What are the best depictions of Time Travel?

[Q99]

The question is, "By standing here, have I perturbed the fertilization of any ova?" Is my presence in the room sufficient to cause the effect in question? How much change does it take to result in a different sperm reaching the egg or a different egg leaving the ovary? There is no way to test this in reality. We cannot assume "a couple of air molecules hit people at a different angle" or some such is sufficient cause to make this happen.

The example a person standing in one place for five minutes? This is more than a few air molecules- I believe it's trillions. Also, it's introducing new future DNA into the local bacteria/viral mix as large quantities of future-bacteria fall off you (some of the future bacteria will live and become millions/billions/etc. of bacteria, some'll be eaten but it's eaters will absorb the DNA. Either way, it's staying around).

A person standing in one place is *ridiculously* macro scale on the size of physics. This is literally multiple cubic feet of atomics displaced at the time of arrival, and continuing to make an ever-growing disturbance the longer it lasts (including, of course, every breath exchanging oxygen for carbondioxide, picking up some other molecules, leaving a different mix). Five minutes? If there's no airflow, that means nigh-every air molecule in the room will be affected significantly (it'll be hotter, it'll be in different configuration and courses) and likewise the molecules in the walls, door, and floor, and when the door's open, all that changed air comes out. In my hypothetical *outside* event, and air travels in it at, say, 6 inches a second, then by the time you leave the disturbance has left a 150 foot trail (or an airvent or crack in the door could do similar). Carrying, among other things, future bacteria.

And all the change needs to hit is the placement of an individual cell for it to be obvious to humans.

The question is not if it causes a macro-visible change, but when. And that's a hypothetical not-seen-by-anyone event. Actual "go behind someone, say 'Hey,' then immediately vanish," automatically makes it macro.

A sufficiently large cause will result in a large enough effect that amplification and the process we call "the butterfly effect" come into play. But a sufficiently small cause is just as likely to be swamped by all the other (unchanged) events taking place. As I mentioned, you cannot assume that changing the course of one butterfly will change the course of a hurricane, just because the hurricane is somehow linked to the butterfly in a way that creates more than literally zero connection between them.

Ah, 'swamped'. Here's the thing- even if a small change is, to outside appearances, overwhelmed by an existing mix, it does not actually go away unless an exact counter-force happens to appear, that didn't appear before, and matches it (and note, running into something head-on, that doesn't stop the change from persisting, that means the change is now "this thing that used to have the momentum sufficient to do X now doesn't because it used it canceling out this momentum caused by the change, and thus it won't bump into and slow down this *other* thing later on that it would've instead).

If it was a truly small change, a literal few atoms or such, it'd possibly take a ridiculously long time before it has any macro effect, but it won't actually vanish, it'll just move around. And this isn't that small a change physics-wise.

Or, to put it another way, we're running smack into entropy here. Energy cannot be destroyed.

Something being swamped sounds simple, but swamping a small event among pre-existing one is hiding it, not canceling it.

[Ziggy Stardust]

While it's true that the energy doesn't vanish and is redistributed throughout the system, you are implicitly assuming that ANY input must necessarily have a large output and that it isn't possible for the energy to be distributed uniformly throughout the system to some infinitesimal degree. Remember that the butterfly effect is just a metaphor for the operation of deterministic non-linear systems. It doesn't imply that any and all changes to anything will always result in some massive change (nor does it imbue particles with magical properties in order to cause such changes), only that the state is sensitive to initial conditions.

[Simon_Jester]

Right.

Again, if one butterfly doesn't happen to flap its wings at the right time, in all probability the hurricane still happens. It's just that we can't be sure we know what the hurricane will do far in advance. Because we lack knowledge not only of the actions of that particular butterfly, but of ALL the microscale features of the system. The cumulative effect of all microscale features is what has this massive influence that causes things to become unpredictable. This does not mean each individual micro-change has world-altering effect.

One germ might infect someone and make them very sick in a life-altering way. It often doesn't.

One conversation might change someone's life. It usually doesn't.

One jostle might result in different sperm fertilizing the same egg, but we don't really know and have no way to test it. And even if true it may well turn out that in a lot of important ways, having everyone born after time T be a biologically different person matters less than we think- because while the individual actions are different, the statistical effects may be similar.

[LadyTevar]

Idea I haven't seen, but want to-

Someone comes back after altering the past, meets their alternate.. and then uses mental technology to transfer their memories over/merge with that one, so the resulting person is effectively both versions in one.

Amusingly enough, I've been kicking that idea around for a while. Have to get permission from a couple people to use their characters before I write it

[Darth Holbytlan]

Right.

Again, if one butterfly doesn't happen to flap its wings at the right time, in all probability the hurricane still happens. It's just that we can't be sure we know what the hurricane will do far in advance. Because we lack knowledge not only of the actions of that particular butterfly, but of ALL the microscale features of the system. The cumulative effect of all microscale features is what has this massive influence that causes things to become unpredictable. This does not mean each individual micro-change has world-altering effect.

No, that's the entire point of chaotic systems. Every microscale change is amplified into macroscale differences given enough time; start off such a system with two almost identical initial conditions and, although they may seem to act the same way for a while, they eventually, inevitably diverge into two completely different paths. This is one of the reasons chaotic systems like the weather are only predictable for a few weeks out—it's completely infeasible to gather accurate enough information to make good predictions for longer than that.

A quick lookup suggests that the rate of doubling of errors in weather is about 5 days. Given that and the scale difference between a butterfly and the whole planet, it would take under 5 months for an errant flap to completely change the weather. This is not a case of the same hurricane probably happening, but a guarantee that you will end up with completely different hurricanes traveling completely different paths. And that's true for the actions every single butterfly (and time traveler) on the planet.

This all falls out from the mathematics of chaotic systems and holds for all of them. And pretty much every system we deal with is chaotic on a long enough scale. Even planetary orbits are chaotic and start to lose precision over millions of years. The good news is that many systems we depend on are stable (or mostly stable) over longer periods of time. Weather is quite unpredictable, for instance, but climate is comparatively stable—you may have different hurricanes, but you'll still have hurricane season, spring, and winter for a good long time.

[Simon_Jester]

While I will not pretend knowledge of chaos theory sufficient to debate someone who knows the subject well (what's your background?)...

The point I'm trying to get at is that even within a chaotic system, there are often attractors. There are processes that are relatively insulated against the micro-scale change processes (i.e. because of the human body's attempt to maintain homeostasis).

A system is chaotic because some tiny changes in initial conditions lead to massive changes in final conditions. So far as I know, I need not be the case that every tiny change in initial conditions lead to massive changes in final conditions.

[Ziggy Stardust]

No, that's the entire point of chaotic systems. Every microscale change is amplified into macroscale differences given enough time; start off such a system with two almost identical initial conditions and, although they may seem to act the same way for a while, they eventually, inevitably diverge into two completely different paths. This is one of the reasons chaotic systems like the weather are only predictable for a few weeks out—it's completely infeasible to gather accurate enough information to make good predictions for longer than that.

A quick lookup suggests that the rate of doubling of errors in weather is about 5 days. Given that and the scale difference between a butterfly and the whole planet, it would take under 5 months for an errant flap to completely change the weather. This is not a case of the same hurricane probably happening, but a guarantee that you will end up with completely different hurricanes traveling completely different paths. And that's true for the actions every single butterfly (and time traveler) on the planet.

This all falls out from the mathematics of chaotic systems and holds for all of them. And pretty much every system we deal with is chaotic on a long enough scale. Even planetary orbits are chaotic and start to lose precision over millions of years. The good news is that many systems we depend on are stable (or mostly stable) over longer periods of time. Weather is quite unpredictable, for instance, but climate is comparatively stable—you may have different hurricanes, but you'll still have hurricane season, spring, and winter for a good long time.

Doesn't the mere fact that weather doesn't exponentially accelerate into world-consuming storms of chaos energy act as proof that not all microscale changes result in macroscale output? A chaotic system is simply a deterministic system that is highly dependent, in a non-linear fashion, on its initial conditions (and further has the property of recurrence). The reason weather isn't easy to predict is because we have imperfect knowledge of those initial conditions, not because every single possible change of input always results in humongous changes of output as you suggest. Quite simply, that isn't a feature of a chaotic system. There is no rule that says every single microscale change results in macroscale differences. Nor does the behavior of chaotic systems imbue particles with magical properties in order to cause such macroscale changes. The fact that most chaotic systems operate around attractors, as Simon said, is evidence enough of this; an attractor by definition results from the fact that a large subset of the parameter space for the initial conditions will result in similar output. Remember, the butterfly theory is just a metaphor for the mathematical properties of a chaotic system, NOT a literal description of how butterflies effect the weather.

If ALL small changes of input always let to large changes of output as you claim, weather wouldn't exhibit the properties it does, because the world would have been destroyed by sharknadoes or whatever by now. Weather clearly operates within certain bounds (i.e. around attractors), which inherently constrains the parameter space of the initial conditions. By definition, that makes it mathematically impossible for every possible change of initial conditions to result in large output.

[Darth Holbytlan]

Let me try to explain in more detail and see if it clarifies matters.

A system is usually represented as a phase space, which is a space where each point represents a specific set of parameter values.

For example, in a weather simulation you might represent the temperature with one parameter, the pressure with another, the humidity with another, and the wind speed and direction with three more. That would cover the behavior at just one point, so you would have a set of those 6 parameters for each voxel in the atmosphere. The result is a high-dimensional space (of 6n dimensions, where n is the total number of voxels) where each point represents a specific possible state of the world. (A more realistic representation might involve parameters for each particle in the atmosphere and its motion, but the idea is the same either way.)

Differential equations drive the change in state over time, so the point representing the current state moves through the phase space over time. If you know the exact measurement of every parameter at one time, you know the exact point in phase space and can, in principle, derive exactly where the point will be at any time in the future—and therefore exactly what state the system will be then. In practice, we never know that; what we know is that the point is within some neighborhood within the phase space, and the points in that subset will move around in phase space over time. You start with a subset representing possible starting states and end up with a different subset representing possible ending states.

We can certainly imagine systems where the neighborhood representing the possible phase space states stays nice and compact, just moving around the phase space over time. We can also image ones where the neighborhood is compressed over time, reducing in volume and so making our predictions in the long run more accurate. But such cases aren't chaotic and don't represent cases where prediction is difficult.

Actual chaotic systems involve both expansion and contraction of a subset moving through phase space. It is stretched and folded over time, eventually stretching out across the entire attractor. The volume of the subset doesn't necessarily increase—it can actually shrink. But the expected distance between any two points in the subset grows until it is indistinguishable from the attractor as a whole. At that point, any normal outcome is equally possible.

While I will not pretend knowledge of chaos theory sufficient to debate someone who knows the subject well (what's your background?)...

I have a Bachelors in Mathematics, but in this matter I'm just an educated layman. I've never formally studied the subject.

The point I'm trying to get at is that even within a chaotic system, there are often attractors. There are processes that are relatively insulated against the micro-scale change processes (i.e. because of the human body's attempt to maintain homeostasis).

Yes, there are attractors, but there is a big difference between a chaotic system having an attractor and it being stable in the sense I am describing. Climate is a good example of an attractor for the weather. Regardless of our imperfections in measuring the atmosphere or predicting butterflies, the weather doesn't blow up into a worldwide storm. We still have more or less normal summers and winters with an annual hurricane season with a roughly predictable number of hurricanes. Basically, anything you could have predicted a year in advance about the weather will still hold whether or not butterfly X flaps its wing. It's the specifics that you typically can't predict that can end up changing. Whether or not a hurricane appears on a particular day and whether it hits New Orleans or Galveston or nothing is what will change.

A system is chaotic because some tiny changes in initial conditions lead to massive changes in final conditions. So far as I know, I need not be the case that every tiny change in initial conditions lead to massive changes in final conditions.

Strictly speaking, there is some subset of changes that would just fade out—distinct points in phase space that will just move closer and closer forever. But no actual change would fall into that set.

Here's my understanding: Chaotic systems involve both expansion and contraction components; to hit this sitation, the change needs to happen only in the directions that contract and not those that expand. Omitting the one or more expansion components results in the surface of changes that don't cause divergence having a lower dimensionality than the space of possible changes; any particular change hits that surface with probability 0. That never happens, so in practice the results always diverge.

If ALL small changes of input always let to large changes of output as you claim, weather wouldn't exhibit the properties it does, because the world would have been destroyed by sharknadoes or whatever by now.

Ziggy, I'm not sure what you think I'm saying, but that doesn't follow at all. The result of these perturbations is that, over sufficient time, the outcomes become randomized not abnormal.

The evolution of the phase space is a lot like a taffy pull: If you put some food coloring at one place in the taffy and then run the machine, the color will be stretched over the entire thing, but that doesn't mean that the taffy will somehow grow and envelope everything. Yet we are still unable to predict where any particular molecule of the food coloring will end up.

[Ziggy Stardust]

Ziggy, I'm not sure what you think I'm saying, but that doesn't follow at all. The result of these perturbations is that, over sufficient time, the outcomes become randomized not abnormal.

Which is ... exactly what I was saying? The notion that a butterfly flapping its wings, or that simply standing in a room for five minutes, will result in abnormal perturbation is ridiculous. It results in outcomes that are essentially randomized in the sense we don't have enough information to measure all the input parameters, but it does not result in magical outcomes. Just because the outcomes are random and hard to predict does not mean they are abnormal; in fact, they are far more likely to fall into the realm of probability space that is indistinguishable for normal background random variance anyway.

[Simon_Jester]

To be fair, some perturbations of a system are "normal" and randomizing the outcome of the system will change the outcome noticeably.

Take, for example, a roulette table. Small perturbations bumping the table result in the ball bouncing to different places, because unless the table is rigged, all outcomes are more or less equally likely. Which means different people win the money- a large outcome from a small perturbation.

If we model a roulette wheel as a chaotic system, the attractor isn't "the ball lands on 17." The attractor is "the ball lands SOMEWHERE." We can predict the ball will land on some number without knowing the exact details of everything happening. But subtle changes in the details can affect which numbers.

When it comes to how this affects the "butterfly effect" in time travel, the real question is: what constitutes an interconnected system, and when does re-randomizing the outcomes of a seemingly random event (like the weather) have large-scale consequences?

[Q99]

While it's true that the energy doesn't vanish and is redistributed throughout the system, you are implicitly assuming that ANY input must necessarily have a large output and that it isn't possible for the energy to be distributed uniformly throughout the system to some infinitesimal degree. Remember that the butterfly effect is just a metaphor for the operation of deterministic non-linear systems. It doesn't imply that any and all changes to anything will always result in some massive change (nor does it imbue particles with magical properties in order to cause such changes), only that the state is sensitive to initial conditions.

Wow, if you've got a mechanism for massive dispersal like that, I'd like to know it!

Also keep in mind, we're talking about chemicals and atoms being replaced with different chemicals and atoms, lifeforms that don't *exist* being added, and temperature being affected across cubic meters of atoms, localized.

If there's any scientific process where so much as a single atom just spread out it's energy in an inperceptible way, I am unaware of it.

Right.

Again, if one butterfly doesn't happen to flap its wings at the right time, in all probability the hurricane still happens. It's just that we can't be sure we know what the hurricane will do far in advance. Because we lack knowledge not only of the actions of that particular butterfly, but of ALL the microscale features of the system. The cumulative effect of all microscale features is what has this massive influence that causes things to become unpredictable. This does not mean each individual micro-change has world-altering effect.

It means different hurricanes happen. Ones that to a glance, are nigh identical, but have differences.

Initially, slightly different. Who cares of Hurricane Andrew, 30 years after the initial travel, is half a meter to the right? But Hurricane Andrew being a meter to the right means that the next Hurricane is 10 meters, because it's no longer being affected by a small change, it's being affected by all the change of a hurricane being on a different course. And then the *next* one is affected by that.

So Hurricane Andrew, in the 90s, missing by half a meter, likely means Hurricane Katrina is missing New Orleans. And *that's* a big change.

One germ might infect someone and make them very sick in a life-altering way. It often doesn't.

But a change to a germ ecosystem means that as long as any descendant of that original germ, *or* the descendant of a germ that germ replaced, *or* a germ altered by the change in competition with the germ, eventually resulting in different sicknesses.

Remember with germs, it's almost never one germ. Bacteria reproduce rapidly. Drop down 20 new bacteria and, ok, some are going to die off and be nothing but food for other bacteria (which is itself a change, but a small one that'll take much longer to have an impact- but eventually 'these germs doing slightly better means someone does/doesn't get sick when they would' happens), but a few will spread and become thousands, millions, billions over time. It's an ecosystem change.

Bacteria are fantastic for multiplying change due to the fact they themselves multiply. And exchange genetic material- they pick up code from what they eat. The bacterial world is constantly in a state of tons of bacteria dying and being replaced by rapidly-growing bacteria. A bacteria that just evolved last year could have hundreds of billions of descendants now. We *know* stands where that's happened- and the change isn't just whether or not future-bacteria do that, it's that that sort of thing always happens, and the presence or lack of competition/food/etc. affects when other bacteria do it.

One conversation might change someone's life. It usually doesn't.

But a change to someone's pattern of conversations going forward means if a life-changed conversation ever happens, it won't be the exact same conversation in the same circumstances. Which could mean it happens sooner, it could means it happens later, it could change someone's life in a slightly different way. If you're a minute late at the start of a day and miss a conversation, your next conversation isn't going to happen as if it never happened. You say 'hi' different, you say 'bye,' different. You're a bit rushed so you get hungry sooner, or maybe you have a snack you didn't, or skip eating to not be late... and then your next action is taken in that context. You will never return to the exact same track you were on before, even if the events are very similar because you're driving with the same intent in mind. Which is fine, up until you hit something that needs only a minor change to go sideways.

One jostle might result in different sperm fertilizing the same egg, but we don't really know and have no way to test it.

Oh, that one we totally do. 'How small objects move when touch,' is a known testable thing, and 'how reproductive cells work,' well, that's literally tested every single time reproduction happens.

That, of all examples, is the most easily demonstrated one because it literally happens every single time. We know what reproductive cells contain, we know the effects of that code, and we know what replacing that code does. And the rest is straightforward fluid mechanics on a normal scale- something we are also very very solid on.

Nothing in that process is a mystery.

And even if true it may well turn out that in a lot of important ways, having everyone born after time T be a biologically different person matters less than we think- because while the individual actions are different, the statistical effects may be similar.

Similar, but different. And a lasting difference will, over time, change. Change time in the 60s and we'll still have a US now, we'll probably even have *very similar* political events, but we will have an ever-growing number of different people and events happening slightly differently or at different times. Eventually, that results in larger changes.


Chaos theory's been talked about, but I want to emphasize Entropy and the fact that changes don't go away. That 'perfectly spread out the energy into the system in a way to minimize the effect'? That is a mind-boggling suggestion of a scale far more immense in it's implications than a mere 'stand in one place for 5 minutes and change the future in significant ways'.

It'd change so much of what we know of physics, it'd mean even macro-scale amounts of matter and energy can effectively just *vanish*, giving entropy the middle finder... and it just-happening to happen right after time travel? Woo-ee! The implications on probability.... that seems like it'd require an active force or several... ! Well, like I say, that boggles my mind!

[Crossroads Inc.]

Long ago I wrote up a rather detailed list of changes to history to create a world in which Russia became a constitutional Monarchy, and the Soviet Union never existed... Now, I am pretty sure that with such a change, 90% of anyone was born from 1930 and after that would never exist. But hey, oh well, new stuff will happen.

Sounds pretty cool, and yea, you'd have a different set of people! But handwaving for familiarity reasons and to make it more enjoyable is fun.

Nope, nothing of the sort. No "handwaving" to make things familiar. I didn't really speculate too much beyond the year 1940 because to be blunt, there is no way of knowing how thing could have progressed, only making guesses about certain things that would NOT happen.
No Cold War, No "Red Menace" no "Cultural revolution" in china, or purging of 1000's of years of history in more than a dozen countries across the planet... I'm sure you can extrapolate further on how far things would be different...


That said...
i find it amusing... and once more a sign of the nature of this Forum... That the argument as a whole has become as convoluted and "science-ey" as it is discussing collapsing wave space and chaos functions...
I do find the discussion of weather to be interesting... One would imagine it would be rather independent of the whims of men... If industrial changes of a sufficient nature were made it could conceivably change somewhat. The notion that a Hurricane ends up hitting a few meters in one direction instead of another is one that I could certainly see.

I will offer that I have very little in the way of "actual" scientific knowledge for the following thoughts...
But I do wonder if perhaps some aren't over thinking things a little bit? The discussion of changes made via nature, and the MASSIVELY annoying butterflies which seem hell bent on disrupting things... Well, aren't the only changes one can make to history, basically done to HUMAN history? I mean no matter who many times you re run the clock as it were... there is no reason for a butterfly to flap ANY differently unless an outside force acts upon it, IE, a Human.

I mean, the discussion itself.. Is it most academic currently? Something just along the lines of "Well IF it DID flap differently... What would happen?"

[Q99]

Nope, nothing of the sort. No "handwaving" to make things familiar. I didn't really speculate too much beyond the year 1940 because to be blunt, there is no way of knowing how thing could have progressed, only making guesses about certain things that would NOT happen.
No Cold War, No "Red Menace" no "Cultural revolution" in china, or purging of 1000's of years of history in more than a dozen countries across the planet... I'm sure you can extrapolate further on how far things would be different...

*Nods*

I do find the discussion of weather to be interesting... One would imagine it would be rather independent of the whims of men... If industrial changes of a sufficient nature were made it could conceivably change somewhat. The notion that a Hurricane ends up hitting a few meters in one direction instead of another is one that I could certainly see.

I will offer that I have very little in the way of "actual" scientific knowledge for the following thoughts...
But I do wonder if perhaps some aren't over thinking things a little bit? The discussion of changes made via nature, and the MASSIVELY annoying butterflies which seem hell bent on disrupting things... Well, aren't the only changes one can make to history, basically done to HUMAN history? I mean no matter who many times you re run the clock as it were... there is no reason for a butterfly to flap ANY differently unless an outside force acts upon it, IE, a Human.

I mean, the discussion itself.. Is it most academic currently? Something just along the lines of "Well IF it DID flap differently... What would happen?"

Really, any temporal change falls into that. A human's gonna do what it's gonna do, and there is no 'different' sans time travel.


And most of these things would apply if we time traveled a butterfly back as well! Or, well, practically anything.

Transporting a sterile grain of sand back would have an effect... eventually.... but as it lacks some of the large and obvious change mechanisms that even a Butterfly has, it'd be a total crapshoot to when a noticeable change would be affected by such a small difference.

[Tribble]

DBZ of all things has a pretty good time travel story during the Cell Saga. It follows the alternate universe theory, where every trip to the past results in a new universe being created while the original timeline remains intact. What's notable is that each trip to the past causes big changes and there appears to be at least 5 different timelines at play:

The "original" timeline, where time travel was not involved.
The "main" timeline that both Cell and Trunks travelled to. This is the timeline that the viewers are following.
Trunk's future timeline.
Cell's future timeline.
A timeline where Trunks travelled to the past, but Cell didn't.

[Crossroads Inc.]

Well,one of the things you usually don't have to deal about with the "multi universe timeline" thing.. Is that normally, the other timelines don't come back to bite you... That was something about DBZ that DIDN'T make sense, is just how the changes to the time line in Universe A some how caused Universe B to get screwed over... But.. Eh.. DBZ you know, so I don't think much about it.

[Q99]

A change in a timeline only caused trouble in other ones with the newly-created one in turn sent something back, I thought? Which is fine. It's been awhile since I've watched the non-abridged version so I could be wrong.

Even if Trunks prevents the bad timeline by saving Goku, on his return to the bad timeline he still has to beat the duo himself, after all. No characters just fading out.

DBZ of all things has a pretty good time travel story during the Cell Saga. It follows the alternate universe theory, where every trip to the past results in a new universe being created while the original timeline remains intact. What's notable is that each trip to the past causes big changes and there appears to be at least 5 different timelines at play:

The "original" timeline, where time travel was not involved.
The "main" timeline that both Cell and Trunks travelled to. This is the timeline that the viewers are following.
Trunk's future timeline.
Cell's future timeline.
A timeline where Trunks travelled to the past, but Cell didn't.

Oh yes, one wouldn't expect good time travel in a show like DBZ, but I think it's one of the best portrayals of that model in pop culture- probably the most popular.

It's interesting that in Cell's timeline, Trunks (and Cell, not that anyone knew about him) just... vanished from history.

[Tribble]

A change in a timeline only caused trouble in other ones with the newly-created one in turn sent something back, I thought? Which is fine. It's been awhile since I've watched the non-abridged version so I could be wrong.

Even if Trunks prevents the bad timeline by saving Goku, on his return to the bad timeline he still has to beat the duo himself, after all. No characters just fading out.

That's right. The rules of DBZ time travel seem to be:

a) every instance of time travel creates an alternate timeline
b) every instance of time travel also alters the alternate timeline so that it is impossible to have the original chain of events occur in the exact same way as the original timeline
c) no paradoxes are created, since a time travel is not technically travelling to their own past
d) altering one universe's past does not affect another
e) a time traveller going back into the future will go back into his timeline rather than the alternate universe that he created via time travel

Basically Trunk's couldn't effect his past, but he could effect his future with whatever he brought back with him. In his case, it was a big powerup that let him curbstomp his timeline's androids and Cell.

Oh yes, one wouldn't expect good time travel in a show like DBZ, but I think it's one of the best portrayals of that model in pop culture- probably the most popular.

Ya, I was actually kind of surprised how good the time travel story was, which is why I thought I'd mention it. Of course, we'll never know how much of it was Toriyama's actual intent vs him just forgetting parts of the story as he went along (for those not in the know Toriyama is notorious for this) but it turned out well

It's interesting that in Cell's timeline, Trunks (and Cell, not that anyone knew about him) just... vanished from history.

Ya, that timeline is perhaps the worst, since everyone apart from Bulma is gone... good news is that Babidi would never have the ability to unleash Majin Buu and Frieza would never be resurrected, so I suppose there's at least that.

What's also interesting is that in Cell's timeline Trunks had apparently already time travelled at least once (since Cell mentioned that his Trunks had been responsible for killing Frieza rather than Goku), and he had figured out a way to beat the androids, but it's clear that he had not done so via powerup since Cell was able to kill him with ease. We'll never know for sure what went on though fan speculation is that he figured out how to deactivate the androids via remote rather than fighting them.

[Q99]

That's right. The rules of DBZ time travel seem to be:

a) every instance of time travel creates an alternate timeline
b) every instance of time travel also alters the alternate timeline so that it is impossible to have the original chain of events occur in the exact same way as the original timeline
c) no paradoxes are created, since a time travel is not technically travelling to their own past
d) altering one universe's past does not affect another
e) a time traveller going back into the future will go back into his timeline rather than the alternate universe that he created via time travel

Basically Trunk's couldn't effect his past, but he could effect his future with whatever he brought back with him. In his case, it was a big powerup that let him curbstomp his timeline's androids and Cell.

Yea, that and the satisfaction of making a 'good timeline'.

That's how one does timetravel!

Ya, I was actually kind of surprised how good the time travel story was, which is why I thought I'd mention it. Of course, we'll never know how much of it was Toriyama's actual intent vs him just forgetting parts of the story as he went along (for those not in the know Toriyama is notorious for this) but it turned out well

Heh, that'd be ironic, but it works in the end.

Ya, that timeline is perhaps the worst, since everyone apart from Bulma is gone... good news is that Babidi would never have the ability to unleash Majin Buu and Frieza would never be resurrected, so I suppose there's at least that.

No defenders, but no threats anyway, so kinda a wash.

Hm, I wonder what happened to Babidi in that timeline... I mean, it would've happened way before Trunks was old enough to time travel, so I wonder if Gohan or maybe even the Androids killed him before he was able to unleash anything (or could've just the Supreme Kai came up with a plan that worked better).

What's also interesting is that in Cell's timeline Trunks had apparently already time travelled at least once (since Cell mentioned that his Trunks had been responsible for killing Frieza rather than Goku), and he had figured out a way to beat the androids, but it's clear that he had not done so via powerup since Cell was able to kill him with ease. We'll never know for sure what went on though fan speculation is that he figured out how to deactivate the androids via remote rather than fighting them.

Even Imperfect Cell's stronger than the Androids, and he got Trunks by surprise. Once he got a little drain going, what would be fairly even power levels can rapidly go to.... well, what we saw. So I think that Trunks likely powered up some.