[extropy-chat] unidirectional thrust

[scerir]

> "Acceleration can only be defined
> as relative acceleration of a point
> relative to other bodies. This circumstance
> indicates that it is meaningless to ascribe
> to a body a resistance relative to acceleration
> as such (inertial resistance of bodies
> in the sense of classical mechanics); much rather,
> it must be required that the appearence of
> an inertial resistance be tied to the relative
> acceleration of the considered body relative to
> other bodies. It must be required that the inertial
> resistance of a body can be increased by bringing
> unaccelerated ponderable masses into the
> neighborhood of the body."
> - A.Einstein (1913)

There is something more specific, about the Mach-(Mike)
principle, that Einstein also wrote in 1913. 

[Mass A, and masses B,C, ... in its neighborhood. What
if masses B,C,... are not still but they are accelerated 
together with the mass A? In this case the increase 
of the inertial resistance in A, surrounded by B,C,...,
should be overcompensated by the acceleration of B,C,...
This is the issue.] 

"The acceleration of the masses B,C,... must induce
an accelerating force on [mass] A that is in the same 
direction as the acceleration. One sees in this way
that the extra accelerating force must overcompensate
the increase of the inertia caused by the mere presence
of B,C,..., since in accordance with the relation
between energy and inertia of systems the system
A,B,C,... as a whole must have a smaller inertia
the smaller is its gravitational energy." 

Btw, in the literature it is possible to find between 10 and
20 different Mach principles. Of course possible Machian 
'effects' are not independent of these many and different
Machian principles. 

Mach-1:  Newton's gravitational constant G is a dynamical field 
         (Brans-Dicke Theory)
Mach-2:  an isolated body in otherwise empty space has no inertia
Mach-3:  local inertial frames are affected by the cosmic motion 
         and distribution of matter
Mach-4:  the universe is spatially closed 
Mach-5:  the total energy, angular, and linear momentum of 
         the universe are zero 
Mach-6:  inertial mass is affected by the global distribution 
         of matter
Mach-7:  take away all matter, there is no more space 
Mach-8:  '4 pai rho G T^2' is a definite number of order unity 
         (T is the Hubble time, rho is the mean density of the
         universe)
Mach-9:  the theory contains no absolute elements (general 
         covariance)
Mach-10: overall rigid rotations and translations of a system 
         are unobservable 
Mach-11: there is a 'dual' Mach principle, it is about the 
         relativity of time