The universe is expanding.....

[julius2]

What is the point of reference?

 

 

[MigL]

If you have a line with points on it 1 unit apart, and then expand the separation between the points to 2 units, it has expanded.
If you have a balloon with points on it 1 unit apart, and then blow up the balloon such that the points are 2 units apart, it also has expanded.
If you have a cubic crystal lattice where atoms are at points on a cube 1 unit apart, and then expand the separation between atoms to 2 units, it also has expanded.

In one dimension, 2 dimensions or 3 dimensions, the expansion is observed equivalently from every point.
IOW, every point is an equivalent reference, and unfortunately, you don't understand expansion.

[iNow]

https://hubblesite.org/mission-and-telescope/hubble-30th-anniversary/hubbles-exciting-universe/measuring-the-universes-expansion-rate

[julius2]

1 hour ago, iNow said:

https://hubblesite.org/mission-and-telescope/hubble-30th-anniversary/hubbles-exciting-universe/measuring-the-universes-expansion-rate

This is a very good article.

It is interesting how they try to calculate the Hubble constant - expansion rate. One book by Kaku mentioned that the universe was accelerating at an increasing rate and would somewhat approach a "runaway" problem.

Interesting that your article mentions that there was an implication that the universe is younger than the age of the Earth. Logically speaking this would result in a "false" result. But the "wording" of this, I actually agree with. In other words we don't understand the science exactly perfectly.

It is also interesting about the "error factors". So you can estimate the age of the universe to be 9.7 billion years or up to 19.5 billion years. In other words there seems to be some contention about the age of the universe, meaning that the calculation for the age is up for DEBATE.

It seems that the point of reference we use is us here on Earth. Is it possible to use another point of reference? E.g. would our result change if we picked an arbitrary star out there as the point of reference?

1 hour ago, MigL said:

If you have a line with points on it 1 unit apart, and then expand the separation between the points to 2 units, it has expanded.
If you have a balloon with points on it 1 unit apart, and then blow up the balloon such that the points are 2 units apart, it also has expanded.
If you have a cubic crystal lattice where atoms are at points on a cube 1 unit apart, and then expand the separation between atoms to 2 units, it also has expanded.

In one dimension, 2 dimensions or 3 dimensions, the expansion is observed equivalently from every point.
IOW, every point is an equivalent reference, and unfortunately, you don't understand expansion.

I agree surfaces can be more difficult to understand than a simple straight line.

[iNow]

8 hours ago, julius2 said:

Is it possible to use another point of reference?

yes

8 hours ago, julius2 said:

would our result change if we picked an arbitrary star out there as the point of reference?

no

[swansont]

11 hours ago, julius2 said:

What is the point of reference?

Doesn't matter; the expansion is not from a single point.  

We use the earth because that's where we are.

[julius2]

4 hours ago, swansont said:

Doesn't matter; the expansion is not from a single point.  

We use the earth because that's where we are.

I like what MigL wrote above.

Expansion is not that simple. He gave examples using different "volume" definitions.

5 hours ago, iNow said:

yes

no

Okay, so we agree that we could use another point of reference.

I guess when science literature says that the universe is expanding, they mean us (people) see it expanding as we stand on the Earth.

Is Earth the best viewpoint from which to make the expansion assessment.

From literature I have read, research has been able to use sophisticated techniques regarding geometry. For example combining multiple radio telescopes on Earth from which to "see" deeper in to the universe.

[Mordred]

Due to the Cosmological principle and the homogeneous and isotropic expansion no point of reference has any preference for showing expansion.

 It might be easier to understand expansion as a decreasing energy/density. This should lead you to the FLRW metric acceleration equations and the relevant equations of state for radiation, matter and Lambda.

The rate of volume change are determined by that equation. In essence the FLRW metric treats the universe as a perfect fluid with adiabatic and isentropic expansion.

Should also indicate another piece of evidence of expansion (density changes and CMB blackbody temperature changes.) 

Edited July 29 by Mordred

[swansont]

1 hour ago, julius2 said:

Is Earth the best viewpoint from which to make the expansion assessment.

As I said, we use the earth because that’s where we are. That makes it best purely from a practical standpoint, much like choosing a particular frame of reference makes it easier to solve a problem. You won’t get a different answer by using another frame, as Mordred notes above.