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Originally posted by Moduli
Jeeze, he obviously doesn't want your hand-holdy grade school differential calculus answers; clearly he meant he wants to see the full-blown differential geometric calculation, which he can accurately analyze with his advanced degree in math .
Originally posted by wirehead
Originally posted by Moduli
Jeeze, he obviously doesn't want your hand-holdy grade school differential calculus answers; clearly he meant he wants to see the full-blown differential geometric calculation, which he can accurately analyze with his advanced degree in math .
I would have loved to have derived the Friedmann metric from assumptions of isotropy and homogeneity, but I'm afraid I'm not yet familiar enough with general relativity!
Originally posted by Moduli
Pick up a copy of MTW from Amazon then .
Originally posted by wirehead
See my above post where I do exactly this. Unless you don't consider relativity to be experimentally validated? In which case I'd be happy to run down a quick history of its experimental validation and acceptance.
Originally posted by Angelic Resurrection
Originally posted by wirehead
See my above post where I do exactly this. Unless you don't consider relativity to be experimentally validated? In which case I'd be happy to run down a quick history of its experimental validation and acceptance.
Poppycock. Its only validated and accepted by people who want GR to reign indefinately
regardless.
Anyway you will keep going in circles over this
Originally posted by Moduli
And, you know, experiments. And field theory. And solid state physics, like the kind used to make your LCD screen, or hard drives, or ipad, or hundreds of other solid state devices. Oh, and all of electromagnetism, that's all relativistic, too. It's trivial to show that electromagnetism is contained in relativity.
Originally posted by wirehead
... and astronomical observations of classically occluded stars during an eclipse, decay of orbits due to gravitational waves, gravitational lensing, gravitational redshift, the recent observation of frame-dragging due to earth's rotation, time dilation of half-lives of cosmic ray particles, even the construction and operation of GPS satellites, and literally every replicable test of relativity conducted to date.
Okay. We can write the metric of space as ds^2 = -c^2 dt + a(t)^2 * (dr^2 + S(r)^2 do^2)
where a(t) is a variable scale factor, S is a curve parameterization (0 for flat space, +1 for positive curvature, -1 for negative curvature, depending on your model.)
dt, dr and do are the differentials of time, distance and angular size, respectively, which contribute to the distance measure ds.
You can write down equations describing the dynamics of the scale factor accordingly. By solving these equations, you'll then have your description of how space expands or contracts depending on the density and equation of state of the fields which inhabit the space. Then you can play around adding/subtracting matter, radiation, and a cosmological constant, and see how the universe behaves.
This is what Einstein called the Cosmological constant in his field equations. And this negative pressure, according to those same field equations (which have been so successful at describing gravitational effects), causes metric expansion.
Huh? Point literally any telescope at any galaxy besides Andromeda and you will verify the redshift.
edit: or do you take issue with the idea that light can be redshifted? This is observed in laboratories on earth on a daily basis.
Nobody is touting a theory as fact. These are the models which best fit the data and our understanding of physics, to date.
Evidence for dark matter can be found in galactic rotation curves, galactic dynamics within galaxy clusters, gravitational lensing of said clusters, microlensing which has recently been observed not even originating near luminous matter, and solutions to the Friedmann equations which result in a flat universe such as ours.
See my above post where I do exactly this. Unless you don't consider relativity to be experimentally validated? In which case I'd be happy to run down a quick history of its experimental validation and acceptance.
Originally posted by Aim64C
There are other theories with equal amounts of supporting evidence (not a huge qualifying mark) - many of which resolve the issue without the involvement of gravity gremlins.
Einstein's field equations do not define space as anything other than a metric derived from the propagation of light. It is treated as a derived (yet arbitrary) metric.
The problem is that this doesn't actually work to explain volumetric expansion of space. Applying special relativity, I can argue that a ball thrown into the air is experiencing the effects of volumetric expansion brought about by a dark energy as opposed to a physical force.
Originally posted by Aim64C
Doesn't really do much to explain how space expands - since you've not really defined space as anything other than the arbitrarily established units spanning two objects.
Originally posted by Aim64C
In this case: Movement results in spectral shifts of objects into longer and shorter wavelengths respective of receding or approaching emitters. Red shift is observed, therefor said objects are moving away.
Of course - this isn't volumetric expansion of space - this is spontaneous emission of energy from the zero point that can, at least in theory, react kinetically.
That's different than a physical alteration of space. Though when your only agreed upon concept of space is the distance between two points - there's obviously going to be debate over whether or not this constitutes an expansion of physical space or merely implied space.
Originally posted by ImaFungi
yupp thats my biggest problem,..,,.,.. if its not made of anything,,, it does not exist,,,,,
the surface of the earth can be curved because it is a 3d object,,, a shape,.,.,.. space is not an object or shape,.,.,.,
Originally posted by ImaFungi
ok,,, so lets say space is infinite,,,, beyond the current scope of the physical universe space "exists" in infinite directions in all directions for infinity,,..,,..,..,,.
the space between the items of the physical universe is arbitrary and only results from the physical properties, laws and forces of these physical bodies,, and how they react with each other..,.its the same "kind" of space that exists infinitely beyond the universe,,, its just that matter happens to be present in this area,,.,.,.
this is what i mean when i say space does not exist,,., or do you think that space,,, the space between the matter of the physical universe is unique in and of itself compared to space that may be surrounding the universe,,,,, and if so,,, would it only be unique because the properties it shows when we observe matter interacting at distances make it seem like there is more to the empty distance between celestial objects then; the absence of objects .,, ,,.
Originally posted by zeta55
I am not saying there is a central point on the outside of the baloon, where all the galaxies are moving away from each other. All I am saying is there is a central point inside the baloon, from which everything is moving away from 360 degrees.
Originally posted by ImaFungi
also i understand that space must exist,,,,, the distance between objects is real and true,,,,, but when i say space does not exist,,, im trying to understand if that distance is composed of anything,,,,, or is it thought like i think the big bang insinuates that the separating of matter is what draws this space/distance into "existence" for it is necessary for the matter to exist in the way matter exists and in turn the "nothingness" of space gains existence...edit on 8-7-2012 by ImaFungi because: (no reason given)
Originally posted by wirehead
So, the central point in the 3D balloon corresponds to a central point in 4D space, which means it has to be located not just in 3D space but in space and time. Therefore, it's not just a place but an event. The central point from which everything is expanding is located back in time.