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This is interesting because the most "realistic" (i.e. still not realistic) depictions of time travel in fiction involve travelling through a singularity or wormhole. So you probably have to be in space to start with, but also both ends of the wormhole have mass so they can be orbiting a planet or star and stay within a stable distance of it. It solves this particular problem (just leaving the other usual problem of causality!) It also proves your point since it does allow travelling in space, in fact it allows travelling faster than light.

I think the converse is true as well, that if faster than light travel is possible then time travel must be possible, at least if you take relativity at face value. As others have pointed out there's no universal reference frame, and for any journey that is faster than light in one reference frame, there is another frame in which the journey goes backwards in time.

Goodbye

I'd caveat this by saying more signals is best done with two lanes. For two-way single-lane track you need everything in one signalling block to avoid gridlocks

Two lanes everywhere is the simplest and most conventional solution for this. But I might be tempted to just make the big loop one-way and turn it into a massive roundabout

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Don't forget your arms-jumper-umbrella!

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