March 19, 2014 • 45 mins
Seriously, is time travel possible? We take a look at the philosophy and physics of time travel.
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Episode Transcript
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Speaker 1 (00:00):
Brought to you by Toyota. Let's go places. Welcome to
Forward Thinking. Hey everyone, and welcome to Forward Thinking, the
podcast that looks the future and says, tell me, dr
where are we going this time? I'm Jonathan Strickland, I'm
(00:20):
Lauren Vocabon, and I'm Joe McCormick. Joe, I I've got
a question for you. Okay, I've really been thinking about
this for a while. What if I had if I
had to nail you down and say, what movie that
involves time travel do you feel really gets it right?
What's the best depiction of time travel in the movies?
What would you say? Well, I don't know if it's
(00:42):
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
(01:02):
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
(01:22):
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,
(01:45):
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,
(02:08):
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
(02:30):
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,
(02:52):
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
(03:14):
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
(03:35):
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,
(03:55):
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,
(04:15):
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.
(04:36):
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
(04:58):
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
(05:18):
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
(05:40):
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,
(06:01):
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
(06:23):
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,
(06:44):
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
(07:04):
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
(07:26):
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
(07:47):
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
(08:09):
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
(08:30):
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.
(08:50):
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
(09:13):
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
(09:34):
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
(09:56):
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.
(10:19):
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
(10:40):
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.
(11:03):
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
(11:24):
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
(11:44):
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
(12:05):
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.
(12:29):
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,
(12:50):
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
(13:14):
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
(13:37):
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
(13:57):
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
(14:17):
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
(14:39):
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,
(15:02):
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,
(15:23):
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
(15:46):
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.
(16:08):
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
(16:29):
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,
(16:54):
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
(17:16):
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,
(17:38):
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
(17:59):
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
(18:21):
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,
(18:42):
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
(19:06):
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,
(19:27):
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
(19:48):
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
(20:10):
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
(20:34):
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
(20:57):
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
(21:19):
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
(21:41):
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
(22:01):
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
(22:22):
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
(22:44):
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
(23:07):
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
(23:30):
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
(23:51):
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
(24:13):
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,
(24:34):
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
(24:57):
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
(25:18):
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,
(25:38):
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
(25:59):
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
(26:20):
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
(26:42):
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.
(27:02):
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
(27:24):
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
(27:47):
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
(28:09):
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
(28:31):
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
(28:52):
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
(29:13):
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
(29:33):
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
(29:55):
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
(30:17):
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
(30:38):
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
(30:59):
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,
(31:19):
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,
(31:42):
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
(32:04):
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
(32:25):
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
(32:49):
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
(33:13):
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
(33:35):
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
(33:58):
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
(34:20):
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
(34:42):
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
(35:04):
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.
(35:26):
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
(35:48):
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
(36:09):
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
(36:32):
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
(36:55):
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
(37:17):
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
(37:40):
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
(38:02):
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
(38:23):
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
(38:44):
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,
(39:04):
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
(39:25):
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
(39:46):
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
(40:07):
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
(40:27):
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
(40:51):
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
(41:11):
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
(41:33):
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
(41:54):
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
(42:15):
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,
(42:38):
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,
(43:01):
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
(43:21):
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
(43:41):
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,
(44:03):
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
(44:25):
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,
(44:46):
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
(45:10):
to you by Toyota. Let's go places
Brought to you by Toyota. Let's go places. Welcome to
Forward Thinking. Hey everyone, and welcome to Forward Thinking, the
podcast that looks the future and says, tell me, dr
where are we going this time? I'm Jonathan Strickland, I'm
(00:20):
Lauren Vocabon, and I'm Joe McCormick. Joe, I I've got
a question for you. Okay, I've really been thinking about
this for a while. What if I had if I
had to nail you down and say, what movie that
involves time travel do you feel really gets it right?
What's the best depiction of time travel in the movies?
What would you say? Well, I don't know if it's
(00:42):
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
(01:02):
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
(01:22):
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,
(01:45):
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,
(02:08):
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
(02:30):
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,
(02:52):
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
(03:14):
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
(03:35):
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,
(03:55):
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,
(04:15):
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.
(04:36):
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
(04:58):
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
(05:18):
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
(05:40):
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,
(06:01):
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
(06:23):
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,
(06:44):
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
(07:04):
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
(07:26):
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
(07:47):
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
(08:09):
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
(08:30):
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.
(08:50):
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
(09:13):
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
(09:34):
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
(09:56):
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.
(10:19):
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
(10:40):
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.
(11:03):
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
(11:24):
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
(11:44):
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
(12:05):
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.
(12:29):
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,
(12:50):
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
(13:14):
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
(13:37):
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
(13:57):
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
(14:17):
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
(14:39):
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,
(15:02):
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,
(15:23):
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
(15:46):
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.
(16:08):
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
(16:29):
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,
(16:54):
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
(17:16):
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,
(17:38):
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
(17:59):
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
(18:21):
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,
(18:42):
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
(19:06):
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,
(19:27):
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
(19:48):
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
(20:10):
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
(20:34):
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
(20:57):
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
(21:19):
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
(21:41):
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
(22:01):
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
(22:22):
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
(22:44):
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
(23:07):
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
(23:30):
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
(23:51):
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
(24:13):
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,
(24:34):
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
(24:57):
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
(25:18):
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,
(25:38):
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
(25:59):
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
(26:20):
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
(26:42):
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.
(27:02):
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
(27:24):
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
(27:47):
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
(28:09):
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
(28:31):
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
(28:52):
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
(29:13):
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
(29:33):
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
(29:55):
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
(30:17):
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
(30:38):
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
(30:59):
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,
(31:19):
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,
(31:42):
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
(32:04):
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
(32:25):
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
(32:49):
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
(33:13):
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
(33:35):
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
(33:58):
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
(34:20):
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
(34:42):
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
(35:04):
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.
(35:26):
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
(35:48):
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
(36:09):
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
(36:32):
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
(36:55):
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
(37:17):
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
(37:40):
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
(38:02):
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
(38:23):
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
(38:44):
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,
(39:04):
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
(39:25):
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
(39:46):
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
(40:07):
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
(40:27):
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
(40:51):
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
(41:11):
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
(41:33):
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
(41:54):
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
(42:15):
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,
(42:38):
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,
(43:01):
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
(43:21):
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
(43:41):
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,
(44:03):
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
(44:25):
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,
(44:46):
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
(45:10):
to you by Toyota. Let's go places
Fw:Thinking News
Hosts And Creators
Jonathan Strickland
Joe McCormick
Lauren Vogelbaum
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