[ExI] Time Travel Reconsidered

[Adrian Tymes]

On Tue, Nov 3, 2026, 7:33 PM BillK via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

> I gave your comment to Qwen AI and asked for an explanation.
> The answer was complicated, as time travel usually gets weird!
>

And that analysis missed the objection.

If a CTC exists, the geometry of the universe allows a continuous,
> forward-moving path (a timelike curve) that eventually loops back to that
> exact 4D coordinate.
>

The objection does not discuss returning to the exact same 4D coordinate.

4. Correcting the "Beside Yourself" Misconception
> You mentioned: *"You instead wind up at some other spatial coordinate at
> the exact same time."*
> This is where the translation from math to English gets tricky. The null
> coordinate u is not "time" in the traditional sense; it is a mixture of
> space and time (a light wave).
> If you travel on a path where u increases, but you somehow magically
> managed to return to your starting spatial coordinates (x,y,z), you would
> *not* be at the "same time." Because your u coordinate has increased
> (say, from 5 to 8), you are now intersecting a completely different light
> wave. In the geometry of that universe, you have arrived in the *future*.
> To arrive in the *past* (to form a CTC), you would have to travel
> backward through the light waves (from u=8 back down to u=5). But the
> "three lines of math" prove that the geometry of the universe physically
> forbids a massive object from moving backward through a light wave.
>

The form of time travel in the objection is not returning to the same
(u,x,y,z).  It is returning to the same u at some other (x,y,z).

>
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