Lifeboat Foundation

A team of researchers affiliated with several institutions in France has revisited the idea of improving on estimates of the upper limit of the mass of a graviton. In their paper published in the journal Physical Review Letters, the group describes their accurate measurement of the parameters of planetary bodies and what they found.

Einstein’s theory of general relativity suggests that the gravity of large masses that warps spacetime comes from a theoretical massless particle called the graviton. Scientists have been trying for many years to either prove the theory correct or disprove it by finding a way to show that it has mass. One approach to such a proof involves studying the speed of the expansion of the universe—this approach has suggested that if the graviton does have a mass, its upper limit would be approximately 10 ⁻³² electron-volts. Unfortunately, this result is based on a lot of assumptions, many of which are still controversial. Another way to do it is by studying planetary orbital deviations that could only come from a nonzero graviton mass—and starting with the assumption that if a graviton has zero mass, then like the photon, it should travel at the speed of light. In this new effort, the researchers have found a way to improve the accuracy of this approach.

The work involved temporarily freezing the motion of the stars and planets at different points in time—the first was the year 2000. The researchers found the masses, positions and speed of the sun, the planets and several asteroids for that year. They then ran equations that allowed them to roll forward in time to 2017 and back to 1913 and forward again as needed. These time periods were chosen because the team was able to find usable data for them. In running the calculations, the researchers found that they were able to come up with an estimation for the upper limit of the graviton of 6.76 × 10 ⁻²³—with a probability of 90 percent. The researchers note that their number was very close to that found by a team using data from the LIGO interferometers, but suggest that any similarities were purely coincidence.

https://www.youtube.com/watch?v=iNqqOLscOBY

Sean Carroll is a theoretical physicist at Caltech and Santa Fe Institute specializing in quantum mechanics, arrow of time, cosmology, and gravitation. He is the author of several popular books including his latest on quantum mechanics (Something Deeply Hidden) and is a host of a great podcast called Mindscape. This conversation is part of the Artificial Intelligence podcast.

This is the second time Sean has been on the podcast. You can watch the first time here: https://www.youtube.com/watch?v=l-NJrvyRo0c

Continue reading “Sean Carroll: Quantum Mechanics and the Many-Worlds Interpretation” »

EPFL researchers, with colleagues at the University of Cambridge and IBM Research-Zurich, unravel novel dynamics in the interaction between light and mechanical motion with significant implications for quantum measurements designed to evade the influence of the detector in the notorious ‘back action limit’ problem.

The limits of classical measurements of mechanical motion have been pushed beyond expectations in recent years, e.g. in the first direct observation of gravitational waves, which were manifested as tiny displacements of mirrors in kilometer-scale optical interferometers. On the microscopic scale, atomic- and magnetic-resonance force microscopes can now reveal the atomic structure of materials and even sense the spins of single atoms.

But the sensitivity that we can achieve using purely conventional means is limited. For example, Heisenberg’s uncertainty principle in quantum mechanics implies the presence of “measurement backaction”: the exact knowledge of the location of a particle invariably destroys any knowledge of its momentum, and thus of predicting any of its future locations.

The main component of the LUX-ZEPLIN dark-matter detector has been installed at the Sanford Underground Research Facility in Lead, South Dakota.

The central cryostat for the experiment, which weighs about 2200 kg, was successfully lowered some 1500 m underground last week. Over the coming months, the detector will be wrapped in layers of insulation and then next year be filled with around 10 tonnes of ultra-pure liquid xenon.

LUX-ZEPLIN is expected to begin operation in July 2020 when it will become the largest direct detection dark-matter experiment in the US. It will search for weakly interacting massive particles – a leading dark-matter candidate – with scientists hoping to capture flashes of light that are produced when dark-matter particles interact with the heavy xenon atoms.

A brand-new particle has possibly emerged and is altering the future destiny of our entire cosmos, a physicist says.

Metasurfaces are optically thin metamaterials that can control the wavefront of light completely, although they are primarily used to control the phase of light. In a new report, Adam C. Overvig and colleagues in the departments of Applied Physics and Applied Mathematics at the Columbia University and the Center for Functional Nanomaterials at the Brookhaven National Laboratory in New York, U.S., presented a novel study approach, now published on Light: Science & Applications. The simple concept used meta-atoms with a varying degree of form birefringence and angles of rotation to create high-efficiency dielectric metasurfaces with ability to control optical amplitude (maximum extent of a vibration) and phase at one or two frequencies. The work opened applications in computer-generated holography to faithfully reproduce the phase and amplitude of a target holographic scene without using iterative algorithms that are typically required during phase-only holography.

The team demonstrated all-dielectric metasurface holograms with independent and complete control of the amplitude and phase. They used two simultaneous optical frequencies to generate two-dimensional (2-D) and 3D holograms in the study. The phase-amplitude metasurfaces allowed additional features that could not be attained with phase-only holography. The features included artifact-free 2-D holograms, the ability to encode separate phase and amplitude profiles at the object plane and encode intensity profiles at the metasurface and object planes separately. Using the method, the scientists also controlled the surface textures of 3D holographic objects.

Light waves possess four key properties including amplitude, phase, polarization and optical impedance. Materials scientists use metamaterials or “metasurfaces” to tune these properties at specific frequencies with subwavelength, spatial resolution. Researchers can also engineer individual structures or “meta-atoms” to facilitate a variety of optical functionalities. Device functionality is presently limited by the ability to control and integrate all four properties of light independently in the lab. Setbacks include challenges of developing individual meta-atoms with varying responses at a desired frequency with a single fabrication protocol. Research studies previously used metallic scatterers due to their strong light-matter interactions to eliminate inherent optical losses relative to metals while using lossless dielectric platforms for high-efficiency phase control—the single most important property for wavefront control.

Researchers at the Kavli Institute for the Physics and Mathematics of the Universe (WPI) and Tohoku University in Japan have recently identified an anomaly in the electromagnetic duality of Maxwell Theory. This anomaly, outlined in a paper published in Physical Review Letters, could play an important role in the consistency of string theory.

The recent study is a collaboration between Yuji Tachikawa and Kazuya Yonekura, two string theorists, and Chang-Tse Hsieh, a condensed matter theorist. Although the study started off as an investigation into string theory, it also has implications for other areas of physics.

In current physics theory, classical electromagnetism is described by Maxwell’s equations, which were first introduced by physicist James Clerk Maxwell around 1865. Objects governed by these equations include electric and magnetic fields, electrically charged particles (e.g., electrons and protons), and magnetic monopoles (i.e. hypothetical particles carrying single magnetic poles).

As an astronomer, there is no better feeling than achieving “first light” with a new instrument or telescope. It is the culmination of years of preparations and construction of new hardware, which for the first time collects light particles from an astronomical object.

This is usually followed by a sigh of relief and then the excitement of all the new science that is now possible.

On October 22, the Dark Energy Spectroscopic Instrument (DESI) on the Mayall Telescope in Arizona, US, achieved first light. This is a huge leap in our ability to measure galaxy distances – enabling a new era of mapping the structures in the Universe.

Have you ever wondered how the Sun creates the energy that we get from it every day and how the other elements besides hydrogen have formed in our universe? Perhaps you know that this is due to fusion reactions where four nuclei of hydrogen join together to produce a helium nucleus. Such nucleosynthesis processes are possible solely due to the existence, in the first place, of stable deuterons, which are made up of a proton and a neutron.

Probing deeper, one finds that a deuteron consists of six light quarks. Interestingly, the strong interaction between quarks, which brings stability to deuterons, also allows for various other six-quark combinations, leading to the possible formation of many other deuteron-like nuclei. However, no such nuclei, though theoretically speculated about and searched for experimentally many times, have yet been observed.

All this may get changed with an exciting new finding, where, using a state-of-the-art first-principles calculation of lattice quantum chromodynamics (QCD), the basic theory of strong interactions, a definite prediction of the existence of other deuteron-like nuclei has been made by TIFR’s physicists. Using the computational facility of the Indian Lattice Gauge Theory Initiative (ILGTI), Prof. Nilmani Mathur and postdoctoral fellow Parikshit Junnarkar in the Department of Theoretical Physics have predicted a set of exotic nuclei, which are not to be found in the Periodic Table. The masses of these new exotic nuclei have also been calculated precisely.