time travel

[bigtimecow]

alright, i am pretty convinced that time travel (atleast into the past) is impossible, but i would just like to discuss it in a... hypothetical? form.


i have a big question that has been eating at me since i've seen any movies about time travel:

so like, in back to the future when marty goes back to the future (at the end) he watches himself (from afar) in the parking lot and the whole incident with him going back in time. this happens in a lot of movies and i just don't understand how this place in time works out.

so here are two timelines:
1. marty1 goes back in time, does his shit, then goes back to the future and continues living his life
2. (witnessed by marty1) marty2 goes back in time, and i guess does his shit, then goes back to the future and continues living his life.

now, if this were true, wouldn't marty2 go back to the future at the same time, in the same exact place, etc. etc. as marty1? and then marty1 wouldn't witness marty2 going back in time because they would be like, standing right next to eachother.

i might have just answered my own question, further proving that time travel isn't possible. or my thought process is incorrect. i'm not sure.

i know in some movies the time traveler kills his/her double from the past, which i guess kind of works, but i'm not really sure.

your thoughts?

[Esuohlim]

Time travel is a very fascinating subject to me and every time I am inspired to write a short story it's always based on time travel, particularly with the paradoxes involved.

I once wrote one for a class in high school that starts out with a kid having his life saved by his future self (who dies in the process), and then after 12 hours of events the story ends right back where it started only he himself does the saving/dying . Throughout he deliberates about the futility of the situation, and of course the events are all set in stone whether he likes it or not as it had already happened and even his false sense of free will can't get him out of the infinite loop his life had ended up in

[Pub Lover]

Effect results in cause? Spacetime is only linear from our perspective? Maybe there was only ever one timeline? Or maybe timetravel is too complicated for Hollywood script writers that are just shooting for entertainment & not logical plausibility.

Anyway, time travel is easy. All you need is a series of four circulating laser light beams swirling spacetime.

And to be smaller than a sub-atomic particle.

[bigtimecow]

i guess there is actually only 1 timeline, but there are like... 2 subtimelines?

[Tadao]

There is only 1 timeline for your personal existence, you may think you have altered it, but you really didn't.

[MetalMilitia]

I read an article recently which proposed that time doesn't really exist. To me sounds just bizarre enough to be true. So I suggest a scenario of:

1. marty1 doesn't go back in time.

[Dr. Boogie]

If time doesn't exist, then how come it takes a pizza 30-45 minutes to get to my house?

[Sleazeappeal]

As 3-dimensional beings, we are isolated to a single timeline. Even if we did travel to the past and alter things, all that would do is create an alternate timeline that we would be unable to shift ourselves to upon our return to the present.

[Sethomas]

If someone went back in time to alter the past then we'd know about it from the past. Hence, if you wanted to destroy the universe with the grandfather paradox, you'd be wise to ask your grandfather if he remembers any strange encounters with someone resembling yourself. If he says "no", then it's obvious that you will never undertake a mission to the past that involves him, so you fail. If he says "yeah, I kicked his fucking ass and then he died", then you will have the interesting experience of living out the rest of your days with the known and immutable fate of getting killed by your grandfather with all imagined conceptions of free will being shattered.

[AChimp]

It's the same Marty, but a different version of him, from a separate point in time that happened to go back in time to a point where he already existed.

Imagine you going back in time to write this post, then returning to the present, then going back in time again but to some time slightly different (maybe a few seconds earlier or later). You'd be in the same situation as the movie and get to see yourself typing :O

[AlliSabbah]

Bah and double bah!!! Next thing you people will be saying that we are able to make machines to fly through the sky.

All myths and hullabaloo.

[Esuohlim]

Originally Posted by Sethomas

If someone went back in time to alter the past then we'd know about it from the past. Hence, if you wanted to destroy the universe with the grandfather paradox, you'd be wise to ask your grandfather if he remembers any strange encounters with someone resembling yourself. If he says "no", then it's obvious that you will never undertake a mission to the past that involves him, so you fail. If he says "yeah, I kicked his fucking ass and then he died", then you will have the interesting experience of living out the rest of your days with the known and immutable fate of getting killed by your grandfather with all imagined conceptions of free will being shattered.

This is what's interesting about the "going back in time to kill your parent/grandparent/etc." paradox. Even if time travel were possible killing an ancestor would be impossible because it would have had already happened, but it couldn't have happened because the killer would never have been born

So if any of you guys plan on going back in time and killing your deadbeat father don't bother because you obviously must have done it wrong already.

[Pub Lover]

Multiple Universe Theory.
In which non-linear time travel is impossible without causing Seth's absolute past scenario, but you can travel to alternate dimensions where different stuff happened. If you have both non-absolute past AND multiverse my head hurts, so quit doing that one tv.

[Esuohlim]

With that theory and some higher dimensions, maybe instead of going back in time and altering the future you could instead just skip ahead straight to the altered future and save some trouble.

[Pub Lover]

The math to find the perfect universe would consume your entire life.

In progressive time you can kill your ancestors, cause yourself to unexist but not undo events that resulted in that situation as those events did happen in a non-time element, which is really just multiverse craziness badly thought out.

[bigtimecow]

Originally Posted by MetalMilitia

I read an article recently which proposed that time doesn't really exist. To me sounds just bizarre enough to be true. So I suggest a scenario of:

this makes sense. but i mean, time obviously exists because it... "happens." but yeah, we have no sense of time without clocks. and the "units" of time or whatever are completely made up by us humans.

but yeah, i know now for sure that time travel to the past is completely impossible because of the whole anything that you do back then would have already happened.

[Tadao]

But you would have to wait till the future to find out that you went to the past to do whatever you did. Unless you saw your future self do it or someone told you that they saw you do it. In either case, you wouldn't believe your own eyes or the person telling you the story.

So how again do you know that time travel to the past can't happen?

[bigtimecow]

wait, why would i have to wait til the future to find out what i did?

[Tadao]

Because in order for there to be a past to go to, the future must happen. Or I guess the now works, but still... even if you went back in time this second to do something in the past, your past would have known you did something unless you went up to yourself and told yourself that you did that. But you might not for some reason, so your past might not know what you did until the future.

I guess you could go find the past you and tell yourself about your antics, but you didn't obviously.

[Dr. Octogonopus]

The way I understand it, it's technically possible to travel backwards in time. It would just take immense amounts of energy, more than can be created from all the earthly materials. But, it is impossible to travel forwards, because it does not exist yet. So, in a way, if you had perfected cryogenics, you could put yourself in cryo, hope you get revived, and eventually go back into your proper timeframe. But it would be waaay more trouble than it's worth.

[Sethomas]

Time travel to the future is quite a bit easier than into the past. All you have to do is manipulate your frame of reference so that it observes time pass slower than your surroundings. It's extremely minute, but if you actually go jogging for a few minutes rather than sit still then you will have actually observed more time to have passed because of time dilation. (Your mental "watch" will tick billionths or whatever of a percent slower than the stationary world, so when you stop jogging, you are further into the future than if you remained stationary.)

[Fathom Zero]

Not strictly time travel, but speaking of multiple universes, I figured out a way to make Maxwell's Demon feasible.

[Colonel Flagg]

Suggested reading: "Timemaster" by Robert L. Forward. It deals with many of the very questions raised in this thread, in an engaging and compelling narrative.

[executioneer]

didn't they already get a beam of light to arrive at its destination before it left in an experiment

could they use this to communicate... with the past

[Tadao]

Originally Posted by executioneer

didn't they already get a beam of light to arrive at its destination before it left in an experiment

could they use this to communicate... with the past

I need news articles before I even begin to believe it happened.