David Appell

Cosmic rays seen at Earth show a wide range of particle energies, from 107 electron-volts (eV) to more than 1020 eV, the latter being about the same as the kinetic energy of a 450 gram football (soccer ball) being kicked ...

About a billion years ago, Earth started to come into its own. It was past the awkwardness of its younger years full of growing pains and turmoil: comet strikes and slimy water, including the Great Oxidation Event that flipped ...

When you're looking for signs of extraterrestrial intelligence, it helps to know what you're looking for and to go about it in the most efficient way. But work so far has generally not done so, writes Benjamin Zuckerman, ...

In thermodynamics, an "adiabatic process" is a system change that transfers no heat in or out of the system. Any and all energy change in that system are therefore accomplished by doing work on the system, work being action ...

Climate scientists like to keep their accounting books neat and balanced. As climate change alters energy flows all across the planet, which in turn causes effects like sea level rise, ice melt and more, keeping close track ...

Whenever humans arrive on Mars, they're going to find it a difficult place to exist. Mars is cold, with an average surface temperature of -55°C; temperatures can plunge to -125°C with dust storms lasting months; its atmosphere ...

When you go out to run errands on the weekend, you're on a "tour" as defined by human mobility researchers. Same if you book a guided tour of a famous city or take a trip on a cruise boat that reaches multiple ports. A characteristic ...

Will humanity extend into the far future? It's likely many of us think it should. The problem is that each of us, individually and collectively, act otherwise—we are destroying the environment and climate at every turn. Now ...

Ultrathin, conductive films such as those made of graphene are widely used in modern optoelectronic devices, but it has been thought that their efficacy is fundamentally limited: they can absorb at most half of the incident ...

There is no measurement that can directly observe the wave function of a quantum mechanical system, but the wave function is still enormously useful as its (complex) square represents the probability density of the system ...

A new study of climate extremes since 1988 finds that many regions have seen increases in deaths due to floods, storms and extreme temperatures. In human terms, the harm comes not just from deaths, but also from lost labor ...

Hypervelocity stars have, since the 1920s, been an important tool that allows astronomers to study the properties of the Milky Way galaxy, such as its gravitational potential and the distribution of matter. Now astronomers ...

Scientists in China have performed an experiment first proposed by Albert Einstein almost a century ago when he sought to disprove the quantum mechanical principle of complementarity put forth by Niels Bohr and his school ...

For experimental physicists, the latest measurement of the muon is the best of times. For theorists there's still work to do.

With the discovery of ever more exoplanets—over 6,000 now—scientists, of course, want to know if they are habitable for life. (At least, life as we know it.) But assessing habitability is a difficult task, as information ...