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The Rest Is Science

How To Prove You're A Time Traveller

22 Apr 2026

Transcription

Chapter 1: What is the main topic discussed in this episode?

1.297 - 15.718 Hannah Fry

Welcome to The Rest Is Science. I'm Hannah Fry. And I'm Michael Stevens. And this is Field Notes, which is the part of the week where Michael and I are supposed to take a bit easier to turn up and just answer your questions and show each other an object and have a lovely old time.

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16.319 - 24.351 Hannah Fry

And frankly, you guys don't notice the amount of effort that we put in in the other one because you like this one just as much.

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24.331 - 35.64 Michael Stevens

Well, you know what? It's the magic that we have, Hannah. We should try to do something really boring. Like how few views can we get on a podcast episode?

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35.772 - 39.097 Hannah Fry

Make that the challenge, yeah. See what we can optimize for.

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39.117 - 64.716 Michael Stevens

We could do just like a clip show. Like, not a best of clip show, but a worst of clip show. The moments where jokes fell flat, where we said something kind of wrong. Unfortunately, it's not going to be today because it's absolutely jam-packed full of amazing stuff. I know. Today's is actually good. Today, I want to show off a tool I invented that helps solve a problem that will never happen.

64.932 - 79.38 Hannah Fry

We've done something a bit different today. We've done something a bit upside down. We've gone through the mailbag and we have found questions that are all to do with time travel or sort of unexpectedly popping out of existence in one place and popping up somewhere else.

79.478 - 101.689 Michael Stevens

So I'm going to begin with a question for you, Hannah, and this is also for all the listeners out there. Okay. If I were to time travel you right now at this instant with what you have on your person to today, okay, this exact same day, but in 2007. Right. How would you prove that you were from the future?

108.807 - 111.591 Hannah Fry

This episode is brought to you by Cancer Research UK.

111.952 - 132.305 Michael Stevens

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.

Chapter 2: How can you prove you're a time traveler?

365.396 - 391.211 Michael Stevens

But this thing will stay on you At all times. And it is an emergency tool to prove that you've traveled through time to the people in the past. The way it works – and I want to hear what your thoughts are because I'm not saying this is perfect. But what this gives you is a timeline with some bars on it showing famous, widely known things that were lost – And then later found.

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393.374 - 403.368 Hannah Fry

Oh. So. So hold on. We know where they are now because we live in the future. But if you go back in time, people don't know where they're hidden.

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403.688 - 426.485 Michael Stevens

Exactly. Because you can't just go back with like a diagram of an iPhone to say the 50s and show people, see, this is a future technology. They'll just think that you're really smart and came up with it. You know? But could you go back with the exact coordinates of the Titanic? Yes, you could. And so this slap bracelet gives you... the timeline, and the GPS coordinates.

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426.845 - 448.707 Michael Stevens

So if you go back to say, let's say you pull a Marty McFly, you go back to the 1950s, you can say, okay, guys, well, the Titanic has been lost, but it hasn't been found yet. But it can be found at 41 degrees north, 49 west, and some change. And they'll go, wow, how did you know that? You must be a sea expert. And you're like, no, no, no, I can also tell you where...

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448.687 - 468.911 Michael Stevens

Let's see what's another good one for the 80s. I can also tell you where the HMS Endurance or the Shackleton ship is. Oh, nice. So they're stuck going either this guy independently discovered these two sunken ships. or traveled through time, in which case I believe time travel is the better explanation.

469.731 - 488.949 Michael Stevens

We've also got Archimedes' Ostomachion, the method of mechanical theorems, which was lost in 1204 and not recovered until 1906. We've got the Baltimore Gold Hoard, which was lost in 1856 and found in 1934. The Sutton Hoo Ship Burial from the 7th century, lost until 1938.

489.049 - 491.772 Hannah Fry

I don't know what that one is. What's that one?

491.752 - 511.274 Michael Stevens

I can't tell you any more details, Hannah. I'm just helping time travelers. I'm not a history teacher. It was our science writer, Scott Frank. I'll give him a shout out. He's the one who found this. I'm like, they need to overlap. There must always be at least two things for every year. Because you can't just prove it with one. You could just have got lucky. Can't prove it with one.

511.354 - 533.878 Michael Stevens

With one, you're just a good looker. But with multiples, especially different types of things, like a shipwreck, a gold hoard, and an ancient manuscript, come on. You're a time traveler. You're from a time... when these things have been found. And unlike the result of a sporting event or a lottery, you can immediately have people go out and verify your claim. Hang on.

Chapter 3: What challenges do time travelers face in gaining credibility?

743.781 - 770.879 Michael Stevens

You know, the problem is that your body changes, your skin changes, and so the inch changes. But again, as a sign of like, I'm a maker and I'm a measurer and I love quantities and quantification, it's a great tattoo to have. But we struggled with this at the Curiosity Box, trying to come up with a shirt that had rulers on it because inevitably the shirt will stretch.

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771.299 - 795.235 Michael Stevens

The shirt is a material that moves. It's just not useful as a measuring tape. It can be useful for, you know, formulas and conversion tables. That's great. We've done two shirts that have that property. But this is so far the best I've been able to come up with. And I'm just now realizing that this is the prototype. The real ones we made were adult sized. Look at that.

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795.215 - 798.48 Hannah Fry

Ah, more space for more coordinates.

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798.72 - 814.843 Michael Stevens

This is for your time traveling children. This is an adult slap bracelet. It is like really long, by the way. You could wear it as a neckerchief. You could. Yeah. Let's see if I can. Oh, no, I can't. Look at that.

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814.925 - 827.268 Hannah Fry

Any of you who are listening rather than watching, you just missed the absolute delight of watching Michael Stephenson, face of Spain, slap himself in the neck with a slap bracelet.

827.588 - 839.794 Michael Stevens

I'm kind of a Gastoni guy. My neck is too thick. Even my pie tape won't tell me the diameter of my neck. It's just not long enough. Well, that'll be for a future item. Look at that. See? Doesn't make it.

840.354 - 840.955 Hannah Fry

So close.

841.275 - 841.856 Michael Stevens

So close.

842.296 - 847.422 Hannah Fry

Careful now. You have to lift up your head quite far to get your beard out of the way. I don't want you to get your top job vertigo.

Chapter 4: What unique tools can help a time traveler?

1377.456 - 1394.709 Michael Stevens

I had never thought of that before. But yeah, I mean, 150 million years ago, you can go further than that before there are even early mammals. And then you're really in trouble because the mammalian diet needed to be there for mammals forever. which we are, to exist.

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1395.27 - 1403.421 Michael Stevens

Now, I feel like I could maybe eat some fish, but you're saying that the food chain is probably pretty contaminated with stuff that we're not ready for.

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1403.481 - 1424.294 Hannah Fry

Absolutely. Absolutely. I mean, you probably would be able to. You probably would be able to, but it's not... I mean, you're really going to struggle. Also, by the way, it's not just the food, because if you're going back 150 million years ago, the CO2 levels... are five to 10 times higher than you've got today. So you are going to be perpetually out of breath, basically.

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1424.774 - 1432.849 Hannah Fry

You might be trying to hunt down a dinosaur to eat them, but you're going to be suffering from CO2 toxicity just trying to get dino steak.

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1433.41 - 1463.851 Michael Stevens

That's wild. How have I never thought of that before? Yeah, of course. It'd be easier to go to Mars. Right. than to go live in the early Jurassic, but you're on Earth, and yet it's just not for you yet. The air isn't right. If you're a vegan, sorry. If you're willing to hunt living creatures, you don't have any chicken. You've basically got... fish, sharks, reptiles.

1464.813 - 1467.097 Michael Stevens

Other than that, you've got a bunch of like tree bark.

1467.398 - 1484.928 Hannah Fry

Yeah. Bit of tree bark. That's it. Not even any grass. Can't even chew on any grass. So no wheat. No wheat, no grains, nothing. Yeah. It's going to be, it's going to be, you're going to have a terrible time. And no one around to tell about the bracelet. Okay, here's a question from Adam.

1485.649 - 1502.755 Hannah Fry

I really like this question because, of course, everything that's going on with Artemis at the moment, that amazing expedition around the dark side of the moon. Adam asks, what would the lag on a FaceTime call be like from space or from the moon? Oh, yeah.

1503.376 - 1529.557 Michael Stevens

What would it be like? So, you know, the lag... That we get in FaceTime calls is caused by all kinds of factors. But ultimately, at the very end, even if your technology is perfect, you're always bound by the speed of light. The speed at which an electromagnetic signal travels. It's finite. And it's really fast. But... When you talk about really long distances, it becomes a big problem.

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