weird equations. Let’s talk a little bit about redshift in regular cosmology first.
Classically, redshift is characterized in terms of the dimensionless 
Which relates the observed and emitted wavelength (or frequency) of an object. For relativistic settings, we add corrections to this equation to prevent objects from appearing to travel faster than the speed of light (remember special relativity).
When we want to describe the cosmological redshift (due to the expansion of an FLRW universe), we define a very similar
Where 
Shu sets up redshift in a different manner:
So this isn’t quite an expression for cosmological redshift, in fact, I am not totally sure what it is. Interestingly, without addressing the fact that the speed of light is no longer finite, Shu comes to an expression for the B-band peak magnitude (apparent magnitude) for the supernova of interest to correlate with the redshift data,
![m_B = \beta + 5 \log{\gamma_o(1 + z)\sin{[z,\gamma_o]}}](http://s0.wp.com/latex.php?latex=m_B+%3D+%5Cbeta+%2B+5+%5Clog%7B%5Cgamma_o%281+%2B+z%29%5Csin%7B%5Bz%2C%5Cgamma_o%5D%7D%7D&bg=f0f0f0&fg=555555&s=0 "m_B = \beta + 5 \log{\gamma_o(1 + z)\sin{[z,\gamma_o]}}")
With arbitrary parameters that were fit to idealize the results, (which frankly, is a pretty common place sighting in physics). Finally, we come to a nice looking graph:
Now here is why people decided to take this paper semi-seriously – the data and theoretical predictions sort of match up! Is that impressive? No, it’s really not, because the laws of physics have been ignored along the way. I too can come up with an arbitrary curve to match a data set and assign some questionable interpretations to it (try 
This isn’t physics. Frankly, this has nothing to do with anything.
The prediction of singularities represents a breakdown of general relativity.
No, no it does not. Removal of the causal structure of spacetime does represent a breakdown of general relativity, however.
With our models asserting that the spatial section of the universe is a 3-sphere, the flatness problem disappears automatically.
No, this just completely ignores the flatness problem.
Without the big bang origin and with the universe being accelerating in the epoch when γ(t) < 7 / 8 , our models may thus provide a solution to the horizon problem.
Again, no. Assuming the universe is reasonably large, there should be parts of it what have never “met” (and without the Big Bang, inflation can’t even come in to save it), which makes the fact that they have apparently similar temperature and other physical properties just as anomalous as before. ie. the horizon problem is still there (just without the Big Bang, we probably wouldn’t refer to it as a horizon), it just hasn’t been addressed.
In this model, you have to wonder what the author attributes the CMB to.
Yes, if you pick and choose what physics to ignore you can arrive at meaningless equations.
[0] 
Wun-Yi Shu (2010). Cosmological Models with No Big Bang arXiv arXiv: 1007.1750v1
[1] Riess, A., Filippenko, A., Challis, P., Clocchiatti, A., Diercks, A., Garnavich, P., Gilliland, R., Hogan, C., Jha, S., Kirshner, R., Leibundgut, B., Phillips, M., Reiss, D., Schmidt, B., Schommer, R., Smith, R., Spyromilio, J., Stubbs, C., Suntzeff, N., & Tonry, J. (1998). Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant The Astronomical Journal, 116 (3), 1009-1038 DOI: 10.1086/300499
[2] Perlmutter, S., Aldering, G., Goldhaber, G., Knop, R., Nugent, P., Castro, P., Deustua, S., Fabbro, S., Goobar, A., Groom, D., Hook, I., Kim, A., Kim, M., Lee, J., Nunes, N., Pain, R., Pennypacker, C., Quimby, R., Lidman, C., Ellis, R., Irwin, M., McMahon, R., Ruiz‐Lapuente, P., Walton, N., Schaefer, B., Boyle, B., Filippenko, A., Matheson, T., Fruchter, A., Panagia, N., Newberg, H., Couch, W., & Project, T. (1999). Measurements of Ω and Λ from 42 High‐Redshift Supernovae The Astrophysical Journal, 517 (2), 565-586 DOI: 10.1086/307221
[3] Hubble, E. (1929). A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae Proceedings of the National Academy of Sciences, 15 (3), 168-173 DOI: 10.1073/pnas.15.3.168
[4] Bianchi, E., Rovelli, C., & Kolb, R. (2010). Cosmology forum: Is dark energy really a mystery? Nature, 466 (7304), 321-322 DOI: 10.1038/466321a
[5] Sean M. Carroll (2000). The Cosmological Constant LivingRev.Rel.4:1,2001 arXiv: astro-ph/0004075v2
Note: There has been an unusual amount of anti-Big Bang hype this week (see “Big Bang? A Critical Review” by Ashwini Kumar Lal for some more nonsense).
Edit: I apologize for the date of publish appearing as July 27th (when I started it, as opposed to when I actually wrote it on August 1st) and messing some links up (was briefly at http://badphysics.wordpress.com/2010/08/01/nobang/).
July 27, 2010 10 Comments
From Sasselov's presentation at TEDGLobal.
At a conference in Oxford that became an online TED Talk last week, Kepler co-investigator Dimitar Sasselov said, “planets like our own Earth are out there. Our Milky Way galaxy is rich in this kind of planet”. Typically, this wouldn’t seem that exciting, except that Sasselov was accidentally presenting this based on data from NASA’s Kepler, that while known to the scientists working on the project, was meant to be kept private, and within the group, until February 2011. While the results are still preliminary, it appears that Kepler is actually identifying Earth-like exo-planets within our galaxy… but don’ t tell anyone.
For more, see Data Leak: Galaxy Rich in Earth-Like Planets, Dimitar Sasselov: How we found hundreds of Earth-like planets (TED).
Paul A Crowther, Olivier Schnurr, Raphael Hirschi, Norhasliza Yusof, Richard J Parker, Simon P Goodwin, & Hasan Abu Kassim (2010). The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 ⊙ stellar mass limit Monthly Notices of the Royal Astronomical Society arXiv: 1007.3284v1
A few weeks ago, Paul Crowther and team presented results suggesting that there must be super massive stars in the Large Magellanic Cloud galaxy that would exceed the currently accepted theoretical limit for stellar mass of 150 solar masses. It appears that they now have an almost confirmation of these super massive stars, in the R136 cluster in the Large Magellanic Cloud, existing at a whopping 300 solar masses (well beyond the theoretical limit). It’s time for astrophysicists to revise stellar models.
For more, see The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M⊙ stellar mass limit [pdf], It’s bigger, farther, faster…, Stars Just Got Bigger, Most massive stars in Universe discovered, Heftiest stars discovered.
Brown, W., Anderson, J., Gnedin, O., Bond, H., Geller, M., Kenyon, S., & Livio, M. (2010). A GALACTIC ORIGIN FOR HE 0437–5439, THE HYPERVELOCITY STAR NEAR THE LARGE MAGELLANIC CLOUD The Astrophysical Journal, 719 (1) DOI: 10.1088/2041-8205/719/1/L23
Generally, very large stars have short lives, so the blue giant, HE 0437-5439, had previously been a puzzle to astrophysicists who had placed its age well over the expected limited for a star of its class (the age estimate was originally based on assumptions of how long the star must have been travelling to have taken it outside of the boundaries of the Milky Way). Now they speculate that it has travelled as far as it has, not because it is an unusually long lived blue giant, but because it has only (relatively) recently become a blue giant. The theory suggests that HE 0437-5439 started out as two fairly average stars, like our sun, that were ejected from their orbits around the same time and merged, forming an especially massive star. Sure, why not.
For more, see ScienceShot: Speeding Star Was Born on the Run, Strange star tossed out of galaxy.
Hodges-Kluck, E., Reynolds, C., Miller, M., & Cheung, C. (2010). A DEEP OBSERVATION OF THE X-SHAPED RADIO GALAXY 4C +00.58: A CANDIDATE FOR MERGER-INDUCED REORIENTATION? The Astrophysical Journal, 717 (1) DOI: 10.1088/2041-8205/717/1/L37
NASA’s Chandra X-ray Observatory has put out a press release this week on observations of a black hole that seems to contradict recent work on recoiling black holes. The unusual jets from 4C+00.58 were analyzed and it was found that the normal hydrodynamic models used to explain black hole “wings” did not fit. Thus, other models were proposed. It wasn’t the most exciting paper.
For more, see Black Hole Jerked Around Twice.
It’s ICHEP2010 this week, so high energy physics is all aflutter with new results. I’m only going to pick out a couple of most exciting for now though.
At the 35th International Conference on High Energy Physics in Paris this week, Fermilab presented the culmination of the CDF and DZero experiments’ data in the Higgs search, showing that now another 25% of the expected mass range can be eliminated (ie. if the Higgs had mass in that range, they would have found it). The narrower the range for the Higgs to exist in, the faster those working on the LHC should be able to identify possible candidates. Sure, the Tevatron was saving this up for the conference so they could simultaneously put forth their proposal to stay running until 2014 in a “hey guys, we’re still useful!” bid, but, regardless, it’s an exciting result.
For more, see Fermilab experiments narrow allowed mass range for Higgs boson, New limits on Higgs mass announced, Higgs boson still eludes capture – but now we know where it isn’t, No Sighting of Higgs, But Fermilab Physicists Say They May Be Close, Fermilab hones in on Higgs mass, Fermilab experiments narrow allowed mass range for Higgs boson.
Also at ICHEP this week, the CMS and ATLAS experiments presented their first top quark candidates at the LHC. Yes, this isn’t anything new for physics, but it does prove that the LHC is on track and working just as planned and that is exciting.
For more, see Europe reaches the top, err, the top reaches Europe.
Remember the news from the D0 Experiment on the apparent CP violation in the 
For more, see D0 says: neither dead nor alive.
For more results from ICHEP2010, read their results blog.
Seth Lloyd, Lorenzo Maccone, Raul Garcia-Patron, Vittorio Giovannetti, & Yutaka Shikano (2010). The quantum mechanics of time travel through post-selected teleportation arXiv arXiv: 1007.2615v2
Lloyd et al. put forth a theoretical out for time travel paradoxes by forbidding all events that would result in such a paradox (via post-selection). While the concept is a little foreign in relativity (despite not sounding it), the quantum community has been making good use of post-selection in similar situations for quite some time. Lloyd et al. does this here, fairly successfully, by basically putting a quantum mechanical twist on closed timelike curves (everyone’s favourite paradox makers). If this model will actually turn out to have any meaning is anyone’s guess at this point (although, as is the norm, the authors are hopeful for a quantum gravity tie in). Personally, my favourite part of the paper was the full inclusion of the famous Feynman anecdote about the phone call from Wheeler:
I received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, “Feynman, I know why all electrons have the same charge and the same mass.”
“Why?”
“Because, they are all the same electron!”
And, then he explained on the telephone, “Suppose that the world lines which we were ordinarily considering before in time and space – instead of only going up in time were a tremendous knot, and then, when we cut through the knot, by the plane corresponding to a fixed time, we would see many, many world lines and that would represent many electrons, except for one thing. If in one section this is an ordinary electron world line, in the section in which it reversed itself and is coming back from the future we have the wrong sign to the proper time – to the proper four velocities – and that’s equivalent to changing the sign of the charge, and, therefore, that part
of a path would act like a positron.”
For more, see Taming time travel.
July 19, 2010 6 Comments
Why this week was so dense in astrophysics and cosmology, I have no idea.
Credit: Courbin, Meylan, Djorgovski, et al., EPFL/Caltech/WMKO.
F. Courbin, M. Tewes, S. G. Djorgovski, D. Sluse, A. Mahabal, F. Rerat, & G. Meylan (2010). First case of strong gravitational lensing by a QSO : SDSS J0013+1523 at z = 0.120 Astronomy & Astrophysics arXiv: 1002.4991v2
Observations from the W. M. Keck Observatory in Hawaii have lead to the first identification of a distant galaxy seen with the aid of gravitational lensing caused by a quasar. Previously, gravitational lensing has been used to identify massive galaxies in front of quasars, not behind, so this is something new for astronomy. Being able to “see past” the bright light of quasars to look at objects “behind” them, could be an important new technique for astrophysics.
For more, see ScienceShot: A Quasi-Stellar Looking Glass, Astronomers Discover an Unusual Cosmic Lens, See A Quasar Gravitationally Lens a Galaxy (for the First Time!)
Butt, Y. (2009). Beyond the myth of the supernova-remnant origin of cosmic rays Nature, 460 (7256), 701-704 DOI: 10.1038/nature08127
An interesting letter in Physics Today this month by Yousaf Butt, from the Harvard–Smithsonian Center for Astrophysics, draws attention to the fact that supernova remnants may not actually be the most likely cause for cosmic rays reaching earth (as he pointed out in his Nature paper last year that was apparently somewhat forgotten by a few of his colleagues). Butt argues that it’s not a trivial matter to distinguish between isolated supernova remnants and superbubbles, as cosmic ray sources, and that astronomers and astrophysicists shouldn’t be so quick to label a cause when they’re lacking in confirmation. This is an excellent thing to keep in mind, regardless of field.
For more, see Cosmic rays’ origins unclear (the Physics Today letter).
Daniel T. Cumberbatch, Joyce. A. Guzik, Joseph Silk, L. Scott Watson, & Stephen M. West (2010). Light WIMPs in the Sun: Constraints from Helioseismology arXiv arXiv: 1005.5102v1
From the introduction:
The recently revised solar abundances result in solar models that cannot reproduce currently observed helioseismic data. In this letter we explore the role of WIMPs in modifying the thermal gradient of the Sun.
Credit: B. Rakouskas - Dark Matter ruins emission/absorption picture?
When we realise we have an observation that doesn’t fit our current theories we have two options: find something wrong with the observation or its interpretation, or, create a new theory. Why you’d chose WIMPs to be an element in your new theory, I have no idea, but that is what they did. Is our sun actually, in any way, made up of dark matter? I would seriously, seriously doubt it… New Scientist, on the other hand, is not as credulous as I am. The authors weren’t able to fully model the sun with a WIMPy core (there are a huge number of parameters, you can’t blame them), but they do suggest that if it were possible to come up with a model for our sun that could contain dark matter:
…both direct detection and accelerator probes may be complemented by using the Sun as a probe of dark matter.
That’s nice, however incredibly improbable it may be. In conclusion, the sun is more confusing than we thought (but it still probably has nothing to do with dark matter).
For more, see Heart of darkness could explain sun mysteries (New Scientist), Beneath that blazing facade.
Miller, J. (2010). Laboratory experiment shows that noise can be lessened for LISA Physics Today, 63 (7) DOI: 10.1063/1.3463616
Turns out, if LISA actually ever gets built, it might work. Maybe.
Eugenio Bianchi, & Carlo Rovelli (2010). Why all these prejudices against a constant? arXiv arXiv: 1002.3966v3
Nature had a great piece this week on the dark energy debate – ie. do we even need dark energy? Bianchi and Rovelli argue, quite well, that no, we do not (why add in dark energy without anything to explain it when you can get the same physics by keeping the non-vanishing cosmological constant that general relativity came with in the first place?) . They have a very accessible arXiv piece which is well worth a read, although the Cosmology Forum in Nature, that gives Rocky Kolb’s pro dark energy stance too, is certainly better than any summary I could give here.
For more, see Cosmology forum: Is dark energy really a mystery?.
Attila Meszaros, Lajos G. Balazs, Zsolt Bagoly, & Peter Veres (2010). Impact on cosmology of the celestial anisotropy of the short gamma-ray bursts Baltic Astronomy, Vol.18, 293-296 (2009) arXiv: 1005.1558v1
The abstract, short and sweet:
Recently the anisotropy of the short gamma-ray bursts detected by BATSE was announced (Vavrek et al. 2008). The impact of this discovery on cosmology is discussed. It is shown that the anisotropy found may cause the breakdown of the cosmological principle.
This is actually a rather neat little paper (typesetting aside). The authors argue that the Cosmological Principle requires the universe to be homogeneous and isotropic (in a broad sense) and recent observations of anisotropy thus suggest a breakdown in this principle. This honestly sounds quite reasonable, except for the fact that the Cosmological Principle (ie. the fact that their are no preferred reference frames) is pretty fundamental to general relativity. To me, the problem doesn’t quite lie with the Cosmological Principle, but lies with the interpretation of this homogeneity and isotropy requirement. We know the universe is not homogeneous and isotropic on all levels (the existence of animals, planets, galaxies, etc. easily demonstrate this), so what is so fundamental about it being homogeneous and isotropic on a larger scale? The authors claim this requirement only needs to hold for spacetime “larger than the size of any structure (void, filament, supercluster, etc.)”, but what about that scale is so fundamental? As far a general relativity is concerned, nothing. The universe is *not* homogeneous and isotropic (sorry, FLRW cosmology), so we shouldn’t feel the need to bundle that up with Cosmological Principle (no preferred reference frames).
For more, see June 2010 Notes of the Alternative Cosmology Group [pdf].
Chris Clarkson, & Roy Maartens (2010). Inhomogeneity and the foundations of concordance cosmology Class. Quantum Grav. 27 124008 (2010) arXiv: 1005.2165v2
From the introduction:
The unresolved nature of
As cosmology goes, I think this is actually pretty exciting. The authors do a great job throwing a few wrenches into the standard concordance model. Based on the usual assumptions in modern cosmology, of a homogeneous, unexciting, spacetime, it appears that, given our current observations, dark energy is a must (different interpretation than Bianchi and Rovelli, of course). However, and this relates to the previous article, who really says our spacetime needs to be homogeneous? It appears that by just making our spacetime a tiny bit more complicated, adding in allowance for spatial inhomogeneity, we may be able to escape the dark energy problem entirely.
Until we demonstrate observationally that the Universe is homogeneous on large scales, we should consider inhomogeneous spacetimes even if they are philosophically uncomfortable, particularly in light of the fact that in their simplest incarnation they can explain away the dark energy problem through inhomogeneity, without apparently causing other problems.
I hope to see more along these lines in cosmology very soon.
For more, see June 2010 Notes of the Alternative Cosmology Group [pdf].
Mosconi, M., et al . (2010). Neutron physics of the Re/Os clock. I. Measurement of the (n,γ) cross sections of ^{186,187,188}Os at the CERN n_TOF facility Physical Review C, 82 (1) DOI: 10.1103/PhysRevC.82.015802
Rhenium-187, believed to be produced in the first stellar explosions in our young galaxy, and its decay parent, Osmium-187, are currently being studied by CERN to help get a better feel for the age of our galaxy. By looking at the relative concentrations of Osmium-187 and Rhenium-187 in our galaxy (and knowing how long it really takes Osmium-187 to decay, thanks to CERN and Karlsruhe experiments), astrophysicists should be able to get a much more accurate date for the formation of our Milky Way.
For more, see Refining a Cosmic Clock: Particle Accelerator Research Helps Narrow Down the Age of Our Galaxy.
Nikodem J. Poplawski (2010). Cosmology with torsion – an alternative to cosmic inflation arXiv arXiv: 1007.0587v1
A snippet of the abstract:
The Einstein-Cartan-Kibble-Sciama theory of gravity provides a simple scenario in early cosmology which is alternative to standard cosmic inflation and does not require scalar fields… This scenario also suggests that the contraction of our Universe preceding the state of minimum radius could correspond to the dynamics of matter inside the event horizon of a newly formed black hole existing in another universe.
I’m just going to leave this one, but I will point out that “could correspond” and “having evidence to suggest a correspondence” are two very different things.
For more, see Why Our Universe Must Have Been Born Inside a Black Hole (MIT Tech Review arXiv Blog).
The CDF Collaboration, & T. Aaltonen (2009). Measurement of $d\sigma/dy$ of Drell-Yan $e^+e^-$ pairs in the $Z$ Mass Region from $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV Physics Letters arXiv: 0908.3914v4
From Fermilab:
Members of the CDF Rochester group have extracted the rapidity distribution from a sample of approximately 170,000 Z bosons decaying into positrons and electrons. The measurement confirmed that the most recent parton distribution functions accurately describe the fractional momentum distribution of quarks in the proton.
Honestly, I don’t know why this is exciting. Everyone likes validation, I guess.
For more, see Result of the Week: Quark speed, Jiyeon Han’s PhD thesis, “The Di erential Cross Section Distribution of Drell-Yan Dielectron Pairs in the Z Boson Mass Region” [pdf].
For more, see Forget the Large Hadron Collider. All hail Cern’s new, straight-line atom smasher, World lays groundwork for future linear collider, CERN: ILC to be build 2012-2019.
Petr Hořava & Charles M. Melby-Thompson (2010). General Covariance in Quantum Gravity at a Lifshitz Point arXiv arXiv: 1007.2410v1
Back in 2009, Hořava-Lifshitz gravity was exceptionally exciting. Unfortunately for Petr Hořava, it didn’t take long before people found some strange inconsistencies in the theory that didn’t match up with reality. Were these inconsistencies ever really resolved? Somewhat (see: New formulation of Horava-Lifshitz quantum gravity as a master constraint theory and Projectable Version of Horava-Lifshitz Gravity), but doubters certainly still remained. Two weeks ago, Petr Hořava presented his latest, “General Covariance in Quantum Gravity at a Lifshitz Point” at GR19 to mixed reviews (the paper is now out on the arXiv). The newest formulation of Hořava-Lifshitz gravity exhibits anisotropic scaling at short distances and reproduces much of (but not all) general relativity at long distances. Has it resolved all of the issues of the original Hořava gravity theory? It doesn’t appear so, although detailed work is still pending.
Samuel E. Gralla, & Robert M. Wald (2009). Derivation of Gravitational Self-Force arXiv arXiv: 0907.0414v1
The Gravitational Self-Force, the force on a body moving through a gravitational field caused by the mass/energy of the body itself, seems to be becoming a little bit of a hot topic lately amongst some relativists (see: High-Accuracy Comparison between the Post-Newtonian and Self-Force Dynamics of Black-Hole Binaries). Wald presented his latest (from last year) on how to address corrections to geodesic motion due to the “gravitational self-force” of a particle two weeks ago and, while honestly, it isn’t exceptionally exciting, it is very important to have figured out in order to put GR predictions on an even more accurate level. We know that massive bodies curve spacetime and that has to apply to even our test particles, so it’s worthwhile to make sure we actually know how to handle those corrections, analytically.
For more, see Wald’s Introduction to Gravitational Self-Force.
J. Ambjorn, A. Goerlich, J. Jurkiewicz, & R. Loll (2010). CDT—an Entropic Theory of Quantum Gravity arXiv arXiv: 1007.2560v1
The article (a lecture series, really) starts off explaining why a lattice formulation, based off of causal dynamical triangulation, could lead to a promising theory of quantum gravity (a theory of the background – like CDT gives – is always a good start if you want to recover GR… maybe not if you want QFT, but that’s a different matter) and then sort of progresses briefly into an Erik Verlinde style entropic interpretation of CDT with some tie ins to Hořava-Lifshitz gravity in the end. Other than being an interesting combination of trendy theories, I’m not sure what else this paper has to offer in terms of new insights (although if does give a good discussion on CDT).
-Sarah Kavassalis
July 14, 2010 13 Comments
Somewhat late, but I suppose it’s better than nothing (still in conference recovery mode as well as needing to actually get some work done myself).
Pakull, M., Soria, R., & Motch, C. (2010). A 300-parsec-long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793 Nature, 466 (7303), 209-212 DOI: 10.1038/nature09168
ESO’s Very Large Telescope and NASA’s Chandra X-ray telescope have shown evidence for what astronomers like to call a stellar black hole (I make the distinction between what astronomers/astrophysicists call a black hole and what relativists call a black hole because there is actually a huge difference, but that’s for a lengthier article) exhuding unusually powerful particle jets (they call these “black hole”/particle jet objects microquasars when they’re relativity small like this). This is the first observation of an object of this kind, and it suggests there might be some interesting things to learn on how these objects energize particles and how they form in the first place.
For more, see Black hole blows big bubble, Black-hole bubble stuns astronomers, Black Hole Blows Massive Gas Bubble.
Tommaso Dorigo, an experimentalist at both the CMS at CERN and the CDF at Fermilabs, wrote about rumours, on the 8th, of a possible 3-sigma Higgs Boson result from the CDF experiment. Naturally, a variety of news agencies jumped on these non-results, saying how, amazingly, the Tevatron had beat the LHC to a Higgs result. Like much of what news agencies jump on in the sciences, these were nothing more than unsubstantiated rumours that Fermilab wasn’t even trying to spread. Apparently, the rumours came out of the fact that the CDF team will be presenting some Higgs related results at the International Conference on High Energy Physics (ICHEP) in Paris in a few weeks on new Higgs mass bounds, not, of course, on the discovery of the Higgs. Why did this story get out of hand so fast? Who knows, although I would be willing to bet that it has something to do with news outlets having journalists instead of scientists filtering the content of their hype stories.
For more, see: Rumors About A Light Higgs (the original gossip), Higgs boson: is a result imminent? (foolish hype begins; thanks New Scientist!), Large Hadron Collider rival Tevatron ‘has found Higgs boson’, say rumours (more gossip), Did Someone Just Find the ‘God Particle’? (the internet sure loves wild speculation), Higgs boson discovery rumours false, say Tevatron scientists, Rumors, drawing on science, The Rumored Rumor Had Been Rumored Before, Detailed rumor: gluon+b goes to b+Higgs: MSSM with large beta.
Pohl, R., Antognini, A., Nez, F., Amaro, F., Biraben, F., Cardoso, J., Covita, D., Dax, A., Dhawan, S., Fernandes, L., Giesen, A., Graf, T., Hänsch, T., Indelicato, P., Julien, L., Kao, C., Knowles, P., Le Bigot, E., Liu, Y., Lopes, J., Ludhova, L., Monteiro, C., Mulhauser, F., Nebel, T., Rabinowitz, P., dos Santos, J., Schaller, L., Schuhmann, K., Schwob, C., Taqqu, D., Veloso, J., & Kottmann, F. (2010). The size of the proton Nature, 466 (7303), 213-216 DOI: 10.1038/nature09250
Now this could be exciting news! At the start of the week, a letter by Randolf Pohl and his team appeared in Nature giving experimental results suggesting that the charge radius of the proton may actually be quite a bit smaller than we had previously thought. Using the Lamb shift of muonic hydrogen (a proton with a muon instead of an electron) to determine the root-mean-squared value of the proton’s charge radius, the team has come up with a value, 4% smaller than previous measurements. This is actually quite a significant percentage difference, considering the accuracy to which these measurments have been made. This 4% remains completely unexplained right now and it could suggest a need to revise our understanding of quantum electrodynamics (QED), considered to be one of the most accurate theories of all time.
For more, see Proton is smaller than we thought, Quantum electrodynamics: A chink in the armour?, Shrinking the proton, The Incredible Shrinking Proton?.
Speaking of wild speculation thanks to news agencies: So for some reason, the New York Times decided to do an article on Verlinde’s entropic gravity work, from back this winter, which had created a bit of buzz back then (not that we all felt it deserved), and now the buzz has begun again amongst the general public. For those who’ve read the paper and thought to themselves, “Huh? People are still talking about this?”, don’t worry, physicists aren’t really still talking it. Why some journalists thought to themselves, “now is the time to write an article on this”, I don’t know, but it hasn’t been turning relativist heads since, basically back in January, where people kind of decided that the interesting parts weren’t especially new, and the new parts weren’t especially interesting. If you’re curious, just go read the actual paper, it’s *not* a hard read, by any means, and don’t listen to the hype that was not written by physicists.
For more, see: NY Times Article: A Scientist Takes On Gravity.
John Swain (2010). Black Holes and the Strong CP Problem arXiv arXiv: 1005.1097v2
I’m putting this under GR instead of High Energy because I think the implications are awfully profound. So here is a little paper from a couple of months ago that I am awfully taken with right now. The Strong CP Problem isn’t one that relativists probably think of much (it turns out, they should), but it is well known to particle physicists. Several attempts at quantum gravity try to resolve this issue (as in, why QCD doesn’t break CP symmetry), but, it turns out, it isn’t even a problem that needs to be resolved so long as one allows for the existence of at least one (real, in the proper GR , topological puncture of the spacetime manifold, sense) black hole, anywhere, in the universe. The implications that this concept could (and should) have for the topological nature of our spacetime seem rather profound (especially with the great analogy that John draws with Dirac’s argument for charge quantization and monopoles), as well as implications/paradoxes that black hole evaporation could allow for. I honestly expect that we should (and will be) seeing more come out of this in the near future.
Side note: I could also mention Lee’s latest Doubly Special Relativity paper, or Sean Carroll’s and Heywood Tam’s Cosmological Fine-Tuning paper from this week, but I won’t.
