What we don't know about gravity

Discussion in 'Physics & Math' started by Agesilaus, Sep 24, 2002.

  1. Agesilaus Registered Senior Member

    Messages:
    30
    I've been impressed by a number of sources lately on how little we know about gravity:

    1) G is only known to one part in 10,000 and various measurements do not fall in each others error bands.

    2) Measurements of G do not seem to be converging

    3) A different value of G has to be used in solar models to make the models work. This sounds like a fudge factor to me.

    4) A french group is suggesting that G varies with magnetic field strength. Going along with this is the fact that G measurements at different points on the earth's surface do vary.

    5) We have no idea if gravity is propagated at c or is instantaneous

    6) Altho current gravity wave detectors should have been able to detect
    gravity waves, according to current theory, no one has ever done so.

    7) Some groups have claimed that Foucalt pendulum periods change during solar eclipses.

    It seems as if we have almost no real understanding of gravity. What do you think.
     
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  3. James R Just this guy, you know? Staff Member

    Messages:
    37,093
    <i>1) G is only known to one part in 10,000 and various measurements do not fall in each others error bands.

    2) Measurements of G do not seem to be converging </i>

    Not entirely true. Measurements of G are converging, and also getting more accurate.

    <i>3) A different value of G has to be used in solar models to make the models work. This sounds like a fudge factor to me.</i>

    Do you have a reference for this, or examples?

    <i>4) A french group is suggesting that G varies with magnetic field strength. Going along with this is the fact that G measurements at different points on the earth's surface do vary.</i>

    G varies on Earth due to the equatorial bulge.

    Do you have a reference to this French group's work? Which French group?

    <i>5) We have no idea if gravity is propagated at c or is instantaneous</i>

    General relativity suggests it propagates at c. That gives us an idea.

    <i>6) Altho current gravity wave detectors should have been able to detect gravity waves, according to current theory, no one has ever done so.</i>

    Gravitational wave detection is a very difficult technical challenge. The main problem is separating signal from noise. Currently, several laser interferometric detectors are being built specifically for this purpose at a cost of millions of dollars.

    <i>7) Some groups have claimed that Foucalt pendulum periods change during solar eclipses.</i>

    Which groups? Reference?

    <i>It seems as if we have almost no real understanding of gravity. What do you think.</i>

    I think you're wrong.
     
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  5. Phrenetic :D Registered Senior Member

    Messages:
    155
    That depends on what you consider a "real understanding".
     
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