Consistent time travel, (ab)using the power

[jseah]

I was contemplating what could be done with time travel and would like to ask the playground for ideas.

Specifically this scenario:
You gain a superpower that allows you to specify a point in time in the future or past within 1 week of the current time you are in now. You instantly travel to that time, as well as any small objects you are holding (+clothes) but not large suitcases or bags.

This is time travel of the consistent type. Aka, the most confusing to use. When you time travel backwards, there will exist two versions of you. Changing the past is not possible, because if you did change the past, it would not have been what it was before you traveled. (inconsistent time loops don't occur)

EDIT: from post #40:

<..> I'm not asking for answers to questions that arise from this. Nor am I even asking for the questions themselves.

I am just looking for more complex applications of the time travel power. More complex than those I just put up that is.

While I do acknowledge that many questions and problems are put up by my definitions of how this time travel superpower works, I am not looking for them.
I am aware of the implications on determinism and have thought about the sorts of experiments you can run with this. (one of them is to determine if there is a global hidden variable behind quantum mechanics. The Bell Test Experiments rule out local hidden variables, but not global ones)

There are two major assumptions with the existence of this time travel power.

1. The universe is deterministic, at least on the quantum level
2. In any time travel situation, paradoxes (inconsistent loops) never occur. A consistent time loop always exists regardless of the setup.

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So, what can you do with this? I have thought of a few things:

Locking a key into its own box
You have a box and a key that locks it.
A future you arrives with key in hand and places the future key into the box. The present you locks the box with the present key then travels back into the past with the present key to be your future self.
Now, your 'future' self who is the only copy left is holding a locked box with the key to that lock inside the box.

Taking the key out of the box is similarly possible.

Time loop logic

The one-atom key
You have a locked box. You have lost the key and don't know where it is.
A future you arrives from the future with a key and unlocks the box.

In doing so, the key breaks and you repair it at a locksmith who reforges the metal into an identical key (to the eye at least) and finds he has to add a tiny amount.
The present you takes the reforged key and goes back into the past to be your future self.

The key in this loop is made of copies of the same few atoms (not enough by themselves to make a key) that the locksmith used to repair the key.

Future preemption
A random gunman on the run from the police holds you at gunpoint. Before he can pull the trigger, a future you appears with his gun and shoots him.
The present you then steals the gunman's gun and goes back in time to be the future you.

Future knowledge
You don't know you have this superpower. A future you appears and teaches you how to time travel so you can use it to go back into the past to teach yourself.

A more mundane version of this is obtaining future stock market prices 1 day ahead and using that to make insane amounts of money.

Or in the case of the one-atom key, your future self could find the key for you, give it to you and tell you where it was.

[DoctorGlock]

Have you by any chance played continuum? Because this is making my PTSD from that flare up.

[navar100]

http://www.imdb.com/title/tt0167720/

[The Reverend]

Step one. Travel one week forward every day to read the news, observe stock prices, and copy lotto numbers.

Step two. Effectively become god.

[Ravens_cry]

"Consistent" time travel gives me more headaches than a basket of weasels with tap dancing shoes inside a a reciprocating steam engine boiler.
Sure, when it only involves things like billiard ball collisions it can appear plausible, but when things get more complex, like with human beings, it gets patently absurd if we are allowed even a modicum of free will.

[GungHo]

Step one. Travel one week forward every day to read the news, observe stock prices, and copy lotto numbers.

Avoid flying DeLoreans.

[Blacky the Blackball]

Have you by any chance played continuum? Because this is making my PTSD from that flare up.

I (eventually) managed to get my hands on a copy of that game last week, and I'm still reading through it.

It seems to assume that the players and GM can think in four dimensions...

[DoctorGlock]

I (eventually) managed to get my hands on a copy of that game last week, and I'm still reading through it.

It seems to assume that the players and GM can think in four dimensions...

Eh, understanding the time flow isn't that hard, you really just need to remember to keep causality intact. The annoying part is writing down every little detail because if you forgot anything you frag yourself into last century. And my GM remembered and wrote down everything. Still, it was good practice for keeping my DM on track when I played a time traveling wizard in 3.5.

Still... so much paperwork...

Also yeah, that book was impossible to get. And the few bits of narcissist floating around are even harder.

[Zale]

This is why I hate time travel.

And in the last two, wouldn't you end up with an infinite number of yourselves having to go back forever?

[Radar]

This is why I hate time travel.

And in the last two, wouldn't you end up with an infinite number of yourselves having to go back forever?

No, you loop only once.

Now if we are talking about fully consistant time travel, then you cannot possibly cause paradox, since every time travel is already accounted for (as in 12 Apes for example). You can use it to your advantage:

Precognitive harm immunity
Travel a week into the future and look for future you. If he's alive and unharmed, then nothing you'll do in the upcoming week will cause you significant harm. You can do any crazy stunt without winning Darwin Award!

[jseah]

This is why I hate time travel.

And in the last two, wouldn't you end up with an infinite number of yourselves having to go back forever?

No.

In all the examples, the present you becomes the future you by going back in time.

By your own subjective experience of time, you lived through the same period of time twice.

Step one. Travel one week forward every day to read the news, observe stock prices, and copy lotto numbers.

Step two. Effectively become god.

This is just part of future knowledge.

You can do this too:
Observe stock market. Find a stock that has risen by an acceptable amount since yesterday.
Log into your account and "find" that you have 100 000 shares of that stock. Sell them all.
You time travel back in time to yesterday and buy those 100 000 shares. Time travel back since waiting is boring.

Now you just bought the shares you sold after you sold them. At least to you. To the stock market, you did it the normal way.

Note that this works with apples / physical objects as well.

"Consistent" time travel gives me more headaches than a basket of weasels with tap dancing shoes inside a a reciprocating steam engine boiler.
Sure, when it only involves things like billiard ball collisions it can appear plausible, but when things get more complex, like with human beings, it gets patently absurd if we are allowed even a modicum of free will.

Why not? Inconsistent loops don't happen. That's all.

Consistent loops do not rule out free will.

Free will + circumstance = action

Time loops are part of the circumstance portion. The only time loops that are consistent are those that, after you add free will, result in an action that you do time travel.

Free will not compromised.

[Blacky the Blackball]

No, you loop only once.

Now if we are talking about fully consistant time travel, then you cannot possibly cause paradox, since every time travel is already accounted for (as in 12 Apes for example).

The way the Continuum game works, you can cause apparent paradox, but the conflict in your memories of what happened cause you "frag" until the paradox is resolved (usually by someone - possibly you - faking things so that the apparent paradox turns out not to have been one after all).

Precognitive harm immunity
Travel a week into the future and look for future you. If he's alive and unharmed, then nothing you'll do in the upcoming week will cause you significant harm. You can do any crazy stunt without winning Darwin Award!

Until your enemy kills you and then has someone impersonate you in order to fool your past self who travelled forward into thinking you'd still be alive when you actually wouldn't...

[Radar]

Until your enemy kills you and then has someone impersonate you in order to fool your past self who travelled forward into thinking you'd still be alive when you actually wouldn't...

It's easy to counter: the best part of using secret passwords while contacting yourself is, that you never have to share it with anyone. If you contact your future self, you don't even need to have a set password - you can make one up right there and the future you should know it for obvious reasons.

Yes, the system isn't ideal, but it gives you a serious advantage.

[kieza]

The bit I always liked about Continuum was the slipspan: need a screwdriver? It's in the first place you look. Need a getaway car? The first car you pass on the street has keys in the first place you look. You just have to go back sometime in the future when you have free time in order to set things up, and then return everything if you stole it from somewhere else. You can even wait a couple of months until errand day: go grocery shopping, fix leaky faucet, steal car for past self, mow lawn, pick up stolen car from past self and return to two seconds after you stole it, do dishes.

It even works for skills: if you need to know how to steal a getaway car, you just span to some timeframe where you're safe from interruption, spend a month practicing, and then span back to the moment when you needed to hotwire it.

It does require a little four-dimensional thinking, though. The one time I got a group to play it, they gave up around the time that they fragged themselves by accidentally killing someone before he could span back and frag them himself.

[Fortuna]

The bit I always liked about Continuum was the slipspan: need a screwdriver? It's in the first place you look. Need a getaway car? The first car you pass on the street has keys in the first place you look. You just have to go back sometime in the future when you have free time in order to set things up, and then return everything if you stole it from somewhere else. You can even wait a couple of months until errand day: go grocery shopping, fix leaky faucet, steal car for past self, mow lawn, pick up stolen car from past self and return to two seconds after you stole it, do dishes.

It even works for skills: if you need to know how to steal a getaway car, you just span to some timeframe where you're safe from interruption, spend a month practicing, and then span back to the moment when you needed to hotwire it.

It does require a little four-dimensional thinking, though. The one time I got a group to play it, they gave up around the time that they fragged themselves by accidentally killing someone before he could span back and frag them himself.

Sounds like Bill and Ted: The Game. WANT!

[Infernalbargain]

Well consistent time travel requires enforcing smooth temporal boundary conditions. With this in mind, none of the scenarios presented thus far are compatible with any kind of consistent time travel.

[jseah]

Well consistent time travel requires enforcing smooth temporal boundary conditions. With this in mind, none of the scenarios presented thus far are compatible with any kind of consistent time travel.

Do you mind pointing out just how it breaks down?

What do you mean by smooth temporal boundary conditions?

Precognitive harm immunity
Travel a week into the future and look for future you. If he's alive and unharmed, then nothing you'll do in the upcoming week will cause you significant harm. You can do any crazy stunt without winning Darwin Award!

Well, you don't have to look, since you'll remember to be there.

The problem with this one is that by seeing your future self alive and healthy, does not garuantee that risky actions aren't risky.

All it does is say, "you are alive and healthy", and nothing about how you get there.

The trip you planned to go bungee jumping might be canceled. The plane you planned to skydive from has the pilot on break. etc.

Now, if your future self says "oh sure, the bungee jump was hilarious and awesome at the same time!", then you know that it will be safe.
Unless your future self was having a joke on you and you didn't really go after all. Or that it was terrifying and not at all fun. =P

Spoiler

Show

You are trying to break into a military base with nothing but the clothes on your back. Mission is to steal the commander's bathroom keys. You don't know anything about the layout.

Future self appears and gives you a military grade laser pointer and a complete map of the base stitched from copies of various fire escape plans.

You get told to climb the electric fence. Which has been deactivated by a future self in the base. The alarm this would have caused is also deactivated by another future self. The guards watching the cameras are sleeping after a future you slipped them a shot of their own sleeping gas.

The landmine goes off in the distance, even if its currently in your hands. As the guards investigate, you climb over the fence. The guard in the watchtower isn't there as he failed to turn up for duty (legit, your future self knows this because he was told when he was you) and the person in charge of the log book can't find it (it turns up under the guy's bed later)

You follow the arrows on the map and communicate go/stop using the laser pointer with a future self camping out on the roof to avoid the guards investigating the mine.

Once inside, you deactivate the electric fence, alarm, wipe the logs and erase tracks. As an afterthought, the bathroom keys turn up in the commander's wine cupboard, forgotten under an old report, and you didn't need to search for it. A set of instructions on how to use the mine is acquired, and copies of every single fire escape plan.

Once outside, you bury the mine and set it off by trailing a heavy flat tire behind you, stolen from the garbage dump. Then you go steal the log book and return it a few hours later in the guy's bunk. You get reminded by the furthest future self over a phone to go use the sleeping gas.
In a mistake, you knock yourself out and a future you turns up with an 'acquired' gas mask to rescue you. A number of other future yous also exit the base around here.

After you wake up, you go back and tell yourself the required information in the right places.

----------------------------------------------------

Perhaps I should have clarified what I was looking for.

I am trying to think of a situation where you would need to have two interlocking loops.
I don't mean things like the hostage situation x8 (8 gunmen, 8 future yous to shoot them, etc.). That's just a loop nested in itself 8 times.

Eg. a future you and a past you appear. And somehow you need the past you to do something that the future yous can't.

[hewhosaysfish]

Now, if your future self says "oh sure, the bungee jump was hilarious and awesome at the same time!", then you know that it will be safe.
Unless your future self was having a joke on you and you didn't really go after all. Or that it was terrifying and not at all fun. =P

Maybe he's only saying that to you because that's what he remembers being told when he was you and he doesn't want to "frag" himself...

[jseah]

Maybe he's only saying that to you because that's what he remembers being told when he was you and he doesn't want to "frag" himself...

'fragging' yourself doesn't apply in this particular version of time travel.

This is consistent time travel. You won't be doing anything that doesn't match what happened / will happen / is happening.

IE. your future self won't be saying that because he wants the timeline to be consistent. If he wouldn't have said it, you wouldn't have heard it said.

[Yukitsu]

The hardest thing I've ever done with consistent time travel was have my past self beat my future self without dying (in either incarnation) without meeting, and without paradox. The hardest part was that the character was a diviner.

The other thing I do, as watch closely for any sort of news of "X artifact was lost forever" through history. Because if it's going to be gone, who's to say I'm not the thief what did it? For my character, who had time travel going back significantly further, I had a pretty large backlog of old supposedly lost relics.

[NichG]

The thing to remember is that consistent time travel is itself inconsistent with a use-at-will power. That is to say, someone could try to time travel with the express purpose of creating a paradox. The important thing to get down is what sort of things happen to prevent that, because for self-consistent time travel something must prevent it. To decide this, you need some sort of principle. I'm going to propose it to be the Path of Least Resistance.

So take Postcognitive Immunity for example. You've got someone who intends to go forward a week, find themselves alive, and then do all sorts of crazy stunts that would normally get them killed using the immunity given by self-consistent time travel. The easiest answer to this situation is that they find themselves dead every single time, of a massive brain hemorrhage that occurred instantly upon their return to the present. Or even better, they find themselves missing, and when they ask why, its because they traveled forward a week and never returned. Subsequently, for whatever reason, their power will not work to travel back into that week.

Path of Least Resistance generally rules out the spontaneous creation of time-looped objects like the one-atom key. The one-atom key requires that the key be in exactly the same configuration at two points in a loop. The more mass involved in this, the more unlikely that requirement is to be met only because of thermal agitation. So the chance of discovering a one-atom key equivalent looks like exp(-10^24). Even being a bit more lenient, you're far more likely to discover a one-atom key made of adamantine in a freezer than a one-atom key made of lead during summer, because of the reduced thermal effects and wear effects making it difficult to execute the loop.

So what can you still do under Path of Least Resistance? Non-loops are okay, like going back in time to save yourself. Ostensibly though the universe has to be paid off, because you dying is more likely (less opportunity for inconsistency) than you saving yourself and both are consistent outcomes. Paying off the universe would consist of somehow making it so that a self-consistent path is more likely in the long run if you survived than if you died, so it probably involves interacting with other time travelers. If, for example, you plan to kill another time traveler who travels more often than yourself, then the universe is more likely to let you save yourself.

You can also do the trick of locking the key inside a box that it opens, but your best bet is to do that trick with someone who isn't you. The reason being, if it is you you have to wait for yourself to show up, but if its someone else you can proactively seek them out. Better yet if its someone you never met until the travel event.

[Re'ozul]

I like consistent time travel.

My favourite ways of using it:

When there is a big Lottery jackpot, stay away from your home city for the day before the Lottery Numbers are drawn as well as the day afterwards (avoid all interaction, cheap motel works, just sleep all day and night if you want or read a book).
Now drive home and see wether you claimed the price (did your future self leave you a message from the past?). If so, go back in time and claim the price avoiding yourself at the time you exist twice.

Day trading.
Rent a second flat, live two days for every one until you have enough money to stop. Though you will age twice as fast.

Yeah, standard get-rich stuff but I'd rather not temper with it too much.

[Jothki]

Consistent time travel does have its occasional disadvantages. No Time to Explain is a good example. It's not completely consistent, but close enough to show the point.

[Infernalbargain]

Do you mind pointing out just how it breaks down?

What do you mean by smooth temporal boundary conditions?

Imagine a wave function that completely describes the state of everything in the entire universe. By smooth, I mean that there are no sudden changes in it (like there is in the step function) and there are no sudden changes in its rate of change (like there is in the absolute value function). An example of a temporal boundary condition is that at 4am CDT I was asleep; basically it is an association of a state with a time.

The best way to think of a time machine is as a probability warping device. This solves a lot of the famous paradoxes such as the grandfather paradox. Since the universal wave function can collapse into any particular state upon observation, we must ask what is the probability of it collapsing into a particular state? Which is more probable, your grandson appearing out of the time machine and killing you or your time machine breaks? It takes a lot of probability warping in order for a person to travel back in time (because the wave function needs to be perturbed greatly to produce another person), thereby a lot of normally immensely improbable things would become suddenly highly probable in the presence of any time machine powerful enough to transport a person. Suffices to say that we quite frankly cannot predict what will happen. At all. And no, whatever you're thinking of will not be certain.

[Ravens_cry]

Why not? Inconsistent loops don't happen. That's all.

Consistent loops do not rule out free will.

Free will + circumstance = action

Time loops are part of the circumstance portion. The only time loops that are consistent are those that, after you add free will, result in an action that you do time travel.

Free will not compromised.

Let's say I go back in time and using period material I fashion an explosive device and I decide to set it off in a certain place at a certain time, because when I witnessed that time and place without time travel and there was no explosion.
Or even the simple task of meeting myself for the less homicidally inclined.
What's stopping me?
The "principle" says there is no paradoxes and there is only one timeline, yet it is so easy to create one in such a world as it could practically be said to be harder not to create paradoxes with time travel.

[Blacky the Blackball]

'fragging' yourself doesn't apply in this particular version of time travel.

This is consistent time travel. You won't be doing anything that doesn't match what happened / will happen / is happening.

The way Continuum works (that's the game that uses the context of frag), time travel is consistent.

It is the apparent inconsistency that causes frag - and that apparent inconsistency must be resolved (by very careful actions by yourself or another time traveller) for the frag to go away.

Any true paradox that does not get resolved will end up destroying the universe.

IE. your future self won't be saying that because he wants the timeline to be consistent. If he wouldn't have said it, you wouldn't have heard it said.

The problem comes when future self decides to say something different to what past self remembers hearing.

For consistent time travel to work as simply as you say, you have to totally deny free will to anyone - and that doesn't make for a good RPG.

The way Continuum would handle that would be that by deciding to say something different to what your past self remembers hearing, you've fragged yourself - and it's a nasty frag too because there's no easy way to resolve the apparent paradox.

To get rid of the frag, you'd have to (or preferably arrange for someone else to) find yourself after the original conversation, and then alter your memories through hypnosis or tech means.

That would resolve the apparent paradox. You actually always said the thing that your elder self decides to say, and you only remember it differently because someone altered the memories of it that your younger self had.

Of course, since you don't remember having had your memories altered, that would have to be done surreptitiously.

Plus, if other people were there and heard what your elder had actually said they would have to have their memories altered accordingly so they also remember your elder saying the same thing that you remember them saying.

Plus, if you acted on what you remember your elder saying then whoever altered your memories would have to make sure that they did it in a way that didn't stop you acting in the way you did.

[jseah]

I'm going to propose it to be the Path of Least Resistance.

The problem with this is that consistent time travel can only work in a universe that is deterministic.

Or at least deterministic in the quantum wave functions.

Determinism means that unless a future you has affected things, whatever would have happened without a future you will happen.

If you did not visit one week into the future to check yourself, it does not affect whether the bungee rope you chose would have a small nick and break when you jump with it.

Imagine a wave function that completely describes the state of everything in the entire universe. By smooth, I mean that there are no sudden changes in it (like there is in the step function) and there are no sudden changes in its rate of change (like there is in the absolute value function). An example of a temporal boundary condition is that at 4am CDT I was asleep; basically it is an association of a state with a time.

The time travel is basically a closed time-like curve. The universal wavefunction will interact with its future self when you time travel. It's not a cut/paste kind of time teleportation.
EDIT: sorry, yes, apparently I am confused. It IS time teleportation if you don't exist in all the intervening periods of time when travelling backwards.

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NichG & Infernal Bargain:
On the other hand, resolving which of the many consistent loops happen comes under quantum mechanics.

There was an interesting paper linked the wikipedia page I mentioned in the first post. That one calculated the trajectory of a billard ball through a closed time-like curve that would classically generate a paradox (knock itself out of the path leading to the wormhole)

They eventually concluded that no billard ball arrangement was not resolvable in a consistent manner by the future billard ball.
IE. there is no way to arrange things such that a paradox is inevitable. I am using this particular assumption.

Futhermore, they did a quantum sum over histories and found they could assign a probability of occurence to each individual path of the billard ball and all those that were inconsistent had a probability of 0.

And of course, if we are invoking the universal wavefunction, then in some sense, *every* single path with a non-zero probability happened. The billard ball is just entangled with its future self.

The "principle" says there is no paradoxes and there is only one timeline, yet it is so easy to create one in such a world as it could practically be said to be harder not to create paradoxes with time travel.

If you look at the billard ball example.

The billard ball is heading towards the time wormhole. If it isn't deflected, it will enter the wormhole in such a way as to knock itself off course. This is known.

If nothing comes out of the wormhole to deflect the ball, the ball will go in (and this is paradoxical already since nothing came out and something went in)
This paradox is not resolvable without invoking the future. Remember deterministic universe? (or the universal wave function interacts in a deterministic manner)
There won't be a chance deflection of the ball if there wasn't going to be one. Yes, you can use this to test if something will interrupt the time travel. Yes, this is information travelling backwards in time. Not at all surprising given we have time travel, no?

However, the authors of that paper think there is always a consistent solution and this solution involves the future billard ball.

In such a case of attempting to create a paradox, and in the case that chance events aren't going to stop you (if they were, it's not a paradox), then the only way to generate consistent loops is to have something arrive from the future that generates the consistent loop.

[NichG]

The problem with this is that consistent time travel can only work in a universe that is deterministic.

Or at least deterministic in the quantum wave functions.

Determinism means that unless a future you has affected things, whatever would have happened without a future you will happen.

I think it'd be slightly easier in a non-deterministic universe. Basically, one could imagine inconsistencies that are small enough that they can be explained away by thermal noise. For instance, lets say you have a closed space-like curve for a single fleck of dust (I always get confused - spacelike curves are the ones that lie outside of the lightcone I thought, not timelike). This particular fleck of dust happens to only have 3 atoms in it, but because of an inconsistency it comes through with one of the atoms having an extra neutron. That path would have a zero weight in a deterministic universe (and the set of paths with non-zero weight that include time travel is probably of measure zero, but I can't prove that).

Now lets add some thermal or quantum indeterminancy with an energy scale E0 (this'd be proportional to hbar but I don't think its the Planck energy, which is huge; it probably has to do with the time that the inconsistency is required to persist before it can be corrected). Now the path has a weight exp(-E/E0) where E is the mass energy of the neutron (~940MeV). Thats still vanishingly small if we compare it to say the thermal energy at room temperature (0.025 eV or so), even for a neutron, but at least its non-zero.

So, not much easier, but a little bit

[Ravens_cry]

jseah
On billiard balls:
Which is where things get silly. What stops me, who? Not me, if I have free will. Not anyone else if they have free will.
If I simply drop dead, why wasn't my body discovered?
If you want less headaches, just go for alternative timelines. Of course, now you can only change one future and not your own and if the time line is quantum brittle you can never go back to your original time line without the ability to move sideways in time, but at least you don't have to worry about the universe playing temporal billiards.

[jseah]

Part of the assumptions inherent in all this is that it is impossible to generate a situation that has NO consistent solutions.

Ravens_cry:
Your free will with and without time travel is still limited by circumstances. You can think of doing whatever you want, but whether you actually do it successfully (or at all) depends on whether you could.
You can't fly without wings. You can't cause paradoxes. They're not inherent limiters of free will.

The assumption in consistent-only time travel is that anything that would lead to inconsistency is impossible.

And chance events unconnected to the time travel aren't affected. A random meteor strike that would not happen if you never tried time travelling won't suddenly happen if you plan to create a paradox.
Unless the act of planning causes it or something arriving from the future causes it, random stuff just stays that way.

You might plan to do this basic paradox:
5 minutes from now, I will time travel from the future and tell myself a secret password. But when I actually time travel myself, I will mention a password that is different from the one I heard from my future self.

The you that arrives from the future would not simply fulfill the paradox as you plan since that would be... well, inconsistent.
The future you would be acting in such a way to cause you to act in a consistent fashion.


If you think about it, the amount of free will you have here is exactly the same as the situation of an advertisement convincing you to go buy a new pair of socks.

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That said, I am still trying to think of a pair of linked time loops that do something that can't be done with only 1 loop, however nested.

Maybe if I had two locked boxes that contain the other's key...