[Intro]

Hank: Stephen Hawking is in the news again and you know what that means. It means that the media are trying to figure out what he is talking about. To their credit they want to tell us what is going on with the world's most famous theoretical physicist, it's just that doing that involves writing about theoretical physics.

Fortunately, we're here to help, and just in time because Hawking recently announced that he'd come up with an answer to one of the biggest questions in physics: what happens to the stuff that gets swallowed up by a black hole? Like.. good question right?

Now if Hawking has figured out the solution to this, it will probably be a while before we know exactly what it is. So let's start with the basics. 

A black hole forms when a star collapses creating an area of space with such a strong gravitational pull that, once you cross a certain point known as the Event Horizon, nothing can escape. It's the point of no return, whatever gets past that Event Horizon is not coming back out.

But there's a problem, and it has to do with something that Hawking himself proposed back in the 1970's. Black holes actually emit radiation, which is weird right? An object with gravitation so strong that even light can't escape it, but then also releases radiation?

This energy has became known as "Hawking Radiation," but black holes don't just keep spewing it out forever, they release it until there is nothing left and then the black hole dies.

But according to Hawking's calculations, the radiation's properties (like it's energy and intensity) don't depend on anything that entered the black hole. You could study the radiation from a black hole all you wanted and you'll never be able to tell what it had originally swallowed.

All the original properties of that matter and energy that entered the black hole -what physicist call "information"- were being lost. Forever. But that violates one of the fundamental law of quantum mechanics and physicist don't like it when that happens. 

The long question here is the one that says that just like energy, information must always be conserved throughout the universe; it can't be created or destroyed unless the Black Hole Information Paradox was born. 

Physicist describe it as being like when you burn something- like say a piece of wood- and it turns to ash. Now it is true that you can't  just grab all of the atoms that were released in the charcoal and the CO2 and make a piece of wood out of it. But on a quantum mechanical level, you technically could because all of it's original atoms are still around. But that can't be true for information that falls into a black hole. 

Once it crosses the Event Horizon it's lost forever and you can't even learn anything about it from the Hawking Radiation that the hole then spits out.

So physicists- including Hawking-have been trying to solve this paradox for a long time, and last week, at what was appropriately called the Hawking Radiation Conference- that guy's got a lot of stuff named after him- Hawking explained his latest try at a solution. 

He suggested that as the information passes the Event Horizon, it leaves a kind of imprint on the Event Horizon. And all those imprints are able to affect the way the black hole emits Hawking Radiation, so the information isn't being lost after all. But so far, that's all we got.

Now based on what Hawking said in his eight minute talk at the meeting, it sounds like what he might be describing as something known as the "Holographic Principle." This is an idea that was developed by Gerard't Hooft and Leonard Susskind in the 1990's. They figured that all the information from a three.dimensional particle could be stored in only two dimensions- kind of how a 3D hologram can be represented as a 2D picture- so if the Event Horizon was like some sort of surface, the information of the matter and energy passing through it could still be imprinted on it, instead of being lost.

For the next few decades after the two proposed this theory, there was a long and famous debate about whether Information was really being lost inside of a black hole with Hawking saying that yes, it had to be. In fact, Susskind wrote a whole book about it and called it "The Black Hole War" and Hawking even had a bet going with some of his colleges...

In 2004 he said that he had probably lost that bet and that there had to be some way for the information to get out of the black hole again. So he gave the winning physicists a baseball Encyclopedia as his reward and then set about figuring out exactly how information could possibly escape a black hole: the best trap in the universe.

Now he seems to have taken an interest in the Holographic Principle or something very  much like it and the whole scientific world - including us-  wants to know more about what he is thinking.

But until Hawking and his colleagues public their latest findings- which may not be for another few months- we won't know all of the details.  But maybe then, maybe, the Information Paradox will be at least a little less of a mystery.

Thank you for watching this episode of SciShow Space News and thank you specially to our patrons on Patreon who helped make this episode possible. If you wanna help us make episodes like this, you go to patreon.com/scishow, and if you just wanna keep getting smarter with us, you go to youtube.com/scishowspace  and subscribe.

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