维瑟 我是杰克 如果你能回到过去
Vsauce, I’m Jake and if you could go back
in time and stop yourself from being born,
Or should I say…can you?
Because if you went back in time and made it
so you weren’t born then you wouldn’t
be alive to go back in time to stop your birth.
It’s the Retrosuicide Paradox.
where something that you can do
but it doesn’t mean that something you can complete.
Just like I can go to the store to buy an avocado
but it doesn’t mean I should leave the store with one.
For time travel, the timeline self corrects in a way.
But…actually…I’m getting ahead of myself.
Let’s travel back to the beginning.
维瑟 我是杰克 时间旅行本身就是个悖论
Vsauce, I’m Jake and time travel is a paradox itself
which means that any paradox created by the idea of time travel
is paradox in a paradox.
It’s The Paradox Paradox.
Allow me to explain,
With the Retrosuicide Paradox the idea is that things
that have happened in the past are fixed points.
They can not be changed
because changing them would change all of time coming after that past event.
And since you going back in time needs to happen,
there would be no way to follow through with killing your younger self.
But that’s only if we assume that time is one straight line
where the past dictates the present
if time travel were possible, the present would also dictate the past.
it’s a self-fulfilling cycle.
We can travel in any direction of space
but can we travel in any direction in time?
Australia and China both exist even though
they don’t exist right here with me in this location.
So one could argue that yesterday and tomorrow exist
even though they don’t exist right here…right now.
But the fact is, yesterday and tomorrow don’t exist.
I can’t revisit yesterday and I can’tskip forward into tomorrow.
Changing the hands on a clock changes your personal time
but not external time.
External time is the rate at which time moves
which is a constant, consistent rate.
When it comes to time being relative,
that is personal time.
If you slowed down the rate of your body to such a degree
that every function of yourbeing were affected,
from your perspective people would be whizzing by
but from everyone else’s perspective
you would look frozen.
However, external time is still moving at the same rate.
It’s just your perception that feels different.
It is the Time Discrepancy Paradox,
where there has to be a difference
between time and time
which we know there isn’t.
In most time travel stories it works like this:
Subject A leaves Point A and immediately goes back in time to Point B.
Then after doing what they need to do,
they come back to Point A.
But this is where another and more sinister paradox is created.
If we go back to this timeline,
when Subject A goes back in time only they go back.
而曾经的主角A 或称主角A2 仍在向A点前进
The version of them in the past, Subject A2 is still moving towards Point A
when they go back in time which means
they have created a closed time loop in a way.
If Subject A travels back to right when they left Point A,
Subject A2 will already be going back to Point B.
That instance will occur forever.
So everytime you travel through time
you will always be creating a loop
no matter if you go into the past or the future
because you right now are time travelling,
but you a day ago, you a year ago, isn’t.
That you is still moving up on the timeline to that fixed point you created, Point A.
So it also begs the question,
does that mean that if you left that timeline at Point A and went to the past
would you not exist in the present and moving forward or in the future?
Time doesn’t stop just because you aren’t there.
So instead of continuing on your timeline
you have now imprisoned yourself or yourselves into a loop.
It creates an infinite amount of you
that resets every time you hit Point A.
Because you take you in that moment in time.
So it creates another paradox,
the Double-Occupancy Paradox,
which is how can there be more than one of your current self?
We think of ourselves as oneself.
Also, side note:
This brings up an additional paradox which is the Paradox of Freedom.
Let’s say like in our scenario above,
you, Subject A, travels back in time from Point A
thus creating a closed time loop
在这之中 另一个”你” 即主角A2一到达A点
where a version of you will always go back in time
once they reach Point A.
You think that you were the one to choose to go back in time at that specific moment,
but, were you?
If it is a closed time loop then you might not be subject A,
but more statistically possible
is that you are Subject A20 or A5000.
So even though you felt like you had the freedom to choose that decision,
it had already been decided for you.
Ok. Let’s go back to that timeline
and imagine something different.
The most likely scenario is that only the present exists.
The past is gone and the future has yet to be written.
But as I mentioned earlier the past has been written
so it could be that the past and present exist
but not the future.
In this scenario you could go back in time
since the past did, by all accounts, happen.
You just wouldn’t be able to change it.
But if that were true then so would the third scenario
which is most commonly thought of when thinking about time travel.
就是“过去” “现在” “将来”都存在
That the past, present and future all exist
and you can travel to any of them.
That would mean that all 3 –
past, present, future – are happening concurrently.
Think of it as three timelines running on top of one another.
So when you go forward in time,
it isn’t on your timeline.
It is on the timeline above you.
And if you want to go into the past from the future,
you’d intersect with the present with your timeline.
It’s important to note that if you left the present to go into the future,
you are now gone.
So if you spend a week in the future,
there is a week in the present where you just don’t exist anymore.
One of my favorite thought experiments about time travel is this.
If time travel were to exist then it has always existed
as the physical machine can exist at all points in time.
So even if it were invented 100 years from now
it still exists now and since the beginning of time.
And it is important to remember,
even in the 3 timelines theory,
if you went back in time you can see the past
but you can’t interact with it.
You can’t change it
because it would still disrupt the present and future timelines.
However, there is another theory
that allows time travel to not be a paradox,
by doing so would also make it so no time travel paradox would be paradoxical.
In this theory, if we revisit the first paradox we talked about,
the Retrosuicide Paradox.
you’d go back in time and you could in fact kill your younger self
and you would no longer exist…on that timeline.
By doing that act the timeline splits.
So what was timeline 1 creates a timeline 2.
Timeline 1 has you go back in time and commit retrosuicide
while timeline 2 continues as normal.
Time has still self corrected itself by making a new copy of events
as they were supposed to be,
that’s timeline 2, not as you made them, timeline 1.
If this were true,
we could be living on anyone of these timelines.
They fracture from the time we knew
to what we think we know,
but we’d have no idea either way.
That means there are multiple timelines.
an analogy in a sense for the multiverse theory,
that there are parallel universes,
each time we travel through time,
we aren’t actually moving through three concurrent timelines
or new timelines are being created
but actually we are travelling to a different universe that’s similar to our own.
And if that’s the case…
I need to keep traveling until I find the right one.
Thanks for watching.