A mysterious concept changed the way we understand reality.

Einstein's theory showed that time itself is affected by gravity.

Dive down to rare stromatolites—key clues to the evolution of virtually all complex life.

What does this geological wonder reveal about North America’s deep history?

Sea levels will rise by the same amount all over the world, right? Wrong. Here’s why.

Cyber threats from nation states and lone hackers are a persistent threat to America’s critical infrastructure.

We asked scientists, “What are your favorite images from space?” Here’s what they said.

The universe’s smallest particles fly down from space and emit from a radioactive rod.

How has this unique structure, built on a seismic fault, survived centuries of quakes? Airing February 25, 2015 at 9 pm on PBS

How did early engineers carve tombs into rock cliffs and funnel water to this desert city? Airing February 18, 2015 at 9 pm on PBS

1500 years ago, how did the Romans engineer bloody spectacles and reenact sea battles?

Explore the forces behind deadly landslides—and the danger zones for the next big one. Airing November 19, 2014 at 9 pm on PBS

Could parallel universes exist? If so, what would they look like and how would they form?

As the epidemic threatens to spiral out of control, scientists race to find a cure. Airing October 8, 2014 at 10 pm on PBS

The zombie apocalypse is here, and calculus explains why we can’t quite finish them off.

You're being chased by zombies, and understanding tangent vectors may save your life.

Almost a century ago, paleontologists found the first tantalizing hints of a monster even bigger than Tyrannosaurus rex, perhaps the largest predator ever to roam the Earth: spectacular fossil bones from a dinosaur dubbed Spinosaurus. But the fossils were completely destroyed during a World War II Allied bombing raid, leaving only drawings, questions, and a mystery: What was Spinosaurus?

In central China, a vast underground mausoleum conceals a life-size terracotta army of cavalry, infantry, horses, chariots, weapons, administrators, acrobats, and musicians, all built to serve China's first emperor, Qin Shi Huang Di, in the afterlife. Lost and forgotten for over 2,200 years, this clay army, 8,000-strong, stands poised to help the First Emperor rule again beyond the grave.

The first stage in human flight didn’t begin with the Wright brothers at Kitty Hawk, but with daring inventors and aeronauts in 18th century Paris. In a period of just 19 months, humanity not only left the ground for the first time but thanks to a handful of brilliant and colorful pioneers, developed all the essential features of today's hot air air and gas balloons.

When World War I began in 1914, the air forces of the opposing nations consisted of handfuls of rickety biplanes from which pilots occasionally took pot shots at one another with rifles. By the war’s end, the essential blueprint of the modern fighter had emerged: it was now an efficient killing machine that limited the average life expectancy of a front line pilot to just a few weeks.