# Favourite SF paradoxes



## Mighty mouse (Nov 15, 2006)

All prescients seem to die young

If time travel were possible you could go back 20 minutes to put a bomb under your chair to go off 10 minutes later.


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## Sharukem (Nov 15, 2006)

Mighty mouse said:


> All prescients seem to die young
> 
> If time travel were possible you could go back 20 minutes to put a bomb under your chair to go off 10 minutes later.


yes you could do that but what would the point of it?  And if time travel was possible people would use it to their advantage by changing the past which would therefore change the future and completely mess up what we have today. Like I know people that still want the fur trade to be going on instead of money becasue they think that it would be better, yet there are people who want to bring back those who are already passed away like Alexander Graham Bell. And if they did that then we wouldn't have our phones and crapt like that. But yes I would find time traveling quite interesting in my mind. But to do it that is a whole other matter.


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## Mighty mouse (Nov 15, 2006)

The way I see time travel working (outside of the relativistic type) is that whilst possible you would have to do it in a side dimension allowing observation but no causal contact. 
Some law of quantum physics will doubtless prevent causal contact and stop you having any fun


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## SpaceShip (Nov 15, 2006)

That sounds a bit like having your fortune told!  How awful would it be to be watching something in the future that was absolutely, heartbreakingly awful and not be able to do anything about it except - if it weren't too far in the future - waiting for that event to actually happen!  No - don't like that thought.


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## BookStop (Nov 15, 2006)

You should try _The Time Traveller's Wife. _Excellent book that adresses that very issue.


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## Pyan (Nov 15, 2006)

_Life-line_ by Heinlein covers it well, too. And try _By His Bootstraps_ (same author) for an amazing paradox story.


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## Mighty mouse (Nov 15, 2006)

> That sounds a bit like having your fortune told! How awful would it be to be watching something in the future that was absolutely, heartbreakingly awful and not be able to do anything about it except - if it weren't too far in the future - waiting for that event to actually happen! No - don't like that thought.



No worries, I reckon time travel will only work backwards, otherwise it would conflict with free will.
In turn that would conflict with my proof that God exists which is:
If he didn't the universe would be a lot more fun


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## SpaceShip (Nov 15, 2006)

Mighty mouse said:


> No worries, I reckon time travel will only work backwards, otherwise it would conflict with free will.
> In turn that would conflict with my proof that God exists which is:
> If he didn't the universe would be a lot more fun


I think the Doctor might have something to say about your first sentence.
I'm sure I don't agree with your second.


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## Andrew Hook (Nov 15, 2006)

Of course, the paradox is: if time travel is possible then where are all the time travellers?

Liked "The Time Traveller's Wife" a lot, by the way. A very intricate and emotive book, but also a good story well told.


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## steve12553 (Nov 16, 2006)

Mighty mouse said:


> All prescients seem to die young
> 
> If time travel were possible you could go back 20 minutes to put a bomb under your chair to go off 10 minutes later.


 
Probably would add 20 minutes to the timer on the bomb which would be found by you in time to take it back in time to set it to go off  too late to allow you to find it in time to take it back into time............................

Either that or when the bomb went off the you that set up the timer would cease to exist so the bomb would fail to go off. The explosion would sit on the verge of happening and maybe you would just sit there in that living hell almost blowing up for eternity.


Or.........


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## SpaceShip (Nov 16, 2006)

Eh? .........


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## j d worthington (Nov 16, 2006)

Similar to the "Grandfather Paradox": You go back in time and shoot your grandfather before he and your grandmother met. But in doing so, you make sure they had no children, so your father/mother didn't exist, so neither do you. Which means that you can't go back in time and shoot him, so they do meet, have children, and your father and mother get together and have you. Then you go back in time and shoot your grandfather before he and your grandmother meet, so they have no children, and so.....

I think mine is the one that serves as the frame and running thread throughout Van Vogt's *The Weapon Shops of Isher*. And, no, I won't explain that one here, as it would spoil the story for those who haven't read it... and I think it culminates in one of the nicest final lines in all fiction.


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## Mighty mouse (Nov 16, 2006)

I wander what the time travel process is, say

1. You and bomb go back 20 minutes and co exist with previous self
2. You and bomb somehow replace the previous self
3. We have a mind so the physical person is unchanged but the mind goes back 20 minutes
4. It would only work by replacing atom for atom on a quantum level so you would have to slice a cube containing you and bomb from the present and interchange it with a cube in the past.

The question also arises what do you 'remember' in each case?

In relativistic time travel I think it occurs because of differences between different frames of reference. In non relativistic time travel are you are talking about moving between frames of reference?

In guess my personal take is that time travel proper is not possible as it negates the role of God.


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## Harpo (Nov 16, 2006)

Andrew Hook said:


> Of course, the paradox is: if time travel is possible then where are all the time travellers?


Simple answer - when we get time travel it will be a matter of machines within which we travel through time.  The machines themselves will not travel.  
Suppose a time machine is built and it works for fifty years before breaking down.  A person could travel anywhen during those fifty years.  At the time when the machine breaks  down, a new machine would be built alongside it, which work operate for the next fifty years (or however long).  It'll be like elevators which each cover a section of skyscraper levels.

So - no time travellers until the first time machine gets invented and switched on.  I predict december 21st 2012


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## j d worthington (Nov 16, 2006)

Harpo said:


> Simple answer - when we get time travel it will be a matter of machines within which we travel through time. The machines themselves will not travel.
> Suppose a time machine is built and it works for fifty years before breaking down. A person could travel anywhen during those fifty years. At the time when the machine breaks down, a new machine would be built alongside it, which work operate for the next fifty years (or however long). It'll be like elevators which each cover a section of skyscraper levels.
> 
> So - no time travellers until the first time machine gets invented and switched on. I predict december 21st 2012


 
I've seen you talk about this idea before, Harpo, and it's an interesting idea... but I have a question: How do you see it working, precisely? I mean, if the machine doesn't move, how do they travel in time? Is it physical travel? Mental travel (and if so, how does that work, since all the indications are that personality, soul, whatever you choose to call it, is an epiphenomena of the brain's functioning ... inseparable from the structure of the brain itself). And do they have any sort of interaction with the time they travel into? What happens to their atoms in the present, and where do the atoms that would comprise their being in that time come from? Etc.....


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## SpaceShip (Nov 16, 2006)

I wonder if this thread would have happened at all if I had been able to travel back in time and kill the man who discovered dynamite and the one who was careless enough to tear an atom in two!


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## steve12553 (Nov 16, 2006)

SpaceShip said:


> I wonder if this thread would have happened at all if I had been able to travel back in time and kill the man who discovered dynamite and the one who was careless enough to tear an atom in two!


 
Surely one of the two products saved a key ancestor of yours in a way that drew no attension and allowed you to exist to go back to.........
Hence the paradox. People don't keep near adequate notes on everday life.


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## Harpo (Nov 16, 2006)

j. d. worthington said:


> I've seen you talk about this idea before, Harpo, and it's an interesting idea... but I have a question: How do you see it working, precisely? I mean, if the machine doesn't move, how do they travel in time? Is it physical travel? Mental travel (and if so, how does that work, since all the indications are that personality, soul, whatever you choose to call it, is an epiphenomena of the brain's functioning ... inseparable from the structure of the brain itself). And do they have any sort of interaction with the time they travel into? What happens to their atoms in the present, and where do the atoms that would comprise their being in that time come from? Etc.....



Today I discovered that Ronald Mallett has the same idea, that time machines themselves actually stay put, the time travelling is done within them.
As for how it works, ask him:
courant.com | On The Long Road To Making Time Travel A Future Reality


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## Tau Zero (Nov 19, 2006)

Andrew Hook said:


> Of course, the paradox is: if time travel is possible then where are all the time travellers?


 
There are two possible answers:

1. Time travel is not possible.

2. Mankind does not survive long enough to develop the technology.


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## Andrew Hook (Nov 19, 2006)

Has anyone here seen the movie _Primer_? Quite relevant to this topic I think. I loved it, but it took some time for what was happening to work it's way into my head.


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## steve12553 (Nov 19, 2006)

Tau Zero said:


> There are two possible answers:
> 
> 1. Time travel is not possible.
> 
> 2. Mankind does not survive long enough to develop the technology.


Or natural law forbids interfernce. Or interference does not allow memory of events with 2 results.  Or.........


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## Tau Zero (Nov 20, 2006)

I've always thought that if you're going to time travel, then you have to cross into a parallel universe.  In other words, you can't go back in your own time stream, but traveling into the past takes you to a parallel universe where the differences are to slight to notice.  In that time stream you can do whatever you want to change their future and when you return, you return to the time stream your left.  Whatever you did in the past to the "other" universe has no effect on yours.  

In this case there is no paradox. I can go into the past, meet and kill my past self and return to my present.  I would still exist, because in my time stream, i never died.  In the other universe, i was killed.


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## manephelien (Nov 20, 2006)

Barring the possibility of going to different parallel universes, I believe that the past is fixed and we'll never be able to go there. The future is another matter, since it hasn't happened yet and there are nearly infinite opportunities. However, I'm not sure anyone'd care to take the risk of going 200 years into the future and find an Earth destroyed by nuclear war or climate change. If we ever build a starship that travels even at a fraction of the speed of light, relativistic time dilation effects will ensure that the people who use them will travel into the future, but that's strictly a one-way trip.


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## j d worthington (Nov 20, 2006)

manephelien said:


> Barring the possibility of going to different parallel universes, I believe that the past is fixed and we'll never be able to go there. The future is another matter, since it hasn't happened yet and there are nearly infinite opportunities.


 
Just as a point of argument... are you sure about that last? Have you considered the possibility that the future, too, is a deterministic one, the inevitable outcome of all that has gone before... that it may in fact exist, but we just aren't equipped to see it yet (the time-frame idea)? The other tends to indicate free-will, and I'm not sure that's a valid concept, when one really examines it. Perhaps, with the uncertainties introduced by quantum physics it may be ... but I rather doubt it. Again, it may just be that we are too limited in perspective to be able to tell that whatever choice we make was already predetermined by our biological and social heritage combined with our own personality and the antecedent and circumjacent circumstances.... Something to think about, anyway.


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## Mighty mouse (Nov 20, 2006)

Are you not just arguing from the point of view of God? a viewpoint which has to be deterministic.
Whether God exists and whether she plays dice or not aside, the universe certainly does play dice according to quantum electrodynamics and unless you are God free will for all intents and purposes therefore exists.
Is free will therefore a relativistic concept?


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## ElJayDee (Nov 21, 2006)

If time machines are invented, I think it will be a look only device. That is it will be like a telescope you reactivate photons as they were at a particular time and you see what was. You cannot interact with or alter it.


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## Paige Turner (Nov 21, 2006)

ElJayDee said:


> If time machines are invented, I think it will be a look only device. That is it will be like a telescope you reactivate photons as they were at a particular time and you see what was. You cannot interact with or alter it.



Or can you? _Macroscope_ by Piers Anthony. Good book, as I recall.


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## steve12553 (Nov 22, 2006)

Check Heisenberg's Uncertainty Theory. If you measure something or view it, you affect it.


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