A question about time travel

[GMMichael]

Well, the thing is, in MWI... there's no such thing as a random event. Randomness is only a perception from the point of view of a creature with limited perception of the whole. . .

So, in science fiction, there's no such thing as "breaking the laws of physics". We are positing that time travel is possible - it is therefore within the laws of physics, and not breaking them. In the MWI, everything that is possible happens in some world (and perhaps in many of them).

I thought the suggestion was that time travel is not possible, but it would seem possible if you traveled to another world that looked...historical.
My above ideas stemmed from "everything that is possible," but by your description of sci-fi MWI, anything happens regardless of how possible it is.

By the way, I have yet to experience a jar of Vegemite, so for all I know it doesn't exist as anything more than an odd comment that appeared through a wormhole spoken by someone in a far-off galaxy.

 

[Umbran]

I thought the suggestion was that time travel is not possible, but it would seem possible if you traveled to another world that looked...historical.
My above ideas stemmed from "everything that is possible," but by your description of sci-fi MWI, anything happens regardless of how possible it is.

No. I guess... how much do you know about quantum mechanics?

Schrodinger's equation gives you what we call a quantum wavefunction. From it, we can determine the probability that we will find a quantum system in a particular state. There are states that are strictly impossible (though, there are fewer of those than you might think), and there is zero possibility of finding the system in that state. Other states have varying degrees of possibility.

When we actually take a measurement of the system, we find it in only one state. The transition - from many possible states to one actual state - bothered many in the early days of quantum mechanics. The idea that there was something not strictly determined by physical laws left them... uncomfortable.

The MWI is an answer to that. Strictly speaking, in the MWI, there is no transition. There is no collapse from probability to reality - there's just many realities.

Thus, all possible things happen. Things that are strictly impossible still don't happen.

The point is that, if what we expect time travel (going back in your own timeline) is strictly prohibited by physics, jumping to a different member of the MWI ensemble of universes may still be possible. And the "time" of you landing there would seem to be arbitrary.

By the way, I have yet to experience a jar of Vegemite, so for all I know it doesn't exist as anything more than an odd comment that appeared through a wormhole spoken by someone in a far-off galaxy.

I have been in the presence of Vegemite. You may consider it as real as you consider me, for whatever that might be worth.

 

[MarkB]

So, in a MWI setting with access to time travel, if you are even seriously considering going back and changing the past, that would mean that there are already parallel worlds out there in which you had followed through on that decision, and gone back and changed the past - a whole infinite variety of them in which every possible outcome of your interference had played out.

In which case, you could decide not to bother going back, and instead just step over to the present-day of one of those timelines in which your actions had had your desired effect.

 

[Richards]

I remember reading a short story by Larry Niven in which, shortly after the MWI theory was proven to be true, there was a sudden wave of suicides. People realized that, if anything that can happen does in fact happen in an alternate timeline somewhere, then killing yourself is no big deal - there's an infinite number of versions of you where you didn't kill yourself. And if one universe is the one where you kill yourself right now, why not make it be this universe?

Johnathan

 

[Umbran]

So, in a MWI setting with access to time travel, if you are even seriously considering going back and changing the past, that would mean that there are already parallel worlds out there in which you had followed through on that decision, and gone back and changed the past - a whole infinite variety of them in which every possible outcome of your interference had played out.

Yep. And in the version of time travel where you must jump to a parallel world.. the fact that while you may make the world better in so doing, it isn't your world. You have to hope that your world of origin is one in which an alternate you jumps in and does the work for you.

I remember reading a short story by Larry Niven in which, shortly after the MWI theory was proven to be true, there was a sudden wave of suicides.

Yeah, I vaguely recall that one. The fact of the matter is that MWI renders the universe (wit its entire ensemble or parralels) to be deterministic. And deterministic worlds are... kinda nihilistic.

 

[MarkB]

I remember reading a short story by Larry Niven in which, shortly after the MWI theory was proven to be true, there was a sudden wave of suicides. People realized that, if anything that can happen does in fact happen in an alternate timeline somewhere, then killing yourself is no big deal - there's an infinite number of versions of you where you didn't kill yourself. And if one universe is the one where you kill yourself right now, why not make it be this universe?

Johnathan

I recall that one too. There was travel and trade between parallel worlds, and one of the issues for the pilots who made those journeys was a phenomenon called "the broadening of the bands" - when you visited another world and then went to jump back to your own world, there wasn't just one world to jump back to - there was an ever-multiplying number of versions of 'your' world branching out from the moment you left it. Which one do you go back to?

And part of the point wasn't that the whole concept drove people to suicide - it was that people idly toy with the idea of suicide on many occasions, and the universe the story took place in just happened to be one of the ones down that unlikely timeline in which everyone who had contemplated suicide had gone through with it.

 

[aramis erak]

I thought the suggestion was that time travel is not possible, but it would seem possible if you traveled to another world that looked...historical.
My above ideas stemmed from "everything that is possible," but by your description of sci-fi MWI, anything happens regardless of how possible it is.

By the way, I have yet to experience a jar of Vegemite, so for all I know it doesn't exist as anything more than an odd comment that appeared through a wormhole spoken by someone in a far-off galaxy.

Many Worlds doesn't allow/require/benefit from time travel.

More simply, in the Many Worlds Interpretation, Anything that by physical laws could happen will happen; each possible difference is a separate timeline.

And each possible timeline already exists (otherwise you're creating universes by the plank time).
Any that can't exist simply won't exist. All that can already exist.

 

[pming]

Hiya!

I didn't read the whole thread, so I'll just say my peace and how I handled Time Travel in a SUPERS! game I run every now and then.

Time Travel involves two possible outcomes of any particular event that the PC's become involved in. They are "Eventualities" and "Impossibilities". It takes some copious amount of note taking when the PC's are "in a different time", but it's worth it.

Basically, if the PC's go back in time to, say, stop a car from crashing into a building for some reason...and they Succeed: Then that even was an "Eventuality". If it was allowed to happen, then EVENTUALLY the time would turn out what the PC's experienced in their 'original timeline'. But...if they Fail...then it is an "Impossibility". This means that no matter WHAT the PC's do after failing to stop it, including trying to go back in time to try again...they WILL FAIL. There is absolutely NOTHING that can stop it (and I'm the GM, so I just make sure it happens).

For example, the PC tries to use a "Storm Powers" to use a strong gust of wind to slow the car to a near stop as it gently bumps into the front door of the building. Yay! The PC's succeeded! That event was at the "Eventuality" stage in the timeline (if the PC's weren't there, it would happen). Crisis averted and when they go back to their own time, all is good...or at least not the way it was. BUT... Lets say the PC uses his Storm Power to use a strong gust of wind to slow the car to a near stop...but rolls badly and fails. Well, that is now an "Impossibility". No matter WHAT they do, when they get back to their 'timeline', whatever event occurred due to the crash into the building DID occur. The PC's can go back over and over, and SOMETHING would always cause the building to 'collapse'. The car hits a power pole which falls onto the building lighting it on fire...or the car causes a bus to swerve and run into the building, or the car they thought was the one wasn't, and 30 seconds later the real car runs into it, etc, etc.

Anyway, that's how I managed to overcome the "problem" of Paradoxes and such. There are no such thing. If something would cause a Paradox...then it is already an Impossibility. You can't go back in time to prevent the experiment that gave you your time traveling powers, for example.

Maybe that will help with the OP, maybe not. Hope it does.

^_^

Paul L. Ming

 

[Umbran]

Many Worlds doesn't allow/require/benefit from time travel.

Correct. MWI works just fine if time travel is not possible. We are merely discussing the characteristics of time travel under the MWI.

And each possible timeline already exists (otherwise you're creating universes by the plank time).
Any that can't exist simply won't exist. All that can already exist.

And, it is that very last, "All that can exist already exist," which is a little strange, but fairly accurate.

The MWI leans strongly into the idea that the experience of the passage of time is an illusion of our perspective, and the Einsteinian idea that time is just another dimension equivalent to the physical ones we are used to. The MWI is thoroughly deterministic - the end state is fully determined by the starting conditions and the laws of physics. Everything you might try to do to change that is, by definition, determined by those laws, and is part of the ensemble.

Which means that free will is also an illusion in MWI. Which is why it is kinda nihilistic.

 

[Nytmare]

So, in a MWI setting with access to time travel, if you are even seriously considering going back and changing the past, that would mean that there are already parallel worlds out there in which you had followed through on that decision, and gone back and changed the past - a whole infinite variety of them in which every possible outcome of your interference had played out.

In which case, you could decide not to bother going back, and instead just step over to the present-day of one of those timelines in which your actions had had your desired effect.

Well there is no changing the past unless you invent an event that "broke" the rules and damaged or destroyed all of the possible worlds and collapsed them down into a singularity.