Time travel into the past is logically possible

[radagast]

Originally posted by Spacestar
You know, many persons think that traveling trough time involve paradoxes.

Spacestar,
In the simplest view of time travel, paradoxes are a given possibility. If (time travel) paradoxes could exist in reality is something we couldn't know until we have time travel to play with. Since reality does tend to abhore paradoxes, I suspect you are right, however just assuming that a paradox cannot occur is an assumption. You cannot use this assumption to prove itself.

Their arguments normally are of this kind: "If you did have a time machine right now, and you could step into it and travel back to some earlier time. Your actions in that time might then prevent yourself from ever growing up and becoming a time traveller, and thus not step into the time machine. So, the claim that there could be a time machine is self-contradictory". People, this argument is fallacious. Does the very concept of time travel entail contradictions? Does the possibility of murdering yourself as a child show that time travel is an impossibility?
The answer is: there is NO POSSIBILITY, if you travel into the past, of murdering yourself as a child.

You seem to have discovered paradoxes and are trying to prove that it cannot occur because it is a paradox. The whole reason things are paradoxes is that they produce a logical impossibility. By this reasoning, all paradoxes have NO POSSIBILITY of occurring. This is an argument flaw. You cannot acknowledge that paradoxes are defined as logical impossibilities, then use that definition to prove them impossible. The key aspect of paradoxes involves the exacting conditions that require them. This generally involves mathematically precise declaration of conditions - under such conditions a paradox is required under the conditions specified. That doesn't mean that the paradox will translate into reality.

In truth, all paradoxes, that appear to be testable, have been shown that there is some underlying assumption that is fallacious. Zeno's paradox involved an assumption that you couldn't perform an infinite number of actions (the actions are not discrete). The apparent assumption, causing trouble in the twin paradox, revolves around the effects of acceleration.

..snip...
I cannot change the future - by anything I have done, am doing, or will do - from what it is going to be. ..snip..

The implication of the above statement is time travel isn't possible, since the time traveler just being there (in the past), is a change in what occurred. A presumption that this is not the case is required to consider time travel.

 

[Mentat]

Originally posted by radagast
And if that's a given, then time travel would be impossible.

Then time travel's impossible (which is what I've been saying anyway), unless you can see a way out of such a semantic problem

I certainly don't want to appear insulting, but you don't seem to grasp the concept of time as a dimension. If an event occurred at point x,y,z, t then traveling to that point in time and space (well close to that in space), would bring you to all aspects that happened.

With all due respect, I think you have failed to grasp the concept; you see, you are referring to traveling along all four dimensions to a point on all four dimensions. Now, try to put this into practice. You see, if I were to travel from the seat that I am sitting into the desk across the room, I will have gone to a different point on spacetime, but will have been going "forward" in time the entire time (inspite of my movement in space). So, I can travel to any point on spacetime freely, but there are three dimensions (possibly more) of space, and only one of time. What I'm saying is that my movement is constantly "forward" in time (along with everything else in the known Universe), but my movement is free in the spatial dimensions. The only known way to travel in any other direction on the one time axis is to travel faster than c in space.

Now, the reason I mention this is because you speak of things that "exist at certain points of the four dimensions". However, according to the very semantics of the issue, nothing exists at previous points on the t dimension. All of space and matter and energy has been moving "forward" in time along with me, and I would thus have nothing to "go back to".

To traverse backwards in time, the 'now' has to change backwards, just as movement in space changes the 'here'. Without this, then time cannot be a dimensional axis.

Sure, this is possible in principle, but (again) in practice it is quite illogical, since I have three (or more) spatial dimensions which allow me to "turn around" and "go back". Alas, there is only one dimension of time, and thus no way to "turn around", so the only way to travel backward is to leave the rest of reality and regress in time (which regression you yourself have said was impossible).

 

[Mentat]

Originally posted by radagast
You are not treating time as a dimensional axis. If there is only the 'now' then there can be no other points on the time axis, hence, no axis at all.

But there are other points on the axis, there's just nothing at these points.

For time to be a dimensional axis, then everything at that point along the time axis would be just exactly as it had been. Again, you don't seem to grasp the concept of time as an axis. If nothing were there, then nothing would have ever been there at that point in time and space.

Not true. Remember the analogy of the spark on the wire. If the spark continues to travel along the wire, there are points that it "has traversed but is no longer traversing" and points that it "has yet to traverse". If all of space and matter and energy are the "spark" in the analogy, then there is nothing at any of the other points on the time axis.

If I draw half a parabola, one axis representing distance along a spatial axis (say height), and one representing time. When I draw the line, I represent where something is at that point in time. To go to that point in time means that 'that something' was there. That's what time time axis and graph implies.

Yes, something WAS there, but it is not anymore. Think of the analogy you are using further: If you draw a parabola then all points on the line are manifest at the same time. However, this is not so with time, because of the very semantics of the issue. How can all points of time exist "at the same time"?

One extra spatial dimension. I don't think it requires a second time axis, but that doesn't imply
our personal time is decoupled from the time axis - an implied requirement of time travel.

The way to visualize it is to assume we are two dimensional creatures living in an infinitely thin sheet of paper, within a stack of papers. To move into a parrallel sheet of paper requires us to move perpendicular to all dimensions we are aware of, just enough to get into the next sheet of paper. It would appear as a completely new/different universe. Then traversal backwards in time means that the natural motions of things (as time flows backwards) ensures nothing will run into us (being our new plane is empty, as we specified earlier).

This is a very good analogy, and it only serves to prove my point further: in the analogy, all of reality (which is two-dimensional, in the analogy) moves into different sheets of paper on a constant basis. Thus, if some crazy 2D being decided he wanted to travel backward in time (and somehow accomplished it), he would go to a vacant piece of paper.

 

[radagast]

Originally posted by Mentat
Yes, something WAS there, but it is not anymore. Think of the analogy you are using further: If you draw a parabola then all points on the line are manifest at the same time. However, this is not so with time, because of the very semantics of the issue. How can all points of time exist "at the same time"?

Of course something WAS there AT THAT POINT IN TIME, the same point in time your traveler wants to visit. If he goes back to that point in time and nothing is at x,y,z,t then it was never there! That's what time travel is - going back to where and when things were.

AGAIN, you are assuming time travel doesn't or cannot exist, implicitly in your discourse.

Again, think about the parabola describing an object's one dimensional motion - if the parabola didn't cross the point x,t then the object was never at x at time t. Let me put it differently. Just because the object isn't there now, if we went back and time and it wasn't there at time 't', then there would be a gap in the graph - the graph shows where the object was (in x) at that point in time. To go back in time means the object had to be there or there could be no continuity of the graph at that point in time.

Mentat, I am in no way trying to insult you, but what approx level of education have you had, with respect to math and physics? Perhaps I'm just taking a mental block on your part for a lack of grounding in the areas I'm talking about.

If you have the basic function f(t)=x, then when you change the time t, backwards, you get where it was at x - if you go back to time t, it has to be at x, otherwise - by definition, you haven't traveled back to time t.

The same could be said of function f(t)=x,y,z.

The reason you cannot visualize objects existing thru a duration of time is it put's the world squarely into 4 dimensions, and we have a hard time thinking in four dimensions.

 

[radagast]

Originally posted by Mentat
Then time travel's impossible (which is what I've been saying anyway), unless you can see a way out of such a semantic problem

If you believe time travel is impossible, fine. But, you cannot take time travel as impossible as a given, then try and use things you derive from that as proof that time travel is impossible. It's a circular logic flaw.

 

[radagast]

quote:
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Originally posted by radagast
You are not treating time as a dimensional axis. If there is only the 'now' then there can be no other points on the time axis, hence, no axis at all.

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But there are other points on the axis, there's just nothing at these points.

Then all graphs that have time as an axis would have no points except at the present.

If the only active point on a time axis (ever) is the present, that can be used to locate an object, then it is not an axis.

Dimensional axes enable us to locate things in space (or space-time). If you are saying that going back to a point, in space-time, where something existed, and it isn't there, then you haven't traveled in time to that point in space. That would be what time travel is.

 

[radagast]

Originally posted by Mentat
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For time to be a dimensional axis, then everything at that point along the time axis would be just exactly as it had been. Again, you don't seem to grasp the concept of time as an axis. If nothing were there, then nothing would have ever been there at that point in time and space.

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Not true. Remember the analogy of the spark on the wire. If the spark continues to travel along the wire, there are points that it "has traversed but is no longer traversing" and points that it "has yet to traverse". If all of space and matter and energy are the "spark" in the analogy, then there is nothing at any of the other points on the time axis.

Extended analogy flaw. One) sparks don't travel down wires, electrons and eletromotive force do, but I digress. Two) You are simply defining motion. Change in position with respect to time - yet you still fail to see that reversing the time, reverses the motion (AS defined by the X,Y,Z,T coordinate system we refer to as space-time). Disregarding IF time travel is possible, positing it as possible, forces things to return to all those same positions as the position in time reverses. Otherwise you're saying the past is an illusion that never really existed. To travel back in time means you're in the past only from the perspective of the present. To the traverler, he would experience it all as his current now.

This is a very good analogy, and it only serves to prove my point further: in the analogy, all of reality (which is two-dimensional, in the analogy) moves into different sheets of paper on a constant basis. Thus, if some crazy 2D being decided he wanted to travel backward in time (and somehow accomplished it), he would go to a vacant piece of paper.

He only time-travels within the parallel (Y) plane. The only purpose for the two dimensional creature to shift into the parallel plane, was to avoid colliding with himself as he attempts to travel backwards in time. Since he doesn't exist in the parallel plane at the same place he starts, he cannot spatially collide with himself (occupy the same sets of coordinates in X,Y,T), if he shifts to a different position along Y.

 

[radagast]

quote: Mentat
The very word, "past", means that which used to exist. If it is that which used to exist, then it doesn't exist anymore.

But using the phrase 'used to exist' is using a subtle time reference that's of dubious meaning when referring to existence in time. A more dimensional definition would be the word past refers to things at a prior point in time. They don't exist at this point in time like they did at a prior point in time, but that doesn't mean they don't exist in the four dimensional manifold of space time, at that point in time.

 

[radagast]

Originally posted by Mentat
With all due respect, I think you have failed to grasp the concept; you see, you are referring to traveling along all four dimensions to a point on all four dimensions. Now, try to put this into practice. You see, if I were to travel from the seat that I am sitting into the desk across the room, I will have gone to a different point on spacetime, but will have been going "forward" in time the entire time (inspite of my movement in space). So, I can travel to any point on spacetime freely, but there are three dimensions (possibly more) of space, and only one of time. What I'm saying is that my movement is constantly "forward" in time (along with everything else in the known Universe), but my movement is free in the spatial dimensions. The only known way to travel in any other direction on the one time axis is to travel faster than c in space.

You are only bringing up that we have no current mechanism for traveling back in time. No argument there - but that wasn't the initial discussion. The initial discussion had to do with the logic of traveling back in time. The above just concerns never having experienced it and that we don't know how to.

Now, the reason I mention this is because you speak of things that "exist at certain points of the four dimensions". However, according to the very semantics of the issue, nothing exists at previous points on the t dimension.

Prove it.

My point being is this is an unsupported statement that violates all current concepts of dimensional usage.

If we say something existed at x,y,z two days ago, then by traveling back to two days ago, existed changes to exists for the traveler. This is basic coordinate geometry - just because there have been special behaviours observed for a coordinate axis doesn't mean we cease to treat all the points, but one, as non-existent.

All of space and matter and energy has been moving "forward" in time along with me, and I would thus have nothing to "go back to".

Again, prove it. This is another unsupported statement. Traveling back in time implies to everything at that point in time. If I am at x,y,z at 10 am then move ten feet along the x-axis at 11 am, time travel dictates that I existed at 10am at x,y,z - so to travel back in time, so that I could observe point x,y,z requires that my previous self is at x,y,z at 10 AM. That's what the coordinate system using time as a coordinate requires.

Sure, this is possible in principle, but (again) in practice it is quite illogical, since I have three (or more) spatial dimensions which allow me to "turn around" and "go back".

Logic is not the issue - you are bring up an issue of how, i.e. what mechanism. That is outside the discussion since we have said this was a discussion of being illogical. You are failing to show that going back in time is illogical. Please stick to standard informal logical arguments and demostrate this is so.

Alas, there is only one dimension of time, and thus no way to "turn around", so the only way to travel backward is to leave the rest of reality and regress in time (which regression you yourself have said was impossible).

Again, a how, not an illogical impossibility. Saying there is no way to turn around either has to be shown as impossible, or is simply that we currently have no such mechanism. Theoretically we have the mechanism of jumping to faster than c, but that's still a 'how'. Perhaps it's a practical impossibility if no how is determined, but not an error in the logic of what is currently presented.

 

[Spacestar]

Thank you, Mentat, I’m glad to be here.

I think “predestined” is not precisely the term to be used here, since it implies that events are set on stone, or that we cannot alter time events because they are already determined. But as I said before, it is exactly our deliberations and actions that determine the way things are, were or will be. I’m not arguing that whatever we do is futile.

For example: suppose a visitor were to arrive here and now from the year 2045. He shakes my hand, and then sits and chats with me about what is in store during the next years. I take notes and record them in my diary. A year from now, I even publish some of these notes. The visitor from the future (year 2045) has not changed the past (i.e. the past relative to the year 2045): he has contributed to making the past just the way it was. By traveling back to the year 2003, he caused certain events to occur in 2003 and in 2004. Nothing was changed from the way it was; but the past was changed from the way it would have been if he had not traveled back from 2045 to 2003.

…it doesn't really effect the paradox that I've been talking about (which is that, if you travel to a moment before the time you start travelling, then you haven't started traveling yet, so how did you get to where you are?). Can you see some way how it could be applied to my paradox? Or are they unrelated?

I see that what you’re talking about is not the same kind of time travel that most of us here are referring to. You’re referring to time travel from your own three dimensional perspective, that is, to time travel in a manner that you would revive past experiences in a first person basis, but that sort of time travel is meaningless. Since your mind and rest of the body, would also be pushed backward or forward in time, therefore you wouldn’t remember of whether you time traveled or not. Actually, from that perspective you haven’t time traveled at all (no pun intended).

In the simplest view of time travel, paradoxes are a given possibility. If (time travel) paradoxes could exist in reality is something we couldn't know until we have time travel to play with. Since reality does tend to abhore paradoxes, I suspect you are right, however just assuming that a paradox cannot occur is an assumption. You cannot use this assumption to prove itself.

Well, at least it is theoretically right until confirmed by hard evidence.

You seem to have discovered paradoxes and are trying to prove that it cannot occur because it is a paradox. The whole reason things are paradoxes is that they produce a logical impossibility. By this reasoning, all paradoxes have NO POSSIBILITY of occurring. This is an argument flaw. You cannot acknowledge that paradoxes are defined as logical impossibilities, then use that definition to prove them impossible. The key aspect of paradoxes involves the exacting conditions that require them. This generally involves mathematically precise declaration of conditions - under such conditions a paradox is required under the conditions specified. That doesn't mean that the paradox will translate into reality.

Does it seem that way? Believe me, I didn’t take my conclusions out of such a vague reasoning. In fact, the reason why I consider the grandfather paradox as illogical is because the argument explicitly commits a modal fallacy. Let me explain:
Since it is possible that someone should have prevented your grandparents from having met one another, and since it is impossible for you to travel into the past and to have prevented your grandparents from having met one another, you conclude that it is thus impossible to travel into the past. Let "P" stand for "preventing your grandparents from meeting" and "T" stand for "travel into the past" (patched up as needed to be proper statements). Then the argument is:

#P
~#(T & P)
---------------------
therefore ~#T

The argument is invalid. From the conjoint impossibility of T and P, and the possibility of P, the impossibility of T does not follow. (Just to drive the point home, now let "T" stand for "the coffee table is four-sided" and let "P" stand for "the coffee table is six-sided".)

Arguments like the “grandfather paradox” have been persisting for ages, they are especially tricky because they involve what are called modal concepts, in particular the notions of possibility and impossibility.

Of course a time machine which allowed one to change the past is logically impossible, but making that the (unrealizable) goal is to trivialize the problem, to pose it in a question-begging manner, to stack the deck. Even if one does stack the deck in this way, there still remains the question: Is it logically possible to build a time machine which allows travel into the past where one does not change the past? And the answer to this latter, nontrivial, version of the question is: yes.

What is logically impossible is that BOTH one travels into the past AND changes the past (from what it was). But so long as one does not change the past, there is no logical contradiction in positing travel into the past.

The implication of the above statement is time travel isn't possible, since the time traveler just being there (in the past), is a change in what occurred. A presumption that this is not the case is required to consider time travel.

Allow me to say that your quoting of my statement is incomplete, because I also said that although we cannot change the past, we can change the past from the way it might have been. When I argue for the logical possibility of travel into the past, I do not mean as a disembodied watcher of past events. I mean as a 'real' participant in the activity of the past.

 

[radagast]

Originally posted by Spacestar
Does it seem that way? Believe me, I didn’t take my conclusions out of such a vague reasoning. In fact, the reason why I consider the grandfather paradox as illogical is because the argument explicitly commits a modal fallacy. Let me explain:
Since it is possible that someone should have prevented your grandparents from having met one another, and since it is impossible for you to travel into the past and to have prevented your grandparents from having met one another, you conclude that it is thus impossible to travel into the past.

Excuse me? I have never argued that time travel was impossible because of paradoxes. In fact I've heard extremely few ever argue that. I suspect, before you start arguing what I am claiming and not claiming, you read my posts.

Let "P" stand for "preventing your grandparents from meeting" and "T" stand for "travel into the past" (patched up as needed to be proper statements). Then the argument is:

#P
~#(T & P)
---------------------
therefore ~#T

The argument is invalid. From the conjoint impossibility of T and P, and the possibility of P, the impossibility of T does not follow. (Just to drive the point home, now let "T" stand for "the coffee table is four-sided" and let "P" stand for "the coffee table is six-sided".)

Straw man argument flaw. It's a straw man, because you are putting arguments in my mouth that I've not made.

Of course a time machine which allowed one to change the past is logically impossible,

This is a statement, not an argument. You have not shown the above to be true, unless of course, you are stating that paradoxes, being logically impossible, force time travel to be logically impossible.

What is logically impossible is that BOTH one travels into the past AND changes the past (from what it was). But so long as one does not change the past, there is no logical contradiction in positing travel into the past.

While Mentat may have made that statement, I have not.

Allow me to say that your quoting of my statement is incomplete, because I also said that although we cannot change the past, we can change the past from the way it might have been. When I argue for the logical possibility of travel into the past, I do not mean as a disembodied watcher of past events. I mean as a 'real' participant in the activity of the past.

Pardon me, but to say that you can travel into the past and not change the past, yet be a real participant in the past AND can change the past from the way it might have been, sounds like semantic double talk. I will assume there is just a breakdown in communication and wait for elaboration.

 

[Spacestar]

Originally posted by Spacestar
Does it seem that way? Believe me, I didn’t take my conclusions out of such a vague reasoning. In fact, the reason why I consider the grandfather paradox as illogical is because the argument explicitly commits a modal fallacy. Let me explain:
Since it is possible that someone should have prevented your grandparents from having met one another, and since it is impossible for you to travel into the past and to have prevented your grandparents from having met one another, you conclude that it is thus impossible to travel into the past.

Excuse me? I have never argued that time travel was impossible because of paradoxes. In fact I've heard extremely few ever argue that. I suspect, before you start arguing what I am claiming and not claiming, you read my posts.

Hold on, I think we have a misunderstanding here.

I was explaining what I think to be the general feeling on the so-called grandfather paradox. I wasn’t exactly addressing your statements at that point. I’m not necessarily saying that is your point of view. I’m sorry about the confusion.

Let "P" stand for "preventing your grandparents from meeting" and "T" stand for "travel into the past" (patched up as needed to be proper statements). Then the argument is:

#P
~#(T & P)
---------------------
therefore ~#T

The argument is invalid. From the conjoint impossibility of T and P, and the possibility of P, the impossibility of T does not follow. (Just to drive the point home, now let "T" stand for "the coffee table is four-sided" and let "P" stand for "the coffee table is six-sided".)

Straw man argument flaw. It's a straw man, because you are putting arguments in my mouth that I've not made.

Let me offer a counter:

Pretend ad hominem flaw. Instead of staying on the point that I’m trying to make, you begin to act hurt, as if I’m viciously giving a false imprint of your statements, changing the focus.

This is a statement, not an argument. You have not shown the above to be true, unless of course, you are stating that paradoxes, being logically impossible, force time travel to be logically impossible.

Yes, it is a statement, but I have explained before why I believe the statement to be true.

Pardon me, but to say that you can travel into the past and not change the past, yet be a real participant in the past AND can change the past from the way it might have been, sounds like semantic double talk. I will assume there is just a breakdown in communication and wait for elaboration.

I suggest that you take a look at the example in the beginning of my last post, which illustrates clearly my point.

 

[radagast]

Originally posted by Spacestar
Hold on, I think we have a misunderstanding here.

I was explaining what I think to be the general feeling on the so-called grandfather paradox. I wasn’t exactly addressing your statements at that point. I’m not necessarily saying that is your point of view. I’m sorry about the confusion.

OK, that wasn't clear. Misunderstanding acknowledged.

Just as an aside, I do feel compelled to say I've never heard someone use the grandfather paradox used to justify that time travel was logically impossible.

...Straw man argument flaw...

Let me offer a counter:

Pretend ad hominem flaw. Instead of staying on the point that I’m trying to make, you begin to act hurt, as if I’m viciously giving a false imprint of your statements, changing the focus.

Acting hurt?!? I am pretty think skinned when it comes to online activities, so I really don't think you hit the mark, there.

Let me clarify, I don't defend statements I'm not making or stand behind. I would think that was common sense. If you want to fight that fight, find someone that believes it. If you are in a debate, and attack issues I've not raised, nor back up, then there is no onus for me to defend/debate them.

Just so I'm crystal clear, I see no reason to disagree with the statement that the grandfather paradox doesn't logically invalidate time travel (assuming that was what you were saying).

Yes, it is a statement, but I have explained before why I believe the statement to be true.


I suggest that you take a look at the example in the beginning of my last post, which illustrates clearly my point.

Perhaps I'm just missing your points, but I've not seen where you made the statements that you say you have. If they were made in another thread, then I will freely admit I didn't see them. If in this thread, then I haven't recognised them for what you say they are.

 

[Spacestar]

Just as an aside, I do feel compelled to say I've never heard someone use the grandfather paradox used to justify that time travel was logically impossible.

But, the paradoxes (including the grandfather paradox) play an important part in the analysis of the logical/physical possibility of time travel.

It is to my knowledge that most people think of that kind of time travel that meets the demand “ Ho, I wish I could go back and make Adolf Hitler slip on a banana peel and die at the age of seven." So, that is a notion of time travel that properly translates into the modal argument, since it means a logical impossibility, and probably also a physical impossibility for the reason that it violates causation.

Let me clarify, I don't defend statements I'm not making or stand behind. I would think that was common sense. If you want to fight that fight, find someone that believes it. If you are in a debate, and attack issues I've not raised, nor back up, then there is no onus for me to defend/debate them.

Basically, I’ve joined this message board to share my ideas and premises, but I’m also here to discuss other points of view. Mainly because such conduct refreshes current theories, allowing new insights and mental connections not previously made. Thus I personally see a great importance in debating new theories; even if they are contrary to your convictions. Essentially, that is what makes science go on.

Just so I'm crystal clear, I see no reason to disagree with the statement that the grandfather paradox doesn't logically invalidate time travel (assuming that was what you were saying).

All right, so please tell me, what makes you to not disagree with the statement?

 

[radagast]

Originally posted by Spacestar
But, the paradoxes (including the grandfather paradox) play an important part in the analysis of the logical/physical possibility of time travel.

It is to my knowledge that most people think of that kind of time travel that meets the demand “ Ho, I wish I could go back and make Adolf Hitler slip on a banana peel and die at the age of seven." So, that is a notion of time travel that properly translates into the modal argument, since it means a logical impossibility, and probably also a physical impossibility for the reason that it violates causation.

You are correct that most view time travel as just what you say. This has been helped by the fact that virtually every SF story dealing with time travel does would, in fact, trigger a paradox.

This view of time travel assumes the most basic idea of time travel, with instant propagation of changes from an event, a single time axis, a single universe, and most importantly that other laws don't permit the exact type of paradox to occur. The twin paradox is a paradox within the constraints of the special theory of relativity. Just because it is actually a paradox doesn't invalidate all of the special theory - this is what I am understanding you to say.

Let me clarify, I don't defend statements I'm not making or stand behind. I would think that was common sense. If you want to fight that fight, find someone that believes it. If you are in a debate, and attack issues I've not raised, nor back up, then there is no onus for me to defend/debate them.

Basically, I’ve joined this message board to share my ideas and premises, but I’m also here to discuss other points of view. Mainly because such conduct refreshes current theories, allowing new insights and mental connections not previously made. Thus I personally see a great importance in debating new theories; even if they are contrary to your convictions. Essentially, that is what makes science go on.

Debate is fine, however, as I stated earlier, if you are debating points I don't disagree with, it's not much of a debate.

All right, so please tell me, what makes you to not disagree with the statement?

Since, at this point, which statement is not clear, I'll review things as I've seen them stated, leaving out any side issues.

OK, to begin with you state that many people think time travel involves paradoxes.

To which I state that under the most basic ideas of time travel, they do. You have to understand that under the most basic ideas of time travel, time travel (into the past) is a given, and the ability to interact in that past is also a given.

Now, to say that a paradox invalidates this because they are logically impossible, only reiterates the definition of a paradox. Many things appear to be paradoxes that are no, in real life. Zeno's paradox. The idea that an electron could, apparently, be a particle and a wave also appeared to be a paradox.

 

[elas]

Surely you should differentiate between "Time Travel" and "History Travel". While it may be possible to travel back in time that does not necessarily mean you are also traveling back in history.
A body that lives for 60yrs go back 40yrs and live another 50yrs will be 50yrs old with a 110yr history. This treats time in the manner used by Dr Brownoski author of "The Ascent of Man".

 

[radagast]

Originally posted by elas
Surely you should differentiate between "Time Travel" and "History Travel". While it may be possible to travel back in time that does not necessarily mean you are also traveling back in history.
A body that lives for 60yrs go back 40yrs and live another 50yrs will be 50yrs old with a 110yr history. This treats time in the manner used by Dr Brownoski author of "The Ascent of Man".

Obviously, going back in time, when it is the time travelers personal time, is of little value, since they would simply regress, losing all they had gained in knowledge, experience, et. al.

Most, when referring to time travel, are speaking of traveling back to a prior point along the time axis (i.e. in history, with reference to the travelers starting point), without a corrosponding change in the travelers personal time (i.e. the traveler doesn't regress in age, memories, or personally experienced history).

I have not read Dr. Brownoski's book, but that sounds more like age regression than time travel.

 

[Spacestar]

The twin paradox is a paradox within the constraints of the special theory of relativity. Just because it is actually a paradox doesn't invalidate all of the special theory - this is what I am understanding you to say.

Yes, basically that’s what I’m saying. Paradoxes arise when we don’t take into account (out of unawareness or disregard) all the aspects concerning the issue. Not that they indeed occur in reality.
For instance, the twin paradox comes to mind when we consider time to be absolute, but when we comprehend the relative nature of time, the paradox doesn’t occur. Moreover, I’d like to add that such a paradox can be resolved quite simply by a careful and correct application of the principles of relativity. As a matter of fact, it is relativity that turns time travel into a physical possibility.

Surely you should differentiate between "Time Travel" and "History Travel". While it may be possible to travel back in time that does not necessarily mean you are also traveling back in history.
A body that lives for 60yrs go back 40yrs and live another 50yrs will be 50yrs old with a 110yr history. This treats time in the manner used by Dr Brownoski author of "The Ascent of Man".

I agree with Radagast, that does not fit the definition of time travel.

How you’d quantify that? You would have to be in another reference frame, that is, in a position that would suit the actual definition of time travel (as you say “history travel”).

I have to say that your argument is rhetorical.

 

[radagast]

Originally posted by Spacestar
Yes, basically that’s what I’m saying. Paradoxes arise when we don’t take into account (out of unawareness or disregard) all the aspects concerning the issue. Not that they indeed occur in reality.
For instance, the twin paradox comes to mind when we consider time to be absolute, but when we comprehend the relative nature of time, the paradox doesn’t occur. Moreover, I’d like to add that such a paradox can be resolved quite simply by a careful and correct application of the principles of relativity. As a matter of fact, it is relativity that turns time travel into a physical possibility.

Perhaps we were much closer to agreeing than was apparent.

That said, with specific reference to the twin paradox: I did believe the twin paradox was more based on the effects of accelleration (GR) invalidating certain aspects of special relativity. As I understand it, after one of the twins left Earth (or wherever they started), each twin could say that the other was the one traveling close to the speed of light [since in their frame of reference, it could appear that the other was the traveler], so the other would see the other as younger. Then once the twins returned to the same frame of reference, each would expect the other to actually be younger. Obviously, once their frames of reference merge, this cannot be, hence the paradox. General relativity, removed the fact that one could always see the other as the one traveling at a high fraction of c, when it came down to measuring apparent age at the end of the round trip.

Perhaps I've just misinterpreted what you've said, or it's always possible, with my limited understanding of relativity, that the twin paradox is much more trivial than I'd thought.

 

[elas]

Obviously, going back in time, when it is the time travelers personal time, is of little value, since they would simply regress, losing all they had gained in knowledge, experience, et. al.

It's obvious that you do not have Windows XP or you would know that you can regress without loss of memory!.
Bronowski was a great mathematician who worked for universities in several countries usually by invitation. He was also a great educator whose TV lectures remain unsurpassed. His one hour lecture on time contained several definitions, each of which were analysed; his own preference was indeed decay reversal.
One aspect not mentioned by Bronowski that struck me with my chapel upbringing, is that decay reversal matches the two statements on time given in the New Testament.
This is not my subject and I certainly do not want to start a religous debate, so I will retreat to the audience, thanks for letting me get a word in.

 

[pelastration]

My problems with the possibility of 'Time Travel'.

First I refer to a post on a old-old mkaku forum :
"Subject: time travel
Guys,
I am here and now in Belgium. I drink now a glass of wine. White wine from China ... made some years ago ... smooth, tasty and cool too.
That bottle contains about 600 billion atoms. These atoms move in an exciting way, ... it seems the bottle smiles even to me ... but most of those atoms will disappear soon in my body and a complex enzyme process will starts. Maybe I will have tomorrow an headache ;-) causing traffic jams in the microtubules in my brain proteins. How many billion brain cells with have flashing connections ... 16 billion?
That's only the wine and my body ... but there are billions of people, cars, trillions of drops in the Pacific and decay events like the fires in California. Time travel will reverse them all ... what an energy! It's now time ... to take another glass of wine and phone Einstein. Cheers. Dirk"

Time travel would implicate in a dynamic model of the Universe: a reverse (!) of all those particles movements and a reversal of there combinations in atoms and molecules, and reverse of all local and universal processes. And each is related to moves of fundamental particles each with a numbers of specific characteristics such as spin, electron orbitals, emission of photons, etc.
In time travel there are also questions such as: Would time travel be a local event? So does the total Universe continues to progress during the traveling back of a local reference frame (the traveller).

In Time travel the term: "Past" is oversimplified.
"Past" includes (1) all historical events which are still active now in the "Present", but (2) Past includes also historical events which decayed. All must reversed. :/

To finalize: We may not mix "Time" and "Grow". The velocity in Growth and Decay can be expressed in a Time sequence. Time is a local expression of that growth/decay process view from an observer/participant in his reference frame. But Time is not the process itself.
The reverse of a local growth process is called a 'decay' but it doesn't means the reverse (i.e. a sudden anti-spin) of the molecules, atoms and particles. Decay just means that the some couplings don't hold anymore. Time continues while the decay process progresses.

So TT? Impossible.

Dirk

 

[radagast]

Originally posted by elas
Obviously, going back in time, when it is the time travelers personal time, is of little value, since they would simply regress, losing all they had gained in knowledge, experience, et. al.

It's obvious that you do not have Windows XP or you would know that you can regress without loss of memory!.

XP doesn't 'go back in time', it merely recovers the state prior to a given point. It does, however, 'lose memory', since it's the memory of a virus, registry modification problem, or some other such problem that you are trying to get XP to forget.

Bronowski was a great mathematician who worked for universities in several countries usually by invitation. He was also a great educator whose TV lectures remain unsurpassed. His one hour lecture on time contained several definitions, each of which were analysed; his own preference was indeed decay reversal.

While intriguing, these don't match regressing in personal time, since everything, including memory, would regress without clarifying the important differences between reversing a persons personal history (time) and the 'decay reversal' Bronowski speaks of.

 

[Spacestar]

That said, with specific reference to the twin paradox: I did believe the twin paradox was more based on the effects of accelleration (GR) invalidating certain aspects of special relativity. As I understand it, after one of the twins left Earth (or wherever they started), each twin could say that the other was the one traveling close to the speed of light [since in their frame of reference, it could appear that the other was the traveler], so the other would see the other as younger. Then once the twins returned to the same frame of reference, each would expect the other to actually be younger. Obviously, once their frames of reference merge, this cannot be, hence the paradox. General relativity, removed the fact that one could always see the other as the one traveling at a high fraction of c, when it came down to measuring apparent age at the end of the round trip.

Perhaps I've just misinterpreted what you've said, or it's always possible, with my limited understanding of relativity, that the twin paradox is much more trivial than I'd thought.

In addition to the GR approach, the better way to clarify why the paradox does not occur, is to realize that the two situations are not symmetrical. The apparent paradox occurs when the situation is faultily analyzed from the moving observer point of view. All the frames of reference are not equivalent, only the so-called inertial frames (in which Newton’s laws hold). The moving observer frame is not inertial while it is accelerating. And this is detectable by carrying out relativistic calculations using a sequence of inertial frames that at each instant during acceleration are momentarily at rest to the moving observer. Because these frames have different velocities, the systematic difference in the way that clocks are synchronized from one frame to the next must be taken into account. Reference frames are only equivalent when at rest with respect to each other (inertial frames, relatively nonaccelerating ).

I think the twin paradox inadvertently emphasizes the consequences of relativity.

It's obvious that you do not have Windows XP or you would know that you can regress without loss of memory!

Are you saying that windows XP can regress in time?!?

Wow, windows XP is always surprising me

…his own preference was indeed decay reversal.

Decay reversal is not time reversal; it is reforming.

Decay and growth are two continuous processes that take time like any other process, not that they are the ‘arrows’ of time itself.

Time travel would implicate in a dynamic model of the Universe: a reverse (!) of all those particles movements and a reversal of there combinations in atoms and molecules, and reverse of all local and universal processes. And each is related to moves of fundamental particles each with a numbers of specific characteristics such as spin, electron orbitals, emission of photons, etc.
In time travel there are also questions such as: Would time travel be a local event? So does the total Universe continues to progress during the traveling back of a local reference frame (the traveller).

In Time travel the term: "Past" is oversimplified.
"Past" includes (1) all historical events which are still active now in the "Present", but (2) Past includes also historical events which decayed. All must reversed. :/

Time travel is not a physical impossibility if you consider time as a dimension. But it sounds impossible if you consider time as a moving entity that you would need to rewind or invert its spin in order to time travel.

 

[Mentat]

My apologies for the delay in response.

Originally Posted by Radagast:
Of course something WAS there AT THAT POINT IN TIME, the same point in time your traveler wants to visit. If he goes back to that point in time and nothing is at x,y,z,t then it was never there! That's what time travel is - going back to where and when things were.

Not good enough, IMO, since to say that something "was" there, but isn't there in the present time, precludes it's being there now (obviously). IOW, you cannot expect to find something "still there", if it's the past, since all things that are "still there" (by the very semantics of the issue) are in the present.

Think of this, if the prospective time traveller has been traveling forward in time (note: not replicating infinite copies of himself along the t dimension, but continuing to move along it as you would along a spatial dimension) for his whole life, and has not traveled into a void of nothingness, then (obviously) the rest of the Universe has moved along with him (note again: not replicating infinite copies of itself along the t dimension, just moving along it like anything would move along the spatial dimensions).

And, if the rest of the Universe has moved on, then what is there to "go back" to?

Again, think about the parabola describing an object's one dimensional motion - if the parabola didn't cross the point x,t then the object was never at x at time t. Let me put it differently. Just because the object isn't there now, if we went back and time and it wasn't there at time 't', then there would be a gap in the graph - the graph shows where the object was (in x) at that point in time. To go back in time means the object had to be there or there could be no continuity of the graph at that point in time.

I think you may be missing the point, radagast (no offense). A graph of things shows what exists now (this is obvious, because the graph exists now). Thus, a graph may be able to represent many points (and objects on these points) on the spatial dimensions, but the temporal dimension cannot be shown on the graph, since it only shows what exists, and things that "used to exist" but don't "now" (in the "present") do not exist (again, by the very semantics of the issue).

Here, let me use another analogy, and try to make my point more clear. We will assume that time is the fourth dimension for us, and so for the "Flatlander" it is the third dimension. Now, let's imagine that the entire Universe is "Flatland". So, in normal occurance, all things traveling below c are traveling forward in time, but no Flatlander can concieve of time, because that is the third dimension, and is beyond their conceptual abilities. Anyway, we can imagine that all of Flatland (which is all of the Universe) is a piece of paper - and the movement along the "time" axis is someone's picking up the paper (since "up" is "forward" movement in the t dimension, in our analogy). Now, the entire Universe has to move along this axis, more or less together. So, if everything is moving up this axis, then the poor doomed flatlander who happens to find a way to travel backward along the up/down axis (which is "time" in the analogy), will find himself separated from the Universe, won't he?

Mentat, I am in no way trying to insult you, but what approx level of education have you had, with respect to math and physics? Perhaps I'm just taking a mental block on your part for a lack of grounding in the areas I'm talking about.

No offense, taken, I have a reasonable grasp of mathematics and physics, but there is perhaps a mental block to understanding what you are trying to tell me. I'm sorry if this frustrates you, but I thank you for your patience.

If you have the basic function f(t)=x, then when you change the time t, backwards, you get where it was at x - if you go back to time t, it has to be at x, otherwise - by definition, you haven't traveled back to time t.

The same could be said of function f(t)=x,y,z.

The reason you cannot visualize objects existing thru a duration of time is it put's the world squarely into 4 dimensions, and we have a hard time thinking in four dimensions.

Well, that's why I used the "Flatland" analogy, so that we could conceive of it in three dimensions, like we're used to.

Anyway, you speak of just changing the function of t, but ignore the logical barrier to treating it as a spatial dimension (which is basically what you are doing, btw, or so it seems to me), and that logical barrier is brought up in the previous analogy.

 

[elas]

It seems to me that you are implying that time cannot be changed (forwards or backwards) without changing the other dimensions. Does this not make time unique in that it is not only different from other dimensions but also has a different set of rules, if so, why?

 

[radagast]

Originally posted by Mentat
My apologies for the delay in response.



Not good enough, IMO, since to say that something "was" there, but isn't there in the present time, precludes it's being there now (obviously).

Of course it is not there now, it is there 'then'. That is the whole point of time travel. Now isn't then. If you go back in time, the 'then' becomes the time traveler's now. At that point in time, things are there, otherwise we don't have a past. You are mixing up the present time and the past. The past isn't a place in space, but in time. If you travel back to that place in time, then all the 'things' that were at that place at that time are at that place at that time - it is the basic definition of 'back in time'.

Been busy myself, don't know how much of the responses I'll be able to get to.

 

[radagast]

Originally posted by Mentat


I think you may be missing the point, radagast (no offense). A graph of things shows what exists now (this is obvious, because the graph exists now). Thus, a graph may be able to represent many points (and objects on these points) on the spatial dimensions, but the temporal dimension cannot be shown on the graph, since it only shows what exists, and things that "used to exist" but don't "now" (in the "present") do not exist (again, by the very semantics of the issue).

Though the temporal dimension cannot be shown, it can be represented in a graph. I've done it countless times in physics and math.

Plotting y=40s - 32s² does exactly that. It is representing where in along the y-axis our hypothetical point/object/falling ball was at the point when s was equal to the point along the time axis. True, the object isn't at that point now, but then again, now is not in the past - where the time traveler is going.

The time traveler has a destination of where something "used to exist". That is a destination in space-time. Once he gets to that point in space time, the things that were there will be there. If they weren't, then he didn't get to that point in space time. There is no concept of 'nothing is there, now' because now doesn't refer to the past, and certainly not to a point, in space-time, in the past.

It sounds like what your trying to say, once it's boiled down is that 'you cannot travel into the past, because it is the past'.

 

[Mentat]

Originally posted by radagast
Though the temporal dimension cannot be shown, it can be represented in a graph. I've done it countless times in physics and math.

Plotting y=40s - 32s² does exactly that. It is representing where in along the y-axis our hypothetical point/object/falling ball was at the point when s was equal to the point along the time axis. True, the object isn't at that point now, but then again, now is not in the past - where the time traveler is going.

The time traveler has a destination of where something "used to exist". That is a destination in space-time. Once he gets to that point in space time, the things that were there will be there. If they weren't, then he didn't get to that point in space time. There is no concept of 'nothing is there, now' because now doesn't refer to the past, and certainly not to a point, in space-time, in the past.

It sounds like what your trying to say, once it's boiled down is that 'you cannot travel into the past, because it is the past'.

That is pretty much what I'm saying, but I still think it's a valid point, since you cannot change the past from being the past. I'm saying this because:

1) If you could move the "present" back to another point in time, then everyone else would be in the future.

2) If, instead, you move yourself out of the present, and into the past, then you have the same argument that I was using before (you cannot be in the past, because to "be" is to be now).

BTW, the problem with moving the "present" into the past, with everyone else in the future, is that nothing that they "are doing" (please take note of the "are doing" part, since it's written in the present tense) has happened yet. You effectively destroy everything but yourself, since they have yet to come into existence (they are in the future).

Also, as to representing where something was on a graph, that is no big effort when compared to trying to plot a point where the object, A, exists and then plot a point where all other objects exist. We do not all exist in the past (unless you subscribe to the idea that we are constantly replicating new versions of ourselves, and that that is what traveling through time really is - in which case, I have some logical and scientific problems with that for you), and so the time traveller is removing himself from the rest of us to...where?

 

[radagast]

Originally posted by Mentat
That is pretty much what I'm saying, but I still think it's a valid point, since you cannot change the past from being the past. I'm saying this because:

1) If you could move the "present" back to another point in time, then everyone else would be in the future.

Assuming that the people from the present existed at the time in the past you plan to visit, then their former selves (and even your own former self) would exist where you went. The history of their existence states that they were at a given set of coordinates in space time, assuming you go back to a given temporal offset and close to the same physical coordinates as they existed in 'our' history, then you, as the time traveler would have to see them. With you, the time traveler, in the past and given the general rules of cause and effect, the future would then be somewhat fluid, since any changes you effected by being in the past, ripple through time altering events that followed those points in space-time.

2) If, instead, you move yourself out of the present, and into the past, then you have the same argument that I was using before (you cannot be in the past, because to "be" is to be now).

This is a statement, not an argument. Your initial argument was that time travel was illogical, inherently. This is only a statement that you cannot go into the past because it's in the past.

If you remember, one of the premises of this discussion was that we, hypothetically, have a method to go back into the past. Given that, you need to show the logical inconsistency that this sets up. If it always created a paradox, then that would be something forming a good argument, but just travel into the past doesn't create a true paradox.

BTW, the problem with moving the "present" into the past, with everyone else in the future, is that nothing that they "are doing" (please take note of the "are doing" part, since it's written in the present tense) has happened yet. You effectively destroy everything but yourself, since they have yet to come into existence (they are in the future).

Also, as to representing where something was on a graph, that is no big effort when compared to trying to plot a point where the object, A, exists and then plot a point where all other objects exist.

If time is an a dimension, then we are required to have all those versions of ourselves in the past. Spacetime describes a set of four coordinates that can locate things in space and time. If 'Sam' existed at x,y,z,t - where t is in the past, then if backwards travel in time is possible, and we were able to travel to t at coordinates very close to x,y,z, then by the definitions of a coordinate system 'Sam' would have to be there. The act of visiting the past could, as mentioned prior, alter events leading to the present, as well as the state of the present.

We do not all exist in the past (unless you subscribe to the idea that we are constantly replicating new versions of ourselves, and that that is what traveling through time really is - in which case, I have some logical and scientific problems with that for you), and so the time traveller is removing himself from the rest of us to...where?

The idea of replicating is not accurate. If I move from place x to x+5. At some point in time I existed along all points between x and x+5 (assuming straight line movement). I didn't replicate myself. If I had been a point, then my motion would have produced a line in space and time. I hadn't replicated myself, I just existed at all those points in space-time. In fact, had my 'point' self had not moved, but existed thru a span of time, it would still form a line. A line orthoganol to all three spatial dimensions, but parrallel to the time access (but I digress). Going back in time is like producing a line (not a geometric line, just a contiguous set of points) that is discontinous in time at the point my 'point' self jumped back in time. It proceeds from a position in the present, jumping (or moving outside of our normal three-dimensional hyperplane) to a position in time previous. The prior self existed back there just as the my 'point' existences motion thru time produced a line

Let's add a dimension.

Let's use an example of two dimensional space with time as a third. We will use a cartoon, where all the cartoons are written like a child would draw them - with no overlap - this will be our bounded two dimensional space, with each frame being an instant in time. If we pick a particular point in the cartoon as 'now', then reverse the film a number of frames, that reverses time. You'll notice that the position in the film corrosponds to time and that there are things back in time. If we take a character from the present of our film, draw him into the past frames (as he looked in the present) then he has traveled to the past (given his past is defined by the positions, on the frames prior, in the film).

Now for a little depth.

Now let's generalize the film, making each frame of our movie, three dimensional. True, the film will take a lot more space, but still the analogy will hold. Time travel would be going back to a previous frame in the picture. The only difference between that time travel and the one we speak of is 'cause and effect' - by going back to a point in time previous to now, we start causing/changing things that were not events in our original history. If there is something that was changed that would effect the time traveler or his decision/ability to travel back in time, then we have a paradox.

There is some conjecture that the entire universe is basically the described 4D movie, with each frame being the hypothetical smallest unit of time (the time it takes light to traverse the distance of Planck's length) by the physical dimensions of the universe, and that all the past and future already exists, and only our consciousness is stepping thru the frames. In this scenerio, time travel would be logically impossible.

 

[radagast]

content deleted: remedying a carelessly clicked quote button.