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Mass creates Volumetric Space

  1. May 2, 2010 #1
    Hello everyone. I am new to the physics forum so bare with me. Thanks in advance.

    I would like to create a compelling argument for or against the title of this thread. To this end I would like to start with some questions about distance.

    How does the curve of space-time relate to the distance from the 'bottom' of the gravity well to the 'top'? Do we measure the curve itself? Do we draw a straight line underneath the curve, from the bottom of the well to the top? Or Do we start at the top and measure horizontally across till we are directly above the center of the well?

    Or, and I fear this is the most probable, is there a far more complicated method?

    (I am well aware that a gravity well's space-time curvature is more analogous to a Density, with the object of mass at the most dense center point. But I'm am using the common 'bowling ball depression' description to make the question's language more accessible.)

    I ask these questions to get an answer to weather space-time grows or stretches when bending. Considering the bowling ball on the bed, the bend that occurs pulls the sides of the bed inward resulting, in a topographical sense, with more area of bed existing around the bowling ball. Considering space does not have an 'edge of the bed' one could say then that space 'grows' around bodies of mass. The statement 'Mass creates space' does not fall easily on the ears of most knowledgeable physicists.

    I must restrain myself from asking anything more until the first few are underway. Please feel free to get technical.
  2. jcsd
  3. May 2, 2010 #2
    I would have to say mass does not create space. The 'curving' of spacetime is a description of the motion of an object near a gravitating body. It would follow a path given by the geodesic equation (which is a geodesic). I have never heard of space being a physical thing that can bend or distort in general relativity, but I think string theory considers space made of something physical (not sure about that, never studied strings). So I don't think there is actually anything to 'stretch' or 'create' from the GR point of view.

    I'm not sure what you mean by measuring the bottom to the top of a gravity well. The gravitational force extends to infinity so you would only have decreasing potentials and the geodesic would approach a straight line as you move farther away from the gravitational source. If you are wanting to measure the angle of deflection of the motion (not sure if that is what you were getting at), you may want to have a look at this page which shows a sample calculation of light bending around a star: http://www.mathpages.com/rr/s6-03/6-03.htm
  4. May 3, 2010 #3
    Excellent. After doing a little digging I came across a few additions to the discussion. First of all this:

    http://www.metaresearch.org/cosmology/gravity/spacetime.asp [Broken]

    Which ends with a harsh critique of Riemann. (ouch).
    Yet in all its argument against curved space it states "
    The extra bending [of light] is most easily explained as a refraction effect in the space-time or light-carrying medium ". Which seem extremely vague to me, and almost refers to a Aether. I thought we were all past that.

    And so I am brought to ask the super basic question :

    Why does light bend around objects of mass?

    Some people say that light's wave proprieties curve its path around objects. Some people say that the photons of light carry a small amount of mass and that mass interacts with the other object to curve the path.

    I ask this question to determine whether some property of light is responsible or if 'straight' lines are actually curved in the presence of mass.

    Furthermore, if one were to stand on the object of mass and measure the beam of light at this 'curved/bent' moment, does it appear curved or bent in this frame of reference. And if so, in what way?
    Last edited by a moderator: May 4, 2017
  5. May 3, 2010 #4


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    Staff: Mentor

    We are, at least the vast majority of professional physicists are. But you can find opponents to any theory, no matter how well established it is. Tom van Flandern, whose site you linked to, has been the subject of discussion here before. You might like to check out some of the threads that a Google search turns up:

    Last edited by a moderator: May 4, 2017
  6. May 8, 2010 #5
    Alright, now I know these graphs have their problems but I have to use it as a visual aid. This is in regards to the statement "Curved space is contained within curved space-time" and "mass curves the entire 4-dimensional manifold, both space and time".

    Simple question : In the below diagram of curved space-time, is the distance between A and B, shorter than the distance between C and D? (Assuming the only difference between the two relations is the space-time distortion between C and D)

  7. May 8, 2010 #6
    Not as simple as it seems as the picture depicts an Euclidean hyperspace, however spacetime is not an Euclidean hyperspace.

    Hint: think triangle inequality. :wink:
  8. May 11, 2010 #7
    Here is another way of asking this question.

    Lets say I am hanging out in 'free space' with no gravitation effects acting on me besides my self and a huge pile of gold. I decide to forge my pile of gold into a perfectly straight gold bar. To achieve such perfect straightness I use the very geodesic lines of the flat and perfect free space I am in. My straight gold bar is as perfect as can be.


    Let say I ship this gold bar to a place next to a very massive neutron star while I stay in "free space". I'm pretty worried about my perfect gold bar so I look over at it....


    Do I see any deformation of the image? Is the image deformed or is the bar deformed relatively to me in free space? Reasoning being that the bar is still aligning to the geodesics of the space that it is in, which has changed.
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