Paradox example

For SF games played by any normal people, the best solution is to throw out the Relativistic view of the universe. People don't understand it anyhow, and it just causes problems. An explanation like my 'sub-space currents' simulates many relativistic effects. Further, it is much closer to people's intuitive understanding, and allows for FTL without causality worries.

Now - as far as various people's explanations of why there isn't a problem... well, they're wrong.

Relativistic time dilation does not mean that time is flowing at different rates at different places. It also means more than just the slowing down of people's time as they approach c. Time 'dilation' can and does produce a reordering of events.

As a quick paradox example:

An observer on Earth sees a box disappear on Earth, and microseconds later (i.e. before a lightspeed signal could travel there) a box appears on the Moon. The Earth observer watches on a telescope, and then subtracts off the lightspeed delay to get the exact time it appeared.

Now a spaceship zooming past Earth towards the Moon views these same events. It is traveling at 0.9c, so there is considerable dilation effects between its view of things and the Earth's. It watches these two events by telescope and subtracts off the lightspeed delay. It finds that the 2nd box appeared on the Moon first, then perhaps a second later, the box disappeared on Earth.

Now, if there were FTL teleportation, this would be an instant violation of causality. The same box teleports from the Earth to the Moon. However, to the spaceship it appears on the Moon first. If the spaceship can sense that appearance by an FTL messenger, it can stop the teleportation from occuring on Earth before the box disappears. Instant time paradox.

However, if there is a lightspeed limit, then this is not a violation of causality. The appearance of the box on the Moon cannot be caused by the disappearance of the box on Earth, because it takes light at least a second to travel to the Moon. Hence - they are different boxes. If the spaceship stops the Earth box from disappearing, there is no paradox.

The basis of this is in the formula for translation between two frames. Where the new (primed/apostrophied) frame is moving at velocity v along the x-axis of the old frame:

x' = (gamma)x - v(gamma)t

y' = y

z' = z

t' = (gamma)t - (v/c2)(gamma)x

Note this last term, which means that where something is in the old frame makes a difference in when it is seen in the new.