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The force of gravity can only be observed between two or more bodies

  1. May 11, 2005 #1
    Is it possible to build a logical argument on the following line?
    1) The force of gravity can only be observed between two or more bodies.
    2) The claim that a single body has a gravitational field is purely theoretical; it cannot be observed.
    3) If the only demonstrable gravity force is a force between two or more bodies; is it not possible to claim that a single body does not generate a gravity field unless gravity exists in the form of gravitons that then become the (unobserved) second body.
    4) Gravity then is not the effect that mass has on space and time, but it is the effect that mass has on gravitons and it requires time for that effect to spread through the graviton field.
    5) That means that if we are to accept the current theory that a single mass has a gravity field; then we have also to accept by the same theoretical implications, the existence of gravitons.
  2. jcsd
  3. May 11, 2005 #2
    What do you mean by a body? The fact that a planet was formed at all is evidence of its gravitational field, let alone any interaction with the sun, the moon, its own atmosphere, etc. Hawking radiation would be evidence of the gravitational field of a black hole, even if it had no other body to exert a gravitational attraction upon. The lifecycle of a star would be another sign, as red giants collapse under their own gravity, as can massive white dwarfs to form neutron stars.
  4. May 11, 2005 #3
    El Hombre makes a very good point. When you say 'body' I assume you're talking about moons, or at least a stone falling to Earth. These bodies are composed of many, many atoms, which are in turn composed of many subatomic particles. The only way to truly see the effect of gravity on 2 'bodies' would be by studying 2 subatomic particles. Unfortunately, at this (subatomic) scale, the other forces (electromagnetic, strong and weak nuclear) are tremendously more powerful, thus making gravitational interactions extremely difficult or maybe even impossible to isolate the force due to gravity.

    Try this experiment (don't really, but think about it): Put a glass of water on your mattress and lay down beside it. Unless you've got one of those really expensive new mattresses, your body should depress the mattress enough to knock the glass over. Now try it again without the glass. You're *still* making a depression in the mattress, even though there's no glass to tip over. If the mattress is analagous to space-time and your body is analagous to the Sun, I don't see why you'd need a graviton.
  5. May 12, 2005 #4
    Grogs understands where I am trying to go. All we have to do is replace the mattress; but do we use empty space or a field of gravitons. My case is that it would be logical to use gravitons: after all, how can 'nothing' be distorted?
    The claim that a single particle generates a gravity field is unproven speculation and no more valid than using gravitons, but the existance of gravitons is generally accepted and the claim is, I sugest, more believable.
  6. May 12, 2005 #5


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    I wouldn't say that it is an unproven speculation. First, we do know that gravity does have an impact on photons (which disproves prior theory that only mass was impacted by gravity). Second, gravity has a highly specific form which is not inconsistent with single body gravitation. Third, we have the de Sitter space equations which show the perturbations of equations of gravity for empty space make sense. Fourth, we have a model of gravity in which single body gravity makes sense (GR).

    The existence of gravitons is hardly generally accepted. It is also not at all clear that the rank 2 tensor of graviton theory is really the same as the rank 2 tensor of GR, and to the extent that there may be differences, that the experiment would support graviton rather than GR. Indeed, we have no working graviton model in existence and no evidence for their exists, while we do have a gravity field model in existence that works and has been verified by experiment.

    The "how can 'nothing' be distorted" argument proves too much. Why should the light take more time to cross a small amount of nothing than a large amount of nothing? Why should there be a constant like the permiability of empty space? Why should QED equations imply that a vacuum has energy? How do we even know that time-space is "nothing"? It sounds a lot like the "air" is nothing arguments advanced before gases were well understood.
    Last edited: May 12, 2005
  7. May 12, 2005 #6
    The point you raise about photons and mass is why I originally used the term bodies instead of mass.
    The rest of your case seems to be a good arguement for there being something in space, the question is what form does it take?
  8. May 13, 2005 #7
    gravitons nor gravitational fields exists. they are both just abstract concepts that try to explain something that has not yet been conceived. want to know something else? electric fields dont exist either!
  9. May 14, 2005 #8
    This question was a lead into my question on the Casimer effect, I think it has now bottomed out and should be discontinued. My thanks to those who gave intelligent replies.
  10. May 14, 2005 #9
    Once you insist there is only one object in the world, and you want to argue something about it's interation, it is metaphysics. We can not prove in this case interation takes place, but in the reverse, we also can not prove it does not exist.

    But we believe that, if the object now is put into another world, so that it can interact with other objects, it's intrinsic property does not change. Although the object interacting with other objects is not intrinstic, but the field it makes is an intrinstic property(at most have some relations with the spacetime), and there is evidence that it is really field, not other things, then we can infer that even if it is the only creature by God, it sends out field.

    Of course, non-interative can not completely passed into the quantum level, and the argument is classical.

  11. May 16, 2005 #10
  12. May 23, 2005 #11


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    law of inertia:
    A body moved sufficiently far enough from other bodies would either remain at a state of rest or move at a uniform velocity and direction.

    This law tells us something about the bodies when there is no external force applied (i.e that of an electromagnetic force between charged particles, neither of gravity)

    we assume that the object does not at all have any external application of force on it.
    so we can say that no other objects are nearby and effect the body through means of gravity.

    if we take this one step further,
    we take the first part of the law of inertia and imagine the body remaining at rest.
    we now say, is this body at rest because there is no external force applied to it, or , is it because gravity - or rather a graitational medium is attracting it at equal force in equal directions...?
    here we assume to say, that rather than a body and another body interact by ways of emmiting gravity, that the disturbance of this gravitational medium is the cause and affect of gravity.

    say that two lead balls of identical mass - both made purely of lead - and at the same size - obviously - where is a portion of space that was unaffected by external applications of force.

    Now, newton states that each particle in the universe attracts each other particle, ''universal gravity''. However describing this classically, how can two balls made from the exact same elements attract one another? if we try to describe this by way of electromagnetism we must say that there is an equal but opposite force. How can you discriminate against the same particles?

    There must be an equal but opposite gravity between these balls, originating not from the bodies themselves but by the disturbance in the space around them. Then one could come to the conclusion that a gravity medium exists and that mass or energy disturbs it.......possibly a fermion field with a boson graviton interaction...
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