Of all the problems and riddles in science, the question of time travel is one that particularly
captures the imagination.
It’s long been a favorite for science fiction writers, but today it’s at the heart of
many a real world study and thought experiment, as well.
So, this is Unveiled, and today we’re taking a closer look at the different types of time
travel you should know about.
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If time travel has a map, so to speak, that map would be kind of like a tree, with branches
sprouting off that then sprout more branches, and then more, and so on.
From the very beginning, it’s not as though this is a black and white, chalk and cheese,
A and B sort of thing…
it’s much more nuanced than that, with many gray areas, and much more interesting, as
a result.
In the tree of time travel, then, the trunk effectively doubles up as the initial timeline
itself - original, unaltered, and clean.
From there, the first big branching off heads in two directions: forwards time travel and
backwards.
We’ve covered the fundamental differences between the two in many videos before now,
but to briefly recap:
Forwards travel is generally deemed to be technically possible, if the traveler were
to only travel fast enough.
Backwards time travel is thought either much more difficult or physically impossible under
the laws as we currently know them.
Then, for backwards time travel to work, we’d require some major bending of reality and
hugely advanced physical and technical knowhow.
The most popular strategy being that backwards travel might be possible were we to somehow
build and reliably use a well-placed wormhole.
From here, there are many further directions we can head down.
Forwards time travel offers usually the more straightforward routes, though.
And, sometimes powered by the real world rules of time dilation, the mechanics aren’t usually
too tricky.
Yet, often, the biggest questions with forward travel surround the idea of inevitability.
Is an event in the future fixed?
Is it fated to happen?
Or is it entirely your decision what happens and when?
In science fiction, this is sometimes explored via a foretelling or prophecy; some kind of
advanced, super-prediction that a character can either follow or fight against.
If they fight against it and change it, then the future isn’t fixed.
If they fight against but eventually succumb to the prophecy, no matter what they choose
to do, then their fate was apparently sealed from the very beginning.
Forwards time travel is something like following a predetermined route in a GPS sat-nav, here…
while the journey might deviate every now and then, the destination is always the same.
This idea of inevitability is perhaps even more key with backwards time travel, however.
Imagining a time when all the physical complexities (and apparent impossibilities) of backward
travel are solved, it all depends on how exactly your original timeline responds to your revisiting
the past.
In one scenario, the timeline itself - that trunk of your time tree - absorbs any meddling
that you might achieve and emerges unchanged.
While in another it reacts to it in some way, changing its shape as a result.
The first option is sometimes called a “fixed timeline”, while the second is referred
to as an “unfixed”, “dynamic” or “changing timeline”.
In a fixed timeline, you might travel back in time with the aim of preventing something
that happened in the present…
but, whatever you try, time always plays out the same way.
Maybe you’d like a redo after a terrible test score or a disastrous job interview,
and so you jump back to before those things happened to try again.
Only, no matter what you attempt, you always fail at the test or interview, exactly as
you did before.
In some science fiction examples, this also means that you always choose to go back in
time to resolve it, too… which is where the idea of a time loop comes into play.
In a fixed timeline, it would be all too easy to become trapped inside one of those.
In an unfixed timeline, however, there’s much more freedom.
Or, at least, there appears to be.
Now, you can go back in time and successfully change the present, rerouting yourself into
a seemingly different future as a direct result.
Your timeline has responded to the changes made, and perhaps become all the stronger
because of them.
It’s as though you will’ve upcycled your life, adding to it - and presumably improving
it - in endless different ways.
However, loop-ish paradoxes are still very possible.
The infamous grandfather paradox most clearly demonstrates how.
Say you went back in time and killed your own grandfather, thereby preventing your own
birth…
all of that could still only happen if you were alive in the first place to travel back.
So it would be as though your birth, life, and ultimately fatal time travel episode would
have to be played as if on repeat, forever and ever, trapped in some other reality and
totally inaccessible to anyone else.
In fact, really, with some versions of “changing timelines” there’d be no way that we (you
or me) right now could know whether reality is already full of such temporal prisons…
which is, perhaps, a little disturbing.
And round about here is where most ideas on time travel stopped up until just a few decades
ago.
We could potentially rearrange standalone timelines, crossing them over with the lives
of others, but it has traditionally always been difficult to go further.
Now, however, theorists and writers have another well of essentially infinite possibility to
go to; the multiverse.
As the idea of parallel worlds, many worlds, and alternate timelines has filtered into
mainstream science, models of time travel have been fleshed out with countless new dimensions,
directions and capabilities.
In everything from elite academia to Hollywood blockbuster, the multiverse is now a kind
of ultimate endpoint.
With time travel specifically, the multiverse offers travelers the chance to move backwards
and forwards in time, but each time they do so they access another version of the reality
that they had just left.
In this way, it’s suddenly quite easy to make changes to the seeming past and/or future
along any timeline, because actually you’re working on a new canvas everytime.
A canvas that’s very, very similar to your old life, but isn’t actually your old life,
at all… so the paradoxes are kept at bay.
Here, the idea is that you really could travel back to improve a test score or give better
answers for that job you wanted so badly…
it’s just that when you eventually make the grade or get the job, you do so in a slightly
different edition of your own life.
Your friends and family, your home, your favorite foods and TV shows, everything else is all
still there, it’s just that in the grand mesh of a multiversal reality you’re now
operating at a slightly different point.
For some, the mixing of time travel with the multiverse doesn’t really sit right.
Given that it has such a massive, even unending scope, the multiverse might be viewed as something
of a cheat card, for time travel in science fiction.
But, still, as bizarre as it all sounds, it is a theory that scientists are taking more
and more seriously - with some even claiming that the existence of the multiverse is inevitable,
in itself.
But what’s your verdict?
From some perspectives, at their heart, most time travel models are an exploration of cause
and effect, and of whether those two things can ever be properly flipped on their heads.
Alternatively, time travel can be seen as a device to test the fatalistic nature of
the universe…
or perhaps it only really reveals the true randomness of reality?
The “tree” of time we started with is certainly not a straightforward structure.
It’s gnarled and tangled, with many branches laden with possibility.
Climbing that tree is no easy task, then, even after the immense physical challenges
to achieve genuine time travel have been worked out.
And for now, unfortunately, we are still at that very early stage where we need to invent
the thing first, before we can properly plan how it might work out in practice.
Nevertheless, it’s never a bad idea to plan ahead.
So, those are the different types of time travel you should know about.
What do you think?
Is there anything we missed?
Let us know in the comments, check out these other clips from Unveiled, and make sure you
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