If you went back in time and killed your grand-father or your father before you're even born, would you be alive now?

I’m sorry, but your scenario is just not possible. Where do you think you came from without your grandfather and father? And even if you managed to survive somehow, how could you give birth to your grandfather? How could you make sure the child you give birth to become your grandfather and give birth to your father, who then gave birth to you?

What do you mean, @Mimishu1995 ?

I don’t quite follow your answer.

You’re talking about ‘me giving birth to my grandfather’. What do you mean by that? My question is not about me giving birth to my grandfather, but about the paradox of a person having killed their own grandfather or father.

You say “you will be alive. And so will be your father or your grand-father whom you have just killed”

How do you think that will happen without you giving birth?

@Mimishu1995 When I say that we will all be alive, I mean that nobody will ever be killed at all. :)

Note that one of the topics to this question is Philosophy. It’s a philosophical question actually.

No, I don’t think you would be alive. If you killed your grandfather, you wouldn’t have your father, and you wouldn’t exist, let alone being your grandfather’s father.

Care to elaborate how you think you can stay alive?

@Mimishu1995 Please wait a little, I’ll send you a private message and explain it to you.

This is known as the grandfather paradox

Depends. We talking Back to the Future time travel rules or Avengers Endgame time travel rules?

I default to assuming everything that is possible, is possible because it is possible.

So presupposing that rapid reverse time travel is possible, and given the butterfly effect and that any disturbance of the past would be likely to create such unforeseeable ripples into the future as to likely cause a paradox, which is by definition, impossible, I have to believe that space time is happy to be full of holes. I don’t believe that it would cause any problem, besides legal ones, if you killed your grandfather. You would continue to exist. If you returned to the future, depending on the configuration, you’d either end up in your native timeline, unchanged, or in a new, completely changed one.

I believe time travel is impossible (no matter what Einstein says, lol) but it makes for really awesome syfy movies and shows. But this scenario does hurt my head to think about. So I’ll leave it to you @AhYem to tell me your take on this. :)

If your grandfather ceased to exist before your father was conceived, you would cease to exist as soon as you showed up in the past and caused the conceiving to not occur.
There are multiple time lines that are possible as described in in the movie Back to the Future III.

All part and parcel of an example of a classic time paradox.

Several possibilities:
1. When you travel back in time to kill your grandfather, you always went back in time to kill your grandfather. You will fail to kill him, because you already failed, and you have always failed.
2. You travel back in time to kill your grandfather, you kill your grandfather, and this act causes a split into an alternate timeline, where you are never born. You still exist.
3. You travel back in time to an alternate past, kill your alternate grandfather, and your alternate self will never be born, but you still exist.
4. You travel back in time to kill your grandfather, you kill your grandfather, and you will never be born. But you still exist, because the act of time-travel disconnected you from causality, and prevents any changes in the timeline to affect your current self existing in the past.

Someone should name a paradox after that. :)

So, first of all, time travel is fictional at this point, so any speculation on what would happen depends on the rules of time and time travel in your particular fictional work. The two most common models are the branching multiverse style of time travel (like what Back to the Future uses) and the other is sort of claiming that causality works in both directions (like 12 Monkeys).

Under the branching model, you go back in time, you kill your grandfather and your actions cause time to ‘branch’. You came from branch A where your grandfather lived and you were born, but now that you killed him, you begin naturally living branch B where he’s dead and you were never born.

The collection of molecules called You still exist and travel down branch B. The idea that you would fade away like in Back to the Future is…kind of silly, but you are now in a timeline where you will never be born. If you travel FORWARD, you would be travelling further down branch B. You can’t get to branch A anymore. Even if you went back in time to stop yourself from killing your grandfather, you’d really just be creating branch C which has some similarities with A. Indeed, EVERY choice and variable causes a branch, not just major ones, but focussing only on major events simplifies things.

The other way to look at it is the 12 Monkeys style. This model of time travel in fiction usually portrays the time traveller as either UNABLE to change the past or indeed being on of the CAUSES of the past.

In this example, you might go back in time, kill your grandfather, and then find that you still get born because that was never really your grandfather. Your mom had an affair and your father was a cuckold who raised another man’s son unawares. And the family stories that you heard growing up left out the time your grandfather was brutally murdered by some weird stranger. For example.

This form of time travel storytelling is more interesting than the branching style…but it’s also harder to do WELL. It’s just easier to do the branching thing.

#1 on @ragingloli’s list is the “whatever happened, happened”/Lost view of time travel and my personal favorite (I’m sure it has an earlier precedent in media, but I was first exposed to it in the TV show Lost). In this view, time travel to change the past is futile because your traveling to the past “already happened” (such that you might stumble across a black and white photo of yourself from the 1930s before you’ve actually traveled there. It happened in the past but hasn’t happened in your present yet). So that’s the perspective I usually take when it comes to time travel and I posit that you could not kill your grandfather because you exist, proving your attempt to kill him was not successful and something had to come along and stop it somehow.

Or perhaps it happens á la Futurama, in which Fry goes back in time and runs into his young grandfather, becomes convinced his grandfather is going to die and attempts to protect him, but ends up causing his death. Fry then meets his young grandmother, but is convinced that she cannot be his grandmother since his grandfather just died and he still exists, and proceeds to sleep with her. But as it turns out, “whatever happened, happened” is the rule here, she was his grandmother and Fry is actually his own grandfather. xD

The “real” answer?

There is no “real” known answer to how or whether it is possible to go “back in time”.

I tend to think it is not possible, at all, except using imagination, fiction, memory, dreams, or other things that have no actual effect on what actually happened.

IF you believe there are multiple timelines, or a continuum of possibilities, or that existence is a thing of imagination, then sure you could go do that in another time thread, but you couldn’t affect the past that led to your own existence at all, or you’d change that past, and even just going “back in time” would mean you had changed that timeline, so you must be in another reality than the one that created you.

Say our protagonist is Al, his wife is Babs, and Al’s pal is Sal.

Al is the first time traveller. He and Sal go back to before they were born.

Al kills Al’s grandfather Alton (because he’s a massive psychopathic berserker, naturally).

Alton looks pretty dead to Al, in the past he’s seeing.

Al and Sal go on to live their lives in the past, as psychopaths from the future. A new history plays out for them.

Does Babs, and all of history after this egomaniacal murder experiment happens, vanish? No, I expect Babs is just relieved that Al and Sal disappeared.

Two perceptions of events continue. Implying an infinite number of perspectives on existence.

If “travelling back in time” is even possible (I bet not), and IF there were only one universe which was affected by any such travel, then some ancient alien psychopaths trillions of years ago would have learned to do this, and be rebooting reality endlessly ever after/before. Which would be even more nuts than the idea of endless timelines (which I can at least imagine might be true).

And honestly, option 2 is really just option 3, because the split would happen when you arrive in the past, and your matter starts interacting with past matter. The moment your body displaces air molecules, your body reflects/absorbs photons, and your mass warps space-time ever so slightly, the past is changed.

How could I go back in time to kill them if I don’t exist due to killing my g’father and/or father?
The answer seems simple…I don’t exist.

So far nobody has written “the real” answer to my question, but some of your answers were very interesting. @smudges‘s answer comes closest to it, it’s just slightly different than the “real answer” that I will tell you in a couple days. I’d like to have some more answers before I tell it to you.

@AhYem so is your purpose of asking this question to start a discussion or to ask us to read your mind and guess the answer you have in your head?

The Grandfather’s paradox is a well-known paradox that is documented and debated. And there is no real answer to it, because time travel isn’t a thing yet. There are several possibility that can happen, just like many of us here has stated. There is a reason why there is an entire Wikipedia page on it.

You on the other hand are so sure of the answer you call it the “real” answer. Are we supposed to guess what kind of answer you gave in your mind?

I thank every one who have answered my question or participated in the discussion.

Now I’ll tell you the “real answer” to that quasi-paradox.

It isn’t even a paradox, to begin with, because a paradox either doesn’t have an answer, or has multiple possible ones. However, this one has only one answer, and it goes like this:

It is not possible for anyone to go back in time and endanger their own existence.

And now the explanation to it.

If you went back in time – provided such a thing was possible – in order to kill either one of your direct ancestors or yourself, and if you were successful, it would mean this:

You either killed yourself or prevented yourself from being born.

That means, you would quit to exist the moment you did the action.

But then again, it means that you have never been there at all.

And if you have never existed, how would you ever be able to do anything? How would you be able to go to the past and do anything there, if you didn’t exist at all?

Your own existence can be endangered by something that exists. It can’t be endangered by anything that does not exist.

So, if you could ever go back in time, aiming to make an end to your existence or to “undo” yourself, all you could do there would be one of these options:

- You aim your gun at yourself/your direct ancestor, and the gun doesn’t fire, or you miss, or you kill another person there and have to flee before being arrested,
– You can’t get the means that are necessary to perform your action,
– You can’t locate the person who you want to kill,
– Something happens that prevents you from doing it,
– You change your mind,
– You can’t remember why you wanted to see yourself or your direct ancestor, and all you do is just talk to them or simply observe them.

You may even end up in a sort of time-loop for a period of time, in which you fire your gun, the person falls dead, you experience a jump back in time, you fire your gun, the person falls dead, you experience a jump back in time… and so on, till the moment you decide you have your nose full of it.

You can never successfully accomplish such a “mission”, due to the simple fact that it is IM-POS-SI-BLE. You can’t kill yourself, because the moment you kill yourself you cease to exist, and if you don’t exist you can’t go back in time to kill anyone.

There is a very good situation that we can use as an analogy to this problematic.

The moment of your killing either yourself or your direct ancestor can be compared to the moment when an actor makes a mistake while a movie is being shot, after which the movie director yells CUT!!! and their action becomes undone, although the actor did perform it. It doesn’t become a part of the movie. The actor did something for real, but it was “cut out” of the movie, just as it had never been done. It gets cut off the movie because the movie director doesn’t allow it to become part of “his reality”.

The actor doing the mistake is you trying to kill yourself in the past.

The movie director is the corresponding Law inside our Reality that doesn’t allow such a thing to happen.

You cant eat water, you can only drink it.

You can’t kill yourself in the past, or prevent yourself from being born.

Once again, thank you all for answering my question about that alleged paradox.

Your line of thinking has several assumptions about how events get caused, as well as how time and the universe work.

The section where you list things that must happen instead, is the thinking of a sci fi writer inventing a story, not someone thinking rationally about cause and effect that makes sense. It assumes that there is only one stream of events, and only one universe, or something like that, and that some writer-like (or philosopher-like) process would “reset” the one situation to avoid a paradox.

I would say instead that rather, clearly either time and the universe don’t allow time travel at all, or if they do work in a way that resembles being able “to go back in time”, that must cause some sort of new experience of a timeline, that does NOT depend on it being the same as the past that created you.

Otherwise, the moment you “appeared” in the past, you WOULD change the past to something other than happened before. Just by being “in the past” at all would contradict the past you came from, whether or not you try to kill anyone, and that’s just as disruptive to the universe.

So if it can happen, then there’s at least one additional timeline created when that happens. If it can happen, it seem much more likely that there’s a (perhaps infinite) continuum of possible timelines.

Yup. That’s the real right answer.

Asker is right that paradoxes can’t exist, but is fixated on one of many potential resolutions.

What would make a good science fiction story would be someone trying to commit suicide by traveling back in time to kill their presumptive father only to have nothing happen affecting the time line as they stood over the dead body.

“Motheeeeeeeeer!”