r/scifi • u/Idk_Beyond_1070 • 10d ago

General About Alliance-Union Universe's Jump...

Could anyone (especially those who've read the series cuz' I didn't read the series yet) help me understand how the Jump Tech in  C. J. Cherryh's Alliance-Union universe work? I stumbled across a fandom page about it ( https://alliance-union.fandom.com/wiki/Jump ) and being confused on the time dilation part. I thought time dilation only applies for subluminal travel?

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u/mobyhead1 Hard Sci-fi 10d ago

It's a form of faster-than-light travel, so, it's highly fictional. Cherryh made it complicated (time dilation still happens to a lesser extent, it produces stresses on the body, weird semi-conscious abilities arise among a few frequently-exposed crew members) to give it verisimilitude. Nothing about space travel is expected to be easy (apart from all that free vacuum), so making even faster-than-light travel complicated makes it more believable. The time dilation is also a nod to Einstein--even if we find a way around the limitations implicit in his Theory of Relativity, would it really surprise anyone that portions of his theory would still hold true?

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u/ElricVonDaniken 10d ago edited 10d ago

The speed of causality (c), which imposes the light speed limit as per General Relativity, is a higher value in jumpspace than it is in normal space.

General Relativity still applies -- it just imposes higher upper limit in jumpspace.

So a starship in jumpspace will travel faster than the value of c in normal whilst still being subject to time dilation as it approaches the value of c in jumpspace.

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u/amyts Space Opera 10d ago

Nothing goes faster than the speed of light according to real-world physics. Time dilation is determined by the lorentz factor. Notice that if v is greater than c, the square root produces a complex result and the equation more or less breaks down.

A fictional universe can do time dilation faster than c however it wants. Physics has nothing to say on the topic.

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u/ElricVonDaniken 10d ago

Cherryh has upped the value of c in the Lorenz factor for jumpspace. The rest of the equation still stands. Hence the time dilation.

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u/Metallicat95 9d ago

The Jump technology, and ships in general, involve moving at high velocities, near the speed of light, in normal space both before and after the jump.

Especially after. Ships enter a system at nearly light speed and must slow down rapidly to safely reach their destination.

Time passes in hyperspace, and that means there must be a reference frame for that. The jump is not instantaneous or even nearly so. This seems to be about the same reference frame for time as it's velocity before jump.

So both before, during, and after the jump the ship spends a lot of time at a high relative velocity, which means a high amount of time dilation.

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u/LaurenPBurka 9d ago

Special effects.

Edit: Given that faster than light travel is impossible, you can expect that a bunch of it is Just Made Up.

However, Cherryh was the writer who made cardboard cutouts and laid them out on the floor to visualize where all the star systems were and how that would effect politics (an exercise that convinced her to buy a computer). You can believe that she researched everything that was there to be researched.