The Science of Black Holes: Hawking Radiation Explained


Black holes are one of the most intriguing features of our universe. They were originally predicted by the equations in Einstein’s theory of general relativity in 1915. Many scientists doubted the existence of black holes throughout the 20th century, assuming they were merely a mathematical glitch in an incomplete theory. However, modern physicists almost unanimously accept that black holes exist. In fact, current theories in cosmology posit that supermassive black holes are at the center of almost every major galaxy.

For decades scientists assumed that once matter passes beyond the event horizon, it’s trapped inside the black hole for eternity. According to a quantum physics theory developed by Stephen Hawking, that may not be the case after all.

Is It Possible for Matter to Escape a Black Hole?

Nothing can escape a black hole in the conventional sense. The reason they’re called black holes is because not even light moves fast enough to escape their gravitational pull – the event horizon is a literal sphere of blackness. Since nothing in the universe can travel faster than light, it’s impossible for anything to move fast enough to escape the gravity of a singularity.

However, physicist Stephen Hawking developed a theory known as “Hawking radiation” that demonstrates how black holes can actually lose mass and evaporate. This theory is now widely accepted in the theoretical physics community.

Virtual Particles and Anti-Particles

Quantum field theory predicts that throughout the entirety of space there are pairs of virtual particles and anti-particles that briefly spring into existence. Due to their opposite charges, the virtual particle pairs quickly annihilate each other back out of existence. The scale on which this happens is unimaginably small: virtual particles are billions of times smaller than a single atom, and they generally exist for less than a nanosecond before they detonate themselves out of reality.

Hawking Radiation in Action

If two virtual particles spring into existence on the very edge of a black hole’s event horizon, one particle can fall in while the other slingshots away before annihilation occurs. The second particle is as close to the horizon as physically possible without falling in, so it winds up partially orbiting the black hole before being slung off into space.

However, the conservation of energy still applies: energy cannot be created or destroyed within our universe. That means the black hole must lose a bit of mass equivalent to the mass of the escaping particle that was newly created. The black hole basically substitutes one of its own particles for the virtual particle that got away.

It’s one of the many weird, counter-intuitive predictions of quantum mechanics. Essentially, the black hole is radiating subatomic particles, but since those particles originate on the very edge of the event horizon, they don’t have to violate the universal speed limit of light to escape. It turns out black holes may not be entirely black after all.

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