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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.

Comments (100)

  1. Endgame: Steals his theory

  2. There is a picture of 5 singers at 00:03. It disappears very quick.

  3. u may try to kill but…u will not be able to kill anyway….he would be saved any ways….so u will be born

  4. try to find a solution for bootstrap and predestination paradox.

  5. This video basically invokes a solution to the Grandfather paradox that implies that the laws of logic are false and then claims that the answer given is logically consistent and non-paradoxical. wtf

  6. avengers endgame certainly went for the alternate timeline creation. can someone needs to explain to me the outlander tv show time travel theory… is it the loop one?

  7. Whats with all the end Game CRAP???
    Fucking idiots kids

  8. 1 question tho

    Why would you kill your grandfather??

  9. I still don't get it

  10. Alternating time is boring. So what about consistent time loop?

  11. But wait is your traveling to the past actually you are doing your future u know, I mean think about this u have a time machine and then u go back in time well basically u are going back duh but what if going back is technically you are continuing going to your future, so if I kill my grandfather and u never born then time space will continue i think it won’t be like “so he didn’t born so he couldn’t kill his grandfather the nothing happened here, his grandfather is still alive” I think that it may happen could be that the time just continue with a new timeline where ur grandfather die and u never born. I think instead of doing a time paradox u will be doing timelines 1 when u never born and the original one where u travel back in time

  12. Electrons can do this. They are small. Wavelike, probabilistic superposition May not exist for anything larger than say a large Hadron. Or it might, but not to the degree that entire copies of worlds exist. Perhaps just copies of the small small , like electrons.

  13. Plot twist: His grandmother have 2 husbands.

  14. what if you or one of you'r paretns were adopted and it's not you'r biological grandfather

  15. okay let me just say one thing
    if we can go back in time and kill our Grandfather… Than it's Done He's Dead Something you didn't know called Dragon ball z they solved this years ago with Future Tranks Story
    IT always Creats a new universe. which Also makes the multi-Verse

  16. Btw why would you go back in time to kill someone? Aren’t you going to accidentally kill or destroy a part of yourself?

  17. did anyone else see that when he said one direction, a picture of one direction popped up ?

  18. I like Alternate Timeline theory

  19. I think there’s another solution. If time were made in such a way that no paradoxes could ever occur. For example, your grandfather always talks about how his mother died by an attempted murder, and you thought he was stupid because an attempted murder that killed someone succeeded and wasn’t just attempted. Finally, you couldn’t take it anymore and try to kill him in the past, but his mother jumps out and takes the bullet instead of him, and you realize it was an attempted murder that killed his mother, because it was you trying to kill your grandfather, but then the police show up and arrest you before you can fire again to kill him. Here, time travel manages to resolve itself as if it knew what you were going to do all along, which technically it did, since, well, it’s all of time. Future and Past.

  20. Had to slow the video down to 0.75 and watch twice ?

  21. I think That when you kill the grandfather You just bite the dust and the grandfather doesnt revive himself so you made completely new timeline where your family tree got chopped

  22. 0:03 keep pause ting then you well see something

  23. We can't travel back in time because past is past not a place

    Get it?

  24. Love you buddy….u r superb

  25. I killed my grandfather but my parents only disappeared, not me. Why?

  26. 0:03 the band one direction

  27. 1:09 lol, Tony Stark was trying to do that

  28. Damnit Barry, what’d you do this time

  29. My grandpa is cool but not my class teacher..So i can kill her right now?No paradox straight forward murder?

  30. I didn't get this one's, but I like this kind of videos

  31. But what if time travel is real, and some of the events that happened are caused by time travels trying to change the past, thus creating a new future ? What if we're living in a possibility of the infinite ones of the future?

  32. The comment section is just weird. Comparing and arguing with the fiction time travel theories of a fantasy movie with the fiction time travel theories of an animated show with the fictional time travel theories of a Netflix series. The worst part is that those people literally believe that they know everything about time travel just because they watched a tv show or an anime.

  33. Are you the writer of Dark?!

  34. Wonderfully explained and animations always help! For others… this is a classic, modern and well explained take on “schrodinger's cat” and quantum mechanics applied to time travel. I buy it…

  35. How would this quantum superposition of simulationiously being dead and alive look without knowledge of this concept?

  36. If your grandfather died due to you killing him after time travel to before you were born then it would most likely result in many timeline varations such as follows.

    Varations 1: An alternate time line is created in which you murdered your grandfather but you still exist in the same alternate time line.

    Varation 2: The same thing happens as Varation one, but you die due to your grandfather's death.

    Varation 3: The same thing happens as example one, but infinite versions of your future selves
    come back to murder your already murdered grandfather.

    Varation 4: A grandfather paradox is created.

    Varation 5: A grandfather paradox is created, but as a result infinite time lines of examples one through three are created.

    Varation 6: Your father was adopted.

    Varation 7: The future of the original timeline after the point of your time travel is deleted and the time line is " rerouted " to the alternate timeline.

    ( Continue to mix all varations above until every possible version is created. )

  37. I am still confused about the superposition part….
    Can anyone explain it to me???

  38. I thing you just born from somebody else

  39. I believe that if you time travel you create another reality. It’s like creating your clone. He’s like you but not YOU.

  40. Can we just talk about how in order to even get this paradox some kid had to murder his grandfather.

  41. Which Type of Software does He Use ??

  42. Stop giving me an existencial crisis

  43. If Person A went back in time to kill their grandfather, wouldn't you cease to exist and create a different timeline or alternate universe?

  44. What if your grandfather kills you?

  45. You discount the Many Worlds interpretation of quantum mechanics, then proceed to plead for a special version of it with only two worlds… invoking quantum superposition isn't an explanation here. Either the timeline has to be self-consistent, or its Many Worlds, or its a single mutable timeline where creating this sort of paradox is somehow allowed.

  46. google sponsored you?

  47. I used the grandfather to destroy the grandfather

  48. Or.. I could be smart and not kill my grandfather…

  49. Thats not right.
    When you go back in time and kill your grandfather, you will dissapear after you killed him. You will dissapear but your actions won't. So PARADOX SOLVED!!

  50. Isn't it right that only quantum object can be in a super postition?
    So I think that the solution is not 100% right.

  51. Okay, okay, I heard everything you just said , buuuut……. dumb it even more down

  52. What if you go back in time and frick your grandma?

  53. What kind of monster would kill their grandfather when he was a child?

  54. I prefer determinism which says that if you EVER go back in time you WON’T kill your grandfather because you ARE alive.
    Whatever you do, you won’t do that. Your very life is the consequence of those actions you (from your point of view) are going to make, but in the space-time continuum have already been made.

  55. but which grandfather?

  56. I believe free will dosent exist
    So u are physically unable to kill you grandfather
    you might be able to go back in time but you cant change the past

  57. So it’s Avengers: Endgame.

  58. If i could go back in time the first thing i would do is show myself how retarded people are in 2019 so that i could kill myself and dont have to see cringe and stupid people

  59. This is suicide is extra steps

  60. I do time travel AMA

  61. Me: watching this vid explaining paradoxes
    Also me knowing everything of time time travelling because of The Flash

  62. You just become your own grandfather like in Futurama

  63. 0:04 glitch *some (five) guys doing a band

  64. Very complicated to understand

  65. Wow,looks like Marvel saw this and made Endgame

  66. 0:04 one direction -_-

  67. There is something I found strange in such theories. Why humans are so essentials to space-time? When I see a problem like this one, I think this: space can’t be created if there is no time. An event in the pass cannot be influenced by an event that should qui be happening. If I go in the past killing my grandfather, I would not disappear because the events that leaded to my birth are not existing. By this theory, you can also say that destiny is a joke.

  68. Does that mean every action when you time travelling is meaningless? Because when you change something then the you whose future has been changed wont do any time travelling because there is no reason to

  69. I think that somehow you would fail to kill your grandfather, thus no paradox.

  70. Your Grandfather is Shrödinger's Cat.

  71. Just have sex with your grandma no biggie

  72. I have understand : The Paradox do no exist , because time travels are impossible

  73. If you killed your grandfather in the past you would instantly disappear then your grandmother would marry someone else and have kids and make new timeline

  74. I have two solutions.
    1. Back to the Future Solution: If you kill your grandfather, you simply fade out of existence. Just like 2015 Biff changed the past so that he gives his 1955 counterpart the Sports Almanac.
    2. Different time Solution: If you kill your grandfather, your grandmother will simply marry another man, producing an entirely different version of your parents, which, in turn, produces an entirely different version of you.

  75. I think you misunderstood why or how the grandfather theory exists. The point is not to kill your grandfather. it’s the fact that if you go back in time and change anything, due to the butterfly effect it results in you somehow not being born, you can’t go back in time to create that butterfly effect that caused it and whatever you do changes the outcome of the future. you’re also not exactly stuck in a time loop because you’ll never realise anything about it since only something greater will be able to record different time realities which if we are being realistic and hurts to say is fictional. I mean it starts getting annoying when ppl just rebrand and sell superposition instead of talking actual other sci fi shit that I could get high off and imagine about in my kid life

  76. My brain fell out whilst watching this

  77. "Ah, this f-ing guy…didn't I go back in time and kill you?" "Yes, but since I was dead, there was no longer a reason for you to go back in time and kill me, so I was no longer dead! Don't you know anything about time paradoxes?"

  78. You must go to the negative speed force. That place isn't affected by timeline changes…

    The Flash people out there

  79. 1:39 Schrödinger's grandfather

  80. Or in other words: even when you live, you're dead inside.

    Nuff said ;-:

  81. Then everything had already happened that means he does not make that decision because its already written.

  82. But what if you went into the future and killed yourself, would that then happen in your future?

  83. Another simple answer would be that another man married your grandmother. Thus you would still be born. But who you killed would no longer be your grandfather. However, you may be completely different appearance-wise. Maybe that man who is now your grandfather had a gene that managed to change and shape your family today. You could be different in ethnicity, gender, hair colour, etc. It's a weird thing to think about.

  84. Dragon Ball is one of the few stories that follow split time lines. I always felt split timelines made more sense and you avoid paradoxes that way.

  85. rick and morty in a nutshell

  86. Time travel DOES NOT EXIST. Dont know why peole are believing it does

  87. You were right about how you killing your grandfather you would just continue on living normally and that is true. Because otherwise lets say for the instance of the kid disappearing, that would imply that the future has an effect on the present. Which makes no sense. If future me were to kill my grandfather then I would already be nonexistent. Since future me has already murdered my grandfather and I am still here. Therefore time is linear. Boom

  88. wait, if you destroy dib in the past, then he won't ever be your enemy, then you won't have to send a robot back to destroy him, then he will be your enemy the you will have to send a robot back- *explodes*

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