[ExI] Pesky Neutrinos

[Adrian Tymes]

2011/11/1 john clark <jonkc at bellsouth.net>

> --- On *Mon, 10/31/11, Adrian Tymes <atymes at gmail.com>* wrote:
> "Say you have 2 points, A and B.  Both start off at time T, according to
> their local clocks (previously synchronized to some third source"
>
> But if they are moving relative to each other the clocks will not remain
> synchronized, each will see the others clock as running slow; this has
> nothing to do wit theory, its a experimental fact that has been observed
> many times in the lab and so will remain true even if Einstein is wrong.


Sorry, I thought it was implied: A and B, themselves, are not moving
relative to one another.  The only thing that moves relative to them, that
we're concerned about for this example, is signals between them.


> "Someone at A asks a question at time T.  The question contains a
> representation of T, so others can know when - according to their own
> clocks - it was asked."
>
> But the "T" at point A and the "T" at point B are NOT the same.


Actually, they are.  That's the whole point of synchronizing to some third
source: A and B have a guarantee that, at any given moment, whatever time A
thinks it is (say, however many seconds since some event) is the same time
B thinks it is.  So long as they remain motionless with respect to one
another, of course.


> "The question is transmitted by some means - FTL or not - and arrives at
> point B at time T+X as measured by B's clock, X being the transit time."
>
> So when A sends the question the fellow at point A looks at his clock and
> is says 3PM, and through a telescope he looks at the clock at point B and
> it says 2PM.
>
>
> "Someone at point B transmits a reply"
>
> So when he sends his answer the fellow at point B looks at his clock and
> is says 2PM and through a telescope he looks at the clock at point A and it
> says 1PM.


Sure, if they're a light-hour apart.


>  "It arrives at point A at time T+X+Y as measured by A's clock."
>
> Your notation is all screwed up, you're using the same symbol "T" for A's
> clock as observed by A and A's clock as observer by B and B's clock as
> observed by B and B's clock as observed by A, and that just won't work
> because they are all different.


No, it's for A's as observed by A and B's as observed by B.  It is not for
A's as observed by B nor B's as observed by A.

The reply arrives at A at 1PM on A's clock plus the time it takes to make a
> round trip between A and B. Nature always arranges things so that if the
> message speed is limited by the speed of light you will never get a answer
> before you ask a question, so in this example the round trip message time
> would be 2 hours or more so the answer to your question would always arrive
> after 3PM, the time according to your clock you asked the question. But if
> your message can move faster than light you could get the answer before
> 3PM, and that would be very odd indeed.
>

Let us say B got the question at 1:30 PM by B's clock, and A got the answer
at 2 PM by A's clock.

Faster than light, yes.  B would not observe - via light - A sending the
question until 2 PM, long after B has received and replied to it via some
non-light means.

Time travel, no.  1:30 PM is after 1 PM, and 2 PM is after both 1:30 PM and
(most importantly) 1 PM.

That is the essence of my question: why does FTL imply time travel?  Yes,
different amounts of time may pass for the traveler than for people at the
source & destination, but by the context that matters - time for the people
who are not traveling FTL, even if they are interacting with people or
things that are - effects do not happen before their causes.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.extropy.org/pipermail/extropy-chat/attachments/20111101/7497fa7e/attachment.html>