Any arguments for time travel back in time (the past)?

[PhysicsILike]

Theres the Butterfly effect and Grandfather paradox which makes logical time travel into the past difficult. Is there any theory or anything which suggests it may be possible?

 

[Emanresu56]

I don't know about any theories, but I can think of two possibilities that could happen if time travel into the past was possible.

1. If you kill your grandfather, then you can't travel back into the future.
2. If you kill your grandfather, then you cease to exist.

But, perhaps, if you kill your grandfather, it wouldn't matter if you killed him in the past, because you already exist in the future.

 

[Ivan Seeking]

By the butterfly effect I assume that you mean the multiplicative effects of changing history. This was misinterpreted the first time which is why the thread was deleted.

I think it is fair to say that while the door hasn't been closed entirely on travel to the past, it may be that the energy requirements would far exceed anything possible for the foreseeable future - maybe beyond anything that will ever be possible. There is also the [physics based] argument that one could only travel back to the point in time that the time machine is first turned on.

The Future of Spacetime [2002] has a nice series of essays on this subject.

 

[pallidin]

One possible scenario which "might" permit this would be such that the "travel back" demands "observable only" with no possible actual interaction.
Just my thoughts...

 

[Raap]

Travelling to the past is simple; just move all particles back to the way they were at the time you want to be.

 

[PhysicsILike]

By the butterfly effect I assume that you mean the multiplicative effects of changing history. This was misinterpreted the first time which is why the thread was deleted.

I think it is fair to say that while the door hasn't been closed entirely on travel to the past, it may be that the energy requirements would far exceed anything possible for the foreseeable future - maybe beyond anything that will ever be possible. There is also the [physics based] argument that one could only travel back to the point in time that the time machine is first turned on.

The Future of Spacetime [2002] has a nice series of essays on this subject.

Yep that's what i meant (the multiplicative effects). What else does it mean?
I got a warning and email saying "Crackpot discussions are not allowed here on ther PF" and it was my third post , I was going to leave the forum if that was a crackpot discussion. (adj.Foolish; harebrained: a crackpot notion).

Anyway I found this, http://en.wikipedia.org/wiki/Novikov_self-consistency_principle .

Quoting the Wikipedia Encyclopedia (which I can legally do - It is for the public by the public. Although we should not allways rely on it I checked out some other sites and the Novikov self consistency principle is real.)

The Novikov Principle is able to circumvent most commonly-cited paradoxes which are often alleged to exist should time travel be possible (and are often claimed to make it impossible). A common example of the principle in action is the idea of preventing disasters from happening in the past and the potential paradoxes this may cause (notably the idea that preventing the disaster would remove the motive for the traveler to go back and prevent it and so on). The Novikov self-consistency principle states that a time traveler would not be able to do so.

An example is the Titanic sinking; even if there were time travelers on the Titanic, they obviously failed to stop the ship from sinking. The Novikov Principle does not allow a time traveler to change the past in any way, but it does allow them to affect past events in a way that produces no inconsistencies—for example, a time traveler could rescue people from a disaster, and replace them with realistic corpses seconds before it occurs. Providing that the rescuees do not re-emerge until after the time traveler first journeyed into the past, his/her motivation to create the time machine and travel into the past will be preserved. (See Millennium.) In this example, it must always have been true that the people were rescued by a time traveler and replaced with realistic corpses, there was no "original" history where they were actually killed, since the notion of "changing" the past is ruled out completely by the self-consistency principle.

 

[PhysicsILike]

By the butterfly effect I assume that you mean the multiplicative effects of changing history. This was misinterpreted the first time which is why the thread was deleted.

I think it is fair to say that while the door hasn't been closed entirely on travel to the past, it may be that the energy requirements would far exceed anything possible for the foreseeable future - maybe beyond anything that will ever be possible. There is also the [physics based] argument that one could only travel back to the point in time that the time machine is first turned on.

The Future of Spacetime [2002] has a nice series of essays on this subject.

Thanks for the essay recommendation I will look them up.

Ahh the energy requirments that would/could make it impossible. But even before we try because of the butterfly effect it makes it "logically impossible". Like how in the cosmological argument a being that can exist before it existed to make it self exist is logically impossible as it would have to exist before it existed lol.

 

[skeptic2]

I think it is fair to say that while the door hasn't been closed entirely on travel to the past,...
The Future of Spacetime [2002] has a nice series of essays on this subject.

Aren't causality and the 2nd Law of Thermodynamics two doors that are closed pretty tightly against time travel to the past?

 

[Lambda3]

Travelling to the past is simple; just move all particles back to the way they were at the time you want to be.

Your proposition is correct if one only wants to travel to an instantaneous moment in the past. After that moment, though, the particles wouldn't necessarily behave in the same way as they did in the past.

 

[cshum00]

There is a simple conflict to think about when traveling time.

Two objects cannot be at the same space and time. So when you travel back to time, the volume position where your body us at the present must be completely void on the specific time of past you will travel in; otherwise your body will be conflicting with the mass on that position at that time.

Edit: There is another one i just thought of. Let's say that time travel is instantaneous and you travel to the past today at 1:00PM back to the time you started to travel at 1:00PM. So you will not be in a future anymore and your time is completely cut off up to 1:00PM. What will become of the volume which your body used to occupy? Your body is not there in the future because you traveled back in time. But there cannot be anything else because your body is occupying it for all eternity since 1:00PM.

Edit2: I mean travel back to when you finished traveling to the past; since that is the exact time when that space is available. In other words, you exist but do not exist paradox with time traveling.

 

[Vals509]

When you travel back in time, according to relativity you must be able to go at or faster than the speed of light, 300,000 km/s. If theoretically we are able to achieve this it is still impossible to go back in time because when we travel faster than light then effect precedes cause, which means that is things happen before they are actually seen by other like the athletes running before the race has even started. Since we live in a world of effect coming after cause i.e; the athletes running after the race has started, the notionthat the reverse should happen is impossible. Hence it is impossible to travel back in time according to me.

 

[nottheone]

I think that there certain concepts that only exist in the human imagination, they don't exist in reality. One of them is the concept of infinity. Nothing is infinite. As we learn more and more almost everything that we ever thought was infinite has turned out not to be. When infinity creeps into math it is usually a sign of a mistake isn't it?

Time travel to the past would require infinity in various forms. I believe that for this reason alone it isn't even remotely possible.

It would require every possible (as opposed to the actual configuration that supposedly could be deduced at the end of time) configuration (position, energy, etc.) of every particle in the universe at every instant from the big bang to the end of time to exist simultaneously. The actual configuration is the way things are without time travel, the possible would encompass changes that would inevitably occur with travel to the past, it WOULD change the future.

In actuality there may not be that much difference between the 2 since the only thing that can change anything from it's normal path as governed by the laws of physics is life. Life introduces a random factor so anything involved with life can't be deduced by the laws of physics. You can be a physics god but the laws of physics will not explain the existence of a lunar lander on the moon or one particular crater on a certain comet.

 

[confinement]

Most discussions of time travel are elementary at best, and nonsense at worst. There are, however, solutions in General Relativity that contain closed-time-like curves. We cannot take these solutions too literally, as they tend to occur in artificial situations e.g. von Neumann discovered such solutions in a rotating-universe model , and because GR, as a non-quantum theory, is not the final word on spacetime.

 

[skeptic2]

It seems that the conception of most of us have about traveling back in time is similar to the movie Back to the Future in which a person from the present travels back to the past but remaining as he is in the present. This view presumes that somehow the time traveler continues to travel forward in time while the rest of the universe has traveled backwards.

If travel back in time were possible it would mean rewinding the whole universe to that time. The Earth would have to orbit backwards and even air molecules would have to retrace their exact paths from the present to the past. All aging and knowledge gained would also have to be reversed. Anybody arriving in the past from the present would do so naively without any of the knowledge time from which he came.

The whole point of returning to the past of course, is doing so with the knowledge of the present. However this seems to always involve the potential for paradoxes or absurdities - great for movies but very problematic in practice.

 

[Nick89]

It seems that the conception of most of us have about traveling back in time is similar to the movie Back to the Future in which a person from the present travels back to the past but remaining as he is in the present. This view presumes that somehow the time traveler continues to travel forward in time while the rest of the universe has traveled backwards.

If travel back in time were possible it would mean rewinding the whole universe to that time. The Earth would have to orbit backwards and even air molecules would have to retrace their exact paths from the present to the past. All aging and knowledge gained would also have to be reversed. Anybody arriving in the past from the present would do so naively without any of the knowledge time from which he came.

The whole point of returning to the past of course, is doing so with the knowledge of the present. However this seems to always involve the potential for paradoxes or absurdities - great for movies but very problematic in practice.

Exactly the way I have always thought of time travel. Maybe we are all time traveling now and then, we just don't know it because our memories of 'the future' don't exist in 'the past'.

 

[PhysicsILike]

Exactly the way I have always thought of time travel. Maybe we are all time traveling now and then, we just don't know it because our memories of 'the future' don't exist in 'the past'.

I get what you mean but I don't understand it. How can we be time traveling now and how can we not know because our memories of the future don't exist in the past.

Please can you explain this because it sounds really interesting and I don't get it.

 

[nottheone]

Say our lives are being played out from a recording like a DVD. Everything is there, past present and future, but we are only seeing the moment being played. Who is to say what we think is playing forward really isn't playing backwards?

 

[Colin1]

Your proposition is correct if one only wants to travel to an instantaneous moment in the past. After that moment, though, the particles wouldn't necessarily behave in the same way as they did in the past.

...and he's right, of course - it's simple

 

[gmax137]

I think it was Steven Hawking who asked, if time trvel is possible, "where are all the tourists from the future?"

 

[nottheone]

Originally Posted by Lambda3 View Post

"Your proposition is correct if one only wants to travel to an instantaneous moment in the past. After that moment, though, the particles wouldn't necessarily behave in the same way as they did in the past."

...and he's right, of course - it's simple"

He is? If you go into THE past, and every particle has EXACTLY the same properties, every particle that isn't being directly affected by your instantaneous presence in the past would act exactly as it did before. The longer you spend in the past the more particles you will affect which will in turn affect particles on their own creating a growing area of effect. If you were to appear for just an instant in the past the effect would be almost unnoticeable, butterfly effect notwithstanding, if you stayed there the effect would grow but it wouldn't change anything at all on Alpha Centauri.

 

[Alfi]

One of the better ( imo only ) sci-fi films with time travel as the theme I've seen is 'Primer' (2004)

The acting/screenplay/dialog is not the best but I enjoyed their treatment of the paradoxes involved.

 

[PhysicsILike]

One of the better ( imo only ) sci-fi films with time travel as the theme I've seen is 'Primer' (2004)

The acting/screenplay/dialog is not the best but I enjoyed their treatment of the paradoxes involved.

Thanks for that movie recommendation I’m going to watch that tonight, looks a fair bit complicated though with the Feynman diagrams and the directors no nonsense approach to dumbing down

 

[Colin1]

I think it was Steven Hawking who asked, if time travel is possible, "where are all the tourists from the future?"

Well
I don't think their visible absence necessarily precludes time travel.

They probably read history in much the way we do and would no doubt understand what a paranoid, covetous generation of humanity we are (were); in short, a time-traveller from the future would likely be abducted by some agency, not necessarily governmental, who wanted the inside track on the future.

The term 'tourist' also suggests they have commercialised time travel.

They'd likely be a archaeo-scientific survey team who knew how to blend in. If they had any sense.

 

[ThomasT]

Theres the Butterfly effect and Grandfather paradox which makes logical time travel into the past difficult. Is there any theory or anything which suggests it may be possible?

It depends on the physical meaning of the PAST. Does it exist for eternity, 'somewhen'? Or are spatial configurations transitory? General relativity allows backward time travel in principle. But that doesn't necessarily mean that the dynamics of the physical universe allow it. Is the universe really evolving, ie., continually changing, or is it a static laminate of spacetime slices that we worm our way around in?

My personal view is that the universe is continually evolving, that universal spatial configurations are transitory, and that there is a fundamental wave dynamic, operating at all scales, defining the 'arrow of time' and prohibiting, in principle, backward time travel.

I agree with the posters who said that going back in time would involve reconstructing the universal spatial configurations that correspond to the time you want to (re)visit.

Afaik, however, there's no definitive final word on this.

 

[BoundByAxioms]

One of the better ( imo only ) sci-fi films with time travel as the theme I've seen is 'Primer' (2004)

The acting/screenplay/dialog is not the best but I enjoyed their treatment of the paradoxes involved.

It's funny you mentioned that movie: the moment I saw this thread I immediately signed on to it so I could recommend that people watch it. I liked that movie, even though it was extremely confusing.

 

[PhysicsILike]

It's funny you mentioned that movie: the moment I saw this thread I immediately signed on to it so I could recommend that people watch it. I liked that movie, even though it was extremely confusing.

I just watched it , I did not get it at all. Damm that was complicated.

 

[Alfi]

It sort of makes more sense if you go back in time and watch it again.

 

[BoundByAxioms]

There's a few websites you can look at that sort of explain that movie..

 

[PhysicsILike]

It sort of makes more sense if you go back in time and watch it again.

I have just come back to the future and watched it and I get it now. (Of course I hid my self in a room for 3hours so when I go back in time I don't bump into myself. I also used a particle machine to create a bubble around me making sure I don't affect anything, even the atmosphere was not disturbed. I then used an invisible cloak stood behind my self the first time I watched it so I could watch it again.) - This would create no paradox.

 

[Kronos5253]

Time is nothing more than a way to express and measure motion.

Going back in time would be moving in a negative direction, which is impossible (read improbable), because motion always has to be in a positive direction, correct? :)

 

[Alfi]

I have just come back to the future and watched it and I get it now. (Of course I hid my self in a room for 3hours so when I go back in time I don't bump into myself. I also used a particle machine to create a bubble around me making sure I don't affect anything, even the atmosphere was not disturbed. I then used an invisible cloak stood behind my self the first time I watched it so I could watch it again.) - This would create no paradox.

Strange eh? It seems to require that second viewing. One loop and it all becomes crystal clear.


Kronos - don't analyze, . ... well unless you went back twice.

correct?

lol - no sure eh?

 

[naikaj]

i was reading the book "the universe in a nutshell" by stephan hawking, and i came across a section of time travel.. as per what i understood was that time travel IS possible.. it said that there were 2 people say,A and B. they made a wormhole in January. A would board a spaceship and would travel at nearly the speed of light carrying carrying one end of the wormhole, while B would wait on the Earth near the other end of the wormhole.. A would travel around the universe and come back to earth.. A would then go into his end of the wormhole (at say, 4:00PM on march 21) and would come out at 2:00AM on march 19.. it would happen due to the same reasons as the "twins paradox"
. please correct me if I'm wrong but this is what I've interpreted...

 

[a4mula]

Something that hasn't been mentioned is the Everett Many Worlds Interpretation.

http://en.wikipedia.org/wiki/Many-worlds_interpretation

In this system (which has a fairly sound basis) you nulify many time travel paradoxes. We do know that if a closed timelike curve were to exist it's mathmatically sound that travel to the past is possible.

When incorporated with the above theory the past that you would travel to would be unique to the one you left. The mere act of appearing would instantly create a new reality in which any change you made would affect that reality only. You could kill your grandfather and in that world you would never be born. However because this reality is entirely different from the reality you originated in, it would have no causality reprocussions.

This would also explain Hawkins' quote away quite nicely. There are no tourists because the moment they traveled in time they'd create their own personal reality.

While this all seems to be quite the Sci-Fi channel special it has fairly sound physics and mathmatics. Check it out.

 

[naikaj]

ok i got wat u said but then why does the grandfather paradox still exist?? like if i were to go into the past and kill my grandfather then wat difference would it actually make.. i just woudnt vanish into thin air.. i already exist.. and about the space tourists from the future, can't it be that we are the first humans to travel into the future with every passing second, so as no one exists in the future how can the come back,, even if they have the technology.. look at it as if u r watching a video.. so how can you rewind without going forward.. you have to watch atleast 1sec to rewind... ppl please correct me if I'm on the wrong track.

 

[Focus]

ok i got wat u said but then why does the grandfather paradox still exist?? like if i were to go into the past and kill my grandfather then wat difference would it actually make.. i just woudnt vanish into thin air.. i already exist

If you take something even simpler, you go back in time and kill your self (say 5 days before you discovered the time machine) and sat around without building the machine. This means that you never built the time machine to actually go back and kill yourself. That is what the paradox is.

The grandfather paradox is the same, if you killed your grandfather then you wouldn't have been born in the first place thus you couldn't have gone back in time and killed your grandfather.

I don't think traveling back in time is possible, it is wishful thinking. Stick to sci-fi if you like the idea.