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Gravitational attractions

  1. Apr 21, 2003 #1
    [SOLVED] gravitational attractions

    why matter like to attract. does matter repel other matter just as like charges do according to coloumb 's law. how do we know that matter attracts only and does not repel
  2. jcsd
  3. Apr 21, 2003 #2
    i can only say that no one can prove or deny the existance of negative mass. it's out of our experience.we just do not have enough evidence. but if negative mass exists then oposite masses do repel according to gravity law.
  4. Apr 21, 2003 #3


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    Re: Re: gravitational attractions

    I wouldn't go that far. The best explanation so far for the observed accelerarted expansion of the universe is gravitational repulsion. Einstein's equations allow for it and that's the way it appears to be.

  5. Apr 21, 2003 #4
    I wonder the same thing rspandher,
    after all it seems like nature is all about dichotomy for every negative there seems to be a positive so why not anti-gravity? Why don't the planets repel instead of only attract? I came up with a notion they might possibly explain this a year ago, but it works great in theory just
    not so well mathematically.
    Check out the topic "a physics expirement with magnets and a vote pole", and give it your guess, the results of the expirement don't really prove anything but may suprise a lot of people. Later,
    I'll post what inference might be drawn from this expirement and it has implications on gravity.
  6. Apr 22, 2003 #5


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    Re: Re: gravitational attractions

    Not sure I agree, there. Maybe it's just a matter of semantics, though.

    Although we currently lack any way of directly observing negative energy, its properties have been predicted and these predicted properties have been observed. To me, this is a situation roughly analogous to saying, "we've observed a very large star collapsing, and in the final stage of collapse it vanished. In the location where this disappearance occurred, there is now an area of space from which nothing escapes, not even light." Although it is impossible to directly "observe" a black hole, I would consider the above statement to be proof of one's existence.

    In the same way, something that behaves in exactly the manner that negative energy is predicted to behave has been observed. To me, this constitutes compelling evidence (if not absolute proof) that negative energy does exist. One of these predicted behaviors is that negative energy is gravitationally repulsive.
  7. Apr 22, 2003 #6


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    Staff: Mentor

    Sounds like the questin is a little more basic, guys - he's asking about how gravity works, ie. Relativity.

    Einstien showed that gravity is a result of massive objects bending space. The 2d analogy is a bowling ball on a trampoline. Put two next to each other and their combined warping of space (the trampoline) makes them attract. This also explains why light is affected even though it has no mass. It follows a straight path over the curved space.
  8. Apr 22, 2003 #7


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    That is not what Einstein showed. Einstein did show that gravity **can** curve spacetime. That doesn't mean that gravity **is** curved spacetime. In fact you can have gravity without spacetime curvature. Think of curvature as tidal forces. One does not say "gravity is tidal force" - the reason being is that tidal force is a *difference* in gravitational force. Hope that was clear.

    Think of gravity as being of the same nature as a non-inertial frame - is the spacetime is curved the the equivalence is said to be "local" in that you can't transform the gravitational field away in a finite region.

  9. Apr 23, 2003 #8
    but what cause the attractions between matter. like electrostatic forces charges attract or repel but what property of matter produce the gravitational field. what is in the matter that cause a field in the space. is that the particles which make up matter or something else.
  10. Apr 23, 2003 #9
    Place a bowling ball on a sheet and hold the corners tightly, so the sheet is suspended. Then place a tennis ball on the outside and watch it roll towards the bowling ball, or center of the sheet. This is, I think, a good example of how gravity works, the object distorts space-time and causes it to 'bend' and have 'ripples' in it. Now, there is no particle of such that is the agent of gravity, maybe the graviton, but there really isn't a means by which gravity works, on the distortion of space-time.

    EDIT: Unless I'm wrong of course:smile:

    If an object is moving like this:
    and there is an object down the way

    and the gravitational field of that object is large enough to intersect with the course of the moving object, then the object will fall into its "ripple" and you will observe gravity, like so.

    Last edited: Apr 23, 2003
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