The UNiverse seems less smooth than theory

If so, there will need some new understanding. Since Einstein's application of his grand theory, GRT, to comprehending the cosmos, a lot of observations have been achieved during the past years, especially about the cosmological structure on large scales. This allows one to make relatively accurate estimate about the mass and energy distribution, by calibration with GRT. Great fitting has been found if dark matter and dark energy are presumed up till now, when people find that, the universe is much more clumpier than expected on larger scale.

Thomas et al. use publicly-released catalogs from the Sloan Digital Sky Survey to select more than 700,000 galaxies whose observed colors indicate a significant redshift and are therefore presumed to be at large cosmological distances. They use the redshift of the galaxies, combined with their observed positions on the sky, to create a rough three-dimensional map of the galaxies in space and to assess the homogeneity on scales of a couple of billion light years. One complication is that Thomas et al. measure the density of galaxies, not the density of all matter, but we expect that fluctuations of these two densities about their means to be proportional; the constant of proportionality can be calibrated by observations on smaller scales. Indeed, on small scales the galaxy data are in good agreement with the standard model. On the largest scales, the fluctuations in galaxy density are expected to be of order a percent of the mean density, but Thomas et al. find fluctuations double this prediction. This result then suggests that the universe is less homogeneous than expected. [http://physics.aps.org/articles/v4/47]

Metastable states are important in reality

Metastable states are common in nature: supercooled or superheated liquid are daily examples. These states are not the lowest-energy state, and, by thermodynamic principles, one should not expect them to be long-lived in nature. Indeed, they exist only under very stringent conditions, and very little disturbance can push the system off to a stable state around. Thermodynamically stable states dwell on one of the global minima of the free energy, around which, however, local minima might exist that are separated from the global minima by energy barriers. When a system has not reached the stable states, it will be constantly kicked by its surroundings and eventually transits from where it is in to a stable state after some period (the life of the metastable state). The interesting point is that, the life time can sometimes be very long and real transitions can hardly be seen, a situation similar to ergodicity breaking. For example, diamond has a higher energy than graphite, but it can exist for ever. The reason is because the time to make the transition is cosmologically long, due to the hugely high barrier. Another material is graphene, which should not be stable according to Wagner-Mermin-Honberg theorem. Yet, it was produced in 2004. Glasses are the third examples, in which case, transition has been frustrated by its structure. In the case of supercooled water, the transition is suppressed by distilling process.

Study blames plasma flow for quiet sun

Our sun is maintained by converting gravitational energy into electromagnetic energy (e.g., visible and invisible radiations). The temperature is so high that the solar matter exists only in gas of light ions and electrons. These are charged particles. Their motions may take the form of the so-called 'plasma', which has these charges moving in a coherent and collective way, appearing as waves. The dynamics are quite nonlinear and intricate. Associated with such plasma, the electromagnetic fields will also change, and have been well known following a very regular pattern. One way to notice this pattern is by counting the intensity of the so-called sunspots, which are caused by pop-ups of strong magnetic energy flow from interior to the surface, like a cork decorated with flares carrying a huge amount of energy that may partly reach the earth. The latest solar cycle peaked in 2001 and was supposed to end in 2008. However, there is something unusual with this cycle: the sun appears too sluggish, with an extra number of spotless days. Now researchers came up with an explanation, which seems under debate [http://www.wired.com/wiredscience/2011/03/spotless-sun-model/]:

Now, Dibyendu Nandy of the Indian Institute of Science Education and Research and colleagues offer an explanation: A “conveyor belt” of plasma inside the sun ran quickly at first and then slowed down.

Nandy and colleagues at Montana State University and the Harvard-Smithsonian Center for Astrophysics ran a computer simulation of magnetic flow inside the sun for 210 sunspot cycles. They randomly varied the speed of plasma flow around a loop called the meridional circulation, which carries magnetic fields from the sun’s interior to its surface and from the equator to the poles.

Observations suggest that the fastest flow runs around 22 meters per second (49 miles per hour). Nandy’s model looked at speeds between 15 and 30 meters per second (33 to 67 miles per hour).

The model found that a fast flow followed by a slow flow reproduced both the weak magnetic field and the dearth of sunspots observed in the last solar minimum.

....

Unfortunately, observations of the sun’s surface seem to directly contradict the new model.

“We’re in this quandary, this clash between theory and observations,” said NASA astronomer David Hathaway, who analyzed 13 years of data from the Solar and Heliospheric Observatory (SOHO) that tracked the movement of charged material near the surface of the sun.

Hathaway agrees that a fast flow can cause weak magnetic fields and fewer sunspots. But his observations, published March 12, 2010 in Science, suggest that the meridional flow was slow in the first half of the last solar cycle, from about 1996 to 2000. Only after the solar maximum did the flow speed up.

“That’s where there’s a problem,” Hathaway said. “We see one thing, they want the opposite to explain the observations.”

Nandy and colleagues point out that the SOHO observations only see plasma moving at the surface of the sun, not in the deep interior where sunspots are born. The surface flows might not reflect what’s going on underneath, he says.

“In an analogy that you might be able to relate to, one could ask, do ripples on the surface of the sea indicate how ocean currents determine the migration of aquatic animals deeper inside?” Nandy said.

Hathaway argues that changes in the surface should be transmitted to the interior at the speed of sound, and should reach the creation zone in half an hour or less. The disagreement between theory and data means there must be a problem with the models, he says.

Critical Casirmir effect

Sticky situations

Illustration: A. Gambassi et al., Phys. Rev. E (2009)

Critical Casimir effect in classical binary liquid mixtures

A. Gambassi, A. Maciołek, C. Hertlein, U. Nellen, L. Helden, C. Bechinger, and S. Dietrich

Phys. Rev. E 80, 061143 (Published December 31, 2009)

ShareThis Statistical Mechanics Soft Matter

When two conducting plates are brought in close proximity to one another, vacuum fluctuations in the electromagnetic field between them create a pressure. This effective force, known as the Casimir effect, has a thermodynamic analog: the “critical Casimir effect.” In this case, thermal fluctuations of a local order parameter (such as density) near a continuous phase transition can attract or repel nearby objects when they are in confinement.

In 2008, a team of scientists in Germany presented direct experimental evidence for the critical Casimir effect by measuring the femtonewton forces that develop between a colloidal sphere and a flat silica surface when both are immersed in a liquid near a critical point [1]. Now, writing in Physical Review E, Andrea Gambassi, now at SISSA in Trieste, Italy, and collaborators at the Max Planck Institute for Metals Research, the University of Stuttgart, and the Polish Academy of Sciences, follow up on this seminal experiment and present a comprehensive examination of their experimental results and theory for the critical Casimir effect.

Success in fabricating MEMS and NEMS (micro- and nanoelectromechanical systems) made it possible to explore facets of the quantum Casimir effect that had for many years only been theoretical curiosities. With the availability of tools to track and measure the minute forces between particles in suspension, scientists are able to do the same with the critical Casimir effect. In fact, it may be possible to tune this thermodynamically driven force in small-scale devices so it offsets the attractive (and potentially damaging) force associated with the quantum Casimir effect. Given its detail, Gambassi et al.’s paper may well become standard reading in this emerging field. – Jessica Thomas

[1] C. Hertlein et al., Nature 451, 172 (2008).