Documentary 2015| Uuniverse Documentary | Time Travel | BBC Documentary,
ou’re going forward. Finding a way to travel backwards requires breaking the speed of light, which so far seems impossible. But now, strange-but-true phenomena such as quantum nonlocality, where particles instantly teleport across vast distances, may give us a way to make the dream of traveling back and forth through time a reality. Step into a time machine and rewrite history, bring loved ones back to life, control our destinies.

But if we succeed, what are the consequences of such freedom? Will we get trapped in a plethora of paradoxes and multiple universes that will destroy the fabric of the universe? Einstein said that nothing travels faster than the speed of light, but when physicists look at how entangled particles behave, they get stuck in a mirage in which that tenet appears not to be true.

Physicists don't fully understand entanglement, beyond it being a relationship between particles. If you want to know what entanglement looks like, pull up a chair to an experiment that has produced it. Researchers at the University of Nice-Sophia Antipolis and the University of Geneva shone a laser made of photons, the basic units of light, into the crystal. When the laser's photons hit irregularities in the crystal, single photons sometimes split into two. These daughter photons were related to one another, and to their parent photon, in how much energy they had.

You can think of the parent photon as being like a train, and the crystal like many bumps. When the train hit the bumps, it broke into two chains of cars with related directions and speeds. These daughter photons weren't just related, but entangled. Particles are entangled if they're related in one property but random in the rest.