On Mon, 18 Feb 2008 09:05:23 -0800 (PST), Crown-Horned Snorkack
<chornedsnorkack@[EMAIL PROTECTED]
> wrote:
>On 17 veebr, 22:25, thro...@[EMAIL PROTECTED]
(Wayne Throop) wrote:
>> : Crown-Horned Snorkack <chornedsnork...@[EMAIL PROTECTED]
>
>> : If you have multiple frames where FTL could occur, how do you avoid
>> : time travel?
>> Is that the goal now? Well, OK, but note that your originnal question
>> was
>> If the roundtrip time between A and B by FTL is exactly zero, and
>> signals sent A to B at FTL and back B to A arrive after a finite
>> time, how do you avoid a preferred frame?
>> which doesn't involve avoiding time travel. But if that's the goal,
>> then the usual way is some mechanism embodying the so-called
>> chronological protection conjecture.
>Ah, I see.
> Often illustrated by wormholes;
>> you can connect any two spacelike separated events with wormholes,
>> so there are "multiple frames where FTL could occur", but if you try
>> to move your wormhole ends to have a timelike separation (or indeed
>> establish any network of wormholes with a closed timelike curve), you
>> must first have a closed lightlike curve, and that would collapse your
>> wormhole network. There are reasons to suppose this would indeed
occur.
>> So. You "avoid timetravel" because if you try it, your FTL widdget
>> implodes before you accomplish it. (Note that this is not the same
issue
>> Niven raised in "theory and practice of time travel", and turned into
>> a short story, but it has much the same effect).
>So... you have a pair of wormholes whose ends have spacelike
>separation, like one end (A) at Earth and the other (B) 3 years in
>past on Alpha Centauri - getting through wormhole and back to Earth at
>lightspeed takes 1,3 years.
>Now, you have another pair of wormholes whose ends also have spacelike
>separation - like C near Earth and D 3 years in future 4,3 light years
>from Earth, but in a direction different from Alpha Centauri, such
>that B is more than 6 light years away from B.
>Now you move D. Does it mean that when D reaches 6 light years from B,
>A, B, C and D all collapse? Or just C and D?
If D actually reaches six light-years from B (and all numbers cited are
absolutely precise), then A,B,C,and D all collapse due to instantaneous,
infinite virtual-quantum-fluctuation feedback.
In practice, I suspect actual wormholes would collapse due to finite
feedback when D is 6+epsilon light-years from B. And if one wormhole
pair is more resilient to collapse than another, it could be that the
"epsilon" associated with an A-B collapse is smaller than that for a
C-D collapse, and so C and D collapse first.
Or vice versa, and this would have nothing to do with which wormhole
you think you are moving. Instead, it would be a function of things
like the wormhole throat cross-section and the ammount of excess
negative-energy bracing, and anything more than WAG handwaving is
beyond my Math-fu at the moment.
>Chronological protection conjecture does, in any case, look more
>complex that the existence of an unique preferred frame for all FTL
>travel, which would easily assure chronological protection.
Right. What you'd wind up with, is a manifold which locally divides
FTL-possible and FTL-impossible reference frames, varying in time and
space such that things like "wormhole to a point 4.3 light-years to
galactic North and 3 years into the local past" is possible in some
places and not in others.
And this manifold is purely an artifact of wormhole construction or
other FTL activity. If you're the first one on the block with a
spiffy new warp drive, you can fire it up for its first trip in any
direction at any speed you like.
Just be careful planning your return trip. And note that "first"
and "block" can be globally ambiguous, so you'll want to coordinate
with your neighbors before making any long trips. Indeed, you may
want to get together with your neighbors and hire a traffic cop to
non-destructively regulate such activity. Speeding tickets can be
unpleasant, but much less so than spontaneously-exploding star****ps.
--
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