The exploration here is heavily dependent on the Equilibrium and I don’t think it is a consequence of the numbered assumtions or a carry over of a similarity with the real world. It is common for physicist to assume the world timeline is stable as it makes it more manegable to imagine things but I don’t think it is a result. Absent actually having time travel we don’t have good way of testing this.
Note that if you take the world of Primer and consider the boxes to be in a separate (but connected throught the box opening) universse you get something that is fairly analogous to the lane setup. Primers world does not require stability and is quite different than envisioned here.
Symmetry → Twoway traffic
Clarifying that symmetry is that all the detail being microscopically same in the central epoch and events being connected in classically mechanistc way we get that if we paced bioth timelines side by side they would be equal in all the details. A further consequence of this is that every time you switch your cosmic twin is going to switch to the place you just left. The cosmic twin is also going to have exactly the same psychological experience as you are going to have. What they are going to experience is the your past few moments just seen reversed. But this is also what you are just about to experience. Thus even if on an ontological level there is a distinction of the timelines, for a lot of practical purposes we can fuse them as a single lane that goes both ways. Then this starts to look a lot like the world of Tenet. Also even with the basics of switching twice it is really easy to make a gemini incident even without cosmic twins.
Unexperienced history
If the highwayversians are not the branches of the tree of evolution why would they be a sexual species? While there can be no chronal mechanics for equilbirium selection it doesn’t mean the absence of achronal mechanisms. The idea of “pushing the equilbrium” could be turned that in a chain of unstable timelines pushing into unstable timelines if it ever (timeful word employed not in chronal sense) reaches a stable stable sense it will tend to lock there. Thus unstable timelines would not be impossible but merely ontologically transient (althought being percieving chronal time in the stable configuration could not have ever experienced them). This could be turned into a “achronal tree of life”, highwayversians are sexual because the first species that caused an unstable timeline was sexual. In successive timelines the island of higwayversians became more separated from the same-timeline other chronal life. An equilbrium or stable tree of life will not push the bubbles further apart but will those that have grown going. But their states would not totally be uncorrelated, with larger differences there would be more changes needed and every change risks the transition becoming stable “too early”.
Preservation of basis
In the RPG continuum the reason why the past is stable and relatively unharrased is that the Inheritors need the Hour of Inheritance to take place as it does for them to exist. For spanners having an unstable age is actively painful and lethal (frag). Being given the guaranteed gift of assured stable age would seem what would seem like a deathwish desperately sought for but never granted. I guess it does mean that a spanner has the option of healing frag while a highway versian is totally barred from making As/As nots. For highwayversians they might know that in order to exist and have bodies at all the central epoch needs to be connected to the start of the universe, so they might want to forbid or be secure in the knowledge that trying to mess up too much with the non-switching life fails. This might spring a profession / department of border security that intercepts movement away from the central epoch. For life that wishes to not switch this could mean that 3/4rds into the lifetime of the universe there are hunters that seek out to destroy life and matter living that way into the future. To parallel the other intellectual property call that socially set line as “point of entry” because it forms an event horizon that switching life can’t push out of but matter makig up the bodies of the center life needs to be collected in. This line could be set to different depths in different parts. The size of inside region which is accesible to civilised switchers could be dependent on the amount of border patrolling work and having too little matter to circulate could make the world too interconnected (is there a difference betwen building a country out of 10000 atoms or 1000? How much matter is needed to hedge against radioactive decay from cosmic rays?). Maybe size of the habited area is a point of political contention for the switchers
Overcrowding
Either a life occupies new time or it keeps turning into the same time. If the central epoch is more conductive to switching then it would seem that having the choice of moving inward or outward it would be prefererable to move inward (as outward life would mean you would live a less-switchy life). So the center is probably going to be real dense with switchers. All of the universe wants be in that tiny sphere of the central epoch which could mean that there would be natural or artifical selection on who gets to visit/utilise it. Like the result that if there was a wormhole providing time travel then a radiation could loop and pile up accumulating more and more to eventually collapse the wormhole . Like in Expanse there is a division between “inners” and “belters” there could be division of “inners” and “flatters” those who get to utilise it. Maybe if you are downthrodden it would be tempting to get the benefits of switching even if there were no guarantees of safety. Also all transmission lines of frozen people or messages also need to serve all of history at once. Solving that capacity issues could be serious if it is cheap to use for everyone (is 20 million cryo pods to cover 10 years of centralwards travel enough for everyone in that timeperiod (and all the pass throught traffic from the previous century and the previous througth traffic from the previous millenia))
Danger mitigation
If you had no preknowledge whether the switching location was safe, you would probably want to try to switch too high and then try to come down in some safe manner. Having a parachute and shooting yourself with a cannon high up could make for quite a lot of elevation difference. Or maybe it would be safer bet to first climb a mountain and then swich on the ground with parachute on? For ground known to experience changes a lot “transition stations” which by public service are designed to stay stationary could be useful from a civilization viewpoint. Having a structure that instead of laying on the ground is directly floating on the magma being able to float regardless of what the stone around it is doing. Or maybe having blips that either rely on athmosphere staying stable to maintain reliable altitude or active adjustment to actively keep at constant gps height. Maybe you want build a big incline that you can safely start rolling on from variety of heights. For actually getting the information I would think that such a boring solution of “historical” height maps would be in great demand.
Socials
Chronies use, “up” for global future, “down” for global past, “yet” for personal future and “age” for personal past. Using left and right analogs would seem to be confusing if spatial right and left are still used quite a lot. If highwayvesians do not care on which age of the target they talk to why would they target their messages to a specific timestamp. It is also somewhat trivial for a recipient to rememeber their younger selfs location and not have it automatically compromised to outsiders.
Learning
Why in universe would the higway traversian think that pushing the equibrium actually be a thing? They would seem to be like anti-inductors in doing research because it has not worked the previous times either! If there were allowed to be less than optimal people then I could suppose that there could be a statistical correlation between the luck of people that have “good character” so that people that counterfactually would have done something are well off and people that counterfactually would not have done something are not so well. However it also means that the biggest “equilibirum pushers” are almost never tested on their commitments and I could imagine some psychological hiccups on taking on herculean efforts after a lifetime of handdowns.
The exploration here is heavily dependent on the Equilibrium and I don’t think it is a consequence of the numbered assumtions or a carry over of a similarity with the real world. It is common for physicist to assume the world timeline is stable as it makes it more manegable to imagine things but I don’t think it is a result. Absent actually having time travel we don’t have good way of testing this.
Note that if you take the world of Primer and consider the boxes to be in a separate (but connected throught the box opening) universse you get something that is fairly analogous to the lane setup. Primers world does not require stability and is quite different than envisioned here.
Symmetry → Twoway traffic
Clarifying that symmetry is that all the detail being microscopically same in the central epoch and events being connected in classically mechanistc way we get that if we paced bioth timelines side by side they would be equal in all the details. A further consequence of this is that every time you switch your cosmic twin is going to switch to the place you just left. The cosmic twin is also going to have exactly the same psychological experience as you are going to have. What they are going to experience is the your past few moments just seen reversed. But this is also what you are just about to experience. Thus even if on an ontological level there is a distinction of the timelines, for a lot of practical purposes we can fuse them as a single lane that goes both ways. Then this starts to look a lot like the world of Tenet. Also even with the basics of switching twice it is really easy to make a gemini incident even without cosmic twins.
Unexperienced history
If the highwayversians are not the branches of the tree of evolution why would they be a sexual species? While there can be no chronal mechanics for equilbirium selection it doesn’t mean the absence of achronal mechanisms. The idea of “pushing the equilbrium” could be turned that in a chain of unstable timelines pushing into unstable timelines if it ever (timeful word employed not in chronal sense) reaches a stable stable sense it will tend to lock there. Thus unstable timelines would not be impossible but merely ontologically transient (althought being percieving chronal time in the stable configuration could not have ever experienced them). This could be turned into a “achronal tree of life”, highwayversians are sexual because the first species that caused an unstable timeline was sexual. In successive timelines the island of higwayversians became more separated from the same-timeline other chronal life. An equilbrium or stable tree of life will not push the bubbles further apart but will those that have grown going. But their states would not totally be uncorrelated, with larger differences there would be more changes needed and every change risks the transition becoming stable “too early”.
Preservation of basis
In the RPG continuum the reason why the past is stable and relatively unharrased is that the Inheritors need the Hour of Inheritance to take place as it does for them to exist. For spanners having an unstable age is actively painful and lethal (frag). Being given the guaranteed gift of assured stable age would seem what would seem like a deathwish desperately sought for but never granted. I guess it does mean that a spanner has the option of healing frag while a highway versian is totally barred from making As/As nots. For highwayversians they might know that in order to exist and have bodies at all the central epoch needs to be connected to the start of the universe, so they might want to forbid or be secure in the knowledge that trying to mess up too much with the non-switching life fails. This might spring a profession / department of border security that intercepts movement away from the central epoch. For life that wishes to not switch this could mean that 3/4rds into the lifetime of the universe there are hunters that seek out to destroy life and matter living that way into the future. To parallel the other intellectual property call that socially set line as “point of entry” because it forms an event horizon that switching life can’t push out of but matter makig up the bodies of the center life needs to be collected in. This line could be set to different depths in different parts. The size of inside region which is accesible to civilised switchers could be dependent on the amount of border patrolling work and having too little matter to circulate could make the world too interconnected (is there a difference betwen building a country out of 10000 atoms or 1000? How much matter is needed to hedge against radioactive decay from cosmic rays?). Maybe size of the habited area is a point of political contention for the switchers
Overcrowding
Either a life occupies new time or it keeps turning into the same time. If the central epoch is more conductive to switching then it would seem that having the choice of moving inward or outward it would be prefererable to move inward (as outward life would mean you would live a less-switchy life). So the center is probably going to be real dense with switchers. All of the universe wants be in that tiny sphere of the central epoch which could mean that there would be natural or artifical selection on who gets to visit/utilise it. Like the result that if there was a wormhole providing time travel then a radiation could loop and pile up accumulating more and more to eventually collapse the wormhole . Like in Expanse there is a division between “inners” and “belters” there could be division of “inners” and “flatters” those who get to utilise it. Maybe if you are downthrodden it would be tempting to get the benefits of switching even if there were no guarantees of safety. Also all transmission lines of frozen people or messages also need to serve all of history at once. Solving that capacity issues could be serious if it is cheap to use for everyone (is 20 million cryo pods to cover 10 years of centralwards travel enough for everyone in that timeperiod (and all the pass throught traffic from the previous century and the previous througth traffic from the previous millenia))
Danger mitigation
If you had no preknowledge whether the switching location was safe, you would probably want to try to switch too high and then try to come down in some safe manner. Having a parachute and shooting yourself with a cannon high up could make for quite a lot of elevation difference. Or maybe it would be safer bet to first climb a mountain and then swich on the ground with parachute on? For ground known to experience changes a lot “transition stations” which by public service are designed to stay stationary could be useful from a civilization viewpoint. Having a structure that instead of laying on the ground is directly floating on the magma being able to float regardless of what the stone around it is doing. Or maybe having blips that either rely on athmosphere staying stable to maintain reliable altitude or active adjustment to actively keep at constant gps height. Maybe you want build a big incline that you can safely start rolling on from variety of heights. For actually getting the information I would think that such a boring solution of “historical” height maps would be in great demand.
Socials
Chronies use, “up” for global future, “down” for global past, “yet” for personal future and “age” for personal past. Using left and right analogs would seem to be confusing if spatial right and left are still used quite a lot. If highwayvesians do not care on which age of the target they talk to why would they target their messages to a specific timestamp. It is also somewhat trivial for a recipient to rememeber their younger selfs location and not have it automatically compromised to outsiders.
Learning
Why in universe would the higway traversian think that pushing the equibrium actually be a thing? They would seem to be like anti-inductors in doing research because it has not worked the previous times either! If there were allowed to be less than optimal people then I could suppose that there could be a statistical correlation between the luck of people that have “good character” so that people that counterfactually would have done something are well off and people that counterfactually would not have done something are not so well. However it also means that the biggest “equilibirum pushers” are almost never tested on their commitments and I could imagine some psychological hiccups on taking on herculean efforts after a lifetime of handdowns.