Relativity

New calculations extend Einstein's general theory of relativity into the universe's first few moments

A framework that relies on college-level mathematics could describe what happens to particles in so-called spacetime rips, gravity fluctuations such as those that occur during the birth of a black hole

Newly developed optical clocks are so precise that they register the passage of time differently at elevations of just a few dozen centimeters or velocities of a few meters per second

Cosmic inflation may have left a telltale imprint on the universe that could be detected in the coming years

A timely Q&A with physicist Sean Carroll about how our one-way trip from past to future is entangled with entropy and the origin of the universe

Modifications to the theory of gravity could account for observational discrepancies, but not without introducing other complications

The ripples in spacetime predicted by general relativity remain one of the most sought-after prizes in physics, and new research narrows estimates of their prevalence

The possibility of "swimming" and "gliding" in curved, empty space shows that even after nine decades, Einstein's theory of general relativity continues to amaze

Acting Editor in Chief Mariette DiChristina introduces the August 2009 issue of Scientific American

An object hundreds or thousands of times the mass of the sun would represent an elusive class of black hole

Entanglement, like many quantum effects, violates some of our deepest intuitions about the world. It may also undermine Einstein's special theory of relativity

The gravitationally repulsive presence, thought to make up most of the universe, shows its effect on the development of galaxy clusters