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just watched the new haruhi episode and it ended up in an discussion with a friend on what happens when you time-travel.
we didn't really succeed in solving this on a common ground so maybe someone from here could explain it to me:
when you travel back in time three years and WAIT there until you are in the present again (let's say you are frozen so you don't age), is there an alternate reality from where you departed which WENT ON (without you because "time doesn't wait" - my friend's argument) or is it just ONE reality/present which you "reach again" after three years (so for someone from the present where you departed and who observes it it would look like the second you departed you pop up again)?
so the question is, are there multiple realities which alternate in their structure, so multiple arrows of time or is there just ONE arrow. (do you reach your one present where you departed vs are you in an alternate reality and the reality where you departed you don't exist anymore because the time doesn't wait).
I hope I could make clear what I mean / what our controversy was about and maybe someone who studies physics, or just someone who can think logically very well can make clear to me what's the right perspective to view this.
feel free to discuss! (watching the new haruhi episode isn't necessary if you have understood the basic problem).
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Well, if you go back in time and killed your grandfather (the old thought experiement) would you cease to exist?
The answer is no because as soon as you travel back in time you enter a parrallel universe in which you travelled back in time, and you can do anything because in this universe the future (that you travelled back from) doesn't eist yet and can be altered by you in any means that you see fit.
So an easier way of looking at it is that at any point in which you exist, the future does NOT exist yet, so it is subject to change.
So yeah in a sci-fi world time can have many lines rather than one continuous one.
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Quantum physics does mention something about this and that there are multiple possible futures for one reality but only one past for each reality. It is not possible to know which future one reality would have but maybe you can work to establish a future that you want to happen.
I think that people still know about your existence in the dimension that you departed, you just lose your presence there and time will still flow in that dimension. You might not reach the same reality because it is in a totally different dimension.
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The way I tend to view it is that it must be different universes or time travel must be impossible.
If time travel was possible in a single universe system, all it takes is one guy with bad intentions to kill us all and I don't think I'm dead yet.
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What if you could time travel 1 hour ago?
Would go appear at the same universe that you came from? Wouldn't you see yourself and cause a paradox?
If you can see yourself and interact with your past self, doesnt that mean that you are now in a universe where you were meant to appear at that given time?
You can confirm you are not in the same universe that you were 1 hour ago because you never saw yourself appear out of nowhere 1 hour ago, remember?
So for time travel to be possible you must be able to time travel to another universe where you were meant to come to existance at that precise time.
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Well you guys are arguing about something theoretical so there is no real answer. But i would think that unless you did nothing to effect the time period you traveled to, then there would be an alternate reality. But i don't think your original time period would go on without you. the time period you traveled to would have two of you and when you got to the exact time that you time traveled the other copy of you would disappear and you would be the only one there.... oh but wait if you messed up the the......fuck if you time traveled the universe would implode and we would all cease to exist.
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Or as I read somewhere, you can only travel foreward. In that book the only thing you could do which looked like traveling backwards is looking. You couldn't interfere, obs only.
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time travel, as much as you make theories and stuff like that, literally doesn't make any sense at all!
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First off, theoretically, time travel is possible, however it is not presented at all how you all think it is.
You have to understand how time functions and the way gravity effects time. In order to travel in the past, you would have to create a wormhole (You do this by colliding two sub atomic particles (think large hadron collider except 50x as large and it has to be built in space) until it creates a super heated plasma which is around 10 trillion degrees, when this happens you would have to increase the energy to the ball by using lasers this then allows the wormhole to exist eternally), one in which is at 'normal' time (what we know of as time on this planet) and then the other is somewhere with huge gravitational time distortion (effect of slowing time). At this point, the wormhole is as small as sub-atomic particle, this is when you would have to enlarge it by feeding it more energy. In this light you can see how at one place you have two different times, one going on as normal 'present' the other going much more slowly and 'in the past'.
It is the same as looking out into the stars. What we see is the past. This is how we are able to use doppler effect and other measurements to create a picture of the universe.
Anyways, it is impossible to 'go back in time' like they do in Sci-Fi. It doesn't work that way.
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From what littler about quantum physics that I understand, it is technically possible to time travel if one were able to travel faster than the speed of light. Because of relativity, as traveling close to the speed of light causes time in realspace to rapidly "slow down," some theorists believe that surpassing the speed of light would allow one to travel backwards in time compared to realspace. Of course, it would also depend how fast compared to the speed of light one is traveling.
Of course, traveling faster than the speed of light is impossible.
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haha that got me thinking.
so i guess 90% of the stars we see when we look up may be already dead? o,o
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On May 22 2009 23:49 Caller wrote:
From what littler about quantum physics that I understand, it is technically possible to time travel if one were able to travel faster than the speed of light. Because of relativity, as traveling close to the speed of light causes time in realspace to rapidly "slow down," some theorists believe that surpassing the speed of light would allow one to travel backwards in time compared to realspace. Of course, it would also depend how fast compared to the speed of light one is traveling.
Of course, traveling faster than the speed of light is impossible.
It is not impossible (theoretically anyways). The universe expanded, and is expanding faster than the SoL.
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what i have to say about time travelling is that most likely it would kill you. Consider that you somehow had a physical portal to one hour ago. It is anchored in time at exactly one hour ago. Now, while we generally count time in the seconds, time constantly passes by. As you stuck your hand through the portal, the first cells to go through would end up in a different place than the cells behind them and so on and so forth. This is really hard to explain, but basically you would end up as a bunch of cells seperated by nanoseconds in time. The only way to survive time travel would be to go through instantly, everything at the same time.
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i'd be happy to time travel just 1 hour ago, so i could see what the numbers of the lottery will be.
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On May 23 2009 01:09 ghermination wrote:
what i have to say about time travelling is that most likely it would kill you. Consider that you somehow had a physical portal to one hour ago. It is anchored in time at exactly one hour ago. Now, while we generally count time in the seconds, time constantly passes by. As you stuck your hand through the portal, the first cells to go through would end up in a different place than the cells behind them and so on and so forth. This is really hard to explain, but basically you would end up as a bunch of cells seperated by nanoseconds in time. The only way to survive time travel would be to go through instantly, everything at the same time.
no, the entrance and exit of a "wormhole" would have the same eigentime. But the TNG episode with the warbird is nice, i agree
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On May 23 2009 01:09 ghermination wrote:
what i have to say about time travelling is that most likely it would kill you. Consider that you somehow had a physical portal to one hour ago. It is anchored in time at exactly one hour ago. Now, while we generally count time in the seconds, time constantly passes by. As you stuck your hand through the portal, the first cells to go through would end up in a different place than the cells behind them and so on and so forth. This is really hard to explain, but basically you would end up as a bunch of cells seperated by nanoseconds in time. The only way to survive time travel would be to go through instantly, everything at the same time.
Wrong. Read what I explained earlier. That 'portal' you are talking about is called a wormhole. Time is based around gravity. Special Relativity and General Relativity, couple that with reading about gravity will give you a greater understanding of time, time dilation, (there is actually, no time at the center of a black hole).
It is impossible 'to go back in time' like you think about in Sci-Fi. You wouldn't be going back '1 hour' of time in that space, you would be slowing time down, so that 1 hour in that time dilation field, is actually say, 5 years at 'earth time'. It's a complicated mess.
You can't 'rewind' time.
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On May 22 2009 23:50 Aegraen wrote:Show nested quote +On May 22 2009 23:49 Caller wrote:
From what littler about quantum physics that I understand, it is technically possible to time travel if one were able to travel faster than the speed of light. Because of relativity, as traveling close to the speed of light causes time in realspace to rapidly "slow down," some theorists believe that surpassing the speed of light would allow one to travel backwards in time compared to realspace. Of course, it would also depend how fast compared to the speed of light one is traveling.
Of course, traveling faster than the speed of light is impossible. It is not impossible (theoretically anyways). The universe expanded, and is expanding faster than the SoL.
its impossible, what makes you say "theoretically anyways"? your example is flawed. spacetime does expand not any mass or something. its pretty simple, you cant accelerate any reel mass on the speed of light. since we have mass, gg. you also cant move detectable information faster than light.
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Time travel in films doesn't make sense because they move to the position they were at the time.
For instance if you went back in time merely a few minutes. You would reappear in the middle of space and die very fast, because the Earth is constantly moving.
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On May 23 2009 01:38 aqui wrote:Show nested quote +On May 22 2009 23:50 Aegraen wrote:On May 22 2009 23:49 Caller wrote:
From what littler about quantum physics that I understand, it is technically possible to time travel if one were able to travel faster than the speed of light. Because of relativity, as traveling close to the speed of light causes time in realspace to rapidly "slow down," some theorists believe that surpassing the speed of light would allow one to travel backwards in time compared to realspace. Of course, it would also depend how fast compared to the speed of light one is traveling.
Of course, traveling faster than the speed of light is impossible. It is not impossible (theoretically anyways). The universe expanded, and is expanding faster than the SoL. its impossible, what makes you say "theoretically anyways"? your example is flawed. spacetime does expand not any mass or something. its pretty simple, you cant accelerate any reel mass on the speed of light. since we have mass, gg. you also cant move detectable information faster than light.
Scharnhorst Effect for one.
Coupled with the Casimir Effect, and Alcubierre drive, the theories are there.
When we finally figure out dark matter, and dark energy, I'm sure there will be ways. This is how the universe is expanding FTL. Dark energy/matter will be the secret mark my words. (That and manipulation of time space)
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United States24753 Posts
Haha these discussions are always enjoyable to read. The same things always end up happening.
I have to agree with those saying that time travel as we see it in fiction is mostly beyond anything we have reason to suspect we are capable of....
Relating time travel to actual science is nice, but people seem to get too confident in their conclusions. It's important to identify how speculative everything you say is, even if you took it from a professor of physics.
Also, I see people always throw around 'quantum mechanics' and then say stuff which has almost nothing to do with quantum at all. To those of you who actually have a reasonable understanding of general relativity, if any, then you are the only ones who have a hope of forming a reasonable opinion on this topic... and even then this is all pure speculation.
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if i ignore the mechanics of supposed time travel, and look only at the variants not breaking causality at the first look i can imagine no possibility not violating some physics. one possibility would be a closed loop in spacetime. a lightbeam i.e. traveling in circles in spacetime through our wormhole timemachine. this would not e able to take information form the future to the past hat was not already there else it wouldnt be a loop.. so a human in a timeloop would need to be "reset" which is bc ofc.also the light should not interact with anything, bcos any interaction with the quantum field(pardon my french) would be random by nature thus wouldnt allow for a loop.
the possibility also not violation causality is creating another universe. but where does it get its mass? also our universe would lose the mass of the timetraveller, which on the first look violates energy conservation.Maybe there is a simple solution for this massproblem i dont see, dunno.
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Korea (South)1541 Posts
those r both separate theories and ones we could never test... also it depends on ur terminology, some people don't consider reality jumping to be time traveling...
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On May 23 2009 01:55 micronesia wrote:
Haha these discussions are always enjoyable to read. The same things always end up happening.
I have to agree with those saying that time travel as we see it in fiction is mostly beyond anything we have reason to suspect we are capable of....
Relating time travel to actual science is nice, but people seem to get too confident in their conclusions. It's important to identify how speculative everything you say is, even if you took it from a professor of physics.
Also, I see people always throw around 'quantum mechanics' and then say stuff which has almost nothing to do with quantum at all. To those of you who actually have a reasonable understanding of general relativity, if any, then you are the only ones who have a hope of forming a reasonable opinion on this topic... and even then this is all pure speculation.
the thread is rather about the causal implications than about the actual mechanics.
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On May 23 2009 01:50 Aegraen wrote:Show nested quote +On May 23 2009 01:38 aqui wrote:On May 22 2009 23:50 Aegraen wrote:On May 22 2009 23:49 Caller wrote:
From what littler about quantum physics that I understand, it is technically possible to time travel if one were able to travel faster than the speed of light. Because of relativity, as traveling close to the speed of light causes time in realspace to rapidly "slow down," some theorists believe that surpassing the speed of light would allow one to travel backwards in time compared to realspace. Of course, it would also depend how fast compared to the speed of light one is traveling.
Of course, traveling faster than the speed of light is impossible. It is not impossible (theoretically anyways). The universe expanded, and is expanding faster than the SoL. its impossible, what makes you say "theoretically anyways"? your example is flawed. spacetime does expand not any mass or something. its pretty simple, you cant accelerate any reel mass on the speed of light. since we have mass, gg. you also cant move detectable information faster than light. Scharnhorst Effect for one. Coupled with the Casimir Effect, and Alcubierre drive, the theories are there. When we finally figure out dark matter, and dark energy, I'm sure there will be ways. This is how the universe is expanding FTL. Dark energy/matter will be the secret mark my words. (That and manipulation of time space)
ill answer that when im back later. oi
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On May 23 2009 02:03 aqui wrote:
if i ignore the mechanics of supposed time travel, and look only at the variants not breaking causality at the first look i can imagine no possibility not violating some physics. one possibility would be a closed loop in spacetime. a lightbeam i.e. traveling in circles in spacetime through our wormhole timemachine. this would not e able to take information form the future to the past hat was not already there else it wouldnt be a loop.. so a human in a timeloop would need to be "reset" which is bc ofc.also the light should not interact with anything, bcos any interaction with the quantum field(pardon my french) would be random by nature thus wouldnt allow for a loop.
the possibility also not violation causality is creating another universe. but where does it get its mass? also our universe would lose the mass of the timetraveller, which on the first look violates energy conservation.Maybe there is a simple solution for this massproblem i dont see, dunno.
The only plausible solution to the dilemma of 'how do humans travel across great distances and not die' is that of either 1. Wormholes 2. Time Dilation, the latter having significantly more problems to tend to than the former (namely any matter that stands in the way will pulverize the vessel and secondly, that of great quantities of energy needed).
The latter also having the problem that, when you get back, you will essentially have lived for hundreds of thousands - millions of years 'into the future' so to say.
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On May 23 2009 01:50 Aegraen wrote:Show nested quote +On May 23 2009 01:38 aqui wrote:On May 22 2009 23:50 Aegraen wrote:On May 22 2009 23:49 Caller wrote:
From what littler about quantum physics that I understand, it is technically possible to time travel if one were able to travel faster than the speed of light. Because of relativity, as traveling close to the speed of light causes time in realspace to rapidly "slow down," some theorists believe that surpassing the speed of light would allow one to travel backwards in time compared to realspace. Of course, it would also depend how fast compared to the speed of light one is traveling.
Of course, traveling faster than the speed of light is impossible. It is not impossible (theoretically anyways). The universe expanded, and is expanding faster than the SoL. its impossible, what makes you say "theoretically anyways"? your example is flawed. spacetime does expand not any mass or something. its pretty simple, you cant accelerate any reel mass on the speed of light. since we have mass, gg. you also cant move detectable information faster than light. Scharnhorst Effect for one. Coupled with the Casimir Effect, and Alcubierre drive, the theories are there. When we finally figure out dark matter, and dark energy, I'm sure there will be ways. This is how the universe is expanding FTL. Dark energy/matter will be the secret mark my words. (That and manipulation of time space)
the low energetic modes which cant be excited between your plates are also very unlikely to be excited in vaccum, also the timescale for the excitations we are talking about are bordering the plancktime/causality. also taking into account that your confinement has to be very small ( this way you could also argue with the uncertainty principles that some photons might be faster than light) the effect is neglectable on reasonable times/spaces and most certainly cant be used on a macroscopis scale.
Alcubierre drive or Warp Drive. I dont know how this is supposed to work but this is no more an example for an object moving through space with a velocity faster than light than the expansion of the universe is. locally the dude in your "warp bubble" isnt moving at all. ergo no time dilation in the sense that you travel backwards in time.
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As I see it there are only two positions one can take on time travel:
Reasonable person:
- There is no way I could possibly know given my limited knowledge. Too many variables are still unkown.
Forum troll:
- I think this would happen: "blablabla"
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On May 22 2009 23:50 EsX_Raptor wrote:
haha that got me thinking.
so i guess 90% of the stars we see when we look up may be already dead? o,o
Most star live for extra-ordinary amounts of time hundreds of millions or years, there probably still there but are now red giants, brown dwarfs, etc... most of the stars we can see in constellations are within our galaxy so theres no chance there "burned out" as we speak.
Its when Hubble or other telescopes starts looking Deeper into the cosmo that things may be different there now.
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if you travel back in time 10 minutes, wouldn't you run into yourself, who then will go back in time 10 minutes from now
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On May 23 2009 05:55 VIB wrote:
As I see it there are only two positions one can take on time travel:
Reasonable person:
- There is no way I could possibly know given my limited knowledge. Too many variables are still unkown.
Forum troll:
- I think this would happen: "blablabla"
Your branding someone with an imagination as a troll? Surely at the moment we haven't the foggiest of what could happen, but taking someone down a notch for expressing an idea is a hindrance at best.
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On May 23 2009 09:31 SkY wrote:Show nested quote +On May 23 2009 05:55 VIB wrote:
As I see it there are only two positions one can take on time travel:
Reasonable person:
- There is no way I could possibly know given my limited knowledge. Too many variables are still unkown.
Forum troll:
- I think this would happen: "blablabla" Your branding someone with an imagination as a troll? Surely at the moment we haven't the foggiest of what could happen, but taking someone down a notch for expressing an idea is a hindrance at best. I think that what you're missing is the existence of something we call a "bad idea". Beating your head against the wall, is, by definition, an "idea". But it doesn't mean you're any less of an idiot for having such fertile imagination 
Being humble enough to admit you do not have enough knowledge to extrapolate any further. Is often, the best (aka reasonable) idea you could possibly have.
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United States17042 Posts
There are two common ways of viewing time travel (that have been played with in common science fiction anyway). One way is the "loop" theory of time, where everything is on one track. This is expressed in douglas adam's famous book (most notably anyway, there are several other places, like in harry potter).
The other way of viewing time travel is the "parallel universe theory" which says that when you travel back in time, you'll go to a different future, where different things happened. This is expressed in michael criton's book timeline, as well as in + Show Spoiler +
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EPT
