Stephen Hawking's black hole theory proved right

New study analyzes gravitational waves to confirm the late Stephen Hawking's black hole area theorem.

Stephen Hawking's black hole theory proved right

Model of spiraling black holes that are merging with each other.

Credit: NASA's Goddard Space Flight Center
  • A new paper confirms Stephen Hawking's black hole area theorem.
  • The researchers used gravitational wave data to prove the theorem.
  • The data came from Caltech and MIT's Advanced Laser Interferometer Gravitational-Wave Observatory.

The late Stephen Hawking's black hole area theorem is correct, a new study shows. Scientists used gravitational waves to prove the famous British physicist's idea, which may lead to uncovering more underlying laws of the universe.

The theorem, elaborated by Hawking in 1971, uses Einstein's theory of general relativity as a springboard to conclude that it is not possible for the surface area of a black hole to become smaller over time. The theorem parallels the second law of thermodynamics that says the entropy (disorder) of a closed system can't decrease over time. Since the entropy of a black hole is proportional to its surface area, both must continue to increase.

As a black hole gobbles up more matter, its mass and surface area grow. But as it grows, it also spins faster, which decreases its surface area. Hawking's theorem maintains that the increase in surface area that comes from the added mass would always be larger than the decrease in surface area because of the added spin.

Will Farr, one of the co-authors of the study that was published in Physical Review Letters, said their finding demonstrates that "black hole areas are something fundamental and important." His colleague Maximiliano Isi agreed in an interview with Live Science: "Black holes have an entropy, and it's proportional to their area. It's not just a funny coincidence, it's a deep fact about the world that they reveal."

The research team based their conclusions on the data from the gravitational waves spotted by Caltech and MIT's Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015.

What are gravitational waves?

Gravitational waves are "ripples" in spacetime, predicted by Albert Einstein in 1916, that are created by very violent processes happening in space. Einstein showed that very massive, accelerating space objects like neutron stars or black holes that orbit each other could cause disturbances in spacetime. Like the ripples produced by tossing a rock into a lake, they would bring about "waves" of spacetime that would spread in all directions.

As LIGO shared, "These cosmic ripples would travel at the speed of light, carrying with them information about their origins, as well as clues to the nature of gravity itself."

The gravitational waves discovered by LIGO's 3,000-kilometer-long laser beam, which can detect the smallest distortions in spacetime, were generated 1.3 billion years ago by two giant black holes that were quickly spiraling toward each other.

What Stephen Hawking would have discovered if he lived longer | NASA's Michelle Thaller | Big Think

Confirming Hawking's black hole area theorem

The researchers separated the signal into two parts, depending on whether it was from before or after the black holes merged. This allowed them to figure out the mass and spin of the original black holes as well as the mass and spin of the merged black hole. With this information, they calculated the surface areas of the black holes before and after the merger.

"As they spin around each other faster and faster, the gravitational waves increase in amplitude more and more until they eventually plunge into each other — making this big burst of waves," Isi elaborated. "What you're left with is a new black hole that's in this excited state, which you can then study by analyzing how it's vibrating. It's like if you ping a bell, the specific pitches and durations it rings with will tell you the structure of that bell, and also what it's made out of."

The surface area of the resulting black holes was larger than the combined area of the original black holes. This conformed to Hawking's area law.

    Every 27.5 million years, the Earth’s heart beats catastrophically

    Geologists discover a rhythm to major geologic events.

    Credit: desertsolitaire/Adobe Stock
    Surprising Science
    • It appears that Earth has a geologic "pulse," with clusters of major events occurring every 27.5 million years.
    • Working with the most accurate dating methods available, the authors of the study constructed a new history of the last 260 million years.
    • Exactly why these cycles occur remains unknown, but there are some interesting theories.
    Keep reading Show less

    Babble hypothesis shows key factor to becoming a leader

    Research shows that those who spend more time speaking tend to emerge as the leaders of groups, regardless of their intelligence.

    Man speaking in front of a group.

    Credit: Adobe Stock / saksit.
    Surprising Science
  • A new study proposes the "babble hypothesis" of becoming a group leader.
  • Researchers show that intelligence is not the most important factor in leadership.
  • Those who talk the most tend to emerge as group leaders.
  • Keep reading Show less

    The first three minutes: going backward to the beginning of time with Steven Weinberg (Part 1)

    The great theoretical physicist Steven Weinberg passed away on July 23. This is our tribute.

    Credit: Billy Huynh via Unsplash
    • The recent passing of the great theoretical physicist Steven Weinberg brought back memories of how his book got me into the study of cosmology.
    • Going back in time, toward the cosmic infancy, is a spectacular effort that combines experimental and theoretical ingenuity. Modern cosmology is an experimental science.
    • The cosmic story is, ultimately, our own. Our roots reach down to the earliest moments after creation.
    Keep reading Show less
    Surprising Science

    Ancient Greek military ship found in legendary, submerged Egyptian city

    Long before Alexandria became the center of Egyptian trade, there was Thônis-Heracleion. But then it sank.