I’m currently in the process of re-world-building the Tomorrow News Network series, and a key part of that is getting to know how science works in the T.N.N. universe (a.k.a. the chronoverse). Moving on from so-called primitive science, we now come to:
The term “light-speed engine” is something of a misnomer. Nothing with mass can travel at the speed of light, but it is possible for a spaceship to reach a significant fraction of that speed.
By the 25th Century, a trip from Earth to Mars would only take an hour or two. A trip to Neptune would take a few days, and a voyage to the nearest star (Proxima Centauri) could be done in about a decade. However, such journeys come with a cost.
The Price of General Relativity
In relativistic physics, acceleration through space is directly linked to acceleration through time. This effect, known as time dilation, was predicted by Einstein’s theory of general relativity all the way back in 1915.
Time dilation has its advantages. During long journeys, time flys by—literally! That decade-long journey to Proxima might seem like only a year or two for the crew of a time-dilated spaceship.
But the hard truth about space travel is that you can never truly come home. Brave, young travelers who venture out into deep space will likely return home, still young, to find that everyone they once knew has grown old or passed away due to old age.
For civilizations just starting to spread their wings, time dilation is a nuisance and a curse. It leads to a lot of painful goodbyes as people accelerate into the future, and it creates enormous challenges for maintaining a cohesive social order across star systems.
The Pauper’s Time Machine
However, relativistic time dilation allows for what’s sometimes called a pauper’s time machine. By pushing a light-speed drive system to its limits, wannabe time travelers can travel hundreds or thousands or even millions of years into the future.
Of course this method of time travel only allows you to travel into the future; it will not take you into the past. In that sense, the pauper’s time machine is not a true time machine.
To travel backward in time, you’d have to find a way to travel faster than light. And that’s impossible. Or is it?
In the next Science in the Chronoverse post, we’ll see how jump drives work, and we’ll find out why jump drive technology doesn’t cause time travel paradoxes.
P.S.: If this interpretation of general relativity interests you, may I suggest The Forever War by Joe Haldeman. Among other things, it’s a great story of time dilation and difficult homecomings.