In 1961 Rolf Landauer linked information and thermodynamic entropy by showing that erasing or combining bits of memory must be accompanied by an increase in entropy. For the first time since then, a team of physicists have experimentally verified this principle.

According to Landauer’s principle, any logically irreversible transformation of information results in, at best, some small dissipation of heat. The specific amount depends on the operating temperature—per bit, it amounts to around 3×10-21 joules at room temperature. This energy is the Landauer limit, and controls the maximum energy efficiency of computers (it's similar to the Carnot efficiency in heat engines, both of which are related to entropy).

Measuring such a tiny amount of energy in a memory storage devices is, to say the least, challenging. But now, a team from École Normale Supérieure, the University of Kaiserslautern, and the University of Augsburg has managed to do so.






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Like his buddy Richard Dawkins, the evolutionary biologist who wrote the Afterward to his book, physicist Lawrence Krauss does not have a ton of patience for theology. Or American schools. Or God. Krauss seems totally unimpressed by deities in general.

In 2009, Krauss gave a lecture entitled "A Universe from Nothing" for the Atheist Alliance International Conference. It became a YouTube sensation, with over a million hits. His book is essentially a transcript of the talk; it has the same quotes, the same jokes, the same disparaging remarks about religion. 
But the talk loses something in translation. Online, the figures are in color, whereas in the book they are in black and white, and Krauss has a speaking style that many find compelling. If you like seeing things in print, or want to underline them and review them over and over, read the book; if you are more of an oral learner, or only have an hour to devote to the subject, watch the video. But be warned that Dr. Krauss is wearing a shirt that is the exact same color as the wall behind him, which is kind of disconcerting—like his torso is transparent or something.






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Those of you who know my writing will know that I don't use many analogies. Analogies have a very useful place in helping people understand difficult concepts, but they also have a tendency to be a end up strained beyond their limits. Now, imagine how I would react to a whole new field of physics that might be best described as "physics by analogy."

The whole field is based on the premise that, when two physically very different situations can be described using the same mathematical model, the conclusions drawn from one situation can be applied to the other. Unfortunately, this is usually applied in situations where the physics in one situation—black holes, for instance—are so extreme that it is difficult, if not impossible, to test any of the conclusions.

It appears I must adjust my attitude and admit that the field as a whole is not useless. I reached this conclusion after reading a paper that uses sound propagation in Bose Einstein condensates (BEC) to throw light on the origin of the largest discrepancy between two calculations ever seen.







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One of the key concepts in physics is that of a phase transition. Ice melting to form water is one example; another is the transition between magnetic and non-magnetic forms of iron. The underlying physics of these transitions is a story about correlations. Understanding a phase transition and, indeed, a phase of matter, is all about understanding the growth of correlations.

You would think that one of the cleanest and best understood physical systems wouldn't have a lot to offer physicists in terms of understanding correlations that develop through a phase transition. However, physicists got a bit of a surprise when they looked at particular correlations that arise as a dilute gas is cooled down until it forms a Bose Einstein condensate (BEC).






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Understanding dunes is important, since he who controls the Spice controls the Universe… That’s the last Dune joke, I promise.

Understanding the mechanisms behind desert sand dune formation and evolution actually is useful, since migrating dune fields threaten agricultural areas and human habitats. At the edges of dune fields, habitats can transition from lifeless deserts to areas covered in vegetation over fairly short distances. Various factors, such as the supply and transport rates of sand and groundwater, along with vegetation density, have all been proposed as key influences on this transition point, but nobody has come up with a model describing the evolution of dune fields.

Until now, that is. A team led by Douglas Jerolmack, joined by others at the Universities of Pennsylvania, Alabama, and Temple University, published a paper in a recent issue of Nature Geoscience that focused on the gypsum dunes of White Sands National Monument, New Mexico. The team came up with a model describing both the transport of the sand that forms the dunes and the changes in vegetation, relating to the levels of groundwater underneath the sand.






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It has been a busy week in the world of particle physics, with attention focused on the home of the LHC: CERN. This year, the LHC generated five inverse femtobarns worth of data—nearly half the amount generated during the entire lifetime of the Tevatron—before shutting down the proton program a few weeks ago. From now until its scheduled winter shutdown, the LHC will be doing lead ion collisions to examine the quark-gluon interactions that dominated the Universe immediately after the Big Bang.

In the mean time, analysis of the data has continued, and some significant news has come out this week. A further dissection of last year's data has placed tighter limits on where the Higgs boson, which provides mass to other particles, might be hiding (assuming it exists). Meanwhile, the LHCb detector, which studies particles that contain heavy quarks, has found an anomalous behavior that might hint at physics beyond the Standard Model. And the LHC accelerator chain has sent some more neutrinos to detectors at Italy's Gran Sasso, which has helped them eliminate some potential sources of error in their faster-than-light findings. We'll take a look at each of these in turn.







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Relativity is the reigning theory of gravity. In situations where we can measure it directly, such as binary neutron stars, its predictions match the real world with remarkable precision. And, when supplemented with inflation and dark matter, relativity nicely reproduces the large-scale structure of the Universe. But this reliance on other models like dark matter means that we don't have a direct, large-scale test of relativity. Now, scientists have measured the redshifting of light by galaxy clusters to give use the biggest test of relativity yet. Their results show that relativity passes muster, while modified forms of Newtownian gravity fall short.

Light emitted by distant objects rarely makes it to Earth at the same wavelength that it started out at. The fabric of the Universe is expanding, which causes a redshift. Most objects are also moving relative to the Earth, which adds a Doppler shift to the light. Finally, light that has to climb out of a large gravity well on its way to Earth also gets red-shifted.

In theory, it should be easy to account for the distance and Doppler shift; anything that's left over should be the effect of gravity. Unfortunately, even with something as massive as a galaxy cluster, the gravity-induced redshift is about two orders of magnitude smaller than a typical Doppler shift. On top of that, the motion of galaxies within clusters should be random relative to the Earth, creating a broad, Gaussian distribution of color shifts. Picking a gravitational signal out of that curve would require a large data set to help cut down on the statistical noise.







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One of the things that isn't widely advertised in science is that progress often looks a bit like this video—things get done, but the results are rarely quite what you expect. A recent example of this two steps forward, one step back progress may be the study of the recently observed excess positrons coming from the center of our galaxy.

Although there are many possible astrophysical explanations, none of them were that clean or appealing, leaving one alternative attractive: dark matter. Dark matter is thought to be made up of weakly interacting massive particles, which every now and again collide and annihilate. One particular pathway for the annihilation results in positrons with about the same energy of those seen coming from the core of the galaxy. Hey, presto! thought some scientists. We may have seen dark matter decays, which then allow us to pin down dark matter. Oh and incidentally, the medal should be pinned on my left—that's your right—lapel.

But, as a recent Physical Review Paper shows, the excess may be real, but if it comes from dark matter, we have some serious cosmological problems on the horizon.






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