Understanding Expansion of Space

[Monsterboy]

http://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html
I need someone to clarify the below point on the drawbacks the Big bang theory

•The Horizon Problem:
distant regions of space in opposite directions of the sky are so far apart that, assuming standard big bang expansion, they could never have been in causal contact with each other. This is because the light travel time them exceeds the age of the universe. Yet the uniformity of the cosmic microwave background temperature tells us that these regions must have been in contact with each other in the past.

Have we really found out any distant galaxies or clumps of matter which satisfies the highlighted point ?

 

[phinds]

http://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html
I need someone to clarify the below point on the drawbacks the Big bang theoryHave we really found out any distant galaxies or clumps of matter which satisfies the highlighted point ?

I don't understand your question. As far as I am aware ALL distant galaxies (when you go out far enough) satisfy the bolded statement so why would you ask if any do? In what way do you see this as a drawback to the Big Bang Theory?

 

[Monsterboy]

I don't understand your question. As far as I am aware ALL distant galaxies (when you go out far enough) satisfy the bolded statement so why would you ask if any do?

You mean we have observed galaxies so far away that they simply could not have been together 13.7 billion years ago and yet we stick to the model because we have no other choice right now ?

 

[Monsterboy]

In what way do you see this as a drawback to the Big Bang Theory?

It is given as one of the drawbacks in the link i provided.

 

[Monsterboy]

Oops sorry I messed up, I didn't read the whole page the later part of the page does explain how inflation theory does get rid of the drawbacks.

 

[rootone]

Inflation is the most popular explanation for this discrepancy,
https://en.wikipedia.org/wiki/Inflation_(cosmology)
The idea works well, but however it's still really just a hypothesis.
Maybe future technology will allow us to see further back in time than the CMB, and then the hypothesis might be validated.

 

[phinds]

You mean we have observed galaxies so far away that they simply could not have been together 13.7 billion years ago

We observer the CMB and observe its uniformity to 1 part in 100,000 and draw the inescapable conclusion that things farther away than the most distant galaxies we can observer must have been in contact at some point to reach such amazing thermodynamic equilibrium.

and yet we stick to the model because we have no other choice right now ?

No, we stick to the model because it explains all available evidence. That's what we always do in science. Inflation is considered the most likely way for the thermodynamic equilibrium to have occurred but since the Big Bang Theory does not start until AFTER inflation, the fact that inflation is not an establish fact has no impact on the BB Theory.

 

[Monsterboy]

I got confused with the terms "The Big Bang theory" and "Standard big bang theory " , only the former includes inflation right ?

 

[phinds]

I got confused with the terms "The Big Bang theory" and "Standard big bang theory " , only the former includes inflation right ?

No, as I specifically stated, the Big Bang Theory starts at the end of inflation (assuming it even existed) and goes from there. I don't understand the distinction you are making between two seemingly identical terms.

 

[Monsterboy]

No, as I specifically stated, the Big Bang Theory starts at the end of inflation (assuming it even existed) and goes from there. I don't understand the distinction you are making between two seemingly identical terms.

Yea thanks , all this time I thought inflation theory was the early part of the big bang theory hence all the confusion , well I guess this is what happens when all your knowledge of cosmology comes from science documentaries and website articles.

 

[phinds]

Yea thanks , all this time I thought inflation theory was the early part of the big bang theory hence all the confusion , well I guess this is what happens when all your knowledge of cosmology comes from science documentaries and website articles.

I had EXACTLY the same problem/belief until quite recently when @PeterDonis kindly set me straight, as he so often has to do w/ my uninformed ramblings

 

[Chronos]

Under the laws of thermodynamics, the CMB could never have reached thermal equilibrium across the entire sky without being in causal contact at point in the history of the universe. Inflation solves this problem because the light travel time limit is relaxed. This, however, leads to other sillines like computing the allowable size of the observable universe at the onset of inflation - which fosters the unfounded notion the universe must be finite.

 

[Tom Mcfarland]

I am new to this forum, so please forgive me if I am not behaving properly.
What I read above, regarding the expansion of space, sounds like the insertion
of additional space rather than "expansion". Which is being proposed?

That is, "expansion of space between A and B" would dilate of the path,
including the dilation of any measuring units such as parsecs or light years.
An observer would never notice the dilation.

The "insertion of additional space" between A and B would leave the measuring
units unaltered. An observer would notice the insertion. For example, if the
initial state was "AB" and I insert space to "A B", you notice it. If I merely
type AB using a bigger font (that is, dilate), nothing seems changed.

 

[phinds]

I am new to this forum, so please forgive me if I am not behaving properly.
What I read above, regarding the expansion of space, sounds like the insertion
of additional space rather than "expansion". Which is being proposed?

That is, "expansion of space between A and B" would dilate of the path,
including the dilation of any measuring units such as parsecs or light years.
An observer would never notice the dilation.

The "insertion of additional space" between A and B would leave the measuring
units unaltered. An observer would notice the insertion. For example, if the
initial state was "AB" and I insert space to "A B", you notice it. If I merely
type AB using a bigger font (that is, dilate), nothing seems changed.

Google "metric expansion" and check out the link in my signature.

 

[Drakkith]

I am new to this forum, so please forgive me if I am not behaving properly.
What I read above, regarding the expansion of space, sounds like the insertion
of additional space rather than "expansion". Which is being proposed?

Neither "insertion" nor "dilation" takes place. The distance between objects simply increases over time. Space is not a substance and trying to model it as something that can be created and inserted is... problematic. One might then be required to treat a ball falling to the Earth as the removal or deletion of space between the ball and the Earth.

 

[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"

To quote, you can click the "Reply" button at the bottom right of any post to immediately place the entire post in the reply box. You can also click the +Quote button to add it to a que of posts that you can then add to the reply box all at once by clicking Insert Quotes at the bottom left of the reply box (only shows up if you have posts in the quote que). You can also highlight text inside of a post and a small popup should appear containing the Reply and +Quote buttons.

 

[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 ...