How To Use a Black Hole To See Your Past

8:55Hannah Fry:So that's 10 to the minus 9.

8:58Michael Stevens:10 to the minus 9 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.

9:37Michael Stevens: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.

10:26Michael Stevens:It's basically live, face-to-face is live. But if I could see photons from that sphere of photons that left me 100 years ago, well, I'd have to be 100 light years away to see them, but I would be able to see myself 100 years ago. Bad example, because I wasn't here 100 years ago. But you see what I mean, right?

10:44Hannah Fry:I don't know, Michael. That beard is starting to suggest otherwise.

10:49Michael Stevens: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 100 years old are cracking up right now.

11:00Hannah Fry: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.

11:09Michael Stevens: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.

11:30Hannah Fry:Which is still a real sliver of time, like a really small amount of time, to be absolutely clear. You know, 5 ,000 out of a billion would be one second.

11:40Michael Stevens:Yes, a billion nanoseconds, 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, you know, eight or nine minutes. And that brings up all kinds of big questions about like, but when did the sun actually turn blue?

12:18Michael Stevens: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 go back in time.

12:29Hannah Fry:Well, yeah, because I mean, I guess the question is for who? Like the sun turned blue for who?

12:36Michael Stevens: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.

12:52Hannah Fry:I'm just thinking about this 30 centimetres. 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 Earthshine photo that has now been plastered everywhere, so 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.

13:25Michael Stevens:Exactly.

13:25Hannah Fry:And that's enough to, like, feel a difference.

13:28Michael Stevens:Yeah, it is. It is. And 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.

14:12Michael Stevens: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?

14:36Hannah Fry:I do feel like they missed 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, a dog or something. And then like demonstrate.

14:53Michael Stevens:Oh, wow. They could have. Yeah, they could have used atomic clocks and the known dilation caused by their travel speed and gravitational effects. effects.

15:05Hannah Fry:Because time is not moving in the same speed, right, on this extremely fast-moving rocket and on Earth.

15:11Michael Stevens: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, you know, football field-sized telescope and like 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 like the pin not even touching the balloon yet. And we'd be like, whoa, who's right?

15:37Hannah Fry:When did the balloon get bought? Yeah, right. It's the same thing. It's the same paradox.

15:41Michael Stevens:I can't believe they got so distracted by the moon that they forgot to do this much cooler thing.

15:47Hannah Fry: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.

15:54Michael Stevens:But this is going to be a slow walk towards an answer, by the way, because I'm going to keep getting distracted. I want to 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 trillionths 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.

16:38Michael Stevens:So that means it takes sound 280 microseconds to go from here to here across my thumb. That's a millionth of a second.

16:49Hannah Fry:Yeah.

16:49Michael Stevens:I can even measure how many micro Everest's long my thumb is. So it's about, it's about seven millionths of Everest's 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.

17:17Hannah Fry:I always think it's a bit of a shame. You know how people, the 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 the millions of Everest is just, that feels much

17:37Michael Stevens:more intuitive. It does, right? We all know what a millionth of Everest is. Scientists should be using that more in their public announcements.

17:47Hannah Fry:I mean, hey, why not? The meter is one 40 ,000th of the Earth's circumference. I mean, it's the same idea.

17:53Michael Stevens: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.

18:11Hannah Fry:40 ,008, yeah.

18:12Michael Stevens: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 hole's 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 the black hole. It can get bent, right? Get bent. That's what a black hole says to light, 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.

19:09Michael Stevens: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.

19:26Hannah Fry:You go there, the photon effectively like 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 donut universe where you can carry on looking all the way around like the pac-man universe where you look around and then see the back of your own head okay i'm with you

19:45Michael Stevens:exactly exactly but smaller you know just 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.

20:23Hannah Fry:So this is your mirror, essentially.

20:26Michael Stevens:This is our mirror.

20:27Hannah Fry:That there are some photos that are being sent back.

20:30Michael Stevens: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.

20:42Hannah Fry: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.

20:52Michael Stevens:So to be specific, Gaia BH1, which was discovered in September of 2022 by Kareem El-Badri, by the way, we're discovering a lot of black holes now. This one is only 1 ,560 light years away.

21:06Hannah Fry:Hang 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. That's right. Right. We haven't missed the birth and death of Jesus.

21:16Michael Stevens:We'd have to keep watching for 1 ,000 years.

21:18Hannah Fry:Yeah.

21:19Michael Stevens: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 slingshotted 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?

21:44Hannah Fry:Okay, let's think. I mean, Pythagoras is around then. There is this tree, this olive tree in Crete, that would have been sort of the oldest tree in the world. And that would have been a little sapling.

22:00Michael Stevens:That's cute. I'm looking up the Wikipedia page for the year 1094 BC. Right.

22:07Hannah Fry:The pyramids are already, you know, 1500 years old by this point.

22:11Michael Stevens:Wow. You could watch tomb robbers in the Valley of Kings.

22:17Hannah Fry:You could. You could. I think there's something about Israel, King David in Israel, maybe.

22:25Michael Stevens:Ramses XI was the Egyptian pharaoh during the 12th dynasty. We could check out what he was up to.

22:33Hannah Fry:This is around the time of the invention of cavalry.

22:38Michael Stevens:Oh, interesting.

22:39Hannah Fry:In Eurasia, you know, breeding horses that are large enough to be ridden into battle. That's quite fun.

22:45Michael Stevens:Yeah, it would keep us busy. And every day we would see one more day in the future so we could 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 going to run into gas and dust and it's going to spread out. And there's going to 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.

23:27Michael Stevens: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.

24:02Hannah Fry:Of Earth? Originally of Earth?

24:04Michael Stevens:Originally of Earth. Yeah.

24:06Hannah Fry:You are ambitious. Go on.

24:09Michael Stevens:Oh, yeah. I'm not going to. I'm starting with a lot of ambition here. So we're trying to we're trying to take a picture such that each pixel is just one centimeter.

24:17Hannah Fry: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, you know, that's probably like two or three pixels. But a sheep is way bigger than two or three centimeters.

24:41Michael Stevens:Okay, I've got my answer now. What did you find?

24:47Hannah Fry:I found that the commercial satellites have about 30 centimeters per pixel. So you want something that's 30 times better? We're going to be better than them.

24:59Michael Stevens:I want to be able to like read a large print book.

25:02Hannah Fry:Okay. Okay. And then the spy satellites, the sort of top secret ones, they are about 10 centimeters per pixel.

25:11Michael Stevens:10? Only 10? Well, you know, obviously I'm glossing over.

25:16Hannah Fry:You want to be able to tell what time it is on someone's wristwatch. That's sort of like the resolution you're looking for.

25:22Michael Stevens:That would be awesome. Yeah. I want to be able to see the expressions on people's faces. I want to be able to see what, like, you know, Genghis Khan looked like. Genghis Khan. I said Kong, like King Kong. But 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 1.5 trillion kilometers wide. Right. For reference, Pluto is only about 6 billion kilometers away from the sun.

26:11Michael Stevens:So we need a telescope that is orders of magnitude larger than our own solar system.

26:17Hannah Fry:Than the solar system. Amazing.

26:18Michael Stevens:Yeah, and 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.

26:40Hannah Fry:I mean, look, you just really, really, really want to know what Gekka's car looked like. And I understand that ambition.

26:45Michael Stevens: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.

26:53Hannah Fry:Yeah. Yeah. Yeah. I mean, what you're saying is it's technically possible, just difficult.

26:59Michael Stevens:It's technically possible. Yeah.

27:01Hannah Fry:Well, hold on. Before we get to that, shall we take a little break?

27:03Michael Stevens:Yes.

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27:37Hannah Fry:It builds on TracerX, the world's largest cancer evolution study, which tracked lung cancer cells over many years to uncover the disease's earliest warning signs. LungVax is designed to train the immune system to spot these signs early on, destroying 40 cells before cancer develops.

27:56Michael Stevens:So it's not treatment, but preventative, with the potential to stop lung cancer before it starts. The first stage of the trial starts this year, focusing on people at higher risk.

28:07Hannah Fry:It shows what long-term research makes possible.

28:10Michael Stevens: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.

28:29Michael Stevens: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. It 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.

29:11Hannah Fry:Yeah, no, that's exactly right.

29:12Michael Stevens: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.

29:53Michael Stevens: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.

30:27Hannah Fry: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.

30:44Michael Stevens: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 you and I's lifetime.

31:15Hannah Fry: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, have a mirror that's like a meter wide, get this incredible image of the universe that you otherwise wouldn't have access to, you know, really amp up the sort of the power of your telescope. But what are you going to do then? How are you going to get it back?

31:38Michael Stevens: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.

32:19Michael Stevens: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, you know. But listen to this. Using the sun as a telescope would allow a brightness factor of one trillion times.

33:00Michael Stevens:So things become a trillion times brighter than they are to the naked eye and a magnification of 100 billion times.

33:10Hannah Fry:Wait, what do we get from James Webb? What does that give us? Because comparing to the naked eye He's like, well, I mean, you can't see very much from the naked eye at all.

33:17Michael Stevens: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.

33:36Hannah Fry:Okay, it's quite far away from a centimeter, isn't it? Yes.

33:39Michael Stevens: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, you know, 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 its 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.

34:15Michael Stevens: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 tenth of that.

34:56Hannah Fry:And that's what you get for a pixel.

34:59Michael Stevens:That's what you get for a pixel from James Webb.

35:02Hannah Fry: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 rather than a distance metric like, centimeters. You don't know how far away this stuff is, right? All you have is your field division. That's the most sensible way to split up the size of the image that you can possibly see.

35:22Michael Stevens:So James Webb has a resolution of a tenth of an arc second, but this proposed solar gravitational lens would have a resolution of a ten billionth of an arc second.

35:35Hannah Fry:Whoa. Yeah.

35:38Michael Stevens:So like a billion times better.

35:39Hannah Fry:You are seeing way more. Wow.

35:44Michael Stevens: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.

36:05Hannah Fry:Right. Okay, this is a lot better. This is a lot better.

36:09Michael Stevens: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 want to 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.

36:38Hannah Fry:Oh, yeah. Yeah. I mean, you can see the outline of the coasts. Yeah. I mean, that's incredible. You can see, I mean, 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 know, you can see clouds, you can see, there's incredible. That's absolutely incredible.

37:02Michael Stevens:Yeah.

37:03Hannah Fry:You'd get a proper image of what exoplanets look like.

37:06Michael Stevens:And that's for an exoplanet 100 light years away. It would look like that, except with its own terrain and weather. But, you know, the closest exoplanet is like, you know, Proxima Centauri b. That's only a handful of light years away. Like, give me a break. That'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's about 10 times further away than Pluto.

37:39Hannah Fry: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.

37:50Michael Stevens: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 cell 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.

38:35Michael Stevens: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.

39:08Hannah Fry:Wait, tell me again what this project is called, Focal.

39:10Michael Stevens: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. A hundred light years? It's going to take a hundred 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 experience.

39:56Michael Stevens: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.

40:03Hannah Fry:I'd like to see it too. I think it's also worth saying, I mean, look, 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. I mean, 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, all of the things that come up in this podcast so often. What are the edges of the universe?

40:42Hannah Fry: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 a 180. I'm now the biggest proponent for it of all.

40:58Michael Stevens: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. Like 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 artist 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.

41:40Michael Stevens: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, you know, 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.

42:21Michael Stevens: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. Right. So 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.

43:00Hannah Fry:Not far at all. Get there in a few days.

43:02Michael Stevens:Okay. So 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, the focal point is about four times as far away as the moon, about one and a half million kilometers, which is where the James Webb telescope is.

43:45Michael Stevens:Okay, we can put things there. And the amplification power, like theoretically of such a telescope would be 45 ,000 times. I think more realistically, Kipping has said it's more like 22 ,500.

43:59Hannah Fry:That's still amazing.

44:00Michael Stevens:That would effectively mean that a meter wide telescope would act like it would have the power of, because of assistance from Earth's atmosphere, the power of a 150-meter telescope. To put that in perspective, the James Webb Telescope, six and a half meters. Wow.

44:19Hannah Fry:Wow. Why are we doing this? This is great.

44:23Michael Stevens:Well, I don't know. I think, honestly, I think that we will do it. I've switched.

44:28Hannah Fry:Forget the focal project.

44:31Michael Stevens: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. Like, 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.

45:04Hannah Fry:yeah at least not fast enough to satisfy our curiosity within our 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.

45:41Michael Stevens: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, 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.

46:19Hannah Fry: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 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 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

47:05Michael Stevens: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.

47:20Hannah Fry:Why would you not do that? I mean, that would be pretty fun.

47:23Michael Stevens: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 um 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

47:48Hannah Fry:celestial what could it have a cv 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 You need to get every single person on earth to sign a waiver.

48:06Michael Stevens:You would. Yeah, you would. Or maybe there could be a team in charge of the feed and they like 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.

48:23Hannah Fry:Michael, have you not just reinvented the era of smartphones and deep fakes? Is that?

48:29Michael Stevens: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.

48:39Hannah Fry:You know, I think that feels like a very lovely place to stop. So we should say thank you for watching and listening to The Rest of 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?

48:58Michael Stevens:Here, 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 the rest is science at goal hanger dot com.

49:11Hannah Fry:That didn't sound like you were reading at all, 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. And what they do is they get you to read some Winnie the Pooh. And imagine you're reading it to like 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 in to the rest is science at goalhanger.com.

49:51Hannah Fry:And that's basically how you practice changing your tone so that you're not just stuck between two levels.

49:57Michael Stevens:It like 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 like actual news stories.

50:08Hannah Fry:Anyway, you can hear more of our robotic reading when you join us on future episodes of The Rest of Science. We'll see you next time.

50:17Michael Stevens:Yep. Hold on. Let me just look at the script. Bye.