Expansion of Universe

[ErnieM]

Mass is a basic property of all matters (baryonic and non-baryonic). Gravity is also an observed property of all matters. Taken together, they make all matters in the universe to attract and form structures from the atomic to the galactic levels. Between all matters, from the atomic to clusters of galaxies is a void and empty space. This space is observed expanding giving the impression specially at the galactic scale, that clusters of galaxies are "moving" away fast from "us" and and away from each other and that the rate of expansion is also increasing. 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? Is "space" uniform across the universe? 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?

[Chris Peterson]

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.

[ErnieM]

In reply to

Is "space" uniform across the universe?

Chris Peterson wrote

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.

Scientists have discovered "voids" in space and the biggest one so far is this
http://www.newscientist.com/article/dn1 ... cross.html

Do these voids also expand? If so, at what rate? Is the rate the same as the "space" containing matter (visible and dark matter)? What would it mean if the rate of expansion were found to be different?