# Re: Block Universes

`On Tue, Mar 4, 2014 at 5:45 PM, Jesse Mazer <laserma...@gmail.com> wrote:`
```
>
>
> I promise you the example has nothing to do with any frames other than the
> ones in which each pair is at rest. Again, the only assumptions about
> p-time that I make in deriving the contradiction are:
>
> ASSUMPTION 1. If two observers are at rest in the same inertial frame,
> then events on their worldlines that are simultaneous in their rest frame
> are also simultaneous in p-time
>
> ASSUMPTION 2. If two observers cross paths at a single point in spacetime
> P, and observer #1's proper time at P is T1 while observer #2's proper time
> at P is T2, then the event of observer #1's clock showing T1 is
> simultaneous in p-time with the event of observer #2's clock showing T2.
>
> ASSUMPTION 3. p-time simultaneity is transitive
>
> That's it! I make no other assumptions about p-time simultaneity. But if
> you want to actually see how the contradiction is derived, there's really
> no shortcut besides looking at the math. If you are willing to do that, can
> what I asked again, with a few cosmetic modifications:
>
> Please have another look at the specific numbers I gave for x(t),
> coordinate position as a function of coordinate time, and T(t), proper time
> as a function of coordinate time, for each observer (expressed using the
> inertial frame where A and B are at rest, and C and D are moving at 0.8c),
> and then tell me if you agree or disagree with the following two statements:
>
> For A: x(t) = 25, T(t) = t
> For B: x(t) = 0, T(t) = t
> For C: x(t) = 0.8c * t, T(t) = 0.6*t
> For D: x(t) = [0.8c * t] + 9, T(t) = 0.6*t - 12
>
> --given the x(t) functions for B and C, we can see that they both pass
> through the point in spacetime with coordinates x=0, t=0. Given their T(t)
> functions, we can see that B has a proper time T=0 at those coordinates,
> and C also has a proper time T=0 at those coordinates. Therefore, by
> ASSUMPTION 1 above, the event of B's proper time clock reading T=0 is
> simultaneous in p-time with the event of C's proper time clock reading T=0.
> Agree or disagree?
>
> --given the x(t) functions for A and D, we can see that they both pass
> through the point in spacetime with coordinates x=25, t=20. Given their
> T(t) functions, we can see that A has a proper time T=20 at those
> coordinates, and D has a proper time T=0 at those coordinates. Therefore,
> by ASSUMPTION 1 above, the event of A's proper time clock reading T=20 is
> simultaneous in p-time with the event of D's proper time clock reading T=0.
> Agree or disagree?
>

Another little correction--in the last two paragraphs there, where I said
"Therefore, by ASSUMPTION 1 above", I should have written "ASSUMPTION 2",
since in both cases I was deriving p-time simultaneity from the fact that
two clock readings happened at the same point in spacetime.

Jesse

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