# Time travel: Back in Time



## Arize1959 (Dec 12, 2016)

Could be possible to travel back in time by means of anti-gravity?

Considering the hypothesis/principle that everything in the Universe has poles I thought about the subject of Gravity in the Universe as having as anti-pole Anti-Gravity with some inverse properties.

In exactly the same way as Gravity pushes down (warping the fabric of space-time) Anti-Gravity pushes up.

In the same way as Gravity slow down time (time dilation) Anti-Gravity slow down time too.

And in the reverse way as Gravity points to the future (the time's arrow), Anti-Gravity would point to the past!...

So Anti-Gravity would be a way of traveling to the past and the higher the time dilation and the bending of space-time the more rapidly one goes to the past.

That's it...

Arize
ps. sorry my bad english


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## chrispenycate (Dec 12, 2016)

Without gravity there would be no down, or for that matter up. so antigravity by your definition would just be gravity in the other direction.And there is no reason for an equivalence between reversed entropy and replacement of a centripetal force by a centrifugal (within the influence of which life as we  know it becomes very much less viable surface tension is an important factor at a cellular level), any more than inverting the charge on various subatomic particles (antimatter) would send them zooming back through time. Not good hard SF, though you might get away with it for science fantasy.


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## Stewart Hotston (Dec 12, 2016)

Hi @Arize1959. In the strictest sense of how we understand things to actually work? No. Not even close. Gravity doesn't push down. Gravity is a force that all material objects exert on one another and scales in accordance with the amount of mass they have. The greater the mass, the greater the aggregated gravitational presence.

More importantly, there is no direction in space. There simply is space. Imagine yourself on the surface of an inflated football...which way is up and which way is down? There are neither. There is simply the surface of the football. Spacetime is even weirder than that.

Also, gravity does not point to the future. Indeed, nothing points to the future. Technically general relativity and quantum mechanics don't really recognise time as real in a substantive objective way. They allow us to construct schema for how we experience time and why that is.

Time dilation isn't travelling to before your current present. What it does do is mean that your experience of time is different to people who experience time dilated at a different ratio to you. Classically this means that people travelling a very high fractions of the speed of light (say 0.99c) would experience time passing much more slowly relative to people travelling at non-relativistic speeds but this takes neither of them to before their experienced present moment. Does that make sense?

In terms of mechanisms for time travel? Well, setting aside that it can't happen for humans...my advice would be that if you want to use it don't worry about the hard science and think instead of the drama.


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## SilentRoamer (Dec 12, 2016)

Stewart Hotston said:


> Hi @Arize1959Also, gravity does not point to the future. Indeed, nothing points to the future.



I liked your post as it was very well parsed. Although things do point to the future - everything does. All of our World Lines point forwards in time.

I always like the idea of doing a few round trips of the solar system for a while at close to C and then dropping back into Earth to check the progress of humanity.


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## Arize1959 (Dec 12, 2016)

Hi, I will answer following the sequence of reasoning:

Without gravity there would be no down, or for that matter up. so antigravity by your definition would just be gravity in the other direction.

*Arize1959*: Actually not, antigravity is not gravity in the other direction, in the same sense as the north pole is not the south pole in another direction, or the centrifugal force is not the centripetal force in another direction, or the exit is not the entrance in another direction, as a woman is not a man contrariwise etc, etc... This doesn't make sense, it is a misunderstanding. They are all opposite things , pole and antipole,  positive and negative, plus and minus, with reversed properties.

And there is no reason for an equivalence between reversed entropy and replacement of a centripetal force by a centrifugal (within the influence of which life as we  know it becomes very much less viable surface tension is an important factor at a cellular level), any more than inverting the charge on various subatomic particles (antimatter) would send them zooming back through time. Not good hard SF, though you might get away with it for science fantasy.

*Arize1959*: I would like to point out that a centripetal force is pointing to a center (within) while a centrifugal force is pointing in the inverse direction (without) so that they are forces with inverted properties, and this is the distinction between gravity and antigravity. When I say that antigravity points to the past I am holding on strictly to the Principle of Polarity in the Universe (which I believe). As I have pointed out gravity and antigravity are not the same thing with inverted directions, they are opposites. Therefore if gravity points to the future (as is the case) , antigravity must point to the past, to stay in accordance with this principle of polarity in the Universe as I have stated.


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## Arize1959 (Dec 12, 2016)

Stewart Hotston said:


> Hi @Arize1959.
> 
> Also, gravity does not point to the future. Indeed, nothing points to the future. Technically general relativity and quantum mechanics don't really recognise time as real in a substantive objective way. They allow us to construct schema for how we experience time and why that is.



Arize1959: You have to think fouth-dimensionally!...  Time is real. Time is the fourth dimension besides the other three dimensions of space. Without time there would be no duration, no permanence,  no existence... Without time the Universe could not expanding because the Universe as we know it is a three dimensional space expanding in the fourth-dimension which have two directions: Past and Future.


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## Stewart Hotston (Dec 12, 2016)

Ok - you've pretty much abandoned science in your explanation in favour of a philosophical world view. Fair enough, but then I'm confused as to why you'd even want people with a hard science background (and mine is a PhD in quantum mechanics with a Masters that focused on the philosophy of spacetime (among other things)) to comment on your ideas?

To be honest I'm not sure where to begin with your misconceptions of spacetime - so probably the best way to move forward is to think about something specific you'd like to ask and I'll be more than happy to tell you the hard scientific understanding of it.

I've just seen your second response - dude, you don't think in four dimensions. Time is, technically, indistinguishable from space in its simplest mathematical formulations. Time is simply the measure of changes in space (as no two things can occupy the same location) and vice versa. Further, I'm typically used to thinking in N-dimensional topologies and to take the current vogue theories of substance of space (i.e. string theory and even some formulations of supersymmetry) they're in 7, 9, 10 and 13 dimensions (with some niche ones with even higher folding requirements) - 4 is really inadequate.


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## HanaBi (Dec 18, 2016)

Slightly off-topic, but I was watching an episode from "The Universe" TV series last night, and it covering the possibilities of TT, with special emphasis on "The Grandfather Paradox" 

Grandfather paradox - Wikipedia

But then the program discussed further the possibility that if TT also mean travelling into the future as well as the past, would it mean that someone in the future has travelled back in time to our Time and is preventing us from discovering TT. In which case the The Grandfather Paradox is pertinent.

And if TT did become a reality, would the inventor want to share the idea, or keep it to him/herself and indulge slipping through Time, having adventures, preventing major disasters and becoming rich through always knowing the lottery numbers and how to cheat at exams!

Personally, I hope TT is never discovered: far too dangerous.


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## Stewart Hotston (Dec 18, 2016)

As with most advanced hard scientific endeavours there is no 'inventor' but entire teams sponsored by HUGE backing in the form of governments and, very occasionally, supranational corporations. As such I doubt any single member of a team would be able to stymie a discovery like this.

My favourite treatment of the grandfather paradox is one in Futurama which treated it as the absurdity it really is. The issue is one of complexity (in the specific sense used in the mathematics of chaotic systems) - the arrival of ANY item or person into the past would immediately change the future and that person would then not exist to travel back in time to stop existing etc. It is a self cancelling operation, or I suppose, in the mathematical sense, a self-absorbing state.

The paradox only really exists if one believes in a linear passage of time but then again, the refutation of said paradox also only exists in this case. If the future is not caused by the past then one could become one's own grandpa but then it wouldn't be a paradox because you'd either be slipping sideways in time (ala many worlds or many minds theory) OR you're in a time loop and were always having been going to be your own ancestor/descendent and there's nothing to be done about it.

bta @HanaBi is one of my favourite movies


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## BAYLOR (Dec 18, 2016)

Time Travel , if possible is a bad idea.  You go into the past and do anything even breath the air it could have dire consequences  on the timeline . Your libel to come back to the present  and find You just prevented the Cubs from winning the 2016 world series.


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## tinkerdan (Dec 19, 2016)

We are all time travelers.
We start in the past and move to the future; and yet we stay constantly in the present.
The present is like a prison where we are all stuck.

There are two platforms-the past where the train left and the future to which it will arrive. The train is the present. (Perhaps somewhere out there is this immense wild area where a road (time) extends forever in each direction.)
But we do perceive the movement forward; we just never reach the future. We can look back but we can't see the past because the present is all around us.
We are always heading forward-traveling toward the future. Even if we walk backwards we will remain in the present: heading toward the future. 

There could be a problem with real time travel if you subscribe to a universe that expands; most specifically if you look at the Earth as the train. If we step off this time travel device that keeps us locked in the present, to go backwards; we could have a long walk to the past which was left billions of miles behind us.
On the other hand; if all of space and time--the universe--is our train and you subscribe to an expanding universe that started at platform big bang and is heading to platform big crunch. Then perhaps things aren't moving at all and the Earth will remain in one place throughout all of time. Yet at best maybe the universe is rotating around the Big bang platform as it expands and that would still mean that we're never in the same place twice. (Or the odds of that are pretty rare.) Traveling through time might look like stepping off the train onto a temporary platform in the big wild. Moving back in time and remaining within the local of Earth (or your dropout point), would require that the platform be able to to move along the trajectory of the Earth as it travels in either direction-forward or backward in time.

A small time jump in either direction could leave you off the Earth-ahead or behind it. A large jump could leave you lost in space. Stopping time might look like running the vehicle into an immovable object.

But getting back to gravity and time; two things of which we know probably less than there is to know and probably equally as well one than we do the other. Yet both are used to measure other things, so we have a fair idea of the the constant nature of each with enough confidence to use them. There is a lot we need to know about them; but I can't help but think that time might be something that would be quite wasted if there were no intelligent life to experience its ever present nature.


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## BAYLOR (Dec 19, 2016)

We live and exist in four dimensions, but can only see three of them.


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## HanaBi (Dec 19, 2016)

Stewart Hotston said:


> As with most advanced hard scientific endeavours there is no 'inventor' but entire teams sponsored by HUGE backing in the form of governments and, very occasionally, supranational corporations. As such I doubt any single member of a team would be able to stymie a discovery like this.
> 
> My favourite treatment of the grandfather paradox is one in Futurama which treated it as the absurdity it really is. The issue is one of complexity (in the specific sense used in the mathematics of chaotic systems) - the arrival of ANY item or person into the past would immediately change the future and that person would then not exist to travel back in time to stop existing etc. It is a self cancelling operation, or I suppose, in the mathematical sense, a self-absorbing state.
> 
> ...



Of course then there's the discussion regarding parallel universes, in which scientists believe you can jump to the future or the past and intervene in something that has yet to happen, or has happened, but will only be noticed in a universe parallel to our own rather than our actual universe. They went onto say there could be billions of parallel universes where TT could be possible to just through (worm holes perhaps?), so that a person's intervention with past events will only affect them - thus making the Grandfather Paradox redundant. (That's my understanding anyway)

And yes, "HanaBi" is a favourite film of mine too, not least because I'm a big fan of Takeshi Kitano


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## Stewart Hotston (Dec 19, 2016)

ah yes, the parallel universe argument. It's an interesting get out clause because it means the complexity issue can be ignored without having to actually understand the problems!

For me the issues with traversing to different quantum wave systems (which is what going to a parallel universe actually is) are as follows:

1. You're changing the total amount of energy in your home system and the one you arrive at, thus violating the laws of conservation of energy
2. You're more practically adding matter to somewhere where matter already exists - this might sound trivial but actually, no two things can ever occupy the same space, so in arriving you'd probably cause some sort of humungous explosion/catastrophic event within the fabric of spacetime
3. Not only would you need a time travel machine you'd need a machine capable of changing quantum systems
4. If you change someone else's future it won't impact your own for sure but then what's the point as the world you're changing is different from your home - so you could make things better/worse for them but not help yourself in any way (I suppose you could try to persuade them to come back to yours and do you a favour!)

In an infinite system of parallel universes there would be an infinite number of systems the same as yours so you could, conceivably, change one of those so the person there, who is indistinguishable from you but an infinite number of systems would remain unaffected. Infinity is a funny thing because it depending on the type of infinity it contains further infinities within itself. This class of numbers - omega numbers - is an entire branch of mathematics all by itself and is completely fascinating.

But I'm drifting off time travel. The tangential issues surrounding shifting to a parallel universe mean that what you gain in the possibility of time travel you probably lose by dying along the way and not actually being able to influence your own world.


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## Stewart Hotston (Dec 19, 2016)

tinkerdan said:


> We are all time travelers.
> We start in the past and move to the future; and yet we stay constantly in the present.
> The present is like a prison where we are all stuck.
> 
> ...



I think you've misunderstood what we do understand about these things. Time only 'exists' because we experience it. The universe itself, cold and unsentient as it is, has no need for time. Beyond the sense that time only exists as it's experienced, there are very strong anti-realist mathematical arguments that suggest time is not real in any substantive way except as we've constructed it to make sense of the way we travel through life. (I'm a critical realist, but then my view of spacetime is that space and time are effectively equivalencies).

As for stepping off earth and coming back to find it gone? However, from a relativistic point of view time is literally the movement of one space to another frame. i.e. without expansion of our brane there is no time to be experienced or otherwise. In other words I'd really not be worried about losing my 'place' to return to if I went time travelling.

I agree that it would be a 'waste' if there were no people here to experience time, but then I think it would also have a host of other wasted things like no one appreciating beauty, love, hope, good steak, wine, whisky and Netflix original series.


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## tinkerdan (Dec 20, 2016)

It begins to sound like you believe time is confined to Earth and that would be a fatal mistake.



Stewart Hotston said:


> I think you've misunderstood what we do understand about these things. Time only 'exists' because we experience it. The universe itself, cold and unsentient as it is, has no need for time. Beyond the sense that time only exists as it's experienced, there are very strong anti-realist mathematical arguments that suggest time is not real in any substantive way except as we've constructed it to make sense of the way we travel through life. (I'm a critical realist, but then my view of spacetime is that space and time are effectively equivalencies).
> 
> As for stepping off earth and coming back to find it gone? However, from a relativistic point of view time is literally the movement of one space to another frame. i.e. without expansion of our brane there is no time to be experienced or otherwise. In other words I'd really not be worried about losing my 'place' to return to if I went time travelling.
> 
> I agree that it would be a 'waste' if there were no people here to experience time, but then I think it would also have a host of other wasted things like no one appreciating beauty, love, hope, good steak, wine, whisky and Netflix original series.



Only if the the time you are in were confined to earth would you even consider that stepping from one Frame to another (not space to frame--not even sure what that might be.) You would be doing so at the place where Earth is at that time and the Earth most likely never is in the same place twice. You had best make sure that you have some sort of environmental suit on before you try or you won't have to worry about making it back. Still you could end up inside the sun.


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## SilentRoamer (Dec 21, 2016)

Tinkerdan i don't want to speak for Stewart Hotston but I think you are missing his point.

The crux of his point is that spacetime is a discreet entity and so treating space and time as seperate mathematical constructs creates a false equivalence.


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## HanaBi (Dec 21, 2016)

In my way of thinking we're far from understanding the complexities of the Universe and how it works. 

we have the theories, but they're constantly being revised every few years as new technology and a better understanding helps us see through the dark, so to speak.

Time Travel is still just conjecture. 

Einstein's great equations, will someday come under scrutiny, and for all we know could be disproved. Which would throw everything we've ever learnt about astronomy and astrophysics into a cocked hat


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## SilentRoamer (Dec 21, 2016)

HanaBi said:


> Einstein's great equations, will someday come under scrutiny, and for all we know could be disproved. Which would throw everything we've ever learnt about astronomy and astrophysics into a cocked hat



Equally likely pink Unicorns powered by Rainbow Dust will solve all our problems. 

Not to be trite (okay that was fairly trite) but Einsteins theories (much as Newtons did) hold upto rigorous scrutiny and if they need revision I doubt they will ever need throwing into a cocked hat!

Although I for one welcome the new rule of our Pink Horned Equine leaders.


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## mosaix (Dec 21, 2016)

BAYLOR said:


> ...  and find You just prevented the Cubs from winning the 2016 world series.



But you wouldn't know it. Your new timeline would include everything, including all your memories. People could be traveling back in time and changing history all the time. Our timelines could be changing every single second and we would never know it. Our timeline is exactly that - our timeline, and it includes _everything. _You would have no way of knowing what your old timeline was and so have nothing to compare with.


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## SilentRoamer (Dec 21, 2016)

mosaix said:


> But you wouldn't know it. Your new timeline would include everything, including all your memories. People could be traveling back in time and changing history all the time. Our timelines could be changing every single second and we would never know it. Our timeline is exactly that - our timeline, and it includes _everything. _You would have no way of knowing what your old timeline was and so have nothing to compare with.



This is only one view of how causality re-asserts itself though. It takes the view there is one distinct and unalterable timeline and in this view of causality any time travel would result in a paradoxical situation.

You don't have to subscribe to a single timeline theory though - you could just as easily postulate creating of separate timelines (or alternative realities).

Or you could use Novikovs self consistency principle and argue that this was always the timeline as time re-asserts itself.


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## Vertigo (Dec 21, 2016)

I have a couple of problems with the multiple timelines approach:

At what point does another timeline branch off? Is it when I decide to take the car to the shops instead of walking? Is it when I glance out of the window and so am a second later turning the kettle off? It's not going to only happen when a major decision could swing either of two ways, in fact, if it happens at all, it must be every single time a quantum probability event could swing one way or another and that means there are, throughout the universe, countless trillions of new timelines branching off every nanosecond. Which really pushes my suspension of disbelief a little too far and also brings up my other problem:

Each timeline is another universe... just where does all the matter and energy come from to keep creating trillions of new universes from... well, nothing...


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## SilentRoamer (Dec 21, 2016)

Vertigo said:


> Each timeline is another universe... just where does all the matter and energy come from to keep creating trillions of new universes from... well, nothing...



I would agree that multiple timelines (read: multiple universes) would require a new branch everytime there was any possibility for a differential - down to the level of Quantum indeterminacy. 

Where does all the matter and energy come from to create a single Universe though? My understanding was that we currently expect the Universe to have zero energy, if this is the case then trillions of Universes are as likely as 1. Even if the Universe has an energy value (either positive or negative) it doesn't preclude their being alternative U's.

Just something to think about.


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## HanaBi (Dec 21, 2016)

and even if there are trillions of universes out there, what is "outside" of these multi-universe clusters for them to be expanding into?


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## Vertigo (Dec 21, 2016)

SilentRoamer said:


> I would agree that multiple timelines (read: multiple universes) would require a new branch everytime there was any possibility for a differential - down to the level of Quantum indeterminacy.
> 
> Where does all the matter and energy come from to create a single Universe though? My understanding was that we currently expect the Universe to have zero energy, if this is the case then trillions of Universes are as likely as 1. Even if the Universe has an energy value (either positive or negative) it doesn't preclude their being alternative U's.
> 
> Just something to think about.



Sadly that doesn't work for me; I see a big difference between the creation of a universe in a chaotic 'big bang" with theoretically a balance of matter and anti-matter meaning not energy/matter debt, and the creation of another universe fully formed and organised in every detail down to the thoughts in every sentient being's head (or whatever). I just can't see any way of making that believable for me.


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## Vertigo (Dec 21, 2016)

HanaBi said:


> and even if there are trillions of universes out there, what is "outside" of these multi-universe clusters for them to be expanding into?


An I think that's a classic mis-thought; there is no 'outside,' there can't be as the universe _is_ space-time and so there is no 'outside' it and there is no 'other' space just as there is no 'before.' You must remember that, as I understand it, the expansion of the universe is not so much a case of 'stuff' expanding out into space it is actually case of space itself expanding.


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## HanaBi (Dec 21, 2016)

Vertigo said:


> An I think that's a classic mis-thought; there is no 'outside,' there can't be as the universe _is_ space-time and so there is no 'outside' it and there is no 'other' space just as there is no 'before.' You must remember that, as I understand it, the expansion of the universe i*s not so much a case of 'stuff' expanding out into space it is actually case of space itself expanding.*



But that is what "boggles" my mind: the theory that space is expanding into "something" even if this something hasn't actually been created yet. 

But anyway, I'm taking this thread slightly off-topic. Apologies.


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## Vertigo (Dec 21, 2016)

HanaBi said:


> But that is what "boggles" my mind: the theory that space is expanding into "something" even if this something hasn't actually been created yet.
> 
> But anyway, I'm taking this thread slightly off-topic. Apologies.



It's always thoroughly boggled my mind as well . I've always thought if I was religious this is the area I'd point my finger at for evidence of a God.


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## HanaBi (Dec 21, 2016)

now we're venturing into the world of teleological existentialism, lol


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## tinkerdan (Dec 21, 2016)

No you are not off topic::


HanaBi said:


> But that is what "boggles" my mind: the theory that space is expanding into "something" even if this something hasn't actually been created yet.
> 
> But anyway, I'm taking this thread slightly off-topic. Apologies.



::Since (it) Space-time was mentioned as something that can't be separated and it is space-time that is expanding out there if you believe that we live in an expanding universe.

And by the way space-time seems to be separated by the great hyphen since the spell checker doesn't like it the other way.

So yes when we consider space time and the great hyphen together we get back to how little we understand things like gravity and space time although maybe we shouldn't separate gravity because I have a feeling without gravity space-time wouldn't work. Perhaps the hyphen is gravity.


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## Arize1959 (Dec 21, 2016)

HanaBi said:


> But that is what "boggles" my mind: the theory that space is expanding into "something" even if this something hasn't actually been created yet.
> 
> But anyway, I'm taking this thread slightly off-topic. Apologies.



Hi, I think  the correct answer to your question is in the answer below given by Manuel Costa in Quora's site:

If-the-universe-is-expanding-then-what-does-it-expand-into

"Manuel Costa, Physics enthusiast
Written Dec 16, 2014
This answer was originally posted under the following question and has since been moved here.

If the Universe exploded from a singularity and ever since, it expands, then what does it expand into?
In a 3D-sense I picture the Universe as a globe which keeps increasing in size like a balloon that is blown up. Inside, the Univers. But outside? Are there other balloons, err universes?

The analogy of a balloon is sometimes misleading because people think of the universe as being within the volume of that balloon, but in fact in that analogy the universe is the surface of that ballon! Only thinking of our universe as the surface of the balloon can you reconcile the fact that we see everything moving away from everything else in the universe in a uniform way, and that there is no center. Otherwise, the balloon would have a clear center.

Going back a little bit!
There are basically 2 options, either the universe is finite or it isn't.

1) If the universe is infinite it isn't expanding into anything. It just expands within itself. This is a hard to grasp scenario because our minds aren't good at all at dealing with infinity, but that's just how it is...

2) If the universe is finite there are also 2 options, it either has a border or it doesn't.

a. The universe having a border is something pretty strange, it reminds me of when people through the earth was flat, and so at the borders the water from the oceans would fall down, but this explanation isn't really helpful as it kinda requires it to exist within something else. And then the same questions about our universe arise for this container.

b. If it doesn't have a border and it is finite, it must be curved like the surface of a 4 dimensional sphere. I say 4 dimensional because a 4 dimensional sphere has a 3 dimensional surface, like a regular 3 dimensional sphere has a 2 dimensional surface.

This is probably the scenario that can better help you understand the answer to your question.

Since picturing stuff in 4 dimensions is another thing we're not really good at, lets go down one dimension and picture a regular 3 dimensional sphere, in which our universe is the 2 dimensional surface.

If you think of it like this, what is inside (the place where the universe expanded from), and what is outside the sphere (the place where the universe is expanding into?

The answer is the past and the future respectively.

If it isn't clear, think of the universe expanding as a sequence of image frames from a video. At 0 seconds, you have nothing but a dot. Some time later you have a small sphere, and then a bigger one and it gets bigger as you go through the movie. The dimension you're traveling through is TIME!

So the answer is, the universe is expanding through time."


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## Brian G Turner (Dec 21, 2016)

_Babylon 5_ showed how time travel should be handled. 

In short, you cannot change time because it has already occurred. However, you can contribute to the past.

So lots of people could go back in time to kill Hitler - but all they can do is be part of one of the many unsuccessful attempts on his life.


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## Arize1959 (Dec 21, 2016)

Brian G Turner said:


> _Babylon 5_ showed how time travel should be handled.
> 
> In short, you cannot change time because it has already occurred. However, you can contribute to the past.
> 
> So lots of people could go back in time to kill Hitler - but all they can do is be part of one of the many unsuccessful attempts on his life.



In fact this is the most logical answer to the so called Grandfather Paradox...


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## Dave (Dec 21, 2016)

tinkerdan said:


> We are all time travelers.
> We start in the past and move to the future; and yet we stay constantly in the present.
> The present is like a prison where we are all stuck.


Except when we sleep. Then times passes without us being aware of it.
Also when we don't see someone or some place for a few years. Then they grow older and change, but our memories of them do not. 
We can still access the past through photographs, old newspapers and film. That's called history.

Time travel is fantasy. If it could be invented, where are all the tourists?


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## HanaBi (Dec 21, 2016)

A slightly lighter note: time seems to travel rather quickly at weekends, but just drags on and on during working days


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## tinkerdan (Dec 21, 2016)

In the nuthouse::


Dave said:


> Time travel is fantasy. If it could be invented, where are all the tourists?


::muttering something about monkeys.


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## BAYLOR (Dec 22, 2016)

HanaBi said:


> and even if there are trillions of universes out there, what is "outside" of these multi-universe clusters for them to be expanding into?



More universes perhaps ?


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## Cathbad (Dec 22, 2016)

If Time Travel is possible, by its very nature, every time someone comes back, they have changed history - if just by a bent grass blade - and have created a new timeline.

Thus, we would never note a time traveler, because we are no longer in their timeline.


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## J Riff (Dec 22, 2016)

But, timelines have saved the comic book industry, kept Superman alive, and made a lot of SF movies possible.. they must be real.


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## Arize1959 (Dec 22, 2016)

Dave said:


> Time travel is fantasy. If it could be invented, where are all the tourists?



A true paradox refuses to exist... The answer to this question lies in the fact that the Universe must have a Logic inherent to it. To the time traveler the attempt to violate this logic would trigger a resistance or barrier that could roughly resemble the repulsion between magnetic poles of same signal.
To better understand this notion we can roughly compare an edifice with the Universe. An edifice has rooms, corridors, doors and windows rigidly fixed in its structure. So if someone wants to live in a edifice properly, that is without hurting oneself, one will have to use corridors and enter through doors (or windows) to penetrate into an adjacent room.
This is logical for an edifice, because no sane person will try to enter a room through the walls, that is impossible.
In the same manner the Universe has a history arranged in a logical order of events with each effect rigidly following its cause. For a time traveler would be impossible to change the past because this would be equivalent to a cosmic contradiction, an attempt to break the universal logic that would result in an automatic resistance of the Universe.
In other words a tourist from the future who tried to appear publicly to the world of his past would find a natural resistance that could even be fatal!...
Therefore, no tourists from the future would ever try to change the past or appear publicly to the present world. They must be among us, disguised in the present society but none will appear publicly.


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## Vertigo (Dec 22, 2016)

Arize1959 said:


> A true paradox refuses to exist... The answer to this question lies in the fact that the Universe must have a Logic inherent to it. To the time traveler the attempt to violate this logic would trigger a resistance or barrier that could roughly resemble the repulsion between magnetic poles of same signal.
> To better understand this notion we can roughly compare an edifice with the Universe. An edifice has rooms, corridors, doors and windows rigidly fixed in its structure. So if someone wants to live in a edifice properly, that is without hurting oneself, one will have to use corridors and enter through doors (or windows) to penetrate into an adjacent room.
> This is logical for an edifice, because no sane person will try to enter a room through the walls, that is impossible.
> In the same manner the Universe has a history arranged in a logical order of events with each effect rigidly following its cause. For a time traveler would be impossible to change the past because this would be equivalent to a cosmic contradiction, an attempt to break the universal logic that would result in an automatic resistance of the Universe.
> ...


But to continue that argument to its logical conclusion there can therefore be no time travel tourists because by simply being in the past, regardless of how well disguised they are, they are changing the future. Every time they step on an ant they have changed the future, every time they eat they have changed the amount of available food and have changed the future, every time they take a breath they have changed the relative proportions of O2 and CO2 in the atmosphere. They simply cannot be in the past without changing it.


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## Arize1959 (Dec 22, 2016)

Arize1959 said:


> A true paradox refuses to exist... The answer to this question lies in the fact that the Universe must have a Logic inherent to it. To the time traveler the attempt to violate this logic would trigger a resistance or barrier that could roughly resemble the repulsion between magnetic poles of same signal.
> To better understand this notion we can roughly compare an edifice with the Universe. An edifice has rooms, corridors, doors and windows rigidly fixed in its structure. So if someone wants to live in a edifice properly, that is without hurting oneself, one will have to use corridors and enter through doors (or windows) to penetrate into an adjacent room.
> This is logical for an edifice, because no sane person will try to enter a room through the walls, that is impossible.
> In the same manner the Universe has a history arranged in a logical order of events with each effect rigidly following its cause. For a time traveler would be impossible to change the past because this would be equivalent to a cosmic contradiction, an attempt to break the universal logic that would result in an automatic resistance of the Universe.
> ...



Hello,


Let me make some slight changes in my text and include a Note (for posterity):

A true paradox refuses to exist... The answer to this question lies in the fact that the Universe must have a Logic inherent to it. To the time traveler the attempt to violate this logic would trigger a resistance or barrier that could roughly resemble the repulsion between magnetic poles of same signal.
To better understand this notion we can roughly compare an edifice with the Universe. An edifice has rooms, corridors, doors and windows rigidly fixed in its structure. So if someone wants to live in an edifice properly, that is without hurting oneself, one will have to use corridors and enter through doors (or windows) to penetrate into an adjacent room.
This is logical for an edifice, because no sane person will try to enter a room through the walls - that is impossible.
In the same manner the Universe has a history arranged in a logical order of events with each effect rigidly following its cause. For a time traveler would be impossible to change the past because this would be equivalent to a cosmic contradiction, an attempt to break the universal logic that would result in an automatic resistance of the Universe.
In other words a tourist from the future who tried to appear publicly to the world of his past would find a natural barrier that could even be fatal!...
Therefore, no tourists from the future would ever try to change the past or appear openly to the present world. They must be among us, disguised in the present society, but none will appear publicly.


Note: In this approach the wall of the edifice would be equivalent to this logical temporal barrier or resistance and the doors would mean the normal events of history in its logical sequence. We can pass through doors in the same manner as the time traveler must follow the predetermined (to the traveler) events of Time.


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## Arize1959 (Dec 22, 2016)

Vertigo said:


> But to continue that argument to its logical conclusion there can therefore be no time travel tourists because by simply being in the past, regardless of how well disguised they are, they are changing the future. Every time they step on an ant they have changed the future, every time they eat they have changed the amount of available food and have changed the future, every time they take a breath they have changed the relative proportions of O2 and CO2 in the atmosphere. They simply cannot be in the past without changing it.



The time traveler cannot change the future because firstly the future is predetermined from his point of view, secondly because all their acts are already part of history. He can only be part of history, cannot change it.


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## Stewart Hotston (Dec 22, 2016)

@tinkerdan spacetime is a single word. There is no hyphen. I offer this introductory academic text as evidence alongside my own professional experience, m'lud. I would suggest the spellchecker is told to amend its ways.

As for multiple universes, it's a classic response to the Copenhagen interpretation of QM - it's trying to eliminate the need for a conscious mind in the waveform function. The philosophical problems with Copenhagen are myriad but the multi-verse or even the multi-mind interpretations, while also mathematically coherent (they can explain the energy 'deficit' away via existential potentialities - that is that all these possibilities are contained within the wavefunction and hence the energy is also there potential as well) I find them even harder to countenance as plausible. 

Ironically, perhaps, the other main philosophical drive behind many proponents' commitment to many-worlds is to find a way of eliminating God - although it's a very poorly thought through argument to deploy when one properly examines it.

Last I counted there are at least 6 different interpretations of QM that are ALL mathematically coherent and predictively testable - however none of them is really the last word on the subject. We continue to teach Copenhagen at University undergrad level because it was the first and because it's actually the easiest one to understand. The mathematical chops needed to actually understand what's going on in a many-world scheme is not for the faint hearted. 

Bohm (and others) have been a proponent of hidden variables schemes of QM, but these are generally considered less plausible than the other schemes we have even if they're just as coherent (in the technical sense)

As far as time travel goes - the problem with them all is that none of them need or even posit linear time as a requirement. The collapse of a wavefunction isn't really an issue of being one direction in time because there's no really sense that a collapse in a wavefunction is CAUSED by something that came before it. Without that sense of causation then there's no previous 'time' to travel back to that would lead to the time you're in now. You could quite happily travel through time but it would be rather pointless because it's not time as we're generally talking about here - that is, you couldn't be guaranteed that going back and having children with the woman you consider your grandma would CAUSE you to be your own grandpa. 

You might say, 'well if I did it then it follows that I am my own grandpa', but if you're travelling through time using these as your basis then actually, it's entirely likely/probable (because if it's probable it's possible) that you have no connection at all to yourself. I know that sounds a bit mad BUT it's what the math tells us. And that maths makes televisions, MRI, self-driving cars, Hubble, HDD and all manner of other things possible, so we know it's reliable and what it's trying to tell us about 'reality' is hard to understand but true nonetheless.


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## Arize1959 (Dec 22, 2016)

I found the idea interesting. What if...

www . artcomic . com/timetravel/intro.html

INSTRUCTIONS FOR MEETING TIME TRAVELLERS

"How often many of us have wondered about the possibility of science creating such a thing in the future? We've known for countless years that anything imaginable by mankind could one day become a reality. Time and time again, this has been proven to be true. It's inevitable that Time Travel will one day be a reality.

H.G. Wells knew that one day we would be able to send a man to the moon. He also believed that space travel for all of us would follow. Wells said future man would also have the power of Time Travel. If his vision is correct, the instructions in this book are the possibility and foundation of tangible evidence for our present and future societies. Arranging a visit from a person of the future is not an easy task to accomplish. To follow the instructions in this book properly takes a great deal of hard work and careful preparation"


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## Dave (Dec 22, 2016)

Arize1959 said:


> We've known for countless years that anything imaginable by mankind could one day become a reality. Time and time again, this has been proven to be true. It's inevitable that Time Travel will one day be a reality.


Extra-ordinary!
You mean like flying atomic cars, weather control, jet pack mailmen, meal pills, and not forgetting world peace or the end of poverty. These are all possible. Believe me, they are bigly possible folks. Lets make science fiction great again!


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## J Riff (Dec 23, 2016)

Dunno how one would travel in a totally non-physical concept, like time, but we can hope that the Robots figure it out, maybe in 4000 AD or thereabouts, like in this swell EC comic book I'm reading.


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## Arize1959 (Dec 26, 2016)

Hi, I emailed Tim Waters (info@timetravelagents.com), creator of the site Time Travel Agents  timetravelagents . com Maybe you can send an e-mail to him too. My short message below:

Hello,

I tried but I can not create an account in http : // timetravelagents . com / users / new ... there is something wrong with the site, actualize it please.

Obs.The site is a good idea, do not give up.

Meeting a time traveler will probably require a certain state or level of maturity from the person who wants a meeting with one.

Arize


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## Arize1959 (Dec 28, 2016)

Is space-time shaped like a SPIRAL? Universe has a 'golden ratio' that keeps everything in order, researchers claim

www . dailymail . co . uk/sciencetech/article-2862243/Is-space-time-shaped-like-SPIRAL-Universe-golden-ratio-keeps-order-researchers-claim.html

Happy New Year for all time travelers

Arize


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## Vertigo (Dec 28, 2016)

Arize1959 said:


> Is space-time shaped like a SPIRAL? Universe has a 'golden ratio' that keeps everything in order, researchers claim
> 
> www . dailymail . co . uk/sciencetech/article-2862243/Is-space-time-shaped-like-SPIRAL-Universe-golden-ratio-keeps-order-researchers-claim.html
> 
> ...


Interesting and plausible but I'm not quite sure what it would have to do with going back in time?


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## Arize1959 (Dec 28, 2016)

Vertigo said:


> Interesting and plausible but I'm not quite sure what it would have to do with going back in time?



If one is traveling forward or backward in time his trajectory would describe a curve through the arms of the spiral of Time.

Also, this has to do with my Avatar...


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## Vertigo (Dec 28, 2016)

Except I don't think they are saying it is _time_ that is in a spiral but rather the whole structure of spacetime that is a spiral.


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## Boneman (Dec 28, 2016)

Time travel can only be possible into the future, surely? Otherwise someone from the year 7575 (try not to think of Zager and Evans here...) would have come back to visit us, no?


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## Arize1959 (Dec 28, 2016)

Vertigo said:


> Except I don't think they are saying it is _time_ that is in a spiral but rather the whole structure of spacetime that is a spiral.


You are absolutely right!...


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## Arize1959 (Dec 28, 2016)

Boneman said:


> Time travel can only be possible into the future, surely? Otherwise someone from the year 7575 (try not to think of Zager and Evans here...) would have come back to visit us, no?


Let me quote myself:

"(...)
In other words a tourist from the future who tried to appear publicly to the world of his past would find a natural barrier that could even be fatal!...
Therefore, no tourists from the future would ever try to change the past or appear openly to the present world. They must be among us, disguised in the present society, but none will appear publicly."


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## Vertigo (Dec 28, 2016)

Arize1959 said:


> Let me quote myself:
> 
> "(...)
> In other words a tourist from the future who tried to appear publicly to the world of his past would find a natural barrier that could even be fatal!...
> Therefore, no tourists from the future would ever try to change the past or appear openly to the present world. They must be among us, disguised in the present society, but none will appear publicly."


I still say that their mere presence, disguised or otherwise, has changed the past. Their consumption of resources has changed the past. The fact that a disguised time traveller has, for example, parked a car somewhere might mean someone else can't park there and that someone then goes to find another place, has and accident and someone is killed. No matter how careful a 'time traveller' is their mere presence changes the past.


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## Arize1959 (Dec 29, 2016)

Vertigo said:


> I still say that their mere presence, disguised or otherwise, has changed the past. Their consumption of resources has changed the past. The fact that a disguised time traveller has, for example, parked a car somewhere might mean someone else can't park there and that someone then goes to find another place, has and accident and someone is killed. No matter how careful a 'time traveller' is their mere presence changes the past.


As long as the time traveller does not consciously try to change the future, he has no need to be careful at all. He can act freely in any time frame without fearing anything because their actions are already part of the structure of events which make up history. This means that all future actions of the time traveller in the past are already part of the same past, that is before he even comes back from the future. What I want to say is that a time traveller could not come back from the future if he does not exist in the past. So if he points to the past he already exists there.
On the other hand, there would be a problem if the time traveller tried consciously to change the past (or the future). He would collide with a barrier or logical resistance (some type of force field) that would come from the Universe itself. It would be as if you bumped into a wall... and were only allowed to pass through the door. This barrier would prevent the emergence of any possible time paradox. This is a logical constraint in the structure of space-time that cannot be broken.


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## Dave (Dec 29, 2016)

Arize1959 said:


> ...there would be a problem if the time traveller tried consciously to change the past (or the future). He would collide with a barrier or logical resistance (some type of force field) that would come from the Universe itself. It would be as if you bumped into a wall... and were only allowed to pass through the door. This barrier would prevent the emergence of any possible time paradox. This is a logical constraint in the structure of space-time that cannot be broken.


So, are you therefore saying that Time Travel can only exist if supernatural elements are employed to achieve it (logical resistance force fields)? If so, then I would agree with you totally. Only, I don't believe in the supernatural.



mosaix said:


> Your new timeline would include everything, including all your memories. People could be traveling back in time and changing history all the time. Our timelines could be changing every single second and we would never know it. Our timeline is exactly that - our timeline, and it includes _everything. _You would have no way of knowing what your old timeline was and so have nothing to compare with.


In the multiverse, we would not just be the same people with different memories, we would be fundamentally different people with different experiences. The logical extension of that is that every single moment in time has countless different alternative paths. If we can *access* those then they all must exist "somewhere else" in a physical form. That is a whole new meaning for the term "expanding universe." Where did all that matter come from? You can't make it out of "logical resistance force fields."

I'm still looking for an answer to where all the time travellers are. I'm not persuaded that they would all be seeking psychiatric help. Just for a start, there are plenty of people today with wild conspiracy theories (Illuminati and reptilian overlords)  who are not immediately "locked away." 2016 has produced plenty of further crazy political forecasts and lies which people have consumed without question, so why would they question the word of a real time traveller? I expect he could very quickly prove himself with the use of a BTTF "Sports Almanac." I agree that his predictions about 2016 might have been too unbelievable, but we would have soon learned otherwise.

Another question: Where are the flash crowds at important historical events? If you holiday, the vast majority choose the same exciting tourist destinations supported by agents who promote them. Why do historically important people still die without futuristic doctors and medicine to hand?


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## Arize1959 (Dec 29, 2016)

Dave said:


> So, are you therefore saying that Time Travel can only exist if supernatural elements are employed to achieve it (logical resistance force fields)? If so, then I would agree with you totally. Only, I don't believe in the supernatural.
> 
> In the multiverse, we would not just be the same people with different memories, we would be fundamentally different people with different experiences. The logical extension of that is that every single moment in time has countless different alternative paths. If we can *access* those then they all must exist "somewhere else" in a physical form. That is a whole new meaning for the term "expanding universe." Where did all that matter come from? You can't make it out of "logical resistance force fields."
> 
> ...


The logical resistance against the time paradoxes isn't 'supernatural', as I said in an earlier post, it is a Natural barrier, it is logical, it is a natural consequence of the hypothesis that (1) time travel to the past is possible and (2) there is only one version of the past, one timeline.
If it is so, then time paradoxes must arise if the time traveller try to change the past (or the future).And if the time paradoxes must arise a logical and natural constraint (the resistance) in the structure of space-time must arise as well. I don't believe in multiple timelines which is a misconception of quantum mechanics...

As to why people die I believe this depends on the Law of Cause and Effect (karma, which governs evolution) and the will of Divine Providence.


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## Brian G Turner (Jan 5, 2017)

And to follow on from Stewart Hotston's post, there's a piece here in today's New Scientist about the lack of agreement - even interest - among physicists about the different models for Quantum Mechanics:
Physicists can’t agree on what the quantum world looks like


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## Cathbad (Jan 5, 2017)

I have just received a message from my future self.  It says:  "No, time travel isn't possible."  It was dated 01/02/2036.


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## Dave (Jan 5, 2017)

Yes, I also understand the part about leaving a message in the personal column of a Newspaper for my future self to read. I'm a bit more hazy on sending sound files back in time for my earlier self to listen to. If one of you could explain it simply, then I'll send one off immediately.


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## J Riff (Jan 7, 2017)

I see where_ Arrival_ uses a time-travel out. I think we should relegate standard time-travel back into the Fantasy category, until someone figures it out, which they obviously never did..*


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## Vertigo (Jan 8, 2017)

J Riff said:


> I see where_ Arrival_ uses a time-travel out. I think we should relegate standard time-travel back into the Fantasy category, until someone figures it out, *which they obviously never did*..*


Hehe!!!


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## Cathbad (Jan 8, 2017)

J Riff said:


> I see where_ Arrival_ uses a time-travel out. I think we should relegate standard time-travel back into the Fantasy category, until someone figures it out, which they obviously never did..*



Good... good!  We have convinced them!  They'll never know the truth of how we manipulate their fut -

Um.... where's the delete button?


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