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

Colin1

...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

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

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

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

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

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

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 dont 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

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.
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, cant 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.