The Bookwyrm

I just took the ACT. 

I think I did good.

BUT THAT'S IRRELEVANT!

I'm going to do a Fadran style post and rant about Hawking Radiation!

You may have heard of Hawking Radiation before. It's a theory devised by Stephen Hawking that illustrates how black holes could slowly evaporate over time. This is interesting because it means that instead of black holes eternally trapping everything they have inside their event horizons, they will slowly fade away, letting everything inside them escape.

But how does it work, you ask?

It has to do with quantum mechanics.

Before you groan and run away, I promise that I'll do my best to explain this simple. It's still really wacky. So maybe you'll still groan and run away. Ah well.

Let's talk about the Uncertainty Principle.

The Uncertainty Principle is the basis of all quantum mechanics. Everything else in quantum physics is essentially derived from this principle. You may have heard that in quantum physics, simply observing a particle causes it to do weird things. This is true, but not because of any weird interactions of your sentient consciousness with the mechanics of the universe (unfortunately). Let me ask you this: how do you see things?

Answer: Light.

In order to observe something, that something first has to interact with light. When we're on large scales, this is pretty simple; light bounces off the thing and into your eyes. But when we get down to really small particles, the rules change a little.

Let's say you have a particle travelling through space. It has both a position and a speed. Lets now say that you want to know how it's position. In order to do this, we need to take a unit of light - or a "quantum" of light - and bounce it off of the particle. The problem is, light comes in wavelengths. And, light can only interact with things that are larger than it's wavelengths. For example, Microwaves are quite literally too big to fit through the little mesh in the window of your microwave oven. But light at visible wavelengths is small enough to fit through. That's why you can watch your food cook without melting your face off.

So, in order for our light to interact with our particle so we can measure it's position, it needs to have a pretty small wavelength. And, the more precisely we want to measure the position, the smaller wavelength it needs to have.

And here's the problem.

Smaller wavelengths mean higher frequencies, and higher frequencies mean more energy. Quanta of light that have a high enough wavelength to interact with the particle are also going to have high amounts of energy. This means that when the light bounces off the particle so we can observe its position, it changes the momentum of the particle by simple energy transfer. The more precise you want the position measurement, the higher wavelength you need, and thus, the less precise the particle's momentum.

This is the uncertainty principle.

It also works vice versa - the more precise the measurement of momentum, the less precise the position becomes. This creates the reality that we can never truly know where a particle is and how fast it's going. There's a limit to how precisely you can know the properties of a particle. This means that, functionally, particles act more like ambiguous smears of probability than precise points. This allows them to behave as waves, and creates the strange nature of particles that forms the basis of quantum physics.

But wait! I hear your eager minds cry out. What does this have to do with black holes evaporating?

To which I say: Patience. I'm getting there.

The weird thing about the uncertainty principle is what happens when you apply it to empty space. According to certain understandings of quantum mechanics, namely the particle/wave duality, things that normally seem to be waves in our lives (light, electricity, even gravity) have hypothetical "virtual" particles that can be associated with them. Essentially "quanta" of any given force. This means that you could consider any wave of any medium to be made of quanta of the force that that wave is made of. 

Empty space is a field in which these waves can travel, but when there are no waves in it, the measure of the wave in that empty location should be zero. Here's the problem: zero is a precise number. And according to the uncertainty principle, you can't have a precise measurement of a particle, virtual or otherwise. In order to satisfy the uncertainty principle, you have to assume that there are constant tiny little fluctuations in the quantum state of empty space. It's not empty at all; it's constantly buzzing with a faint hum of activity. Like a pool of water that seems motionless until you peer very very very closely to see the tiny rippling of waves.

These tiny waves manifest as particles - oftentimes virtual - appearing two at a time in opposite pairs, traveling apart briefly, then coming back together and annihilating one another. Before you protest that this defies the whole "no creation of matter/energy" thing in thermodynamics, I'll illustrate that one of the particles is positive in mass and energy, while the other is negative in mass and energy at the same value. So the total number of mass/energy in the universe stays the same even before the particles annihilate one another.

But wait! I hear your eager minds cry out, yet again. What does this have to do with black holes evaporating?

To which I say: ...I'm seriously right about to answer that. Just KEEP READING.

Black holes are weird. They do weird things all the time anyway. But when you add the quantum fluctuations of empty space due to the uncertainty principle to a black hole, really weird things start happening.

Let's say that in the space right near a black hole's event horizon, two of these particles come into existence. One of them keeps travelling through the space outside of the event horizon, while the other ends up falling through the event horizon. This causes weird things to happen that I don't understand. Somehow, the gravity of the black hole changes a property of the infalling particle that makes both it and it's counterpart real particles instead of virtual ones. (I don't know how this works. I tried to read wikipedia articles about it and was very confused.) This changing of properties also makes it so that the particles are no longer obligated to annihilate one another, allowing them to travel along different paths. One falls into the black hole. The other continues out into space.

But wait! I hear you say in concern. Wouldn't the infalling particles make the black hole BIGGER? Why does it evaporate?

The answer comes in the weird changing of properties; the infalling particle becomes negative in mass as it falls inwards. If you take a very big number and add a very small negative number, the big number becomes a little smaller. Thus, the tiny negative particle actually shrinks the total mass of the black hole by a little bit. The positive particle continues into the universe, appearing as if it was emitted from the black hole, rather than from the space right above it.

Over trillions and trillions of years, this effect would slowly erode the black hole away, shrinking its mass particle by particle until the amount of mass is no longer large enough to justify a point of infinite density. The event horizon would vanish, and all the remaining mass in the singularity would explode forth in an intense flash of light rivaling the supernovas of the age of stars. The light would wash across the universe, briefly illuminating the black void that had once been filled with stars before they all died out eons ago.

So yeah.

That's Hawking Radiation.