[dlorde]

Interesting. But I didn't understand why space had to be expanding into another medium. Space is the medium. How can there be some other medium? Does not parse. 

Yes, that puzzled me too.

[yor_on]

Nah, or just maybe?
If you look at the universe as a equilibrium you can pick two choices, a dynamically changing equilibrium, or a static. If we now give a constant to a dynamically changing universe, will it not still be a constant? Assuming the universe have a constant balance.

the third assumption is one in where you have dynamically changing universe in where there can't be constants. But that is not what we see. So I think that link is wrong, if it assume "that Planck's constant is not a pure constant at all but a cosmological variable, a point for which some supported was reported in 2013 by Seshavatharam and Lakshminarayana."

My own outlook is that constants are here to stay, they are what define this universe.

[phyti39]

Universe (Latin) and cosmos (Greek) are interchangeable

Originally, I would agree, but I think the meanings have to some extent evolved.  See #116 in this thread.

#116
I think this might be less confusing if John Gribbin’s usage were followed:

Cosmos = everything that exists, or can exist.
Universe = our (in principle) observable portion of spacetime and its contents.
universe = any other universe that may, or may not, exist.

This looks more like semantics than science.
We can’t have complete knowledge of definition 1.
The observable universe and the perceptual universe (spacetime) are contained in def.1.
Definition 3 is redundant and meaningless.
The intended purpose of noting one Latin and the other Greek is to show they are different cultural variations for the same entity, all that is known to exist.

[chiralSPO]

I had originally posted this as a reply on another thread, but it probably belongs in this one:

"If the universe is actually globally homogeneous and isotropic, that means that each point is equivalent to every other point within the universe. This type of symmetry can easily be attained by a sphere, in which any point can be transformed into any other point by a simple rotation of the sphere. If we accept that the universe is flat, it cannot be spherical. A flat plane can also satisfy these conditions (homogeneous and isotropic), but only if it is infinite--in this case any point can be transformed into any other point by translation.

As a chemist, though, I have to point out that this is analogous to our theoretical models of crystals. There are 219 (or 230) space groups--the types of symmetry a crystal structure can have. In each there is an assumption that the entire crystal can be translated in one direction or another to line up with itself again. These models are extremely accurate in their predictions of the properties of all types of crystals. However, the models assume an infinite crystal lattice, which we know is not an accurate depiction of any crystal ever observed/characterized (most of those studied are less than 1mm on a side, >1000000 atoms across, though there are single crystals as large as a meter on a side, and possible even larger). It also turns out that while the models work very well at predicting what goes on inside a crystal, they are very poor models of the boundaries of crystals, which we invoke other models for.

My point is, from the viewpoint of an atom near the center of a crystal, the whole universe is an infinite perfect crystal--the model works perfectly as far as the atom can "see" and beyond. But eventually there is a boundary that is completely inexplicable given a perfect crystal model.

The observable universe appears to be flat, homogeneous and isotropic. But in my opinion, there could very well be inhomogeneity, anisotropy or curvature beyond our observable bubble."

[Bill S]

My point is, from the viewpoint of an atom near the center of a crystal, the whole universe is an infinite perfect crystal--the model works perfectly as far as the atom can "see" and beyond. But eventually there is a boundary that is completely inexplicable given a perfect crystal model.

The observable universe appears to be flat, homogeneous and isotropic. But in my opinion, there could very well be inhomogeneity, anisotropy or curvature beyond our observable bubble."

Interesting point.  We are assured that cosmology would be unworkable without these assumptions, so I suppose it is reasonable to make them, and work with them.  Perhaps trouble comes only when peoples forget that they are assumptions and start treating them as if they were established facts.   

[alancalverd]

Cosmos = everything that exists, or can exist.
Universe = our (in principle) observable portion of spacetime and its contents.
universe = any other universe that may, or may not, exist.

Definition 3 is redundant and meaningless.

Not at all. 1 is the set of all sets, 2 is the finite set bounded by  the Schwarzchild limit, 3 is (1 - 2).

[allan marsh]

If there is zero then there must inevitably be infinity
It took the Romans and those with runic tools to produce zero
Now it is 2014 and infinity is real

[Bill S]

If there is zero then there must inevitably be infinity

I'm not sure that I follow the logic of that.

[chiralSPO]

I agree. Zero (absolute zeros) and infinity go hand in hand.

[Ethos_]

I agree. Zero (absolute zeros) and infinity go hand in hand.

I agree as well.........................And backtracking to earlier posts about nothingness, what else is nothingness but Zero? When one visualizes the "Universe" as finite, then that "nothingness" which lies beyond being nothingness is also part of the "Cosmos". Where the "Universe" is finite, the "Cosmos" is infinite.

[alancalverd]

It's true that zero and infinity are associated, since 1/x→∞ as x→0.

But I don't think the Romans had a useful concept of zero. This seems to have arrived from India via Arabic mathematicians, who had a symbol for zero, that is lacking in Roman numerals.