# RE: starship-design: More Fun with Spacetime

```Ken,

Thanks for trying...<G> but I still don't get it! My problem is identical to contemporary physicists when Michaelson and Morley proved that the speed of light was the same in ALL inertial frames - "that's impossible".

Oh, I follow the math alright, its just the concept which gets me. I have to believe that we are formulating our hypothesis incorrectly or something, that it is a semantic error not a mathematical one. The mathematical equivalent of what is being said here semantically is that 1+1= -(3)!

Something else that I have a problem with was the statement:
>Now, despite all the other problems that come along with this (infinite
>energy, which way is she really going, etc.)  This can lead to a causality
>problem if you have a young man named Dwight travelling back to Earth.  If
>you can travel backwards in time in one reference frame, given the
>priniciple that all reference frames are equivalent, you can also travel
>backwards in time in Earth's reference frame.

I hope what you mean by this is that you can seem to travel backwards in time from an observer in Earth's reference frame, not that you do this in one frame, that in another and that they are both the same despite the fact that they patently are not! Apples are NOT oranges I don't care who says their frames of reference are the same!

Timothy (in a later post) is apparently of like mind. I get the math but I don't like what it is telling me.

Lee,

>Okay here is where you lost me. WHY did you change frames of reference?

I needed to prove that Adding a normal sub-light vector (Dwight's wrong-way
trip) with two identical FTL vectors (Bright and Dwight's FTL trip) can
wind you up with a net spatial movement of zero, and a net time movement
back in time.  This can also be done without the extra sub-light vector,
but then the two FTL vectors will be different, and the one that takes you
"back in time" will of course seem counter-intuitive.  If I tried to go
that route, you would say that only one "type" of FTL travel was possible,
when in fact the two journeys were identical from different frames.

[L. Parker]
what I want to see is a time travel paradox using only one frame of reference, It doesn't really matter whether you use FTL or not that just makes it easier to cause the paradox from my understanding. I want to see that it is not a matter of "substitution error" caused by the change of frame, because I am not so sure that all frames are or must be equal.

In order to spell this out more clearly, I only used one "type" of FTL
journey -- 500c from the current frame of the ship.  In both of the FTL
legs, from Dwight's perspective, the time at Earth advances in a positive
direction.  This way you can't say that the FTL is taking Dwight back in
time and disallow it on those grounds alone.  The back-in-time leg was the
sub-light journey that Dwight starts out with!

[L. Parker]  Woa! How does this sub-light leg end up having a negative time component? I can see how it might APPEAR to, but it isn't really negative.

His journey away from Earth
at 0.4c is the only vector in which time seems to "go backwards" at Earth.

But combined with FTL, this strange but well-established aspect of time --
where a far away event can seem to go backwards in time as you accelerate
away from it -- can turn itself into a paradox.  With FTL you CAN create a
net-negative time travel vector.

[L. Parker]
Experimental test: Suppossedly, physicists have used the Casimir Effect to reduce the vacuum energy sufficiently between to grounded superconductiing plates to transmit a photon through the space between them. very slightly faster, some number times 10 ^-27. The point is IF FTL produces time travel it should be possible to construct this experiment in such a way to measure it.

Any set of events must be explainable in ANY set of frames.  That's the
fundamental principle of relativity.  If the same thing looks different in
two different frames then there's a logical error involved.

[L. Parker]  I guess that is my fundamental objection, and I know it was Einstein's basic insight. However, I just don't believe (quite) this frames business. I sent Steve a quote a few days ago from Einstein complaining about Quantum Theory (it just didn't make sense to him), I feel the same way about some parts of relativity.

Hope that was more illuminating than confusing!

Ken

[L. Parker]  If we have flashlights, why don't we have flashdarks? (Hint, according to relativity we do.)

Lee Parker

```