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Stephen Hawking: Cosmologist of Black Holes
Hawking radiation and the nature of space-time
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Stephen Hawking was a British physicist and cosmologist whose work changed how scientists think about black holes, the universe, and the connection between gravity and quantum physics. He is especially known for predicting that black holes are not completely black, but can emit a tiny amount of radiation now called Hawking radiation. His life and career also showed extraordinary perseverance after he was diagnosed with ALS in his early twenties. Through research, books, lectures, and media appearances, he helped make some of the deepest ideas in physics familiar to millions of people.
Hawking's most famous scientific result came from applying quantum field theory near the event horizon of a black hole. In this picture, quantum effects allow black holes to lose energy very slowly, so their mass can decrease over time. This idea connected thermodynamics, quantum mechanics, and general relativity, three major pillars of modern physics. His work also influenced studies of the Big Bang, singularities, the arrow of time, and the search for a theory that unifies gravity with quantum physics.
Key Facts
- Stephen Hawking lived from 1942 to 2018 and became one of the most recognized scientists of the modern era.
- The Schwarzschild radius of a nonrotating black hole is Rs = 2GM/c^2.
- Hawking radiation gives a black hole a temperature T = ħc^3/(8πGMkB).
- Black hole entropy is proportional to event horizon area: S = kB c^3 A/(4Għ).
- A larger black hole has a lower Hawking temperature because T is proportional to 1/M.
- A Brief History of Time, published in 1988, brought cosmology, black holes, and the origin of the universe to a wide public audience.
Vocabulary
- Black hole
- A region of space where gravity is so strong that nothing, not even light, can escape from inside its event horizon.
- Event horizon
- The boundary around a black hole beyond which escape is impossible for matter or light.
- Hawking radiation
- The predicted thermal radiation emitted by black holes because of quantum effects near the event horizon.
- General relativity
- Einstein's theory that describes gravity as the curvature of spacetime caused by mass and energy.
- Cosmology
- The scientific study of the origin, structure, evolution, and large-scale behavior of the universe.
Common Mistakes to Avoid
- Thinking black holes suck in everything nearby, because objects far from a black hole orbit it according to gravity just as they would orbit any object with the same mass.
- Assuming Hawking radiation is bright for large black holes, because stellar-mass and supermassive black holes have extremely low temperatures and radiate very weakly.
- Confusing the event horizon with the singularity, because the event horizon is a boundary while the singularity is the central region where classical general relativity predicts extreme curvature.
- Treating Hawking's ALS as the reason for his scientific importance, because his lasting scientific legacy comes from his research in black holes, relativity, cosmology, and quantum gravity.
Practice Questions
- 1 Calculate the Schwarzschild radius of a black hole with mass 2.0 x 10^30 kg using Rs = 2GM/c^2, G = 6.67 x 10^-11 N m^2/kg^2, and c = 3.00 x 10^8 m/s.
- 2 A black hole has 10 times the mass of another black hole. Using T = ħc^3/(8πGMkB), how does its Hawking temperature compare to the smaller black hole's temperature?
- 3 Explain why Hawking radiation is important for attempts to connect quantum mechanics, thermodynamics, and general relativity.