Advanced Concepts of Gravity

Excerpt from Atoms to X-Rays: Cosmic Voyages through Computer Simulation and Visualization. [Show ID: 14995]

Category:

Education

Tags:

• science
• gravity
• education

[BaronVonLichtenstein]

I don't know. If there is really such a thing as gravity, how come fat chicks aren't surrounded by thin guys?

[Tetrodioxide]

Yes, it has to do with quantum gravity, but not directly. This is a large-scale consideration, and what it shows is how there would be local clustering of matter initiated by simply displacement. This explains how we then get the localized structures of galaxies, stars, and so on from an initially homogenious universe from displacemnts. What caused these initial local concentrations though?: Quantum flucations in the early universe, which influenced local space as the universe expanded.

[Oxyster7]

@BaronVonLichtenstein fat white chicks are surrounded by skinny black dudes. Perhaps they have different gravitational properties?

[AlgeKalipso]

This is so slow and trivial. I go to Stanford and classes are way faster, at least five times.

[CACBCCCU]

@mindgrapes

I understand. Ignoring anything hypothetically antigravitational about so-called empty space, such as the CC, if all the distances between the mases shrink together, no mass is favoring one side over the other, for a closed ring or an infinite line. Ignoring edge effects, a sufficiently long line would suffice to show the same thing somewhat, but basically the idea seems like a dead end of positively metaphysical proportions and, if so, I'd prefer a +/- mass checkerboard array.

[mindgrapes]

@CACBCCCU OK, well I totally agree with that. But I think that would hold true regardless of whether you took a Newtonian or Einsteinian view of gravity. My original posting was intended to criticize the Newtonian idea (articulated by this lecturer) that if there is an infinite symmetry of gravitational forces the universe wouldn't collapse. I'm arguing, and I think this is implied by GR, that this is not the case (absent a cosmological constant, of course).

[CACBCCCU]

@mindgrapes

What I mean by "nothing to break the symmetry" is that since all the particles appear simultaneously, each of their gravity fields begins expanding and overlapping identically and simultaneously. Because the entire particle distribution is supposed to be symmetrical around every particle it seems evident that all the expanding fields must also be symmetrical around every particle. I guess that's the simplest way I can describe it.

[mindgrapes]

@CACBCCCU Taking your points in reverse order: I *think* the cc does not in itself imply any particular geometry of the universe, as its value would have to be derived observationally. But this is a bit off the original topic...

I'm not sure i followed you with "there's still nothing to break the symmetry" - could you elaborate plz?

My point with the thought experiment was just to avoid any potential confusions introduced by actual observations of the universe

[CACBCCCU]

@mindgrapes It's a strange problem, I'm not sure what the point of it is. Making all the masses appear simultaneously out of nothing doesn't make it any stranger though, I think the result would still be the same. Seems there's still nothing to break the symmetry. FWIW, I'm told Einstein initially thought the universe was infinite, so when he first came up with the cosmological constant it's not clear to me whether it was to keep the universe from collapsing or to give it large-scale flatness.

[mindgrapes]

@CACBCCCU Hmm, ok counterfactual. Suppose an infinite universe of evenly distributed point masses were poofed into existence. My thinking was that because gravity takes time to act over distances, the masses will behave effectively as if they were in a finite distribution, and collapse into each other. Writ large, i suppose you could say the universe remains infinite, but that infinity gets smaller as everything contracts...

Are we saying the same thing in different ways?

[CACBCCCU]

@mindgrapes Seems it couldn't be lightspeed limit if nothing is moving in the first place. I'd say it has to do with Einsteinian gravity's "curving" of spacetime, which I'd call a "positive" or "negative" curvature depending on perspective. In any event it makes hypersurfaces sperical (recall the balloon with dots painted on it model of the universe), not ultimately flat. Einstein's GR universe was "unbounded, but finite" not infinite.

[JohnnieNaked]

@BaronVonLichtenstein Fatness is repellant!