## The nature of time

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frog42
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### The nature of time

For the sake of this question, I will divide myself into three people:

X = Me in the past
Y = Me in the present
Z = Me in the future

In Event-A: I send a message from Y to X. Reality splinters off and Y/Z are unaffected but X's experience changes.

After Event-A, wouldn't any message sent to post-Event-A Y eliminate the presence of Z? How could there be a Z after Event A?

The idea is that Z would have to never receive a message and would instigate any future messages to post-Event-A Y, but after Event-A, it becomes a guarantee that Y would receive any messages from the future before becoming Z.

Charlie!
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### Re: The nature of time

frog42 wrote:For the sake of this question, I will divide myself into three people:

X = Me in the past
Y = Me in the present
Z = Me in the future

In Event-A: I send a message from Y to X. Reality splinters off and Y/Z are unaffected but X's experience changes.

After Event-A, wouldn't any message sent to post-Event-A Y eliminate the presence of Z? How could there be a Z after Event A?

The idea is that Z would have to never receive a message and would instigate any future messages to post-Event-A Y, but after Event-A, it becomes a guarantee that Y would receive any messages from the future before becoming Z.

That's very confusing. But I think you're talking about paradoxes and resolutions

Yeah, an easy way to have paradoxes resolve is to think of the universe as branching upon time travel. So every possible thing would always exist and would never be eliminated from its own perspective, but it might become impossible to get from one particular present to another future.

My favorite method of resolution is actually the "single, coherent universe" one, though. It's the idea that the universe is a static 4-d object, so if you travel to the past, your actions are already predetermined and can't mess up the present. It's a bit too deterministic to be considered true, but it's definitely fun
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### Re: The nature of time

This may be what you're talking about, and as far as I know, it isn't inconsistent with any physical laws.
http://en.wikipedia.org/wiki/Novikov_se ... _principle

One of the links in the article is to a talk Novikov gave that is very helpful, but the site that was hosting it seems to not have it any longer! So.. crank up the Wayback Machine... http://web.archive.org/web/200709271732 ... ntime.html

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eSOANEM
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### Re: The nature of time

This is my personal interpretation of time travel.

In this diagram, the y is in world line A. If he sends a message to x, he cause event EA. This causes world line B to appear and diverge from world line A at the point when event EB (the message arriving) occurs. Z is then unaffected in world line A but ZB will be different because of the divergence caused by EB. For anyone in world line A it will appear as if they have always existed and are the "original" and in world line B it will appear as if they have always existed and are the original and that EB was a strange phenomenon that created world line A.

This sort of is an extension of the no privileged reference frames rule to also apply to universes. As there is no privileged universe, it is impossible for either of the world lines to say that they are the original, that they have not diverged from the original path.

In addition, any event that would normally violate causality would create a new universe and so any time travellers wouldn't be able to return home.

interestingly but slightly irrelevantly, this also provides an explanation for the paradox that if time travel is possible why have we not met any time travellers.

The answer however, requires us to be in the true original world line. Unfortunately, we cannot prove that we are the original, we can just observe that as we haven't had any time travellers, we might be in the original. We wouldn't have any way of telling if a time traveller arrived on the other side of the universe but it would still be enough to separate our world line although the new version of the milky way would probably be largely the same.

As there are no privileged world lines it would probably be better to say that instead of us having to be in the original universe that we must be in the "externally causal" universe. That is the one universe where every action is caused either by an action somewhere within itself at another point in time and where no actions in it are caused by actions in other world lines. This would not mean however, that this universe could not cause events in other world lines, on the contrary, it would have to or else they would not need to exist and could not exist unless something other than a paradoxical event can cause a new world line to be created.

Or at least, our part of the universe must be externally causal.
Last edited by eSOANEM on Fri Sep 04, 2009 2:12 pm UTC, edited 1 time in total.
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frog42
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### Re: The nature of time

I read the Novikov article. I gotta call bullshit. You can "affect" the past but not "change" it? Replacing victims of a disaster with similar corpses wouldn't change anything (or at least not the time-travel event)? Seriously? Super narrow-sighted. Being in the past, you'd use its resources (air, energy, etc.) and returning to the future, those resources would be out of the loop between your present and the past you changed. Doing it one time seems insignificant, but there's no scalability. Way too much room for Chaos.

eSOANEM, you've done a great job illustrating the majority of what I was asking, but the main part is still missing. As soon E(A) occurs, world line A should start receiving messages from "the future", as the technology exists and has been utilized. Would you suggest these messages come from a world line C? In C, assumedly E(A) occurred as in A. So would they not also have been receiving messages from the future after E(A)? Who would they have been receiving messages from?

Soralin
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### Re: The nature of time

frog42 wrote:I read the Novikov article. I gotta call bullshit. You can "affect" the past but not "change" it? Replacing victims of a disaster with similar corpses wouldn't change anything (or at least not the time-travel event)? Seriously? Super narrow-sighted. Being in the past, you'd use its resources (air, energy, etc.) and returning to the future, those resources would be out of the loop between your present and the past you changed. Doing it one time seems insignificant, but there's no scalability. Way too much room for Chaos.

Well it's not that, using the Novikov time travel rules, it's essentially that what happened is what had always happened, that there never was a previous past. You could go back in time and openly rescue a bunch of people, but it would have always been recorded in history that a bunch of time travelers came back and openly rescued those people. Even before you ever went back in time, that what the history would be, there would never have been a separate timeline or instance or anything where they weren't openly rescued by time travelers.

So using the Novikov rules, if history recorded those people as dead, and the corpses as having been retrieved, then that's the way it always was, but it's just that history doesn't have complete knowledge. It's not that you went back in time and replaced the corpses that were found with fakes, it's that they were always fakes that had been replaced by time travelers, no one ever examined the real corpses, because that's the way it has always been, and it's only our lack of knowledge of history that prevents us from knowing this.

As for why they would be replacing the bodies with fakes in the first place, that usually makes no sense at all, other then to try and fit their actions into what they already know had happened.

eSOANEM
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### Re: The nature of time

frog42 wrote:eSOANEM, you've done a great job illustrating the majority of what I was asking, but the main part is still missing. As soon E(A) occurs, world line A should start receiving messages from "the future", as the technology exists and has been utilized. Would you suggest these messages come from a world line C? In C, assumedly E(A) occurred as in A. So would they not also have been receiving messages from the future after E(A)? Who would they have been receiving messages from?

World line B will continue to receive messages from world line A but any messages it sends back would remain in the same universe as the messages would not violate causality and could arrive in the same universe from the past with no horrible, universe destroying paradoxes.

World line A is unchanged as it is simply sending out a message that in its world line can receive. EA would not cause any splits in world line A after creating world line B.

The only situation I can see creating world line C is if World line B was sending messages forwards in time (to try and create a dialogue with world line A) and these messages arrived whilst world line A was still transmitting. In this case, a world line C may be created for the messages from B to arrive in that diverges from world line B at the point when the messages from world line B to its own future would start to be received. In this world line C the messages from world line A would have stopped at the exact moment that the messages from world line B's past appear.

I hope that helps, I'm not entirely sure I understood your question.
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frog42
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### Re: The nature of time

If you found out the Novikov reality was correct, it'd put a significant damper on your desire to time travel.

We're still not seeing quite eye-to-eye on this. I'm not talking about messages being sent forward in time, only back.

World A sends to World B in E(A).

World A sees no results, but is able to confirm the message was received by World B and that World B will now change.

Now possessing the technology, World A waits an hour and sends a message back 55 minutes. Who would receive that message?

eSOANEM
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### Re: The nature of time

ah, OK, that would create a third world line. Otherwise it would be possible to send a message back 5 minutes, they then wait a minute and send a message back 5 minutes and so the original universe could receive an answer before the question thus violating causality.

If the message would have arrived in the right order, I'm not sure what would happen. Of course, you'd be eliminating the whole benefit of time travel comms but it might mean that a third world line would not be created.
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qetzal
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### Re: The nature of time

eSOANEM wrote:interestingly but slightly irrelevantly, this also provides an explanation for the paradox that if time travel is possible why have we not met any time travellers.

The answer however, requires us to be in the true original world line. Unfortunately, we cannot prove that we are the original, we can just observe that as we haven't had any time travellers, we might be in the original.

I don't see how that follows. If backwards time travel is what splits world lines, and if we haven't had any time travellers so far, we must be in the original world line. (If other things can split world lines, then I don't see how one world line can be designated the 'original.')

eSOANEM
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### Re: The nature of time

you are correct that if the entire universe had no time travellers then (assuming only backwards time travel can split universes) then we must be the original universe.

Of course, if there is a time traveller beyond the observable universe then to us it may seem that we are the original universe but because of the uncertainty over whether or not there is a time traveller who just has not been observed, we cannot be certain that we are the original universe.

Although I also like to make a sort of illegitimate child of this and the many worlds interpretation leading to time travel causing separate strands each made up of different universes created by the many worlds interpretation.

In this case, the total world line system would look like a fraying rope with the number of threads growing exponentially as you get further from the beginning.
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douglasm
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### Re: The nature of time

frog42 wrote:If you found out the Novikov reality was correct, it'd put a significant damper on your desire to time travel.

In some ways, maybe, but time travel would still be extremely useful. For example, any problem that can conceivably be solved by guess and check can be solved by a single guess and check with the use of time travel. Simply set up a device that takes a guess as its input, checks it, outputs the original guess if it is correct, and outputs a different guess if incorrect. Design the guess generation mechanism so that it will in theory cover the entire range of possible guesses. Take the output, send it through a time machine, and hook it up to the input. Turn the machine on. The only* consistent scenario is that a correct guess will be spontaneously generated instantly.

Now apply this to the stock market, with the problem being "what is one stock that will at least double its value tomorrow?"

* It might be theoretically possible for the circuit to instead assume some state that does not readily correspond to a specific guess, for example if a voltage difference is halfway between the values for 1 and 0, but any such state would be so extremely unstable that it would never occur unless there is no correct guess.

derick
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### Re: The nature of time

Charlie! wrote:
frog42 wrote:For the sake of this question, I will divide myself into three people:

X = Me in the past
Y = Me in the present
Z = Me in the future

In Event-A: I send a message from Y to X. Reality splinters off and Y/Z are unaffected but X's experience changes.

After Event-A, wouldn't any message sent to post-Event-A Y eliminate the presence of Z? How could there be a Z after Event A?

The idea is that Z would have to never receive a message and would instigate any future messages to post-Event-A Y, but after Event-A, it becomes a guarantee that Y would receive any messages from the future before becoming Z.

That's very confusing. But I think you're talking about paradoxes and resolutions

Yeah, an easy way to have paradoxes resolve is to think of the universe as branching upon time travel. So every possible thing would always exist and would never be eliminated from its own perspective, but it might become impossible to get from one particular present to another future.

My favorite method of resolution is actually the "single, coherent universe" one, though. It's the idea that the universe is a static 4-d object, so if you travel to the past, your actions are already predetermined and can't mess up the present. It's a bit too deterministic to be considered true, but it's definitely fun

It seems that the only resolution of free will and an objective Aristotelian/Newtonian external reality is that this static 4D object contains an astronomical, yet finite, number of alternative paths through time.

gmalivuk
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### Re: The nature of time

derick wrote:It seems that the only resolution of free will and an objective Aristotelian/Newtonian external reality is that this static 4D object contains an astronomical, yet finite, number of alternative paths through time.

And?
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derick
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### Re: The nature of time

gmalivuk wrote:
derick wrote:It seems that the only resolution of free will and an objective Aristotelian/Newtonian external reality is that this static 4D object contains an astronomical, yet finite, number of alternative paths through time.

And?

And what? Are you implying this is obvious and not worth saying in order to discourage me (i.e. "no one cares gtfo"), or is there something I should be getting at that I'm not? Do you think I'm implying something this doesn't actually link to?

gmalivuk
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### Re: The nature of time

More that it seemed you were saying that as an argument against the possibility, and I was wondering what, if anything, would suggest against such a huge number of branches.
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derick
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### Re: The nature of time

gmalivuk wrote:More that it seemed you were saying that as an argument against the possibility, and I was wondering what, if anything, would suggest against such a huge number of branches.

Ah, now I see. I gave you the wrong impression. Indeed there is no "and"! If anything, I feel this is a great defense of the compatibility of those views. I don't agree with the association between free will and supernatrualism or indeterminism. The number of possible "instances" would be simply massive though. Much, much higher than the number of subatomic particles in the universe. It's slightly beautiful to think of.

I've read a lot about cosmology and I like coming to amateur guesses about how it relates to free will and paradoxes people talk about all the time. I've found myself coming to lots of "conclusions;" I'm sure they're all wrong or at least incomplete and inexact by virtue of being uninformed, as I'm by no means a physicist, but I am confident in my conclusion that the universe makes a lot more "sense" and things can be sorted out a lot better than people think.

I think one mistake people come to is taking "conceptually/hypothetically unlimited" or "astronomical beyond anything we can conceive" to mean "infinite," and another is taking things we don't have the tools to figure out yet and saying "God did it." Both of these lead one to be tempted by either supernaturalism or Kantian skepticism/indeterminism/"nothing is anything and we can't know."

frog42
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### Re: The nature of time

OK, So we're beginning to see things on the same level.

In my last scenario, you said we would have created a World Line C when we waited 1 hour and sent a message back 55 minutes. Essentially, this means World Line A can NEVER receive messages from the future... They have invented a time machine that sends messages to the past, but every message simply ends up in an off-shoot reality.

In this view of reality, you haven't really created a time machine, just a way to send messages to otherwise identical parallel universes that simply started a bit later than yours.

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### Re: The nature of time

yes. That is my view of absolute backwards "time travel". It only exists as a one way ticket to a parallel universe it creates or as a diagonal jump into another world line.
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