# Is gravity inherent in mass? **URL:** \ **Category:** Factual Questions\ **Created:** [August 19, 2007, 5:01pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154 "2007-08-19T17:01:16Z")\ **Posts on this page:** 11\ **Page:** 3
**Author:** ![bob\_co](https://avatars.discourse-cdn.com/v4/letter/b/b3f665/32.png) [@bob\_co](https://boards.straightdope.com/u/bob_co)\ **Post date:** [August 22, 2007, 5:59am UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/41 "2007-08-22T05:59:52Z")
[QUOTE=Larry Borgia] [This might interest you.](http://en.wikipedia.org/wiki/Torsion_bar_experiment) [/QUOTE] I have not seen that before. Tip’o the hat to you. Now show me the anti-graviton 😉 It still seems to me that we are trying to expain something with a sub-atomic particle that just isn’t. I’ll be quiet now. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [August 22, 2007, 11:24am UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/42 "2007-08-22T11:24:38Z")
[QUOTE=Polerius] As a side note, can any of our resident physicists show us the equations for mass warping space? Maybe a two-dimensional space example to keep it simple? Or are they too complex? [/QUOTE] What you’re looking for are the [Einstein Field Equations](http://en.wikipedia.org/wiki/Einstein_field_equation), which can be more compactly summarized in the [Einstein tensor](http://en.wikipedia.org/wiki/Einstein_tensor), or more generally the [Ricci curvature tensor](http://en.wikipedia.org/wiki/Ricci_tensor). You’ll need to spend at least a couple of years studying at the graduate level before you can claim to really understand what’s going on with these. These represent a four dimensional spacetime mapped onto a pseudo-Riemannian (Lorentzian) manifold; a 2+1 dimensional spacetime would have a distinctly different treatment. Stranger ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 22, 2007, 11:32am UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/43 "2007-08-22T11:32:22Z")
[QUOTE=Chronos] Ah, gotcha. I hadn’t checked out that image before. While the specifics don’t really match, **Mangetout** does have the right idea that “curvature” represents a distortion in the distances between points. He just didn’t illustrate the right sort of distortion. [/QUOTE] Sorry, that was a limitation of the graphics package I used (and it was a quick-and-dirty job). ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 22, 2007, 11:33am UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/44 "2007-08-22T11:33:46Z")
[QUOTE=mr. jp] But after they pass the planet, they curve away again? [/QUOTE] Sorry, no. It’s a crappy illustration, that’s all. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [August 22, 2007, 2:37pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/45 "2007-08-22T14:37:01Z")
[QUOTE=Stranger On A Train] What you’re looking for are the [Einstein Field Equations](http://en.wikipedia.org/wiki/Einstein_field_equation), which can be more compactly summarized in the [Einstein tensor](http://en.wikipedia.org/wiki/Einstein_tensor), or more generally the [Ricci curvature tensor](http://en.wikipedia.org/wiki/Ricci_tensor). You’ll need to spend at least a couple of years studying at the graduate level before you can claim to really understand what’s going on with these. These represent a four dimensional spacetime mapped onto a pseudo-Riemannian (Lorentzian) manifold; a 2+1 dimensional spacetime would have a distinctly different treatment. [/QUOTE] And then you’ll need several more years of research studies to _actually_ understand them. I know from experience: good ol’ [Math 666](http://www.math.ohio-state.edu/courses/666), the quarter of hellish indices. 😃 ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [August 22, 2007, 5:21pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/46 "2007-08-22T17:21:22Z")
The idea of gridlines in warped space, and objects in motion drifting smoothly along the gridlines (which from the right viewpoint look curved), is misleading. The warping doesn’t happen in the 0th order of time, but rather in the first time derivative of space. If the gridlines were purely spatial, then something going past a planet would be redirected in the same direction regardless of its speed. But of course this isn’t the case - the faster something goes, the less its path changes. The first time derivative of space is an important system. The speed c is an absolute bound all the way around this system, and apparently has to be if causality exists (causality being the ability of causes to cause effects and the ability of effects to have causes). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 22, 2007, 5:32pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/47 "2007-08-22T17:32:01Z")
> [@](#): > > I know from experience: good ol’ Math 666, the quarter of hellish indices. Eh, it doesn’t get really bad until your superscripts and subscripts start getting superscripts and subscripts on them. Really, though, tensor math isn’t actually all that hard. A tensor equation is actually just a convenient way of lumping together a bunch of equations relating the components. Once you learn the tricks, you can work with four or sixteen or 64 equations at once just as easily as you could one at a time (provided that the variables have the right relationships among them to make tensors out of them, which many things in physics do). ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [August 22, 2007, 5:42pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/48 "2007-08-22T17:42:39Z")
[QUOTE=Stranger On A Train] Of course, there is not, to our knowledge, anything like negative gravity which pushes things away… [/QUOTE] Is it possible that it could be a negative gravity rather than a dark energy that is pushing the galaxy clusters apart? ---
**Author:** ![RiverRunner](https://avatars.discourse-cdn.com/v4/letter/r/977dab/32.png) [@RiverRunner](https://boards.straightdope.com/u/RiverRunner)\ **Post date:** [August 22, 2007, 5:44pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/49 "2007-08-22T17:44:56Z")
[QUOTE=Chronos] Once you learn the tricks, you can work with four or sixteen or 64 equations at once just as easily as you could one at a time (provided that the variables have the right relationships among them to make tensors out of them, which many things in physics do). [/QUOTE] That may be, but the longer I live the tensor I get. RR ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 22, 2007, 6:52pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/50 "2007-08-22T18:52:37Z")
[QUOTE=Liberal] Is it possible that it could be a negative gravity rather than a dark energy that is pushing the galaxy clusters apart? [/QUOTE] Probably not, because whatever force is acting to accelerate the expansion of the universe appears to become stronger with increasing distance. Negative gravity would decrease in strength by the inverse square law, just like normal gravity, only it would act in the opposite direction–pushing apart instead of pulling together. ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [August 22, 2007, 7:32pm UTC](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154/51 "2007-08-22T19:32:01Z")
Thanks, QED! 🙂 [Previous page](https://boards.straightdope.com/t/is-gravity-inherent-in-mass/416154.md?page=2)