ErnieM wrote:Mass is a basic property of all matters (baryonic and non-baryonic). Gravity is also an observed property of all matters.
Gravity is not a property of matter, but a consequence of how matter affects spacetime.
Given that these galaxies, including the Milky Way, within a cluster orbit one another from their respective cluster's gravitational center. Completing a revolution takes millions of our years or hundreds of human generations. The observation data on which astronomers are extrapolating their conclusions is less than a generation. How definitive are these conclusions?
Extremely definitive. We don't examine the expansion of space by how much things have moved (which would be nearly impossible in the short time we've been observing), but by the rate of expansion we can measure.
Is "space" uniform across the universe?
I'm not sure what exactly you mean by that. Certainly, there is no indication that any regions of space have different properties than others, or that physical laws are different in different places.
At what direction are the points of references moving relative to the cluster's orbital paths and each other? Is is not conceivable, even probable that there reference points (sources of red shifts) are in their natural orbital expansion stages hence giving the "appearance" the whole universe is expanding?
We see ONLY redshifts for distant objects, and the redshift increases with distance. Surely, if what we observe were a consequence of some sort of orbital motion, we should see blueshift as well?
If everything we look at is redshifted, it means everything is moving away from us, and away from each other. When this observation was first made, it was thought that this was actually a Doppler phenomenon. But current theory suggests it is caused by spacetime expansion- an explanation that fits better with observation than Doppler motion.
[quote="ErnieM"]Mass is a basic property of all matters (baryonic and non-baryonic). Gravity is also an observed property of all matters.[/quote]
Gravity is not a property of matter, but a consequence of how matter affects spacetime.
[quote]Given that these galaxies, including the Milky Way, within a cluster orbit one another from their respective cluster's gravitational center. Completing a revolution takes millions of our years or hundreds of human generations. The observation data on which astronomers are extrapolating their conclusions is less than a generation. How definitive are these conclusions?[/quote]
Extremely definitive. We don't examine the expansion of space by how much things have moved (which would be nearly impossible in the short time we've been observing), but by the rate of expansion we can measure.
[quote]Is "space" uniform across the universe?[/quote]
I'm not sure what exactly you mean by that. Certainly, there is no indication that any regions of space have different properties than others, or that physical laws are different in different places.
[quote]At what direction are the points of references moving relative to the cluster's orbital paths and each other? Is is not conceivable, even probable that there reference points (sources of red shifts) are in their natural orbital expansion stages hence giving the "appearance" the whole universe is expanding?[/quote]
We see ONLY redshifts for distant objects, and the redshift increases with distance. Surely, if what we observe were a consequence of some sort of orbital motion, we should see blueshift as well?
If everything we look at is redshifted, it means everything is moving away from us, and away from each other. When this observation was first made, it was thought that this was actually a Doppler phenomenon. But current theory suggests it is caused by spacetime expansion- an explanation that fits better with observation than Doppler motion.