GOSFORD: New insight into how waves spread in different kinds of artificial materials could shed light on how disorder affects quantum materials such as superconductors.

Since waves are used in all kinds of applications, from medical imaging to electronics, the physics behind disorder is fundamental to the understanding of how imperfections in the materials that compose these technologies affect wave behaviour.

“While disorder and imperfections are impossible to avoid in materials, there is much we do not understand about how disorder affects their properties,” said co-author Brian DeMarco from the University of Illinois in the U.S., of the paper published in Science today.

Read full news item here.

Sep 13, 2011

Could the Sun test alternative theories of gravity?

Alternatives to Einstein’s general theory of relativity can be investigated by studying the Sun. That is the claim of a group of physicists in Portugal who have found that a variation of a theory put forward nearly a century ago by Arthur Eddington is constrained but not ruled out by observations of solar neutrinos and solar acoustic waves.

General relativity, which describes gravity as the curvature of space–time by massive objects, has so far passed every experimental and observational test dreamed up by physicists. But the theory does present a number of problems. In addition to the difficulty of unifying it with quantum mechanics and the challenge to explain the nature of dark matter and dark energy, there remains the conceptual problem of singularities, where the laws of physics break down.

Since Einstein introduced general relativity in 1916, many alternatives have been proposed. Last year Máximo Bañados of the Pontifical Catholic University in Chile and Pedro Ferreira of Oxford University reported a variant of a theory originally put forward by the British astrophysicist Arthur Eddington that adds a repulsive gravitational term to general relativity. This has the virtue of not requiring singularities, and as a result does not predict that the universe originated from a Big Bang, nor does it imply the formation of black holes.

Looking inside a star

When considering a gravitational field within a vacuum, this Eddington-inspired theory is equivalent to general relativity but predicts different effects for gravity acting within matter. The ideal place to look for such differences would be inside neutron stars – but the interiors of neutron stars are not understood sufficiently to compare the theories.

The answer, say Jordi Casanellas and colleagues at the Technical University of Lisbon, is to use the Sun. While a much less extreme source of gravity than a neutron star, the inner workings of the Sun are described accurately by solar models. Casanellas’s group has calculated that even in its non-relativistic Newtonian form, the Eddington-inspired theory should predict measurable differences in solar output compared with standard gravitational theory.

The Lisbon researchers have shown that the presence of the repulsive gravity term in the theory of Bañados and Ferreira is similar to setting a different value for the gravitational constant inside matter. And with the strength of gravity higher or lower than it would otherwise be inside the Sun, the inner solar temperature is also modified because the Sun is assumed to be in hydrostatic equilibrium. This means that the inward pressure of its mass is balanced by the outward thermal pressure generated by the fusion reactions within it. A higher temperature implies a greater rate of fusion burning, which in turn implies higher emission rates of solar neutrinos.

Altering acoustic waves

Similarly, a different strength of gravity inside the Sun implies a variation in its density distribution, which should modify the propagation of acoustic waves measured using the techniques of helioseismology.

Casanellas and co-workers have shown that observations made by neutrino telescopes of the solar neutrino flux coming from the proton–proton chain reaction that produces boron-8 significantly constrain the correction to general relativity, calculating an upper limit to the effective gravitational constant. Combined with a lower limit obtained from helioseismic data, the researchers are able to put a significant constraint on the Eddington-inspired theory. However, they point out that their calculations do not rule out such a theory.

The researchers say that improving on these upper and lower limits will be difficult because of uncertainties in a few of the parameters within solar models, such as the abundance of helium on the solar surface. As such, more sensitive measurements of neutrino fluxes are unlikely to have much of an impact. But they believe their approach could be used to constrain other alternative theories of gravity.

Further testing on Earth

Ultimately, adds team member Paolo Pani, such theories could be tested experimentally by measuring, for example, the gravitational attraction between a metal ball inserted into a hole in the ground and the mass of the Earth surrounding it. The idea would be to make the hole just big enough for the ball to fit and no more, so that what is measured is the strength of gravity through matter and not the surrounding void (in this case air). However, Pani points out that doing so would be a considerable experimental challenge.

Clifford Will of Washington University in St Louis, US, described the latest work as a “nice example of using the Sun as a laboratory for probing fundamental physics” but added that “it’s not yet clear whether the bounds proposed by this paper present serious threats to alternative gravity theories”.

The research is reported at arXiv:1109.0249.

Aug 23, 2011

Who discovered that E = mc²? It’s not as easy a question as you might think. Scientists ranging from James Clerk Maxwell and Max von Laue to a string of now-obscure early 20th-century physicists have been proposed as the true discovers of the mass–energy equivalence now popularly credited to Einstein’s theory of special relativity. These claims have spawned headlines accusing Einstein of plagiarism, but many are spurious or barely supported. Yet two physicists have now shown that Einstein’s famous formula does have a complicated and somewhat ambiguous genesis – which has little to do with relativity.

One of the more plausible precursors to E = mc² is attributed to Fritz Hasenöhrl, a physics professor at the University of Vienna. In a 1904 paper Hasenöhrl clearly wrote down the equation E = 3/8mc². Where did he get it from, and why is the constant of proportionality wrong? Stephen Boughn of Haverford College in Pennsylvania and Tony Rothman of Princeton University examine this question in a paper submitted to the arXiv preprint server.

Hasenöhrl’s name has a certain notoriety now, as he is commonly invoked by anti-Einstein cranks. His reputation as the man who really discovered E = mc² owes much to the efforts of the antisemitic and pro-Nazi physics Nobel laureate Philipp Lenard, who sought to separate Einstein’s name from the theory of relativity so that it was not seen as a product of “Jewish science”.

‘Leading Austrian physicist of his day’

Yet all this does Hasenöhrl a disservice. He was Ludwig Boltzmann’s student and successor at Vienna, and was lauded by Erwin Schrödinger among others. “Hasenöhrl was probably the leading Austrian physicist of his day”, Rothman told physicsworld.com. He might have achieved much more if he had not been killed in the First World War.

The relationship of energy and mass was already being widely discussed by the time Hasenöhrl considered the matter. Henri Poincaré had stated that electromagnetic radiation had a momentum and thus effectively a mass, according to E = mc². German physicist Max Abraham argued that a moving electron interacts with its own field, E₀, to acquire an apparent mass given by E₀ = 3/4 mc². All this was based on classical electrodynamics, assuming an ether theory. “Hasenöhrl, Poincaré, Abraham and others suggested that there must be an inertial mass associated with electromagnetic energy, even though they may have disagreed on the constant of proportionality”, says Boughn.

Photo of Fritz Hasenöhrl published in 1933. (Courtesy: AIP Emilio Segrè Visual Archives, Brittle Books Collection, Physics Today Collection)Photo of Fritz Hasenöhrl published in 1933. (Courtesy: AIP Emilio Segrè Visual Archives, Brittle Books Collection, Physics Today Collection) Fritz Hasenöhrl

Robert Crease, a philosopher and historian of science at Stony Brook University in New York, agrees. “Historians often say that, had there been no Einstein, the community would have converged on special relativity shortly”, he says. “Events were pushing them kicking and screaming in that direction.” Boughn and Rothman’s work, he says, shows that Hasenöhrl was among those headed this way.

Hasenöhrl approached the problem by asking whether a black body emitting radiation changes in mass when it is moving relative to the observer. He calculated that the motion adds a mass of 3/8c² times the radiant energy. The following year he corrected this to 3/4c².

A different style of scientific paper

However, no-one has properly studied Hasenöhrl’s derivation to understand his reasoning or why the prefactor is wrong, claim Bough and Rothman. That’s not easy, they admit. “The papers are by today’s standards presented in a cumbersome manner and are not free of error. The greatest hindrance is that they are written from an obsolete world view, which can only confuse the reader steeped in relativistic physics.” Even Enrico Fermi apparently did not bother to read Hasenöhrl’s papers properly before concluding wrongly that the discrepant 3/4 prefactor was due to the electron self-energy identified by Abraham.

“What Hasenöhrl really missed in his calculation was the idea that if the radiators in his cavity are emitting radiation, they must be losing mass, so his calculation wasn’t consistent”, says Rothman. “Nevertheless, he got half of it right. If he had merely said that E is proportional to m, history would probably have been kinder to him.”

But if that’s the case, where does relativity come into it? Actually, perhaps it doesn’t. While Einstein’s celebrated 1905 paper, “On the electrodynamics of moving bodies”, clearly laid down the foundations of relativity by abandoning the ether and making the speed of light invariant, his derivation of E = mc² did not depend on those assumptions. You can get the right answer with classical physics, says Rothman, all in an ether theory without c being either constant or the limiting speed. “Although Einstein begins relativistically, he approximates away all the relativistic bits, and you are left with what is basically a classical calculation.”

A controversial issue

Physicist Clifford Will of Washington University in St Louis, a specialist on relativity, considers the preprint “very interesting”. Boughn and Rothman “are well-regarded physicists”, he says, and as a result he “tend[s] to trust their analysis”. However, the controversies that have been previously aroused over the issue of priority perhaps account for some of the reluctance of historians of physics to comment when contacted by physicsworld.com.

Did Einstein know of Hasenöhrl’s work? “I can’t prove it, but I am reasonably certain that Einstein must have done, and just decided to do it better”, says Rothman. But failure to cite it was not inconsistent with the conventions of the time. In any event, Einstein asserted his priority for the mass–energy relationship when this was challenged by Johannes Stark (who credited it in 1907 to Max Planck). Both Hasenöhrl and Einstein were at the famous first Solvay conference in 1911, along with most of the other illustrious physicists of the time. “One can only imagine the conversations”, say Boughn and Rothman.

Rothman told physicsworld.com that he had run across Hasenöhrl’s name a number of times but with no real explanation as to what he did. “One of my old professors, E C G Sudarshan, once remarked that he gave Hasenöhrl credit for mass–energy equivalence. So around Christmas-time last year, I said to Steve, ‘why don’t we spend a couple hours after lunch one day looking at Hasenöhrl’s papers and see what he did wrong?’ Well, two hours turned into eight months, because the problem ended up being extremely difficult.”

About the author

Philip Ball is a science writer based in the UK

http://physicsworld.com/cws/article/news/46941

Viewing image 1 of 2

In the diagram a light trajectory is shown. The light ray enters the device, completes a loop, bounces off the mirror twice and leaves the cloak with its original direction restored (A).

Credit: Perczel et al & New J. Phys.

Panel (B) gives a closer view of the vicinity of the inner branch of the cloak. Objects placed within the white region are invisible.

Credit: Perczel et al & New J. Phys.

PERTH: One of the roadblocks in the development of invisibility cloaking has been cleared by an unlikely new inventor – an undergraduate student from the UK.

By introducing a unique optical device into a cloaking system, Janos Perczel from the University of St Andrews in Scotland has discovered that invisibility cloaking can still operate at speeds below the normal speed of light, known as subluminal light speeds.

See full article here

As NASA prepares to wrap up its shuttle program, leaving open questions about what comes next for U.S. human spaceflight, the next big thing in NASA’s astronomy program has been dealt a blow. The James Webb Space Telescope, a tennis court–size spacecraft that would take up a position in deep space to peer farther than ever into the cosmos, has been in development as a replacement for and successor to the Hubble Space Telescope, which has already logged 21 years in orbit. But the House Appropriations Committee, in a bill announced July 6, proposed axing the project entirely this week, citing mismanagement and bad budgeting.

http://www.scientificamerican.com/blog/post.cfm?id=threat-of-james-webb-space-telescop-2011-07-07&WT.mc_id=SA_WR_20110714

by Estelle Asmodelle

The colours in this image were modified to emphasize the planet’s atmospheric features. Neptune’s Great Dark Spot stands out as the most prominent feature on the left. The two key features Karkoschka used can also be seen: the fainter Dark Spot 2 and the South Polar Feature, which are locked to the planet’s rotation.Credit: Erich Karkoschka

TUCSON: The first accurate measurement of Neptune’s rotational period has been determined by tracking specific atmospheric features. A day on Neptune lasts precisely 15 hours, 57 minutes and 59 seconds.

This finding adds to our knowledge of the fundamental properties of Neptune and also provides a mechanism for understanding how Neptune’s mass is distributed. The study could lead to a better understanding of the giant gas planets in general.

http://www.cosmosmagazine.com/news/4474/neptunes-day-measured

NEW METHOD OF MAPPING THE UNIVERSE USING QUASARS -BOSS.

The biggest 3-D map of the distant universe ever made, using light from 14,000 quasars – supermassive black holes at the centers of galaxies billions of light years away – has been constructed by scientists with the third Sloan Digital Sky Survey (SDSS-III).

See the Phyorg article here: http://www.physorg.com/news/2011-05-distant-universe-d-boss-job.html

Or sciencecodex here: http://www.sciencecodex.com/measuring_the_distant_universe_in_3d

THE HUNTING OF DARK MATTER

The race to detect dark matter has yielded mostly confusion. But the larger, more sensitive detectors being built could change that picture soon.

If you did yet get this PDF now is a good time to download it

Article on Nature website: http://www.nature.com/news/2011/110323/pdf/471433a.pdf

THE NEW MOST MASSIVE OBJECT – CURRENT TITLE HOLDER ANYWAY:

The most massive known object in the young universe, a galaxy cluster dubbed SPT-CLJ2106-5844, is also a probe of conditions in the young universe. This image combines optical and infrared images with intensity contours from the Chandra X-ray Observatory.

Phyorg article here: http://www.physorg.com/news/2011-04-massive-distant.html

SUPER LUMINIOUS SUPERNOVA

Images of SN 2008am obtained with the Keck I telescope’s Low Resolution Imaging Spectrometer (LRIS).Credit: D. Perley & J. Bloom / W.M. Keck Observatory

The Keck I Telescope has played a key role in unraveling the mysteries of one of the brightest supernovas ever discovered.

http://www.physorg.com/news/2011-04-keck-telescope-images-super-luminous-supernova.html

DOES DARK MATTER LINK GAMMA RAYS TO GALACTIC HAZE?

Fermi’s view of the Milky Way and beyond

Annihilating dark matter at the heart of the Milky Way could account for signals detected by two space telescopes, according to a pair of US physicists.

IOP website: http://physicsworld.com/cws/article/news/45804

ANITMATTER DETECTOR READY

A heavyweight, and controversial, cosmic-ray detector is set to head for the International Space Station.

Nature website: http://www.nature.com/news/2011/110428/full/news.2011.260.html

THE MAGNETIC UNIVERSE

We live in a magnetic universe, but much about magnetism at cosmic scales remains unknown.

The magnetic field at the Milky Way’s core is at least 10 times stronger than that of the rest of the galaxy.

Cosmos: http://www.cosmosmagazine.com/node/4248/full

Another universe tugging on ours? Maybe not, researchers say

A new study from the University at Buffalo contradicts the dark flow theory, showing that exploding stars in different parts of the universe do not appear to be moving in sync. Working with data on 557 such stars, called supernovae, UB scientists deduced that while the supernovae closest to Earth all shared a common motion in one direction, supernovae further out were heading somewhere else. An article announcing the research results will appear in a forthcoming edition of the peer-reviewed Journal of Cosmology and Astroparticle Physics.

Phyorg: http://www.physorg.com/news/2011-04-universe.html

Astronomers mull merger of missions

Cosmic-origins scientists convene with exoplanet hunters.

NASA’s constrained budget is encouraging some creative pairings. This week, scientists eager to find other habitable worlds explored the possibility that a future space telescope for probing the origins of stars and galaxies could serve their needs as well.

Nature: http://www.nature.com/news/2011/110427/full/472402a.html

Xenon100: ‘We hope to detect the largest proportion of the matter in space’

 

The underground laboratory at Gran Sasso in Italy is the home of the Xenon100 experiment, which is being conducted as an international collaboration that includes the Heidelberg-based Max Planck Institute for Nuclear Physics to detect the mysterious particles directly. The researchers recently published the evaluations of one hundred days of measurement time. The result: although there is no significant signal for dark matter as yet, the world’s best limits for the masses and interaction strengths of the WIMPs have been obtained, and already noticeably reach into the predicted range.

Phyorg: http://www.physorg.com/news/2011-04-xenon100-largest-proportion-space.html

Scientists suggest spacetime has no time dimension

The concept of time as a way to measure the duration of events is not only deeply intuitive, it also plays an important role in our mathematical descriptions of physical systems. For instance, we define an object’s speed as its displacement per a given time. But some researchers theorize that this Newtonian idea of time as an absolute quantity that flows on its own, along with the idea that time is the fourth dimension of spacetime, are incorrect. They propose to replace these concepts of time with a view that corresponds more accurately to the physical world: time as a measure of the numerical order of change.

http://www.physorg.com/news/2011-04-scientists-spacetime-dimension.html