Black Holes, Part 3: The Future

It's a tremendous presentation. It's available on YouTube for your viewing, and I'll make sure that there is a link to it on the landing page for this episode. It's Stuff to Blow your Mind dot com. Now, it's funny. This is gonna be our third episode in a row on black holes, and this will be the last one for now. We will probably revisit the subject again in the future, because even in three whole episodes, there's no way to even come close to exploring all of the interesting stuff

about black holes. But we're here for part three. In the first part, we explored the sort of the idea history of black holes, like where they came from conceptually before anybody had ever looked up and seen one. And then in the second episode we tried to talk about ways of inferring the physical existence of black holes, not just the theoretical framework underlying them, but how we can

detect them out there in the universe. And then in today's episode, we wanted to sort of like, uh, just do a grab bag of interesting outstanding questions about black holes or thought experiments involving what we know about black holes today. Yeah, then we'll get into some sort of sci fi ideas here as well for sure, which, of course, uh brings us back to the topic of cinematic betrayals of black holes. We talked a little bit about the

Disney movie The Black Hole. In the previous episodes we talked about Interstellar and how Interstellar is is actually a pretty good um scientific model to look at as far as depictions of black holes in cinema. But then of course there's Event Horizon, Oh is there? This was the Paul W. S Anderson film, arguably in my mind, the best um Paul W. S Anderson film. What would be the other candidate for the best Paul W. S Anderson film one of the Resident Evils, I guess one of

the seven or Eight Resident Evils or Mortal Kombat. You know you can go with that. That was his film prior to Event Horizon. No, I don't want to be mean, but to be generous, we could say not this generation's most highbrow filmmaker. Not to say that that that you and I are purely highbrow of Cinnema enthusiasts. No, we love some trash, and boy's Event Horizon some delectable nineties trash. It's it's got funny c g I. It's got get to the Chopper kind of stuff. It's got a great cast. Actually,

it's got hilariously bad writing. It's uh yeah, it's solid B movie territory. It certainly is in that it has uh well, I mean for starters. It's it's certainly not a beam of you if when it comes to the amount of money that's enter this thing. But in terms of of of of looking when you look at it as a whole, there are a lot of problems when you but when you look at some of the of the elements that go into making the film, there are

a lot of things I like about it. I think the ship looks really cool, this ideal leather punk spaceship, yeah, I mean it looks like a cathedral. They I like how it incorporates some of these, um these these very obvious elements from films like the Shining uh you know, two thousand and one of Space Odyssey Solaris and brings them all to together. I bet you like the soundtrack,

don't you. Well. I thought I was gonna like the soundtrack because it's been a long time since I've seen this, like possibly since high school, and I rewatched rewatched it before we went into to to record this episode. The main thing I was remembering here was that, oh yeah, Orbital worked on the soundtrack Orbital of course, or Legends of the electronic genre that for instance there the Orbital too is a classic, and I recommend everyone who's into

electronic and ambience you should check it out. They were also on the soundtrack of the Paul ws Anderson film Mortal Kombat. Yeah, so that that soundtrack was pretty awesome back in the day. But you know me, I love a good electronic score. So I went back to View of the Horizon expecting there to be a lot more Orbital, a lot more electronic uh nuance. But the thing is,

it's not just an orbital score. It's orbital and Michael Common, and Michael Common brings the the orchestral stuff into this equation, and it really felt like there was far It was a far more traditional film score than I really wanted to hear. It's one of those beat you over the head horror scores, you know, I hope you want some was Yeah. Yeah, so it did not really Uh it did did not really please me on that level. Um,

but I you know, I like this. I like the ship, I like some of the horror elements, and the cast is so good that you can forgive a lot of things, like when Sam neil Is is your lead actor, it forgives a lot of sins. And he, arguably, I would argue, plays the best possible pinhead in this true he essentially becomes a cinebyte in this film, and in doing so, he's like he's a cut above any other cinematic cinebyte. Yeah.

You could argue that Event Horizon is a very bad movie, but that it might be in a way the best Hell raisor sequel. Yeah, yeah, I would agree with that. Now, of course, that the harder Why are we talking about Event Horizon? As we touched we've discussed already in There's a black Hole episodes. The event horizon is the point at which light cannot escape the gravity of the singularity. It's the point of no return, right, So you've got

this incredibly dense core at the middle of a black hole. Say, if your black hole is the remnant of a collapse star. You know, your star goes supernova, blasts a lot of its material out into space, and then it's got this remnant leftover that's very din It's within what's known as short shield radius, and if it's within that radius, it will collapse upon itself in this weird process that even

now we're still trying to understand most fully. It will collapse it this way that it looks like it collapses towards infinite density, and it creates this sphere around it where anything that goes inside the sphere never comes out again. It cannot overcome the force of gravity. It just becomes

part of the black hole. Right. And in the film Event Arizon, the essential science the argument that is made uh when when Sam Neil's character Like is forced to explain this to the crew of a spaceship who apparently have no idea how space works. Uh. Apparently the Event Horizon spaceship creates an artificial singularity which is then used to open a wormhole of some sort. And that's that's his about is is? Uh? Is detailed as the explanation

gets so also they go to Hell? Well, yes, but that's that's how they get there through the wormhole, or the wormhole goes through Hell. I've done a little vague here. So why have we spent so much time talking about Event Horizon. Here's why, because I'm going to argue that I think a scientifically accurate movie about going to a black hole could be scarier than a movie where you need to put hell and demons in there. All right, Well, that that can be the argument we make during the

course of this episode for sure. Okay, well, I think we should talk about what would be like if you want to fall into a black hole. Let's say you get a hanker and you're saying, I want to approach infinite density. Hey it's two thousand eighteen. Yeah, you know, I totally understand that desire. I feel flabby, I feel kind of bloated. I'm going for infinite density now, So you say I'm going to fall into a black hole.

You've decided to hop into a spaceship, travel out into the universe, and intentionally fly straight into a very big black hole. Now, there are a lot of people who have written about this subject, trying to imagine what it would be like, the subjective experience of approaching a black hole, crossing the event her Eisen, and then falling in. Uh there. I think Neil de grass Tyson actually has a book about it. I haven't read that book, but I've read

a bunch of stuff about this. Probably the best explanation I've read, and one of my main sources here is going to be an explanation from the astrophysicist Ethan Siegel, who is astrophysicist and a science blogger. He runs the Starts with a Bang blog. Do you ever read that, Robert? He writes good stuff about astrophysics. Um so, so he's got an exploration here that I think is pretty good.

So he says, Okay, you imagine you're approaching a black hole, and if the black hole were the mass of Earth, the sphere that you do you'd be approaching would only be about one centimeter in radius or about two centimeters wide. If the black hole were about the mass of the Sun, the sphere would only be about three kilometers in radius or about six kilometers wide. So the actual spheres of the event horizon that you would see are are much smaller than a lot of the other things you'd encounter

out in the universe. That is, unless you're coming up against one of the biggest ones, like say, a super massive black hole. The kinds of that are at the center of galaxies, So as you approach the black hole from a kind of normal orbital distance. One of the funny things is that, first of all, you might not immediately notice anything strange about the gravity. The gravitational influence you would feel would be a lot like approaching or

orbiting a star of the same mass. And to reiterate, if a star the size of our Sun were suddenly magically turned into a black hole. Uh and by the way, this would not ever happen in point of fact, because our son is not massive enough to naturally become a black hole. But if you were to buy magic turn it into a black hole of the same mass, Earth would simply continue orbiting. It wouldn't be immediately sucked in or anything. Things would get very weird on Earth but

but yeah, we would not be sucked into the black hole. Right. But once you got closer, then things really do start to get weirder, especially when you get very close. So as you approach the black hole, first of all, you would notice that as you get closer, the black back hole gets bigger faster than any normal object would as you approached it. So you might have a normal sense of Okay, I'm flying towards a planet, or I'm flying

towards a star. At a certain speed, you can have a pretty predictable rate of its expansion to take up more and more degrees of your field of view. Right as you near a black hole, the black hole actually gets bigger faster than any normal object would because rays of light beaming towards you passing all around the black hole are bent dramatically inward. Now, remember what we'd actually be seeing out there is you'd see sort of a

black disc with light warped around it. Remember the short shield radius, the distance from the center of the black hole to the event horizon. Uh. The the event horizon, of course, is the sphere catastrophe, the point beyond which nothing, not even light can escape. And as you approach that sphere. More closely, the apparent short shield radius from your point

of view will grow dramatically. A seagull rights that by the time you're about ten schwart shield radii away from the black holes, about ten of the radius of the black hole away from it, it will appear so big that it will blot out your entire forward forward facing view right, so if you're looking toward it, it will be your entire field of view. A normal object of the same size at that distance would only appear to be about the size of your fist at an arm's length.

Then you go deeper and you can reach There are several sort of stops along the way. One of the stops you would reach along the way is what's known as the innermost stable circular orbit, or the I s c O. This is sort of the last filling station before you head down to the border. The I s c O is about one point five times the radius of the event horizon, and it's what it sounds like based on the name. It's the closest that particles can orbit the black hole in a stable circle. Go any

closer and it's all downhill, pretty much literally. By the time you reach the I s c O. If you face a black hole, you will see nothing but black in the direction of the black hole, and the event horizon will appear to take up your your whole field of view. But here's the crazy part. You keep going down past the I s c OH and of course total blackness will still take up your entire field of view if you look toward the black hole. But here's what happens if you turn around and look away. And

I'll explore this in a couple of different ways. First, a scenario one. This is where you imagine it's only you falling in. It's not light or other stuff falling in with you. And this is not how it would probably really be, just to illustrate the gravitational influences involved. If you keep going toward the black hole and you turn back and look away from it as you're falling in, you will see total darkness begin to creep in from every direction as well in the direction you came from.

So you're looking backward, and you will see what looks like a membrane of total darkness closing in all around, and your view of the stars the universe will shrink down to a circle in the direction opposite of the black hole. Just try to imagine that your whole view of the universe being bent and crushed down into a shrinking circle that's receding behind you rapidly. Well again it is so I can't imagine that to a certain extent. Yeah, all starlight dies in a shrinking circle. That that's that's

in your past like that. But at this point it's important to remember you have not crossed the event horizon yet, you're just approaching it. So at this point, if you were to change your mind and say, hey, I want to get out of here, uh, there is in principle still hope if you have a powerful enough spaceship you could turn around. You could pile it back towards that shrinking circle of starlight and escape the black hole, at

least in theory. But it is at this point going to be a really powerful uphill climb against the gravity of the black hole. But let's say, you know, I don't want to escape, I just want to keep falling.

So that's what you do. Assuming you keep looking towards that shrinking circle of are light behind you where you came from, it will eventually shrink down to a point like light source as you near the boundary, as you near the event horizon, and right before you cross the event horizon, the light from that point will cycle through an array of colors due to what's known as gravitational blue shifting, so you'll see red than white, than blue.

And at this point, all the low frequency radiation in the universe, stuff like the cosmic microwave background, which stuff which is like microwaves and radio waves, not stuff that's normally visible, will shift up because of the blue shift of the electromagnetic spectrum. It'll shift up into the visible spectrum, and you'll actually be able to see the cosmic microwave background as a visible blue with your eyes. Then finally you hit the border. Okay, so you crossed the event horizon.

What do you see in this toy scenario where light is not falling in with you, you will see nothing at all. You have entered ultimate darkness and this point there is no escape, no matter what. So let's say you say, no, I changed my mind after I crossed the event horizon. I want to pilot my spaceship back in the direction I came from. So that should be easy, right, You just turn around and you come back in exactly the opposite direction. You've been traveling. Too bad, you can't

do it. If you try, you will discover to your great surprise that the direction that used to be the direction you came from is now downhill into the center of the black hole. And in fact, every direction you try to go in is downhill into the center of the black hole. It is the perfect pit. It is a pit in which the only direction is down. You're going into that thing no matter what in any travel you do would only speed your travel towards the center of the thing. That's kind of mind bending to to

to think about. But yeah, essentially all all roads lead to Rome at this point. The remaining question is how long does it take you to get to Rome? Right, so you've crossed, you can't go back, how long do you fall before you sort of reach the center of this thing? Seagull rights that quote as you crossed the horizon at the super massive four million solar mass black

hole at the galactic center, believe it or not. Despite the fact that we're talking about an event horizon that might be around a light hour in diameter in our reference frame, it would only take around twenty seconds to reach the singularity once you cross the event horizon. Now, remember that first scenario was kind of a toy scenario where light is falling is not falling in with you. That's just to like see what the gravitational effects are. The physics of the effects are on display, But we

created a kind of unrealistic scenario. So in reality, you would probably not be approaching and entering a black hole alone, but you'd be approaching and entering along with a huge

tide of light and radiation. And this would mean that in reality, your picture of the universe would not shrink to a point behind you as you approached the black hole, but would remain a kind of warped division of the sky following you down through the darkness after you crossed the event horizon, and that light that you would see would be the light that's been sucked toward and into

the event horizon with you. But as as we've been talking about before, unless you just assume some kind of technological or magical form of invincibility, it's highly possible given various factors. There are a lot of different ways that a black hole could be but it's highly possible that you would die at pretty much every stage of the scenario would be describing um for several reasons, one of which is what's been classically known as spaghettification. I've certainly

heard Neil de grass Tyson speak about this. It's one of the astrophysicists favorite concepts. Uh So, as you approach the center of gravity of smaller classes of black holes, title forces would work you up good and title forces occur when an object is stretched and deformed because of an imbalance of gravitational forces at different parts of the object. We've talked before about Jupiter's moon Io. You know, Io is one of the most I think it might be

the most volcanically active object in the Solar System. If it's not the most, it's one of the most. It's got these volcanoes erupting. What's causing all of this heat and and geologic activity inside Io It's believed to be tidal forces of Jupiter acting on the planet that you know, Jupiter. It's close enough to Jupiter that Jupiter is kind of working the planet with its gravity, and so as you're falling into a black hole, a similar kind of working

would happen on you. Basically, imagine you're falling feet first into a relatively small black hole. At a certain radius from the black holes center, you would start to notice that the force of gravity pulling your feet is a lot stronger than the force of gravity pulling your head. And since Einstein, we know that the experience of gravity is subjectively equivalent to the experience of acceleration through space. Right.

Gravity is just like being in an accelerating room. So imagine you're falling feet first and you discover that your feet are accelerating faster than your head is. If you were otherwise still alive, when this started to happen to you, it would stretch your body out until it ripped into pieces, and then those pieces would get stretched and ripped into smaller and smaller pieces, until you're just kind of a wet carbon particle jelly streaming through toward a point of

infinite density. Also worth noting, if you did a cannonball into the singularity, Uh, then all of this would happen. But first, I'm not sure that has any impact in anybody's decision making. Oh, it has a lot of impact. Somebody should work that up that that should be a paper. Yeah, how would the body react? Uh? As a side note, you might have heard me mention smaller black holes here.

Why Why did I mention smaller black holes? It's kind of counterintuitive, but actually smaller black holes will tend to kill you faster through tidal forces than larger black holes will. A much larger black hole actually has a more gentle gradient of gravity acceleration. But so we've been imagining one type of way of picturing this awesome event, the what

what it's like to pass into a black hole? One of the things that I want to think about is, once you're within the event horizon of a black hole, does it even make sense to talk about you falling into the black hole? To talk about you and the black hole as separate objects if you can literally never leave no matter what, you are no longer an entity separate from the black hole itself. You are part of the black hole, and the black hole is you. That's true.

Like you're no longer a denizen of the larger universe. You're denizen of that particular black hole. H and yeah, and arguably a part of its substance. Yeah. So maybe maybe a more transcendent way of thinking about it would be to say, okay, when you fall into a black hole, it doesn't just kill you. You get to become it consolation price. Yeah, alright, On that note, we're going to take a break and when we come back, we will discuss more of the mysteries and wonders within the black hole.

Thank alright, we're back now. One of the things I know they talked about in the Darkness Visible event you saw in New York was the relationship between black holes and entropy? What what was the deal here? Alright, I'm gonna I'm gonna attempt to explain all of this and uh and I do just want to advise listeners more than usual that if if this doesn't completely make sense, do check out the talk, because I get to hear a pair of experts discuss it, uh in with more

time and with with greater expertise. But but I will attempt to to summarize here. It is astrophysics. It is it is astrophysics, and we are talking about black holes. So one of the more interesting points brought up in the talk was that string theory actually helps us make sense of what's known as the intropy problem with black holes.

The basic problem being is that is that how can a black hole be in a high entropy state if everything inside it is super condensed to a state of less entropy than normal matter, whereas the missing entropy and the thing is. According to string theory, you can say, well, the missing the missing intropy can be found in the six microscopic spatial dimensions that exist in addition to the three spatial dimensions that we can observe. And yes, I realize all that kind of may have sounded to some

of you, like, uh, like a monologue from Ghostbusters. But but but it does it does make sense. Okay, So basics on string theory. String theory is an unproven hypothetical framework in physics that explain that goes toward explaining the more ultimate nature of our universe. We've got the Standard model, and you've got particles, and you've got energy and all that, and you're like, does something lie underneath all this? What

generates its string theory? That the very basic version is that it posits that underneath all of our model of particle physics and everything are these vibrating strings. And these strings make up space, time and particles, and they can vibrate in different ways that create different kinds of phenomena and objects in our universe. Is that is that kind

of close approximation. Uh, And so under string theory, it's this sort of mathematical framework we haven't been able to fully test yet, but under this mathematical framework, it is believed that there are more dimensions than just the three space dimensions and the one time dimension that we observe, right, and they're necessary for string theory to work. Um like this,

this basically emerges from the math. And one of the things that that that Brian Green pointed out in the World Science Festival talk is that for for a long time this was kind of not really a dirty secret of string theory, but it was one of those things that was necessary by the math. But it wasn't something that necessarily they were putting out there first like saying, uh,

you know, headline six dimensions, additional spatial dimensions. It was more like, we have this this this attempt to understand the universe and oh, by the way, six dimensional spatial dimensions. And we should mention that Brian Green is a big fan of string theory, been working on string three for years, but not everybody in the physics community is uh. String theory has plenty of critics, people who say, you know, this is an even science. It's not testable yet, so

how could you you know? But the people who work on it say, well, we're trying to create a theoretical framework and maybe sometime in the future we could do tests to try to confirm it or disconfirm it. Yes. Now the other side of this, of course, is the entropy we're talking about. So the second law of thermot thermodynamic states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic dynamic systems increases,

So things are going from low intropy to higher entropy. Um. The example that Brian Green throws out is that if you have a book's worth of page is stacked on top of each other in order, uh, that is low entropy, and then you throw it into the air and all the pages fall on the ground. Well, now it's gone to a high entroview state. In the former the low

entropy state, less information was required to describe it. But in the because you just say, oh, well the information on page X is on the sixth page, etcetera, you'll find them in order in this stack. But now everything is in a high entropy state. You need more information to tell you where where everything is. You say, okay, page six is, well, it's it's over here, um in the middle of the field near pages you know, eight hundred and page seventy two, that sort of thing with

a weasel chewin on it. Right, So when we looked back to black holes, yeah, you have to account the wee but in the weasels moving around, you gotta track the weasel. See, it's so much easier to keep track of everything when it's just in a stack. This is why good housekeeping is essential. So back to black holes. Though, when black holes merge, the area of the event horizon holds onto the entropy. But there's this lost information. Uh, and this is probably it's probably a terrible way of

thinking about it. So please, you know, don't like really hold onto this or make a T shirt out of it. But if two circus clowns were to into a single clown, you might expect to have a circus clown with twice as many articles of clown clothing, twice as many buzzers, twice as many flowers and other like clown gimmicks. Right, uh, twice as much face paint. But no, there's something missing. Where did the missing clown gimmicks go? Where did the

missing entropy go? Where the missing information go? Or it seems to be missing? Uh, seems to be there, seems to be a loss of information. Uh. Intropy is supposed to increase, but this would seem to be a decrease in entropy, which violates that second loft thermo dynamics. And then scientists also found an area increase in merging black holes,

seeming to line up with the increase in entropy. UH. The area of the event horizon is somehow holding onto the information that's inside the black hole, and Stephen Hawking argued that there was a connection between the black hole area in intropy. There must be information, but the horizon is is featureless. There's no room for information there to be deciphered. So if you solve all of this with Einstein's equations, the black hole would seem to have zero entropy.

It would seem to be a perfectly ordered state. But that can't be right now. Basically, as Brian Green described at the World Science Festival, you have these extra dimensions and string theory that emerges kind of a remainder, a kind of a problem, and with black holes you have this problem of missing introview, and when you combine the two, the problems would seem to kind of cancel each other out. Uh and in a way but possibly reveal what could

be going on inside a black hole. It's still a puzzle. It's still a big mystery. You know, where does the intropy go when the black hole evaporates and uh, it radiates particles and this hawking radiation when it vanishes, what happens to the information? Uh? All and all of this is based on the math, by the way. Um, but it's yeah, it's it's it's fascinating. This is another one of those areas where where we were chasing the math to find the black hole, and we're still chasing the

math to understand exactly how it's functioning. Yeah, this is one of the frontiers of science. I mean, it's an exciting realm because it's a place where you've got to have this, uh, this sort of clever cooperation between indirect kinds of observations from the experimentalists and clever innovations by the theorists, the people coming up with the mathematical framework in the theory. I mean, you can't like sample a

black hole and just say, Okay, let's see what's going on. Right, So I realized a lot of that is is very difficult to relate to the human experience. So I think it's time to move on and talk about black holes and time. We've talked about like the sort of the visual experience and the the spatial experience of approaching and then injuring a black hole crossing its event arise, and but then there's this whole question about what happens with

time because we're talking about space time. We're talking about an object that warps space time with its incredible math. Yeah. Now, one thing that's absolutely true that we know is that time is relative. So the outside observers version of what happens to you when you enter a black hole might be very different than your subjective experience of what happens to you when you enter a black hole, because you're

not experiencing time in the same way. Yeah. Like, one of the key things that will touch on again here is you talk about these scenarios where one person enters the black hole and one person watches from behind the one in the front looks back at the one in the back. But then you cannot have a third observer who can see both inside a black hole and outside of the black hole like that. There that once you

cross the event arise and that's it. Yeah, okay, well I think we've got to take a quick break and then after that we will come back and explore black holes in time than all right, we're back, so key and all of this is a phenomenon called time dilation, which we've discussed in the show before. This is the idea that time passes more slowly the closer you approach the speed of light, which of course is an unbreakable

cosmic speed limit. Now, one thing we need to say there, though, is that the What what that means when you say is, let's say you get in a spaceship and you approach the speed of light, is that time passes more slowly relative to other observers for you, Uh, it doesn't necessarily mean that you would feel like you're living in slow motion. In fact, what it means is that you are living

in normal time. But say if you get in a spaceship, travel at the speed of light or not at the speed of light, close to the speed of light, and come back even though it felt like time was passing normally for you. You might get back to Earth and then realize a lot of time has passed on Earth,

where it seemed like much less time had passed for you. Right, And this is one of those things you could say is true on Earth as it is in heaven, because the the hands of a clock in a speeding train are going to move ever so slightly slower than those in a stationary On a stationary clock, the difference would not be humanly noticeable, but when the train pulled back around to the station and the two clocks would be

off by billions of a second um. If such a train could attain nine point nine nine nine percent light speed, only one year would pass on board for every two hundred and twenty three years back at the train station, even though for the passengers it would feel like time was moving normally. Right, This would all be a matter of like comparing notes and uh and like looking at stop watches when you return. That's the thing. But speed

isn't the only factor that affects time. On a much smaller scale, mass also influences time, so time slows down the closer you are to the center of a massive object. This is something that was explored to great effect in the movie Interstellar, which we mentioned earlier. You get really close to the supermassive black hole and and you're gonna have some real problems sinking up with your person way

back in the space station. Yeah, indeed. Uh. And and you know, based on this, we know that there are places in the universe where time speeds up in places where it slows down. Uh. Time, as it's often pointed out, runs a little bit faster in space than it does down on Earth. A clock aboard and orbiting satellite experiences time dilation due to both the speed of its orbit and it's greater distance from the center of Earth's gravity.

And we actually do have to make adjustments for this, like for GPS satellites, Uh, they need occasional we we need to occasionally adjust timekeeping between GPS satellites and what's going on on Earth. So so that's the real world version of this, like the accessible version of this that actually impacts life on Earth. But then there's the Then then we return to black holes though, because the closer one gets to a black hole, the stronger the gravity

would be. And this is gonna have a dramatic effect on time making a supermassive black hole, in Hawkings words, a sort of natural time machine. The trick would be to avoid falling in, hitting just the right trajectory and your your spaceship or even your time ship. I guess it would be at this point it to orbit around the event horizon. High speed would keep you stable, but time would slow down by half. So you could take say a five year journey to travel ten years into

the future. That might not seem like a lot, but it's ultimately the best the universe offers as far as time travel goes without getting into the paradox producing feedback loop destroying aspects of wormholes. Right now, this would only be travel into the future. I think, as we've discussed before, when people ask is time travel possible the questions the answer to the question seems to me travel into the past absolutely not. Travel into the future is not only possible,

it is known to be real. Yeah, And it gets in this weird scenario where someone could say, Hey, you wanna you wanna get to let's say it's eighteen now, you want to get to the year Yes, all right, Well, how how many years do you want to take to get there? You want to take the standard ten. Do you want to take five? Well, if you want it to want to get there in five years, uh, you know, uh relativistically, then you're gonna have to jump on this spaceship.

And all of our physics tells us this would work. But that's outside the event horizon. What what's time like? Uh? Within the event horizon? Yeah? Does it even make sense to say from an outside observer's perspective that anything happens inside a black hole? Is that even a meaningful concept? I mean, we're it certainly gets into an area where these are all decent questions, you know, because you sort of you can do this with a sort of physics breakdown.

But then ultimately, yeah, what does it mean to be within the event horizon? Yeah? By the way, I meant that not to say that nothing happens. It was just I don't actually know the answer to that question. Well, I looked into this, and I was reading an article on Ask an Astronomer by Harvard physics graduate students Sarah Slater and uh and and she had this fascinating nugget. She's she's shared that quote. Everyone inside the event to

horizon is a psychic whoa explain that okay. So she points out that outside of the event horizon, there are two criteria for remembering something. One it has to have been in the past, and two, it has to have happened at a distance no more than what light could have traveled since it happened. Okay. So that sort of means like, we can't remember events that took place farther away than the observable universe because it would have taken light longer than the history of the universe to cross

that distance to reach us. There's no way we could have that information, right, I mean, this is like basically I'm gonna put that on the shelf and say that's space and time as it relates to our our ability to remember something. But inside the event horizon, things get flipped around space and time you could say, become switched. So now these are the two These are the two criteria within the event horizon for remembering something. One it has to have happened farther from the center of the

black hole, uh than where you are right now. And number two, if T is in the letter T is the time that it would take light to travel to you from the location of the event, then it happened either no more than tea hours ago or tea hours into the future. So I'm gonna just read this direct quote from her quote if you look away from the center. And again this goes back to our earlier ideas of crossing the event horizon and looking back or trying to

look back. She says, quote, if you look away from the center, though, you can see two images of everything, one from tea hours in the past and one from tea hours in the future. For nearby objects, these two images will look just the same, since t will be very small due the due to the large speed of light. For far away objects, though, they could be completely different. So you could see the past beginning of something and it's few your end. At the same time, spacetime is twisted.

And then there's this. If you were to enter a black hole, theoretically speaking, an outside observer might watch you crash and burn on the event arise and destroyed by all that hawking radiation, all of your information spread out across the face of the dark sphere. Uh because again the information can't be lost, but your experience would be one of free fall for the rest of your life. And in short, this is the firewall paradox. Uh, there's no third witness who can see both within and without

the event Arizona. And to me, that's all just mind going to try and and uh and and contemplate. Yeah, I feel like I'm still trying to understand it. Um. I mean it drives home the way that black holes are kind of They're great because they are a reality that brings to life all of these impossible relativity experiments that people try to use to explain how weird spacetime

really is. One of the things we talked about in the last episode is you know, if you were to just go based on your intuitions, you'd probably think, well, space and time are are fixed, and the speed of light is can be moved all around. But in fact it's exactly the opposite. Speed of light is fixed speed of light and a vacuum is fixed and space and time can be stretched all around. And you can't really internalize that. But people try to come up with all

these impossible scenarios to illustrate the principle. At the black hole, you don't have to come up with scenarios. This just apparently is what black holes do. Now. At this point in the podcast, is we're beginning to wind down here, I thought it might be fun to just talk about a couple of questions that that frequently come up. Either some of these we have received as emails from people, and then others are just sort of general questions that

arise from sci fi treatments of black holes, including event Horizon. Okay, so the first one is if and I know we've received this from listeners, if I'm pulled into a black hole, will I then come back out of a white hole? And I think sometimes this is an area where we we fall into the trap of thinking of black holes more as wormholes. But the white hole concept is in fact a byproduct of general relativity. But it's even more of a mathematical phantom. In many respects, it is the

reverse of a black hole. It's not a place where matter is lost, but rather a place where matter is born. I've seen it explained as sort of like the Big Bang singularity but not but not quite the same. But it also can't actually exist in our universe. Yeah, so I hadn't heard this. I've heard the white holes were still kind of a speculative possibility. Well, this is, well, my understanding of it and again this could be that this could be incorrect, and I may have to be

corrected on this later. But my understand my my understanding of it that it is that it emerges from the math. But it's one of these things that emerges from the math that that we're like, well, that doesn't really square up with what we we actually expect to see in the universe. Astrophysicist Karen master Is once described it this way, quote, there is only such a thing as a white hole in the theory of black holes, and no such thing

is possible, is possible physically. Well, I'm sure she knows a million times more about this than I do, but I would just point out that that used to be what the astronomers said about black holes. Yeah, but I'm

not using that to say white holes exist. I mean, I'm sure she's probably drawing on a lot of facts that that I'm not aware of my But basically, my my read from this information is that the answer to if if I go into a black hole, I come out a white hole, the answer is is probably no. And probably you're thinking more about a wormhole here, You're not really you're not really picturing what a black hole and indeed, a white hole would actually be well, I'm

more I'm inclined to take the astrophysicists word on it, so so I'll go with that. No, no white holes. Okay. So another frequently asked question, and this one's a lot more fun I have to have to say, is could we one day harness the power of a black hole? Perhaps like what we see an event horizon, it's a black hole. Drive tell me event horizon as possible. Kay, let's hear it. Okay, So, first of all, this is probably a good time to refresh everyone on the Kardashian scale,

which we referenced earlier. This is the idea that this is just like a very rough way of understanding like what would be the technological levels of possible um civilizations in the universe. And it's judge based on how much energy you can take control of, right and like truly take control of. So, for instance, Type one civilizations are masters of planetary energy, meaning they can harness this some energy of an entire world. We're not there yet, no,

we would still be a type zero civilization. Type to civilizations can summon the power of an entire star system, and those would be I mean these would be godlike entities if we were to encounter them, if I remember correctly, like the the the aliens we encounter in two thousand and one Space Odyssey are probably Type two. Yeah, so

they know you. Dyson's fears would be an example. So if you you create a structure that can harness and make usable all of the radiation coming off of a star, and then Type three civilizations command energy on a galactic scale, and that we can't even picture that that's god like to a level that it's yeah, I think it's difficult for us to even summon. Yeah, it's difficult for me to even imagine that as well, it would do because Type two civilizations would appear as God's Type three. We

I don't know, we don't even know they're there. If we could, they could be all in the room with us. And who are we? Who are we to to to to even notice them? So anyway, harvesting the power of a black hole sounds exactly like the type of thing a Type to civilization would be into um and in fact, even a Type zero civilization like our own can think of a few ways one might go about it. So remember that hawking radiation that we've mentioned already that's emitted

by a black hole. Well one to harvest that, yeah, just turned into a nuclear reactor. Well in, physicist George unrou and Robert Wald suggested that one could essentially lower a bucket toward the event horizon, collect this radiation, and then drawl it back out. Now, if you let the bucket go through the event horizon, you would not be able to get it back right, Yeah, there's no that the light cannot escape, and certainly a type two Kardashian bucket would not be able to escape. Right. That would

be like the black holes. Like the neighbor who you know, your frisbee goes in their yard and that's my bucket. Now. Now, there's some problems with this though, because the tension of the rope here is an issue. Adam Brown of the Princeton Center of for the Theoretical Science countered that the rope descending towards such high gravity would only be able to support its own mass, not the additional mass of

this mind hawking radiation. Plus, as you know, it also needs to be able to withstand the crazy hey heat of hawking radiation, as with the bucket. Now in albion Lawrence and A. Mill Martinique of the University of Chicago proposed that we could instead dip strings into the black hole and hawking radiation would climb up out on its own. So this would be like I've seen it compared to U like the like an oil wick in a in

an oil lantern. So you're not getting anything back from beyond the event horizon, but you're harvesting the hawking radiation around it. Yeah, kind of almost like luring it out. So you know, this is this is an interesting think about and you would be able to to to mind just a colossal amount of energy this way. But what about doing more of this event horizon model Event Horizon the movie? What about actually, you say, capturing a small black hole, maybe a primordial black hole, using that to

power your space or making your own singularity. Well, on one hand, that sounds kind of impossible, But on the other hand, we should be clear that a black hole doesn't have to come from a star in principle at least, I mean, we we don't have any technology for like making big old black holes. But in order to create a black hole, all you have to do is get an amount of mass within Swart shield radius. Right. And if you can do that, you've made a black hole.

It doesn't have to be a collapse stellar remnant, right, And then arguably you could make one out of energy instead of just pure mass. So this is what's known as a swart shield. Google blitz, Google blitz, google blitz. Yes, sounds like a brand of blender or something, yeah, or a delicious breakfast cereal or part of your your complete breakfast. So this is the brainchild of theoretical physicist John Archibald Wheeler Wheeler and uh, it's the google blitz is German

for ball lightning. Uh. And the idea is that these are These would be concentrations of energy so intense that they form their own event horizons and collapse on themselves. And it would need for this to work to be for this to be something you could actually utilize, it would need to be smaller than a proton. It would be incredibly hot, but if you could contain it, you'd

have just immense energy at your disposal. Now, I'm not the biggest star Trek the next generation buff I like watched all these episodes, I think every evening at nine pm back in um in middle school, watched them on syndication, But it's been a long time since I've viewed them. You went down to the planets, to the pottered plants. Oh, yeah, I I think I watched them them all back in

the day. But there was an episode that I do not directly remember, titled Timescape, and it reveals that a Romulan warbird is powered by one of these uh sword shield google blitz uh and it didn't, but it ends up resulting in all these temporal anomalies. Uh. And that's you know, the plot of the show is like, what's happening to time? Oh, it's something that Romulans did. Um. I don't remember it myself, but I've seen it cited

as a as as an episode that utilizes this concept. Yeah, if Wheeler wants to try it out, I'd say let's go with Wheeler's I D idea. But I like thinking of it. This. What if you create this uh this this artificial black hole or this uh this this little lightning ball and then you drop it on the floor. That's got to be the worst. It's you know, it's bad enough when you say, drop a hummingbird feeder onto

the kitchen floor and you get sugar water everywhere. What happens when you drop a black hole that's hard to clean up? Here's a hint. It's sticky, And I think that sums up the whole episode right there. Well, you know, I would say that there's all kinds of other black hole stuff we didn't even get to. So maybe we can come back again in the future. I just figured

three episodes in a row, that's a lot. We probably shouldn't push it to four this week, I I think, so we have to move on to other topics and then we can return later because, as we've already touched on the the exploration of black holes is ongoing. It is far from a closed book. Yeah, we're learning. We're learning new stuff about black holes this year, especially with say, the research into Sagittarys, a star in the middle of

our galaxy going on just this year. Yeah. So hey, maybe at the end of we can come back and we just we can discuss what we know now about about singularities that we did not know just a year earlier.

One of the most interesting things mentioned in that World Science Festival event that we keep referring to is the idea that observations of black holes that are just now coming online, Like what we're finally learning about sagittarys a star in fact, seems to be though this could this could change, but at least seems in initial observations to be challenging some of the findings of general relativity. Yeah, so what do you what do you do with that?

What happens when you do an experiment you think it's a well designed experiment, but then it disagrees with Einstein? Well it's it's yeah, I mean, if they discussed in that of that talk, it's like you you, first of all, you might question, well, one of my results actually saying, but then you may be reaching the point where you're having to move beyond, uh, these theories and work with

new theories. So as we learn more about black holes, we're not just learning more about this arguably kind of abstract seeming thing that has no direct influence over our lives here on Earth. But it changed. But they have the ability to change our understanding of the cosmos itself. I mean, wouldn't it be a fascinating thing if we were alive to see a new better theory of gravity emerge? It would? It would? It would it would change everything.

It's like it's like them. It's it's kind of like when they made another Blade Runner movie, except except even more ground shaking. You know, like you grow up thinking you're only going to ever have that one, and then they go and make another one, and then likewise you we would be living in a in a world in which we had our third gravitational theory, So third major one. Yeah, that would be really cool. Yeah. So yeah, astrophysicists, please

go out there and break Einstein kick his butt. Alright, Well, on that note, we're going to uh, we're going to rock it away from the event horizon. Now, we are going to close this episode out. As always, we urge you to check out Stuff to Blow your Mind dot com. That's the mothership. That's what we'll find all the podcast episodes. You'll find videos and blog posts there as well, also links out to our various social media accounts. Oh it's

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