Solution to the Grandfather Paradox

Solution to the Grandfather Paradox


As far as we know, time only moves in one
direction – forward – but if you could loop back to visit the universe at an earlier
point in time, a famous paradox arises. What if you killed your grandfather when he was
a child? Then your father or mother wouldn’t have been born, so you wouldn’t have been
born, so you wouldn’t have been able to go back in time to kill your grandfather in the
first place. Paradox. The simplest resolution to the grandfather
paradox is that when you go back in time, you’re actually not going back into your own
history but to a copy, and everything you do there influences the new alternate future
of that universe, not your own past. But that’s boring, because it just avoids the paradox. If what you do when you go back in time actually
influences your own past, and the effects of your time travel do loop back to the present…future…past
– no problem. Let’s just follow the paradoxical timeline through BEYOND its paradoxical conclusion.
You go back in time, kill your grandfather, thus you aren’t born so you can’t go back
in time, thus your grandfather isn’t killed, thus you are born, so you go back in time
and kill your grandfather, and so on… I’m showing this as a linear series of events
but really it’s two entangled histories happening in parallel. Is that even possible? Well,
I don’t know about the time travel part, but subatomic particles regularly do multiple
different things in parallel – it’s called quantum superposition and is responsible for
the weirdness of the double slit experiment, many properties of atoms and molecules, fusion
in the sun’s core, and so on. So if the universe were to exist in a superposition
of two states – your grandfather is alive and your grandfather is dead – then the
natural result is a superposition of two states: you’re born and able to go back in time to
kill your grandfather, and you’re not born. And the natural result of these is a superposition
of two states – your grandfather is dead and your grandfather is alive – and so,
at least from a logical perspective, this looping timeline is entirely consistent and
there’s no paradox. And a similar paradox-free solution can be obtained by viewing the problem
as a steady-state solution to a Markov chain – but I won’t go into that here. Now of course nothing about these solutions
to the grandfather paradox suggests that closed time loops are actually possible – in fact,
some of the implications this kind of time loop have in the study of complexity theory
seem to suggest that time loops – and thus time travel into the past – must be impossible.
But the main point is sometimes we think a situation creates a paradox when it doesn’t,
and really the only paradox is how our thinking can be twisted enough to dream up time-traveling
murderous grandsons, but not twisted enough to think about twisting time.

100 thoughts on “Solution to the Grandfather Paradox”

  • So if you kill your grandfather as a child, , the universe will glitch out and be stuck forever playing the two superimposed time loops forever? Maybe this is how the universe ends…

  • We are never truly living in the present, because it takes a certain amount of time for light and sound to reach your eyes and ears.

  • My question is: What did your grandfather do that was so bad that you would want to go back in time to kill him?

  • Thomas Rowley says:

    Back in around grade five or six I had become quite interested in how things work in the real world, I had just gotten out of the superpower phase and sat down to think about why superpowers wouldn't work as intended and I eventually reached time travel.

    It was so hard to explain to myself let alone others how time travel would possibly work and inevitably fail. Paradoxes were so fun to find.

  • Arunkumar Mahendran says:

    Simple solution : why would anyone kill there grandfather ?……they will do any other good job…😆

  • What about your future . If u go back the in past and kill your grandfather , you will have no future because u will be dead . Blah blah blah things happen and then in the next timeline you are alive again but u still have no future because u will travel in the past again

  • Einstein proved that time is a local property and to go 'back in time' you would have to go forwards in time (your time) and make the entire universe go back in time (global time). It also follows that you would have to make the entire universe go back in time …. at the same time … otherwise some parts would have changed position resulting in an uneven rewinding of time resulting in a different universe.
    So in conclusion, no.

  • Littlebrownjules Gaming says:

    What? No?

    Your picture would just disappear. I’ve seen back to the future. I know what I’m talking about

  • I don't know about you, but I don't need to time travel to kill my grandfather. I've already done it once and twice with my great grandparents.

  • Jonathan strange says:

    if you go back in time, and changes something, wont that just delete the timeline you came from and, create a hole new timeline and then it will just go on from that?

  • But if we go back to a copy of our past it does influence us right! 'cause we would be living in the copy while
    at the same time we would be living in the original situation in which we never died.( it probably would be us but our consciousness would be present in the copy past)
    I don't think, I will be able to explain my question to you .

  • Lovro Markovič says:

    my way of solving it in two quik metheods
    1) don't kil your grandfather
    2) or just don't invent/use time travel in the first place

  • PieFaceTheAmazing / GDSuperScythe says:

    Same thing about saying it’s Opposite Day but bc it Opposite Day ur saying it’s not Opposite Day.

  • Bantham Nobilis says:

    WRONG! You're applying the paradox to quantum physics but the two have NOTHING to do with each other, and you ARE assuming there is a parallel Universe. When you ignore facts, any conclusion can be possible.

  • Interesting theory, however doesn't look complete as it doesn't explain the sobreposition of states past the point the subject travelled back in time, its kind of like the future line ceases to exist to turn into a loop of two overlapping states.

    Very much like the Polchinski’s Paradox, considering a billiard ball enters a wormhole, and emerges out the other end in the past just in time to collide with its younger version and stop it going into the wormhole in the first place. Considering that there would be a sobreposition of states, how would those converge on the n+1 moment after the time travel occurred?

  • I mean I figured if it happened to loop in your own timeline, time and space would resolve itself like that one creepy pasta story about a man whom in his childhood days befriended a genius prodigy who was very meticulous about things. They both hung out for one summer find things like skulls and what not then he suddenly disappeared. Years later the man gets a knock on his door (same house) and it was his friend all grown up who needed help with an experiment. Long story short the prodigy built a time machine and kept going back to the past to see if things changed meeting with his young prodigious meticulous, where he killed animals and placed thin into the past. The man followed his "friend" only to discover his twisted plot was to see what would happen if he killed the man in the past. Long long story short the man asks his old friend how he dies in the past but was puzzled because the younger evil genius was the one who killed him creating a weird loop killing the older evil genius which brings the man back in the same place (his house) in the presence with no memory of what took place but heard a knock at the door answering to one one there.

  • Electro Technoix says:

    How do you start a paradox I think where someone from the future comes to the past and save himself/herself so that he/she would exist in the future.

  • The boring copycat theory is the only plausible theory when dealing with the possibility of time travel. The other theories require you to be able to shift the entire universe back to a certain time, which is obviously utterly impossible withoit magic or a fuck ton of energy, which no device would ever be conceivable much less built and able to run properly

  • David Henderson says:

    Three years from now a game will be created…I won't tell you its name but…SPOILER ALERT…the little blonde girl has BROWN EYES!
    Deal with it!

  • Well going back in time and killing your grandfather will change the world line to a world where you are dead and you never created a time machine. But that doesn't mean the events of the original world line never happened.
    In fact, the world line has already been changed before to avoid world war 3 and the takeover of the world by CERN in 2036.

  • Porkchop's Papi says:

    You can't go back to a time before you existed because 1: that time no longer exists, & 2: since you weren't there the first time, there would be no physical place for you to fit in to since no two things can occupy the same space at the same time. I'm assuming thats still true.

  • Amina King Brown says:

    How do you know my grand pa wasn't a fertile 8 year old and didn't have any standards and had already ya know grandfathered my grandma

  • Oh and I got to know it's an NP problem ! Even more curious now ! Although I don't know much about it, but I did come across examples of NP problem in maths

  • Reverse of this :

    You go back in time, find your great grandmother, father your grandfather, and then kill yourself in the present…. Double loop ?

  • William Ray Preston says:

    This doesn’t fix the problem of the paradox, instead of closing your time loop you are essentially creating a new reality every time the loop circles around, because if you were to go back and kill your grandfather so that he never existed to create you, then this person was never your grandfather in the time loop, and you would circle around again to kill your own grandfather who was never the same person that you killed , because that person would never have existed, and in the same way you would not be the same person every time the loop would circle around, because your parents would be different parents since the man you killed could have never had your parents, this just complicates things further

  • Deathnotefan97 says:

    There is of course a third possibility

    Time is static and cannot be changed, so you physically cannot kill your grandfather no matter what you try

  • Lorenzo Santoro says:

    …and then the superstates can collide in one possible solution, that is where you don't kill your grandfather

  • Your understanding is as bad as the solution you said earlier in the video, Ur just literally saying “Theres no such thing as time travel” and thats just avoiding the paradox aswell

  • So l travel back time and killed my grandfather and I'm not born and I can't kill my grandfather so I'm born and travel back in time and killed my grandfather and I'm not born so I can't kill my grandfather so I'm born.

  • But, when you go back in time, you leave the present (thats a time where you exist) and in the past you kill your grandfather, you wont be born, and you will erase yourself from existence? Isnt that what you want to do when you kill your grandpa? You erase yourself, you cant get something for free unless you pay something back, so you either deal with yourself being erased from existence when you kill him or you dont kill him and live on

  • Mathu Van Vuuren says:

    Finally I found something similar to something I came up with some time ago, I was thinking about time travel and came up with something similar to the grandfather paradox (also I only just found out about the grandfather paradox being confirmed, because I thought I made it up but in a different theory) but as I tried to explain it to my friend he couldn't seem to understand what I was going on about, I do understand that its a bit confusing and we don't exactly learn these things in school so its understandable but I finally found a video explaining something that has to do with what I was looking for, and honestly it's pretty simple really.

  • Atley Guilbeau says:

    You genius, I've been trying to prove the causal loop theoretically correct for about a year now, thank you so much, I will include you in any other discoveries I might make related to this. Thank you again, I hope you have a great life

  • I have a hypothesis. What about quantum memory time stamps? Every electrical impulse from the mind leaves and imprint in space / time as our galaxy moves through the universe. Like a music record it leaves an imprint of all memories and can be accessed on a quantum level. You can acess other memories from the past by jumping from one memory to the next one as you go back in time due to the physical interactions of that individual with others. You could also use that data to bring people back to life with rapid growth cloning etc and implementation of these quantum memory time stamps. The memories would be stored in dark matter on a quantum level. You could also acess this and relive the memories virtually. Our brains seem to work on a quantum level so we should be able to acess those memories if the right frequency is accessed. Video is just for fun https://youtu.be/zyhbRhLTRTQ

  • EVERYTIME I THINK OF SOMETHING KNEW SOME SUPER GENIUS THINKS OF IT FIRST BEFORE I EVEN KNOW IT

    I didnt know endgame used it

    ok now to watch jojo

  • Halil Mencütekin says:

    Am i the only one who finds it annoying that people commenting about Avengers Endgame on every fucking video about time travel related concepts.

  • Heres a better quesrion. What did your grandfather do that's so bad you are okay with not existing just to kill him as a child

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