> You forgot about the time continuum difference involving the chord
> dissected by the radii of the earths surface.

FWIW - the transit time through a frictionless straight tunnel using only
gravity as the motive force is constant regardless of source and
destination. A figure of 90 minutes comes to mind but may well be wrong.

As tunnels get longer gravity component gets larger so speed increases.
eg Tunnels from London to Lands End, or Birmingham to Belfast or Peking to
Prague all have the same transit times.

May get rather hot at mid point on some longer routes.


        RM

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