Of the known fundamental forces, gravity stands out. Rather than being caused by force-carrying particles jumping between matter particles, gravity can be explained as the bending of space and time. In episode 13 of Subatomic Stories, Fermilab scientist Don Lincoln briefly sketches Einstein’s theory of general relativity — our current theory of gravity — and mentions some tests that prove that it’s right.

The inability of scientists to create a theory of quantum gravity arises from long-standing tensions between general relativity and quantum mechanics. There have been few approaches with any success. Don Lincoln explains one of the few promising ideas, called loop quantum gravity, in this 9-minute video.

Two cars, heading toward one another head-on at a velocity, have a closing velocity of twice that velocity. But at very high speeds, this intuition of adding velocities wrong. In this 9-minute video, Don Lincoln explains how to add velocities in a relativistic environment.

Relativity has many mind-bending consequences, but one of the weirdest is the idea that objects in motion get shorter. Bizarre or not, Don Lincoln explains just how it works in this 11-minute video.

In the famous twin paradox, one twin travels a great distance at the speed of light and returns, much younger than the other twin. Who is moving, and who isn’t? In this 13-minute video, Don Lincoln explains the perplexing puzzle.

Einstein’s special theory of relativity is notorious for being easy to misuse, with the result that sometimes result in claims of paradoxes. In this 11-minute video, Don Lincoln describes the commonly claimed time dilation paradox and shows how to resolve it.

Welcome to the first in a series by Don Lincoln on relativity. In this 12-minute video, he lays out what relativity is all about — not slow-moving clocks and shrinking objects, but instead on … well, watch and see.