Eli5 how does Hawking radiation works?


What’s the mechanism behind it?

What’s the actual conversion process of mass to light or heat energy?

In: 0

This is VERY simplified but bear with me

So the understanding is that there are always pairs of particles and antiparticles popping in and out of existence. Normally they just annihilate each other since their charges cancel out. However, at the edge of a black hole since gravity is so strong, under the right circumstances the negative side of the pair falls into the black hole and the positive gets ejected into space. Since the antiparticle has negative energy this “subtracts” energy from the black hole.

So there are 2 ways to look at this: the layman particle – antiparticle way, and the correct way. Lets start with some basics that lead to the layman explanation.

**Heisenberg uncertainty principle**

The HUP is usually expressed as the fact that you cant know the exact position and momentum of a particle at the same time, there is always some uncertainty that is unrelated to technology and is instead is fundamental. We can also use the HUP to show that energy and time have this same uncertainty. This means on very short time scales we cant know exactly how much energy a particle(or field) has.

**Quantum Fields**

When referencing the HUP we talked about particles but in modern physics we actually mean excitation in fields. This seems a little weird but there is only a little we need to take from this. A field is just an area where some particle has the potential to exist, with the probability of finding said particle is proportional to the value of the field at that location. Due to the HUP though we know that there is never a exact location where this particle is and therefore there is also never a exact value of the field. So even in empty space these fields will not have 0 value and instead fluctuate.

**Virtual Particles**

Combining the idea from HUP that energy on small time scales is uncertain and the concept of particles are just excitations of a field we now get virtual particles. VP are just a result of very short lived random fluctuations of quantum fields. Due to conservation laws these VPs must come in particle/antiparticle pairs.

**The Layman explanation**

The layman explanation to Hawking Radiation comes from looking at the universe as an accountant doing an audit would. There is one underlying thing we care about in our audit: conservation of energy. So lets say at time T1 we audit the universe and see that there are 100 particles and nothing else. Then at T2 we audit the universe and see that there are now 50 particles and 1 black hole. We can infer through conservation of energy that 50 of the former particles are now inside the event horizon of the black hole. If at T3 we audit and find 51 particle and a black hole then our only explanation for this is that 1 particle has left the black hole. But nothing can escape the event horizon so how can this be?

The layman explanation says that virtual particles near the black hole are coming into and out of existence and sometimes 1 will fall in and the other will escape. Since we care about conservation above all else we say the antiparticle fell in and the “real” particle escaped. The anti particle then decreases the energy of the black hole to balance our need for conservation.

That is the layman explanation and unfortunately it is completely wrong and has a few major problems.


1. Hawking Radiation is mostly photons which are their own antiparticle, so whichever one falls in doesn’t matter at all.

2. Hawking Radiation doesn’t come just from the event horizon it can come from fairly far away.

3. There should be no biased to which virtual particle falls and which escapes. And anti particles don’t have negative energy anyway.

4. The big one, virtual particles aren’t real. They have never been observed and couldn’t be observed. They are a math trick. It would be like adding 1 apple to a group of 4 apples and asking where the plus sign is in the real world.


In reality Hawking Radiation comes from looking at quantum fields in curved spacetime rather than flat spacetime that we are used to. This is far to complex to explain to even an undergrade in physics.