(urth) relative time travel

[Gerry Quinn]

From: "Jeff Wilson" <jwilson at io.com>
> 1. Each day, a train 600,000 km long (two light seconds) traveling north
> at 90% light speed pulls through a station 600,000 long without slowing.

I'm not sure your figures are right here...

If these are the lengths observed by the native (as it appears), then the 
rest length of the train is more like 1,400,000 km.  The mail agents will 
take this into account when discussing who acted first.  In their frame of 
reference the station is only 250,000 km long.  Logic will force them to 
conclude that the pickup happened first.

Let's assume that they are going at only 86.7 % of c, so the time dilation 
factor is only 2.  The train is 4 light seconds long.  The station is 2 
light seconds long, but they will observe it to have contracted to 1 light 
second long.  So they will expect that the pickup will happen about 3 
seconds before the drop off (a little more in fact as they are going at less 
than light speed, say 3.5 seconds).

> 6. The mail agent at the front of the train sees the pickup happen, then
> drop-off happen much later.

He sees the drop-off happen 7.5 seconds after he does the pickup.

> 7.The mail agent at the rear of the train sees the drop-off happen, then
> the pick-up happen a short time later.

He sees the pickup happen 0.5 seconds after he does the drop-off.


> 11 The next day, the oppressed native calls on some pagan OT being for the 
> power to travel instantaneously, and synchronizes his watch with the
> station clock, after accounting for the time for light to travel to his
> position.
>
> 13. From his distant position, at 12:00:00, he travels instantly to the
> mail car at the front of the train and attacks the mail agent, felling him 
> instantly. He then looks toward the rear of the train, and sees the other 
> mail agent busy and distracted with the business of getting his mail bag 
> ready to be snagged by a hook at the "next" station.

Okay.  If he simply waited 7.5 seconds he would see the drop-off, but he 
doesn't have time.  He briefly glances out the window and sees that the 
station clock reads 11:59:59 (it's a light second further away compared to 
his starting point), then he waits 0.2 seconds.  He observes that the clock 
now reads 11:59:59.01 (he has travelled 0.18 light seconds further from the 
clock, and it is also running slowly in his frame of reference).

> 14. The oppressed native instantly travels to the rear of the train, and 
> even allowing for a couple of seconds of light lag, as he arrives, he sees 
> the second mail agent is still getting his bag ready. The oppressed native 
> attacks and kills him, too.

Okay.  While he waited 0.2 seconds at the front watching the clock, the 
train travelled 0.18 of a light second forward in the reference frame of the 
station.  So from here the clock reads 11:59.59.19.

> 15. The victorious native exults for a while but then, fearing the train 
> may stop at this "next" station, travels instantly back to his original 
> obersvation position.
>
> 16. He arrives, unnoticed by "another" oppressed native who is intent on a 
> wristwatch and subsequently disappears in a puff of Molochian prayer.
>
> 17. Puzzled but not knowing how to investigate the "other" native's 
> appearance, the native enjoys a victory beverage while waiting for the 
> light of his triumph to arrive. He does a spittake when he sees himself 
> attack the rear-end mail agent *before* the train reaches *this* station, 
> and then *later* sees the front-end agent slain just as the front of the 
> train emerges - in the reverse order of how he recalls the events.

He's not all that surprised.  He knows that the point where he killed the 
rear agent was 0.18 light seconds closer to him, so naturally he will see 
that happen first.  He killed the agents at 12:00:00 and 12:00.00.1 
respectively, so the light from the second killing arrives 0.08 seconds 
before that from the first.

- Gerry Quinn