Time travel is not forbidden by the laws of nature, but to build a time machine, we would need to understand more about those laws and how to subvert them than we do now. And every day, science does learn more. In this film Horizon meets the scientists working on the cutting edge of discovery - men and women who may discover how to build wormholes, manipulate entangled photons or build fully functioning time crystals. In short, these scientists may enable an engineer of the future to do what we have so far been only able to imagine - to build a machine that allows us travel back and forward in time at the touch of a button. It could be you! Science fiction? Watch this film.

Genius lies somewhere in the human mind, bringing mathematical insight, sparking artistic inspiration and enabling some to see what most cannot. Might we augment our biology with technology to unlock the genius inside us all?

Boy or girl? It’s the eternal question. But that question may have more than two answers. Science reveals the line between male and female is blurred. And the battle of the sexes is happening deep within our cells. Are there more than two sexes?

We live under a billion unblinking eyes - a global surveillance system that solves crime and uncovers terrorist plots. But are we ready for a world without secrets - where not even our homes are off-limits and corporations know our every desire?

Hosted by Morgan Freeman, this series explores the deepest mysteries of existence. These questions have been pondered by the most exquisite minds of the human race. Now, science has evolved to the point where hard facts and evidence may be able to provide us with answers instead of philosophical theories. In the first episode of the season 7, terrorists, like any group, have a cause to rally around. But for them, the cause justifies the deliberate targeting of innocent civilians. How can they think that way? Now, science is peering into the dark heart of terror networks to find out why.

Every 17 minutes in America, someone is killed with a gun. Politicians can't seem to stop the violence. But epidemiologists, psychologists and big data crunchers are discovering that gun crime spreads like a virus -and science may be able to stop its spread.