# Time travel analysis again: Weird phenomenon when trying to think about grandfather p

Discussion in 'Pseudoscience' started by Secret, Dec 17, 2013.

1. ### SecretRegistered Senior Member

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299
NB: This thread is placed here as the nature of the question is deamed too speculative to be placed in the physics and maths subforum, despite it is trying to obtain an answer in terms of mainstream science from the sciforum members

So I was thinking about the Grandfather paradox again after watching Primer and reading a bunch of time travel related articles (which I am still reading when this post was written)

I then thought about a possible model of time travel and tried to investigate on what happens

In order to take "decision" out of the equation (because it can complicate things), I simplify the grandfather paradox, which is commonly portrayed as "you go back in time and kill you grandfather" into

"There's a billard ball travelling inertially along the x direction with a velocity v<<c (so that special relativity effects become negligible) which then travel back in time (via CTC or Primer like reverse time) and on colliding with its past self, knock its past self off course so that it can no longer travel back (thus a grandfather paradox is created)"

because of how the minimal requirement of the grandfather paradox is that "An entity travels back in time to prevent its past from travelling in the first place"

http://plato.stanford.edu/entries/time-travel-phys/
that by considering a spacetime with closed timelike curves (CTCs),
I am still wondering about what happen if a grandfather paradox occur in time travel models where the timeline is malleable (something like Back to The Future), known as type 3 time travelling models in scifi

From what I understand about time, there cannot be just one time axis as otherwise all overwrites will take place "at the same time" and you only get to see the latest revision of history of the timeline, thus I suspect time travel in these stories are at least 2 time dimensional (which I call them t and tau) and there units are seconds (s) and hyperseconds (hs) respectively. Points are notated as (t,tau). Thus t is time that we are familiar with, while tau is a continuum where the changes in the timeline is plotted (as if the entire timeline(t) is a 'block' of some sort and that tau records the changes that happens on this spacetime 'block' due to time travel)

[Assumptions]
Assume t and tau have the same ratio (i.e. 1s in t is the same as 1hs in tau)
Assume ripple effects can only propagate at maximum the speed c

So for any non time travellers that is travelling inertially with v<<c, its worldline will look like this (Fig 1)
For a time traveller entering a CTC, its worldline will look like this (Fig 2)
For a time traveller entering a Primer like time travelling box, its worldline will look like this (Fig 3)

So for a time traveller trying to initiate a grandfather paradox in a CTC, it will look like this (Fig 4a)
(From bottom left to top right)
(Frame of the time travelling ball that initiate the grandfather paradox)
1. There's a time travelling ball A that travel towards a wormhole to its left. (diagonal mint green line)
2. At (1,1), the ball have entered the wormhole and found itself in (0,1), which then knock its past self (A2) off course from the wormhole in a glancing elastic collision, thus creating a grandfather paradox
3. The ball A then continue to travel somewhere in the opposite direction (long diagonal mint green line that follows)

(Frame of A's copy (A2) at tau=1hs)
1. (0,1) A2 is knocked off course by A, history is changed in an inconsistent way and a ripple effect is generated
2. (1,2) Ripple effect propagates (pink line), there is no A2 that travel back to (0,2) to knock its past (A3) off course, thus A3 go into the wormhole like what A does and initiate the same series of events (pink diagonal and mint green vertical line at tau=3hs)
3. Meanwhile, A2 travel to a different direction thus it never entered the wormhole (long red diagonal line)

and so on...

For a time traveller trying to initiate a grandfather paradox via a Primer box, it will look like this (Fig 4b)
(From bottom left to top right, all vertical lines are projections on the t axis, as events happening on the t axis is what (we assume) an entity can perceive)
(Frame of the time travelling ball that initiate the grandfather paradox)
1. There's a time travelling ball A that travel towards a Primer box to its left. (diagonal mint green line)
2. At (1,1), the ball have entered the Primer box and found itself in (0,2), which then knock its past self (A2) off course from the wormhole in a glancing elastic collision, thus creating a grandfather paradox
3. The ball A then continue to travel somewhere in the opposite direction (long diagonal mint green line that follows)

(Frame of A's copy (A2) at tau=2hs)
1. (0,2) A2 is knocked off course by A, history is changed in an inconsistent way and a ripple effect is generated
2. (1,3) Ripple effect propagates (pink line), there is no A2 that travel back to (0,4) to knock its past (A3) off course, thus A3 go into the Primer box like what A does and initiate the same series of events (red diagonal and pink diagonal at tau=4hs)
3. Meanwhile, A2 travel to a different direction thus it never entered the Primer box (long red diagonal line)

and so on...

Observations:
1. Therefore to the time travelling ball and other observers, it seems the past of the time travelling ball alternates discontinuously between "time travelled ("grandfather lived" state) and "not time travelled" ("grandfather dead" state). As time (both t and tau) progress, this whole "dead" and "alive" states propagates as a whole like a wave with the source at t=0s
2. It seems the ripple effect will never catch up with A as it is always 1s (or 2s in the Primer box scenario) behind A. Thus it seems to suggest that a time traveller can do anything it wants and will not be erased from existence unless under special conditions
3. If A travels back in time again (e.g. via another wormhole or Primer box), then using these graphs it seems its worldline will intersect with the red line (the ripple effect). Thus it seems to suggest it will then be erased from existence since at the point of intersection, the ripple effect had caught up with the time traveller. A still exist before it is wiped out by the ripple effect since the ripple effect only took place at a certain tau
4. When the time interval between going from the past to present and then back to past to cause the gradnfather paradox tends to zero (i.e. length of the base of the triangles tend to zero), the oscillations in the timeline tends to infinity as it move to larger tau. Thus the opposite versions of histories (the "dead" and "alive" state) are only being separated by an infinitestimal amount
5. As seen by A and its hyper later copies as it look back to the past as it marches along tau, it seems what A can see in its immediate past is that everything proceed as the "alive" state with only at one instance of tau (tau=2hs in CTC scenario and tau=3hs in Primer box scenario) the history is in the "dead" state

Questions (numbered according to the observations):
1. This is weird, did I made a logical error in my deductions, or is it really what theoretically will happen given my assumptions stated above. Are discontinuities in events in time allowed?
2. This is even weird, is it really true that the ripple effect will never catch up?
3. Actually, how to interpret the physically meaning of the intersections?
4. This is pathological, how to deal with this infinite oscillating history?
5. This is also weird, did I made a mistake in my deduction?

6. Using mainstreams physics as we know it, is self consistent time travel the only solution? Is there exists any theories that can address the grandfather paradox without forbidding it to happen (other than Many Worlds Interpretaton, which some still thought it had not adequately address the paradox), or is there any concrete result that can rule out all possible types of grandfather paradoxes that can theoretically happen?

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3. ### andy1033Truth SeekerValued Senior Member

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1,060
I do not believe in the grand father paradox. I think its a very stupid idea, and shows the limited mind of humans to work out anything in a grand scale. What is the past really? I doubt the past really as solid as you would like to think.

If time travel exists and i think it does, then it means your whole life in effect is meaningless. But i bet humans would then take it to mean something else which it does not mean.

I personally think the grand father paradox is stupid. Humans like to believe they are the greatest thing in the universe when they are not. The laws are not governed by them, by the universe or what created the universe. I think the grand father paradox is stupid, and like what humans normally do, it places too much trust and faith in what we see as the past.

To go into time travel, humans would have to understand what is the past, and i doubt it is as stable or absolute as you imply with that stupid grandfather paradox rule.

What really is history. Plus humans only ever know the present.
^^
This i assume plays alot into time.

5. ### DinosaurRational SkepticValued Senior Member

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4,885
Time travel into the past can result in interesting SciFi. It is not a possible technology due to all sorts of paradox problems.

The paradox problems can be resolved: The cost is some violation of mass/energy conservation laws.

The grandfather paradox can be resolved by requiring the creation of an alternate universe in which the future time traveler does not exist.

The time traveler has the choice of continuing to live in that alternate universe with the option of returning to his original universe at any time. The energy requirements of universe creation are considerable & surely violate some conservation laws.​

Asimov (I think) wrote a cute time travel story, in which some intelligent characters wonder why there seemed to be no time travelers from the future. In this story, time travel into the future is not possible (It does not exist yet).

Time travelers into the past tinker in hopes of improving either their future or the future of some group.

The above question is answered, when some time traveler tinkering in the past causes the time machine not to have been invented. The only people aware of the time machine are a few individuals who had traveled to a time prior to the invention of the time machine & who would live the rest of their lives in that past.​

BTW: The bold remark above indicates to me that the Many Worlds interpretation of Quantum Theory is invalid, although it is accepted by many with impressive credentials.

I think it is accepted because it is easiest to understand. Some folks would rather believe a silly explanation they can understand than a more valid one which is mind boggling and/or incomplete.

Note that Many Worlds implies the creation of a universe for each possible outcome of a quantum process. This implies the creation of more than billions universes each second. Each quantum process in each new universe spawns more universes at a rate exceeding billions per second.

It is easy to understand, but the implications make it appear absurd.

7. ### Uncle PythagorasBannedBanned

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Paradox are often mental tests, and the Universe is physical. Mathematical models can also include both physical, and mental ideas. The problem with time is that it is a mental image that is being treated as a physical representation of reality. If it is physical then it has to fit in our physical Universe, and has to have a position where it can be observed. If I can be in many positions in the Universe, I walk, I leave a trail of information behind me. If that information has to become a solid to bump into, it has to exist with physics that can change data into a solid. Where is this information trailing behind me that can become a solid? If we can find the information then we can clone someone from their own trailing Data. The more you talk about time, the more you become aware that time is a stupid idea... data is not trailing around all over the place. Time has no position to sit in our Universe. The multiverse idea is a mental idea, and also has no physics to sit in a single location. You can only fold information into holes with depth. The depth of the hole has to allow energy to escape. Basically you can leave a scent behind you, and it evaporates away. Physics are all about things that work in reality. Time doesn't work in reality.

8. ### GrumpyCurmudgeon of LucidityValued Senior Member

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1,876
Time travel inside this Universe is simply not possible. The past no longer exists, only the present exists. It may be that the inside of a BH is a short circuit trip through a wormhole into the past, but the only destination would be the Big Bang, thus no paradox.

Grumpy

9. ### SecretRegistered Senior Member

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299
I don't quite understand what you mean by "the past is not as stable or absolute as implied by the grandfather paradox", do you mean the past can be changed or something more subtle?

In the past, I used to be a strong supporter of many worlds interpretation, since it can resolve one of the most annoying of the time paradoxes (grandfather paradox). (And who doesn't love the idea of parellel universes to visit in (soft) scifi stories)
But throughout the three years when I analyse time travel stories one by one and plot timelines of them (including classics such as The Time Traveler's Wife and A Sound of Thunder, movies like Looper and Primer, various video games and anime like Final Fantasy XIII-2) and read about the physics literature about time travel (the stanford link quoted in the OP, post selection in CTCs, how CTCs violate the Heisenberg unvertainty principle etc.). I have drawn timelines using the Many World's Interpretation (strictly speaking the pop science version of branching parallel universes. They are sometimes known as type 4 time travel models in scifi)

I then thought of a way to explain things like Bootstrap Paradox (aka Ontological paradox) and predestination paradox using the type 4 models, by using what's the gist of Many worlds interpretation (the itallcised statement in your quote) is that every single event branches the universe, so what's the problem of having said branch looping back to itself and having the very descision to time travel an event that can branch the universe?. Thus the origin of the information (such as the steps to build a time machine by a scientists) can be thought of as originated from the quantum version of the future scientist formed the moment when said scientist's future self decided to travel back (although he can choose not to, which creates another branch which has nothing to do with the bootstrap paradox, and then he will thought the information of building the time machine cames from the moment he received that some time in the past)

But after I tried out this idea, I ran into another problem (besides the obvious energy issue in creating a parallel universe)
-The freewill of the quantum copies. E.g. using the scientist bootstrap paradox example above, it seems the scientist that travel back is there solely to close the loop, he has no choice at all until he complete the task related to closing the loop (because he is already representing one of the many choices the scientist can take), so in certain sense his action is predestinated and his future is fixed
-It seems a time traveler can do anything he/she wants, and would not suffer from anything, as whatever change happens on another branch. This result in the model being too perfect (I cannot remember exactly the guy who quote a statement, but it goes something like "A model that can always be made to fit any observations and data is in certain sense unfalsifiable and is useless")

The horror film Triangle and more importantly, Looper eventually result in the abandonment of the model I mentioned above and go for something that is closer to common sense. I then started to investigate the hypertime models (details of it as shown in the OP) but then I am trying to find a way to have the model to make the same outcomes without the possibly fictious hypertime axis, and this is where I am now. From what I 'learnt' from Primer, there's an issue similar to the 2nd point in the type 4 models shown above in that the time traveler can do anything he/she wants as the ripple effect never catches up with them (Since by SR, all information cannot exceed c), but I am thinking I might have misinterpreted something and I have no idea what that is

Literature on time travel out there I read so far focused on time travel models where consistency is a necessary factor, thus grandfather praradox is not possible at all. The other model that is also came across in the literature is the Many World's Interpretation. Is there any other models proposed out there in the mainstream that is not Many worlds or modles that forbidden grandfather paradoxes?

As mentioned in the OP, there's indeed a recent paper that suggest theoretically we can clone information from the past if time travel (specifically in the form of CTCs) exist http://www.sciencedaily.com/releases/2013/12/131208090633.htm ,although I don not really understand the details of it

But as Grumpy mentioned, a universe where time does not exist or is an emergent phenomeon there cannot be any time travel as there is no "time" to travel on

Last edited: Dec 23, 2013
10. ### GrumpyCurmudgeon of LucidityValued Senior Member

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1,876
Secret

Time and space are structural qualities of spacetime, not emergent or non-existent. Spacetime IS the Universe. But time in this Universe is really only half of a dimension, it is missing the freedom of movement either way that the three dimensions of space all have. The Standard model requires 11 dimensions in total, all but the four are "rolled up" in the Quantum, some scientists think entangled particles are connected through these dimensions by wormholes. Some BH math suggests wormholes and backward time travel, so are BHs connected back in time to the Big Bang, the only White Hole we know existed? That would probably be the only time travel to the past that could happen. No grandfather paradox, no multiple universes needed. And the Universe becomes like a big virtual particle, borrowing energy from the future for an event that already happened in the past. Just a Quantum Fluctuation of unusual size.

Grumpy

11. ### SecretRegistered Senior Member

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299
Supplmentary: Ooops I should have added an "if" in my last paragraph ,because I am using that quote to response to Uncle Pythagoras as (I think that particular quote) of yours is responding to Uncle Pythagoras (i.e. I ma not saying you think time is an illusion)

Main thing:

Sounds like a predestination paradox to me, everything is predetermined from the very start, seems quite a pessimistic but reasonable scenario
[RANT]The annoying thing is that despite so much evidence suggesting that there is no such thing as freewill, freewill is still not completely ruled out by science as far I know, making it somehow like "Teetering on some sort false hope" (roughly trying to phrase what I am trying to say...)[/RANT]

Another thing which is more related to the topic at hand is if all BH are mapped to the white hole that is known as the big bang, does it mean the Big bang borrow energy from all BH that will exist after the big bang in order for the universe to bootstrap itself into existence? If I rmb correctly GR and SR mentioned about how spacetime is like a 'block' where past present and future all coexist, then in such case it seems the universe is like a huge feedback loop or closed (even isolated) system with energy conserved?

And then there's more complicate stuff out there in the literature, such as a cyclic universe model where there is no big bang, I am wondering how do they deal with black holes (espeically the Kerr Black holes, as the singularity can be ring shaped in those thus potentially create a Einstein Rosen Bridge) e.g. where is the other exit?

I rmb this is quite a recent thing. What I don't understand is if entanglement are just wormholes, and we known how wormhole connects one spacetime to another, then why we cannot use these wormholes (entanglement) to transmit information <there's an extra phrase here for this FAQ related to entanglement, but I forgot the phrase itself, maybe you can fill it in for me>? How are these wormholes different from the Transversible wormholes that is sometimes mentioned in theoretical physics?