Quote:
Originally Posted by socratus  =============
It was time when idea of vacuum was clear to everybody
because if the planets travel without friction in it,
it means the vacuum is an empty space.
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Sorry that it seems too haste to conclude that
planets travel without friction in vacuum. Actually, the rotation of the Earth seems slowing down - perhaps due to tidal forces, gravity pulls, meteor bombardments, mass increment and the likes. But we cannot exclude the possible presence of tiny viscosity (if in fluid/continuum) or what you called friction (interacts between interfaces of solids). Viscosity, if any, should be in the scale of Planck constant. So, really too difficult to be detected.
Best Regards. Bottomlander