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.

Bitcoin, the beautiful anonymity of cash, but cash that wasn't printed by governments. Instead, it was made by a bit of code, powered by citizens of the internet, and you could trust it. Today, anyone can buy cryptocurrency. A few signups, type in your credit card number, and trade in your money for digital cash. And with a few more steps, you can use Bitcoin to buy what the majority of Bitcoin is spent on: Illegal services. Virtual currencies can pose challenges for law enforcement, given the appeal they have among those seeking to conceal.
Is digital cash the next revolution? Learn about this anonymous currency and why it's so coveted.

Scientists on the BICEP and Planck missions are attempting to solve a mystery about the earliest moments of our universe, by searching for patterns in the Cosmic Microwave Background (CMB). If successful, the missions will help to answer the biggest question anyone can ask: how did our universe begin?

On November 25th, 1915, Einstein published his greatest work: General Relativity. The theory transformed our understanding of nature’s laws and the entire history of the cosmos, reaching back to the origin of time itself. Now, in celebration of the 100th anniversary of Einstein’s achievement, discover the inside story of Einstein’s masterpiece". The story begins with the intuitive thought experiments that set Einstein off on his quest and traces the revolution in cosmology that is still playing out in today’s labs and observatories. Discover the simple but powerful ideas at the heart of relativity, illuminating the theory—and Einstein’s brilliance—as never before. From the first spark of an idea to the discovery of the expanding universe, the Big Bang, black holes, and dark energy, NOVA uncovers the inspired insights and brilliant breakthroughs of “the perfect theory.”

In the concluding episode of the series, Jim encounters ever larger cosmic structures to reveal the latest breakthroughs in our understanding of the universe. For example, Jim comes face to face with our galactic home, the Milky Way, a monstrous structure sculpted by the gravitational forces of dark matter. Jim finds out from pioneering researcher Adrian Fabian about the black hole at its centre, whose strange behaviour includes emitting the lowest note that can be heard in the cosmos.
At an even greater scale, Jim encounters huge structures such as the Laniakea Supercluster, of which the Milky Way is only a tiny part. Then there’s the 'Giant Arc', a collection of galaxies that account for more than three per cent of the observable universe. Jim learns from its discoverer, British PhD student Alexia Lopez, that this gargantuan structure is forcing scientists to reassess their theory of how the universe evolves and may overturn some of the most fundamental principles in physics.

Facebook is a company that has grown from nothing to be worth half a trillion dollars in just 15 years. Today nearly a third of all humans are using it, and yet we rarely get to see the people actually in charge of the biggest social network in the world.
The company has suffered a series of deepening scandals and intense media scrutiny. In 2018, their mission - to connect everyone on the planet - seemed to be going dramatically wrong. Data leaks, fake news and hacks on user security were threatening to destroy everything Mark Zuckerberg had built.
Yet throughout this difficult time, the company allowed the filmakers to follow key members of the team trying to fix the problems and secure the platform. This film goes behind the scenes and follows the teams inside Facebook. It tackles difficult questions, like how our data is used and what content should and shouldn’t be on the site, but also shows how Facebook works, what the teams are doing to secure it, and reveals a hidden technological playground, where some of the smartest engineers in the world are being hired to build systems and technology no one has built before.