Time travel into the past is logically possible

[Mentat]

Originally posted by radagast
Mentat,
Just to clarify, I am withdrawing from the debate with you, on this subject. No insult or emnity intended, but our positions haven't changed for some time, and just debating to debate isn't something I see much point in. I'm sure we will lock horns on other (perhaps less intractible) issues in the future.

Alright, if that's what you want to do. I would much appreciate it if you addressed the points in my previous post, but you (of course) don't have to if you don't want to.

 

[radagast]

I will try to answer, since it seems to be a point of clarification, not a point I'm trying to argue.

Think of a person as a string, where the width and breadth of the string represent the width and breadth of a person - as well as it's position with respect to the two dimensions (this example will have to dispense height since I'll be borrowing that dimension for time and humans are poor at visualizing 4D objects). A person would not keep 'replicating themselves, but it would be the continuation of their 4D self. Now, without time travel, the string would be required to always be both continuous and differentiable with respect to the time axis - no catastrophes allowed. Once time travel is introduced, either that string becomes discontinous at the point where the traveler travels back in time, or shifts into a parallel 3D plane to travel backwards in time. At this point the string would double back on itself (thru the parallel hyperplane), until it reenters normal time flow (thus the leading edge again points back in the direction of the flow of time's arrow) and our hyperplane. Yes, the leading edge of the string could encounter points where it's prior existence is located, assuming their spatial coordinates are close and the time coordinate matches (time with respect to some arbitrary measure along the time axis, not the travelers personal/experiential time). Both the traveler and his 'previous' self would and could interact since their experiential time front's (experiential moments) would coincide within time. This would be fraught with the danger of a paradox, assuming the earlier aspect of the traveler could decide not to travel back in time.

This was meant as way of presenting the concept I've been trying to get across, not as a point of argumentation.

 

[selfAdjoint]

Why doe the string have to double back? It can gradually (smoothly) turn and head backwards without intersecting itself, then when it has gone back far enough, turn again and rejoin itself. Things like this can happen in solutions of the general relativity equations. They are called closed timelike curves, or CTCs.

 

[radagast]

Double back only referred to the change of direction with respect to the time axis. How sharply that change or orientation takes place was outside the scope of the discussion. I never meant to imply the string/person ever intersected itself in all four coordinates.

 

[selfAdjoint]

Okay, but in that case I don't see your point about a singularity. Could you clarify that?

 

[radagast]

Originally posted by selfAdjoint
Okay, but in that case I don't see your point about a singularity. Could you clarify that?

Singularity? I've not commented on a singularity, could you elaborate on what you believe I've said.

 

[selfAdjoint]

This is what I was referring to.

Now, without time travel, the string would be required to always be both continuous and differentiable with respect to the time axis - no catastrophes allowed. Once time travel is introduced, either that string becomes discontinous at the point where the traveler travels back in time, or shifts into a parallel 3D plane to travel backwards in time. At this point the string would double back on itself (thru the parallel hyperplane), until it reenters normal time flow (thus the leading edge again points back in the direction of the flow of time's arrow) and our hyperplane

The singularity I meant was the failure of continuity or differentiability in the worldline, or at least the proper time (your string, or mapping of it into the time axis).

 

[radagast]

To be quite candid, I'm still not exactly certain what exactly your question is asking, but I'll address something that has bothered me and with luck it will be related.

When I've considered the consequences of time travel, it always seems that their has to be a second time dimension - such that there is usually no change (motion, but no change) in t' as the universe progresses along t, until backward time travel (in t). This also handles the problems of paradoxes, since the timeline has changed as it progresses along t' with every backwards t incursion.

From my limited playing with the relativity equations it seems that the idea of a second time axis pops out when speeds exceed c, as negative value on an imaginary time axis. An imaginary time would be orthoganol to our primary time axis, and as far as I can see, identical to the previously mentioned t'.

 

[Spacestar]

I’m sorry for my delay. Hope you guys are still around.

Any non-trivial time travel into the past would require the travellers personal memory/history/timeline to remain intact - in effect removing him from a point in time where he still had his experiences and memory and plopping him into a time previous to the time of departure. Assuming no quantum annihilation of the wormholes, wormhole physics predicts this would be possible.

If we are considering time travel in its accurate meaning, of course that the traveler’s memory/history/time line must remain intact. Or should I say, the aspiration to surf one’s time line. But that doesn’t mean that moving back in time is the same as changing the past from what we memorize. Time traveling could mean contributing to the framework of time as well. The possibility of wormholes may corroborate the idea of time travel, not its consequences.

Some conjectures state that that is exact what would happen, branching a parrallel timeline. This certainly handles any problems of paradox.

How that would discard a paradox? To my understanding, that involves a paradox, since that would imply giving two futures to a point in space/time (the future is and it isn’t) – from the perspective of someone in the past, the traveler would come from the future, yet not from the future?! Logically that produces a paradox.

However, violating causation assumes that all history that the traveller lived through is inviolate (assuming I'm understanding you correctly). Causation is based on very basic things we have observed in working in the natural universe. Time travel, assuming one timeline, would tip causation on it's ear. You cannot say that because everything we've seen (in regards to causation) wouldn't remain the same with time travel, therefore time travel is irrational is taking the cart before the horse - causation is considered extremely hard and fast, because we seen not contraditions - however, assuming we come up with a method of time travel - which we haven't seen either - means our 'laws of the universe ' have to expand to account for them. If you are speaking of the specifics of a paradox, then all bets are off. A paradox is, by it's definition, a logical inconsistency.

The possibility of time travel is also based on our understanding of nature and its laws. So at this point I’m not certain how “natural” time travel is, but the theory of relativity indicates that time travel is pretty “natural”, since according to Einstein’s theory, time is relative by nature. A good example is to imagine the speed and acceleration of a particle orbiting near a black hole. The gravitational force of the black hole would induce the particle to speeds near the speed of light (or even beyond, seeing as even light can escape when near a black hole), causing the particle to literally time travel naturally. Which, according to relativity does not violate causation, as we know. Also, saying that time travel might eventually alter causation does not support your point of view, because you are appealing to an argument to the future, that we don’t know if will be valid.

I am going completely by memory on how this was to be done - it seems like it was a from something written by Robert L. Forward. I've also seen references to the same by John Cramer and Stephen Hawkings. They referred to them as time travel, so I bow to their greater knowledge in the area. Since Hawking was concerned with paradoxes and the potential causability problems of a timewise wormhole, I assume that he regarded these as true time travel, not interdimensional travel.

[By interdimensional travel, I presume you mean between 3D hyperplanes??]

Yes, which are identically the same as orthogonal universes, or "hyperframes". The physics behind orthogonal dimensions or levels (multiple valued basic dimensional functions) are either not very known or severely disregarded on the current interpretation of relativity (of course that doesn’t take its consistency). Nonetheless, it was approached by Hugh Everett for his doctoral thesis in 1956, and the thesis was published in 1957 (See Hugh Everett, III, The Many-Worlds Interpretation of Quantum Mechanics: A Fundamental Exposition, with papers by J. A. Wheeer, B. S. DeWitt, L. N. Cooper and D. Van Vechten, and N. Graham; eds. Bryce S. Dewitt and Neill Graam, Princeton Series in Physics, Princeton University Press, 1973.).

 

[hey.like]

If the time systems is not sole

If the time system isn't sole, it is formed in mass system and a beautiful universy. but the later is absolute and semi-dimension. to travel in time is in this semi-dimension . if to travel in mass systems time , it is puzzle very still.

 

[hey.like]

Only a light particle

Only a light particle, it is everywhere. but it is different from this world. only it is not exist , we can get it information. as the time or space dimension action, naturely , it is not enable to get some information in it , only it is not exist but its action is clear. in this way the different unit space-time is ease to do the time travel , but it is not in this world, it is errors to get in some another world and get the world space-time exist or unexist hold way. Naturely it is safety for this world like so many light particle.