Time Travel

[Bynary Fission]

Alright, I came up with this thought spontaneously while getting a shower, and I had to discuss it further. This is solely an opinion, so please don't take it as me proclaiming it as fact.

People say that time travel, if ever possible, will be strictly in the past, because the future hasn't happened. Many believe that time travel will be possible, given the exploitation and harnessing of quantum physics. But, after what I thought, it hasn't happened and never will happen. Lets say that by 2040 we invented a time machine that is capable of transporting a person across the time-space continuum somehow, someway. After a few years of clearances and debate, it was cleared for use, and a few technologically advanced individuals (referring to the equipment they carried) went back 100 years to try and stop the Holocaust. Wouldn't they have done it already? Ahh, but that presents a paradox. How can you go back in time, when in 1940 technically you would have come from the future, which hasn't happened at that time? I will go in-depth on this.

Lets say you went back to the year 1900. You entered through some way, perhaps a wormhole created by manipulating quantum foam at the Planck length (Given we had instruments that precise), or the disassembling of you at the molecular level and reappearing at a different place in the space-time continuum. Then, once you enter, somebody will probably notice you. That's an issue, isn't it? But lets say you weren't stupid enough to transport to a public facility. Then, what happens? You just came from the future, but the future hasn't supposedly happened yet. Then how did you come to the era you did? Mind boggling isn't it. Perhaps it is akin to the dream paradox.

Many people have dreams that supposedly predict something in the future or remember something in the past that you never experienced. The future predictions seem to come true many times. They say that when we are awake, we are on a vertical position on the time-space continuum. We cannot teleport, nor can we jump back and forth in time. We are always in the present, never in the past or future. We are static. But when you dream, we are said to switch from being vertical to being horizontal. We can teleport. We can jump to any time we want. If we want to defy physics, go ahead. If you want to create a world out of nothing, do it. You can literally do everything in a dream. So why do we say we are limited to one side of the time-space continuum?

To address my original statement, if we had invented a time machine, we'd already have people coming from the future to us. If we went back to 1900, then we came from the future. But if it isn't written, then why did we come from the "unwritten future"? It's already been written, at least in my opinion. You can made decisions, yes. But maybe you are destined to make that decision. After all, if somebody made a time machine, they'd already be here. Since we came from the future when they teleported back, so would they. So, maybe we live on one part of the infinite time-space continuum. We only see a small part of it, and the body we are born in is the universe's, or even God's way (Depending on how you see him; I don't see him as some big guy in Heaven but I do believe in God, just not in a theological sense) of just showing you the time that we're in, and you play out the person you were assigned to be. Humans can affect the world around them, but we can't affect that which is beyond that, such as time. Time dilation does not count (That acts on physics). If an infinite amount of time exists ahead of us, why did nobody come back to the past and try and change something, such as killing Hitler to try and stop the Holocaust. Because one was never invented. There are many proposed reasons why I believe that time machines will never be invented.

Even if you have good intentions, you will screw things up irreparably. Ever read the Sound of Thunder by Ray Bradbury? While other butterflies would take it's place, it makes a good point. If you do something in the past, it will exponentially increase over time. If you kill a man from 5000 BC, then the possibly billions of people who would come from him would never be born. Say the wife of that person married. Then the effect wouldn't be as bad. But say she didn't. Uh oh. You just screwed mankind for all eternity. Nice going. Another reason is that there are many corrupt, morally depraved people on Earth. Those who appear nice, like suck-ups and sycophants, are not who they appear to be. If they ever got such a privilege to use a time machine, woops. With his ultra-advanced technology, he could overthrow a government with it, especially if he has nanomachines (Maybe a killer version of gray goo ). And third. If time tourism becomes common, then the effects that they would have would be unimaginable. Mass tourism in any given area damages the flora and fauna. Extended amounts of time with this or ultra-heavy tourism would not only eradicate the beauty that brought people to the spot, but it would bring in.....mega corporations. Then you're in serious trouble. If you build something in the past, especially in large quantities, then jesus, who knows what that could do. And besides, who wants a McDonalds in 1850? Bleh. Four, ethical reasons. Hopefully man won't become like China, who has no respect for the environment or human life and exists under a brutal dictatorship without morals.

There was a man named Andrew who said he traveled from the year 2246 to make a fortune off the stock market with his future knowledge of it's trends. To be exact, he made a jaw-dropping 350 MILLION dollars in two weeks. He was investigated, where he made his case. No records of him were found before he appeared. If a man so selfish as to travel back in time, jeopardizing the time-space continuum for his personal wealth at the expense of others (Think of the people who potentially lost millions in investments become some cheat took their money by having a massive unfair advantage over them with his superior knowledge that should never have been there), then I fear the future. If cons like him would be allowed to do such a thing, then who knows what a dystopian future like that would hold. I'm not saying it is, but if people like him are allowed to go back in time for personal gain, then it must be. Maybe mankind is gone before one is invented.

To wrap up my post, I believe that everything happens for a reason. Time is set. It has to happen. But if you tamper with that and go back in time, you change the universe, possibly for the worse. Think of it this way. Lets say a critical line of code in a massive billion-dollar computer was not written right, and a typo was made. Just one typo. An insignificant bundle of pixels made up of 0s and 1s. That could cause a massive systemic failure. Then everything that depends on it shuts down. Then you've got an emergency, especially if it involves the government. Think of that person as the typo. You affect EVERYTHING that goes after it or depends on it. Should we become a Type III civilization, we would have the power to affect the universe itself. Time is not meant to be changed. But if you do...well, the universe if affected with it. Maybe very, ever so slightly, even infinitesimally, but affected nonetheless. If I am wrong, and a time machine is invented...lets just hope that in war, people don't use it to stop it from ever occurring. Maybe it needed to happen, like the American Revolution. Don't play God. As they say, a man's ego is the fragile thing in the universe. It's also as big as it. It needs to go down, possibly broken and humbled before we think we can play God and mess with things that were not meant to be touched.


~Bynary Fission

[devonin]

Time travel to the past presents no paradox once you realise that anything they would do "in our past" -is- the past as we've recorded it. If I am going to go back in time to 1935 to try and kill Hitler before the war starts, I will do so, and have already done so, and clearly I failed in my attempt. There's only one 1935, and if I am going to go back in time to then to try and kill Hitler, the only 1935 has me in it, trying to kill him and, as we've seen, clearly failing.

The trick is to understand the distinction between "can" as it pertains to one's abilities, and "can" as it pertains to an individual attempt. I -can- go back in time and kill my grandfather. I could buy a gun, spend months becoming prefocient in its use, until I am a crack shot, plan out exactly where and when I'd have my best chance, and consider myself up to the task. If anyone -can- succeed, I can. However, that is only the sense of 'can' that pertains to my abilities. The fact that my father and I exist is testament to the fact that even though I am -able- to kill my grandfather, on the occasion in which I attempt to do so, I fail.

Michael Jordan could make a 3-point shot in the final seconds to win the game. If anyone could do it, he could. That doesn't mean that on every attempt he is guarenteed to succeed, nor does his lack of success on a given attempt invalidate the claim that he can do it.

So to sum that up: You can't change the past from our present perspective because all of the changes you are going to make are what has happened. So that suggests that were we to develop time travel to the past, we also obviously developed a strict ruleset governing who can go back in time, and what they can and cannot attempt to do while they do so.

The same lack of apparant catastrophe you use to suggest that time travel will never be invented just as strongly argues for the existance of time travel that has only ever been used wisely.

Alternatively, take the cop out by arguing that time travel necessarily involves travel to a parallel universe.

[Bynary Fission]

Originally Posted by devonin

Time travel to the past presents no paradox once you realise that anything they would do "in our past" -is- the past as we've recorded it. If I am going to go back in time to 1935 to try and kill Hitler before the war starts, I will do so, and have already done so, and clearly I failed in my attempt. There's only one 1935, and if I am going to go back in time to then to try and kill Hitler, the only 1935 has me in it, trying to kill him and, as we've seen, clearly failing.

The trick is to understand the distinction between "can" as it pertains to one's abilities, and "can" as it pertains to an individual attempt. I -can- go back in time and kill my grandfather. I could buy a gun, spend months becoming prefocient in its use, until I am a crack shot, plan out exactly where and when I'd have my best chance, and consider myself up to the task. If anyone -can- succeed, I can. However, that is only the sense of 'can' that pertains to my abilities. The fact that my father and I exist is testament to the fact that even though I am -able- to kill my grandfather, on the occasion in which I attempt to do so, I fail.

Michael Jordan could make a 3-point shot in the final seconds to win the game. If anyone could do it, he could. That doesn't mean that on every attempt he is guarenteed to succeed, nor does his lack of success on a given attempt invalidate the claim that he can do it.

So to sum that up: You can't change the past from our present perspective because all of the changes you are going to make are what has happened. So that suggests that were we to develop time travel to the past, we also obviously developed a strict ruleset governing who can go back in time, and what they can and cannot attempt to do while they do so.

The same lack of apparant catastrophe you use to suggest that time travel will never be invented just as strongly argues for the existance of time travel that has only ever been used wisely.

Alternatively, take the cop out by arguing that time travel necessarily involves travel to a parallel universe.

Well, on your killing your grandfather issue, you already exist. There is nothing that suddenly makes you not exist, however, an alternate version of you would never be born. But since it's impossible (Or, nearly) for everything to spontaneously disappear, killing your grandfather will not necessitate an exception.

For not being able to change the past, changing it would cause an instant change in the future, so in a way it never changed, since time after it went as normal, at least after the point of no return (When you did X act), and the people of the later present would not notice. But you permanently altered the time-space continuum, and you created an alternate timeline, thus resulting in what some see as an alternate universe, but unless you have or can affect the universe itself, the change would be localized to humanity solely.

Finally, even though you won't necessarily succeed in what you saw as the change you wished to occur, that doesn't mean you didn't succeed in changing something else. If you tried to kill your grandfather but missed, then you missed. He still lives, and you will still be born. But maybe you crushed a bug unknowingly. Then you eradicate countless generations of said bug after it, and this may have anywhere from a negligible to catastrophic effect on the world.

~Bynary Fission

[JKPolk]

Most theories I've seen of time travel state that travel will not be possible past the point of their device being switched on. Essentially, if a machine was created in 2012 then time travel, according to current thought, would only be able to go as far back as 2012. Using this methodology, we have nothing to worry about until the first machine is turned on. Then all hell could break loose.

[x6tence]

I see where you are coming from.
By tampering with the past we can drastically change our future. An example of this is if I went back to the perhaps Jurassic time period and killed a roach. I could of potentially killed off a whole species or perhaps cause an extinction to occur.

[devonin]

But as I mentioned above, since any changes you might possibly make to the past have already happened, you clearly didn't do anything catastrophic, or at least catastrophic from our perspective, since we're here and don't find anything to be particularly wrong with the world.

Sure you may have gone back in time and caused say, world war one to happen, but since that's already our accepted past, we have no basis to judge what the alternative could have/would have been, and thus from our perspective, no future time traveller can change the past to something other than what we experienced. Though it is possible that they'd changed it from what it had been when they left, since those changs have already happened they might as well not have. Do you see what I'm getting at?

[Bynary Fission]

Originally Posted by devonin

But as I mentioned above, since any changes you might possibly make to the past have already happened, you clearly didn't do anything catastrophic, or at least catastrophic from our perspective, since we're here and don't find anything to be particularly wrong with the world.

Sure you may have gone back in time and caused say, world war one to happen, but since that's already our accepted past, we have no basis to judge what the alternative could have/would have been, and thus from our perspective, no future time traveller can change the past to something other than what we experienced. Though it is possible that they'd changed it from what it had been when they left, since those changs have already happened they might as well not have. Do you see what I'm getting at?

Precisely. As I stated in my previous post, nobody's gonna notice the new future....except you. But who would want to live in a future that isn't yours? I could not live with that thought.

Plus, if you far enough in the future, somebody might catch you interfering with X, and if they got your face or something in, say, a photo, and matched that to you when you existed in what time you should have been in....ohh I can't say, but there would certainly be a buzz.


~Bynary Fission

[devonin]

I could not live with that thought

By definition, you cannot possibly be aware that this is the case.

You would need to be aware of both the current state of things and the alternative state of things that could have/would have/should have been. Since the very nature of time travel dictates that all changes to our past have already happened, the result of which is the history we already know and accept as true, it is a logical impossibility to be aware of the fact that changes have occured to regret the changes.

[Bynary Fission]

Originally Posted by devonin

By definition, you cannot possibly be aware that this is the case.

You would need to be aware of both the current state of things and the alternative state of things that could have/would have/should have been. Since the very nature of time travel dictates that all changes to our past have already happened, the result of which is the history we already know and accept as true, it is a logical impossibility to be aware of the fact that changes have occured to regret the changes.

But if you experienced two realities, then you are aware of both of them. You were there, you formed memories of both time periods and thus you will be aware of both tangents of existence. You know what happened and accept it as true, therefore, you are aware of both timelines. Like you said, you have to be aware of the alternate and current timelines. You know your timeline's history, and you will soon know the alternate's, so therefore is is possible to regret the changes, since you are the only person to have existed in both timelines.


~Bynary Fission

[Tokzic]

Originally Posted by devonin

The trick is to understand the distinction between "can" as it pertains to one's abilities, and "can" as it pertains to an individual attempt. I -can- go back in time and kill my grandfather. I could buy a gun, spend months becoming prefocient in its use, until I am a crack shot, plan out exactly where and when I'd have my best chance, and consider myself up to the task. If anyone -can- succeed, I can. However, that is only the sense of 'can' that pertains to my abilities. The fact that my father and I exist is testament to the fact that even though I am -able- to kill my grandfather, on the occasion in which I attempt to do so, I fail.

This is very, very wrong.

Let's say you have a friend, Bob, who isn't a very popular guy. He would be murdered on the first of January, 2020, if someone doesn't intervene. But let's say that you go back in time and stop the assassin on the second of January, 2020. If that is history as it's meant to be, then history is also you going back in time to stop Bob's assassin. But how is this possible if history has shown no assassin? If you don't know about an assassin, why would you stop it? And if you don't stop it, won't Bob die?

What if Hitler actually meant to thoroughly bomb the States before he lost the war? What if I'm the guy who stops him from doing this? How am I supposed to know that if I don't do this, Hitler bombs the States, thus completely changing the timeline?

[devonin]

But if you experienced two realities, then you are aware of both of them. You were there, you formed memories of both time periods and thus you will be aware of both tangents of existence.

You did not experience both realities. A nebulous future self that may or may not exist experienced one reality and went back in time to change it, resulting in the sole reality that you are aware of. From your present perspective, changing your own timeline to something other than what it is now is impossible, because you've already made all the changes you're going to. You just haven't gone back to do them yet.

You are already living the results of your future time travel endeavour and nothing about the world as it is seems to me anyway, like something has changed that should have been otherwise, and I suspect it is the same with everyone else.

Let's say you have a friend, Bob, who isn't a very popular guy. He would be murdered on the first of January, 2020, if someone doesn't intervene. But let's say that you go back in time and stop the assassin on the second of January, 2020. If that is history as it's meant to be, then history is also you going back in time to stop Bob's assassin. But how is this possible if history has shown no assassin? If you don't know about an assassin, why would you stop it? And if you don't stop it, won't Bob die?

In order for this to make any sense, we have to assume a situation where the present is say, 2021. Bob has been killed, and as much as nobody liked him, I decide "I'm going to go back in time to 2020 and stop that assassin!" This is where sci-fi likes to start talking about a paradox "If I stop the assassin, he won't die, but if he doesn't die, how would I know about the assassin to go back in time at all, so he'll die" and get a big and unnecessary headache about it.

The simple answer is, if in 2021, Bob has been killed, and it isn't until 2021 that you decide to go back in time to save him, then your 2021 self failed to stop the assassin. I can concieve of any number of reasons why you would fail. Perhaps you tried to stop him and he simply bested you before going on to kill Bob, perhaps you decided the potential risk to the timeline was too great and stopped, perhaps you were stopped by some sort of time police from further up your timeline, perhaps as in the case of a great Red Dwarf episode, you stop the assassin, and then realise that the results would have been worse than Dead Bob and carry out the killing yourself. Regardless, the fact that your 2020 necessarily included your 2021 self trying to stop the killer, and yet your 2020 also includes Bob dead, your 2021 self either failed or didn't try.

[JKPolk]

That "Time Police" thing you mentioned is actually probably one of the most likely situations if this were to arise at all. I find it near impossible to believe that, if time doesn't right itself, there wouldn't be an organization designed specifically to ensure that no one can alter or damage the timeline.

[Tokzic]

Originally Posted by devonin

In order for this to make any sense, we have to assume a situation where the present is say, 2021.

I actually said in my example that you decide to go back in time the next day, but okay, I'll roll with this if you'd prefer it that way.

Originally Posted by devonin

The simple answer is, if in 2021, Bob has been killed, and it isn't until 2021 that you decide to go back in time to save him, then your 2021 self failed to stop the assassin. I can concieve of any number of reasons why you would fail. Perhaps you tried to stop him and he simply bested you before going on to kill Bob, perhaps you decided the potential risk to the timeline was too great and stopped, perhaps you were stopped by some sort of time police from further up your timeline, perhaps as in the case of a great Red Dwarf episode, you stop the assassin, and then realise that the results would have been worse than Dead Bob and carry out the killing yourself. Regardless, the fact that your 2020 necessarily included your 2021 self trying to stop the killer, and yet your 2020 also includes Bob dead, your 2021 self either failed or didn't try.

This doesn't have anything to do with my post. My question isn't addressing what happens if Bob dies, but if Bob lives. If your 2021 self succeeds, Bob lives in 2020; but then you have no indication that you need to go back in time in 2021. Thus, you will not stop the assassin, and thus he dies. But he can't die, or else the timeline would change. So is it just impossible, or do you get the sudden premonition (well, "postmonition", but you know what I mean) that Bob will die unless you go back in time and save him?

[devonin]

Lets try this again.

It is January first 2020. Bob is killed. You go "Oh no! Bob! I never told you I loved you!" and decide on January 2nd that you're going to go back in time to the first and prevent Bob's death.

You see an issue in that -if- you prevent Bob's death, then your January 2nd self won't know he died and thus not resolve himself to go back to the first to save him, creating in your mind, a paradox. That sound about right?

What I'm saying is: From the perspective of January 1st you, There is only one January first It contains you, bob, bob's killer, and a you from the future trying to stop bob's killer. However, Bob died. Thus, you failed to prevent bob's killer from killing bob for whatever reason.

Why you failed to save bob is academic. The fact that you made it to the 2nd of January with a dead Bob is proof enough that your attempt to go back in time to save bob failed, for any of the possible reasons I listed above.

So: January first, You, Bob, Bob's Killer, You from the future. You from the future tries to stop Bob's killer and fails, Bob dies.
January second, You, Bob's corpse, possibly Bob's killer. You resolve to go back in time to the first to save bob.

The account I described above allows for time travel to the past, without creating any temporal or causality paradox.

[Tokzic]

That can't be though. For there to be no paradox, you'd have to not interact with anything at all. Even simple physical sensory presence would change the timeline and create a paradox.

[Reach]

Well, given a modern interpretation of physics, we shouldn't even have to worry about this because it won't be possible. Time as a spatial dimension can be manipulated; however, by manipulating it you're always changing a relative perception of that dimension (i.e. time dilation), it never acts as a line you can travel back and forth on. In order for time travel to be possible there would have to be some chronological record of things that have happened, and right now it doesn't look like there is one.

I don't see any reason to believe there should be one, but even assuming there was, nobody has any idea how this would work. Time could have some sort of higher spatial dimension that represents the change in time over time (what), but that still doesn't mean it records events, nor does it mean we could travel through it...or that if we did it wouldn't just change everything in the process, etc. D:

[devonin]

Originally Posted by Tokzic

That can't be though. For there to be no paradox, you'd have to not interact with anything at all. Even simple physical sensory presence would change the timeline and create a paradox.

Er...changing the timeline != A paradox necessarily

A paradox is "an argument that apparently derives self-contradictory conclusions by valid deduction from acceptable premises"

Your line of reasoning involving going back to save bob, which means that you didn't know bob needed saving, thus couldn't save bob, except you did etc etc was a paradox. I resolved the paradox by claiming that while you did go back in time intending to save bob, you clearly failed, as evidenced by bob's untimely demise. There is no paradox there.

Let me put it yet another way: While it -could- be the case that were it not for time travellers interfering in the past and changing the timeline, our present would be other than what it was, any changes they made are what happened and so regardless of what the potential alternate reality could have been, this is reality. The very "changes" people from the future made, failed to make, or tried to make are what contributed to the reality they elected to try and change.

Since we are not them, we know only what reality is, and that reality might very well include interference from future time travellers. But since we have no insight into the potential realities of the future, since they haven't actually happened, the illusion is perfect, and we simply see reality as it is now, and our past -includes- any and all changes that make have been caused by future time travellers.

[Tokzic]

That's true, and that's why any timeline-modifying action would become a paradox. As you said, the timeline is as it would be when affected by time travel. Replace saving Bob with absolutely any change in your example and you see why it'd be a paradox:

Your line of reasoning involving going back to [do an action], which means that you didn't know [you needed to do an action], thus couldn't [do an action], except you did etc etc was a paradox. I resolved the paradox by claiming that while you did go back in time intending to [do an action], you clearly failed, as evidenced by [the timeline's final result where the action is not done]. There is no paradox there.

[devonin]

Still not seeing a paradox. You're wanting to go change something that happened, and in the end, what happened originally still happens. This allows for you to still form the idea in your original present that you want to go try to change things. That was the crux of your paradox, which becomes resolved.

The only paradox in changing the past is that you could change the past in a way that makes the formation of your original plan to go change the past impossible. If you fail to effect the change you wanted to, the paradox is resolved.

Edit, here's your paradox.


A = Time moving as normal
X = The instant of Bob's Death

When Bob dies at X, time carries on in stream B. B is the reality in which Bob is dead. In reality B you can decide to go back in time to save Bob's life. So you go back in time to just before X and save Bob. Now you are in reality C, the reality in which Bob is alive. In Reality C you are incapable of deciding to go back in time to save Bob, and thus don't, which causes Bob to be dead, rendering reality C impossible despite the fact that you are currently living it.

That's the formulation of a standard causality paradox. Causing something to happen makes it impossible for it to happen.

What I'm saying is, You go from A to B at point X, Bob's death. Reality B is a reality in which you can decide to go save Bob, because Bob is dead. However, I claim that your attempt necessarily fails for one of any number of reasons, as evidenced by the fact that Bob is in fact dead. Reality C never enters into it, because from up the stream in reality B, all the events of A are already set and happened, including your attempt (which fails) to save Bob.

[Bynary Fission]

Originally Posted by devonin

Still not seeing a paradox. You're wanting to go change something that happened, and in the end, what happened originally still happens. This allows for you to still form the idea in your original present that you want to go try to change things. That was the crux of your paradox, which becomes resolved.

The only paradox in changing the past is that you could change the past in a way that makes the formation of your original plan to go change the past impossible. If you fail to effect the change you wanted to, the paradox is resolved.

Edit, here's your paradox.


A = Time moving as normal
X = The instant of Bob's Death

When Bob dies at X, time carries on in stream B. B is the reality in which Bob is dead. In reality B you can decide to go back in time to save Bob's life. So you go back in time to just before X and save Bob. Now you are in reality C, the reality in which Bob is alive. In Reality C you are incapable of deciding to go back in time to save Bob, and thus don't, which causes Bob to be dead, rendering reality C impossible despite the fact that you are currently living it.

That's the formulation of a standard causality paradox. Causing something to happen makes it impossible for it to happen.

What I'm saying is, You go from A to B at point X, Bob's death. Reality B is a reality in which you can decide to go save Bob, because Bob is dead. However, I claim that your attempt necessarily fails for one of any number of reasons, as evidenced by the fact that Bob is in fact dead. Reality C never enters into it, because from up the stream in reality B, all the events of A are already set and happened, including your attempt (which fails) to save Bob.

Perhaps so, but who says you're going to fail? If a guy tries to kill Bob, and succeeds, time progresses as normal. But if he doesn't, and you stop him, then everything changes. If he was a gangster, then many lives will fall by him, causing even bigger changes in the time-space continuum. If he was a bum, then nothing will change that much. If he was a civil rights activist, then all of Earth might be different.

If Bob is dead, you fail. If not, then you plunge time into an alternate reality forever, even if nothing changes. Even the most infinitesimally small change causes perturbations in reality, thus you have created an alternate universe in which Bob lives.

Originally Posted by devonin

The only paradox in changing the past is that you could change the past in a way that makes the formation of your original plan to go change the past impossible. If you fail to effect the change you wanted to, the paradox is resolved.

Edit, here's your paradox.


A = Time moving as normal
X = The instant of Bob's Death

When Bob dies at X, time carries on in stream B. B is the reality in which Bob is dead. In reality B you can decide to go back in time to save Bob's life. So you go back in time to just before X and save Bob. Now you are in reality C, the reality in which Bob is alive. In Reality C you are incapable of deciding to go back in time to save Bob, and thus don't, which causes Bob to be dead, rendering reality C impossible despite the fact that you are currently living it.

That's the formulation of a standard causality paradox. Causing something to happen makes it impossible for it to happen.

This is impossible. Say, the assassin of Martin Luther King Jr. (James Earl Ray) was brought back into the past to kill MLK. If he assassinated him, then he will die. No paradox, nothing. We do not exist in multiple realities. We affect the current time and place we are in. Time cannot place you in such a paradox because you defied it. Time is an abstract concept used to reflect gradually increasing periods from a certain point. We don't exist in multiple realities. We can't be made not to do something because some other universe told us so. What if many assassins throughout history were from the future? We can't prove they were, but we can't prove they weren't. Say some were. Then, nobody would have been assassinated because a time paradox would have prevented it.

A very well-known and accepted theory is that we exist in realities that branch off of ours ad infinitum, and this comes from the fact that your hand blurs when it is waved, and bars of light interfere with each other and produce 4 instead of 6, etc, supposedly caused by interference with you from other universes doing the same action. If this were the case, we would live forever. You stated that you can save bob, but then you could never go back to save him. This was in another reality, which you are no longer within. Now to my point. In one reality you would be dead, another you are reading, another you across the world doing something, but they are all you. This means that in one you would be alive, but another dead. Yet, in many other realities, you are alive, thus making it impossible for you to die at all. I don't believe this theory, but many do, so I state it here to show that this cannot be the case with the casualty paradox.


~Bynary Fission