In Brief

Dying Stephen Hawking changed his mind about Big Bang theory

Famed physicist revised key idea shortly before his death in March

The final piece of work by Professor Stephen Hawking appears to heavily revise one of his most famous theories: that of endless multiple universes, each different from the last.

The newly published paper - completed ten days before the physicist’s death on 14 March, at the age of 76 - ditches the “no boundary theory” that he devised with fellow researcher James Hartle back in 1983. 

The pair proposed that prior to the Big Bang, there was space but no time. So the universe expanded from a single point when it began, but has no time boundaries, making it infinite.

This idea “resolved a difficulty with Einstein’s theory that suggested that the universe began nearly 14 billion years ago but said nothing about how it began”, says the BBC. Yet while Hawking and Hartle had “tied up one loose end”, the new theory created another, the broadcaster adds.

The “no boundary theory” implies that the Big Bang would have led to the creation of infinite universes, each exhibiting physical laws that differ from others.

But if the Big Bang were to birth an infinite number of possible universes, all with different laws of physics, most of them would be hostile to the stable existence of the matter that makes up stars, planets and human beings - and of physics itself as we know it.

As a result, it would remain impossible to explain why the physics of our own universe work as they do, given the variations that other universes may experience.

However, in his final paper, submitted to the Journal of High Energy Physics, Hawking and fellow physicist Thomas Hertog revised the theory, suggesting that the universe does have a boundary - which makes for a “simpler set of alternate universes”, The Times reports.

In the new theory, instead of space being filled with countless universes where entirely different laws of physics apply, these alternate universes may not actually vary that much from one another.

According to The Guardian, the new theory “may provide some comfort to physicists who wonder how, given all the hostile variations thought possible, we find ourselves in a universe well suited to life”.

“In the old theory there were all sorts of universes: some were empty, others were full of matter, some expanded too fast, others were too short-lived. There was huge variation,” Hertog explains. “The mystery was why do we live in this special universe where everything is nicely balanced in order for complexity and life to emerge?

“[The new theory] reduces the multiverse down to a more manageable set of universes which all look alike. Stephen would say that, theoretically, it’s almost like the universe had to be like this. It gives us hope that we can arrive at a fully predictive framework of cosmology.”

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