24 Answers

  1. The murdered grandfather paradox was coined in 1943 by Rene Barzhavel, a French science fiction writer.�

    Its essence lies in the fact that a person uses a time machine to go back in time, where he meets his biological grandfather and kills him so that he does not meet the biological grandmother of this person. It turns out that in connection with the murder of his grandfather, this person is not born, but in fact he continues to exist. It is believed that in the end, the killer would not have been able to travel through time. This meant that his grandfather would still be alive, and the killer himself would be born. His birth gave him the ability to travel through time and kill. It turns out a vicious circle.

    This paradox is a statement to the fact that a person can not travel in time. In any case, in the past for sure. To go back in time and implement your idea, you can add the following conditions to the task::

    • You can't change the past. My grandfather will survive the assassination attempt.
    • The future can't be changed either. A killer will be born.
    • An alternate reality is created, a parallel universe where the killer is not born.
      This video contains footage from the cult movie Back to the future:



  2. The paradox of the murdered grandfather – like any similar paradox is impossible.

    But the meaning of the paradox is simple – if you kill your grandfather, if he did not conceive you, then you will not be born.

    If you kill your grandfather when your grandmother is already pregnant, nothing will change.

    A paradox is impossible due to a violation of the principle of causal relationships.

    If you kill your grandfather/father/If you have lost your grandmother/mother/ancestor, you will not be able to be born, which means you will never be able to go back in time and kill the ancestor. If you are not born, you will never want to kill your ancestor. Thus, the very desire to fulfill the paradox will never lead to the fulfillment of the paradox.

    The funny thing is, you can never even ask someone to kill your ancestor for the same reasons.

  3. The “Murdered Grandfather” Paradox is a Time Paradox, an inconsistency.

    You go back in time and kill your grandfather before you were born. You can't be born that way.

    Question: What happens if?

    Answer: nothing.

    It is based on the indisputable fact that you live in the Present, and whatever you do in the Past, you cannot change the Present, because the consequences of the Present are already felt by you.

    In short: if you killed your Grandfather , you would no longer exist and there would be no one to kill your Grandfather.

    Grandfather is alive and you were born. And so on ad infinitum.

  4. Time travel is one of the most intriguing science fiction concepts. But it raises many questions — both for physicists and philosophers-and can also lead to various paradoxes. “The paradox of the murdered grandfather” is one of them.
    The concept of time travel is widely used in literature and cinema, regardless of genre. Often at the center of all such stories are the changes made by the traveler in the events of the past, which lead to real disasters in the future.

    It is worth remembering at least the story of Ray Bradbury “And the thunder broke”.
    This dilemma, also known as the “murdered grandfather paradox,” represents the main objection of physicists and philosophers to time travel: the possible violation of causality. And while time travel is still just speculation, the likely results of violating the principle of causality and how nature can prevent them are hotly debated among scientists like Stephen Hawking and Kip Thorne.
    What is the “murdered grandfather paradox”?
    The “Murdered Grandfather Paradox” is a hypothetical situation in which a time traveler travels back in time and does something that results in the fact that he never existed (usually the accidental death of the traveler's grandfather is considered), or an event that makes his journey impossible. The paradox is due to the fact that this person was never born. And since he was never there, how could he go back in time and kill Grandpa? Thus, the very idea of time travel leads to a possible violation of causality — the rule that states that the effect is always preceded by the cause.
    What is the “murdered grandfather paradox”?
    Let's imagine a scenario in which a young talented inventor — let's call him Eugene — creates a time machine in 2018. Since Eugene never knew his grandfather, he decides to travel back in time to meet him. After a thorough investigation, he discovers exactly where his grandfather — still young and single — was at 3:43 p.m. on November 22, 1960. He gets into the time machine and begins his journey.
    Unfortunately, Zhenya takes everything literally, and when he found out where his grandfather would be, he went to exactly the right place. He “lands” right where his grandfather should be at that moment… with a very predictable result. After running a quick DNA test, he realizes that it really was his father's father, gets back in the car and waits for his disappearance.
    What to do next
    Physicists and philosophers have proposed several solutions to the paradox. Novikov's principle of self-consistency, developed in the 1970s by the Russian physicist Igor Dmitrievich Novikov (“The Evolution of the Universe”, 1979), suggests the use of geodesic lines to describe the curvature of time (something like the curvature of space is described in Einstein's General Theory of Relativity). These closed, time-like curves will not allow you to break any causal relationships that are on the same curve. The principle also assumes that time travel will only be possible in areas where these closed curves are present — for example, in the presence of wormholes, as described by Kip Thorne and colleagues in the 1988 paper “Wormholes, Time Machines, and the Weak Energy Condition”. In this case, events would be cyclical and self-consistent. This, in turn, implies that time travelers would not have been able to change the past — whether through some physical barrier or lack of opportunity to make such a choice. So no matter how hard Evgeny tried, he would not have been able to land his car on that very spot, even if he had suddenly determined to kill his grandfather.
    This idea was later expanded upon by Caltech students Fernando Escheverria and Gunnar Klinhammer, along with Kip Thorne. In their paper, they presented a billiard ball thrown into the past through a wormhole along a trajectory that would eventually prevent it from falling into it. They argued that the physical properties of the wormhole would change the trajectory of the ball in such a way that it would not be able to interfere with itself, or that the ball could not get into the wormhole due to actual interference from outside.
    Thus, if you follow Novikov's theory, any actions taken by a time traveler become a fait accompli, and observers of these events are not allowed to see the Cauchy horizon.
    Upon returning to 2018, our Eugene discovers that his family's home has disappeared, as well as other traces of his existence. After reading about Novikov's theory and the billiard balls of Caltech scientists, he curses the universe for doing nothing. And at this point, he realizes that maybe the universe did not intervene, because this required some corrective action. He runs back to the time machine to change his own actions and save his future.

    Novikov's solution may look somewhat far-fetched, since it definitely requires a lot of mechanisms that are still unknown to physics. It is for this reason that this solution to the “murdered grandfather paradox” is rejected by the scientific community.
    Can there be a more economical solution to the paradox, based on already existing aspects of physics introduced by other theories? It turns out that such a hypothesis as the multi-world interpretation of quantum mechanics can provide it.
    A multi-world interpretation of quantum mechanics is coming to the rescue!
    A multi-world interpretation of quantum mechanics was proposed by Hugh Everett III in the 1950s as a solution to the wave function collapse problem observed in the famous Jung double-slit experiment.
    As the electron passes through the slit, it can be described by a wave function with a finite probability of passing through either slit # 1 or slit # 2. When the electron appears on the screen, it looks smeared like a wave. And in other cases, it manifests itself as a particle. This is called wave function collapse. In other words, the wave seems to disappear, and a particle remains in its place. This, in turn, is a key factor in the Copenhagen interpretation of quantum mechanics. But scientists didn't understand why the wave function collapsed.
    Everett asked another question: does the wave function collapse at all?
    He presented a situation in which the wave function continues to grow exponentially without collapsing. As a result, the entire universe takes on one of two possible states: the “world” in which the particle passed through slot # 1, and the “world” in which the particle passed through slot # 2. Everett argued that the same” division ” of states occurs in all quantum events, the multiple outcomes of which exist in different worlds in a state of superposition. The wave function looks like it's collapsing to us, because we live in one of these worlds that can't interact with each other.

    Consequently, when Eugene arrives in 1960, the universe is divided. He is no longer in the same world as he came from (let it be World # 1). Instead, he created and occupied a new world. When he travels to the future, he moves along with the timeline of this world. He never existed in it and, in fact, never killed his grandfather. His grandfather continues to exist in good health in the World No. 1.
    Let's summarize
    Of course, none of the proposed solutions and hypotheses make time travel a reality. Einstein's special theory of relativity and limitations on the speed of an object with mass pose serious obstacles to this. Nevertheless, they provide interesting solutions to the puzzle. Ironically, the most plausible solution to the” murdered grandfather paradox ” comes from a single physical hypothesis, which has generated even more fantastic stories than many other ideas and hypotheses expressed by scientists over the past century.
    Curiously, a multi-world interpretation can also answer another time-travel puzzle. If such technology ever becomes anything more than fiction, where are all the time travelers? Why haven't they come to us yet to tell us about their discovery?
    The likely answer is that we live in a primordial world in which time machines are destined to be created. And inventors and their fellow travelers simply fall into other worlds, which they themselves create. If this is true, then the invention of the time machine will lead our world to the fact that many physicists and inventors will disappear from it.

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  6. In my grandmother's office. Well, he killed his grandfather, but his father was still born. Why? And my grandmother made a mess of it. It was necessary for the purity of the experiment to kill not the grandfather, but the grandmother. Since the grandfather might not have had anything to do with the birth of the child:).

  7. It just seems like a paradox. It's very simple. You find yourself in the past not as a person, but as a phantom (ghost) and you can't do anything in it by definition. You are only an observer. Now for the future. You find yourself in a future where you no longer exist. You're dead. Thus, you are again a phantom (ghost) and again only an observer. That is, you can only exist materially in the present. But there is another paradox. You can gain knowledge from the past and future. For example, from dreams. Having been in a dream in the past, you can, for example, solve a crime. And after visiting the future, you can learn, for example, the secret of obtaining energy from a vacuum. It's real. After all, many inventions and discoveries were made in a dream. We need to work in this direction. They may have already beaten us to it.

  8. Dear panelists, It is really IMPOSSIBLE to move into the past in any way and it is IMPOSSIBLE to change anything there! Science admits in principle only one type of “time machine”: if you suddenly start flying at the speed of light, time on your ship will slow down, and when you return to Earth, more years will pass here than on your ship. That is, you will sort of get into the future. At the same time, there is no turning back! Everything else is unscientific fiction.

  9. It's very simple. Your arrival in the past already changes the future. You can kill anyone you want. Edit events. You won't be in any danger. You are a biological organism. Physically, you exist. But you will not be able to “return” to the future. I mean the one you came from. You are already in the future of the timeline in which you now physically exist. You may not be in this timeline. Or maybe there is another you in it. You physically exist outside of time.

  10. everything is simple..there are several realities.one is active .. the others.only possible ones.. going into the past, you automatically turn off the reality that was and turn on one of the possible ones..

  11. I don't understand why you should touch my grandfather. Suppose you go to the safe where you have a gun. You take it and go back in time. In the early morning of the day when you decided to go to the safe. And you kill yourself in bed. Voila paradox. If you killed yourself in the past, who will take the gun out of the safe in the future? And don't touch Grandpa. Have a conscience.

  12. After passing the bridge, you found that it collapsed. But you really need to go back! There are no opportunities to cross!
    You will stay here forever!
    Exit: use the same time machine to return to the moment when you came up with the idea to make the transition and cancel it, otherwise, further travel will be impossible.

  13. And how do you like this option: you go back in time, but you CAN'T kill your grandfather, even if you are a super-killer. Circumstances interfere. In then you go home, pick up old newspapers and find an article about how some crazy person tried to kill a child (your grandfather) but it didn't work out.

  14. I'll try to explain you are and exist, go to the past and kill your grandfather you are and exist again do not disappear, go back to the future you are and exist, but for the rest and for all of you there is no story went differently, for you you were born and your father was born, but for all the others you are not there are no documents for you, although you may have documents with you, you are not in the system, you are an alien, a wanderer, you are from the future or past, no one remembers you and does not know where for everyone else you were not.

  15. Addition to the previous post, the story will be rewritten, there will be changes related to the death of the grandfather, but people are like individuals with their own memory, in the memory of people you will be like, alternative memory, contradicting reality, although everything will indicate that you are not, you will be regardless of whether the grandfather died or not, because you were born and from that moment your story began, regardless, your story exists as long as you exist.

  16. “Travel to the past” is the creation of a spatial matrix model with the motion vector rolled back

    An observer placed in such a matrix will have no connection with the matrix where its original carrier exists. Physically, it is synchronized with the body, which is a clone of it, modeled in this matrix. Therefore, he can kill his grandfather and no paradox will arise.

    If you leave this matrix in motion and make an observation at a point parallel to the point of disconnection from the original carrier, the observer will see an alternative reality, which is a development of the reality where the conditional grandfather of the observer was killed.

  17. I'll try to explain you are and exist, go to the past and kill your grandfather you are and exist again do not disappear, go back to the future you are and exist, but for the rest and for all of you there is no story went differently, for you you were born and your father was born, but for all the others you are not there are no documents for you, although you may have documents with you, you are not in the system, you are an alien, a wanderer, you are from the future or past, no one remembers you and does not know where for everyone else you were not.

  18. And what's paradoxical about that? Well, you get into the past, you kill your grandfather, but this is the present for you, and what does it matter to you that your grandfather will not give birth to anyone? Agree that you don't care at that time, because you are still alive, and the one who should appear is also not in sight. After all, who said that your past is true and that you are really this grandfather's grandson? Therefore, nothing will happen to you.

  19. The paradox of the murdered grandfather (sometimes-the paradox of the murdered father) – if they go back in time and kill their grandfather (father), then he will not give birth to a son who will not go back in time and kill him, but if he is not killed, then he will give birth to a son who will kill him, but then he will not be able to give birth to a son… Etc.

    However, in a more correct theory, there will be no looping, only one more time line will appear, where there is a son, and his grandfather (father) does not exist. Since the son appeared from the father in another time line, where he is alive, then he will not die, too, and there will be no paradox.

  20. If they come up with a trip to the past or some kind of analogue of the “time machine”, then this will confirm the theory that our world is a virtual reality of some higher intelligence, which is exactly what all the religions of the world say.

    And the so-called “time travel” will be a kind of hack of this virtuality, but with one condition, the observer will remain only an observer and everything will be like a ghost.

    That's the answer, an alien in time can only observe events and all he is deprived of the ability to influence the past, especially to kill someone. You can't kill your grandfather, and that's all there is to it…

  21. If you kill grandpa the killer won't be born, the killer won't be born grandpa won't die, grandpa won't die the killer will be born, the killer will be born grandpa will die. This is a paradox because the logic of not only our consciousness but also our third and fourth dimensions will be broken and perhaps the universe will collapse. The fact that we exist means that this will never happen.

  22. There's no way you can go back to your own past. You will return to someone else's past and it will not be your grandfather. You can safely take him down – nothing will happen to you.

  23. For example, a person (let's call him Kolya) goes back in time and kills his grandfather. As a result, Kolya's parents will not be born, and therefore Kolya will not be born either. So he won't go back in time and kill his grandfather. In the end his grandfather will be alive his parents will be born and he will also be born and go back in time and kill his grandfather. And so on ad infinitum.

  24. get in the time machine-go back 50 years-finish off your grandfather at the age of 10-one of your parents is not born – you are not there – no one goes to the past – your grandfather is alive – you are born-go back 50 years, where your grandfather is persistently finished off… and so on endlessly. what a maniac you are! not tired of it? I feel sorry for my grandfather… and the conclusion is that time travel is not possible. it's all nonsense.

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