PAUL E. ALERS/NASA
Physicist Stephen Hawking was one of few scientists to achieve nearly rock-star status. Some scientists considered him a black-hole whisperer for his efforts to divine the secrets of the most mysterious objects of the cosmos. And the public revered him, even if most people couldn’t quite comprehend the physics that kept this scientist busy throughout the decades. But that remarkable career ended today. The 76-year-old physicist died in Cambridge, England.
In one of his best-known discoveries, Hawking determined that black holes are not truly black. Instead, they emit a faint haze of particles. Those particles came to be known as Hawking radiation. This discovery arose at the boundary of gravity and quantum mechanics. And it had remarkable impacts. It suggested that black holes do not live forever. Eventually they must blink out of existence.
But that claim also led to a puzzle known as the “black hole information paradox.” It essentially holds that when a black hole disappears, all of the information that had fallen into it could be lost. And that should not be. As Science News writer Andrew Grant explained in a May 31, 2015 story: Losing that information “violates a central tenet of quantum mechanics: Information cannot be destroyed. Physicists could accept that all the properties of all the particles within a black hole were locked up, forever inaccessible to those outside a black hole . . . But they were not OK with [that information] vanishing without a trace.”
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In a presentation at the KTH Royal Institute of Technology in Stockholm, Sweden, on August 25, 2015, Hawking and two of his colleagues described a possible solution. They proposed that the information about matter that falls into a black hole is actually stored in a boundary area. This boundary is the so-called event horizon that surrounds a black hole. Within that event horizon, not even light can escape a black hole’s grasp. “A layer of light called a hologram slides along the event horizon,” Grant reported at the time. He quoted physicist Andrew Strominger at Harvard University in Cambridge, Mass., as saying: The information is “stuck there, as if it were rowing upstream and getting nowhere.” Strominger was one of Hawking’s collaborators.
Hawking had been a professor at the University of Cambridge. He also wrote a series of popular science books, including a best seller: A Brief History of Time. In clear language, the book described how the universe was born and explained the laws of physics that rule all celestial objects within it.
At age 21, Hawking developed amyotrophic lateral sclerosis (AY-my-oh-TROH-fik LAT-er-ul Sklair-OH-sis), or ALS. It's a debilitating nerve-and-muscle disease. And it left him wheelchair-bound since before he turned 30. Eventually, Hawking would communicate by typing into a machine that spoke his words for him. Few people with ALS survive nearly as long Hawking did. He would go on to use his considerable influence to promote the rights of others with disabilities.
This scientist will be remembered, too, for his sense of humor. It prompted him to sometimes appear as himself on popular television comedies, including The Simpsons and The Big Bang Theory.
Throughout a remarkable career, Hawking let the world know that his disability would not define him. His science would.
amyotrophic lateral sclerosis A disease that attacks and progressively kills motor nerve cells over time. These cells control the movements of many muscle groups. As the motor nerve cells die, people with ALS lose their ability to speak, walk and swallow. ALS sometimes is also called Lou Gehrig’s disease after the 36-year-old baseball player who was stricken with this disease in 1939.
black hole A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.
celestial (in astronomy) Of or relating to the sky, or outer space.
celestial object Any naturally formed objects of substantial size in space. Examples include comets, asteroids, planets, moons, stars and galaxies.
colleague Someone who works with another; a co-worker or team member.
cosmology The science of the origin and development of the cosmos, or universe. People who work in this field are known as cosmologists.
cosmos (adj. cosmic) A term that refers to the universe and everything within it.
event horizon An imaginary sphere that surrounds a black hole. The more massive the black hole, the bigger the sphere. Anything that happens inside the event horizon is invisible, because gravity is so strong that under normal circumstances even light can’t escape. But according to some theories of physics, in certain situations small amounts of radiation can escape.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
Hawking radiation The particles emitted from the event horizon on the outer edges of a black hole. Energy can be converted into a pair of particles. If that happens very close to outer edge of a black hole, one of those particles can tunnel out and become detected — providing the only direct physical clue to the black hole’s presence. These emissions are called Hawking radiation for Stephen Hawking, the famous British physicist who came up with the idea that black holes can emit particles.
haze Fine liquid or solid particles scattered through the atmosphere that make it hard to see. Haze can be caused by harmful substances such as air pollutants or by water vapor.
hologram An image made of light and projected onto a surface, depicting the contents of a space.
information (as opposed to data) Facts provided or trends learned about something or someone, often as a result of studying data.
information paradox (in physics) A problem created by two conflicting ideas about how black holes work and how the universe works. Black holes eventually disappear, and presumably, the information they contain about what’s in them also disappears. But this disappearance breaks a law of quantum mechanics, which says that information is never “lost” to the universe.
mass A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
matter Something that occupies space and has mass. Anything on Earth with matter will have a property described as "weight."
mechanics The study of how things move.
muscle A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.
nerve A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.
paradox An idea or a statement that is true, but that seems logically impossible.
particle A minute amount of something.
physicist A scientist who studies the nature and properties of matter and energy.
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
quantum (pl. quanta) A term that refers to the smallest amount of anything, especially of energy or subatomic mass.
quantum mechanics A branch of physics dealing with the behavior of matter on the scale of atoms or subatomic particles.
radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
tenet An underlying idea, principle or belief — as in something generally believed to be true.
theoretical An adjective for an analysis or assessment of something that based on pre-existing knowledge of how things behave. It is not based on experimental trials. Theoretical research tends to use math — usually performed by computers — to predict how or what will occur for some specified series of conditions. Experimental testing or observations of natural systems will then be needed to confirm what had been predicted.
theory (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.
universe The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).