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re: time travel: presentism, going nowhere and personal time

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Hi James

I like it.  I wrote something a bit similar in an exam once.  Well. Obviously it wasn't in dialogue form, and it didn't involve alice. Both of which, I imagine, dragged my marks down. But still.

The question was 'is backwards time travel compatible with presentism'.  I started with the line 'In this essay I will argue that backwards time travel is compatible with presentism'. Then wrote an answer. Decided it didn't work. Panicked. Then went back through adding in strategic 'not's. then handed it in with the vague hope it might still make some kind of sense.

So, I decided that your way of thinking of time travel in presentism is the only way that makes sense, but then I decided that it wasn't time travel (as you suggest towards the end), which means that time travel can't be possible in presentism.

The problem, I thought, with time travel in presentism normally was that, if you think of the sort of story in Kellor & nelson's paper, it involves causation occurring across temporally distant points, and that seems really difficult to understand if you deny that time is a dimension (which could be warped in some way so that the future was contiguous with the past).  The solution for the presentist was then to say that you could 'rewind' time, so that going back in time just involved causation across temporally contiguous points, exactly like the normal flow of time, except the causation would be backwards causation in some way.  I could rewind time to 2 hours ago and then start it up in the other direction again. There's some difficulties with either me being rewound as well, or there being extra matter created to make a copy of me while I am protected, etc. but I think even ignoring these there is a real problem with saying this is really 'time travel' in any sense.

What does it mean to say that we are 'rewinding time' (which is a phrase you don't use, but bear with me).  That seems to bring up ideas of time as a dimension that you can go back along. It doesn't sound like something open to the presentist. The presentist seems to have to say something about reversing causation or reversing the laws of nature or rewinding the universe. But this is just to say that we will change the current state of the universe such that it is like what it once was.  It doesn't make backwards causation a fundamentally different thing from normal causation, i.e. involving different directions of time; 'time would still be moving forward' as you say.  You can change the state of the universe so that it is exactly similar to some past state of the universe, but that doesn't make it actually that past state of the universe. To call that time travel would seem a bit like making a perfect mock up of ancient Greece and then walking into it claiming to have traveled back in time.

You say 'time would still be moving forward. It would just be that change was happening backwards' and that perhaps this is not a problem if we accept that time and change are the same. But I don't think that helps, because once you accept that I find it difficult to see how you can make sense of the normal use of the phrase 'time travel' at all, so you have to give up on it anyway.

Nick(3)


>>> "James Alexander Cunningham" <0203734C@student.gla.ac.uk> 12/21/05 12:24 AM >>>
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Bit of a Christmas treat for you here. Since I am only really posing a question here I decided to bulk things up a bit and write it as dialogue. Do let me know what you think as I think they are rather fun. I don't have much expertise in this area, and I'm away from libraries so reading up is a bit tricky. I hope you'll still find this interesting.

 The first question that arises when one writes a dialogue is that of characterisation. Well, Plato used actual people in his dialogues, and if it was good enough for him it is good enough for me. In that case who else could my first character be but Alice? The second character was more of a problem. Me? I think I would find that rather awkward. I toyed with various other ideas but a bit of lateral thinking brought me to the obvious answer. The Cheshire Cat. I don't know if our own dear Alice has had any adventures down rabbit holes as a child but if she had maybe something like this might have transpired:


It was growing dark and Alice was lost. The forest was pleasant enough during the day, but as night creped in it became more and more threatening. Shrieks and howls came from across the trees and shining eyes watched her from the undergrowth. She had no way of telling the time. She did not even know what time it usually got dark in this queer new country. Hungry, tired and dejected she sat down. Presently she looked up, and could barely stifle a scream. An enormous cat looked down at her. It was sitting on a bough of a nearby tree, grinning enormously. 
"Good evening." said the Cat, placidly.
"I. . . Good evening" said Alice, remembering her manners. "I wonder if you could help me. I'm lost you see."
"Ah," said the Cat. "You have tried going that way?" nodding in one direction.
"Yes, I've been going round in circles for hours." replied Alice.
"Then you must have gone that way too." said the Cat, nodding in another direction.
"I suppose so. I think I must have gone in every direction." said Alice.
"But if you have been in every direction, and have not gone in the direction you wanted, where could you want to go?" asked the Cat.
"I just want to go back to when I wasn't lost." pleaded Alice.
"Well that is easy." answered the Cat. "Just go back the way you have come."
"But which way is that?" asked Alice, looking around.
"Why, back in time of course." said the Cat, still grinning.
"But," stammered Alice "surely that's impossible."
"Why should it be impossible? You can walk one way or the other. You move in time one way, why not the other?"
"Because time doesn't work like that. Just because we keep moving through time it doesn't mean we are time travelling. To time travel I would have to leave you behind here and now, disappear and re-appear some time in the past." Explained Alice.
"Well why don't you do that?" yawned the Cheshire Cat.
"Because the past doesn't exist, only now exists. You can't travel somewhere that doesn't exist, you know."
"Maybe, maybe not." the Cat said, turning his head first one way then the other. "But even if you're right, that needn't rule out time travel."
"Why not?"
"Well, why do you have to be the one who moves? If the entire world moved ten feet to the left but you stayed still, the effect would be the same as if you moved ten feet to the right. The same thing can happen with time."
"I'm not sure I understand." said Alice, narrowing her eyes slightly.
"Imagine that we have a bubble that holds you in exactly the same state, down to the atoms you are made of for however long you are there. Then suppose that while you are in the bubble the arrow of time turns around. The universe rewinds for, lets say, two hours. The bubble pops, and there you are, back in the past."
"But the universe couldn't rewind while I was in the bubble, because I wouldn't be in it. Everything I did and caused would be absent." objected Alice.
The Cat yawned. "If you like we can say that as you enter the bubble, an exact copy is made of you. One goes in, one stays out."
"But would the copy be me?"  
"It certainly wouldn't be "me", but it would be you." the Cat said.
"I think I understand you. Though I wouldn't be time travelling. Time would still be moving forward. It would just be that change was happening backwards or not at all in my case."
"Is there really a difference between time and change?" asked the Cat.
"Maybe not." replied Alice. "None of this is of very much help though as I ca'n't do any of this anyway."
"In that case," said the Cheshire Cat "I should go that way, if I were you." indicating a path. With that he began to disappear, starting with his tail, until only his grin was left behind.

To be continued if I can be bothered.

I beg forgiveness from both Alice and the shade of Lewis Carroll.




Love you babies.

James






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