Time travel into the past is logically possible

[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.

 

[radagast]

Originally posted by 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?

You may need to add more context. I don't know if you are addressing some of my arguments or mentat's.

Also, you may want to clarify your terms. I assume you mean change a position in time or position along some of the other dimensional axis. Changing a dimension, versus a position along that dimensional axis, is something that would have to be defined.

 

[radagast]

deleted

 

[Spacestar]

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?

When you change time, you also change the three spatial dimensions (y, x, z), for the reason that all the dimensions of space exist in time. That’s why it’s called space/time. In space/time geometry the ‘distance’ between events is given by the by sum of the squares of the space offsets minus the square of the time difference.

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.

To my understanding, what you’re stating is not traveling to the past, but to an alternate past. To travel to the past implies that you follow your space/time line or line of causation. But, if you are considering that traveling to the past obligatorily means that you have to change it from what it was, then you are violating ‘cause and effect’.

Alternatively, let’s say that you do travel to a past where things happen differently, my question is: How you got there?

 

[radagast]

Originally posted by Spacestar
When you change time, you also change the three spatial dimensions (y, x, z), for the reason that all the dimensions of space exist in time. That’s why it’s called space/time. In space/time geometry the ‘distance’ between events is given by the by sum of the squares of the space offsets minus the square of the time difference.

Not to jump into another's discussion, but don't you mean a change in position (or offsets)within the dimensional space. Otherwise I'd like someone to explain what 'changing a dimension' means.

To my understanding, what you’re stating is not traveling to the past, but to an alternate past. To travel to the past implies that you follow your space/time line or line of causation. But, if you are considering that traveling to the past obligatorily means that you have to change it from what it was, then you are violating ‘cause and effect’.

I don't know if you are bringing up a semantic discussion. In other words, when you travel to a point in your past and change it, then semantically, it ceases to be your past, given defining the past as the history we remember/or would remember with perfect knowledge and memory.

Alternate past could mean an, initially, identical past in a parallel universe/parallel dimensional plane. Or it could mean that you have altered your own past (making it an alternate past) by traveling to it. If there is a third meaning, then you'll have to elaborate.

If not, as I see it, then the only violation of 'cause and effect' occurs if a paradox occurs - you go back in time change something such that your present self no longer needs to go back to the past, since he doesn't, the past isn't changed and the present self does decide to go back to the past...

Alternatively, let’s say that you do travel to a past where things happen differently, my question is: How you got there?

Two wormholes will get, potentially, you into the past, according to current theory. Your able to do some interesting things when you are can both create two wormholes and move one of the wormhole's mouth position in space. Tangentially mentioned in http://www.npl.washington.edu/AV/altvw69.html.

 

[Mentat]

Originally posted by radagast
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.

This is interesting though. You say that our "fomer selves" should all be at these different points in time. That implies that we must be producing a "new self" at every one of the smallest intervals of time (otherwise we could run into certain points in time where we all do exist, and certain points where we don't), but this cannot be so if our cells are decaying at different rates, and at different times, can it?

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.

To travel into the past is to imply the existence of the past. You have to have something to go to and, as I've already said before, the past doesn't exist now.

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.

Why is it that you think time works so differently from space? There are not infinite copies of me in space, so why should there be in time? Besides, the fact that I was there at that time, doesn't mean that I'm still there. In fact, it means that I am definitely not still there. All of space and matter/energy has moved on from that point, hasn't it?

Also, with regard to changing the present, that's not completely accurate. We are actually changing the future, since the present is where you are.

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

I disagree. A point's movement through space might produce a "line" but not its movement through time. I say this because a the only reason there is a discernable "line" in space, is because all parts of the line, along with the actual point itself, exist in together in the present. If there were a "line" or "path" through time, then the time axis would all have to exist in the present, which is self-contradictory.

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).

That's the problem. All of the people who believe that time travel is possible try to think of time in terms of frames, but this just doesn't follow. If all of time were frames, then the frames would have to all exist - and the term "exist" is in the present tense.

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.

But that's the point! Don't you realize that set frames of time couldn't possibly be changed?! The fact that going into the past means you change everything after the point you traveled to proves that normal travel along the t axis is not the constant production of new "frames of reality".

 

[radagast]

Originally posted by Mentat
This is interesting though. You say that our "fomer selves" should all be at these different points in time. That implies that we must be producing a "new self" at every one of the smallest intervals of time (otherwise we could run into certain points in time where we all do exist, and certain points where we don't), but this cannot be so if our cells are decaying at different rates, and at different times, can it?

A line is a point, existing through a span along a single dimension. The point doesn't have new selves. The problem your running into is that you assume that we are not truly 4D entities (3spatial, 1Time). As a 4D entity/object we have existence bounded by three spatial dimensions and one time dimension. Our existence in the time dimension starts at our creation and ends with our dissolution. It's impossible to quite visualize, but the idea of a long worm, stretching throughout the span of ones existence is about as close to visualizing it as I can get. This is one of the requirements of a time dimension. It certainly does raise question about the immutability of future events and free will, but it doesn't logically invalidate time travel.

The problem with your above example is that it violates an initial 'given'. The initial premise is that time travel is possble, with your argument being finding the logical inconsistencies that this produces. Your example 'assumes' that time travel is impossible (just the statement that we don't exist in the past implies exactly such). If you wish to assume such, fine, but it does circumvent the debate, as I see it.

Why is it that you think time works so differently from space? There are not infinite copies of me in space,

This is something which may seem to be common sense, but cannot possibly be known. If you exist as an object with size in all four dimensions, and are only aware of three of them, with the time dimension only experienced as the moment, then it's not copies of you, but the continuation of you, just as the continuation of a point thru a span along single dimension is a line segment.

so why should there be in time? Besides, the fact that I was there at that time, doesn't mean that I'm still there. In fact, it means that I am definitely not still there. All of space and matter/energy has moved on from that point, hasn't it?

Not when time is considered a dimension.

Also, with regard to changing the present, that's not completely accurate. We are actually changing the future, since the present is where you are.

Depends on your temporal frame of reference. A person can only take action in the present of his personal temporal frame of reference - this has an effect/alteration on future events/reality from that point in time forward.

I disagree. A point's movement through space might produce a "line" but not its movement through time.

Again, you are treating time as something other than a dimension. It does exactly produce a line segment, just a line perpendicular to the three spatial dimensions. You cannot treat time, in the abstract, as totally different from the other dimensions.

That's the problem. All of the people who believe that time travel is possible try to think of time in terms of frames, but this just doesn't follow. If all of time were frames, then the frames would have to all exist - and the term "exist" is in the present tense.

You cannot use semantics to alter reality. If the past exists, as stated, then it exists and the common usage of the word needs to be expanded.

But that's the point! Don't you realize that set frames of time couldn't possibly be changed?! The fact that going into the past means you change everything after the point you traveled to proves that normal travel along the t axis is not the constant production of new "frames of reality".

Just because it seems impossible or absurd doesn't make it so, any more than the apparent absurdity that time moves at different speeds, depending on what frame of reference you observe, or the apparent absurdity that you cannot precisely state a neutrino's position and momentum.

I say this because a the only reason there is a discernable "line" in space, is because all parts of the line, along with the actual point itself, exist in together in the present. If there were a "line" or "path" through time, then the time axis would all have to exist in the present, which is self-contradictory.

Such people as Stephen Hawkings, John Cramer, and Michio Kaku haven't raised the concerns that you are raising, so perhaps the arguments on the other side of the coin are not quite as illogical as you seem to elude to.

You continually contradict the assumption that time is a dimension of reality, and you seem to ignore the given at the start of this debate. With the two of us deviating on such a basic points, I see further debate to be unfruitful.

 

[Spacestar]

Not to jump into another's discussion, but don't you mean a change in position (or offsets)within the dimensional space. Otherwise I'd like someone to explain what 'changing a dimension' means.

I suppose elas is referring about how and why changing one’s position in time would affect the spatial dimensions.

I don't know if you are bringing up a semantic discussion. In other words, when you travel to a point in your past and change it, then semantically, it ceases to be your past, given defining the past as the history we remember/or would remember with perfect knowledge and memory.

The past it’s obviously what happenens in a prior point to our current position in the space/time line (clearly what we would remember). How can the past be a set of events and be another set of events at the same point in time?

Alternate past could mean an, initially, identical past in a parallel universe/parallel dimensional plane. Or it could mean that you have altered your own past (making it an alternate past) by traveling to it. If there is a third meaning, then you'll have to elaborate.

If not, as I see it, then the only violation of 'cause and effect' occurs if a paradox occurs - you go back in time change something such that your present self no longer needs to go back to the past, since he doesn't, the past isn't changed and the present self does decide to go back to the past...

What I mean is that you appear to be saying that the very act of traveling to the past automatically changes the past from what it was, creating thus an alternate/parallel space/time line. That’s what essentially violates the line of causation; since to get to a previous point in the space/time continuum that you are in, obviously one has to track back the same line of action. And the journey would alter only your personal time, not the space/time continuum itself. Accordingly, your presence in the past is a part of the cause that makes your space/time continuum the way it “is”.

Two wormholes will get you into the past, according to current theory. Your able to do some interesting things when you are can both create two wormholes and move one of the wormhole's mouth position in space.

That’s not what I’m asking.
Please let me reformulate the question: How you’d get in a different past, if you you’re following your space/time line?

And, I’d like to add that the current theory also states that you would need exorbitant amounts of energy (as the mass of Jupiter) to control and generate wormholes. Which, of course is very unpractical. Besides, the shifting the spatial position of the wormholes does not modify your position in the space/time dimensions. Actually, it puts you out of phase with your original dimensions. That’s more like interdimensional travel than time travel.

 

[radagast]

Originally posted by Spacestar
The past it’s obviously what happenens in a prior point to our current position in the space/time line (clearly what we would remember). How can the past be a set of events and be another set of events at the same point in time?

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.

What I mean is that you appear to be saying that the very act of traveling to the past automatically changes the past from what it was, creating thus an alternate/parallel space/time line. That’s what essentially violates the line of causation; since to get to a previous point in the space/time continuum that you are in, obviously one has to track back the same line of action. And the journey would alter only your personal time, not the space/time continuum itself. Accordingly, your presence in the past is a part of the cause that makes your space/time continuum the way it “is”.

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

That’s not what I’m asking.
Please let me reformulate the question: How you’d get in a different past, if you you’re following your space/time line?

As mentioned earlier, the traveller cannot follow his own 'personal' timeline back - assuming we are speaking of none-trivial time travel. I was speaking of just the same kind of time travel as theorized by using timewise wormholes.

And, I’d like to add that the current theory also states that you would need exorbitant amounts of energy (as the mass of Jupiter) to control and generate wormholes. Which, of course is very unpractical.

No argument here. This has always been, from my point of view, a hypothetically and theoretically oriented debate.

Besides, the shifting the spatial position of the wormholes does not modify your position in the space/time dimensions. Actually, it puts you out of phase with your original dimensions. That’s more like interdimensional travel than time travel.

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??]

 

[Mentat]

radagast, with regard to your previous response to my post,

I agree with your point about semantics, the terms would need to be expanded for newly discovered realities, not the other way around. I understand, also, that the great minds of science do not see the same problem that I do with time travel (probably because the problem doesn't really exist, and I just keep running into it due to some predisposition toward deductive logic instead of purely scientific inquiry).

However, I do have one point to mention. If I go back a few days into the past, there would (logically) be another "me" at that point, since I existed at that point, right? If this is so, then at that point in time (which is before this point in time) there were two of me (how long this circumstance existed is irrelevant for now). But then, in the near future, when I decide to go into the past, I will go back to the time where there are already two of me (as it seems there must be, according to the previous sentence) and thus there will be three of me at that point in time. But then, since there are three of me at that point in time, then there have always been three of me at that point in time, and so when I, in the near future decide to go back into the past, I will find three of me already there, and there will thus be four of me. This should go on infinitely, I think.

Also, I don't recall how it is you explain the problem of logic that I presented much earlier in this thread (that if you go back in time to any point before the time you leave, you have not yet left, and so are not yet traveling and thus have no means by which to arrive at this "past" point in time). Could you please address this one again (please forgive me if you've already covered it sufficiently before)?

 

[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.

 

[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.