For the first time, researchers have seen how light behaves during a mysterious phenomenon called ‘imaginary time’
When you shine light through almost any transparent material, the gridlock of electromagnetic fields that make up the atomic alleys and side streets will add a significant amount of time to each photon’s commute.
This delay can tell physicists a lot about how light scatters, revealing details about the matrix of material the photons must navigate. Yet until now, one trick up the theorist’s sleeve for measuring light’s journey – invoking imaginary time – has not been fully understood in practical terms.
According to the latest studies led by Heidelberg University astronomers, low-mass stars quite often host Earth-like planets. Data collected as part of the CARMENES project were the basis of this finding. By analyzing the data, an international research team succeeded in identifying four new exoplanets and determining their properties.
At the same time, the researchers were able to show that Earth-like planets are found quite frequently in the orbit of stars with less than a sixth of the mass of our sun. These findings could support the search for potentially life-sustaining worlds in our cosmic neighborhood. The work is published in the journal Astronomy & Astrophysics.
The CARMENES spectrograph system at the Calar Alto Observatory near Almería (Spain) was developed and built at the Königstuhl Observatory of Heidelberg University. It aids astronomers in the search for exoplanets that orbit so-called M-dwarfs. These stars have a mass of less than one-tenth to half the mass of our sun. M-dwarfs are the most abundant stars in our galaxy. They exhibit tiny periodic movements caused by the gravitational pull of orbiting planets, from which researchers can infer the existence of previously undiscovered worlds.
The original goal of the study was to get this asymmetry to a point of perfect isolation—that is, where there is zero interaction in one direction. They successfully achieved this goal by demonstrating a giant optical isolation effect, where the propagation of light in one direction was a million times easier than in the opposite direction.
But while exploring their test devices, the engineers encountered a surprise. Their approach was so efficient that they could even get past the isolation point to where the sign of the coupling simply flipped and the phase became direction dependent. This was something that had not been seen before in time modulated coupling and is an easy path to photonic gyration.
Going forward, the Illinois researchers will work to expand their findings. They are working with their partners specializing in condensed matter to explore how longer and more elaborate chains of resonators with this kind of tunable couplings could answer fundamental questions on topological physics. Simultaneously, from an engineering standpoint, they aim to create a pure gyrator which is a universal building block of many nonreciprocal devices.
The problem concerns the mathematical properties of solutions to the Navier–Stokes equations, a system of partial differential equations that describe the motion of a fluid in space. Solutions to the Navier–Stokes equations are used in many practical applications. However, theoretical understanding of the solutions to these equations is incomplete. In particular, solutions of the Navier–Stokes equations often include turbulence, which remains one of the greatest unsolved problems in physics, despite its immense importance in science and engineering.
In a recently published paper in Physical Review Letters, scientists propose a comprehensive theoretical framework indicating that gravitational wave signals from black hole mergers are more complex than earlier anticipated.
When two black holes merge in the cosmos, the cataclysmic event doesn’t end with a simple collision. The newly formed black hole continues to vibrate like a struck bell, producing gravitational waves in what scientists call the “ringdown” phase.
Researchers found that the cosmic reverberations involve sophisticated quadratic mode couplings—secondary oscillations that develop when primary modes interact with each other. This nonlinear behavior had been predicted in Einstein’s theory of general relativity, but has never been fully characterized until now.
A Los Alamos collaboration has replicated an important but largely forgotten physics experiment: the first deuterium-tritium (DT) fusion observation. As described in the article published in Physical Review C, the reworking of the previously unheralded experiment confirmed the role of University of Michigan physicist Arthur Ruhlig, whose 1938 experiment and observation of deuterium-tritium fusion likely planted the seed for a physics process that informs national security work and nuclear energy research to this day.
“As we’ve uncovered, Ruhlig’s contribution was to hypothesize that DT fusion happens with very high probability when deuterium and tritium are brought sufficiently close together,” said Mark Chadwick, associate Laboratory director for Science, Computation and Theory at Los Alamos. “Replicating his experiment helped us interpret his work and better understand his role, and what proved to be his essentially correct conclusions. The course of nuclear fuel physics has borne out the profound consequences of Arthur Ruhlig’s clever insight.”
The DT fusion reaction is central to enabling fusion technologies, whether as part of the nation’s nuclear deterrence capabilities or in ongoing efforts to develop fusion for civilian energy. For instance, the deuterium-tritium reaction is at the center of efforts at the National Ignition Facility to harness fusion. Los Alamos physicists developed a theory about where the idea came from—Ruhlig—and then built an experiment that would confirm the import and accuracy of Ruhlig’s suggestion.