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Category: physics – Page 67

In day-to-day life, light seems intangible. We walk through it and create and extinguish it with the flip of a switch. But, like matter, light actually carries a little punch—it has momentum. Light constantly nudges things and can even be used to push spacecraft. Light can also spin objects if it carries orbital angular momentum (OAM)—the property associated with a rotating object’s tendency to keep spinning.

Scientists have known that light can have OAM since the early 90s, and they’ve discovered that the OAM of light is associated with swirls or vortices in the light’s phase—the position of the peaks or troughs of the electromagnetic waves that make up the light. Initially, research on OAM focused on vortices that exist in the cross-section of a light beam—the phase turning like the propeller of a plane flying along the light’s path.

But in recent years, physicists at UMD, led by UMD Physics Professor Howard Milchberg, have discovered that light can carry its OAM in a vortex turned to the side—the phase spins like a wheel on a car, rolling along with the light. The researchers called these light structures spatio-temporal optical vortices (STOVs) and described the momentum they carry as transverse OAM.

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Einstein’s theory of relativity paved the way for black holes’ discovery, but the concept behind their existence was so bizarre that even the scientific visionary was not convinced.

More than a century ago, Albert Einstein stunned the world when he explained the universe through his theory of general relativity. The theory not only described the relationship between space, time, gravity and matter, it opened the door to the theoretical possibility of a particularly mind-boggling phenomenon that would eventually be called black holes.

The concept that explains black holes was so radical, in fact, that Einstein, himself, had strong misgivings. He concluded in a 1939 paper in the Annals of Mathematics that the idea was “not convincing” and the phenomena did not exist “in the real world.”

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Dark matter comprises more than 80% of all matter in the cosmos but is invisible to conventional observation, because it seemingly does not interact with light or electromagnetic fields. Now Dr. Sukanya Chakrabarti, the Pei-Ling Chan Endowed Chair in the College of Science at The University of Alabama in Huntsville (UAH), along with lead author Dr. Tom Donlon, a UAH postdoctoral associate, have written a paper to help illuminate just how much dark matter there is in our galaxy and where it resides by studying the gravitational acceleration of binary pulsars.

Chakrabarti gave a plenary talk on this work and other methods to measure galactic accelerations at the 243rd meeting of the American Astronomical Society in New Orleans in January. The findings are also posted on the arXiv preprint server.

Pulsars are rapidly rotating that blast out pulses of radiation at regular intervals ranging from seconds to milliseconds. A binary pulsar is a pulsar with a companion that allows physicists to test general relativity because of the strong gravitational fields accompanying these objects. “Pulsars are fantastic galactic clocks that have a timing stability that rivals atomic clocks,” Chakrabarti explains.

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There is no doubt that water is significant. Without it, life would never have begun, let alone continue today—not to mention its role in the environment itself, with oceans covering over 70% of Earth.

But despite its ubiquity, liquid water features some electronic intricacies that have long puzzled scientists in chemistry, physics, and technology. For example, the , i.e., the energy stabilization undergone by a free electron when captured by water, has remained poorly characterized from an experimental point of view.

Even today’s most accurate electronic structure has been unable to clarify the picture, which means that important physical quantities like the energy at which electrons from external sources can be injected in liquid water remain elusive. These properties are crucial for understanding the behavior of electrons in water and could play a role in , environmental cycles, and technological applications like solar energy conversion.

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We are always making strides to unravel the mysteries of our universe. Now, a small observatory nestled in the Andes mountains of northern Chile has provided a snapshot of the cosmos in space. This one is clearer than we imagined.

The U.S. National Science Foundation Cosmology Large Angular Scale Surveyor (CLASS), spearheaded by astrophysicists from Johns Hopkins University, mapped a whopping 75 percent of the sky.

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New theoretical work establishes an analogy between systems that are dynamically frustrated, such as glasses, and thermodynamic systems whose members have conflicting goals, such as predator–prey ecosystems.

A system is geometrically frustrated when its members cannot find a configuration that simultaneously minimizes all their interaction energies, as is the case for a two-dimensional antiferromagnet on a triangular lattice. A nonreciprocal system is one whose members have conflicting, asymmetric goals, as exemplified by an ecosystem of predators and prey. New work by Ryo Hanai of Kyoto University, Japan, has identified a powerful mathematical analogy between those two types of dynamical systems [1]. Nonreciprocity alters collective behavior, yet its technological potential is largely untapped. The new link to geometrical frustration will open new prospects for applications.

To appreciate Hanai’s feat, consider how different geometric frustration and nonreciprocity appear at first. Frustration defies the approach that physics students are taught in their introductory classes, based on looking at the world through Hamiltonian dynamics. In this approach, energy is to be minimized and states of matter characterized by their degree of order. Some of the most notable accomplishments in statistical physics have entailed describing changes between states—that is, phase transitions. Glasses challenge that framework. These are systems whose interactions are so spatially frustrated that they cannot find an equilibrium spatial order. But they can find an order that’s “frozen” in time. Even at a nonzero temperature, everything is stuck—and not just in one state. Many different configurations coexist whose energies are nearly the same.

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What can the night sky tell us about the expansion of the universe?

It’s a loaded question, one that researchers across the globe have been trying to answer for decades. Since 2013, they’ve been helped by the Dark Energy Survey (DES), a collaboration of more than 400 scientists at 25 institutions. At Penn, this includes Masao Sako, Arifa Hasan Ahmad and Nada Al Shoaibi Presidential Professor of Physics and Astronomy; Bhuvnesh Jain, Walter H. and Leonore C. Annenberg Professor in the Natural Sciences; Gary Bernstein, Reese W. Flower Professor of Astronomy and Astrophysics; and a handful of others from the Department of Physics & Astronomy.

In 2019, the DES finished collecting data, but analysis and discoveries continue, including one that Sako and colleagues announced recently in which they validated the “cosmic acceleration” model and dark energy’s role in it. That research is one of five recent studies detailed below, in this second iteration of Omnia’s new research roundup.

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