G'morning David, 

 -> But that would mean you'd be a `ghost' at the party surrounding
 -> you, unable to actually interact with events or actors - or to
 -> change the course of the plot...

 DW> I'm not sure that I agree that I wouldn't be able to 
interact. Even if I travelled into the past (though no further 
than the invention of the camera/display/transporter, since 
there'd have to be one there too), there is not necessarily a 
logical conflict involved in my interacting with things.

Err ... I could accept the building of a viewing apparatus that 
then occupied a finite amount of space in the future - but to 
avoid changing any `present' it would need to seem totally light 
and sound absorbent to outside observers.

And that precludes interaction from within it, `cos for `now' to 
stay unchanged nothing could emanate from it - not even one pesky 
photon. 

DW> Causality can be like a step-ladder, with each part supporting 
the other. What I did back then would affect things now, and this 
might affect what I'd decide to do back then. But so what? 
Obviously, I couldn't destroy the world back then, since there 
would be no now, so, since there is a now, something must happen 
to stop me from  doing it.

The simplest explanation being that nobody ever made the trip ?

The nearest you'd get lies in wiring the present with a network of 
sensors which feed a huge databank that can be quizzed at any time 
in the future.

This you might do in 3D, walking through the recorded image ... 
but you'd still be a ghost at the party...

:-)
 
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