How Stephen Hawking's Theorem Was Finally Verified
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Chapter 1: Understanding Hawking’s Theorem
A few years back, the theories first proposed by Stephen Hawking regarding black holes received confirmation, leading to the theorem being named after him. But what does this theorem entail, and how was it validated? Let's delve into the details.
Hawking’s Theorem Explained
In 1971, Stephen Hawking articulated one of the key principles of black hole physics, which states that the area of a black hole's event horizon—the boundary beyond which nothing can escape—can never decrease. This idea laid the groundwork for a new field of study in the early 1970s known as black hole thermodynamics.
In collaboration with James Bardeen and Brandon Carter, Hawking co-authored the seminal paper titled “The Four Laws of Black Hole Mechanics,” outlining four essential characteristics of black holes:
- Zeroth Law: The surface gravity at the event horizon remains constant.
- First Law: This law details the interrelation between variations in mass, event horizon area, angular momentum, and charge when external forces act on a black hole.
- Second Law: This is Hawking’s theorem, which maintains that the area of the event horizon cannot decrease.
- Third Law: It asserts that it is impossible to lower the surface gravity at the event horizon to zero.
The four laws of black holes serve as analogs to the laws of thermodynamics, correlating temperature with surface gravity, energy with mass, and entropy with the area of the event horizon.
Chapter 2: Verifying Hawking’s Theorem
How was Hawking's Theorem Confirmed?
While Hawking's theorem is relatively straightforward to demonstrate mathematically, practical verification has posed significant challenges, which is why it remained unverified for 50 years. Recently, researchers from the Massachusetts Institute of Technology and other institutions successfully confirmed Hawking's theorem regarding event horizon area through gravitational wave observations. Their findings were published in the journal Physical Review Letters and included data from the first gravitational wave signal known as GW150914, detected in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO). This signal was produced by the merger of two black holes.
According to Hawking's theorem, the area of the event horizon of the new black hole formed from this merger should be at least as large as the combined areas of the event horizons of the original black holes. In their recent study, the physicists evaluated the gravitational wave signal from GW150914 before and after the merger. They determined that the total area of the event horizons of the two original black holes was 235,000 square kilometers. In contrast, the newly formed black hole's event horizon area measured 367,000 square kilometers, with a 95% confidence level, implying only a 5% chance of error. This strongly corroborates Hawking's theorem.
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