[ExI] Faster than light??

scerir scerir at alice.it
Sun Sep 25 09:36:22 UTC 2011

----- Original Message ----- 
From: "Adrian Tymes" <atymes at gmail.com>
To: "ExI chat list" <extropy-chat at lists.extropy.org>
Sent: Saturday, September 24, 2011 6:41 PM
Subject: Re: [ExI] Faster than light??

> On Sat, Sep 24, 2011 at 2:28 AM, Eugen Leitl <eugen at leitl.org> wrote:
>> I'd call retrograde signalling in time (which can be
>> indefinite via a chain of routers) and causality violations
>> pretty Earth-shattering.
> I do not see why FTL automatically means time travel.
> Aside from the paper scerir posted, let's take a simple
> example:
> Points A and B are 1 kilometer apart.  They have a
> mechanism for sending, back and forth, signals in 1
> microsecond - a bit over 3 times the speed of light.
> Point A sends a FTL signal to point B.
> Point B then returns a FTL signal to point A.
> From point A's point of view, the second signal was
> received 2 microseconds after the first was sent.
> Perhaps this could allow point B to act on something
> before the physical consequences could ordinarily
> reach it.  (Say, if point A were at the epicenter of an
> earthquake, point B could be prepared for it.  Indeed,
> because earthquakes propagate much more slowly
> than light over fiber optics, this effect - without FTL -
> is being investigated as part of an earthquake warning
> system in California.)
> The only "time travel" comes about if one believes
> that time and causality propagate at the speed of
> light.  If, instead, one believes that all points in the
> universe have their own time, which may pass at
> different rates (thanks to relativity) but each point's
> rate is consistent with itself, then there is no time
> travel.
> Though, even if this did allow for information to be
> sent to the past, it appears that you'd need
> specialized equipment for those relays.  Not all of
> said equipment has been constructed yet, and what
> there is, is not set up in a relay.  Therefore, no
> information can travel from the future into today.
> The earliest point in history that information could
> time travel to, is when said equipment first becomes
> operational.  There would likely also be bandwidth
> limitations; at any point where those are used up,
> that point in history becomes inaccessible to further
> future information, and likely all points before it too.
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