We Get Back In Time

What's the best depiction of time travel in the movies? What would you say? Well, I don't know if it's possible to get time travel right in the movies, because I'm not sure if it's possible to actually do it period. The movie that that convinces me the most is a little, uh indie sci fi movie called Primer. Have you all seen this now? So? Yeah, so in your version, time

travel and evolves getting a storage unit. Yeah, so you run a U haul and you put a little box in it and you go sleep in the box, and um, and then everything gets really confusing. But there there there are a couple of things I really like about the way it depicted time travel. Number one is that it depicts it the technology, the technology aspect of machine they build feels like a real project. You know, you see the scenes where they're designing it, and it doesn't sound

like a bunch of sci fi magic talk. You feel like these are these guys are they're real engineers who were talking about the kinds of problems engineers encounter when they're building a machine. Number two, The thing I like about it is that it's the thing I said before, It gets really confusing when once they keep using the machine,

it's hard to keep track of what's going on. It's a movie that challenges you too, because if you if you aren't willing to really pay attention and listen and try and be engaged, you could be lost before there's any time travel at all. In fact, you can be lost before you realize what the heck they're trying to build. Yeah, definitely, Yeah, all right, Lauren, what about you do you have? Do you have a time travel like a favorite kind of

depiction of time travel? Well, I think that probably the closest to what will eventually be reality is is what the Simpsons portrayed in the Treehouse of Horrors episode Time and Punishments, which of course was was kind of based

on the old Bradberry story. A sound of Thunder is that the one where Homer goes back in time accidentally steps on a on a butterfly and changes everything all right, right, comes back to the to the present and uh and and winds up in what seems to be this amazing perfect dimension, right and well, but but but he goes he goes like they're all like rich and fabulous, and he's like, Marge, give me a donut, and she's like, what's a donut? And then and then he leaves and

then starts again. My favorite part of that one is where he goes back in time and just starts killing things randomly. But that also does try to sort of address a real issue that's possible with time travel. We're time travel a reality, and you were to go way back and change some small thing you have no idea how much of an effect that might have in the future. True, Now, before we get off too far down that road, because we are going to address that, it's my turn, Yeah,

what's your job? Spill and Ted's excellent adventure because Sand Demons High School football rules. Yeah. I actually was just reading about how scientists at M I. T Are working on a time traveling telephone booth. Yeah, yeah, yeah, it's uh, it's it's phenomenal, powered by George Carlin magic. I was about to say, I mean, this has to involve George Carlin very short supply Now, well, I mean just because

he's passed away in this current time. If it's a time machine, then that should that should be no problem, right, Okay, okay, so time travel is really fun for the movies, especially because it creates all these weird questions. We have no experience with which to compare it to, so you can you can almost try anything. Yes, And we of course

have talked about time in a previous episode. We were really talking about time and general relativity and special relativity, and so we're not going to go too far into that, but we will give a little bit of a refresher so that we can have at least a kind of an agreed upon foundation upon which we will build our contraption of time machine that will fall a part of the moment's notice. Yeah, okay, so let's talk about time travel today. Is it possible? Uh? If it is possible.

How might it work? And if it does actually work, what would it mean. Well, it depends on how you define it, because if you just define it as traveling through time, technically we're all doing that, not where Yeah that's a great term. Yeah, well it's true. You just you know, you just have to be and you and you and you would go through time. All right. So, first of all, defining time we've mentioned in our previous episode, it's really hard to do that without it becoming this

kind of crazy recursive, uh you know, tautological definition. So Einstein said time is what you read on a clock. Yeah. One one definition you could apply is say it's the rate of change in the universe. And this is not something that is as globally consistent or universally consistent. In other words, it can you can actually have very localized rates of change that are much different than on the universal scale. As it turns out, time is in fact relative.

It is different depending upon your perspective. And that doesn't just mean it seems relative to different people. You know, based on how long it feels like this horrible movie has been going on, or this lecture or something. It's measurably relative like it actually changes depending on how close you are to say, massive objects, or how fast you're going. Right, that's a gravitational time dilation, yeah, exactly. Yeah. And and both of these, you know, gravitational time dilation and the

speed at which you're traveling. Uh, those those two effects are what make it um necessary for us to have satellites that correct their time gradually, because, as it turns out, the time on their clocks passes at a different rate than the time of our clocks down here on the

ground level. Right. So, even if you were to take a fast airplane trip and you had a very precise clock on board the airplane when you landed, and you compared that against another clock they have been started the exact same time, has that same level of precision, you would see that time had passed at slightly different rates,

not a lot. I mean, it's not like you land and you you land an hour earlier than what you you would have landed, uh if the hadn't gone well, not just speed, but the fact that time is actually passing in a a different rate for you. But it's it

is a tiny amount, it's it's measurable with satellites. It's a little bit more important because one, the effect is larger and tow we're depending upon satellites for things like GPS, and if your time isn't exact, if you haven't corrected for this time dilation, you're not going to get an accurate reading of where you are on Earth based upon those GPS readings. So we already see dilation and effect on today. It's not like it's just hypothetical. Yeah, it's

definitely just an accepted fact of science. But despite the fact that time is relative and influenced by things like nearby massive objects and the speed at which an object is traveling, one thing that we do seem to know about it is that it only seems to move in one direction, right, right. We don't seem to cause and effect goes in one way. Right. You don't have a a an effect and then later a cause happens. You have a cause and then the effect happens. Sort of

the arrow of time. Yeah, and in points and only one direction as far as we can determine, at least intuitively mathematically, it's a different, different matter, I suppose. But first I would also mention that time travel inherently has a paradox attached to it, which is that you get two different, completely different experiences of time, at least based on the type of time travel where there's some time passing for the traveler as well as for the rest

of the universe. So in other words, Joe, if you decide to go back into the past and you're taking some sort of trip where like let's say it's the Tardest from Doctor Who, there's actually time that passes for you as you take this journey. So you're leaving today and you're going back two years into the past, and it doesn't take that long. I mean, there's basically just a series of whoo, whoop whoops, and then any land.

But it's not instantaneous, so you experience time moving forward to an independent observer who I guess has been around for a few centuries. Uh, they will remember the fact that you arrived before you departed. So that's two different experiences of time. My question would be, if there really is this kind of movie style traveling backward through time uh motion, where are you physically well? I mean, space and time are very much connected. We have this whole

idea of the space time continuum. But where is not so much of an issue as when Uh, as it turns out, because at least with the Doctor's tartists, it travels both through space and time. Uh. If you're in a DeLorean going eighty eight miles per hours, somehow you're magically in the right place, uh, the right region as you as you would have been had somehow you've managed to track the Earth. Yeah. That thing is what always mixes me up about a lot of this time travels.

I mean, in addition to many other things like the Dolorean doesn't just appear in the cold reaches of space and parting I fly immediately perishes like Doc Brown. That's a really smart guy. Um, but no, I mean, I mean, with that kind of essential paradox, even the very small differences and in time that happened between us and our satellites, for example, are actually really hard to wrap your mind around. So anything as large as time travel is is necessarily problematic.

Whack I think is the accepted scientific term. Yeah, quite quite whack. Yes, it's wackness is uh is sufficient, It's it's a it's enough of a wackness to actually detect with the naked eye. Okay, so I've got a question, does time travel is there any way, we could just rule it out at the beginning to say no, we just know it's not possible because it violates some law

that we are almost positive cannot be violated. All right, To answer that question, first of all, spoiler alert, According to at least some mathematical models, time travel is at least hypothetically possible. But there's still some things that we have to talk about. For example, the law of conservation. Now we've heard this, right, the idea that you cannot create nor destroy matter or energy. You can convert one into the other, but you cannot actually destroy it or

create it, right, can't make energy disappear or matter. You can convert energy into less useful states. Sure it's never going away, right, right. So in other words, when we are you know, we talk about how systems lose energy, they don't really lose energy so much as they produce other forms of energy that is useful. They're they're pooping out heat. Essentially, heat which is hard to harness, is just diffused. Right. So that law of conservation suggests that

there's a problem with time travel. And that problem is this, if I send something into the past, whether it's a person or an object or time, shame, whatever it is, then that thing will suddenly be in a time where it wasn't before. That seems to suggest that I am actually creating more matter at that moment in time, and that spacetime region then was there before. Does that violate the law of conservation more so than even just creating

a really weird time sonic boom? Yeah. The fact that the fact that something is there that wasn't there before. You had a uh, let's say, a certain amount of matter in that region, and now there's more matter, and it wasn't that you converted energy, it's that you've produced it. Mm hmm. I can tell you what the general answer to this is about how they get around it, which is the idea that in an infinite and unbounded universe, you have regions where conservation takes place. But it's not

a global thing. It's not it's not applied across the entirety of the universe. It's so it's it's kind of complicated, but it's it's assuming that there is an infinite universe, and therefore you're not really creating more matter because the concept of infinite alone means infinite like like there's no more to infinite. You've got that that that alone is you know, it's meaningless. You're not creating a lack or

additional but localized it would be a problem. But if you look at the universe as a whole, as a system and considered infinitely and bounded, you don't apply that that law in that instant. So that's the way of getting around it. Yeah, it's kind of a lot of the stuff we're gonna talk about today with these time

travel rules and the ways to get around it. It reminds me a lot of if you've ever played a a pencil and paper role playing game and you've got one of those players who's trying to find a way around every rule in the game, and that's the way they play the game. I you guys have friends who don't play the game that way. I thought, I thought that was the entire point of the game. I've I've had games where people didn't do that and they were magical.

But at any rate, So another thing we can talk about, does it um? Is it? Is? It? Is it violating space itself? Um? And according to some models of general relativity, time travel is possible through something called a closed timelike curve or c t C which are quote worldlines that end at the same point in space and time as

they begin. And we'll talk more about what c t C s are and how you might be able to travel through time backwards through time in fact, because a lot of people say, oh, time travel would be possible if you're talking about traveling into the future, But traveling into the past is problematic. I mean, especially if you think about using special relativity. So you're just talking about

moving really really fast. So to you, time passes a different rate than it does to someone on some other you know, moving body, right, if they were to look at you, you would appear to be moving in slow motion, right,

and you would see every things sped up back home. So, for instance, if we're talking about here on Earth and Joe leaves to go on an interstellar super fast joy ride, he might go for a year and be traveling at almost the speed of light and return to Earth and it will be like two centuries have passed, but to him a year has passed. Now to that that you could argue is just like basically traveling into the future. Yeah, it's like it's like traveling into the future for you Joe.

For for the rest of us, it's just like boy Joe, you remember him? Whatever happened to that guy? And then maybe someday or descendants would be like, oh, you're this Joe guy who never shows up the things. But at any rate, the CTCs would allow you to travel back in time, assuming that they are actually in play in this particular model general relativity, and we'll get into that in a little bit. Okay, I've got one. Okay, what about basic causality? I mean, can you you've heard of

the grandfather paradix? Obviously you have, Yeah, I wrote the notes right. Well, okay, so the grandfather paradox is a fun one. Uh. This this is a very common one. That's that's mentioned. There are a lot of different variations as well. But the the easy way of saying it is imagine that time travel is in fact possible where you can go back into time and then you go back in time. You're an assassin and you have a specific target that you have to hit in the past.

You travel back in time and your target is eighteen years old, and you assassinate your target. But it turns out your target was actually your grandfather, Your grandfather didn't have kids until he was, you know, in his twenties. So you have killed your grandfather before your your mother or dad were born, which means that you wouldn't have been born, which means you couldn't have gone into the past, which means you couldn't have killed your grandfather. Thus the paradox.

Now we're not saying there's any reason this would need to arise, but if traveling into the past really were possible, why shouldn't you be able to do something like this? Well, again, if through your action you end up negating the ability to even go back in the first place, that's the paradox. Right, You've created an incoherent loop, is what it's called. It's

it's something that could not continue. Uh once it happens like once it once you were successful in doing whatever the task is, and it doesn't have to be kill your grandfather. That's the paradox. But there are a lot of different variations. Generally speaking, what they're saying is, even if time travel were possible, you probably couldn't go back and change anything, because if you did, then it could negate the possibility of you traveling back in time in

the first place. So There's an argument that extends from that, saying that maybe there's no way to affect the past at all. But that also seems like a problem to me, because by appearing in a place, I mean, even if you don't really do much of anything, you're still affecting it, I mean, just by your state of existence there. Sure it's accidentally stepping on a butterfly thing and creating a universe where it rainstonuts. Yeah, it seems like it wouldn't

be possible to go to a place without having any effect. Well, there's some interesting ways around this one too. One is suggesting that you would be able to do whatever you wanted. It's just whatever you did happens to be whatever has happened anyway, That makes more sense to me. So in other words, it's not that you are prevented from doing things, it's that whatever you choose to do is what has happened already and what led to the state of the universe that allowed you to travel back in time in

the first place. And this becomes a coherent causal loop where you end up having You can have variations on this where the only way it could have happened is if you had traveled into the past, which I love.

These two the very popular in science fiction. Well, yeah, I mean one of the one of the big ones that seems to emphasize the strangeness of this kind of loop would be, what if you only know how to invent a time machine because a time traveler from the future came back and showed you how to invent a time machine. Yeah, and there's another great example. In fact, I'll go ahead and say it. Let's just say that, uh, Lauren, you have created a way of uh, you've gone into

the future. You've got a time machine where you can actually move into the future, and you you steal from the future an amazing device, and this steal things all the time, mostly from the future. Yeah. So it's a really cute nutcracker that looks like a sure from an antique store. I have a have a specific example. Lauren, Lauren the chronographer kleptomaniac, steals a device it turns great jelly into strawberry jam, and she travels back in time to present day and starts to thus turn all the

grape jelly into strawberry jam. And she loves that. She's fantastic guests And then as she's you know, she's traveled far into the future to get this amazing device uh on on her her deathbed, many many many years into the future. She then gives this this device to a little vagabond, and and the vagabond, it turns out, ends up being the quote unquote inventor of this device. In other words, this device was never actually invented. It only

exists in this loop of time. It turns out that the adult version of this vagabond is the person from whom Lawrence stole the device in the first place, and this device only exists within this closed time loop. From that perspective, yeah, that doesn't seem to make any sense, because in that case, the device was never actually built.

It always just exactly Yeah. See, it's another one of those kind of and if you've ever read any hind Line, hind Line has got a billion stories that involved this kind of of closed loop where nothing in the story could have happened unless this other thing that hasn't happened had already happened. It just gets more and more confusing

as it goes along. I think it's much more likely that um that grape to strawberry jam converters are a universal constant, and it therefore um that they have to exist.

There must exist, unmust they must at some point exist, right. UM. I also am very fond of the theory that um that the universe kind of kind of equalizes anything that you would do and or try to do in the past, Like if you went back and tried to shoot your grandfather, um that the gun would misfire, or that that's suddenly a strong breeze with the bullet off course, right, or that that a weird reflection gun in your eyes and

messed up your aim. And but the the idea being that the universe itself counteracts anything you try to do and thus prevents it from happening. Uh. I can see that if you're just saying like this is another way of saying that whatever you go back and change is what already happened. If you're talking about the universe having like an active deterrent mechanism, that that seems only possible

if you're positing like time travel, police ghosts. I think that Final Destination has proven beyond a doubt to us that this kind of thing happens at the Great documentary series. But also it doesn't necessarily have to be conscious. It just has to Again, it's very similar to this is what has happened, therefore, this is what will happen if you were to go into the past. But another interesting idea that tries, you know, one way you can try

and get around this. It's sort of similar to what you were talking about with the Simpsons, Lauren, this idea of parallel timelines. This is what it's like in Back to the Future and a lot of stories. Yes, you go back and you change something. It doesn't have to be incorporated into the future you've already experienced. You create a new future. Its branch to split off. So in this sense, some people say, well, technically you're not altering

the past so much as avoiding the present. In other words, in other words, the president present every day, the present that you are from. Let's say, uh, you you have left the present, You've gone into the past. You've made a change in the past that would affect your present, the one that you came from. It splits off the timeline and now you are in a parallel timeline where the the change that you made is fact. It's a

historical fact. And so therefore whatever your present, uh, will be now it will be different from what it was in the timeline you left. But the timeline you left could theorectly still be going on. It's just now it doesn't have you in it because you left UM, and I guess you probably wouldn't be able to get back,

would Yeah, I mean that's not hypothetically. I mean I think that if you can get over there in the first place, then there is surely a clause and she can get back if you were to go back even further into your timeline so that you could stop yourself when you appear the first time in order to change the timeline and thus prevent yourself changing the timeline by going back and changing it again. Maybe I don't know, I need to have like some trees, you know, to

illustrate all this on UM. But yeah, again, some people say that this this ends up being some sort of universe hopping as opposed to time travel in the purest sense of being able to go into the past and change things around. O. Well, let's just say maybe one of these things really can happen. Now we've accepted that based on relativistic physics, you probably could travel into the future. That's not really the problem. We're talking about traveling back

in time. How would you actually do it if one of these models, any of them, at least one of them works, what's the way you get there? Because this is a thing that that legit physicists have legit thought about. I mean there's some there's some not just physicists but also philosophers who have really talked about, you know what, what is the likelihood of this and if if it's possible,

how would it be possible? And some of the models are uh, you know, hypothetically possible but not practical, right, And actually I'd say all of them aren't because if they were practical, we would have totally been doing them already or at least tested them. But one of them would be using what are called Care black holes k e r R or care ring not caring care rings. Uh. So this is after a physicist named Roy care who proposed this back in nine and talked about the concept

of a rotating black hole. That would be a care black hole. And if you're looking for size, it would be about the size of Manhattan, but it would have the mass of our sun, so would be incredibly dense. You know, sun is obviously much larger than the Earth, so for it to be reduced in size to the size of Manhattan, but retain its mass incredibly dense. So the idea of a caring is a ring of collapse neutron stars that are spinning with enough rotational force that,

at least in theory, they would never create a singularity. Now, the singularity is that that point of infinite density, that point that has zero length, infinite mass, so you would never be able to escape from it. Light itself cannot escape from it. Uh. That's not the same as Event Horizon, which is a great movie that we watched for tech stuff, but it's also event horizon is also the zone around

a I call that's the point of no return. Yeah, which is why it's a terrible idea to name your spaceship after don't name don't name your don't name your your cruise ship Iceberg, and don't name your your spaceship event Horizon. But yeah, So the idea with the care ring is that perhaps there would not be a singularity at all. This rotational force would end up preventing that from happening, and the ideas that you might and I stress might be able to pass through such a thing

in a spacecraft. Uh, and not be spaghettified and crushed and killed as a result. Uh. And the idea would be that you would be spit out of the other end, which essentially would be a what is what is in theory called a white hole? I say in theory because we haven't observed one, why these might not actually exist? And yeah, yeah, one of the ideas of that a white hole is essentially I mean, that's like the opposite of black holes, where stuff is being spouted out, like

matter and energy is coming out of this. Uh, you know it would be black hole be one end of it, and white hole would be the other end of it. But while we've observed the black holes, the white holes are still something we don't really see. I'm trying to wrap my brain around that. What would be the opposite of a black hole. It seems like it could be something like a little big bang kind of wouldn't it, like like a continual big bang? Yeah, singularity expanding outward,

putting energy and mass. I would just think of it was the other end of a pipe. Oh way, so wormhole is kind of similar in a way. But um, again, we haven't observed white holes, And one of the other theories is that black holes are are kind of a window into another universe, right, the idea being that there's some sort of hole through our spacetime that connects to some other perhaps space time. Perhaps it's something we can't

even fathom because it's so different from our universe. But why The counter arguments against that is that, well, does that mean our universe is exit only because we can't find any entrances, We don't see any of the the what we you would imagine would be the opposite of that, where stuff is coming from somewhere else, although you could argue maybe dark matter and dark energy or somewhere in there,

because we can't directly observe those at any rate. There's the possibility that you could fly through one of these black holes and thus travel through time, either in the future or in the past, but you wouldn't necessarily be able to control that at all, So it just be kind of where every wherever and whenever you end up, that's where and when you are. It's it's like when the kid goes to make a suicide at the fountain drink machine, except you're doing that with time and space. Yeah,

you just you gotta you gotta blindfold on. You don't know how much lemonade versus Dr Pepper you're putting in that mix. It could be delicious or it could be noxious. Yeah. Similarly, there's the wormhole approach that I just mentioned. So wormhole essentially is curvature of the space time into a tunnel, where going in through one side and popping out the other side, you would end up in a totally different area of space time. Okay, so give us the real scoop. Wormholes.

They're in all these movies and they just they're just magic tunnels basically, well in the movies their magic tunnels. Yeah, yeah, what's the real deal with the wormhole? They exist? Uh? In fact, wormholes, well we think they exist. Again we we we haven't observed them, but mathematically, Einstein and Rosen, who were two pretty smart dudes, uh said, said that it's logical that they exist. Yeah, if you look at it as like a teeny tiny lasting for a split

second basis in large particle accelerators, they technically exist. If you didn't hear me rolling my eyes, I I just rolled them really hard, Okay, Okay, and not that that isn't true that is extremely true and and wonderful and beautiful, and not particularly useful to the conversation that we're having right now, because first of all, none of us are Adam sized, and and second of all, we exist in periods longer than um nanosection. So well, I'm just being pedantic.

So but yes, your point stands, Lauren, there is we have never observed any kind of wormhole. In fact, there may not be a style of wormhole where you could create something that has stability that would allow you to actually pass through it, that would have the size and duration necessary for that to happen. Nor do we really know what would happen if we were to pass through it. One,

don't you end up? Yes, you end up. You end up being in the the arguably the least popular of the Star Trek series on I guess Enterprise probably cases a run for its money or or on a living ship using the word frell a whole lot. But at any rate, Uh, the the issue is, we don't know, one, if it's even possible to create a wormhole or to find a wormhole in nature that would allow us to pass through it, we don't know what would happened to us.

If we did pass through it, and again you wouldn't have the control, right unless you were able to fold space time itself specifically to your desires, you would not be able to determine where and when you would come out the other side. Yet again, kind of like the black hole. So it might be a way of traveling through time, but again it may not be practical. Um. And you know, in order to imagine this, this is the always the hardest thing for me to imagine because

you have to think of space time. It's it's a afford menstional construct as we understand it, right, Yeah, and I've seen some pretty interesting like like gifts of this on the internet. But but I understand that, um, that that is not really inaccurate to pick I mean, I mean, I have a hard enough time perceiving three dimensions and when you add the fourth in there, and like yeah, yeah,

because it's easy enough if we reduced it to two. Right, if we think of the standard example is you have two people holding a sheet taught between them, and then on top of the sheet you lay some sort of object that has mass that that pulls the sheet down, right, it curves, the sheet curves around the object, so even when you're holding it tightly, you see it where it's dipping down depending upon the mass or the weight of

the object. Uh, that determines how how much curve you get. Well, the same thing happens in four dimensional space time, So

space itself curves around massive objects, and time does too. Uh. It's just really hard to imagine that for one thing, you know, even if you're able to imagine it in some kind of abstract three dimensional way, adding a fourth dimension, like you said, Lauren, really hard, I mean not, I certainly it baffles me, sure, and especially once you get past the concept of just a sheet curved by by

like a bowling ball for example. Um. Further, in order to make a wormhole, you have to punch through the sheet with the bowling ball to perhaps another parallel sheet beneath it, or maybe a little bit of the sheet that's on the floor underneath it, and then there's like stars involved. And I don't and I don't follow. Technically you could wrap the sheet around the bowling ball and thus create a tunnel that way, although I don't know

that that makes it any more useful. Another way, maybe thinking about it now, tell me if this is totally off. Is Uh, you drill a hole in an apple, and so if you imagine the two dimensional surface of this apple is actually the three dimensional space world, and that that third dimension of the apple is the fourth dimension of time, you can sort of go through from one

side of the apple to the other. Yeah, you're I can't wait for your time travel movie and you're you're gonna call it the core and the discappointed to find out there's already a movie called that, and there's already a worm in there. That's true. So uh, anyway, wormholes again very much hypothetical when it comes to time travel. There's also the closed time like curves that we mentioned earlier.

So this is um an interesting concept. Comes back to another another big thinker, right, it's it's not a it's

not a new concept. Some of the ways of explaining how to make it work are very new, but it might date back as far as like the nineteen forties with um Kurt Girdle, who was a buddy of Albert Einstein, pretty pretty smart and a little bit nutty mathematician who was was talking about the geometry and movement of the universe and and put forth the idea that these loops might exist, like like if you had a long enough journey um due to the way that that the universe

he thought might spin, that you could loop back on time, right and Uh, then we have the entrance of string theory into the idea of these closed timelike curves. So string theory, it's we're not gonna go too far into it. We could do a whole episode on string theory too. But a string theory, you can imagine that all matter in the universe and talking about all the way down to sub atomic particles, is made up of these these strings that are either either open ended or they're closed

in loops. Uh, and they vibrate in different ways, and you know, superstring theory. Supersymmetrical string theory suggests that the vibrations of the strings are what determine what kind of subotomic particle gets represented. For instance, protons vibrate, the strings

vibrate one way, electrons they vibrate another way. Anyway. One of the concepts here is that by using cosmic strings, either two of them very close together or one sort of attached to a black hole, you could put them under such pressure that you create this closed time like curve. In the universe, which if you were to travel using this close time like curve, you could move back to the point of origin in both space and time when

that curve was created. So you could travel back in time up to the point when that curve was created. You could not travel further back because the curve wasn't around before then, right, unless a dinosaur did this for you, you couldn't go back to the time of dinosaurs exactly. So in other words, if I built one today the furthest back I could travel would be today. I wouldn't be able to go back to yesterday, but any time from here forward, assuming I have a way of harnessing

that I could travel backward. Uh, this could become really useful if you have a short term plan of making a lot of mistakes, and you want to be able to go back and try a lot of different options before you settle on whichever one is going to be the least harmful of all the mistakes you're gonna make. Sort of like creating a safe point. Yes exactly, Yes, you've got three doors ahead of you, and you know two of them lead to certain death. But wait a second.

Every time you go back a few minutes. Is there another one of you there that you have to kill before you can make the decision? An excellent question. I don't know the answer to that. Uh you know, again, this ends up being very much hypothetical. Obviously, no one has actually created one of these closed time like curves that they could travel around it and go back into time. And uh so it's again very much kind of a

philosophical and scholarly discussion, not a practical discussion. Okay, So I wanna raise an issue, which is that all of these things that seem even remotely close to plausible do not happen to be the kind of machines you can build in your garage, like in the very Victorian kind of looking or or or primer like I brought up earlier. You know, some people in their garage want to build a time machine. It doesn't seem like that's the kind

of thing that lets you travel through time. This is the closed time like her of where you wouldn't be building one of those in your garage. But maybe you're building a spaceship in your garage. Well, I guess you could build a spaceship in your garage to go to occur ring you know, yeah, something like that, but it's not a time machine in the sense of, like you

set a dial to nineteen fifty seven. I wonder if this is because time itself exists in a relativistic framework, and you might need relativistic forces which means really really huge or really really energetic, in order to manipulate it. Yeah, there's some studies that have suggested that if you wanted a time machine, you would have to harness the equivalent amount of power that you would find in a galaxy in order to make it work, which is not necessarily practical.

We think we have energy problems now, but when it comes to you know, I want to go back to last Thursday, but I need to harness the power of an entire inner galaxy to do it. It's certainly not convenient from your girl. Okay, So, folks, if you want to know how what we have to do in order to create time travel, go listen to our episode on the Cards Show scale. We need to get to CARDASSHEV level three and then we'll have time travel. Well, assuming

that no one else wants to do anything. Right. Hey, guys, guys, I know you're really crazy about your iPhones. And your kindles and your internets. But we're going to turn all that off so I can go back to last off the galact of irrigation systems and all the life support. Now, what what if we what if all this this talk is truly moot? What if? What if there is no

such thing as the future or the past, only the now? Well, that was Girdle's idea, actually, he he suggested that the end result of his model of the universe UM, which which branched, by the way from from Einstein's theory of general relativity UM, is that since time travel is hypothetically possible within the realms of physics as we understand them,

therefore time it's as we understand it cannot exist. Yeah, I mean, that's that's the The idea is that nothing is ever really in the past or in the future because time travel can exist, uh and and and therefore the past and future don't exist. So, in other words, it would be that you again a time time travel device, but you'd have no destination to go to. There be There'll be no place to go to because there is no past in the sense of a a point in

space time that still is relevant. I'd argue there is no present, that there is no now. Well, you know what, Einstein would agree with you, in the sense that simultaneity is as a concept that doesn't work in Einstein's model with general relativity because it all depends upon your point of reference subjective. Right, yeah, h well, andy, I mean if you try to, I mean, if you actually just sit down and try to think, Okay, what is happening now?

There there is no now and more sitting here. The more you try to examine the idea of an instant of now, it just slips through your It's another one of those things where you know, in order you sit there and think of it on the scale of all right, let's take let's take a unit of time. Let's say it's a minute. All right, well, let's let's break that down.

What's happening this very second? And then you think, wait, you know, you can actually break a second down into smaller and smaller slivers, and you just keep thinking that, well, technically you can just keep reducing be half over and over and over. Paradox Yeah. Yeah, you get to a point where it's not perceptible by humans by any stretch of the imagination, but it's still happening, and it's still significant in a mathematical sense. Yeah. So then you think, well,

wait a minute, how did I ever get from? Especially when you start getting really far away from units of time that we can perceive, you think, how is anything ever happening? Ever? Yeah, I mean when the past nanosecond transitions to the next nanosecond, what's that? What's now in between them? See, that's where a lot of other science fiction comes in, where you have entire worlds that are existing and and and growing and falling apart in the

time between the seconds. So it's a it's there existing in a in a way that is imperceptible to the rest of us because we we only see the seconds. We can't see what's in between them. That's great stuff. But anyway, that the point being that when it comes down to is time travel possible? Will we ever see time travel? There's still a lot of disagreement on it.

You know, mathematically, according to the laws of physics as we understand them, including Einstein's theories of relativity, there's nothing that expressly forbids it from being possible. Well, again, I want to stick with what I said earlier, is that I feel pretty good about time travel into the future. I'm very skeptical about time travel into the past, well, especially since you know, as far as we can say, there's no there's no evidence that we can point to

that it's ever happened before. And you would imagine that if it's in fact possible, someone from the future would have traveled back in time. Their counter arguments against that too, but you can find them posting on the internet. Let's not go into that. I've done a whole podcast about that.

But uh yeah, so, but you know, the classic argument is that if time travel ever is possible to go, you know, if it's ever possible to travel back into the past, then sometime travel traveler from the future needs to come back to this time when we're recording this right now and knock on our door right now. Oh, son of up, Now that was me. I'm just kidding. No, one was actually at the door. No, but that's the art.

If some horrible reptilian did bust in and say, I'm well, that would be you two, I'd be like, hey, look for the record, I did not make fun of retilience. Yeah, I know that would be Yeah, so really, you're just telling me I gotta get new co hosts. Uh all right, So anyway, this, do you guys have anything else you want to say about time travel? I mean, this is this is one of those fun things to talk about, because, like, you start feeling pretty confident, right, the stuff that you

can intuitively grasp, You're you're, you're, you're zooming along. You're like, okay, this makes sense. Then you start getting into some of the math and you think, okay, wait, intuitively that makes no sense, even though the math itself works out. And then the further you go, the more you're like, Okay, now I don't even know what I'm thinking anymore. Our intuitions are great when we need to get the groceries. They are not very good when we need to solve

questions about time and space. Yeah, it's very true. Things on the cosmological scale and on the quantum scale often are they defy our intuition because our our experience is not on that those scales. Yeah, there's no reason our ancestors on this planet ever had to think about time travel. The monolith just appeared and then let's you just go from there. Well, anyway, that wraps up our discussion on time travel. So the jury is still out. Technically, again, mathematically,

there's nothing that specifically says this is completely off limits. Practically, could very well be that there's no practical way to do it, and certainly we don't have any evidence of it that we can point to. And even if there is a practical way to do it, that that practical is in extreme scare quotes, because because practical like blowing up the galaxy is not necessarily right. That's that's not not in my book. That doesn't fall under the category

of practical. But anyway, if you guys have any suggestions for future episodes, you've got some sort of futuristic topic you think we should tackle, let us know. Send us an email or addresses f W Thinking at Discovery dot com, or drop us a line on the social networks we frequent Those include Facebook, Twitter, and Google Plus. We have the handle f W thinking at all three of those, and we will talk to you again in the future

May the Beast. For more on this topic and the future of technology, visit Forward Thinking dot Com Problems brought to you by Toyota. Let's go places