What is Hawking Radiation?
To put it simply: It’s the radiation emitted from a Black Hole and it was, as the name suggests, discovered by Stephen Hawking.
History is not everything but its a start! -John Henrick Clarke
So, let’s see what history has in store for us…
It all started in 1972 when Jacob Beckenstein theorized that Black Holes should have Entropy. So, maybe you’re asking yourself… What is Entropy?
Entropy is a part of thermodynamics and it basically states that Everything must release heat. Unless it is at 0 degree kelvin( -273 degrees celsius). Now this includes a Black Hole. But as we’ve known that black holes have always appeared to absorb things! It never releases things… Even the light coming out undergoes a high degree of redshift due to which the frequency falls below the visible spectrum!
But Jacob thought that there should be some heat still leaving it according to Thermodynamics! This led Stephen Hawking, in 1973, to go to Moscow to meet 2 Soviet Scientists (Sorry I don’t remember their names :P ). They showed Stephen Hawking that Black Holes should be emitting particles according to the Uncertainty Principle (I’ll write about that in future). This led Stephen Hawking in 1974 to publish his paper on Hawking Radiation! Also known as Black Hole Evaporation!
So, that’s it! Enough of history! Now let’s dig into the Physics of it all…
Lets start off with Quantum Physics! It is a field that is often regarded to be a sort of difficult field a.k.a the field that doesn’t make any sense!
“If you think you understand Quantum Mechanics, you don’t understand Quantum Mechanics!” - Richard Feynman
Quantum Mechanics is the physics of everything that is really very very small… Like electrons, atoms, photons etc.
On the other hand General Relativity is for everything BIG! Like Black Holes, stars, planets etc.
Quantum Mechanics appears to be very real…
Stephen Hawking was trying to find a way to demonstrate a Black Hole in the Quantum World!
So, basically, he wasn’t looking at the BIG planets that are being sucked in by the Black Hole….
…. He was rather looking at the tiny little particles and how they interact with the Black Hole. Since General Relativity couldn’t explain why radiation should be coming out of a Black Hole, maybe Quantum Physics could! And most importantly, HE WAS RIGHT!
Stephen Hawking was looking at the specific quantum event called Virtual Particles. Bear with me as I try to explain…
Let’s start off with some basic math…
Let’s think about 0 (zero). 0 is basically nothing, right? And, there are many ways to make 0…
0=0
Let’s play around…
0=1–1 => This is still true and legit!
What you just read is basically what is happening with our Virtual Particles! In our example, 0 was empty. Now, emptiness, when you think about it is something void of everything! I mean there’e nothing in it… But just like 0 also, in space, there are these things called Virtual Particles. These are basically particles of Matter and Anti-Matter!
They’re constantly being created and destroyed immediately! If this doesn’t baffle your mind, then you are devoid of emotions!
A particle of matter appears… and a particle of anti-matter appears. The moment they appear, they also collide and send matter as 1 and anti-matter as -1. They simply annihilate themselves! Just like in our little example… 0=1–1.
Now the reason this can work and doesn’t violate Law of Conservation of Mass, is because anti-matter is the opposite of matter. So, with both of them being created, there is an equal amount of matter and anti-matter, which implied they are literally creating nothing!
For those who are wondering about antimatter…
Anti-Matter is just matter. Only, it is completely opposite! Like, the antimatter equivalent of an electron is a positron! Yeah, it’s positive.
So, what happens when antimatter hits a piece of matter? They annihilate themselves!
Now that we know about Virtual Particles, let’s think about Black Holes!
It’s just a massive cosmic entity that absorbs anything that comes close enough to it!
When scientists directly observe the center of a black hole, they see nothing! This is due to the high degree of redshifting of light. Now, Black Holes, as defined by general relativity, will just keep absorbing and absorbing and just get bigger and bigger!
But that picture changes with Hawking Radiation! Now I strongly recommend you to read this post on the Event Horizon before trying to understand what Hawking Radiation actually is!
The Event Horizon Revamped!
It is the boundary marking the limits of a black hole. With that out of the way, here’s the big question…
How are these so called “Hawking Radiations” able to escape something that even light cannot?
All the physics I just explained is now gonna come together !!!
So what happens is right at the Event Horizon, a virtual particle pair appears. And because of the massive force of the black hole, one of the particles gets sucked into….
….and the other one manages to escape!
So from an outsider’s point of view, one would see particles being radiated out of the black hole! In fact, they are not actually coming out of the Event Horizon, they are actually being created right at the side of the Event Horizon…. and they are seemingly shooting out!
The more these virtual particles pairs, the smaller it will get! Which is why it is also called Black Hole Evaporation. So if a black hole is big enough, it is obviously absorbing a whole lot of things. These radiating particles will be very minor when compared to the massive amount of things it is absorbing. But if it’s a smaller black hole, then that means that it will actually be radiating more than it is absorbing! Which in turn implies that over time, the black hole will get smaller and smaller until eventually it just disappears!
Phew….
That means the black hole, contrary to what general relativity says, if it is small enough to start with, will get smaller and smaller and smaller….
….Until it is gone completely!
And THAT, my friend, is HAWKING RADIATION!!!
Well, here’s one thing that must be bothering you…
Why is it that only the Anti-Matter gets sucked into the Black Hole?
The answer to this is that Virtual particle pairs don’t quiet appear out of nothing! Don’t forget that this is Quantum Mechanics! So things are bound to get weird o.0
When Matter and Anti-Matter collide and annihilate themselves, they release ENERGY! Because even though they are opposites, they’re both still made out of energy. So, the thing is, where does that energy come from? It actually is empty space but that energy that is used to create this particle of matter and this particle of anti-matter, is actually energy taken from the black hole’s potential gravitational energy! So does this crazy fact fit into the puzzle called Hawking Radiation?
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