Time Travel Paradox Ideas - Except Grandfather

[aa1bb2cc]

I'll throw my two cents in:

Read Heinlein's short story called "--All You Zombies--" (http://en.wikipedia.org/wiki/"—All_You_Zombies—"). It probably sets the world record for best time travel story ever. I never quite figured it all out, but I'm pretty confident that every character in the story is the same person. If I recall, it's only 10-20 pages long. Read it. It's worth it.

Here's the full story:
http://faculty.uca.edu/rnovy/Heinlein--All%20you%20zombies.htm

There is a movie based on this story. Its called "Predestination" staring Ethan Hawke.
Its really a good movie with very little cinematic liberty. A must watch

 

[chasrob]

I read this interesting arXiv paper--http://arxiv.org/abs/1505.07489 that helped me understand FTL is time travel. Me, who is mathematically challenged--it has high school algebra equations--mostly heh, heh..

It had 2 pads for the space ship; one launch pad and a landing pad. Weird stuff going on when the flight was superluminal. Ships returning while its optical replica? was taking off, ships returning to the landing pad days before they took off from the launch pad, views from telescopes on Earth showing the ship approaching and leaving the destination at the same time, even the pair meeting at the destination and disappearing... what the ...?

 

[BastianQuinn]

In my experience, a paradox isn't some kind of magical error in space-time that can be harnessed by the plot of a scifi story like "pure chaos" or "reversing the polarity." A paradox generally only signifies that the person performing the thought experiment lacks the knowledge to complete it. (that person is often me)

An example of this is Zeno's paradox which says that crossing a distance is technically crossing half the remaining distance repeatedly (paraphrasing) and claims that there should always be more distance to halve, so it should be impossible to cross any distance. This is a paradox because of the assumptions made in constructing the model. In reality, halving the distance also shortens the time ad infinitum, the kind of thought process that makes integration possible.

All that the grandfather paradox shows is that the assumptions made in constructing that model of time travel are incomplete. Any model of time travel where the actions of the traveler(t_n) could theoretically change the traveler before traveling(t₀) are incomplete. This is why savvy time travel authors come up with rules which preclude a grandfather paradox.

The other "paradox" is said to be meeting yourself, this is said to be related to the Pauli exclusion principal, which is misquoted as stating that "the same matter cannot occupy the same space-time twice." This is a misunderstanding of quantum physics. As I understand it, (and I understand it poorly) even if it had anything to do with time travel, it would be prohibitively difficult to intentionally attempt to have two identical fermions "touch." In layman's terms, this theorem is kind of a mathematical proof that electrons in the same orbital have opposite spins.

Oh, but here's another paradox I have heard. When we move along space, we accelerate and decelerate. If time is a comparable dimension, traversal of it would follow similar rules. (faulty model construction) However, if we attempt to decelerate in order to move backwards in time, when we reach 0 time-velocity, we would be parked at a point in space-time where future-us is constantly arriving, and be unable to pass through the wall of past-us. An infinite number of us would suddenly occupy the same point in space-time, creating a black hole.

 

[skeptic2]

The thing that all backward time travel stories have in common is that the time traveler himself doesn't regress in time, everything else around him does. If the traveler were to regress in time he would get younger and lose his later memories. He would never meet a younger version of himself because he would be that younger version. Unfortunately this doesn't make for an interesting plot. It seems that this split direction of time travel in which the time traveler continues to travel forward in time, i.e. he gets older and accumulates memories, but everything else travels backwards in time, is the crux of the paradox.

 

[BastianQuinn]

The thing that all backward time travel stories have in come is that the time traveler himself doesn't regress in time, everything else around him does. If the traveler were to regress in time he would get younger and lose his later memories. He would never meet a younger version of himself because he would be that younger version. Unfortunately this doesn't make for an interesting plot. It seems that this split direction of time travel in which the time traveler continues to travel forward in time, i.e. he gets older and accumulates memories, but everything else travels backwards in time, is the crux of the paradox.

This is true. Time travel generally fails to specify what exactly is being transported through time, and the more detail a story gives about what is being transported, the more obvious it is that it would not work... at least not as described.

Most instantaneous time traveling such as Back to the Future begs the question: "how does the car know where to come out?" The Earth rotates, the Earth orbits, the Earth's orbit has apsidal precession, the sun moves through the galaxy, etc. etc. etc. The two inertial frames differ wildly, yet the car appears to maintain velocity as if it "blinked" from one point in space-time to another.

Space-time bubble devices like the eponymous Time Machine give the impression of acceleration and deceleration through time, which is problematic as described above.

Situations where the traveler "wakes up in a younger self" ask more questions than they answer. Did the character's mature brain travel back to inhabit his immature skull? So many how.

Then there is what's perceived as the simple solution: the threshold of death. Even if air pressure was somehow a non-issue, it sounds to me like a good way to reintroduce smallpox, the bubonic plague, and polio into the modern world.

In the face of these criticisms, even Terminator logic seems plausible.

 

[rootone]

Transporting matter (in human or other form) into the past, increases the total mass-energy content of the past, and decreases the mass energy content of the future.
I think this could get problematic after a few iterations.

 

[BastianQuinn]

Transporting matter (in human or other form) into the past, increases the total mass-energy content of the past, and decreases the mass energy content of the future.
I think this could get problematic after a few iterations.

Wow... I think this might be the only example of a loop which will always close itself. The source of the extra energy is the point in the future, which will have been a universe with the extra mass-energy to spare, because it manifested when it came from the future. If T_p is the moment in the past that the traveling stuff emerges from the future, and T_f is the moment in the future it leaves for the past, then the mass-energy content of the universe at T_p-1 and T_f+1 are equal. There's nothing extra, just folded through space-time. Mass-energy doesn't age or die, and doesn't care if it's "the same stuff". There is no question of where this extra mass-energy comes from or goes, it does not have to stay in the same form, and the equation will always be balanced. This is merely a method of temporarily increasing the mass-energy content of the universe. Similarly, jumping forward in time reduces the mass-energy content temporarily.

I mean, yeah. doing so might be problematic, as you said, but I was surprised to find such a cleanly closed loop in a time travel model.

 

[cpscdave]

In Stephen Baxters Exultant they have FTL drives, and its possible depending on your FTL path to travel back in time. This causes the main character to travel back in time to before he was sent on a doomed mission.
Like many of the other examples listed this results in 2 versions of himself existing.

Later in the book Humans use these FTL loops to create a computer that can solve any problem instantly. It does this by using the time travel loops.
It first checks the time travel result register, if its empty it processes 1 step of the algorithm. If the step produces the answer it sends the result back in time, otherwise it repeats.
One of the engineers remarks that they can build the computer using very cheap components cause they will never actually do any work.
Always thought this was a fun application of time travel :D

 

[Khashishi]

Pool ball is sent into the corner pocket. The corner pocket is the entrance to a time machine. The exit from the time machine is the side pocket...
If the time travel pool ball deflects the original pool away from the pocket, but then enters the pocket itself, you also have a stable reality. Except now you have a loop created entirely by the time travel pool ball.

Maybe this paper is on your mind:
http://journals.aps.org/prd/abstract/10.1103/PhysRevD.44.1077