Grandfather Paradox.
 

hello, this is my first post, and i was wondering what you guys thought of the Grandfather Paradox.

suppose you have a time machine, and you travel into the past to kill your grandfather before your father is conceived. that would make it so that you would never have been born, so if you were never born how would you be able to go back into the past to kill your grandfather?:confused:

Assuming time travel is in fact possible in a form that allowed you to kill your own grandfather,


I believe in the alternate universe theory, where the universe you had left in your time machine still exists and continues onwards but when you change something in your past it splits off an alternative universe based on that change you made, creating a world where you never existed.

I always have found this question interesting...the whole...time travel paradox.

Lets say you go back in time. You'll now be arriving in a place where everything has a set path toward its future. Definite fate perhaps. Either way everything you see is part of a path that has been traveled, if you interfere with that path the fate of those actions will change, therefore changing the future and so on down the line. I don't think I quite side with the idea of two universes from this point on because there would actually be at least 3 brought on by time travel:

The path that was going to be carried out from the past to the present to the future...without traveling through time.

The path that would be created by traveling through time, and coming back(to the future :orly: ) and moving onward through time.

The path that would be created by changing the past and altering that future.

So there are 3 at least. If you want to consider that there can be no matter created nor destroyed throughout the universe. (assumption of course, who knows some day) then we have to side with an idea that there were already these 3 universes around or else we will have created a problem with the physics.

Furthermore, if there are these 3(or even millions) of undisturbed universes/dimensions we then would have altered the course of these dimensions creating at least two futures for these "undisturbed" dimensions....and so on....so it would seem more likely that traveling in time and changing something can only result in one path toward the future...right?

well, the whole idea of traveling back and changing your own future would get knocked into the can because if we are to assume that the separate dimensional paths theory is false due to conservation of energy/matter throughout the universe we must say that traveling back in time is impossible because we would be adding to a closed system (past)

however, if we could alter the past remotely somehow to create a place where we could subtract one object (say, a tree) and insert another object (person)....we could stay in tune with the physics if the premise of conservation is correct....

then we'd just have a problem with altering the future....so yeah...anyway you slice it....you'll be left with a pickle....

footnotes: time travel should'nt be possible due to conservation of matter (IMO) because the past has no space for addition (matter/energy), and creating multiply dimensions can't happen cus of this either..

Time streams. You go back in time and kill your grandfather and all you've done is create a reality where your grandfather was killed. You still exist because you're in the stream where your grandfather wasn't killed. The thing is, unless your magic time machine can move to different streams, you're stuck in your new stream where you don't exist and you exist as a paradox. Your living grandfather exists in another stream altogether, so in the reality you're stuck in, you have no grandfather and thus lineage.

Unless, of course, you had sex with your grandmother and so became your own grandfather.

If by chance such a thing as this were possible, one theory is that you would become part of a different universe upon killing your grandfather, and no longer exist in this one.

My reading of the Grandfather Clause is that it suggests the impossibility of time travel. I think immortality is the closest one could possibly get to conquering time. We may be able to bend time's effects (think of freezing), but I can't get my mind around actually stepping into another time "dimension" or sending faster-than-light messages that get replies before they are sent.

I am a firm believer in causality within a universe (as opposed to multiple streams in a multiverse). You cannot break the logic of causality. So, this means that it would be impossible to step into a time before you were born. How could you be there if the conditions of your current existence haven't yet been met?

If an grown man came up to me today and told me that he was my grandson (I'm 31 years old), what would happen to him if I were to make a vow of chastity right on the spot? Would he disappear? And before you say, "Well, he's already there, so the fate of your vow must be that it was broken," what about his being there in the first place? Doesn't it suggest that one is capable of changing fate through one's actions? This doesn't work. It's just silly.

Go read The Man who Folded Himself by David Gerrold. It's required reading for this discussion. It's seminal time-travel paradox sci-fi, and BRILLIANTLY executed.

You're a creation of a past in which you didn't go back and kill your grandfather.

Think of time as an infinitely criss-crossing net of probabilities. Each probability is a thread of time that leads to a juncture where another network of probabilities can be chosen; a completely decentralized system whose framework will just be re-routed in the event that one of its probabilities is tampered with. The path from A to B is never only a straight line.

Okay, what about this:

What if you travelled back in time to before your father was conceived, and took your grandparents back with you to the present? Would you one day be able to witness your own birth?

Nope....Mom would be long dead by the time Dad got horny

You can't have paradox.

A new reality is formed as soon as you appear in the past. You might be able to return to your reality but you cannot visit your own past without creating a paradox and since there cannot be a paradox, you must then be in an alternative reality.

As someone who loves a good time travel story (note my avatar and my signature :) ) if classic time travel is indeed possible, then it depends on the rules of the game.

In Connie Willis' book To Say Nothing Of The Dog, the catch is that the Universe just doesn't allow paradoxes. If you tried to go back and kill an ancestor, you wouldn't be able to accomplish it. Despite your best efforts, you might miss your shot, chicken out, "land" too far away or at the wrong time to get the job done etc, etc... All of your actions would result in the same old present. The movie 12 Monkeys goes the same route.

In multiple universe stories, such as The Man Who Folded Himself you can't ever go back to your original timeline so the Grandfather you kill is a different man in many ways. So are you.

I believe this is the greatest hurdle to the notion of classic time travel. It's fun to think of the big paradoxes, but the mere existence of your molecules occupying the area where other molecules are is a paradox in itself. Perhaps this is allowed on the quantum level, but it suggests to me that the Grandfather paradox is Moot.

My favourite story: The Light of Other Days by Arthur C. Clarke and Stephen Baxter has a nifty way around this, but still doesn't allow for paradoxes.

Let's mix it up a bit:

Go back in time and kill yourself.

It can't be done. I am firmly with Baraka_Guru and fresnelly on this one.

I wanna go back in time and prevent myself from making choices by... uh... displacing... other people.

Who doesn't love Futurama?

While I am a firm advocate of multiple history theory since it makes for good fiction (and I've always imagined the world to work like this), we do not know the rules of the game. If it were to work, I imagine the quantum mechanics will hold true as it allows for branching histories. Some theories of QM theories for interference are based off of multiple 'verses' interacting. Interference readily occurs to light waves but it has been shown to affect particles with mass as well. Electrons shot through a double slit cause interference patterns, and even particles as large as protons and even helium ions will create interference patterns when shot through the double-slit.

I think the main rule about time travel is: don't be a prick and ruin it for the rest of us. Like David Tennant as the Doctor said, "Time travel is used strictly for observational purposes, and cheap tricks."

Hmm I think you can't go back in time. If you could get far away enough from the earth (travelling faster than speed of light, which raises a whole other bunch of questions, but anyhow) and look back, you could <i>see</i> events from the past, but you couldn't possibly alter them because they've already happened.

Assuming you can travel backwards in time, there are three ways you can view temporality. Either (a) time is predicated through causality, call this the fatalist perspective, (b) time is linear and now is the focal point of the temporal dimension, call this the linear perspective, or (c) time is non-linear and subjective to the perceiver, call this the non-linear perseptive.

Under the fatalist perspective the grandfather paradox is simply not possible. Even if you travelled back in time to kill your grandfather you simply could not do it. If you killed anyone they could not be your grandfather. Because the universe is purely causal, the entire course of history was set an conception and has headed down a predictable path based on the laws of science. Essentially, your time travel is part of the plan and anything you do in the past was done in your present rather you were aware of the design or not. This is like the Futurama scenario where they WERE the aliens at Roswell, always were, and they were thus a part of their own history and their time travel was predetermined.

Under the linear perspective, you have more of a Back To The Future style scenario. Under this point of view you could kill your grandfather and the results could vary. Either you could create a paradox and time would perpetually loop with you killing your grandfather, then not existing to kill him and thus existing, and so on, or you might go on existing nonetheless in some sort of temporal fail-safe because contradictions such as this simply cannot occur in nature rather we can comprehend the fail-safe or not.

The non-linear perspective is the one I subscribe to. The fatalist POV just leaves a bad taste in my mouth as someone who both believes in some form of free will and someone who is not absolutely convinced by a causal explanation to the universe simply because its easy, observable, and traditional. I also have a problem with the linear perspective because it just seems terribly egocentric. Just because I am solely familiar with my unique consciousness and perspective does not mean that I am the exclusive consciousness and persepctive. Thus the now I am experiencing is not the only now. Your now is an equally valid now, but so is the now of the atomic clock travelling at supersonic speeds that arrives with an earlier time as an identical atomic clock waiting for the jet to circle the globe. Consequently, were I to travel back in time, everyone experiencing that now (my grandfather and everyone else at that meeting in time) is also experiencing now. They are not in the past nor am I. We are all sharing a now, or our present. Under this view I could kill my grandfather without temporal reprecussion because I did not kill him in the "past", I killed him in the "present". Essentially, this view would hold that, though we perceive time as one moment after the next, all time is really existing in the now and is all happening at once. There would be no causal implication to dicking with the past because there is no causation it all just happens/happened/is happening. We simply just can't perceive time in this manner so we are perceive it linearly.

Anyway, I think this exhausts the possibilities. Luckily in only one potential result from one possible reality does a paradox occur and lead to problems for the universe. So purely statistically, odds are we are gonna be alright.

Time travel is a facinating idea, however one that I don't believe is likely possible.

Time itself is simply a concept created by humans in order to think about the past and the future alike, however as far as I know we only live in the present.

Although I agree with what you are getting at here, I don't believe that time is simply a human concept. I think it is rather a measurement. As with all mathematics, we do not create them, we discover them.

I agree with you, you simply sort of expanded or more correctly explained the thought I was trying to convey.