Understanding Expansion of Space

[Tom Mcfarland]

Drakkith writes: "distance between objects simply increases". Translation (?) "the measuring stick (metric) reads more units of distance"
Those extra units either come from the expansion of existing units (that is, "dilation") or they don't ("insertion of new units"). There is
no other alternative, logically. But "dilation" must also expand the measuring stick, so no change would be noticed. I have googled
"metric expansion" but I still see a logical problem

 

[Drakkith]

Those extra units either come from the expansion of existing units (that is, "dilation") or they don't ("insertion of new units"). There is
no other alternative, logically.

Sure there is. The other alternative is that the objects move away from each other. The units neither dilate nor are any extra ones inserted, just like how our units of measurements don't change nor are any inserted just because the pizza guy walks back to his car after delivering my pizza. This is perfectly valid in General Relativity and Cosmology.

. I have googled
"metric expansion" but I still see a logical problem

Then I suggest getting into the details of the math and learning how GR and the standard model of cosmology work.

Below are a few links. Don't be afraid to get lost in them!
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html
https://www.preposterousuniverse.com/grnotes/

Drakkith writes: "distance between objects simply increases". Translation (?) "the measuring stick (metric) reads more units of distance"

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[Tom Mcfarland]

Drakkith:

I am sorry for not being clear. Thank you for your patience.

I was commenting on the expansion of space itself, not the changing relative positions of objects within that space.

I still see the same logical problem, but I will follow your advice and check out the existing models through your links, rather than trouble you further with my naïveté. I do worry that the models might be beautiful formulations of a flawed paradigm.

Sleep well !

 

[Drakkith]

I was commenting on the expansion of space itself, not the changing relative positions of objects within that space.

I know, and that's what I'm attempting to address. The expansion of space has nothing to do with space being created or "space itself" expanding, it has to do with the way that the positions of objects relative to other objects change over time. We can't measure the position of an object relative to some arbitrary location in space without something physically being there (or at least having once been there to cause something observable, like a light pulse from an accelerated particle).

 

[Torbjorn_L]

I got this in my mail box since I commented here ... oh, so long ago. A quick update is that singularities and inflation have been discussed.Irrelevant nitpicking first: Drakkit and phinds claim that singularities would give us no information. This is a fact in physics (signaling theory breakdown), but not in mathematics. (If memory serves, some singularities are sufficiently well behaved to give you one bit of information.)Maybe more interesting: rootone, phinds and Chronos claim that inflation is a hypothesis that is considered most likely to explain the evidence. More precise I hope is that the current standard cosmology, as given by the Planck archive papers, include an inflation like era (that would be the general theory part) and that an inflation field (that would be the specific hypothesis part) has passed a handful of tests but not one outstanding of resulting in - hopefully observable in the cosmic background radiation - primordial gravitational waves. It is hard to know from the literature, but Simon Foundation's Quanta site has described inflation as most popular theory and winning terrain despite the outstanding test. (Maybe those opposed fall aside from age, that is not unheard of?) Chronos claims that it would foster the notion that the universe must be finite, but I do not understand how as it is not an implication (rather the opposite I think, since eternal inflation seems to be a natural ground state of the quantum field) and the opposite hypothesis of an infinite universe is ever more spoken of. Maybe Chronos is thinking of the local out-of-inflation universe?So to the current question of how space expands. Maybe the confusion stems from conflating units with scaling? Cosmologist Susskind has several video series of lectures on the Stanford University site. As I remember it, he describes how cosmologists use a unit-less scale factor to describe increasing (as it were) or decreasing cosmological volumes in relation to unit-full coordinate points of (sufficiently gravitationally unbound) galaxy clusters. At one point in one series he deliberately describes how expansion would in principle insert more “standard unit” separated coordinate points as expansion proceeds.That would describe the involved equations I think, and map to the descriptions of volume increase (or coordinate point insertion). But it would not tell us much on what space is. Adding special relativity would tell us how space and time is related by light cone physics defined by the universal speed limit. And adding general relativity and thermodynamics would tell us that tilting those light cones into closed time-like curves does not seem to make sense, telling us either thermodynamics or general relativity is incomplete (and we already know the latter is). Space of general relativity, already a somewhat unfamiliar system, is not easily grokked it seems to me (who as already noted up thread has never studied it), and that is before we insert it into cosmology and gets the addition of universal quantum fields of the vacuum at various eras ...