Secondly, a black hole formed from radiation emitted by another black hole, making the new black hole entangled with its “supplier”. Firstly, a pair of black holes created at the same time, making them entangled by default. The theory is that a wormhole is actually two black holes linked by quantum entanglement, which can arise in two different ways. Some have theorised that wormholes are linked by a concept known as quantum entanglement, where particles have linked behaviour even at great distances. Wormholes connect distant regions in a region in space-time which has a negative curvature, which can be kept open using matter with negative energy density. According to Professor Hawking, observations of the Universe have shown that it is not sufficiently warped, leaving only the third possibility valid - wormholes. In the bestselling book “A Brief History of Time” by the late Stephen Hawking, three means of time travel were proposed, firstly in a universe where space-time is sufficiently warped, secondly if one travels faster than light and lastly if one is able to travel through a moving wormhole. Time travel has always captured the popular imagination.