Understanding Expansion of Space

[phinds]

By the way, I cannot wrap my head around the Big Bang Theory. A singularity by definition would be symmetrical. How do you explain a sudden explosion that would result in a chaotic background radiation pattern?

No, a singularity would, as has already been explained, be "the place where the math model breaks down". How you leap from that definition to a statement that it would be symmetircal, I do not understand.

 

[Anarion]

No, a singularity would, as has already been explained, be "the place where the math model breaks down". How you leap from that definition to a statement that it would be symmetircal, I do not understand.

So if I understand correctly, a singularity would contain all the information of a prior Universe?

 

[Drakkith]

By the way, I cannot wrap my head around the Big Bang Theory. A singularity by definition would be symmetrical. How do you explain a sudden explosion that would result in a chaotic background radiation pattern?

That's not how the big bang theory describes the very early universe. The CMB was the result of the universe become transparent after recombination, allowing light from the hot gas and plasma to finally propagate freely throughout the universe. The theory also says nothing about any singularity. That's simply the point that the model of the universe stops working, similar to how 1/x stops working if you try to insert 0 in for x. Whether a physical singularity actually existed at t=0 is unknown.

See post #25 in this thread and this article: https://en.wikipedia.org/wiki/Cosmic_microwave_background

So if I understand correctly, a singularity would contain all the information of a prior Universe?

No, not at all. A singularity is something in math where the rules suddenly break down. Like dividing by zero. You cannot get any useful information out of a singularity.

Everyone argues that space-time is flat or curved. What is it is like swiss cheese? Warped in ways we cannot see from a single vantage.

I understand that you are interested in the big bang theory and space and all, but we have rules in this forum which do not allow personal speculation. If you want to learn about the big bang theory then feel free to stay and to ask questions. If you want to propose ideas such as the one quoted, then you will need to find another forum. PF exists to teach people about mainstream physics, not to evaluate personal ideas.

 

[phinds]

So if I understand correctly, a singularity would contain all the information of a prior Universe?

You continue to avoid actually listening to the definition. As Drakkith has explained once again, "singularity" is just a word that stands for a longer phrase. That phrase is "the place where the math model breaks down and tells us NOTHING". You need to stop thinking of the "singularity" as standing from something real. Now it is true that SOMETHING was going on at t=0 but we have no idea what and "singularity" is just a word that expresses that lack of knowledge.

 

[rootone]

So if I understand correctly, a singularity would contain all the information of a prior Universe?

A singularity is not a physical object, it means conditions exist which our best theories and models cannot sensibly describe.
Like infinite density and zero volume, Infinite curvature, but zero distance.
Yes that means our models are not perfect and we don't know what is happening in extreme circumstances that we cannot observe.
However, engineers design a bridge using Newtons laws.
Using general relativity, accepted to be more accurate, would not result in a better bridge and would be needlessly time consuming.

 

[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"

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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 ...