From: ram@zedat.fu-berlin.de   
      
   Richard Livingston  writes:   
   >Simultaneity at a distance is not observable.   
      
     In an inertial system: Place a detector D midway between A   
     and B (using a yardstick). I assume that A, B and D are at   
     rest. Generate two signals at A and B. If they arrive at D   
     at the same time, they were sent at A and B at the same time.   
     This would be a kind of observation, albeit delayed.   
      
   >                                               In our everyday experience   
   >we actually experience the world on our past light cone and think of that   
   >as "now".  This  a misconception.   
      
     For /everyday applications/ it does /not/ seem to be   
     a misconception, and when the difference between past   
     light cone surface and "now" starts to matter, it's   
     not an "everyday experience" anymore.   
      
   >                             I suggest that the only reality is on the   
   >past light cone.  That is something that all observers can agree on.   
      
     The everyday reality consists of the things I can interact   
     with, like an automated teller machine (ATM). To get this   
     type of reality, the "now", in everyday life, needs to be   
     extended somewhat to an extended period of time like "today".   
     It cannot be only infinitesimally short, like a point of time.   
      
     This is the highest degree of reality: Something is very   
     real when one can interact with it, i.e., observe it /and/   
     affect it. Causality implies:   
      
     Systems of the past only have a semi-reality:   
     You can sometimes observe them, but not affect them.   
     For example, the Boston Tea Party. Also, systems of   
     the past are only inferred from records, so it is never   
     completely sure whether they even existed at all.   
      
     Systems of the future only have a semi-reality:   
     You can sometimes affect them, but not observe them.   
     For example, the Earth of the year 2023. Also, one   
     cannot be completely sure whether there will be such   
     an Earth.   
      
   >This is why I think it is a mistake in quantum mechanics to talk about the   
   >instantaneous collapse of the wave function CAUSED BY a measurement   
   >event.  There cannot be a consistent causal explanation directly linking   
   >two events that are outside the light cone.   
      
     When we say "nothing can travel faster than light", this is   
     actually not quite correct. An imagined point can travel faster   
     than light. If I make a spot on the surface of the moon with   
     a laser beam, the spot can move there faster than light.   
      
     It is /energy-impulse transports/, which cannot move faster   
     than light (and therefore also information transports).   
      
     The collapse of an imagined function can be imagined in an   
     inertial frame quite as "everywhere at the same time",   
     as long as no energy-impulse is transported with superluminal   
     speed by this collapse.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)