Shiro no Konran - Castle of Confusion

...is that a multiple of it means something on its own.

This is a personal pet peeve of mine. "Ten thousand times the speed of light" means nothing unless you specifically tie it to an external frame of reference, and if that frame of reference is fixed within our Universe, you are breaking relativity just as blatantly.

An observer can move about the Universe as quickly as they like - going to Alpha Centauri and back in ~7.5 hours is not the problem.

The speed of light is the same in all frames of reference.

Alice looked round her in great surprise. 'Why, I do believe we've been under this tree the whole time! Everything's just as it was!'

'Of course it is,' said the Queen, 'what would you have it?'

'Well, in OUR country,' said Alice, still panting a little, 'you'd generally get to somewhere else--if you ran very fast for a long time, as we've been doing.'

'A slow sort of country!' said the Queen. 'Now, HERE, you see, it takes all the running YOU can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!'

- Alice and the Red Queen, Through the Looking Glass

In Newtonian mechanics, the invariant speed is infinite, rather than light's prorogation velocity. No matter how fast you fly, something moving at an infinite velocity would still be moving at an infinite velocity with respect to you. The speed of light is similar - no matter how fast you move, the a photon still moves at the speed of light.

Although 299,792,458 meters per second is not 'infinite', there are infinities associated with it. It takes an infinite amount of energy for something with mass to reach this speed, and even more to actually surpass it. Playing with this while being bound by the limits of our own Universe simply does not work.

Now is relative.

I think the best illustration of this is the Pole-Barn Paradox.

From the point of view of a farmer in the barn, there will be an instant where the pole fits entirely in the barn due to length contraction, and a gate at each end could be closed for a short time, containing the pole.

From the perspective of the runner carrying the pole, however, this is ludicrously impossible - the pole will exit the other side before he even gets to enter (assuming he's at the middle of the pole) and likewise, he will leave the barn before the back end of the pole enters. To the runner, the gate at the back of the barn closes and opens first, and the gate at the front of the barn closes and opens only after the back end has entered the barn.

The events of the gate's closing are separated in space, rather than in time. We typically present this as saying that the two events are outside of each others' light cones. The order in which they occur - B before A, A before B, or simultaneously - depends entirely on the frame of reference of the observer.

There is no definite order of events that have spacelike separation.

The image on the right is by Acdx from Wikimedia Commons - dual licensed under the GFDL and CC licenses.

As the image shows, if a single photon cannot reach any two events A, B, or C, their ordering is entirely dependent on the velocity of the observer. Distances change, apparent velocities change, the rate of time's progress changes, now changes.

You cannot pick any single observer within the Universe and declare that their perspective is the correct one. This is easiest to demonstrate by taking opposite ends of the Universe - receding from each other at greater than the speed of light, they would not agree on the proper order of many events on Earth, and as far as each other is concerned - they may as well not exist.

Different observers are going to get a different answer, when you say "ten thousand times the speed of light." It begs the immediate question of it can stack with conventional acceleration - you typically give these figures in order to place a limit of some sort - it quickly becomes meaningless. However, tying it with some in-Universe frame of reference is just as bad - and you would work just as well switching back to Galilean relativity.

What to do.

Calling superluminal motion 'difficult' does not quite express the enormity of the problem. Breaking it resembles breaking the fourth wall - in the literary sense - more than it resembles breaking the sound barrier. That is, the speed of light - the rate at which information propagates - is a fundamental property of our Universe.

That is not to say it is explicitly impossible. Merely that say, world peace and youthful immortality are easier. Much easier.

The word technobabble has a negative connotation for a reason. The more you explain, the less you leave to wonder, and the greater chance you have of tripping yourself on your own plot line. Ask yourself, when writing a story, if some phenomenon really needs to be quantized or explained.

For those whose answer is still 'yes', I plan on going over the issue in more detail later.