[TML] White Dwarfs, Black Holes & 100 Diameters

[Jerry W Barrington]

On 11/7/07 1:44 AM, Timothy Little wrote:

> On Tue, Nov 06, 2007 at 03:07:14AM -0500, Jerry W Barrington wrote:
>> 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.
> 
> From quantum mechanics, there are good reasons to suspect that any
> near approach to forming a closed timelike curve would repel the
> formation of that CTC via ...

See below: no CTC is involved.

Of course, I assume "near" means microscopic scale, as usual in QM.

>> 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.
> 
> This is a pretty simple example of a closed timelike curve.  Normal
> flat spacetime with just topological boundary conditions.

Same.

>> No sensible way of defining time travel can prevent this.
> 
> Do you consider the predictions of QM sensible?  ...

<http://en.wikipedia.org/wiki/Closed_timelike_curve>:
"In a Lorentzian manifold, a closed timelike curve (CTC) is a worldline of a
material particle in spacetime that is "closed," returning to its starting
point."

Everything I've seen provides essentially the same definition.

My example did *not* actually produce a CTC.  Yes, in theory it *could*.
Just because you get to your past doesn't mean you try to intersect
yourself.  In any case a true CTC is prevented simply by the fact that once
a particle starts to approach it's prior position, it will be repelled by
the same forces that would normally repel it from a similar particle (like
the Pauli exclusion principle, or simple collision for large scale objects).

What I said was the FTL implies time travel, and that you can't define time
travel in a way that keeps you out of your own past or from changing your
past.  Leonard and I agreed that FTL *is* time travel.  The issue was that
is you *can* TT, nothing prevents you from *affecting* your past.

If I travel into my own past and send myself a message, that changes my past
(I now know the contents of that message), but I don't intersect myself, so
it's not a CTC.



On 11/7/07 1:12 PM, Leonard Erickson wrote:

> No, quantum interactions are such that either you *can't* make the
> trip, or you can only do so in a manner that leaves the past
> "intact".
> 
> Find the list of papers and maybe you are up to the math...

I'm really good at math, but I know my limits.  :P

The thing is that QM and relativity have never been fully reconciled.  So
honestly, all bets are off.

I tend towards Niven's proposal: If time travel exists in a form that allows
changing the past, then the past will be changed repeatedly until a future
is arrived at in which time travel (while theoretically possible) never
actually occurs.