From: tjroberts137@sbcglobal.net   
      
   On 7/14/19 7:56 PM, Nicolaas Vroom wrote:   
   > IMO the most important question to answer is: what is the physical   
   > explanation of length contraction.   
      
   This is really geometrical: both "length contraction" [#] and "time   
   dilation" [#] are simple geometrical projections. No physical properties   
   of anything are changed, but when you measure such properties from   
   frames relative to which an object is moving, you get values different   
   from when it is at rest.   
      
   	Think about it: it must be possible for multiple observers   
   	in multiple frames to observe a given object, and they all   
   	get different values. Geometrical projections do just that,   
   	but ask yourself how any "physical change" of the object   
   	could do it....   
      
   Analogy:   
   Lay down Cartesian coordinates (x,y) on a Euclidean plane, and draw a   
   line segment of unit length angled at 45 degrees to them. Project its   
   endpoints onto the x axis and obtain a "length along the x axis" of   
   0.707; project its endpoints onto the y axis and obtain a "length along   
   the y axis" of 0.707. Clearly if you vary the angle of the line, its   
   length never varies, but its projections onto x and y do vary.   
      
   These projections are directly analogous to "length contraction" and   
   "time dilation", with the line's angle analogous to relative velocity of   
   inertial frames, except the y axis is the time axis, and the geometry is   
   hyperbolic (not Euclidean).   
      
   	[#] I put them in "scare quotes" because these are not very   
   	good names -- they imply a length actually contracts (none   
   	does) and time actually dilates (it doesn't). But they are   
   	solidly established historically.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)