[Science] Time travel? Changing events?

[Nemmerle]

Originally Posted by clan.necrosect

Thanks for actually going to read about 3 body problems rather than just completely disagreeing with me for no reason what-so-ever.

Nice. Also your anology missed the point entirely.

A remaining degree of freedom DEFINES variation/randomness in both local and global systems.

Unexplained variation is just a variation that hasn't been explained yet. Even if in principle it may be impossible to explain it if you have an incomplete set of the relevant variables when you start a calculation you're going to get a remaining degree of freedom. Randomness on the other hand is something that is uncaused. To claim something's random makes a claim that in principle is untestable short of omniscience.

In any case if you want to make u-variation and randomess synonomous definitions then these new definitions don't work in the context you were using them against Afterburner's argument. There wasn't only one way things could unfold because there's unexplained variation. It's not a very solid claim.

Originally Posted by NiteStryker

How many times has that actually happened?

Considering my window is high in the air? Not many.

Originally Posted by Anlushac11

And what if the light is still there and there is no little shit with a flashlight.

Draw the curtains and see if it goes away, check that there's not someone hidding under the bed with a flashlight. Do any of the myriad things to test for actual logical solutions to the problem before you start saying it's random. And if after all that you find that it still doesn't go away, then you write a general explanation for its behaviour and file it under unexplained variations, not, 'randomness.'

[Showd0wN]

Ok unforunately you don't seem to understand how degrees of freedom work mathematically.

Unexplained variation is just a variation that hasn't been explained yet

No it's not.

if you have an incomplete set of the relevant variables when you start a calculation

No actually, even if you know everything you would still not be able to predict the variation, that's sort of the point.

I'm not trying to suggest you can't approximate these variations - hence my use of the word perturbative - simply that since it is impossible to be entirely specific about the outcomes of 3+body events and even infinitessimal changes expanded over time can be extremely important to the outcome of an event (see thought experiments similar to the "electron at the end of the universe") we are left in a position where it is impossible to construct entirely consistent histories (futures/pasts) for any 3+ body system.

I'm trying very much to keep this in the area of "no need for maths"; as I don't think it's fair to venture down that route.

[Mr. Pedantic]

Basically if you have a "2 body" problem (i.e. an interaction between 2 discrete bodies) the result can be calculated exactly.
However, for 3 bodies and beyond one has to use a perturbative approach and you are left with a "remaining degree of freedom" whereby some of the outcomes of the interaction are not well defined and could take a range of values. So here we see an actual "uncertainty" inherent even in Newtonian physics.

I don't understand. Why do you have to calculate the movement of 3 bodies like that instead of being able to model a set of differential equations on the force applied by each body varying with distance?

[Juggernut]

If time travel would've worked we would have known by now. People could time travel to our place and learn us all about it. Basically that's enough to convince me. You try to convince me that this is not okay.

[Afterburner]

Originally Posted by Juggernut

If time travel would've worked we would have known by now. People could time travel to our place and learn us all about it. Basically that's enough to convince me. You try to convince me that this is not okay.

To be fair this argument assumes all points in time coexist. We could be inhabiting the "initial" time line. If the future doesn't exist yet, than no one could have come back in time. Or we could be in a time line where some kind of temporal prime directive is in place, and is being enforced effectivly in the future. Or it could simply be that since time is simply a measurement of change that only the present exists at all, and the "past" and "future" are just alternate configurations of the particle sin the universe.

[AlDaja]

Time travel is nice and all, but other than mathematical perception of what we observe in space, paradox would limit our ability to manipulate or perceive changes to our time line. So even if future generations figure out how to manipulate this phenomenon, we’d never be aware of changes in the timeline if they tampered with past events, because from our perspective nothing has changed. Paradox would also prohibit a traveler from returning to the past for the reason already pointed out, because any alteration would change their future. I’m not certain a traveler to the past would be able to perceive the change, because if they were immune to paradox they wouldn’t have gone back in the first place having knowledge that it would alter their future as well, and maybe not for the better…which may be why no one has, or rather will. In short, paradox from a theoretical perspective makes time travel, as we know it prohibitive, as we are not immune to paradox.

[Afterburner]

Originally Posted by AlDaja

Time travel is nice and all, but other than mathematical perception of what we observe in space, paradox would limit our ability to manipulate or perceive changes to our time line. So even if future generations figure out how to manipulate this phenomenon, we’d never be aware of changes in the timeline if they tampered with past events, because from our perspective nothing has changed. Paradox would also prohibit a traveler from returning to the past for the reason already pointed out, because any alteration would change their future. I’m not certain a traveler to the past would be able to perceive the change, because if they were immune to paradox they wouldn’t have gone back in the first place having knowledge that it would alter their future as well, and maybe not for the better…which may be why no one has, or rather will. In short, paradox from a theoretical perspective makes time travel, as we know it prohibitive, as we are not immune to paradox.

Unless time is branching, and the changes create a new timeline. That eliminates all paradoxes. You kill your grandfather and the you that would have been born in that timeline no longer will be, but you still exist because your grandfather is still alive in your original timeline.

And I don't see why we wouldn't perceive changes if they occured in the here and now. Let's say a time traveling robot tries to kill you to prevent you form becoming the leader of a human resistance in the future. You bloody well know the timeline is being changed because that change is shooting at you right now.

[AlDaja]

Originally Posted by Afterburner

Unless time is branching, and the changes create a new timeline. That eliminates all paradoxes. You kill your grandfather and the you that would have been born in that timeline no longer will be, but you still exist because your grandfather is still alive in your original timeline.

Actually time is branching if we are to believe what the cosmos suggests compared against the science of the day. Paradox might be temporarily extinguished for you for one specific micro-moment during your travel back in time, but not the infinite outcome entirely. If you went back and killed your grandfather, then yes you would cease to exist in that time line you just left, altering the outcome of whatever your family line impacted on that existence and no one outside of yourself, would perceive the change. However, what you didn’t realize is that by doing so you instantaneously created a new existence, in which you do live and so does your grandfather. In this instance you have created a quasality loop for yourself, and the only "change" you've created is the one for yourself. A trap so to speak, so yeah, you would perceive the change (or so we can assume), but no matter what you do to alter events you’ll continue to merge* into each new universe like a ripple spreading out from a pond never to achieve your goal of killing your grandfather, until such time you come upon one where your grandfather, or family line for that matter never existed…and I have no idea how to go about explaining that one. At any rate, the loop in itself is a paradox, other than your perception…so then, yes you would be immune, but not your counterparts in each universe you affected. It begs the question about people who claim to be from the future or other realities; are they being truthful in their plea that they are from where they claim or are they nut jobs? We as a society can discount their claim or believe them. Anyway, the events that unfold from your action have no bearing on the existence of those who continue on after your change; unless you come forward, but then you face contempt from those you interact with without solid tangible evidence to persuade your audience.

And I don't see why we wouldn't perceive changes if they occured in the here and now. Let's say a time traveling robot tries to kill you to prevent you form becoming the leader of a human resistance in the future. You bloody well know the timeline is being changed because that change is shooting at you right now.

That would be perceived because it is a present tense situation. Lets use your example and step back 50 years to examine; any change in say our reality today would not exist for those of us that exist in a parallel universe from that occurrence. What you suggest is nothing new. Parallel Universes is something that was predicted back in the 1900’s. Hitler in our Universe never happened in another and so on and so forth. The theory suggests even now as you and I converse there are infinite possibilities being created some of which take on a parallel existence every second time marches forward. Again, paradox prohibits our awareness of infinite strings branching out from times movement in one direction or another. Now there are some mystics and soothsayers who believe that déjà vu shared by one person or several about a similar existence is our ability to perceive these alternate realities, other cultures (like my mom’s people) believe dreams are windows into our alternate selves. Kinda like looking at a mirror of our self into infinity. Who’s to say? But if we could perceive paradox, it would be highly disruptive, and to be frank human development couldn’t fathom living in a reality where we perceive ourselves in infinite possibilities – the then, the now and the tomorrow. Perhaps one day, but until then we’ll have to contend with God having the only ability to be in many places at once, or so we have come to believe.

*Current contemporary science believes that if one was to alter time one way or another that our string would vibrate into unison with the one we’ve created or merged with, essentially overlapping our counterpart in that existence, eliminating the prospect of meeting yourself in the new timeline and avoiding paradox - other than self realization that we have shifted out of our original existence.

[Afterburner]

To be honest, none of that made sense to me. Let's say you go back in time to kill your grandfather, here is how I perceive it would happen.

You would travel back in time, and at the instant you arrived a new timeline would branch off from yours at that point. If you now kill your grandfather he will be dead in the new timeline, but not the old one. So the you that traveled through time is still alive because the grandfather that gave birth to your father is still alive in your timeline. However in the timeline you just arrived in you are never born. The you from the first timeline is still there though because the grandfather you just killed isn't actually yours, it's parallel you's.

Now of course no one would know that history has changed in the new timeline, because it HASN"T. Nothing changed, you just made a new timeline. The old one is unchanged, and the new one has yet to be, so it can't possibly be changed. That doesn't necessarily mean the new timelnie isn't aware of the fact that it is a new timeline. If you told people and they believed you, for whatever reason, they would know. But still nothing changed, just new stuff was created.

Edit: However, the more I think about it the more a second option makes sense to me. There is no time "line" there is only the present configuration of the universe. IF you alter that configuration to resemble the past you will have apparently traveled backwards in time. Of course, you'd have to make sure the particles that made up you would remain intact in the reconfiguration process. From that point on you would just be running through the actions of the universe again, except with whatever changes your only particles might cause.

Of course, as we already went over, that sort of reconfiguration seems to be impossible. Or at least impossible for humans to artificially induce. I suppose some kind of cosmic force we haven't discovered yet could somehow induce it, though I'd doubt that.

[AlDaja]

Who’s to really say. It is astounding that we humans are capable of realizing the concept of space/time and are aware of it and the possibilities, albeit our species really has no tangible clue about how this phenomenon would actually work beyond conjecture at this point, but it is fun to contemplate.