Time Travel

[MRM]

I was talking about people, not about scientific models. Although I'm habitually interested in the topic, I wouldn't claim to be able to evaluate current scientific models. I'm just an amateur who likes to raise strange questions.

I'am not an time travell expert either, but I was involved in a long discussion about this issue in a german scince fiction forum
But in fact some scientist think that time travel is maybe possible, but as eddie_verdde already said only back to the time the time machine was build ( but this would be enough to tell myself the lotto numbers of next weekend )

And there is even a quote from Hawkins that this issue should be researched because even if it turns out that time travel is not possible it would be interessting to know why not ( seems as no one can tell you so far for sure ... )

We have even found an construction plan somewhere in the inet - you only need 200 neutron stars lined up to form a giant cylinder and they must rotate around each other at least with half lightspeed

Isn't this model prone to circular reasoning - like "you cannot kill your father, because the model wouldn't allow you to kill your father (so something has to happen to prevent it)"?

Well the model simply says that you have no free will and all you do is predetermined and the result of your action ( including timetravel ) can not be a successful murder of your grandfather ...

Yes, that's an implication of this model. Or, more precisely: You can know *your* past, but traveling back to it may not be possible, since the past state of the universe may have changed radically (though without its consequences ever reaching *your* present, since your present is also traveling along the timeline).

In this case you cannot be sure that you can return to your time ( as you know it )

I'm not sure whether this model *requires* meta-time as a fifth dimension. May well be - you do have a point with your explanation that any movement requires a dimension in which it can take place. I'm unsure however whether the four dimensions we have may not be sufficient to explain the effects I'm describing. For example, you can still describe any event with coordinates in the four space-time dimensions, even in "my" theory. However, with this theory, you can't be sure whether you actually find the event you expect there because the past may have changed.

Perhaps this theory is just a variant of the "parallel universes" theory, with the twist that instead of parallel universes, you still have *one* universe, but with a timeline you cannot be sure of and that may switch between different realities.

Interesting discussion

My guess is in that case that they don't "switch" but maybe just smoothly but permanent move around ...

 

[Gargoyle]

I posted a parallel universe (many worlds) reply to this thread without reading all the other replies first. I thought I'd be the only one that would go down this road. Boy was I wrong.

 

[EvilDrummer]

back to the point really quick. before you can build a time machine you should have to discover the flux capacitor.

 

[Gato Loco]

Some believe the solution to that paradox is that you would never be able to achieve such a situation. If you tried to stab your grandfather, you would slip. If you did stab him, he would recover. You get the point.

Or the time machine would break before you use it, which is an extremely likley event with any complex piece of machinery. Hence time travel is impossible for all practical purposes if you intend to use it to change the past.

Actually, I once wrote an undergrad philosophy paper outlining how you could use a time machine to manipulate the probability of random events by blackmailing the universe with the threat of creating paradoxes. Essentially, "If I don't win the lottery I'll go back in time and kill my grandfather." So you win the lottery in order to prevent you from kiling your grandfather. Or God gets fed up and you get struck by lightning instead.

 

[MRM]

Or the time machine would break before you use it, which is an extremely likley event with any complex piece of machinery. Hence time travel is impossible for all practical purposes if you intend to use it to change the past.

Actually, I once wrote an undergrad philosophy paper outlining how you could use a time machine to manipulate the probability of random events by blackmailing the universe with the threat of creating paradoxes. Essentially, "If I don't win the lottery I'll go back in time and kill my grandfather." So you win the lottery in order to prevent you from kiling your grandfather. Or God gets fed up and you get struck by lightning instead.

If you have a time machine you don't have to blackmail anyone to win the lottery - just tell yourself the numbers of next week ...

 

[lolsen]

who said you even need to build a time machine? why couldn't you just jump through a vortex or a wormhole?

 

[Willowmound]

And for your model - for any movement you need an further dimension. For example sopmething simple as a car. It's a 3 dimensional objekt - but you need a 4th dimension ( time ) for movement ( otherwise it would just be a static picture )

And the same is true for timelines - only that timelines are 4 dimensional, the time is allready a part of the timeline, so you would need a fifth dimension ( overtime ? ) to move or change this timeline at all ...

If this 5th dimension didn't exist ( at least not as an overtime ) than the universe is somehow just a static picture of timelines, if you could watch it from outside ( anyone knows what I mean ? )

And if you have this 5th dimension than that would have a pretty strange consequence - you would not have a static past - you simply don't know if that what you read in historybooks or even that what you remember happened because the past could change permanently and I guess we wouldn' even notice that ...

Actually there is no need for a fifth dimension. Time is the foruth dimension, but as we can freely move around the three spatial dimensions, we -- everything -- only and constantly move one way along the fourth dimension. That's how "time keeps ticking". If you have a time machine, what you really have is a contraption that allows you to travel freely in the fourth dimension. That's the idea

 

[MRM]

Actually there is no need for a fifth dimension. Time is the foruth dimension, but as we can freely move around the three spatial dimensions, we -- everything -- only and constantly move one way along the fourth dimension. That's how "time keeps ticking". If you have a time machine, what you really have is a contraption that allows you to travel freely in the fourth dimension. That's the idea

Of yourse you don't need the fifth dimension not in your every day life, and even not for timetravel itself ( as long as you just move along timelines ) but you need the fifth dimension for changing timelines ( changing past events ) - otherwise you could only travel in time without changing anything.

 

[Willowmound]

Well, that's the point of argument, isn't it? Can you alter time?

 

[MRM]

Well, that's the point of argument, isn't it? Can you alter time?

Build me a time machine then I can try to find it out ...

All I know is that you need this over or meta time ( however you want to call it ) to alter the past - maybe it's easier to find out if this exist or not. If not, then you cannot change the past. But I guess not. ( travel in a possible parallel universe is IMO not really a time travel )

 

[Willowmound]

I'll look into it

I had a friend who built a time machine once, but she was on drugs. It worked though!

 

[Viperace]

I am wondering, how many physicists are chatting in this thread. I know there must be at least one

 

[Dikaioma]

Haha, this is a funny thread. Me and my friend were talking about this not too long ago, but we think the pitfall is that people have this idea that time is something that literally exists rather than a mere concept. More of a measurement, rather than a dimension. It's really just a concept, nothing else. Sure, we age, days come and go, but this doesn't prove that time is some place, or thing we can manipulate. I will try my best to try to explain what I mean.

For instance, I remember my 18th birthday. I did have one, it occured at some point before now. But this is the thing... only in my memories is where only place that day really exists. I can only explain that day to you, but I can never go back to that day and have you experience it because it's not a place, or a realm. It happened, and it will never happen again, and it isn't continually happening for me to go back to visit. And about the free will post, that is my argument against people who talk about knowing the future. No one, not even God (if you believe there is one) can know the future. If God knew the future, then that means he has no free will, and everything has been planned out already, and we are all controlled by fate or some other outside influence.

Theories are fun, and umm... can I get another puff please?

 

[Willowmound]

More of a measurement, rather than a dimension. It's really just a concept, nothing else.

I get what you mean, though if we are to be technical, time is by definition a dimension. You need to qualify it in order to locate an event. In other words, you can say something happened this far left of something, this far in front of something, and this far above something, at this particular time. Those are the number of coordinates you need to locate any event in our macrouniverse, giving us three spatial and one temporal dimension.

As for time "just being a concept", this notion breaks down under relativistic circumstances. The faster you go, the more time dilates. Time is completely dependant on speed and mass, and always relative. Don't take my word for it; Einstein proved that time is a thing, if you will, and not just "a concept".

 

[warpus]

Build me a time machine then I can try to find it out ...

All I know is that you need this over or meta time ( however you want to call it ) to alter the past - maybe it's easier to find out if this exist or not. If not, then you cannot change the past. But I guess not. ( travel in a possible parallel universe is IMO not really a time travel )

out of all the quantum physics/string theory books i've read, none of them ever discussed such a concept. there doesn't seem to be a single physicist who thinks that we need such a thing for time travel.

Haha, this is a funny thread. Me and my friend were talking about this not too long ago, but we think the pitfall is that people have this idea that time is something that literally exists rather than a mere concept. More of a measurement, rather than a dimension. It's really just a concept, nothing else. Sure, we age, days come and go, but this doesn't prove that time is some place, or thing we can manipulate. I will try my best to try to explain what I mean.

thing is that in the mathematics of physics and quantum physics time is treated exactly the same as any other dimesion. if it was just an idea and not a coherent construct, then we would not see that work so well in the equations.

 

[holy king]

the problem about time travelling is not that you can go back in time and become your own grandfather or grandmother.
in fact there's nothing about the issue of becoming your own grandmother or grandfather an open minded family could cope with.
the real and ultimate problem about time travelling is the use of tenses...

-douglas adams (as i remember it...)

 

[Dikaioma]

thing is that in the mathematics of physics and quantum physics time is treated exactly the same as any other dimesion. if it was just an idea and not a coherent construct, then we would not see that work so well in the equations.

Correct. Like I said, the idea I am trying to convey is hard for me to explain. Erase the concept argument, that was stupid. In order for us to time travel, you would have to be able to do more than just manipulate time itself, but we can't even do that. We would all agree that there are three basic components that make this reality - Matter, space, and time. Unless we know how to control at least one of these elements, the others will always be nogo. But the thing is, we can't create or destroy matter, space, or time. We can't really manipulate it either. Sure, you can change matter, but you are just transfering energy. Creating a vacuum is just making empty space, but it's still space. It's an area that exists. And then we have time, which is an even harder concept. Can you imagine the power you would have if you could manipulate those three things?

Talking about this sounds just like the idea that a machine can achieve higher awareness. An A.I. can never be equal to a human, because it's inherently less. It's automatically handicapped because the information we give it is limited, let alone everything else that makes a human, human. The creator can't create anything better than itself. It's funny, because I think it is silly to just assume something can't be possible because you don't understand it, like the critics of old that didn't believe in stupid things like steam power, or automobiles. But this is one area that I really do not think can be under our control. I guess whenever we get to meet the aliens that made us, then maybe... j/k

Oh and Douglas Adams kicks ass...

 

[Viperace]

As far as I know, very few physicist even bother with time-travel. The closest one that we can have is maybe from Prof. Aharonov in his 1990 paper submitted to Physical Review Letter. It is a very preliminary idea, and his work received little attention from other physicists. Maybe it is too bizare..


For those physicists who are lurking around, try it out.
WARNING: None physicists/None mathematician and especially those who are good in philosophy please keep out.


Phys. Rev. Lett. 64, 2965–2968 (1990)
Superpositions of time evolutions of a quantum system and a quantum time-translation machine
Yakir Aharonov, Jeeva Anandan, Sandu Popescu, and Lev Vaidman

Received 20 March 1989
A method to obtain a superposition of time evolutions of a quantum system which correspond to different Hamiltonians as well as to different periods of time is derived. Its application to amplification of an effect due to the action of weak forces is considered. A quantum time-translation machine based on the same principle, utilizing the gravitational field, is also considered.

PS: Feel free to PM me for any discussion about the physics aspect. (No philosophy please)

 

[warpus]

Correct. Like I said, the idea I am trying to convey is hard for me to explain. Erase the concept argument, that was stupid. In order for us to time travel, you would have to be able to do more than just manipulate time itself, but we can't even do that. We would all agree that there are three basic components that make this reality - Matter, space, and time. Unless we know how to control at least one of these elements, the others will always be nogo. But the thing is, we can't create or destroy matter, space, or time. We can't really manipulate it either. Sure, you can change matter, but you are just transfering energy. Creating a vacuum is just making empty space, but it's still space. It's an area that exists. And then we have time, which is an even harder concept. Can you imagine the power you would have if you could manipulate those three things?

well, here is how i see it. in order to move through space, we do not manipulate space at all. we are free to move through the 3 visible dimensions of space without the need to manipulate those dimensions at all. i say visible, because according to M-theory there are 8 other dimensions that we do not experience. (they're too small). in any case, i don't know if we necessarily have to modify time to travel through it. it doesn't seem to grok.