Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is Gravity an Attractive Force?

  1. Dec 18, 2004 #1
    Is Gravity a Force of Attraction?

    We are familiar with electromagnetic attraction and we understand how and why it works.

    We do not understand Gravity to my understanding and we are trying to link it and its properties with that of electromagnetic.

    Now we are trying to detect Gravitational Waves.

    Is it possible that Gravity is not an attraction but merely an angular momentum force.

    Could it be that by the fact that mass follows the curvature of space that when space is bent mass that is in motion will experience an angular momentum force due to the bending of space?

    Could this explain Gravity and how it has the same attraction for all mass?
     
    Last edited: Dec 18, 2004
  2. jcsd
  3. Dec 18, 2004 #2
    Yes.
    We do?
    We understand gravity as much as we understand electromagnetism.
    They have already been detected indirectly.

    For details please see - http://www.pas.rochester.edu/~dmw/ast102/Lectures/Lect_19b.pdf

    I don't know how to answer "Is it possible.." questions. Is it possible that Santa Claus really exists? My answer to each is no. But let me reserve that opinion until Dec 26 th, okay? :smile:
    In the first place its "the curvature of spacetime" that you're probably thinking about. That's just a fancy word for tidal gradients. In Newtonian mechanics there were tidal gradients as well and the angular mometum of a particle in an orbit never explained the attractive force of gravity there either.

    Pmb
     
  4. Dec 18, 2004 #3
    If tidal gradients curved inword twords the center of a mass by displacing Space Time then would this create a force of lessor mass twords the center of grater mass?
     
  5. Dec 18, 2004 #4
    You're using the term "tidal gradient" to speak of "spacetime curvature" here. But these two terms mean identically the same thing.

    What you're effectively asking is this
    Please explain what you're asking here? What is it you mean when you say "tidal gradients curved inward"

    Pmb
     
  6. Dec 18, 2004 #5

    Garth

    User Avatar
    Science Advisor
    Gold Member

    Welcome to these Forums Abstruce!

    Before I answer your question I must point out that multiple postings are not allowed. You must start a thread in the most appropriate Forum, if it is the wrong Forum it will be moved.

    You have more or less got the idea behind General Relativity. If you draw a straight line on a flat sheet of paper and bend the paper the line appears 'bent' because the surface on which it is drawn has bent. The line is still the shortest path along the surface of the paper, it is still a "straight line" in that surface.

    In GR freely falling objects have 'straight' world-lines, called geodesics, through space-time; this is because there are no forces, apart from smaller tidal forces, acting on you if you are freely falling.

    However the theory postulates that the presence of mass curves space-time so two initially parallel geodesics may converge. Thus gravity is explained as an effect of the curvature of space-time, a geometric effect rather than a 'real' force. Einstein derived a field equation from this concept that when solved for the gravitational field around the Sun made predictions of the motion of Mercury and the bending of a light ray that were found to be accurately confirmed by observation. When solved for the universe as a whole it predicted the expanding universe and the Big Bang, it is the basis of nearly all modern cosmology.

    "Mass tells space-time how to curve, curved space-time tells mass how to move."


    Garth
     
  7. Dec 18, 2004 #6

    Labguy

    User Avatar
    Science Advisor

    Yes
    Yes, the Grand Unified Theory (GUT). Everything seems to be in order except gravity.
    Gravity waves, Gravitons, maybe as simple as the standard photon duality (particle / wave) scenario; graviton acting like photons with properties of both waves and particles.
    Spelled "Centrifugal". Not likely as centrifugal force is a property measured only on curved (vectored) motion, and is also the force pulling an object toward straight-line motion. The force doing the "pulling", whether by a string on a ball or gravitational attraction is defined as "Centripetal". If gravity is measured as one or the other, it would have to be considered Centripetal.
    Photons follow the curvature of space-time and if gravity is found to have properties similar to photons (gravitons) this would be the case. It would also simplify things a whole lot. Either way, we won't be using the word "centrifugal" much in relation to gravity.
    There are two or three different experiments working or near-future that might help answer this question. I sure hope it is in my lifetime.. :confused:

    BTW, I presume that you and/or other PF readers have seen where the satellite measurements have already seemed to confirm "frame dragging", and exactly to the extent calculated by Einstein. There may (is?) already be a PF thread on this but I haven't seen it, due to not looking for it.
     
  8. Dec 18, 2004 #7
    If the tidal gradient also known as the Fabric of Space Time is displaced by the Earth's mass simmular to an air bubble displacing water the air bubble experiences pressure all around its exterior because it is displacing energy/water. Water is enrgy in its stored state.

    If the tidal gradient AKA space time is distorted as the water is around the air bubble and mass is in motion in the distorded region of the tidal gradient AKA space time then would the mass traveling through the distorted or curved region at a speed less than escape voloicity tend to travel into the center of the distortion?

    I can't see how Gravity could be an attractive force. Because all matter of different types have different attractive properties. It would seem Gravity would be the result of some type of inertia rather than an attractive force.
     
    Last edited: Dec 18, 2004
  9. Dec 18, 2004 #8
    It is not. Spacetime curvature describes the curvature of spacetime. It is not the spacetime itself.

    A bowling ball has more mass than a baseball. It is therefore attracted to the earth with a greater force than the baseball. The force accelerates the balls. The bowling ball has more mass though and therefore, even though the force wants to move it more the mass wants it to move less. However the baseball has less mass and therefore the gravitational force doesn't want it to move much. But it doesn't need to ask it much since it has less mass and is less resistant to the motion. It all winds up meaning that each body accelerates at the same rate.

    Its like this. In Newton's theory

    Gravitational force on a particle with mass m in uniform g-field is

    F = mg

    where g = acceleration due to gravity. The force is related to the mass by

    F = ma

    where a is the acceleration. Therefore

    F = ma = F = mg

    Thus a = g. Therefore the acceleration is independant of the mass.

    The same thing holds true in GR. Its just more complicated to explain in symbols.

    Pete
     
  10. Dec 18, 2004 #9
    Thank you so much for the reply and I am sorry for breaking of the forum rules. I will not do that again.

    This is so exciting to me because I have a dream of helping discover the properties of Gravity.

    I will study "frame dragging" thank you so much.
     
  11. Dec 18, 2004 #10
    Thank you so much for your reply. It is helping me to understand.
     
  12. Dec 18, 2004 #11

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    We already have multiple threads on this topic; this one in Special & General Relativity should be sufficient, so the others have been locked (and the one in GA&C merged here - thanks Garth and Labguy for your posts).

    Abstruce, I would also like to welcome you to Physics Forums. I would also like to reiterate Garth's post - please make sure that you read our guidelines and adhere to them - multiple postings are not permitted.

    Kind Regards
    Nereid
     
    Last edited: Dec 19, 2004
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?