[TML] White Dwarfs, Black Holes & 100 Diameters

[Jerry W Barrington]

On 11/5/07 6:46 PM, Garry Ward wrote:

> No, jump to another system, even if you then jump back, you will arrive a
> bit (perhaps nano seconds) later, not earlier.
> 
> Yeah, I've seen some of those spacetime charts and how they prove you can't
> get there from here in less than decades.
> 
> They remind me of the graphics the ancient greek mathematicians used to
> prove that the distance between you and any object could always be cut in
> half, so you really, really couldn not pick up that cup and the arrow would
> never, ever reach you.
> 
> Escher also was able to draw some interesting things.
> 
> Jump may reposition you in relationship to specific other objects in the
> universe, but to go back in time, you have to reposition all the other
> objects in the universe so they are back into the relationship they were in
> at that pont in time.

I'm not trying to be unpleasant here, but do you have *any* understanding of
relativity at all?  Time is *not* absolute.  The universe doesn't have to be
rearranged for time travel: everything is already there *in the past*.

Your denigration of spacetime diagrams seems to indicate that you don't
really believe relativity, means anything.  You seem to think it's just a
toy for philosopher-scientists to play around with and impress the plebes.

For that matter, I don't recall any ancient diagrams of Zeno's Paradox,
those were drawn recently to illustrate it.



On 11/5/07 6:46 PM, Jeff Zeitlin wrote:

> My problem with the entire relativity-causality-ftl problem has been
> that C, the speed of light in vacuum, has been treated as privileged,
> without an adequate explanation as to WHY.  If (assume FTL) I can
> achieve effective speeds greater than C, why am I doing my observations
> with plain old C-capped methods?  I'll get my information on the state
> of the universe via the same FTL method, and if I do, all of the
> paradoxes appear to fall away.

No, the paradoxes remain.  They aren't determined simply by observation
method.  The way the math works, is you can *actually* travel, thru space,
at FTL, then you can as easily travel into the past.

It doesn't matter if anybody can explain *why* c is an important speed.  It
has been experimentally show that it *is*.  The math follows from that.

Now, Jump, folding space, etc, get around it by not traveling *thru* space,
but they still bump into some of the same issues.



On 11/5/07 6:46 PM, Anthony Jackson wrote:

> Um. Not totally. There is nothing preventing you from measuring the
> average speed of a system and declaring that to be a speed of 0. It
> won't have any special effects within relativity, but it's reasonably
> well defined.

But it's equally well defined to assign that average to the speed of 5 or
-1,000,000,000.  And you have no valid way of choosing one and saying it is
the "right" reference frame, because the physics formulae are supposed to
work in *all* of them.



On 11/5/07 6:46 PM, Leonard Erickson wrote:

> Do note that it *is* possible to have FTL and relativity and retain
> causality. But only *global* casuality. That is, effects will still
> have causes, but for some observers the effect will precede the
> cause.
> 
> This places strict limits on FTL/time travel (the two are the same
> thing under relativity).
> 
> either you won't be able to get into your past (but the past of
> others you don't know about is fair game!) or you will not be able to
> cause any effects that would change your past as you know it.

There's nothing in the formulae to prevent people going into "their own"
past, nor of changing the past.  All those ideas that say you couldn't do
those things are just wishful ways of avoiding the paradoxes.

Suppose you are at Earth, time=0.  You travel to 1.1 ly away, 1 year into
the past.  Your rule allows that, as it is outside your past lightcone.  Now
you take another trip, going back 1.1 ly to Earth again, and another year
into the past.  This is still valid, as it is outside the past lightcone of
*that* point.  But now you are at Earth, 2 years before you started.  No
sensible way of defining time travel can prevent this.

Once you are there, nothing in the formulae *forces* you to take actions
consistent with what "should" be the past.  If nothing else, the butterfly
effect insures that things *will* be different, just because you exist
there.

Time travel is best avoided altogether.  :)