XPost: sci.math   
   From: relativity@paulba.no   
      
   Den 11.11.2025 08:34, skrev Thomas Heger:   
   > Am Montag000010, 10.11.2025 um 18:36 schrieb Tyler Bukoski:   
   >>   
   >> there is no force arting in freefall,   
   >   
   > Well, that depends on the definition of 'force'.   
      
   A force is what makes a mass m accelerate at a. F = ma   
      
   Consider the following scenario:   
   You are inside a small capsule somewhere in space.   
   You are weightless. You can't feel any force acting on you.   
      
   Can you tell if you are 10 million light years from the nearest   
   galaxy, or if you are in orbit around the Earth?   
      
   In the latter case, according to Newtonian Mechanics (NM),   
   a gravitational force will be acting on you.   
   Why don't you feel it?   
      
   >   
   > Usually gravity is considered to be a force, which accelerates objects,   
   > once they are allowed to fall.   
      
   In NM.   
      
   > This force reaches out from planet Earth with invisible hands and pulls   
   > down falling objects with a certain force.   
      
   Quite.   
   Instant action at a distance.   
      
   >   
   > That is certainly not a valid description of what is really happening in   
   > gravity.   
      
   No theory of physics can "describe what's really happening".   
   A theory of physics is a mathematical model of some aspects   
   of nature. The best it can do is to give correct predictions   
   of what will be measured or observed in some experiments.   
      
   >   
   > Unfortunately nobody has a better one.   
   >   
   You can't be ignorant of the fact that 'The General Theory of   
   Physics' (GR) is a much better model of gravitation that NM.   
      
   What forces are acting on you right now?   
   It is the force acting upwards on your butt.   
   You can feel it.   
   It is accelerating you upwards at 9.81 m/s² !   
      
   In GR 'proper acceleration' is what is measured with   
   an accelerometer.   
   An accelerometer measures the force F that is exerted on   
   a known mass m in the accelerometer. The acceleration is   
   a = F/m.   
      
   Now you take your accelerometer and enter the capsule.   
   The mass of the capsule with you in it is M.   
   But this time the capsule is accelerated by a rocket with   
   a force F so that F/M = 9.81 m/s².   
      
   Your accelerometer shows that your acceleration is 9.81 m/s².   
      
   Can you tell if you are stationary (relative to ground)   
   one meter above the ground, or are accelerating somewhere   
   out in space?   
      
      
   In GR, there is no gravitational force.   
   Gravitation is the curvature of spacetime.   
   Mass curve spacetime.   
   There is no 'action at the distance'.   
      
   The mass of the Earth curves spacetime, and satellites   
   do what the local curvature tell them to do.   
      
   Changes in masses (like orbiting Moon) will change the curvature   
   with the speed of light. No instant action at a distance.   
      
   --   
   Paul   
      
   https://paulba.no/   
      
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