From: gerry@bindweed.com   
      
   In article , poutnik@privacy.net says...   
   >   
   > Dne 23/09/2017 v 07:10 Gerry Quinn napsal(a):   
   > > In article , poutnik@privacy.net says...   
   > >>   
   > >>>   
   > >> It can be otherwise.   
   > >>   
   > >> IF Einstein used space and time the same way as Newton,   
   > >> Newton would be right and Einstein wrong.   
   > >>   
   > >> IF Newton used space and time the same way as Einstein,   
   > >> Newton would be wrong and Einstein right.   
   > >>   
   > >> But as both used space and time differently,   
   > >> both are right within definitions and assumptions of their theories.   
   > >   
   > >   
   > > This is it, essentially.  There are some differences in the theories   
   > > themselves, i.e. the exact predictions of gravitational effects   
   > > (famously, the precession of the perihelion of Mercury is in accordance   
   > > with Einstein's rather than Newton's theory) - but in principle it's   
   > > possible to describe an identical theory in either a geometric or a   
   > > force-based model.   
   >   
   > I would not be so sure,   
   > if force model could properly describe all GR effects,   
   > like e.g. gravitational time dilation,   
   > or all consequencies of space-time curvature.   
      
   I'm thinking of an effective field theory based on a spin-2 graviton.   
   Obviously a simple scalar force doesn't work.   
      
   In extreme cases it does get a bit problematic, i.e. where general   
   relativity predicts a non-simple topology, at and inside the   
   Schwarzschild radius of a black hole.  (That's why I've always been   
   certain that general relativity breaks down at the Schwarzschild radius;   
   a belief that is no longer considered particularly eccentric these days   
   I think.)   
      
   But under less extreme conditions, such a theory can be equivalent to   
   general relativity to any practical degree of measurement (unless you   
   count evaporation of a small black hole into Hawking radiation, which is   
   not yet observed but should indeed be observable assuming it happens and   
   we find or make such a black hole.)   
      
   Think of graviton interactions as effectively slowing down photons (as   
   well as other massless fundamental particles such as gravitons   
   themselves.)  Geometry is defined either against an agreed background   
   (force theory) or in terms of the world-lines of light rays   
   (relativity).  When photons are slowed, light rays slow and bend (with   
   respect to the background) and in relativistic terms this is described   
   instead as a change in geometry.   
      
   [Matter can just be thought of as congealed energy, i.e. collections of   
   interacting massless particles, so nothing extra needs to be considered   
   to allow for it.]   
      
   - Gerry Quinn   
      
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