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Cosmology# Hawking radiation

## What is Hawking radiation?

## Discovery of Hawking radiation

## Explanation

## Origin of Hawking radiation

## Formula

## Importance of Hawking radiation

In 1975, **Hawking** published a surprising result that said that, when **quantum theory** is taken into account, apparently **black holes** are not entirely black. He said that, on the contrary, these holes should shine a little with "**Hawking radiation**," which consists of **photons**, **neutrinos** and, to a lesser extent, all kinds of **massive particles**. This has never been observed, since the only black holes we are aware of are those with a lot of hot gas falling into them, whose radiation would completely bog down this small effect.

**Related topics**

Black hole, quantum gravity, event horizon

Hawking radiation is a theory that tries to explain to us how black holes are, like a black hole in space with a large amount of mass that is so concentrated that nothing could escape its gravity, not even its own light.

**Stephen Hawking’s** discovery and his radiation began with a very simple question: do **black holes** emit **heat**? Some time ago, it was determined that black holes were attached to the second law of **thermodynamics**, which means that **entropy** or the measure of disorder could only increase with time, and therefore, everything that has entropy must also have a temperature.

In the 1970s, Hawking, aided by **mathematics**, helped by mathematics, took the temperature of a black hole. He did this by mixing a series of ideas from **Einstein’s theory of relativity** and **quantum** **mechanics** which describes how the smallest components of the universe work.

These are the two main **theories** that seek to find the way the universe works and that have been sought by **scientists** for decades. And both theories come into play on the event horizon of a black hole, the limit beyond which **gravity** is so strong that not even light can **escape**.

This theory revolutionized the knowledge of **black holes**. Based on the **General Relativity** published by **Albert Einstein**, it was thought that nothing could escape the black holes. But **Hawking** claimed in 1975 that black holes were capable of emitting **radiation**, a phenomenon that was dubbed “**Hawking radiation**“.

It arises as a result between **general relativity** and **quantum mechanics** or quantum gravitation. This theory tells us that black holes are not entirely black, but on the contrary can emit **radiation**, which is what we know by the name of Hawking radiation.

There is not yet a **theory** about quantum gravity, but there is a first attempt to know what are the **quantum effects** on **particles** and **radiation** in space. Hawking related quantum concepts to general relativity in the study of black holes in 1975 and discovered an important relationship between **gravity** and **thermodynamics** that leads to Hawking radiation.

In addition, to understand Hawking radiation we must also understand that **vacuum** does not exist, and quantum mechanics is what tells us that vacuum is full of **virtual particles**. Virtual particles are exactly the same as **real ones**, with the only difference that they appear and disappear in very **short** **periods of time**.

And it is here where the **gravitational effect** of **black holes** intervenes. The intense force of gravity that exists near a black hole can create real **particles** from virtual particles.

One of the consequences of **Heisenberg’s uncertainty principle** is the **quantum fluctuations** of the vacuum which consist in the creation of **particle-antiparticle** pairs from vacuum. These particles are “**virtual**“, but the gravity of the black hole transforms them into **real ones**. Such pairs disintegrate each other and reintegrate the energy they borrowed for their formation.

But, there is a probability that one member of the pair will form on the **inside** and the other on the **outside**, causing one of the components of the pair to escape from the black hole. When the particle escapes, the **energy** will come from the black hole. Then the black hole will have to lose energy to compensate for the creation of the two particles it separated.

According to this theory, a black hole loses **mass**, at a rate inversely proportional to it, due to a **quantum effect**. It is worth mentioning that the decrease in mass of a hole by Hawking radiation can only be perceptible in **time scales** and only in microscopically sized **black holes** perhaps remaining from the time immediately after the **Big Bang**.

The formula is the main part for understanding black holes and represents the highest point in Hawking’s career, who worked with his colleague **Jacob Bekenstein**, connecting important **thermodynamic** units such as **entropy**, represented by the initial S, to the physical properties of a black hole, i.e., its **area** (A). The other letters that compose the formula are constants of the universe; k is the **Boltzmann constant**, c is the **speed** of **light**, ħ is the reduced **Planck constant** and G is the constant of **universal gravitation**.

It has been one of the most important achievements in the area of **physics** in the twentieth century because it has allowed to know more deeply the **theory** that explains the whole **universe**. The radiation emanating from **black holes** has been the theory that has challenged the common sense of thousands of scientists worldwide.

It has made it possible to secure **information** about black holes and plays an important **quantum** theory within the universe.

Written by Gabriela Briceño V.

Briceño V., Gabriela. (2019). *Hawking radiation*. Recovered on 8 March, 2023, de Euston96: https://www.euston96.com/en/hawking-radiation/