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

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.

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?

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.

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.

Urban archaeologists dig for stories beneath city streets.

Vaccines work with our immune system to keep us from getting sick.

Vaccination began as a traditional therapy over a thousand years ago.

The polio vaccine's history extends more than fifty years.

Can new technology prevent aircraft like Flight MH370 from disappearing without a trace? Airing October 8 at 9 pm on PBS Please be advised The Boeing Company is a funder of the NOVA series. Please note, however, that no funds from Boeing were applied to this specific episode.

A new global geek squad is harnessing cryptography to stay a step ahead of cybercriminals. Airing September 24, 2014 at 9 pm on PBS

New technology may bypass the need to keep vaccines cold by stabilizing them with silk.

Aquanauts study the health of marine organisms—by becoming their neighbors.

Comets carrying chemicals necessary for life may have come to Earth billions of years ago.

NASA’s Kepler mission lets us search for planets orbiting stars outside our solar system.

Scientists discover evidence for the key ingredients for life on Saturn's moon Enceladus.

Human papillomavirus, or HPV, can cause cervical cancer. Bhutan is the first developing country to welcome the widespread vaccination of girls against HPV, and cervical cancer rates have dropped. Some countries have resisted the vaccine, but in Bhutan even the royal princess is onboard.

The world can be a dangerous place, full of foes large and little. Take deadly infectious diseases. Host David Pogue considers a new kind of vaccine that might save millions of lives, while eliminating the need for refrigeration and scary needles.

Dorothy Roseman describes her close encounters with vaccine-preventable diseases.

Science shows it’s a small world after all—and nature’s networks follow a similar pattern.