Solution to the Grandfather Paradox

What if you went back in time and killed your own grandfather? Would you still be born? Or would you have thus killed yourself? Thanks to Google #sciencegoals for sponsoring this video!

If you could travel back in time, and you killed your grandfather, would you be killing your future self? What do physics, complexity theory, and computer science have to say about this famous murderous time-travel paradox?

And twitter - @minutephysics

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Created by Henry Reich

[hanseleve]

The easy answer: Two timelines
The hard answer: this video
The complicated lore answer: You ARE your grandfather

[awomanshootingsomething]

This would be the worst way to find out you were adopted.

[TravelBass]

I think that, the most "practical" solution would be that the moment "you" leave your current timeline and so become a "time traveler" then you become immune to this kind of paradox. As soon as you leave your own timeline for the first time, you do not belong anymore to that timeline and not to any other timeline either. You basically become a timeless entity.
So, you going back in time to kill your grandfather, would just result in killing your entire family except of you. If you then would get back on your original timeline, your family won't be there anymore, and never have been, but you would still be there.

Another solution would be that "the universe always finds a way". So, if you go back in time and kill your grandfather, then you won't be born and so, "someone else" would be born, and that someone is the one that actually goes back in time to kill you grandfather. If you do not kill your grandfather, then this other "someone else" wouldn't be born.

[pedroalonso]

Another solution: each time you travel to the past, your grandfather is moved to the future.

[atomicnolxix]

They always say "What if you killed your Grandfather"
But they never say "Why would you kill your Grandfather"

[noobxgod]

GrandFather is dead and alive at the same time,
Schrödinger's CAT : Ah Shit, Here we go again!

[SillySyrup]

You could argue that if you did have access to a time machine, it is impossible to kill your grandfather because you already failed. Many people forget that if something happened or didn't happen in the past, then it must stay that way because that moment was solidified into history. You can't "go back and change" the past. For example, if you went back and talked to your past self, then you would have already experienced that at a younger age.

[watchtowerguy]

Both of the solutions you used involved a different form of time than the paradox uses. The first one, you used was the one where you travel back in time, and that creates a new reality, the second one, was the one where there are two interconnected reality’s, where your actions in the past, only effect one reality. The grandfather paradox, uses the form of time travel, where there are no others reality’s in existence, or that can be made. If you use a different form of time, it’s not actually the grandfather paradox, it’s not even a paradox.

[PhantomLizzard]

I had a found a few errors in your understanding; however over all you are somewhat correct





I'm totally kidding, I have no idea what is happening in this video

[haljoa]

Someone complained about something about this comment, now no one shall know what it originally was

[rayray]

You know you’re old when a small kid shoots you saying you’re his grandad.

[felixdaniel]

Another Paradox: If Pinnochio said "My nose will grow now", What happens?

[gbz]

This guy messed with my brain for 2 minutes and 48 seconds straight.

[Ajaykumar-vtlu]

After watching tenet, youtube recommends grandfather paradox.

[h.a.z.m.a.t]

I believe what would happen is that your grandfather would die and then you would continue existing. So if you were to go back to the present then you would spontaneously appear out of nothing. The way I look at this is to look at the timeline as some sort of word document. The original text said that your grandfather survives, but then you went back in time and made an edit. I don’t really know how to express this theory, it’s hard to put it in words. Another way to look at it is the following scenario. There is a division of soldiers and their major general orders them to attack a nearby enemy base. Then the major general decides to at the enemy base is too well defended and orders the soldiers to retreat. Which order will the soldiers listen to. The most recent one.

[Tysto]

I like to imagine that a time machine would only be able to place you back in time on a path that does not create a paradox. After all, it must be able to “see” into the past. You could do anything you want except things that result in you or the time machine not existing. This creates interesting story possibilities, like you fail to kill a villain & later learn he was your own great-great-grandfather, so of COURSE you failed.

[xoocit]

I was explaining this to my friend and his grandfather walked in🤦🏻‍♂️

[sohamdutta]

Just call it, Schrodinger's Grandfather.

[_BONAL_]

I had 3 solutions to this paradox.
1. When you travel back in time you create another timeline
2. When you travel back in time, you travel as a ghost so that you can't interfere with the past.
3. Anything you did in the past couldn't interfere with critical situations that happened already in the present because it was already destined to happen, meaning you would always fail trying to kill your father by whatever you tried to do because that would change the destiny...

Of course the other solution was that the future could be change like you told in the beginning

[youareivan]

I remember reading a collection of short stories I'd checked out from the local library when I was a kid. I'm pretty sure it was a collection of unfinished tales by C.S. Lewis, but I don't remember the title and a quick google search didn't turn up anything. Anyway, the book included a story about time travel where the main character suggests that you can't send something back in time because the atoms that make that thing up in the present already exist in the past being something else. For example the atoms that make up a chair now were part of a tree in the past, so sending that chair back in time would add a chair's worth of extra mass to the total mass of the universe which is a big no no.