David Appell

In the realm of science fiction, Dyson spheres and ringworlds have been staples for decades. But it is well known that the simplest designs are unstable against gravitational forces and would thus be torn apart. Now a scientist ...

Interconnected materials containing networks are ubiquitous in the world around us—rubber, car tires, human and engineered tissues, woven sheets and chain mail armor. Engineers often want these networks to be as strong as ...

How will artificial intelligence affect the distribution of income and wealth this century? After falling through much of the 20th century, income inequality, measured as the fraction of income going to the richest 1% of ...

Heat waves have gotten hotter in the Northern Hemisphere in recent decades. Home to about 90% of the world's population, with the largest fraction living in the mid-latitudes, more frequent and more severe heat waves and ...

Neutron stars are some of the densest objects in the universe. They are the core of a collapsed megastar that went supernova, have a typical radius of 10 km—just slightly more than the altitude of Mt. Everest—and their density ...

Observing the effects of special relativity doesn't necessarily require objects moving at a significant fraction of the speed of light. In fact, length contraction in special relativity explains how electromagnets work. A ...

When quantum electrodynamics, the quantum field theory of electrons and photons, was being developed after World War II, one of the major challenges for theorists was calculating a value for the Lamb shift, the energy of ...

For now, the future of life on Earth is in human hands. But after the anthropocentric era, the situation starts to get dicey. The sun's luminosity is increasing over time, about 1% every 110 million years, so the Earth's ...

In an era of medical care that is increasingly aiming at more targeted medication therapies, more individual therapies and more effective therapies, doctors and scientists want to be able to introduce molecules to the biological ...

Students learning quantum mechanics are taught the Schrodinger equation and how to solve it to obtain a wave function. But a crucial step is skipped because it has puzzled scientists since the earliest days—how does the real, ...

Almost 300 binary mergers have been detected so far, indicated by their passing gravitational waves. These measurements from the world's gravitational wave observatories put constraints on the masses and spins of the merging ...

Einstein's theory of gravity, general relativity, has passed all tests with predictions that are spot-on. One prediction that remains is "gravitational wave memory"—the prediction that a passing gravitational wave will permanently ...

Among the many things global warming will be melting this century—sea ice, land glaciers and tourist businesses in seaside towns across the world—is permafrost. Lying underneath 15% of the northern hemisphere, permafrost ...

Extraterrestrial civilizations need a great deal of energy as they advance up the Kardashev scale. Fossil fuels are finite, wind and solar energy are carbon free but not as efficient as fossil fuels, and traditional nuclear ...

As physicists continue their struggle to find and explain the origin of dark matter, the approximately 80% of the matter in the universe that we can't see and so far haven't been able to detect, researchers have now proposed ...