# Making an internally consistent, logical set of rules for time travel (based off of this video)

Something similar to this.

Okay, so the basic plot structure I want is that there are two parallel timelines, both of them potential futures for our world. These two timelines have become entangled, and now the fabric of their branes are beginning to collide, meaning eventually one or both will either be destroyed or absorbed into the other. Utilizing alien technology (long story), one of these parallel timelines creates a CTC that'll take them back to before the event that triggered the separation to manipulate history in such a way that their timeline becomes more chronologically "certain" and therefore more likely to survive the collision.

What I'm almost "certain" of myself is that this is all absolute bollocks in terms of real quantum mechanics, but I want to make sure it's consistent. Basically, it goes: someone in the original timeline travels back in time for unknown reasons, splitting the universe into two entangled timelines, someone from one of these two timelines travels back in time again to "fix" history so their world survives, the two timelines merge into one (hopefully).

Does this make sense and does anyone with any more insight on time travel have any suggestions to improve it while still maintaining the possibility of there being conflict between two parallel timelines? I feel like if I can just nail down the rules the rest of the story should be easy (without the lingering shadow of logical paradoxes that is).

• If you want some further explaination to the “real” results this video attempts to communicate, try asking on Physics. Aug 19, 2016 at 2:54

The video gives the explanation that the universe is in a state of superposition allow for the existence of the two timelines. This enables two mutually exclusive sets of events to exist in parallel, i.e., the two timelines.

This tangled timelines arose because Axel a time traveller going back and creating the initial event that caused the two timelines to come into existence. Later, further ahead in one of the two timelines, Brad is sent back into the past, before the two timelines split, to make a change to history to ensure that his timeline will survive.

This suggests that whatever Brad did he cause the superposition to collapse or decohere. Effectively this suggests that what happens is something akin to delayed choice experiment devised by John Wheeler in his participatory universe concept concerning quantum mechanics.

To set up a delayed choice protocol to collapse the superposition would involve as said previously, Brad arrives in the past using a closed timelike curve (CTC), he changes something in the past and when this observed in the future, actually this would be back in Brad's present, the present he left when he departed on the CTC.

The most effective method of performing a suitable delayed choice experiment would be to set up an interferometer and follows the path of Brad's CTC. So one end of the interferometer is sitting in the past, prior to the creation of the two timelines, and the other end is located in Brad's own timeline.

By carrying out a standard delayed choice experiment this will make happen the observation that triggers the superposition collapse. Because the delayed choice takes place in past history prior to the separation into two timelines, and the observation made in one of the timelines the superposition collapse will only the one timeline. This will be the timeline from which Brad and his CTC came.

The video cited was probably based on a paper of Seth Lloyd's that proposed a quantum mechanics solution to the problem of time travel and the grandfather paradox. This result is logically similar to that of the tachyon antitelephone argument. Namely, that time travel happens if and only if it doesn't happen. The main difference is that Lloyd wraps the paradox of two contradictory sets of events in a superposition.

This answer is the result of having written too many articles about time travel. Sometimes there's no excuse.