Phil 1.08 Video Version

Hello and welcome to my presentation about the grandfather paradox

for the philosophy of time and time travel.

21 s.

In this presentation first we'll ask the question is time

travel to the past possible.

Well look at that in relation to the grandfather paradox

which will be introduced.

two third we'll look at lewis and vigilance responses to

the grandfather paradox and finally evaluate these responses and talk

about which ones I think the most logical.

So asking the question is time travel to the past

possible? We have to think about what is the definition

of possible.

There are lots of different ways to think about time

travel. So there's also many different ways to question the

scope of possibility in this presentation will be evaluating the

possibility of time travel from a logical standpoint as opposed

to say a physical possibility.

So the question is is time travel to the past

logically possible.

So next we'll introduce the grandfather paradox.

The grandfather paradox is a pretty well known paradox that

argues against the possibility of time travel 1st.

Let's go through some key definitions.

One there's a self defeating act.

So the definition for a self defeating act is an

act. A is self defeating.

If and only if performing a entails a failure to

perform a.

We'll see an example of this when we get to

the grandfather paradox itself.

Next contextual us means a view that an outcome depends

a view that an outcome depends on certain contexts.

Third equivocation is when an argument is presented in which

11 interpretation of a certain portion of the argument is

contradictory with an alternative interpretation and finally it's really important

the definition of can.

But as we'll hear about the future, this one's pretty

controversial, so we'll definitely get to that later.

So now looking at the argument itself, I've broken down

the argument into standard form.

So the grandfather paradox in standard form states one if

time travel is possible, then one can prevent one's own

birth by for example, killing one's grandfather two, but one

cannot prevent one's own birth three.

Therefore time travel is not possible.

So let's look at premise one.

If time travel is possible, then one can prevent one's

own birth, right?

Perhaps killing one's grandfather.

How does this work?

Well, if you look at this picture here, imagine that

you are tim the time traveler.

So about 10, he hates his grandfather, he's an expert

marksman and has all the means to be able to

murder somebody.

Um and he has the murders intent to travel back

in time to kill his grandfather.

So let's say he does that, he goes all the

way back in time and he kills his grandfather.

If tim is successful then his grandfather wouldn't exist, which

means his father wouldn't exist, which means that therefore he

wouldn't exist.

But if he weren't able, if he wasn't existing, then

he wouldn't be able to kill his grandfather.

That's what we would call a self defeating act, because

you're not able to tell your grandfather.

So that's when we look at premise to one cannot

prevent once on birth, because Tim goes back to kill

his grandfather, he won't exist, which means he can't kill

his grandfather.

Therefore, time travel is not possible.

That's the main consistent inconsistency and the grandfather paradox.

So now let's look at some solutions and responses to

the grandfather paradox.

Two notable ones are one by David Lewis and one

by Kadri Vivian.

So, first let's look at louis louis contextual.

This solution says that basically the Can in the context

of the first premise is used differently than the Can

and the second premise.

So he argues that this equivocation on the definition of

Can is what ultimately renders the argument logically invalid.

Zooming in on Can a little bit you can see

that it's been highlighted here in the standard form.

So Lewis argues that Can in the first premise focuses

on some subset of actual effects.

For example, the killer has the expertise means and motives.

So this can is talking about if the killer has

the ability to go back in time, he has the

gun, he has the grandfather or a target in point

blank range, then he can kill his grandfather based on

the facts, the set of facts that leads up to

the possibility of the killing grandfather.

However, in the second premise, this can focuses on the

identity of the target itself and the possibility of a

successful killing attempt.

From a logical standpoint for this can it is impossible.

The killer cannot kill his target because the identity of

target is what allows the killer to exist in the

first place.

So louis contextual a solution, he says that the word

can is context dependent.

So this argument equivocates between premises and therefore is logically

invalid. Now, let's look at vivid in her response to

that equivalent response.

She believes that Lewis's response fails.

She says that the argument does not equivocate because the

time travel can never successfully complete the killing attempt.

How can this be?

Well, looking back at the word, can vigilance says that

what we orderly ordinarily means, when we say that someone

can do something is that she has both the ability

and the opportunity to do so, Vivian argues that the

debate is not about the meaning of can, but rather

if deterministic causes would prevent us from otherwise succeeding.

So therefore, if the statement that someone can do something

is true, then this entails.

The attempt would or at least might succeed.

So when Vivian looks at the standard form, she argues

that can as used here in the first premise can

never be true.

So in the case of the grandfather paradox, the counterfactual

of a successful A kill is always not possible and

always false, no matter how often or how hard the

killer tries, because this kill will always fail and the

claim that the killer can succeed cannot be defended.

Therefore that's what Dublin uses to argue that loses solution

fails. Now looking at that, I think that vigilance response

is correct.

So going deeper into evaluation, Vivian says that no time

traveler can ever kill their younger self or their ancestor

who has yet to pass on their genes, Given that

one it's the ordinary definition of Can into the situation

is set in one of our closest antecedent worlds.

To make this easier.

I'll put Vivian's argument in standard form one, if louis

contextual a solution succeeds in addressing the grandfather paradox, then

the grandfather paradox equivocates on the word Can Premise two

says the grandfather paradox does not equivocate on the word

can Premise three says therefore Lewis's argument fails zooming in

on premise one, this premises, one that links Lewis's solution

to the grandfather paradox.

So the protectionist solution by louis is built upon the

usage of a context dependent word Can as we said

before, Lewis argues that this argument is logically invalid because

the use of canon premise one is different with the

use and premise to and because there's an inconsistency with

the simplification, that's where the logical and validity lies, because

this is basically just explaining Lewis's solution to the grandfather

paradox. I think this premise is pretty true.

Now, looking at the second part, this premise to that

says the grandfather paradox does not equivocate on the word

can. This is where the bulk of vigilance argument lies,

She argues that can and the grandfather paradox is ordinarily

used to express that someone has both the ability and

the opportunity to do something and that an attempt might

at least at some point be successful.

She notes that this ordinarily used version of Can stems

from a philosophical debate between free will and determinism, but

she also goes on to argue that both sides have

the same conception of the word can.

This is because rather than it just being a definitional

debate, the question is more model and it's whether deterministic

causes deprive us of the opportunity to do anything other

than what we in fact do.

So, in easier terms, Vivian says, someone can do something,

if it's true that she tried to do it, she

would or at least might succeed.

She also says that most people would agree that someone

cannot do something if she would fail to do it,

no matter how hard or how many times she tried.

So when applying that to the grandfather paradox, if one

were to try to defend that the use of can

is consistent with the means and motives of the killer,

then violent replies, it's unclear what the killer's abilities and

opportunities are.

So, given that it's unclear what the killer's abilities and

opportunities are combined with.

There is never an occasion in which an attempt is

or can ever be successful, then it follows that the

time traveler simply cannot kill, and thus the murder attempt

will always fail.

Therefore, it can't be strongly defended, that the killer can

be successful as stated, and promised one of the grandfather

paradox. I think her justification for this second premise is

pretty robust.

Therefore, I think that her argument of Lewis's argument fails

is valid and true for most.

So one final consideration that's pretty important in accepting vigilance

argument is to agree that this occurs at the closest

worlds in which the antecedent is true, the world's most

similar to our own.

She claims that any and all closest worlds remotely like

ours where one tries to kill their grandfather, they will

always fail.

That's my opinion.

And then finally, some last thoughts to explore all the

solutions and responses that we've talked about so far assume

movement along a singular, fixed timeline.

Additional thoughts and solutions to the grandfather paradox and the

possibility of time travel also include the addition of multiple

timelines and possible universes.

For example, um, if you time traveled back, maybe at

that point, you branch off the original timeline and start

a new future in which you can impact events there.

There's also a quantum approach which I saw in my

research, which brings up a logically consistent solution, which requires

a parallel existence of two incompatible state in a closed

time loop.

So there's definitely a lot of stuff out there regarding

the grandfather paradox.

But thank you so much for coming to my presentation

today and learning about my thoughts on louis versus sibling

and the grandfather paradox.

Thank you.

Phil 1.08 Video Version

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