Subject: (urth) relative time travel

From: Jeff Wilson <jwilson at io.com>
Date: Sat, 14 May 2011 05:33:42 +0000

Let me try the train analogy. I'll number the steps for reference. You 
guys that already know this will see that I have abstracted numerous 
distracting features out of this account.

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.

2. This is being observed by an oppressed native from a very large
distance off to one side. One day he notices the train has two new mail 
agents stationed at each end.

2. A hook at the head of the train picks up a bag of outgoing mail from
the station. At the same time, the native observes a bag of incoming mail
being picked off by a hook at the entrance of the station platform, and
the station clock calls it 12:00:00 .

4. The native observes the light of the pick-up event travel from the
front of the train toward the back of the train; they meet just a bit
south of the middle of the platform just a bit over a second later. The
station clock reads 12:00:01.

5. Later, the native observes the light from the drop=off event at the
back reach the front of the train far north of the station. The station
clock reads 12:00:20.

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

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

8. The rookie mail agents meet for lunch in the dining car in the middle 
of the train and compare notes of their first day on the high-speed 
train. At first, each one thinks their mail transfer happened first, but...

9. ...allowing for the light-lag, the agent at the read admits the one 
at the front must have happened about a second earlier than his so it's 
light could travel for two seconds and arrive a second afterward.

10. The agent at the front insists that it his transfer must have been 
more like 18 seconds ahead, because he saw the other transfer 20 seconds 
later, and the length of the train only accounts for two seconds.

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.

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.

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.

More clear?

-- 
Jeff Wilson - jwilson at io.com
Computational Intelligence Laboratory - Texas A&M Texarkana
< http://www.tamut.edu/CIL >

---

From: Gerry Quinn <gerryq at indigo.ie>
Date: Sat, 14 May 2011 15:08:06 +0000

From: "Jeff Wilson" <jwilson at io.com>
> 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).

> drop-off happen much later.

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

> 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
> 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).

> 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.

> 16. He arrives, unnoticed by "another" oppressed native who is intent on a 
> wristwatch and subsequently disappears in a puff of Molochian prayer.
>
> 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

---

From: Jeff Wilson <jwilson at io.com>
Date: Sat, 14 May 2011 21:22:49 +0000

On 5/14/2011 10:08 AM, Gerry Quinn wrote:
> 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.

ahem. "You guys that already know this will see that I have abstracted 
numerous distracting features out of this account."

This example is adapted from Richard Morris' TIME'S ARROWS

http://www.amazon.com/Times-Arrows-Scientific-Attitudes-Toward/dp/0671617664/ref=sr_1_1?s=books&ie=UTF8&qid=1305407823&sr=1-1#reader_0671617664

you can search for "lightning" to find his version that dodges length 
contraction by having no background and no definite dimensions.  I tried 
to include some of these to give the less accustomed posters fewer 
indefinite things to envision at once.

---

From: Gerry Quinn <gerryq at indigo.ie>
Date: Sat, 14 May 2011 23:08:05 +0000

> indefinite things to envision at once.

I can search but it doesn't show me the pages.  That's beside the point, 
though. Weren't you trying to show that travel via a wormhole is time 
travel?  I don't think your illustration shows that.  In particular, you 
say:

"16. He arrives, unnoticed by "another" oppressed native who is intent on
a wristwatch and subsequently disappears in a puff of Molochian prayer."

Nope.   He arrives after he left - in my example, 0.4 seconds after he left. 
He doesn't ever meet himself.

To get time travel from instantaneous movement, you need a more complicated 
situation AND certain assumptions involving the reification of some concepts 
from special relativity, which are not provable in our universe, and which 
would certainly be false in a universe in which instantaneous travel was 
possible.

- Gerry Quinn
.

---

From: Jeff Wilson <jwilson at io.com>
Date: Sun, 15 May 2011 01:09:43 +0000

On 5/14/2011 6:08 PM, Gerry Quinn wrote:
> travel?

The wormhole example is much simpler. The negative curvature makes a 
bridge between two portions of space-time, and time progresses 
identically as measured through the wormhole. Their subjective timelines 
remain connected one-for-one despite their relation to the objective, 
external universe's timeline.

So if the traveling terminus is accelerated such that it experiences a 
one year trip while observers see it gone for two years, today's 
traveling terminus is linked to the stationary terminus of a year ago, 
since it has also experienced a year  apart.