Become an Expert: Black Holes Part 2

The infamous, mysterious and unknown: Black Holes. We’ve all thought about them before especially with the late and great Stephen Hawking. What are they?  How do they form? And most mysteriously of all, what happens if you enter a black hole? These are the questions I will be answering in this 2 part series

Firstly, what are black holes? Well, there are two different types of black holes: a stellar black hole and a supermassive black hole. We covered the stellar black hole in part 1 so be sure to check it out. 

The origins of supermassive black holes are still unknown. They are typically 100,000 solar masses, or put another way, 100,000 times the mass of the sun. Unlike the stellar black holes, there are no stars 100,000 times the mass of the sun. However, there are some theories that could explain how these gargantuan beasts came into existence. Just a note, supermassive black holes are found in the centre of galaxies, just like our own.

Credit: APoD – NASA

Theory number one: The gradual increase in the size of black holes. Every now and again, two stellar black holes collide and combine. This sends out gravitational waves but also increases the size of the black hole that is left. After a long period of time, there would be bigger and bigger black holes and eventually supermassive ones. The problem with this theory is that at the rate in which we observe black hole collisions and the current age of the universe, there wouldn’t be enough time to create as many supermassive black holes as we observe today.

This brings us to the second theory: Superstar supernovae. In the early universe when the first stars were forming, the stars that were emerging were supercharged and massive (sometimes hundreds of times more massive than the sun!). Furthermore, the stars had very short lifetimes (usually only 1 million years and the sun is 4.6 billion years old and only halfway through its life!).  I won’t go into the details, but just know these stars were massive and had short lives. With this in mind we could predict that there would be many more supernovae and larger ones at that, so using the idea of the first theory, those black holes could have collided and formed larger ones until they were supermassive. This could also be connected with why the supermassive black holes are always found at the centre of galaxies; because they formed early in the history of the universe. This theory, however, is hard to prove and this debate will probably go on for the rest of yours and my lifetimes. Other than being much larger than stellar black holes, supermassive black holes are very similar. If you would like to know the different parts of a black hole you can read part 1 here

Credit: NASA

Now for the bit, you have all been waiting for: What happens if you go into a black hole? A popular theory, first proposed by the late Stephen Hawking is spaghettification. Spaghettification is the process in which an object is stretched out until ripped apart, supposedly representing spaghetti. This theory is most likely true but only in small, stellar black holes, your fate is much weirder if you enter a supermassive black hole.

Credit: The Bikery Du Nord

Let’s set the scene. You’re aboard a two-person ship and you stop next to a black hole to take some pictures. Your college, Katherine, waits by the door of the spacecraft. For some reason, you get a bit to close the black hole and it sucks you in. Katherine is horrified as she sees you get burnt to ash and be apart of the accretion disk. You, however, are floating nice and happily in the centre of the black hole, not being able to go back or get out of the black hole. You are completely fine and will probably starve or dehydrate if your futuristic space doesn’t have food or water built-in. How come Katherine saw you get burnt to ash but you are completely fine? Well, this takes us onto the almost century-old debate over quantum mechanics and general relativity. Einstein was the one who predicted that you would float endlessly in his general relativity or happiest thought. On the other hand, quantum mechanics would predict that you would be burnt to ash. So which one is right? 

Well, in 2012 the physicists Ahmed Almheiri, Donald Marolf, Joe Polchinski and James Sully, collectively known as AMPS came up with a thought experiment which went a bit like this. Using the idea of quantum entanglement (were two objects are “entangled” in a way where information can be passed to and from the two objects instantly. An object can only be quantum entangled to one other object and only that one other object) Katherine had an object lets say x. She knows it’s entangled to y or z. Y is deep in the black hole and z is in the accretion disk. Katherine then proceeds to put x in an entanglement decoder (a theoretical machine that could figure out what an object is quantum entangled to). What would the machine say? If it said y then relativity is right because y has been reduced to ashes but is still intact. If the reading said z then quantum mechanics is right.

This is it for this two-part series. If you enjoy my content make sure you sign up for my newsletter and share with friends.

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