The idea of a multiverse fascinates physicists as much as sci-fi fans, but if science was able to prove it exists, could every type of universe within it actually be predicted? The late Stephen Hawking believed there was a way to shed light on this cosmic mystery.
Hawking’s final paper, published in the journal High-Energy Physics revisits one of his earlier (and no less mind-blowing) theories. The “no-boundary proposal” considers Einstein’s suggestion that the pre-Big Bang universe was a singularity, an extremely dense and hot micro-speck of matter where the laws of physics didn’t apply. Hawking speculated that time as we know it was nonexistent in this singularity, which had no beginning and no end—infinite and spherical rather than finite and linear. The embryonic universe is thought to have expanded rapidly and spawned parallel worlds during a period known as cosmic inflation.
Something this unfathomable to the human brain eventually made Hawking want to quantify it. Infinite universes open portals to infinite possibilities, but that paradoxically means that there can be no accurate way to test theories about the origins of our own universe or its future. He and physicist Thomas Hertog set out to put theoretical boundaries on his own no-boundary proposal by trying to isolate every unique type of universe that may be floating out there.
"Hawking was not satisfied with this state of affairs," Hertog, who co-authored that paper with Hawking, said to Live Science. "'Let's try to tame the multiverse,' he told me a year ago. So, we set out to develop a method to transform the idea of a multiverse into a coherent, testable scientific framework."
Holography, the idea that three-dimensional information is encrypted on a two-dimensional surface, was ultimately what Hawking and Hertog used to find a connection between Einstein’s theoretical singularity and our universe, which supposedly emerged from it. Some physicists are convinced we live in a holographic universe. They reconciled the wild quantum physics of that singularity with the classical laws of physics that make understanding the behavior of the cosmos possible. Determining a finite number of universes that exist in the multiverse means that the nature of those universes can be predicted.
Before proving that other worlds lurk somewhere in time and space, we still need evidence of a multiverse. Traces of primordial gravitational waves from the Big Bang linger all over the universe in the cold microwave radiation known as the cosmic microwave background (CMB). If an advanced enough satellite ever beams back a CMB energy signal that aligns with Hawking’s model of cosmic inflation, it could mean the multiverse is more than just an element of science fiction.
While more science will be needed to back up Hawking and Hertog’s theory, just the possibility of being a life-form in one of many universes is a thought to keep you up at night.