On 2/27/2012 9:28 AM, Warp wrote:
> clipka<ano### [at] anonymousorg>  wrote:
>> That's /one/ way to interpret the observable effects of gravity, but the
>> force of gravity is not necessarily the /cause/ of the movement, but may
>> instead be just the result of trying to /counter/ that movement.
>> Remember how inertia is not caused by some force of inertia, but instead
>> a force of inertia is caused by trying to counter the inertial movement.
>
>    I don't understand.
>
>    At every single point in the rod you have an acceleration downwards of
> about 9.8 m/s^2 due to gravity.
>
>    What exactly is the force in the opposite direction counteracting this?

I don't think it's any more odd to have a mysterious "force" holding the 
rod up than it is to have a mysterious energy input allowing it to fall. 
  You're really just giving slightly different answers to the same 
paradox.  Which answer is the most "natural" depends on how you treat 
gravity, and formulations of gravity which are mathematically isomorphic 
under normal circumstances seem to differ here.  For instance:

1) An object of mass m in a gravitational field of acceleration g feels 
a force of strength m*g, and by Newton's law moves according to m*g = 
m*dx^2/d^2x

2) An object of mass m in a gravitational field which gives potential 
m*g*x to an object at position x moves along a spacetime path which 
minimizes 0.5*m*(dx/dt)^2 - m*g*h

Under view (1) it seems that the rod should move, but under view (2) it 
seems the rod should stay still.  Of course, based on how portals work 
in the game I think it's clear that things operate more like (1), but 
this is just a fact about the game design and isn't the sort of thing 
you're going to be able to reason about like there's a correct answer 
for in any sort of "real" sense (unless you want to treat the portals as 
wormholes and solve the GR equations on the resulting topology, which I 
sure don't want to do, and which I suspect would turn out like (2) anyway).

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