Category Archives: Theoretical physics

Entanglement shown between photons that never coexist

Posted on by
Reply

Science: The entanglement of two particles (or photons) is a quantum mechanical effect in which measuring one of the particles instantaneously determines the state of the other, regardless of the distance between them. And entanglement can be swapped between pairs of entangled particles by creating two sets of particles and then performing a “projective measurement” of one particle of each pair. The measurement simultaneously entangles and destroys the measured particles, and it entangles the two other particles even if they had previously been measured. Now, Eli Megidish and Hagai Eisenberg of the Hebrew University of Jerusalem and their colleagues have used this swapping technique to entangle two photons that never coexisted. The time-separated effect was predicted by the original quantum theory, but this recent work is the first demonstration of it. The technique could be useful in the development of quantum communications systems.

Planck full-sky map may show evidence of other universes

Posted on by
1

Daily Mail: In 2005 Laura Mersini-Houghton of the University of North Carolina at Chapel Hill and Richard Holman of Carnegie Mellon University suggested that evidence for the existence of other universes would be found in the cosmic microwave background radiation. Early mapping efforts using the Wilkinson Microwave Anisotropy Probe appeared to support some of their claims. Now Mersini-Houghton says that the highly detailed Planck map of that radiation, released in March, provides clear support for their hypothesis. She believes that the apparent imbalance in movement and structure and the presence of a cold spot are signs that there are sources of gravity external to our own universe. However, an earlier evaluation of the Planck data showed no evidence of “dark flow.”

Giant electromagnet to be moved from New York to Illinois

Posted on by
Reply

Quantum Diaries: A 15.24-m-diameter electromagnet built and used in the 1990s at Brookhaven National Laboratory in New York is to be moved to Illinois later this year. The ring-shaped electromagnet and other parts of that original experiment will now be used in the Muon g−2 to study the properties of muons. Transporting the large magnet to Fermilab in Batavia, Illinois, will cost almost 10 times less than building a new ring from scratch. The ring will sail on a barge down the East Coast, pass around Florida, and then head up the Mississippi River before being transferred to a specially designed flatbed truck for the final drive to Fermilab. The ring itself is used to trap and store muons, which “wobble” when held in a magnetic field. Although the amount of wobble measured in the older experiment did not match scientists’ predictions, Fermilab’s more intense and pure beam of muons may help attain a more definitive measurement.

Meson decay at LHC shows matter–antimatter imbalance

Posted on by
1

BBC: One of the detectors at CERN’s Large Hadron Collider is dedicated to studying the decay paths of B mesons—particles made of combinations of quarks. A paper submitted to Physical Review Letters has revealed that the decay path of the Bs meson favors the production of matter over antimatter. Chris Parkes of the University of Manchester in the UK says that one in every four decays exhibits that behavior—known as CP violation. The production of more matter than antimatter is predicted by the standard model, and this is the first evidence that Bs mesons decay as predicted. Other chargeless mesons have also shown that low rate of CP violation. The investigation of the rates of CP violation is part of the effort to understand why there is significantly more matter than antimatter in the universe. If equal amounts of matter and antimatter had been created after the Big Bang, then all the particles would have annihilated each other. However, the rates of CP violation observed so far are not large enough to explain the current proportions of matter and antimatter that exist in the universe today.

Simulated entropic force shows behavior analogous to intelligence

Posted on by

BBC: Entropy is a measure of the number of internal arrangements that a system can exhibit. For a closed system, entropy inevitably increases, as defined by the second law of thermodynamics. A related quantity, causal path entropy, measures the number of possible arrangements a system could have on its way to possible future states. By providing a route toward greater complexity, causal path entropy could conceivably serve as a model for how intelligence develops. With that idea in mind, Alex Wissner-Gross of Harvard University and MIT and Cameron Freer of the University of Hawaii at Manoa have proposed the existence of a force that works to maximize causal path entropy. They created simulations of simple physical systems that accounted for that force and found that the effects were profound—a particle in a box moved to the center and a pendulum on a sliding pivot moved to an inverted position that would be unstable without the force. They then created physical models that reproduced standard animal intelligence tests. The models behaved in ways analogous to the development of tool use and of social cooperation, both characteristics of basic levels of cognition. However, whereas the models are suggestive of a connection between entropy and intelligence, they are descriptive rather than explanatory and don’t give any evidence of the actual existence of a force that maximizes future possible arrangements of a system.

Dark-matter detector records three candidate events

Posted on by

Nature: Between 2003 and 2008 the Cryogenic Dark Matter Search (CDMS) used silicon detectors cooled to 40 mK and located deep in a mine in Minnesota to seek evidence of weakly interacting massive particles (WIMPs), one of the possible forms of dark matter. When a particle collides with the detectors, the interaction is detected as an increase in temperature. Despite the shielding provided by the mine, it is difficult to separate WIMP collisions from background events. Two previous CDMS-detected events have been shown to involve only non-WIMP particles. Now Kevin McCarthy of MIT and his colleagues, who have been analyzing the data collected by the project, have detected three collision events that may be indicative of WIMPs. The three new events occurred when the background should have produced just 0.7 such events. However, the strength of the signal was not strong enough to be considered a true discovery. The interactions, if shown to involve new particles, would give them masses of 8.6 GeV, which is much lower than expected for most theorized WIMPs. The SuperCDMS experiment and other WIMP detectors may provide the evidence necessary to confirm or refute the potential discovery.

Planck data show no signs of dark flow

Posted on by

New Scientist: An analysis of the cosmic microwave background (CMB) map produced by the European Space Agency’s Planck spacecraft has found no evidence of “dark flow”—a stream of galaxy clusters apparently rushing toward the same region of the universe. Dark flow was first suggested in 2008 by the CMB map produced by the Wilkinson Microwave Anisotropy Probe (WMAP). The apparent structural favoritism ran contrary to the generally accepted model of cosmology, however, and attempts to explain it evoked exotic physics. Because not all of the analyses of the WMAP data saw the same dark flow effect, researchers hoped that the next CMB mapping would settle the question. The first analysis of Planck‘s more detailed data, which shows no evidence of that large-scale structural favoritism, appears to have done so. Nevertheless, one of the Planck researchers and the lead author of the original dark flow paper are both working on their own analyses of the new data. 

Three-body problem admits 13 new solutions

Posted on by

Science: When Isaac Newton defined his law of gravity, he used it to determine that two bodies orbiting each other will create an ellipse. It took more than 200 years before a German mathematician, Heinrich Bruns, determined that there was no general solution to describe the path of three bodies orbiting each other in a repeated pattern: Only specific solutions are possible. Since Bruns’s first solution, only two other families of orbits that solve the “three-body problem” have been found. Now, Milovan Šuvakov and Veljko Dmitrašinović of the University of Belgrade in Serbia have used computer simulations to define an additional 13 unique solutions. Starting their simulations with the known solutions, they systematically adjusted the initial conditions until a new solution was found. Surprised by how many solutions they discovered, they had to create a new classification system for the solutions. They developed a “shape-sphere” that depicts where the bodies cannot go in their orbits and determines the relative distances between the bodies. Then the bodies were sorted based on symmetry and other characteristics. The next step will be to determine the stability of the solutions to see if any of the systems may be seen in observations of astronomical objects.

Further collider data continue to clarify nature of the Higgs particle

Posted on by

Los Angeles Times: At the Moriond conference in Italy, groups of researchers from both CERN’s Large Hadron Collider (LHC) and Fermilab’s now-closed Tevatron collider presented more information about the data they have collected in their search for the Higgs boson. Both groups’ findings are in line with CERN’s announcement last July of the potential discovery of the particle associated with the energy field that gives particles mass. Scientists’ reactions to the results continue to be mixed. Although the discovery of the Higgs boson would satisfy a 40-year-old prediction and complete the standard model of particle physics, the standard model does not explain many unknown aspects of the universe. If the data revealing the new particle had been different, it could have opened the door for theories that explain phenomena such as dark matter.

Uncertainty principle demonstrated at macroscopic scale

Posted on by

Science News: Werner Heisenberg’s uncertainty principle is a central tenet of quantum mechanics. It states that one can’t have precise knowledge of both the position and momentum of a particle: Any method of measuring one of the two values for a particle would change both. Now Thomas Purdy and his colleagues at JILA in Boulder, Colorado, have demonstrated that the principle also holds true at the macroscopic level. The researchers created a drum by stretching a flexible silicon nitride skin across a frame 0.5 mm to a side, placed the drum between a pair of mirrors, and cooled the system to 4 K. They then shot a laser through the drum so that the photons bounced back and forth between the mirrors. The photons transferred momentum to the drum before entering a detector that calculated the drum’s position. The picometer-sized vibrations that resulted in the drum were in strict agreement with Heisenberg. Similar setups, albeit on a larger scale, are being used in an attempt to detect gravitational waves. The work of Purdy’s group will be useful for calibrating those instruments.