Re: Macros

Discussion in 'Digital Photography' started by dadiOH, Mar 16, 2013.

  1. dadiOH

    Paul J Gans Guest

    In rec.photo.digital Wolfgang Weisselberg <> wrote:

    >Homogenous hollow sphere (as the only object). Whereever
    >you are inside, the pull is identical in each direction.
    >Therefore a Dyson sphere is inherently stable, but a ringworld
    >would be unstable and needs active stabilization against the
    >tiniest movements.


    A Dyson sphere, or more properly a Dyson shell, is also
    inherently unstable just as Ringworld is. See wiki

    http://en.wikipedia.org/wiki/Dyson_sphere#Dyson_shell

    --
    --- Paul J. Gans
     
    Paul J Gans, May 24, 2013
    #41
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  2. PeterN <> wrote:
    > On 5/22/2013 6:24 AM, Wolfgang Weisselberg wrote:
    >> J. Clarke <> wrote:
    >>> In article <>, ozcvgtt02


    >>>> But still, I'd like a configuration where gravity sources
    >>>> (carefully placed by you) do *not* influence parallel light
    >>>> rays to become non-parallel.


    >>> Wolfgang, I really do not understand why you are harping on this ad-
    >>> nauseum. If you think it has some real relevance to the issue of
    >>> starlight being treated as parallel rays then do explain the relevance.


    >> Naah, it has no real relevance.


    >> Except when "you want to get theoretical" (PeterN's words),
    >> in that case the rays don't stay perfectly parallel except for
    >> a very few configurations (e.g. inside a perfect and hollow
    >> sphere). I had hoped PeterN would think about it or look it up
    >> (and maybe present such a configuration) and thereby understand
    >> that his claim of
    >> | If you want to get theoretical, the gravitational influence of randomly
    >> | distributed objects might very well equalize each other. Therefore the
    >> | rays would remain parallel.
    >> (PeterN in Message-ID:
    >> <51771a0b$0$10833$-secrets.com>)
    >> was wrong.


    >> Thinking about it: he probably knows it by now, he just
    >> *can't* admit that he was not completely right --- strictly
    >> theoretically, that is.
    >> You're right, I should let PeterN from the hook, he's digging
    >> so fast that one can't see very much any more from all dirt
    >> he's throwing up.


    > You simply refuse to understand what "random" means.


    Most people can't understand meanings that you make up for
    words and don't bother to explain.

    Speaking of that: does *your* "might very well equalize each
    other" perhaps be the same as most people's "it hasn't the
    chance of a snowflake in hell to equalize each other"?

    -Wolfgang
     
    Wolfgang Weisselberg, May 24, 2013
    #42
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  3. Paul J Gans <> wrote:
    > In rec.photo.digital Wolfgang Weisselberg <> wrote:


    >>Homogenous hollow sphere (as the only object). Whereever
    >>you are inside, the pull is identical in each direction.
    >>Therefore a Dyson sphere is inherently stable, but a ringworld
    >>would be unstable and needs active stabilization against the
    >>tiniest movements.


    > A Dyson sphere, or more properly a Dyson shell, is also
    > inherently unstable just as Ringworld is. See wiki


    > http://en.wikipedia.org/wiki/Dyson_sphere#Dyson_shell


    I gladly admit that 'inherently stable' might be the wrong word,
    but please explain what happens in Dyson sphere, where the sun
    is off center (and sphere and sun initially not moving against
    each other) and contrast that to what happens to a ringworld
    under the same conditions.

    -Wolfgang
     
    Wolfgang Weisselberg, May 24, 2013
    #43
  4. dadiOH

    Paul J Gans Guest

    In rec.photo.digital Wolfgang Weisselberg <> wrote:
    >Paul J Gans <> wrote:
    >> In rec.photo.digital Wolfgang Weisselberg <> wrote:


    >>>Homogenous hollow sphere (as the only object). Whereever
    >>>you are inside, the pull is identical in each direction.
    >>>Therefore a Dyson sphere is inherently stable, but a ringworld
    >>>would be unstable and needs active stabilization against the
    >>>tiniest movements.


    >> A Dyson sphere, or more properly a Dyson shell, is also
    >> inherently unstable just as Ringworld is. See wiki


    >> http://en.wikipedia.org/wiki/Dyson_sphere#Dyson_shell


    >I gladly admit that 'inherently stable' might be the wrong word,
    >but please explain what happens in Dyson sphere, where the sun
    >is off center (and sphere and sun initially not moving against
    >each other) and contrast that to what happens to a ringworld
    >under the same conditions.


    Same thing. The sphere is just a three dimensional version.

    The attraction of the sun does not provide a restoring force
    to center either one. When off center there is more sphere
    further away than there is sphere nearer the sun. So the
    net attraction works out to be zero.

    Don't take my word for it. Check Google or Wiki.

    --
    --- Paul J. Gans
     
    Paul J Gans, May 24, 2013
    #44
  5. Paul J Gans <> wrote:
    > In rec.photo.digital Wolfgang Weisselberg <> wrote:
    >>Paul J Gans <> wrote:
    >>> In rec.photo.digital Wolfgang Weisselberg <> wrote:


    >>>>Homogenous hollow sphere (as the only object). Whereever
    >>>>you are inside, the pull is identical in each direction.
    >>>>Therefore a Dyson sphere is inherently stable, but a ringworld
    >>>>would be unstable and needs active stabilization against the
    >>>>tiniest movements.


    >>> A Dyson sphere, or more properly a Dyson shell, is also
    >>> inherently unstable just as Ringworld is. See wiki


    >>> http://en.wikipedia.org/wiki/Dyson_sphere#Dyson_shell


    >>I gladly admit that 'inherently stable' might be the wrong word,
    >>but please explain what happens in Dyson sphere, where the sun
    >>is off center (and sphere and sun initially not moving against
    >>each other) and contrast that to what happens to a ringworld
    >>under the same conditions.


    > Same thing. The sphere is just a three dimensional version.


    Interesting claim. Gravitation only works in 2 dimensions?


    > The attraction of the sun does not provide a restoring force
    > to center either one.


    True.

    > When off center there is more sphere
    > further away than there is sphere nearer the sun. So the
    > net attraction works out to be zero.


    For the sphere, yes. Any angle you can find that fills some
    part of the closer half will always be filled on the further
    half, too.

    For the ringworld, no.
    Thought experiment: You move one side of the ring world 1/10th
    the distance to the sun the other side has. Say the ringworld
    is 1000km from upper to lower rim. Pick a square, from the
    upper to the lower rim, and also 1000 km wide. From the corners
    of the square draw straight lines through the middle of the sun.

    Where they meet the far further ring half on the other side:
    what happens? Each km is now 10 km, so we have 10,000 km
    along the ring ... no problem, there's the ring to fill it.
    But the 1000 km height is also 10,000 km high now ... and the
    ring can only fill 1000 km, as IT IS ONLY 1000 km from rim
    to rim! A sphere fills it all (for any shape, actually and
    for any direction), that's why it's stable.

    Therefore the ringworld the closer side will accellerate towards
    the sun as soon as it's ever so slightly off center. That's why
    I called it unstable. The sphere will not, as you agreed.

    > Don't take my word for it. Check Google or Wiki.


    Please do.

    -Wolfgang
     
    Wolfgang Weisselberg, May 25, 2013
    #45
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