Weeks after the death of British physicist Stephen Hawking, his final research paper on the nature of our universe and its place in the wider multiverse was published today in the Journal of High-Energy Physics.
Now it’s up to his co-author, Belgian physicist Thomas Hertog, to keep an eye out for observational evidence for or against Hawking’s “Final Theory.”
The pre-print version of the paper — titled “A Smooth Exit From Eternal Inflation?” — has been circulating for months. It addresses the rather mind-blowing idea that our universe is merely one of the many possible manifestations in a multiverse.
Some theorists say universes could be spawning off each other eternally, creating a virtually infinite array of fractal possibilities. They say our universe just happens to be one of the manifestations where the laws of physics allow for stars, galaxies, planets and life.
Hawking and Hertog say the possibilities aren’t as infinite as those theorists would claim, because eternal inflation is bounded by a smooth, featureless, timeless state of existence.
“When we trace the evolution of our universe backwards in time, at some point we arrive at the threshold of eternal inflation, where our familiar notion of time ceases to have any meaning,” Hertog said in a news release.
The idea runs counter to Hawking’s previously held view that the history of the universe has no boundary. “Now we’re saying that there is a boundary in our past,” Hertog said.
If the hypothesis holds up, it would suggest that our universe is perhaps a little more special than the multiverse concept might otherwise imply.
“We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes,” Cambridge University quoted Hawking as saying before his death in March.
The “Final Theory” isn’t a slam-dunk, as indicated by the question mark in its title. Some scientists say there’s no way to subject the paper’s claims to observational tests, but Hertog insists it’s possible to find evidence backing up (or knocking down) the hypothesis.
“The most promising observable [phenomena], when it comes to our universe, are gravitational waves … that are probably generated at the big bang, basically,” he said in a video explaining the paper.
Hertog said details in the patterns of primordial gravitational waves could show whether Hawking’s Final Theory is on the right track. Such waves would have to have extremely long wavelengths, which means they’re beyond the range detectable by ground-based instruments such as the Laser Interferometer Gravitational-wave Observatory.
The European Space Agency’s Laser Interferometer Space Antenna, or LISA, “should be ideally suited to capture those gravitational waves from the big bang,” Hertog said.
But don’t hold your breath waiting for the answer: LISA isn’t scheduled to launch until 2034.