Physics

The mystery, that is, of why the universe is matter and not equal and oppositely charged antimatter: From Sarah Charley at Symmetry: “We’re looking for hints,” says Stefan Ulmer, spokesperson of the BASE collaboration. “If we find a slight difference between matter and antimatter particles, it won’t tell us why the universe is made of matter and not antimatter, but it would be an important clue.” The BASE measurement shows that the magnetic moments of the proton and antiproton are identical, apart from their opposite signs, within the experimental uncertainty of 0.8 parts per million. The result improves the precision of the previous best measurement by the ATRAP collaboration in 2013, also at CERN, by a factor of six. This Read More ›

FromDaily Galaxy, a revisit of cosmologist Sean Carroll’s From Eternity to Here: The Quest for the Ultimate Theory of Time (2010): The relativity of time depended upon a new theory, and if we stand back, we discover that all views of time are human constructs. If time seems linear, that’s because we humans have modeled it that way in accord with our nervous system. It is just as viable to construct other models of time. For example, your body obeys natural rhythms in accord with the planetary, lunar, and solar cycles. The very notion of “time passing” fits with the firing of neurons in the brain, which have a beginning, middle, and end. If you drop every model, something surprising Read More ›

From Joshua Howgego at New Scientist: On 11 November last year, a small birthday party was held in an apparently unremarkable hangar onthe outskirts of Geneva, Switzerland. Nothing too fancy, just a few people gathered around a cake. The honourees were there. Well, sort of – they were still locked in the cage where they had spent their first year. But then again, there is no other way to treat a brood of antimatter particles. The antimatter realm is so bizarre as to be almost unbelievable: a mirror world of particles that destroy themselves and normal matter whenever the two come into contact. But it’s real enough. Cosmic rays containing antiparticles constantly bombard Earth. A banana blurts out an anti-electron Read More ›

From Nobelist and multiverse proponent* Steven Weinberg at New York Review of Books: Many physicists came to think that the reaction of Einstein and Feynman and others to the unfamiliar aspects of quantum mechanics had been overblown. This used to be my view. His view has changed to: The introduction of probability into the principles of physics was disturbing to past physicists, but the trouble with quantum mechanics is not that it involves probabilities. We can live with that. The trouble is that in quantum mechanics the way that wave functions change with time is governed by an equation, the Schrödinger equation, that does not involve probabilities. It is just as deterministic as Newton’s equations of motion and gravitation. That Read More ›

From Bob Henderson, a finance writer with a physics background, at Nautilus: Einstein and Feynman ushered me into grad school, reality ushered me out. All of my classmates had taken up with advisors who were, like most physicists, experimentalists, the researchers who do the hands-on work of, say, smashing particles together at accelerators to see what comes out. Theorists like Rajeev, or for that matter Einstein and Feynman, who instead do the noodling necessary to explain the results of experiments with math are fewer and further between. A couple of Rochester’s experimentalists had pressured me to drop my dream of doing theory because, they explained, theory was so ridiculously difficult and had so few jobs. But I’d brushed them off. The Read More ›

From Natalie Wolchover at Quanta: Different “grand unified theories” or “GUTs” tying together the strong, weak and electromagnetic forces make a range of predictions about how long protons take to decay. Super-K’s latest analysis finds that the subatomic particles must live, on average, at least 16 billion trillion trillion years, an increase from the minimum proton lifetime of 13 billion trillion trillion years that the team calculated in 2012. The findings, released in October and under review for publication in Physical Review D, rule out a greater range of the predicted proton lifetimes and leave the beloved, 1970s-era grand unification hypothesis as an unproven dream. “By far the most likely way we would ever verify this idea is proton decay,” Read More ›

Thanu Padmanabhan asks: Our knowledge about the universe has increased tremendously in the last three decades or so — thanks to the progress in observations — but our understanding has improved very little. There are several fundamental questions about our universe for which we have no answers within the current, operationally very successful, approach to cosmology. Worse still, we do not even know how to address some of these issues within the conventional approach to cosmology. This fact suggests that we are missing some important theoretical ingredients in the overall description of the cosmos. I will argue that these issues — some of which are not fully appreciated or emphasized in the literature — demand a paradigm shift: We should Read More ›

From Mark Anderson at New Scientist: First test of rival to Einstein’s gravity kills off dark matter A controversial approach to gravity that challenges Albert Einstein and suggests dark matter doesn’t exist has passed its first test. … Now, a team of astronomers studying the distribution of matter in more than 30,000 galaxies say their observations can be explained by an alternative theory that does away with dark matter. If this “modified gravity” is correct, it would up-end hundreds of years of fundamental physics. … To their surprise, they discovered the observed lensing could just as readily be accounted for by a new model of gravity, without invoking dark matter. More. From Dominic Basuto at Sydney Morning Herald: In her Read More ›

From Jesse Emspak at LiveScience: From 1989 to 2000, the European Organization for Nuclear Research (CERN) operated an atom smasher called the Large Electron-Positron Collider (LEP), in which particles were sent crashing into one another at near light speed. A restudy of the data from the now-dismantled LEP collider could prove a hint or just a fluke. When the original LEP experiments were done, the muons were produced in particle collisions (also called “events”) that occurred at certain energies. A graph of particle mass (expressed as energy, per Einstein’s famous E = mc^2) against the number of events per billion electron volts, or GeV, shows a peak at about 10 to 15 GeV and a long “tail” that trails off Read More ›

From James M. Chappell et al. at Frontiers in Physics: The proper description of time remains a key unsolved problem in science. Newton conceived of time as absolute and universal which “flows equably without relation to anything external.” In the nineteenth century, the four-dimensional algebraic structure of the quaternions developed by Hamilton, inspired him to suggest that he could provide a unified representation of space and time. With the publishing of Einstein’s theory of special relativity these ideas then lead to the generally accepted Minkowski spacetime formulation of 1908. Minkowski, though, rejected the formalism of quaternions suggested by Hamilton and adopted an approach using four-vectors. The Minkowski framework is indeed found to provide a versatile formalism for describing the relationship Read More ›

From Emily Conover at Science News, reviewing philosopher James Owen Weatherall’s Void: The strange physics of nothing: In Void: The Strange Physics of Nothing, physicist and philosopher James Owen Weatherall explores how physicists’ beliefs about nothingness have changed over several revolutionary periods. The void, Weatherall argues, is physics distilled to its bare essence. If physicists can’t agree on the properties of empty space, they won’t be able to explain the physics of planets or particles either. Well, they haven’t so far. Under the modern view of quantum physics, various fields pervade all of space, and particles are simply excitations, or waves, in these fields. Even in a vacuum, experiments show, fluctuating fields produce a background of transient particles and antiparticles. Read More ›

From Matthew R. Francis at Symmetry: One reason to think of dark matter as a thermal relic is an interesting coincidence known as the “WIMP miracle.”WIMP stands for “weakly-interacting massive particle,” and WIMPs are the most widely accepted candidates for dark matter. Theory says WIMPs are likely heavier than protons and interact via the weak force, or at least interactions related to the weak force. … Both the primordial light known as the cosmic microwave background and the behavior of galaxies tell us that most dark matter must be slow-moving (“cold” in the language of physics). That means interactions between dark matter particles must be low in strength. “Through what is perhaps a very deep fact about the universe,” Buckley Read More ›

At Forbes: While experiments are telling us that low-energy supersymmetry and extra dimensions probably don’t exist (or are so constrained that they’re irrelevant), there are plenty of pieces of evidence that there’s more to existence than the Standard Model alone. What else is out there? There are five strong, independent lines of inquiry that reveal there’s got to be something. Including: During the last decade, when neutrino masses were constrained for the first time (via neutrino oscillations), it surprised many that they were found to be very low in mass, but to have definitively non-zero masses. Why is that? The general way of explaining this — the see-saw mechanism — typically involves additional, very heavy particles (like, maybe a billion Read More ›

From Dan Scolnic and Adam G. Riess at Scientific American: You might have read otherwise in some headlines lately, but don’t be misled … The recent paper that has generated headlines used a catalog of Type Ia supernovae collected by the community (including us) which has been analyzed numerous times before. But the authors used a different method of implementing the corrections—and we believe this undercuts the accuracy of their results. They assume that the mean properties of supernovae from each of the samples used to measure the expansion history are the same, even though they have been shown to be different and past analyses have accounted for these differences. However, even ignoring these differences, the authors still find that Read More ›

From ScienceDaily: Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery, in the late 1990s, that the universe is expanding at an accelerating pace. Their conclusions were based on analysis of Type Ia supernovae — the spectacular thermonuclear explosion of dying stars — picked up by the Hubble space telescope and large ground-based telescopes. It led to the widespread acceptance of the idea that the universe is dominated by a mysterious substance named ‘dark energy’ that drives this accelerating expansion. Now, a team of scientists led by Professor Subir Sarkar of Oxford University’s Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set — a Read More ›