5 THEORIES SCIENTISTS ARE UNSURE ABOUT

1 INFORMATION PARADOX

Hawking believed that information about the basic properties of the material that made a black hole is stored in a cloud of zero-energy particles surrounding it. This is one of several hypotheses that have been put forward about black holes’ lost material.

2 PRIMORDIAL BLACK HOLES AND DARK MATTER

Hawking was the first person to explore the theory behind black holes that were created soon after the Big Bang in depth. He said that these black holes might make up the mysterious dark matter that astronomers believe permeates the universe.

3 THE MULTIVERSE

Hawking wasn’t happy with the suggestion made by some scientists that any ludicrous situation you can imagine must be happening right now somewhere in one of an infinite number of universes. Instead he proposed a novel mathematical framework that rendered the universe finite.

4 CHRONOLOGY PROTECTION CONJECTURE

Hawking was bothered by the fact that Einstein’s equations allowed backward time travel because he felt that it raised logical paradoxes that shouldn’t be possible. He suggested that some currently unknown law of physics prevents these ‘closed timelike curves’ from occurring – his so-called ‘chronology protection conjecture’.

5 DOOMSDAY PROPHECIES

In his later years, Hawking made a series of bleak prophecies concerning the future of humanity that he may or may not have been totally serious about. These range from the suggestion that the elusive Higgs boson might trigger a vacuum bubble that would gobble up the universe to hostile alien invasions and artificial intelligence (AI) takeovers.