The Science of Radiance
Radiance is a far-future science fiction setting that I used for a linked tabletop scenario and freeform at Sydcon last year, and will revisit in RADIANCE: RELICS at Eye-Con over Easter.
For the most part, Radiance is Plausibly Hard SF, with futuristic science and technology that includes "things that may or may not be possible, but can ( Read more... )
For a brief explanation of how wormholes allow for time travel, look over this section from the Wikipedia article Wormholes: Time Travel:
A wormhole could allow time travel. This could be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around. This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry. For example, if clocks at both mouths both showed the date as 2000 before one mouth was accelerated, and after being taken on a trip at relativistic velocities the accelerated mouth was brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2005 while the stationary mouth's clock read 2010, then a traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2005, in the same region but now five years in the past. Such a configuration of wormholes would allow for a particle's world line to form a closed loop in spacetime, known as a closed timelike curve.
This would certainly violate causality, which is unacceptable. Either we live in an acausal universe, or any phenomena that might allow a violation of causality does not actually exist. Fortunately there is another possibility - that while traversable wormholes are possible, attempting to create a traversable wormhole system that would allow a closed timelike curve is not:
... some analyses using the semiclassical approach to incorporating quantum effects into general relativity indicate that a feedback loop of virtual particles would circulate through the wormhole with ever-increasing intensity, destroying it before any information could be passed through it...
In other words, if you attempt to create a wormhole system that allows the creation of a closed timelike curve, the whole thing implodes.
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Wormholes and Warpgates in Radiance
Every inhabited star system in Radiance has a warpgate. Warpgates temporarily open and stabilise a wormhole between two that star system and another, up to ten parsecs away. Evidence suggests that the warpgates were created by one of the ancient human civilisations, first in one of the central systems (Ancius, Austron, Ixion, Oreus, or Savitar), and then moving ever outwards through the galaxy at relativistic speeds. Travelling from a central star system such as Ancius to a more distant system like Njetker is not only a journey of nearly six parsecs in distance, but hundreds of years into the "future" - however long it took the ancients to transport the original apparatus form the central systems to Khnum in the first place. Travelling from Njetker to Ancius is likewise a journey backwards in time. This does not create a closed timelike curve; a traveller from Njetker to Ancius could send a message back to Njetker, but travelling at the speed of light it would still arrive years after he left. Causality is preserved.
If it became possible to create a new warpgate in the Njetker system and carry it at relativistic speeds to Ancius, this would allow a violation of causality. A traveller could leave Ancius via gate one, arrive in Njetker system in the "future", and then trabel through gate two to reach Ancius in that "future". Upon observing "future Ancius" the traveller could then retrace his journey to "present-day Ancius" and make changes that violate "future Ancius". Fortunately, as gate two is carried towards "future Ancius" the feedback loop of virtual particles between these warpgates causes one or both warpgates to implode. It simply is not possible to create a closed timelike curve-enabling system.
This is some of the theory and thought behind how interstellar travel works in Radiance. It is a lot more involved than you'll need to think about during a typical game!
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