Am 26.02.2012 17:35, schrieb Warp:
> clipka<ano### [at] anonymousorg>  wrote:
>> Why should it?
>
>    Because gravity points down at all points in the rod. There is no force
> in the opposite direction counteracting gravity.
>
>    If the rod were not welded to itself, it would definitely fall (until
> it collides with the borders of the portal or whatever), no? Welding it
> to itself doesn't change this. (Basically the only thing the welding
> achieves is that it stops the rod from tilting.)

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.

The movement due to gravity may instead be a result of quantum 
fluctuations in the position of the object, which favor positions with 
lower potential energy.

>> Downward motion won't put the endless rod into a state of
>> lower potential energy, so it will not happen.
>
>    The rod is not literally endless. It's just that the parts that go
> thrown the portal on the floor are transported to the portal on the ceiling.
> (From a physics point of view this would mean that the energy required to
> transport matter adds to the potential energy of said matter if the endpoint
> is higher than the startpoint.)

Actually that's the one weak point of all the portal stuff: Rather than 
allowing objects to fall through without a change in speed, a real 
working portal technology would have to result in a repelling force at 
the lower portal itself, proportional to the difference in potential energy.

So no automatic "speedy thing goes in, speedy thing comes out".

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