I love gravity. I use it every day.

Discussion in 'Archived Threads 2001-2004' started by BrianW, Nov 8, 2001.

  1. BrianW

    BrianW Cinematographer

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    The most recent episode of Enterprise, although I thoroughly enjoyed it, had me scoffing at the depiction of normal gravity on such a small celestial body. The men would have weighed between 5 and 40 pounds (depending on the comet’s ratio of rock to ice, ultradensity of the rare material in question notwithstanding), which would make jumping out of a one-meter hole a piece of cake. Even if you do slip, injuring your knee in a one-meter fall would be exceedingly difficult under such meager gravity. Even so, with an injured knee, you should still be able to hop on one foot, bounding ten meters at a time, back toward your shuttlecraft, making for a quick escape. (However, keeping your balance while doing this, I must admit, would be next to impossible – at least for me.)
    But Enterprise is not the only SF with gravity gaffes. Highly respected, classic SF literature has them, too. In particular, the Ringworld series of novels, by Larry Niven, depicts a civilization that has converted all its solar system’s mass, excluding their star, into a giant ring orbiting their sun.
    A concentrated, spherical mass, like a planet, usually has an inherently stable orbit. It’s like a marble in a round-bottomed hole. Nudge the marble in any direction, and it will once again seek the bottom of the hole (or orbit about that point) with almost no risk of flying out of the hole. Likewise, if you nudge the Earth, its orbit may become more (or less) elliptical, but only an unspeakably cataclysmic amount of nudging, like a head-on collision with a similarly-sized planet going in the opposite direction, would send the Earth crashing into the sun.
    This is not so with the Ringworld concept. From a gravitational energy point of view, Ringworld is like a marble on top of a round hill. Balance it carefully, and it will sit there indefinitely, but only as long as nothing interacts with it. But give the marble the slightest nudge, and it will roll off the hill, accelerating relentlessly toward its doom. Likewise, Ringworld, with only the slightest of celestial tugs, will inevitably fall and crash into its own sun. The orbit of a ring about a gravity well is inherently unstable, and I wouldn’t bet a civilization on its long term viability.
    Then we have the Dyson Sphere, which is an enormous, hollow sphere, with a radius approximately equal to one astronomical unit, constructed about a star. The people live inside the sphere, and none of the star’s light gets out. From a gravitational energy point of view, this is like a marble resting on a flat surface. Nudge the marble in any direction, and it will continue to go in that direction, without acceleration, until it encounters another force. This means that the net force on the sphere due to the sun’s gravity is zero, regardless of where the sun sits inside the sphere. (Of course, this also assumes that the sphere is rigid enough to withstand asymmetrical, or tidal, forces resulting from migration of the sun away from the center of the sphere.)
    Occupying the flat nether-region between orbital stability and instability, the Dyson Sphere would require thrusters to keep the central sun from creeping too far away from its central location. Slight nudges would need to be dealt with, but only a nudge of equal amount in the opposite direction would be required to stop relative motion between the Dyson Sphere and its central sun. This is not the case with the Ringworld, which continues to accelerate toward the sun after being nudged off the top of its orbital-stability hill.
    But some other aspects of the Dyson Sphere are intriguing as well. Does the sphere spin? Or does its rigidity simply keep its structure from collapsing into the central sun? Even if it does spin, counteraction of the central sun’s gravity would occur only in a plane. The poles of the sphere would still rely on the sphere’s rigidity, even more so if it is spinning, to avoid collapsing into the central sun. If the sphere is not spinning, then the inhabitants would perceive “down” as toward the sun, making their world vastly different from our own.
    If the sphere is spinning just enough to cancel the force of the sun’s gravity at the sphere’s equator, then the sphere’s inhabitants, at the equator, would be weightless. And lest you think that the sphere itself would become the “ground” due to its own gravity, rest assured that the inhabitants would be weightless regardless of the thickness of the sphere. The “marble on a flat surface” applies to the gravitational interaction between the sphere and its inhabitants just as it does to the gravitational interaction between the sphere and the central sun. In other words, the inhabitants, as long as they are inside the sphere, will always experience a net zero force from the sphere’s gravitational attraction. (This assumes uniform thickness and density of the sphere, of course.)
    If the sphere is spinning more than enough to cancel the force of the sun’s gravity at the equator, then the sphere’s interior surface, at the equator, would be “down” and the sun would once again be in the sky as it should be. But this would tax the sphere’s structural integrity immensely. But so what? If a civilization can build a sphere that big, I think it’s safe to assume that they have the engineering prowess to make it unbelievably strong.
    Regardless, no matter what you do regarding the sphere’s spin, inhabitants at the poles would perceive “down” as toward the sun. If the sphere is spinning, the interior civilization might be broken up into classes with the rich elite at the equator with the sun in the sky, while the downtrodden working class citizens live at higher latitudes and at the poles, with only plate steel for a sky, and the unseen sun forever below ground. However, it could be the case that all the sphere’s inhabitants live only at the equator, and that the higher latitudes are uninhabited. But then why would a civilization build a sphere instead of a ring if they didn’t intend to populate the entire structure?
    Why, to keep it from crashing into the sun, of course!
     
  2. Bill Catherall

    Bill Catherall Screenwriter

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    Whoa! I've never thought of doing such a thing. Very intriguing. However, I would venture to say that even building a ring planet or a sphere planet around a star would be impossible. Much like building a stone arch, you have to have a supporting structure in place before you get the keystone in, or else it will collapse in on itself. You would have to coordinate all segments of the sphere or ring to connect at exactly the same moment. Or use thrusters on all the segments to resist the gravitational pull of the star until all segments are in place.
    So along the same lines...would it be impossible to have a spherical shield around earth that didn't use support pillars? Just keep launching geosynchronous satellites until the sky is filled with them. I guess though that once you connect them all then you run into the problems you were talking about. Hmmm. Interesting.
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    Bill [​IMG]
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    [Edited last by Bill Catherall on November 08, 2001 at 11:38 PM]
     
  3. Philip_G

    Philip_G Producer

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    I dislike gravity and spend a good deal of $ and time learning to cheat it [​IMG]
     
  4. Andrew W

    Andrew W Supporting Actor

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    You could at best build a ring around the earth with geosynchrounous satellites. They must be over the equator.
    See: http://liftoff.msfc.nasa.gov/academy.../geo-high.html
    Aurthur C. Clark discusses such an endeavor in "Fountains of Paradise"
    This is a slightly different engineering concept than ringworld since there are spokes to stabilize the ring. (A small benefit of not having a fiery ball as the hub.)
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    Andrew in Austin
     
  5. Inspector Hammer!

    Inspector Hammer! Executive Producer

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    I don't know, I tend to feel a bit wieghed down by it.
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  6. AdrianOC

    AdrianOC Stunt Coordinator

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    Theres no such thing as gravity. The Earth sucks.
    [​IMG]
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    "Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam."
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  7. Mark Schermerhorn

    Mark Schermerhorn Second Unit

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    Brian: I know you know this, but Ringworld isn't exactly realistic sci-fi. It's a humorous novel series, really. The surreal nature of the books are what make them unique. In fact, if the author obeyed and physical laws in the book, it probably wouldn't be very funny.
    With TV shows, it's probably a matter of their budget. They'd have to do a lot of wire work or some other method to give the appearance of no gravity or minimal gravity. At least, thats what I hope it is, and not sloppy writing / fact checking.
     
  8. DonRoeber

    DonRoeber Screenwriter

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    I'm no expert, but my friends who are very big into Sci-Fi tell me that Babylon 5 is the only Sci-Fi tv show ever to handle gravity in space properly. I'm about 5 episodes into season 1 of the vhs tapes of B5, so I really can't argue one way or the other [​IMG]
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    Generating 2048 bits of randomness...
     
  9. BrianW

    BrianW Cinematographer

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    Thanks for your comments, Mark. They’re well worth pointing out. It’s been so long since I’ve read the Ringworld series that I don’t remember it very well. I do, however, recall that Niven built a surreal world that was thoroughly engaging and fun to read. I didn’t mean to imply that his novels were diminished in any way by his solar system design. That would be like impugning Douglas Adams for his super computer design. [​IMG] Alas, I don’t even recall the novel in which the Dyson Sphere was first introduced. The concept was referenced in an episode of ST-TNG, but it certainly didn’t originate there.
    I’m also willing to give them the benefit of the doubt on their treatment of gravity on Enterprise. The constraints are too, well, constraining to depict such an encounter properly without a huge budget. Although they might have done better, I’m willing to let it slide and enjoy the episode for its other strengths.
    Don, your friends are right about B5, at least when it comes to space ship maneuvering. Space ships on B5 (for the most part) operate in Newtonian, rather than aerobatic, fashion, which is accurate. When they really get into it, it is very exciting to watch.
    Bill, good call on the construction technique. I didn’t even think of that. To construct a Dyson sphere, I suppose you could start with a single ring around the equator, orbiting in order to relieve stress during construction. And from there, you could add progressively smaller rings as you work your way toward the poles. Each ring would have to be structurally sound enough laterally not to buckle, and the structure progressing from the equator to the poles would have to be sound enough longitudinally to bear the weight of the rings. You’d have to work in both directions at once. I can’t really thing of anything we do here that is similar. As you pointed out, we don’t really build domes or arches like this. I guess the best analogy I can think of would be the construction of the arch in St. Louis, although that’s only a two-dimensional analogy. Instead of a vertical scaffold support from the ground, that arch employed a rising horizontal scaffold during construction to maintain the structure’s self-supporting integrity. Still, I don’t think we’ll be building any Dyson Spheres any time soon, unless we discover a HUGE batch of unobtainium somewhere.
     
  10. Cees Alons

    Cees Alons Moderator
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    Mark,
    Aren't you mixing up "Ringworld" (Niven) with "Discworld" (Pratchett)?
    Cees
    [Edited last by Cees Alons on November 09, 2001 at 12:29 PM]
     
  11. Mark Schermerhorn

    Mark Schermerhorn Second Unit

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    hahaha, Damn it, Cees, yeah you are correct. I had em mixed up. I've seen the ringworld books but I haven't read them. Whoops. I think the "ring orbiting the sun" confused me a bit as well, since the people in discworld, well, live on a disc. However it is supported on 4 elephants who are standing on top of a turtle if I remember correctly...
     
  12. Rob Willey

    Rob Willey Screenwriter

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    "Gravity is a harsh mistress."
    - The Tick
    Rob
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    "That suits me down to the ground."
     
  13. Ron-P

    Ron-P Producer

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    I love gravity.
    When my glass is tipped just so. It helps direct the flow of beer to my mouth and down to my belly with very little effort on my part.
    Peace Out~ [​IMG]
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    http://home.earthlink.net/~peregrinefalcon
     
  14. Bill Catherall

    Bill Catherall Screenwriter

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    On the subject of actually liking gravity, I find it to be somewhat irritating. The earth's gravitational "constant" seems to be changing as I get older. Every time I step on a scale I find that I'm getting heavier. Also, getting out of bed every morning is getting progressively difficult.
    I also object to the way gravity is preventing me from leaving this planet and exploring other areas of space. Trying to build a craft that has enough fuel to reach escape velocity and withstand the forces at that speed is too expensive. It's got to be some interplanetary plot to keep poor guys like me from seeing all the fun stuff out in space.
    Gravity gets me down.
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    Bill [​IMG]
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  15. Max Leung

    Max Leung Producer

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    Iain Banks didn't like the Ringworld concept either...it would be too unstable, so instead he built a ring orbital. It's a ring habitat that orbits the sun, and is angled in such a way that one side of the ring is exposed to the star while the other is in darkness, and the ring spins. I also liked how antigravity equipment did not work in that world...because there is no gravity, only centrifugal force! So, if you have an anti-gravity suit, don't jump off a building and expect to live. [​IMG]
    ("Consider Phlebas" is his first attempt at SF, BTW...since he writes fiction most of the time, his SF tends to be more character driven than the usual fare. This book later spawned a series of novels, collectively called the "Culture" novels, plus a few unrelated SF work like Feersum Enjinn, et al.)
    Anyhow, how would the inhabits avoid falling into the sun in a Dyson Sphere? If the sphere didn't spin, than they would splatter into the sun, and if it did spin, then the people in the polar regions of the sphere would still fall in, as the centrifugal force is not strong enough to counteract the sun's pull! And, it is definitely true that you would need thrusters of some sort to keep the sphere (or a ring) from drifting. I hope somebody at NASA or whereever did a simulation study to show this is true, although I suppose a simple use of calculas can show this effect.
     
  16. Max Leung

    Max Leung Producer

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  17. John Beavers

    John Beavers Second Unit

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    Are we talking about the fundamental physical force that is responsible for interactions which occur because of mass between particles, between aggregations of matter (as stars and planets), and between particles (as photons) and aggregations of matter, that is 10 to the 39th power times weaker than the strong force, and that extends over infinite distances but is dominant over macroscopic distances especially between aggregations of matter?
     
  18. Alex Spindler

    Alex Spindler Producer

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    Um....yeah
     
  19. Jeffrey Noel

    Jeffrey Noel Screenwriter

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    I had Gravity a couple of years ago. It smelled good but I didn't use it everyday! [​IMG] [​IMG]
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  20. Brad_W

    Brad_W Screenwriter

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