How Time Flies: Ultraprecise Clock Rates Vary with Tiny Differences in Speed and Elevation
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
Primordial Gravitational Waves Provide a Test of Cosmological Theories
Cosmic inflation may have left a telltale imprint on the universe that could be detected in the coming years
What Keeps Time Moving Forward? Blame It on the Big Bang
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
Tweak Gravity: What If There Is No Dark Matter?
Modifications to the theory of gravity could account for observational discrepancies, but not without introducing other complications
Listening for Gravity Waves, Silence Becomes Meaningful
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
Inside This Issue: Neandertals and General Relativity
Acting Editor in Chief Mariette DiChristina introduces the August 2009 issue of Scientific American
Surprises from General Relativity: "Swimming" in Spacetime
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
Astronomers Size Up a Candidate for Midsize Black Hole
An object hundreds or thousands of times the mass of the sun would represent an elusive class of black hole
Was Einstein Wrong?: A Quantum Threat to Special Relativity
Entanglement, like many quantum effects, violates some of our deepest intuitions about the world. It may also undermine Einstein's special theory of relativity
Beyond the Shadow of a Doubt? Dark Energy Independently Confirmed
The gravitationally repulsive presence, thought to make up most of the universe, shows its effect on the development of galaxy clusters
Closing In on the Milky Way's Central Black Hole
New studies track the motion of stars to pin down what holds sway at the heart of our galaxy
Did Researchers Cook Data from the First Test of General Relativity?
Rumors of data mishandling in an historic eclipse study don't gibe