Original version of This story Appears in Quanta Magazine.
At the beginning of time and at the center of each black hole, it is at a point of infinite density, called singularity. To explore these mysteries, we took our knowledge of space, time, gravity, and quantum mechanics and applied it to where all of this stuff simply decomposes. Maybe there is nothing in the universe to challenge imagination. Physicists still believe that if they can provide coherent explanations of strange things and what actually happens around them, then revelation will emerge, perhaps a new understanding of what space and time constitute.
In the late 1960s, some physicists speculated that singularity might be surrounded by a stirring and chaotic area where time and time grow and contract at will. Charles Misner of the University of Maryland called it the “Mixer Universe,” a popular kitchen utensil at the time. If the astronaut is about to fall into a black hole, “one can imagine it mixing the mixture or egg ere eggs together in a way that mixes the body parts of the astronaut, mixing the yolk and white together.”
Einstein’s general theory of relativity is used to describe the gravity of a black hole, which uses a single-field equation to explain the movement of space curves and matter. But the equation uses a mathematical shorthand called a tensor to hide 16 different interwoven equations. Several scientists, including Misner, have designed useful simplified assumptions that allow them to explore scenarios like the Mixmaster Universe.
Without these assumptions, Einstein’s equations would not be analyzed, even if they were too complicated for the numerical simulations at that time. Like the devices they named after, these ideas are outdated. These “dynamics should be very common phenomena of gravity,” said Gerben Oling, a postdoctoral researcher at the University of Edinburgh. “But it’s something that fell off the map.”
Over the past few years, physicists have been using new mathematical tools to revisit the chaos surrounding the singularity. Their goals are dual. One hope is to show that Misner and other proceedings are effective approximations of Einstein’s gravity. The other is to get closer to singularity, hoping that their extremes will help harmonize general relativity with quantum mechanics in quantum gravity theory, the goal of physicists for more than a century. As Sean Hartnoll of the University of Cambridge put it: “It’s time to ripen these ideas.”
The birth of the sound mix chaos
Thorne described the late 1960s as the “golden age” of black hole research. The term “black hole” is only widely used. In September 1969, during a visit to Moscow, Thorne was a manuscript awarded by the famous Ukrainian physicist Evgeny Lifshitz. Together with Vladimir Belinski and Isaak Khalatnikov, Lifschitz discovered a new solution that could use the assumptions designed by the three of them to achieve the singular Einstein’s gravity equation. Lifshitz was worried that Soviet censors would postpone the release of the results because it contradicted the early evidence he co-authored, so he asked Thorne to share it in the West.
Earlier black hole models assumed that perfect symmetry could not be found in nature, for example, a star is a perfect sphere and then poured into a black hole, or there was no net charge. (These assumptions led Einstein to solve Einstein’s equations in its simplest form shortly after Einstein’s publication.) The solutions found by Belinski, Khalatnikov and lifschitz found that after their initials were launched, it might constitute a more realistic situation in a mess. The result is not an internal smoothing of space and time, but a stroll through the ocean of space and time that stretches and compresses in multiple directions.
Thorne smuggled paper back to the United States and mailed a copy to Misner, knowing he was thinking along a similar line. It turns out that Misner and the Misner and Soviet Group independently used similar assumptions and different technologies to independently work on the same idea. More importantly, the BKL group “used it to solve the biggest unsolved problem of the era of mathematical relativity”, Thorne about the existence of so-called “universal” singularity. Belinski, the last surviving member of the BKL trio, recently said in an email that Misner’s vivid description in turn helped him imagine the chaos near the strange things they both revealed.
