# Time Travel



## VKALFIERI (Dec 7, 2017)

Is travel to the past to change something in the future fruitless? 

Is travel to the future fruitless?

How does time travel work?

I've watched a lot of time travel shows and even tried to write a few stories including time travel. 

I've recently been watching The 4400 and it seems kinda fruitless that whoever sends the 4400 people back has enemies that want to stop them from what they're sent back to achieve. 

I mean, won't they just keep sending them back because otherwise if the future is changed the 4400 would never have been sent back in the first place. 

Darn wibbly wobbly timey wimey stuff!


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## Harpo (Dec 7, 2017)

I've been saying this since I arrived here years ago.

Someday, somebody will invent the first Time Machine. But it won't go anywhere, instead people will be able to travel back and forth within it during the time it remains operational (for comparison, think of a lift shaft or a railway line - people travel upon them but the things don't themselves move at all)

Suppose that first machine remains working for, let's say, fifty years before it finally ceases to work.
Because it'll be known when that end-date is, a new time machine can be built alongside the firs one in fifty years, or in forty nine years or whatever, for people to travel even further into the future (again, just like people changing lifts or trains to continue their journeys)

Now suppose that eventually there'll be an entire chain of time machines placed beside each other in this way, allowing time travel for many centuries into the future.
Now imagine the people from the future travelling back in those same machines, all the way back to the time of the very first machine.
They can travel only as far back as the moment when the very first machine is switched on. (Just like passengers in lifts and trains cannot travel in them beyond the lift shafts or railway lines)



Further discussions for your enjoyment:
Temporal Anomalies in Popular Time Travel Movies
an interesting look at time travel...
Time travel: Back in Time
time travel
problems of time travel being common and ordinary


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## Brian G Turner (Dec 7, 2017)

I would recommend you have a read of the Wikipedia page about it, as it's pretty comprehensive and should provide useful pointers: Time travel - Wikipedia


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## farntfar (Dec 7, 2017)

You really should have seen what Vkalfieri's question was before he came back and changed it.


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## Venusian Broon (Dec 7, 2017)

VKALFIERI said:


> Is travel to the past to change something in the future fruitless?


We don't know.



> Is travel to the future fruitless?


Well, we do it constantly, so in that sense no. But I think you mean to 'jump ahead'. For that...we don't know. Because...



> How does time travel work?


...despite some suggestions on how a time machine may have to manipulate spacetime are possible via General Relativity, any practical solution is fraught with paradoxes, almost impossible energy/mass requirements and the fact that even if GR is correct (it isn't in a strict sense, but works very well as an approximation) we are still far away from a true understanding of the nature of time...

So we don't know.


Feel free therefore to speculate any wondrous time nature in writing speculative stories! I have a particular favourite...but you'll have to wait till I write the novel that utilises it.


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## Vladd67 (Dec 7, 2017)

I remember reading in some physics book the theory that if time travel did actually become available you would not be able to travel back before the time machine was invented. I seem to recall diagrams with cones etc.


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## Harpo (Dec 7, 2017)

Makes perfect sense to me, and answers all those "where are they?" questions


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## Venusian Broon (Dec 7, 2017)

Here's a timely Video on the topic of fictional time travel


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## Cathbad (Dec 7, 2017)

Venusian Broon said:


> So we don't know.



I know!

But I won't tell!

Promised, 'ya know.


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## Venusian Broon (Dec 7, 2017)

Cathbad said:


> I know!
> 
> But I won't tell!
> 
> Promised, 'ya know.



I like not knowing. I mean, if we knew everything, then wouldn't it just get _really _dull.


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## farntfar (Dec 7, 2017)

I used to know everything.
But then Cathbad went back and changed it all.


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## Cathbad (Dec 7, 2017)

I have only obeyed orders!!


Hey, that excuse worked for Ollie North!!


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## BAYLOR (Jan 12, 2018)

There is still the issue of the Grandfather's paradox..


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## Harpo (Jan 12, 2018)

BAYLOR said:


> There is still the issue of the Grandfather's paradox..


Not if time-travelling doesn't work that way. If its restricted to all of time _after _the invention of working time machines, then there's no problem.

Either that or the multiverse & alternate timelines, anyway


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## farntfar (Jan 12, 2018)

I went back and killed my grandfather, but he cheated.
He had 2 daughters, just in case.


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## Lumens (Jan 12, 2018)

Ah, you are supposed to go _back_ to kill your grandfather...


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## farntfar (Jan 12, 2018)

Schödinger's grandson's cat did it too.

Boy was that one mixed up cat.


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## mosaix (Jan 15, 2018)

Venusian Broon said:


> I like not knowing. I mean, if we knew everything, then wouldn't it just get _really _dull.



Not sure about that, VB. There's lots of things that I know about, that I've known about for ages, and I still find them very interesting.


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## lynnfredricks (Jan 19, 2018)

VKALFIERI said:


> Is travel to the past to change something in the future fruitless?



No proof needed, there was definitely fruit in the past


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## J Riff (Jan 19, 2018)

And, I thought of a great time travel joke for you, but you didn't like it.


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## Mike Donoghue (Jan 20, 2018)

I've got some food for thought on the matter of _controlling_ the passage of time around you (like in movies), although I'm not sure how it relates to worm holes and the like. Here it goes: temperature is a measure of the average kinetic energy of atoms, molecules, etc. in a specific region of space. If time were to "speed up" around you, the motion of things would also increase, thereby raising their temperature. Well, if time were to "freeze" around you, then everything would suddenly fall to absolute zero! This thought experiment is actually what got me interested in physics when I was a little kid. Anybody know if that is actually the case for time dilation?


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## J Riff (Jan 20, 2018)

If only 'time' was a physical medium, maybe we could figure it out. But tisnt, so there's nothing to get hot or cold about it. Apparently, though, time dilation kicks in at less than the speed of light. Maybe someone can explain that, but it won't be me. )


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