Time After Time Travel

time travel. But I don't really want to focus too much on the various proposed technological approaches to time travel, because those are all either pure science fiction or they're very much hypothetical and based upon lots of of tenuous guesswork. Instead, I'm gonna do something even more outlandish, like how could we tell if time travelers have walked among us? All Right,

so we're gonna talk a little bit about that. I will cover a bit of the philosophy behind time travel, because there's still a debate about whether or not time travel is a technological possibility. I mean, we know that time travel works, because we're doing it right now, traveling forward in time at the rate of sixty minutes per hour. That that's just how time works. However, we also know that if you were able to say, get in a spaceship and push that spaceship too incredible speeds that humans

have never been able to get to. But let's say that you're getting into a spaceship and you're able to accelerate to near the speed of light, like five the speed of light. That is wicked fast. And you know, we know the speed of light is the speed limit for space time in our universe, so you're not gonna go faster than that. And you can't really get mass to the speed of the speed of light as it

has mass. That that's one of the limiting factors. But let's say you can get If you were able to do that, then time to you would seem to pass as normal, like a second would be a second, a minute would be a minute. It would feel exactly the same as if you were anywhere else. However, time with respect to someone who's back on Earth, it would seem

to be very different. It would seem as if the people back on Earth were living out time at a much accelerated rate, and that to them, you are experiencing time at a much slower rate. So let's say you go off on a five year adventure of exploration around the galaxy. So you're zooming around at the speed of light. After five years, you come back home to Earth, it would look like everyone had aged decades while you were gone for just five years. Like you aged five years,

everyone else aged fifty years. Everyone else looks much older to them. It would seem as if time had barely touched you at all. They had lived out their lives decade after decade, and you are barely any older than when you left. So, in a way, that's kind of like time travel, right it would be like you are traveling to the future, but you're doing so in a way that time is still to you, passing exactly the way it always has. It's only when you take the

reference of someone else. Uh, this is why we call it special relativity. That's part of the theory of special relativity. It's relative to the perspective of someone else who's moving at a different speed throughout space time. So that kind of time travel would be totally possible if you could get a spacecraft up to those speeds, which right now would be impossible for us. But if you could, you

would be able to travel to the future. But what if you wanted to travel to the asked ah That would be super duper hard traveling to the future is easy, you just wait. Traveling to the past way more tricky. So, scientifically, based upon what we understand of our universe and the laws of physics as we understand them right now, we would say that if time travel to the past is possible at all, it's probably only possible up to the point where uh are from the point where the time

travel machine was first made. So, in other words, let's say it's Tuesday afternoon and you don't have anything going on, so you build yourself a time machine. Well, any point after Tuesday afternoon, you could use that time machine to travel back to Tuesday afternoon, but you couldn't go to Tuesday morning or Monday, or any point before you had created the time machine. The time machine would be your

point zero. So, sadly, this would mean there's no way for us to go back to the time of the dinosaurs unless we just happened to come across some t rex's old time machine sitting around somewhere or something, or maybe an alien time machine where aliens had visited the Earth millions of years ago, and so we find their time machine. It's still miraculously works. We figured out how to use it, and it doesn't turn us into goo.

That's a lot of ifs. Also, it depends upon aliens having visiting us, so a long shot at best, I guess we could say, however, we can look for evidence to see if time travelers have visited us. So let's say that someone has infened a time machine at some point. Presumably that would mean someone from the future could come back to some point in our past up to present day, any point where the time machine had been made forward, and we would potentially be able to figure that out.

How would we do that? How do we identify the time travelers who secretly walk among us? Well, maybe they would identify themselves. So the first person I want to talk about is someone that I actually did a full episode of tech stuff about years and years ago. This would be John t toor or tight towards t I t O R. This is one of those Internet memes from the early early days of the Internet, back in the late nineties early two thousands, was actually a radio

thing before it was an Internet thing. And the story is that, supposedly, according to the narrative, a guy living in the year twenty six travels back in time, and the purpose for traveling back in time. According to the guy, was that he needed to get a specific compute, one of the early portable computers. And by portable, I mean you could in theory lug it around, but it was super heavy, like many many, many pounds. It was a

nineteen computer, the IBM fifty. I think it was like fifty pounds if I'm not mistaken in weight, not in not in cost. And that, uh, this computer somehow was going to be able to fix a problem that existed in his present day of twenty thirty six, that problem being largely this issue of a Y two K like problem. So if you remember the Y two K issue, it was that a lot of computer programming had designated years

as being two digit numbers. Because this was back in the nineteen hundreds, the late nineteen hundreds, when no one was really thinking, oh, the system I build now is going to be the same one we're gonna rely on thirty years from now. So pro members were building in the shortcut of of you know, abbreviating the year to two digits. The game. By the time this is getting to the point where we're at nine, surely will have

moved on to a different architecture. Software architecture, and they were wrong, because if we can build onto existing structures without having to redo the whole thing, that's usually the choice we make. So the Y two K problem was that no one was really sure what would happen when the year rolled over from to two thousand and all those two digit numbers would now say zero zero instead

of nine nine. Would that mean that the systems would suddenly think that we had rolled over and now the year was nineteen hundred and a lot of those systems were important for things like calculating things like interest and uh, you know, financial issues, and other control systems. There's a worry that things were really going to go pear shaped on January one, two thousand, when all these computer systems might spontaneously fail, and so there's a huge effort made

to fix that. Well, there's a similar issue in Unix, except instead of it being the year two thousand, it would be the year twenty thirty eight. And so John Titor, as he called himself, said that was why he came back in time, was to get hold of this particular computer in order to solve this problem in the future and head off a terrible calamity of all the computer

systems in in the world failing in various ways. The very first appearance of this personality was in a facts that used to be a thing still is in a few rare cases, but the facts that was sent to Art Bell, who was the host of a show called Coast to Coast a m which was really a show that focused on all sorts of weird fringe theories and

paranormal phenomenon and things like that. This is back in nineteen and in that message, the person claimed that the Y two K problem had created a huge catastrophe in the future. And so there were a lot of warnings that John Titor would give. Over the course of the next several years. He would show up on various message boards giving various details about the future according to his travels.

You know, he's making all these these claims that were unsubstantiated, although if you wait around long enough you could find out if they were true. But a lot of his predictions failed failed to play out the way he had said. Like he said, why two K was gonna lead to massive disaster? It didn't. It did cause problems, but nothing nearly on the level that what of what people were afraid of? He said the two thousand four Olympics would

get canceled. They didn't. He also said that by the United States would split into warring factions and there'd be a great civil war, which did not happen. I mean, you could say that people are more polarized than ever before, but we haven't turned into tribal groups that are actually making war on each other in uh, in the way

that he was suggesting. And he did say, however, that he was really from a parallel universe, one that was nearly identical to ours, but that there was probably a deviation between one to two per cent, so that things that happened in his universe may not happen exactly the same way in ours, but largely things would be more or less the same. He also said eventually that the future wasn't necessarily fixed, which is another get out of jail free car card if you're a time traveler. I

guess uh. Eventually, there was some evidence that suggested that this was all the work of a couple of brothers in Florida who had sort of orchestrated the whole thing. There was another person who claimed that he was sort of consulted as part of this and that was kind of a collaborative storytelling exercise that sort of snowballed out of control. So chances are not a real time traveler. So then there was also the sad but fascinating tale of a man who used the pseudonym Bob White among others.

This was back in the early two thousand's and this guy sent out emails in huge blasts, like millions of people were getting these emails, and essentially this was a spam email, but instead of trying to sell something, uh, this spam email was asking for some pretty crazy fictional technology.

It was like a three page long manifesto and it included things saying that the person needed something like an AcBe five by twenty four series time transducing capacitor was built in temporal displacement, which is not a thing, but was asked for. So a guy named Dave Hill responded to this. He found it fascinating and he went so far as to even send an old hard drive, calling it a warp generator. But then he found out that the recipient wasn't just someone like making a joke on

the internet. It was someone who actually seemed to truly believe in what they were saying, and they were showing some signs of paranoia and some other concerns. And it turned out that this was Robert Robbie Todino, who had been sending millions of emails since November two thousand one. He was in his twenties. He had founded a company called RT Marketing, which sent out spam messages about all

sorts of products on behalf of various clients. But he was eventually hit with a five thousand dollar fine from the state of Massachusetts in a cease and desist order for that sort of stuff. That's around the time when he started sending out these anonymous calls for help in obtaining various science e sounding but largely fictional pieces of equipment. And he said that his life had been quote severely tampered with end quote and they needed to find a

way to rewind time to fix it. And he called himself Bob Wyatt or Tim Jones or several other aliases as he corresponded with other people. His father said that Tudino had mental health problems, including dissociative disorder, and that the interactions with people had made it worse. Some people were likely taking advantage of him it's a very sad story. But he was seemingly convinced that time travelers were in fact real and walking among us, but no actual evidence

came from that. So that's one way we can look for time travelers, look for people who claimed to be them. But maybe that won't work. Maybe people are maybe they're a little more shy. So what if we were to ask them to show up at a particular place in time. So that was the thought behind the m i T

Time Traveler Convention. On May seven, two thousand five, students at m i T, who were led by an Electrical engineering and Computer scien it's graduate student named Amal Dora I held an official convention for time travelers and according to Dora, any real lifetime traveler was welcome to show up with no rs VP. They just had to bring proof that he or she was from the future. And and what I think was a pretty clever move. They focused very heavily on getting the word out to the press.

And this wasn't just about night marketing a goofy silly event. It was a vital part of this experiment because by publicizing the event, by spreading the word wide, they could better ensure that people time travelers in the future learn about that convention, that party, and that as a result, they could travel back to that moment in time to attend the party. And as they said, this web page is insufficient. In less than a year, it will be

taken down when I graduate. Spoiler alert, it wasn't taken down. It's still up. And furthermore, the World Wide Web is unlikely to remain in its present form permanently. Probably true, but it's still pretty much the way it was back then. We need volunteers to publish the details of the convention in enduring forms so that the time travelers of future millennia will be aware of the convention. This convention can never be forgotten. We need publicity in major outlets, not

just Internet news. Think New York Times, Washington Post, books, that sort of thing. If you have any strings, please pull them. And you could ask, well, what what can I do? And they said that's great. Uh, write it down on a piece of acid free paper and slip those pieces of paper into obscure books in academic libraries, carve them into a clay tablet. If you write for a newspaper, insert a few details about the convention, tell your friends so that the word of the convention will

be preserved in our oral history. Time travel is a hard problem and it may not be invented until long after m I t itself has faded into oblivion. Thus we ask you to include the latitude longitude information when you publicize the convention. You can also make an absolute commitment to publicize the convention afterwards. In that case, bring a time counsel or whatever it may be to the party, and then bury it afterwards. So I got a lot

of coverage. They even got our rite up in Nature News that was called Time Travelers Snub Conference, So I guess you can see how that turned out. The website, which like I said, is still up to this day, says update. The convention was a mixed success. Unfortunately we had no confirmed time travelers visit us, yet many time travelers could have attended incognito to avoid endless questions about the future. We had a great series of lectures, awesome bands,

and even a DeLorean. We regret having had to turn away visitors, but there was were capacity restrictions governing Morse Hall. Thanks so much to the dozens of people who helped, I've got a lot more to talk about trying to track down those pesky time travelers, but first let's take a little time out to thank our sponsor sticking with these events that are being held for time travelers. On June two thousand nine, Stephen Hawking held a party in

Cambridge for time travelers. All time travelers were invited to come, but the catch was he did not issue the invitation to the party until after the party had already taken place. So the invitation flyer read you are cordially invited to a reception for time Travelers hosted by Professor Stephen Hawking, to be held at the University of Cambridge, Gonville and Caius College, Trinity Street, Cambridge. And then it's gave the exact global positioning coordinates for the party and said champagne

would be served. But I guess it wasn't that rally party because it was it was held at noon, unless I don't know, kay, Cambridge, if you're out there, do you get turned up at noon? If so? Well done? Anyway, Later on, after the party had happened, he publicized the party in the press and on the web, and had an elegantly designed version of this flyer printed up and placed on sale, and said I'm hoping copies of it, in one form or another, will survive for many thousands

of years. Maybe one day someone living in the future will find this information and use a wormhole time machine to come back to my party, proving that time travel will one day be possible. But no one showed up. Hawking later said during an interview at the two thousand twelve Seattle Science Festival, I have experimental evidence that time travel is not possible. I gave a party for time travelers, but I didn't send out the invitations until after the party.

I sat there a long time, but no one came. So I guess Stephen Hawking just kind of watched champagne slowly go flat. So if they're not showing up to our parties, maybe maybe there's some you know, weird laws in the future about time travel and keeping it secret. What if we were to use big data to mind for the presence of time travelers. There is a paper that was written back in or released in It was written before that, titled searching the Internet for Evidence of

Time Travelers. It was written by Robert J. Nemerov and Theresa Wilson over at the Michigan Technological University's physics department, and they looked for evidence of time travelers by sifting

through enormous amounts of data on the Internet. And the idea was that if travelers from the future were to come to the Internet age, they might not, you know, come forward and proclaim themselves as time travelers, but they might leave some sort of race of their presence on the web if you just looked for things that showed evidence of what they called prescient knowledge, in other words, looking for any indications that someone knows about something before

that something actually happens. And they used three main methods to do this. First, they looked back at the web for terms that would not have made any sense at the time they were published, but which now referred to something meaningful. They gave examples. They said, search terms related to comment I sn I S O N, which was not discovered until September twenty first, two thousand twelve. Or Pope Francis, which was formerly Cardinal Jorge Mario Burgoglio uh.

He chose the name Francis in March two thousand thirteen, but before March two thirteen there was no Pope Francis. There never been a Pope Francis, he's the first one. So if they said we find evidence of these terms existing before those dates, that could indicate a time traveler who was googling around or maybe popping on Facebook or Twitter or something and looking for these terms, but it

was before those things had happened. The next method they used was they looked for prescient search terms in search engine history. So again, if let's say that they're not posting to Facebook or Twitter or whatever. Also, Facebook is problematic because you could back date posts for a really long time, so you could actually cheat. You could post about you could set the date on a post to being before the thing actually happened, so that would be it would look like you were a time traveler, but

it was just because Facebook allowed you to do it. Anyway, they said, let's see if there's any evidence of search terms being used before these things happened. Google trends didn't really turn up any interesting results. But then they pointed out Google aggregates this data and it very well. Maybe that if it's a time traveler who's come back to present day, there might not be enough information there for

you to draw an in conclusions. Uh, one of the studies authors happened to have access to the back end for NASA's Astronomy Picture of the Day subsite, so he checked to see if anyone had searched for any evidence of common ice and before it had been discovered. And Third, they invited the future people to travel into the past before the end of August tweet at them with one of two hashtags. They said, if you're a time traveler, go back to the past. Use Twitter and send on

the message and include one of these two hashtags. Either hashtag I can change the past. Two. That would be if the time travelers says yes, I can travel through time and history is plastic, which means the past is changeable. You can go back in time and change things, and the present and the future are not set in stone. The second was hashtag I cannot change the past two, and that would be if time travel works, but it works in a fixed history scenario, which means it's possible.

But the stuff that we experience is already part of the whole time travel thing. Like you, you wouldn't be able to change the future. It would have to be stuff that it's the way it's always happened. It's a little confusing. It actually goes into a principle called self consistency. They were careful to not use the hashtag in search until after their advertisement asking for past tweets in order to prevent time paradoxes, and it didn't turn up any results.

So in the end they discovered no prescient knowledge through any of these inquiries. So that leads to the question of if time travel is possible, why haven't we seen any evidence of it. So, so possibility number one is time travel to the past is impossible. It's just not possible at all, at least not for human beings, or

we never figure out how to do it. The next is that, yes, time travel is possible, but we have that limit of you can only go back as far as a time travel machine has been invented, and so far no one's invented one. That's the next possibility. Then there's the concept of causality branching, or the multiple world's theory, the idea that that our timeline is one of many, and anytime you travel through back through time, you're actually

creating a split from your timeline. So you have your original timeline where everything is the same and nothing in the past gets changed. Then you have the new timeline that splits off to the moment when you travel back to it, and so you can make changes to that, and everything in that timeline is affected by your actions.

But your original timeline, the one you traveled from, continues to go without you in it because you've you've moved away from it, but it doesn't the past events don't get changed round, so you're looking at lots of parallel universes. So this would allow you to do stuff like actually go back in time and to kill yourself or your father,

or your grandfather or or any of your ancestors. And it wouldn't affect you, the person who traveled back, because you're from a parallel timeline, But it would mean that the alternate version of you would either die or never be born because you eliminated them and called blood you, you crazy person. So the other possibility is that maybe time travelers from the future are just hiding from us and are just really really good at it. Uh So that's also a question of how would that be possible.

I mean, people make mistakes all the time, so you would think someone somewhere would have slipped up if they had traveled back in time. There's gotta be some goofs, right, if time travel is possible, some goofs eventually gets hold of time travel and makes a complete mess of things. But we haven't really noticed that. I'm gonna put political commentary aside. Let me take another quick break, and then

we'll conclude our discussion about searching for time travelers. All right, So we talked to a little bit about the different ways that we might be able to to find time travelers. There are a couple of other things I think would be kind of fun to talk about, like, uh, evidence supposedly of time travel. You may have heard about Chaplain's film about the Circus, and there's a image of a

woman in the background. Um, it's this movie was made in nineteen and there's a woman in the background who looks like she's on a smartphone, Like it looks like she's holding a smartphone to her face, and you're thinking, nine, this is someone from the future, but so far in the future that smartphones are no longer a thing. Although it raises interesting questions like what network would that smartphone be on if you had traveled back to nineteen eight.

There's no infrastructure there to support it. It turns out it probably was just a very large hearing aid, because hearing aids of that sort of size, portable hearing aids that you could carry around, but they were quite large, had been around for a few years. Uh. Prototypes have been around for at least a couple of years. One had been patented as early as nineteen twenty four, so

night was still pretty early for that. They might probably were pretty rare, but it seems like a more accurate guests than a woman had time traveled to be an extra and a Charlie Chaplin film. Uh. There's also the famous picture of a group of people standing around looking at a bridge and one of them looks like a hipster from modern day, wearing like a it looks like a print T shirt, and them crazy looking sunglasses. And the picture was taken in ninety one at South Fork

Bridge in gold Bridge, British Columbia. However, upon closer examinations, people pointed out the glasses the guys wearing were totally contemporary. They existed in the forties. They the leather side guards were a little antiquated. It wasn't something that you frequently saw in nineteen forties, but they did exist before then. Uh, And also that the print t shirt he's wearing was actually probably more of a sweater and cardigan layer with

a with a logo knit on the sweaters. In fact, there's some guests that it probably was the logo of a local hockey team, So that kind of puts the the the lid on that particular one. Um, So there are other ones that I've seen h people who supposedly are time travelers. In some cases you would argue this could easily be photoshop, or it could just be a case of, you know, mistaking one thing that was actually quite common during that era as something that came from

outside of that time. Sadly, no no actual hard evidence there either, and I am I am hurt to say that. So what else can we do? Maybe we could provide an incentive for time travelers to show up and and leave evidence of time travel. But to do that, we'd have to figure out what motivates time travelers, like what what would be considered valuable. I mean, if grabbing a drink with one of the most famous scientists of the modern age isn't enough to convince you to pop on

over to Cambridge at noon and have some Champagne. I don't what is so. I'm not sure that we could come up with something even if time travel were possible now. Ultimately, I don't think time travel is going to be possible any time in our lifetimes. Like if we ever do design a time travel device, my guess is it's far into the future. And I also think that the scientists are right on the money that no one will be able to travel back further than the moment when the

time travel machine was made. I think it far more likely that we will develop faster propulsion systems that will ultimately bring special relativity into the situation where we will have some discrepancies between how much time seems to have passed for one person versus another. But that's not quite the same thing, and I don't think it's going to be so dramatic as traveling at the speed of light.

I don't think we're gonna get that fast, but we might get fast enough where you know, the clock on the ship is not going to match the clocks on Earth. We already have to account for this sort of stuff due to both special and general relativity with our satellite systems. I talked a bit about that in a recent episode about how special relativity has to do with the relative

speed of various bodies traveling through spacetime. General general relativity involves time in its relationship with gravity, so both of those things affect the apparent passage of time for respective bodies. And again, it's all relative, right, because your experience of time is dependent upon those factors, And if those factors change, then the way your experience of time happens will like

to you. It will seem the same until you meet up with somebody else who has been going through a different experience, and then you'll realize that they don't match up. And you might say, I don't understand only five minutes have gone by, and the other person says, no, you were gone for an hour, and because of the actual factors involved, you both could be right. It's the crazy thing about relativity. Man, it's awesome. I loved thinking about

this stuff. I didn't really touch on things like wormholes and other hypothetical kind of possibilities, largely because they might end up being a promising way to look at the possibility of time travel. I didn't talk about faster than light travel either, because as far as we can tell, that's not really possible. Uh, but maybe in the future ha ha, I will co into those a little bit more.

Maybe I can get somebody on who's kind of an expert in these sort of physical, uh these physics problems, and to talk about the possibilities and which ones are pure science fiction versus well, hypothetically that's possible, and which ones are no. We might totally do that. I'm very curious what about you, guys, And I'm also curious what's your favorite time travel movie? I want to I want to hear responses because there's so many out there, and

my favorites change. I really like them Back to the Future series, even though if you look at it from a theoretical time travel point of view, it gets super messy. But I really like that series. Uh. I also really like Bill and Ted, and they're excellent adventure I think that one's a lot of fun. I really like time travel movies that don't take it too seriously, because time travel is hard to do well. But there are a few out there, a few serious sci fi movies that

use time travel that do it quite well. Do you have any favorites I want to hear Also, if you have any suggestions for future episodes of tech Stuff. Whether it's a technology, maybe it's a company, maybe it's a person in tech. Let me know. Send me an email. The address is tech stuff at how stuff works dot com. You can go to our website that's tech Stuff podcast dot com. You'll find links to other ways to contact me, like on Facebook or Twitter. You'll find more information about

the show. You'll find all the episodes there. Sorry, does a great job on that, so go check that out. You also can head on over to our store that's over at t public dot com slash tech stuff. Remember, every purchase you make goes to the show. We greatly appreciate it, and we're always having fun coming up with new and uh goofy designs. I mean it's me. You know it's gonna be goofy. I I gave up trying to be cool years ago after it was abundantly clear

I would never achieve that status. So that's all right. I'm all right with who I am now, and that's it for me. I'll talk to you again really soon for more on this and bathands of other topics. Because it how stuff works dot com. Wh whe