early on, Gravity was radically non-Newtonian ??

[Widdekind]

The Schwarzschild solution, whose low-mass limit is Newtonian Gravity, assumes an infinite, flat, spacetime, which is then perturbed by the addition of a spherically symmetric mass. In analogy, it assumes an infinite flat trampoline, or infinite flat rubber sheet.

 

Now, that assumption is not inaccurate, in our current Cosmos, whose Radius of Curvature is 10s Gly's, so that space is almost flat. But, what about shortly after the Big Bang, when spacetime was highly curved ? If spacetime is cosmically closed, into a 3D hypherspherical shell, then, in the early universe, deviations of spacetime, from 'infinite & flat', could have caused deviations, from Schwarzschild-Newtonian Gravity, yes?

[timo]

No one describes the universe as a whole via a Schwarzschild metric. Neither at the current state, nor in the early universe.

Edited April 15, 2011 by timo

[IM Egdall]

Now, that assumption is not inaccurate, in our current Cosmos, whose Radius of Curvature is 10s Gly's, so that space is almost flat.

 

Universe is "almost" flat? Is there a link to this info?

[csmyth3025]

Universe is "almost" flat? Is there a link to this info?

I'm not sure where Widdekind got a present radius of curvature for the universe of 10's of Gly's. If the CMB is considered the limit of the present comoving distance to the edge of the observable universe, then the observable universe today spans a radial comoving distance from the Earth of about 45.7 Gly (about 91.4 Gly in diameter).

(ref. http://en.wikipedia....rvable_universe )

 

According to WMAP data, the CMB indicates that the universe is "almost flat" (flat, +/- 2%):

The WMAP spacecraft can measure the basic parameters of the Big Bang theory including the geometry of the universe. If theuniverse were open, the brightest microwave background fluctuations (or "spots") would be about half a degree across. If theuniverse were flat, the spots would be about 1 degree across. While if the universe were closed, the brightest spots would beabout 1.5 degrees across.

 

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO,Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was knownto be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracyand precision. We now know that the universe is flat with only a 2% margin of error.

 

(ref. http://wmap.gsfc.nas...AP_Universe.pdf - "Shape of the universe")

 

Chris

[csmyth3025]

As a follow-up to my last post, I take it that if the observable universe has negative curvature (-2% lower WMAP limit), then it would be hyperbolic and "open". The so-called "saddle" topography.

 

If the observable universe has positive curvature (+2% upper WMAP limit), then it would be essentially spherical and "closed". In this case the universe would, indeed, have a radius of curvature. Is there is any way to calculate the radius of curvature of the observable universe based on this (+2%) upper limit of the WMAP data?

 

Chris

[Widdekind]

As a follow-up to my last post, I take it that if the observable universe has negative curvature (-2% lower WMAP limit), then it would be hyperbolic and "open". The so-called "saddle" topography.

 

If the observable universe has positive curvature (+2% upper WMAP limit), then it would be essentially spherical and "closed". In this case the universe would, indeed, have a radius of curvature. Is there is any way to calculate the radius of curvature of the observable universe based on this (+2%) upper limit of the WMAP data?

 

Chris

 

I tried to derive the relevant equations in this thread.