How To Use a Black Hole To See Your Past

Welcome to the Rest of Science. I'm Hannah Fry. And I'm Michael Stevens. Today, Hannah, we are going to look into the past by looking up, but not in the usual way. We're not going to be doing the whole like, whoa, when you see the stars, you're seeing them as they were years ago. No, no, no, we're going to be looking at our own pasts in outer space. Am I? How am I going? Am I also going to learn a mnemonic doing this for how many feet are in a mile? Because I can feel one coming. That's not me looking into our past. That's me looking into our future. Believe it or not, Hannah, yes, you will. You've looked into our future. This is an episode where the research I did took me all over the place, and I'm not going to organize it. I'm going to just blast it all over everyone's ears and eyes. Here we go. This episode is brought to you by Cancer Asserts UK. Here's something strange. Your DNA contains more ancient viral fragments than genes. The genes that build our cells make up only 2% of our DNA. And for years, that is what scientists focused on. They treated the rest, the ancient viruses and stuff as junk. But now we know that that hidden majority, sometimes called the dark genome, influences how our biology works and how diseases like cancer behave. It's a reminder that progress rarely comes as a single breakthrough. It builds gradually. Cancer Research UK plays a central role in that progress, supporting decades of research into over 200 types of cancer, work that's helped double survival in the UK over the past 50 years. For more information about Cancer Research UK, their research breakthroughs and how you can support them, visit cancerresearchuk.org forward slash the rest is science. By the way, OK, here's another, this episode's going all over the place. Here's some other cool things I learned while I was doing this research. When it comes to how many feet are in a mile, I've always found it hard to remember until I read a little mnemonic. Just remember five tomatoes, five tomatoes, 5,280, Oh, five, two, eight, O's, five, two, eight, zero, five tomatoes. That's how many feet are in a mile. There you go. Yeah, you're welcome. Or just as an alternative, you could just switch the metric system and not have to bother. I mean, that's just putting that one on the table for you. Just as another option. Look, that's true. You could also remember that there's 1000 meters in a kilometer and you can remember 1000 because it's easy to remember. Exactly. Do you know what's weird is that also the United States is on the metric system. They just have a conversion layer on top of it. Like the inch is defined legally as 2.54 centimeters. No. Are you serious? Yeah, I'm serious. The inch is not described as the distance some, you know, krypton atom vibrates or what. No, it's just 2.54 centimeters. So we're tied to the metric system, but we add a layer of conversion to it. I also found out the other day that in America, instead of calling it the imperial system, which is what we call it here in the UK, you guys call it the English system. And is that true? No, not for me, but maybe other Americans do that. What do people call it? Anyway, when someone said that, I was like, no, no, no, no, no, no, no, no. Don't, no, you're not blaming that one on us. Okay, we saw the light. We switched over. We've been on metric for a long time. No. Have you also seen the flow diagram of what unit you should use to describe something if you're British? Because it is metric at all times, unless you're talking about beer. Oh, yeah. Well, but also speeds on the motorways. Right. Or speeds on the motorways. Or how much you weigh. Yeah. There you can use pounds. Or you can use stones. Just a whole like total other direction. So a centimeter is less than an inch. And if you look at a ruler, I've got a measuring tape here. You can see I've got tick marks for inches and centimeters. Where is there a point where an integer number of centimeters lines up exactly with an integer number of inches? Like it must happen eventually, right? What did you say? One inch is 2.55 centimeters. 2.54 centimeters. OK, 2.54 then. Yeah. But it actually happens sooner than you would think. Yeah, it happens at 50 inches. Does it? 50 inches is exactly 127 centimeters. I can show you. That is satisfying. I can show you right here. If you've, gosh dang it, if you've got a measuring tape, you can hear how messy my office is. Ah. All the cans of soda. Come on. They go, they go. There it is. 50 inches is exactly 127 centimeters. That is satisfying. Guess what? So you've heard that phrase, give them an inch and they'll take a mile. Did you know that that is a corruption of the original phrase, which was, give them an inch and they'll take an L? Where's that from? An L, E-L-L, not like take an L like lose, like loser, but take an L, E-L-L, which is a unit of measurement equal to a qubit, the distance from the forearm in the extended hand. That's an L because L used to mean arm. And that's why we call this an elbow, because it is the bend, the bow of the L, the bend of the arm, the elbow. So give them an inch and they'll take an L turned into, give them an inch and they'll take a mile just because of people mishearing it. Right. And actually, an inch and a mile, give someone an inch and they'll take a mile. I mean, that's really taken the mickey a lot, but give them an inch and they'll take an L. Actually, the distance between an inch and an arm's led this, it's not that bad. So actually people were not being as best-taking before. Right. And I like how today it has the added slang meaning of give them an inch and they'll take an L, give them an inch and they'll lose is what that, I don't know what that would actually mean. But okay, let's get back to telescopes. Okay, so first things first, we are literally talking about looking into Earth's past, our personal pasts by looking up into the sky. I would love to do this. And I have been thinking about doing this as a Vsauce episode for years, but it wasn't really until now that I got the pieces together, what do you know, it's time to record. So we're gonna talk about it now. And I'm literally saying that we could use something like this idea to watch who assassinated JFK and how. We could use this to lip read Albert Einstein's last words. Okay, let me ask you a question though. Can I ask you a question to kick us off? Okay. Yeah. This idea of looking out into the sky and then seeing ourselves, doesn't this require some sort of mirror? Yes. And I think we've briefly mentioned this on the podcast before, but we need a mirror. You know, if a mirror was a hundred light years away and we looked at it through a telescope, we would see Earth as it, we would see ourselves as we were 200 years ago, because that's how long it would take the light to get to the mirror, bounce back and come back to us. As far as we know, there aren't any mirrors out there in outer space or are there mirrors in outer space. No, but kind of. You could watch how the pyramids were built exactly, right? How many people were involved? See which aliens did them? Yeah, we could watch the aliens do it. Probably we would just see people doing it, but which exact technique they used would be resolved once and for all. Anyway, obviously, if we're going to be looking at our own pasts, we're going to be talking about light. So I wanted to show off my light nanosecond ruler. Look at that. Wait, hold on, explain it. Is that how far? It's a ruler like an architect's ruler. It's a triangular prism. It's got three faces and it's just about 30 centimeters long, about a fifth of an inch shorter than a foot. So it's kind of the size of like a regular 12 inch ruler for those of you who are not watching the video stream. This happens to be exactly how far light travels in one nanosecond. So that's 10 to the minus nine. 10 to the minus nine seconds, that's right. In a second, light travels a billion of these if you line them up in a long line. So because it's transparent, I can look through it and I can look at things like I can look at my computer screen where I see your face. And if I put my hand right up against one end and I look in the other, I can see my skin as it was a nanosecond in the past. Because that's how long it took the light that I'm seeing to reach my eyeball. So it gives you a sense of how goodness gracious, like everything we see we're seeing in the past, we only have one way to look and it's a go. And it's really trippy to think about what that means. It means that there is a sphere of light growing with me as the center at all times that contains photons that touched me sometime in the past. And once those hit some detector and are imaged, that image is me as I appeared at the moment that those photons touched me. So all this light that's hitting me, trillions of photons every second, they leave me and they go out into the world and they exist as this ever-growing ghost of what I used to be like, what I used to be doing. And so for someone who's three feet away, they're seeing that photon ghost of me three nanoseconds ago, which is basically nothing. It's basically live, face to face is live. But if I could see photons from that sphere of photons that left me a hundred years ago, well, I'd have to be a hundred light years away to see them, but I would be able to see myself a hundred years ago. Bad example, because I wasn't here a hundred years ago, but you see what I mean, right? I don't know, Michael, that beard is not me to suggest otherwise. Yeah, I have to remind myself to not mention all the times I hung out with silent Cal, President Calvin Coolidge. Any of you who are more than a hundred years old are cracking up right now. So then if you're looking in the mirror, I mean, you are seeing an old version of yourself, essentially, you've never seen yourself as you are in that moment. That's right, yeah, for every 30 centimeters, for about every foot away, something is, you are that many times two, because you got to go there and back, nanoseconds in the past. So what, like something a mile away, you're seeing that as it was 5,280 nanoseconds ago. Which is still a real sliver of time, like a really small amount of time to be absolutely clear. 5,000 out of a billion would be one second. Yes, a billion nanoseconds is, you're finally at one second, but when you look at things that are light years away, you're literally seeing them as they were that many years ago, because that's how long it took light, information from them to reach us. So yeah, not just the light, but their gravitational influence on us. Like the sun is about what, eight light minutes away. So if the sun does anything, like if the sun decided to turn blue, we wouldn't know for about eight or nine minutes. And that brings up all kinds of big questions about like, but when did the sun actually turn blue? I mean, does it make sense to say, oh, the sun actually turned blue eight minutes ago? Because there's no way to verify that. There's no way to like go back in time. Well, yeah, because I mean, I guess the question is, for who? The sun turned blue, for who? This is the question of like, what is happening in the Andromeda galaxy right now? If I could instantaneously teleport there, I would also move into its future relative to what it looks like to Earth. I'm just thinking about this 30 centimeters. So if you have a billion of those, I mean, if you are one light second away, the Artemis crew, when they were circling around the moon and looking back at Earth, the Earth shine photo that has now been, I mean, plastered everywhere, this is the most incredible photo. They were having the same effect, right? They were not looking at the Earth as to how it appeared in that moment, but how it appeared one second ago. Exactly. And that's enough to like feel a difference. Yeah, it is, it is. And by the way that you feel it is mainly through communications because we also are communicating with Artemis or we did through radio waves and those travel at the speed of light. And the Artemis crew became more than a billion of these away from Earth. So they were about 1.3 light seconds away from Earth at their maximum. So it took 1.3 seconds for their messages to get to us using radio waves, which means it took 1.3 seconds for light from us to reach them. So they were looking at Earth as it was 1.3 seconds ago. Now, from that distance, not much changes on Earth in 1.3 seconds that you can see. But you can even get more pedantic about it and say that the part of Earth that was in the middle, like the equator or whatever, the point right below them, that was closer to them than the edges of the Earth in the image because the Earth curves away. So there's a larger light nanosecond difference between the middle of the Earth that they see and the edges, right? It took like an opportunity to set up a camera and very precise atomic clock and then to sort of snap their photos, synchronize the snap to a particular time, right? One on the spaceship, one on Earth. I don't know, like a dog or something. And they like demonstrate. Oh, wow! They could have. Yeah, they could have used atomic clocks and the known dilation caused by their travel speed and gravitational effects. Because time is not moving in the same speed, right? On this extremely fast moving rocket and on Earth. Yeah, there would have been a difference, but they could have synchronized photos from their ship and from Earth. And I think they could have brought themselves like a giant football field-sized telescope and watched someone pop a balloon. And the synchronized photos would be such that on Earth we would see the balloon exploding and for them they would see the pin not even touching the balloon yet. And we'd be like, whoa, who's right? When did the balloon get popped? Yeah, right, it's the same thing, it's the same paradox. I can't believe they got so distracted by the moon that they forgot to do this much cooler thing. Next time, really, they should contact us before going up and we'll give them much better ideas of what kind of experiments they should be running. But this is gonna be a slow walk towards an answer, by the way, because I'm gonna keep getting distracted. I wanna talk about the fact that because this is one light nanosecond, we've broken it down into light picoseconds. I can take this ruler and I can line up like my thumb and I can say, wow, my thumb is about 210 light picoseconds long, so it takes light 210 trillions of a second to get from that knuckle to the tip of my thumb. But don't worry, there's also even less useful measurements on this ruler, because it's got all these sides. We've also got sound microseconds. And my thumb is about a hundred, gosh, I'd say it's about 180 sound microseconds long. So that means it takes sound 280 microseconds to go from here to here across my thumb. That's a, what a millionth of a second. Yeah, I can even measure how many micro-everests long my thumb is. So it's about seven millionths of everests height. So if you got 167,000 of my thumbs, or just probably like human thumbs, roughly, 167,000 human thumbs would be enough stacked on top of each other to be as tall as Everest. That's one of our most asked questions, so I had to address it. I always think it's a bit of a shame. You know how people, there's sort of standard lengths of measurement, it's like, oh, as long as a blue whale, or as big as a football field, or, you know, two double decker buses, I always think that we could have much more imaginative examples than that. You know, I think that the millions of Everest is just, that feels much more intuitive. Yeah, it does, right? We all know what a millionth of Everest is. Scientists should be using that more in their public announcements. I mean, hey, why not? The meter is one 40,000th of the Earth's circumference. I mean, it's the same idea. Yeah, I know, and that, by the way, is like a whole really fun story. We should do a whole episode on the history of units, because it explains why the Earth's circumference is like almost such a round number of meters. It's not a coincidence. It's because of us. 40,008, yeah. 40,008, yeah, yeah. Okay, but anyway, we're trying to talk about looking into the past. So let's now move on to things that we know can really affect light, black holes, right? So the idea here is that obviously a photon of light that has the wrong trajectory can fall into a black hole. Black holes' gravity is so strong, even light, the fastest thing possible cannot escape from it. But if the light has a slightly different trajectory, it can just get deflected by a black hole. It can get bent, right? Get bent. That's what a black hole says to light. It's some light. Now, that means that somewhere in between, there's a trajectory such that a photon will not fall into the black hole, but also will not get bent and escape along a different path. Instead, the photon will orbit the black hole. And these are called photon rings or photon spheres. This is a place where it's outside of the event horizon. So you could go there. You wouldn't be trapped in the black hole, but you could go there and you could look off to the side. And see the back of your head. You go there, the photon effectively bounces off your head, travels around in a circle, and then you is there for you to see it effectively. I mean, this is like our doughnut universe, where you could carry on looking all the way around like the Pac-Man universe, where you look around and then see the back of your head. Okay, I'm with you. Exactly, exactly. But smaller. You know, just the circumference of that particular photon sphere for the black hole. So there are also places where light will be bent 180 degrees. So it'll emanate from a place like my bedroom, circle around the black hole, and come straight back to my bedroom. So I could use a telescope to look at that particular part of space around the black hole. And I could see myself or I could see what was happening, you know, however long ago that light came from that spot. So this is your mirror, essentially. This is our mirror. That there are some photos that are being sent back. That's right. Now the closest black hole to earth is like a thousand light years away, more than that. Let me see, I wrote down the best contenders we know of so far. Yeah, so. A thousand's not bad, you know. A thousand's not bad. A thousand's not bad. We've missed the crucifixion of Jesus, unfortunately. We've missed the birth and death of Jesus Christ. To be specific, Gaia BH1, which was discovered in September of 2022 by Karim Al-Bhadri, by the way. We're discovering a lot of black holes now. This one is only 1,560 light years away. Come on, I got it wrong, because you've got to double it, haven't you? You've got to double it. We can look at 3,000 years ago. Okay, fine. Right. We haven't missed the birth and death of Jesus. We'd have to keep watching for a thousand years. And there might be black holes that are closer, but Gaia BH1 is what 3,120 light year total travel distance there and back. So if we could look at the light that had slingshot it around it, or boomeranged back, I guess that's the right word to use. Boomeranged back, we would see Earth as it was 3,120 years ago. Was there any cool stuff happening back then? Okay, let's think. I mean, Pythagoras is around then. There is this tree, this olive tree in Crete. It would have been sort of the oldest tree in the world. And that would have been a little sapling. That's cute. I'm looking up the Wikipedia page for the year 1094 BC. Right, the pyramids were already, you know, 1,500 years old by this point. Wow. You could watch Tumrobbers in the Valley of Kings. You could. You could. I think there's something about Israel, King David in Israel, maybe. Ramses the 11th was the Egyptian pharaoh during the 12th dynasty. We could check out what he was up to. This is around the time of the invention of cavalry. Oh, interesting. So it's interesting in Eurasia, you know, breeding horses that are large enough to be ridden into battle. That's quite fun. Yeah, we'd keep us busy. And every day we would see one more day in the future. So we could like follow these stories. The problem though is, can you really do this? Can you really do this, Michael? And the answer is no. But the answer is also yes. Obviously, when light travels that far away from earth, there's a lot of light extinction, all right? It's gonna run into gas and dust and it's gonna spread out. And there's gonna be way fewer photons that reach that black hole than originally emanated in all directions from the tomb robbers in the Valley of the Kings, right? Trillions of photons are falling off of them, but only some of them make it to this black hole. And an even smaller percentage actually have just the right trajectory to go around. But if you get a big enough telescope, you can capture these photons. And if you're willing to sacrifice some resolution, you can take some time lapses, put a lot of photos together and you can make some things out. So I've been trying to figure out how big of a telescope you would need. And here's what I came up with. So to make out a detail such that one pixel of your image represents just one centimeter, one square centimeter of area. What of earth, originally of earth? Originally of earth, yeah. You are ambitious, go on. Oh yeah, I'm starting with a lot of ambition here. So we're trying to take a picture such that each pixel is just one centimeter. I remember growing up and there being a new satellite image which could, you could distinguish sheep essentially, right? You could distinguish a sheep in an image. And everyone was very excited about it. And that is, that's probably like two or three pixels, but a sheep is way bigger than two or three centimeters. Okay, I've got my answer now. What did you find? I found that the commercial satellites have about 30 centimeters per pixel. So you want to think this 30 times. We're gonna be better than them. I wanna be able to like read a large print book. Okay, okay. And then the spy satellites are sort of top secret ones. They are about 10 centimeters per pixel. Only 10. Well, obviously I'm glossing over. You don't just wanna be able to, you wanna be able to tell what time it is on someone's wristwatch. That's sort of like the resolution you're looking for. That would be awesome. Yeah, I wanna be able to see the expressions on people's faces. I wanna be able to see what like, Genghis Khan looked like. Sure. Genghis Khan, I said Kong, like King Kong. But, so I mean, there's things I need to learn that don't require telescopes. But also, yeah, I'm looking for this great resolution. But to do this, to get a resolution of one centimeter per pixel from a distance of 3,120 light years, you would need to have a telescope whose primary mirror was 0.18 light years wide. Okay. That's more than one and a half trillion kilometers wide. For reference, Pluto is only about six billion kilometers away from the sun. So we need a telescope that is orders of magnitude larger than our own solar system. Than the solar system, amazing. Yeah, and we couldn't, we wouldn't have to be one big piece. It could be an array of smaller, more manageable to build pieces, but I think that we're limited by the amount of matter in our own solar system. We'd have to destroy the entire solar system, build a whole new thing that's even bigger. And then we could watch tears fall from the eyes of Achilles. I mean, look, you just really, really, really want to know what Gekker's can't look like. And I understand that ambition. I really want to know, and I really want to be able to, you know, watch not a movie about history, but literally watch history. Yeah, yeah, yeah. I mean, what you're saying is it's technically possible, just difficult. It's technically possible, yeah. Well, hold on, before we get to that, shall we take a little break? Yes. This episode is brought to you by Cancer Research UK. In the UK, nearly one in two people will face cancer in their lifetime. The question is, could science stop cancer before it begins? In over the past 50 years, Cancer Research UK has helped double cancer survival in the UK. And that's proof of what research can achieve, like take cervical cancer. Almost every case is caused by HPV, the human papillomavirus. And when scientists uncovered that link, prevention became possible. Indeed, it did by a vaccine. And it's protection that works way before the cancer itself can actually grow. After the vaccine was introduced, cervical cancer rates in England were nearly 90% lower than expected in women in their 20s. I mean, we're now genuinely at a point where this is a disease that is disappearing in young women in the UK. This is something that I really hope my daughters will never have to deal with. For more information about Cancer Research UK, their research, breakthroughs, and how you can support them, visit cancerresearchuk.org forward slash rest is science. Here's a different idea. Instead of building really big telescopes, we can take advantage of the fact that our solar system already contains some accidental telescopes. Go on. Okay, let's talk about the sun. So one of Einstein's big predictions was that a massive body can bend light. Doesn't have to be a black hole. Everything that has mass bends light, even you and me a little bit. But the sun is big enough that it's very noticeable. And this was confirmed years later, after his prediction during a solar eclipse, stars that should have been behind the sun were visible at the edge of the sun. Yeah, no, that's exactly right. So what was happening is that, imagine my fist is the sun, here's a star behind it. That light that's coming off the star and it should go this way and miss the earth, it gets bent by the gravity of the sun and it comes right towards the earth. And so we're able to see things that we shouldn't otherwise see. And this had to be done during an eclipse because of course the sun is too bright otherwise. Well, that's just what a lens does. A lens takes light and it bends it and then that light focuses somewhere else to produce an image. For the sun, its focal length is about 550 AU away from the sun, where an AU is an astronomical unit. That's the distance from the sun to the earth. So 550 times further from the sun, there's a focal point. So you can put a telescope there and you can use the sun to capture an enormous amount of light and send it all to a little telescope, just like a meter in diameter. And this is an actual real proposal. In fact, there's something called focal, which, oh man, I didn't write down what it stands for. But there are projects that have been proposed to the European Space Agency and to NASA to do this. Okay, but this is an enormous distance, 500 times the distance between the earth and the sun. I mean, this is by some order of magnitude, way further than any human-made object has ever traveled, including those that have left our solar system. That's right, yeah. It's like in excess of 80 billion kilometers away. And the furthest human-made thing from earth is the Voyager 1 probe. And it's not even that far yet, not even close. And it's been traveling since the 70s. However, it wasn't built to go really far. It was built to look at planets. We could use solar sails and a slingshot around the sun to get out there within UNI's lifetime. But then when you get there, how are you transmitting any of that data? I mean, all very good. If you can sit in the focal point, you have a mirror that's like a meter wide, get this incredible image of the universe that you otherwise wouldn't have access to, really amput the power of your telescope. But what are you gonna do then? How are you gonna get it back? Well, I mean, you send it back. You send back the data from the telescope, just like Voyager sent back photos of Jupiter. Yeah, but then, I mean, isn't it too far? It's not too far. I mean, look, look, look, look. I'm not the engineer who's building the thing. I'm the boss giving them OKRs. I'm saying, figure it out. And I mean, you're right to bring these concerns up because in order to, here's something really cool we could do with it. We could position it such that an exoplanet that was 100 light years away was exactly behind the sun. And then we could look at the light that came around the edge of the sun. It's all bent around. It's actually, it's called an Einstein ring. The planet wouldn't appear like a planet. It would appear like a ring of light that was all warped around the sun. And then we could piece that back together into an image of the exoplanet. In order to make that work, we would need to have a precision of aiming accuracy. That's about a hundred times what we currently can do. And it would take a long time for us to send and receive instructions from this telescope, of course. But listen to this, using the sun as a telescope would allow a brightness factor of one trillion times. So things become a trillion times brighter than they are to the naked eye. And a magnification of 100 billion times. Wait, what do we get from James Webb? What does that give us? Because comparing to the naked eye is like, well, you can't see very much from the naked eye at all. No, I mean, magnification is kind of the wrong word to use. For like James Webb, it doesn't zoom, doesn't have a zoom, right? It just is like focused at infinity and it takes in what it can. Its optical resolution is about a tenth of an arc second. So that's what a pixel is going to be for the James Webb telescope. Okay, it's quite far away from a centimeter, isn't it? Yes, well, so let's talk about like what an arc second is. It's a way of describing how large the apparent size of something is, right? Like if you're really close to me, your head will take up a lot of my field of view. But if you move further away, your head becomes small. Like right now I can crush your head between my fingers because it's apparent size is very small. It takes up a very small part of my field of view. We can divide up the field of view into degrees, right? 360 degrees would be the whole thing. And then you can divide a degree into what are called arc minutes. And there are 60 arc minutes in each degree. And you can divide an arc minute into 60 arc seconds. Now, to put this into perspective, if you hold out your pinky at arm's length, it covers about one degree of space around you. So 360 of your pinkies could completely surround you. Three fingers like this held at arm's length, that's about five degrees. One of these little, little like hang loose symbols, this is about 25 degrees. So when we're talking about 0.1 arc seconds, we're talking about the distance subtended by my pinky at arm's length, divided by 60, divided by 60 again, and then a 10th of that. And that's what you get for a pixel. That's what you get for a pixel from James Webb. Which is incredible compared to everything we've had before, it's absolutely incredible. It's important to say actually, the reason why they use arc seconds than a distance metric like centimeters, you don't know how far away this stuff is, right? All you have is your field of vision. That's the most sensible way to split up, split up the size of the image that you can possibly see. So James Webb has a resolution of a 10th of an arc second, but this proposed solar gravitational lens would have a resolution of a 10 billionth of an arc second. Whoa. Yeah. Like a billion times better. You are seeing way more, wow. So to put it another way, if we found an exoplanet that was 100 light years away, we could with this telescope, that's what 80 billion kilometers away, use the sun, to see that exoplanet 100 light years away with a resolution of about 25 kilometers per pixel. Right. Okay, this is a lot better. This is a lot better. That's not bad. That means we can see cloud cover, we can see oceans, coastlines, mountain ranges. You could see lights from cities. If you wanna see what 25 kilometer per pixel resolution looks like, just check out photographs from the Discover satellite, which is taking photos of Earth all the time. If you look at them, they just look like Earth. Obviously you can't see buildings, but you can see that that's the planet Earth. It's a globe. Oh yeah, yeah. You can see the outline of the coasts. Yeah, I mean, that's incredible. You can see, you can literally distinguish then between, well, day and night, between water and land. I mean, you can even really probably tell mountain ranges on that. Yeah, the atmospheric, you can see clouds, you can see those incredible. That's absolutely incredible. Yeah, you'd get a proper image of what exoplanets look like. And that's for an exoplanet 100 light years away. It would look like that, except with its own terrain and weather. But the closest exoplanet is like, Proxibus Centauri B, that's only a handful of light years away. Like give me a break, it'd be amazing. There's a lot of problems with this. I mean, one is that it's a long distance, 550 AU, more than 80 billion kilometers away. It has about 10 times further away than Pluto. Okay, that's actually, when you put it that way, that doesn't feel quite so bad. But maybe that's because I'm just forgetting how much closer the Earth is to the sun than it is to Pluto. Yeah, Pluto is far away. I mean, this thing would be far away. Personally, I think that a lot of these issues can be resolved within our lifetimes. And because of the new solar sail technology, that it used to be an idea, now we're actually using it, where you actually have like a big sail that unfolds, and it's pushed by the light pressure of the sun. And that push just keeps happening. So you get acceleration. It just gets faster and faster and faster and faster. We could get them out there. And when I say them, I say them because we might need more than one. It'd be nice to have multiples that are like chained up so that one gets into position. It does its thing. It tries to take the pictures. And then we learn from any mistakes it makes. And then we just wait for the next one. This is a very specific idea. And if you want more information, there's a PBS FaceTime episode about them. And they call this proposal the string of pearls proposal, where you've got a string of these little telescopes that are all moving back into position one after the other, trying their best to capture whatever it is we have put on the other side of the sun for them to see lensed and magnified and embrightened by the sun's gravity. Wait, tell me again what this project is called, focal. Yeah, look up solar gravitational lens. There's a specific proposal called focal. Although it's a difficult task, it's still better than the alternative, which is we never see what these exoplanets look like. Especially within our lifetime, 100 light years. It's going to take 100 years just to get a spacecraft there if it traveled at the speed of light, which it can't. Now we could get it using, I don't know, solar sails and maybe some kind of plasma radioactive propulsion system that would still be developed to get there within, you know, 500 years. But I don't care about that. I don't care what my great, great, great grandkids expect. I don't care what my grandkids experience. No, I take that back. I do. And if that's all we could do, I would do that for them. But I'd like to see these planets. I'd like to see it too. I think it's also, it's also worth saying. I mean, look, so much, we are incredibly biased towards vision, right? As humans, it's our primary sense. It's the way that we explore. And so this is a way to really accelerate the power that we already have. And so we're really exploring the universe as you described. We can't go out there, but if we could only see it, think about how much more we would understand about answering the question of whether we're really alone even, answering the question about, I don't know, like, all of the things that come up in this podcast so often, what are the edges of the universe? What happened before the Big Bang? All of these questions, I've done a complete 180, from thinking it was completely ridiculous science fiction and just scientists looking for funding for outlandish, crazy, wild ideas. I've done 180. I'm now the biggest, the biggest proponent for it at all. You've done a 180, just like the light around the black hole that's going to let me see my path. Yeah, I completely agree. Because at the moment, our images of exoplanets are actually data showing a wobble in a point of light, which is that planet star. We can't even resolve a star to be anything more than a point of light. We can learn what the star is made of by looking at the spectrum emitted from the star, but we can't see an exoplanet. If you look up information about them, there's a lot of artists renderings, but I'm talking about a feasible way. I mean, feasible is kind of in quotes, but a feasible way to image them just like the images we see of Earth, and it would allow us to tell what kind of atmosphere they have, find signs of life. We couldn't communicate with any intelligent life there within our lifetimes because it would take 100 years. What's the best candidate? I feel like the best candidate for an Earth-like exoplanet. 30, 40, 50 light years away, there are some good candidates for Earth-like exoplanets, and we could look at them. I wanted to bring up one more celestial body telescope idea that's even easier than a solar telescope, and that is one that's been pushed pretty hard by David Kipping. He has a YouTube channel where he explains his papers about this on his YouTube channel Cool Worlds, and his thesis, I believe, was about using Earth as a telescope. Now, Earth doesn't have nearly as much gravity as the Sun, but Earth does have something else that bends light, an atmosphere. Light. Light is refracted by Earth's atmosphere, and that effect is much more dramatic than the gravitational deflection. He's calculated out and shown that we could put a telescope four times as far away from Earth as the Moon. Not far at all. Get them in a few days. Okay. Obviously, there are some problems with using the atmosphere as a lens. One is that the atmosphere scatters light. The biggest one is that it's full of things called clouds, which just block the light. However, about 14 kilometers up, there's enough air to refract light. There's few enough clouds that only about 8% of starlight, or just light from outer space, is going to get lost. For light, refracted 14 kilometers above the surface of the Earth, all the way around the planet, and the focal point is about four times as far away as the Moon, about 1.5 million kilometers, which is where the James Webb telescope is. We can put things there. The amplification power, theoretically, of such a telescope would be 45,000 times. I think more realistically, Kipping has said it's more like 22,500. It's still amazing. That would effectively mean that a meter-wide telescope would act like it would have the power of, because of the assistance from Earth's atmosphere, the power of a 150-meter telescope. To put it in perspective, the James Webb telescope, 6.5 meters. Wow. Wow. Why are we doing this? This is great. Well, I don't know. Honestly, I think that we will do it. I've switched. Forget the focal project. I want this one. Because this is our only access to these things that are so far away. It's going to be through light, and we're going to need to use telescopes that already accidentally exist, a.k.a. celestial bodies. The universe provided us with the tools to look across these vast distances, and it provided us with a mind to appreciate them, but the mind can't build them fast enough. That's okay. The universe gave them to us. Yeah. At least not fast enough to satisfy our curiosity within our given lifetimes. I think there's something quite nice about that, though, you know, that we're talking now about exploration that covers such vast distances that uses such gigantic celestial objects to assist them, that this has to be multi-generational endeavors, right? This is not something that you can just, I don't know, have satellites launching in World War II and then land on the moon in the course of a single generation. This is something that's going to take many, many generations in order to be able to successfully do. Yeah. And I think that we, in a way, I think we owe it to future people to start these projects now. I think that we should start solar lens telescopes and Earth atmospheric lens telescopes now for us. But at the same time, we should launch things that in 500 years will reach, you know, an exoplanet, and then 500 years later, send the data, its data will finally be received on Earth. And those people, a thousand years from now, will say, thank you. This is the most incredible gift you guys could have left us, because there's a lot of things we're leaving the future that aren't good. The least we can do is balance it out. With an incredible gift to future generations. One other incredible gift, though, I mean, we could, rather than relying on celestial mirrors, you know, black holes and Einstein rings and so on, we could just do a second project, which was launching just a massive mirror that just hangs out about five light years away, you know? So that from that moment on, you get to rewind 10 years whenever you like. I think, I think I'd like to see that project suggested, you know? Yeah. I guess the way to do it would be, would it just be a mirror or would it be better to send a telescope that then uses some massive object to create a high resolution image, and then it sends that back at light speed to Earth. So we can all tune into a television channel or a live stream on Twitch of Earth five years ago, and we can zoom in close enough to make out our bodies, our facial expressions. Give me a break. Why would you not do that? I mean, that would be pretty fun. Obviously, there's a lot of problems. Our atmosphere is going to scramble up that light. It's going to be really hard to get crisp, clean pictures of faces doing things quickly, but you can see, you know, vaguely where people are maybe. I don't know. It's like, there's a lot of details here that would need to be figured out. A new form of CCTV, but it's like celestial, what could it be? Celestial circuit television. Wow. Do you think there's going to be privacy concerns? Of course there will be. Yeah, I think there definitely would be. Gosh. You need to get every single person on Earth to sign a waiver. You would, yeah. You would. Or maybe there could be a team in charge of the feed, and they randomly insert fake events so that you never know if something's real or not. That way we're protected, and yet you can kind of believe. Michael, have you not just reinvented the era of smartphones and deep fakes? Is that? Yeah. Okay. I'm saying a lot of things that I'm taking back right after I say them. But there's something here that's very beautiful and important. I think that feels like a very lovely place to stop. So we should say thank you for watching and listening to The Rest is Science. Make sure you're following wherever you get your podcasts. Make sure that you like and subscribe on YouTube. Can you tell that I just read that from a script because it feels like words that never naturally leave my mouth? No, it sounded great to me. Did it? Did it sound really authentic? To make it sound better, I will do a worse version. And if you'd like to ask us a question which we might just answer in our Thursday episodes, you can send that to therestiscientsatgolehanger.com. That didn't sound like you were reading a tour, Michael. You know when I first started presenting science shows at the BBC, they sent me into this presenter training thing. Have I told you this before? I don't think I have. Everyone, when they first start, they sound a bit like that when they're reading. They sound really robotic. What they do is they get you to read some Winnie the Pooh and imagine you're reading it to a really small child. Then you read the script in that same voice. Oh, yeah. And if you'd like to ask a question which we might just answer in our Thursday episodes, you can send it into therestiscientsatgolehanger.com. And that's basically how you practice changing your tone so that you're not just stuck between two levels. It slows you down and you wind up reading a bit ahead so you can do the voice. But so in the training, you're having to do this for Winnie the Pooh, but then actual news stories. Exactly. Anyway, you can hear more of our robotic reading when you join us on future episodes of The Rest of the Science. We'll see you next time. Yep, we'll hear a little image. Just look at the script. Bye. The Rest of the Science