If I were to go back in time before I was even conceived, and killed both my parents, what would happen? Would I immediately cease to exist? But if I killed my parents before I was born, thus never existed, how could I ever go back and kill them in the first place? Would the universe explode into a giant question mark.
This is not a general question.
It depends on whether you want a deterministic or non-deterministic Universe.
If you want a non-deterministc Universe, that is, the entire history of the Universe is not predetermined, you get the annoying paradox you just mentioned.
If you want a deterministic Universe, you would find it quite impossible to kill your parents before you were born, because of the fact that you exist.
Now, if you want the real answer, I’m afraid you’ll have to invent a time machine.
I did!
But I’m afraid to use it!
There’s also the multi-worlds theory which would have you continuing to exist, but your parents still get killed.
You would then never be born in that timeline, but it doesn’t matter, because you were born to a different timeline, in which your parents weren’t killed.
I happen to like this one, because it makes the whole question of determinism moot, and it avoids paradoxes as well.
If you’re going to insist on a single-timeline universe, then I’d have to go with the deterministic interpretation, to avoid logical paradoxes such as that. Other paradoxes are still allowed though.
Consider a time traveler brings some valuable bit of information from the future and tells someone in the past. The person in the past is then credited with the discovery of the information. Then years later, a time traveler decides to go back and give the discoverer the information. Where did the information originate?
I know all of the physical laws lined up against time travel, all the reasons it can’t be done, but I still want to weigh in here.
I recently read the novel “The Man Who Folded Himself”, a very interesting time travel novel, and it has some interesting concepts. Without giving away the story (which I never would anyway), it describes time as a series of discrete ‘moments’ we only perceive as a timeline. We can move among those moments, according to the book, usually in one direction only, but with the time machine the protagonist can jump around at will.
But in this fictional universe you have to watch how you’ve changed things, because when you go to your own time you jump to the moment that would follow from your changes. For example, if you killed Hitler as a baby, you would jump back to a moment where Hitler was never a Nazi and the world you created would be very different from the world you left. You’d have to go back and convince yourself not to kill Hitler to change your universe back to normal. Of course, then would have split yourself into at least two versions: One who did go back to tell himself not to kill Hitler and one who did not.
As you can see, time traveling in this fictional universe shows you that there are an infinite number of possible ‘yous’ you might meet in your journeys through time, like there are an infinite number of possible moments you could visit.
So you could kill your parents, and come back to a moment where you never existed. No paradoxes, plenty of messes.
I believe time travel may be one day possible, but I adamantly believe that you cannot change what has happened. To travel into the past you would need to travel to a point where you had already been (to a period of history that you have already encountered), if you can travel to this point, how could (or why would) you change anything? You don’t have the knowledge of the future, it hasn’t come yet. If someone did invent a time machine and used it, they would only be doomed to a never-ending paradox where they would constantly repeat the period of history to which he travelled to.
Even if one COULD avoid this, how would they travel back into time? ie. Would they be in their old body? If so, would the information in their brain magically change to accomodate for the “enlightened” self entering it? Would there be duplicate bodies? Where would this duplicate come from (ie. the matter)?
Even avoiding all this, in Stephen Hawking’s book, A Brief History of Time, he makes reference to why nobody has given the Nazi’s the information to make an atom bomb - why would the time traveller want to do this? (or to kill Hitler, same thing) Such a big impact on the course of history would result in them never having been born (the original paradox of the OP - but we are avoiding all the above for the sake of an example). If we can someday evade all the laws of physics and basic logic, why would one risk all the information attained?
I don’t believe in a multi-worlds theory either (ex. “Sliders”), no, I don’t have any evidence other than there is also no evidence supporting it. It sounds more of a way for science-fiction writers to make money.
I belive the current theory holds that you could kill your parents but you wouldn’t because you didn’t.
Actually, Ian Fan, the multi-worlds interpretation is one of the leading interpretations of quantum physics. To say that there is “no evidence supporting it” is kind of misleading.
Why do you wanna Kill your parents anyway?
I’m just curious, but what kind of evidence is there?
If Time Travel ever gets invented some time in the future, why hasn’t anyone time travelled back to this year to sell us the blueprints of how to travel through time?
A good workaround to this paradox is explained in Michael Crichton’s book ‘Timeline’.
Essentially is says that the chances of anyone actually changing the course of the future by some action in the past, is minimal. That is, history has a “momentum” that makes it very difficult to affect the future. IIRC (it’s been a while since I read the book, and I don’t have it handy at the moment) even if you were able to travel back in time, it would still be difficult to find an opportunity to make a significant, history altering, change.
For example: You travel back to kill Hitler before he has a chance to gain political power and contol of Germany. Even assuming you were able to find him, you still need to be able to get access to him, past bodyguards etc. The chances of one person being able to acheive this are pretty minimal.
Slight hijack, but Crichton didn’t originate the idea in question- Fritz Lieber did. He wrote a whole series of short stories centered on the theme that “reality” is just the current state of a war between two factions, both of whom have perfected time travel, and both of whom used it precisely to change events throughout the timeline in whatever way would most disadvantage the other side. It’s good stuff.
Anyways, one of the things he postulates is called the Law of Conservation of Reality. Essentially, he says that the universe has a way that it “wants” to go, so if you change things slightly, the new direction of reality will be very, very, close to the way it was before. Try to prevent JFK’s assassination, for example, and he may just die in a car crash on the other side of Dealy Plaza. Of course, this particular worldview requires accepting a form of determinism, but it’s still fine for speculation.
Hijack aside, I’m fairly well convinced that time travel to the past is pretty well ruled out by various arguments from entropy. No need for discussions of paradox, since the paradox can’t happen.
Because when they found out I had a time machine they grounded me.:rolleyes:
It was just a question 'Noctum. Just a question.
After all, going back in time and killing my uncle wouldn’t create the same paradox now, would it?
(unless it turned out Unca was actually my dad.:eek: )
It would create an even more interesting paradox if he was actually your mother.
Time travel is always an iffy thing. I prefer the many-worlds theory, eliminating paradoxes. But that whole ‘the universe does what it wants, regardless of what you do’ theory is intriguing as well.
Ian Fan, continuing this hijack:
There is no evidence that supports the “many-worlds” or “no-collapse” interpretation of quantum mechanics over the more standard “Copenhagen” interpretation. The two interpretations make identical predictions about what the observed outcome of any experiment will be, and thus there can be no scientific way to determine which is “true.” It is for that reason that these are normally known as “interpretations” rather than “theories” of quantum mechanics. I believe that the many-worlds interpretation is conceptually much simpler, and should therefore be favored through an application of Occam’s razor, but others disagree.
Sorry to be so narrowminded, but you wouldn’t be able to kill your parents pre-birth because backwards time-travel is so impossible.
I also find it rather amusing that many of you are referencing sci-fi novels. Not enough sci, a little too much fi. Go read some Einstein, Hawking, Minkowski, and Fewning, and get back to me.