What is in Space???

[Mordred]

Mwresearch, if you read my post, I never stated the Higgs field is the same as space time curvature. The Higgs field is a type of scalar field that can be described as a vacuum.Space time curvature is a vectoral Higgs does not replace gravity.

 

The FLRW metric is 100% compatible with the Einstein field equations. The FLRW metric does correlate energy density/pressure relationships via

 

[latex]w=\frac{\rho}{p}[/latex].

 

Every particle and interaction contributes to the above relation in combination, to derive the curvature constant k.

The acceleration equation also uses the same energy density/pressure relations.

 

http://en.m.wikipedia.org/wiki/Friedmann_equations

"from Einstein's field equations of gravitation for the FriedmannLemaîtreRobertsonWalker metric and a perfect fluid with a given mass density \!\rho and pressure \!p. The equations for negative spatial curvature were given by Friedmann in 1924"

 

The acceleration equation is the second one on that page

I thought pressure was force per unit area.

In 3d when you measure the area of a container your describing its volume.

Edited February 26, 2015 by Mordred

[MWresearch]

Perhaps this is just a matter of the interpretation of curvature. From my interpretation, if the mass density and pressure are high, this will not necessarily cause two light beams in opposite directions to converge specially whils holding the time evolution of the universe fixed and drawing a straight line, but only through the time-like closure of the universe wherein it eventually completely contracts after a certain amount of time. If it is put into terms of pressure, a photon should experience equal "pressure" from all sides which leave no net directional change.

Edited February 26, 2015 by MWresearch

[Mordred]

The main difference is in the scale, Gravity is localized, universe geometry is on the scale of the observable universe. Locally that curvature is negligible and impossible to measure. Key note in the latter case the change of energy density/ pressure is over time.

 

In point of detail it was measuring the CMB, in terms of refractive effects that finally allowed us to determine the universe geometry as flat.

 

 

If you look at the stress energy tensor formala above, whether curvature is due to energy/mass density or pressure is related. Energy density though is more accurate in terms of mass as non radiation and non relativistic matter, doesn't generate pressure. Ie slow moving matter.

 

However gravity can and does exert pressure, good example is our atmosphere. Without gravity there would be no difference in atmospheric pressure.

As you know the atmosphere causes refraction, The only difference between our atmosphere and the IGM intergalactic medium is the energy density and scale. Both can be described by vacuum density, with variations in vacuum density.

 

The cosmological constant for example is positive energy density with a negative vacuum EoS. (Some papers described this a negative gravity which is highly misleading,and inaccurate)

Edited February 26, 2015 by Mordred

[MWresearch]

Actually I am thinking it's possible that you were on the right, but that you didn't label your time axis in the diagrams. In a spherical universe, if you were to freeze time, two rays shot in opposite directions or parallel directions would not converge. Do you agree?

[Mordred]

Correct, the FLRW metric is homogeneous and isotropic so there is no change in energy/density/pressure at a specific point in time.

Edited February 26, 2015 by Mordred

[MWresearch]

Ok, then we are on the same page I just misinterpreted your diagrams.

[Mordred]

No prob, it's a good detail for other readers, much of the second page of the universe geometry page uses Barbera Rydens "Introductory to Cosmology" She does a masterful job of breaking down the FLRW metric, in terms of single to multi component toy universes.

(Even after studying close to 30 cosmology textbooks, hers is still my fav intro textbook)

[pavelcherepan]

When you think about the following statements.

 

1) mass is equivelent to energy (e=mc^2)

2) energy is a property of particles.

3) gravity only affects mass

4) space time is any metric coordinate system that includes time as a coordinate.

 

 

In regards to 3, what about mass-less photons? Probably a more correct way to put it would be to say "mass-energy" instead of just "mass".

 

Number 2 also sounds a bit strange to me. The way you put it, it seems like the particles are prime and the energy is just their property, but in fact it's the energy that's basic, right?

[swansont]

Number 2 also sounds a bit strange to me. The way you put it, it seems like the particles are prime and the energy is just their property, but in fact it's the energy that's basic, right?

 

No, it'w correct — energy is a property. It's not a "thing" unto itself.

[Mordred]

Photons follow the curvature geodesics However is not directly influenced by gravity.

 

Look under the photon interactions (electromagnetic)

http://en.m.wikipedia.org/wiki/Photon

Photons have no rest mass, but does have an energy mass equivelence.