### Mach's principle

(the notion that rotation is relative to all the mass of the universe)

**Mach's principle** is a term (coined by Albert Einstein) for the
proposition (pondered by Ernst Mach) that the observed effects of
rotation are due to all the surrounding mass of the universe.
Relativity implies that if the rest of the universe weren't
there, an object's velocity would be moot, and Mach's principle
extends that notion to the object's rotation. The effects of
rotation, i.e., centrifugal force, are due to acceleration, which
according to general relativity (GR) is identical with gravitation, and Mach's
principle is sometimes cited in terms of acceleration and/or gravity
rather than rotation.

In fact, in Einstein's development of GR, he searched for an equation
that converges with the then-existing laws of mechanics and is also
consistent with Mach's principle, but the equation he found that
satisfies the former is not consistent with the latter.

(*physics,theory,rotation*)
**Further reading:**

http://en.wikipedia.org/wiki/Mach%27s_principle

http://en.wikipedia.org/wiki/Absolute_rotation

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