How big is the universe?

[steve_bank]

The finite speed of light ensures there may be light of disant events we can not see.

https://en.wikipedia.org/wiki/Big_Bang


Expansion Of Space
General relativity describes spacetime by a metric, which determines the distances that separate nearby points. The points, which can be galaxies, stars, or other objects, are themselves specified using a coordinate chart or "grid" that is laid down over all spacetime. The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the Friedmann–Lemaître–Robertson–Walker metric (FLRW metric). This metric contains a scale factor, which describes how the size of the universe changes with time. This enables a convenient choice of a coordinate system to be made, called comoving coordinates. In this coordinate system, the grid expands along with the universe, and objects that are moving only because of the expansion of the universe, remain at fixed points on the grid. While their coordinate distance (comoving distance) remains constant, the physical distance between two such co-moving points expands proportionally with the scale factor of the universe.[42]

The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two comoving points. In other words, the Big Bang is not an explosion in space, but rather an expansion of space.[7] Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our universe only on large scales—local concentrations of matter such as our galaxy are gravitationally bound and as such do not experience the large-scale expansion of space.[43]

Horizons
An important feature of the Big Bang spacetime is the presence of particle horizons. Since the universe has a finite age, and light travels at a finite speed, there may be events in the past whose light has not had time to reach us. This places a limit or a past horizon on the most distant objects that can be observed. Conversely, because space is expanding, and more distant objects are receding ever more quickly, light emitted by us today may never "catch up" to very distant objects. This defines a future horizon, which limits the events in the future that we will be able to influence. The presence of either type of horizon depends on the details of the FLRW model that describes our universe.[44]

Our understanding of the universe back to very early times suggests that there is a past horizon, though in practice our view is also limited by the opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to accelerate, there is a future horizon as well.[44]

 

[T.G.G. Moogly]

Does the BB actually yield a finite size?

At the time of the event there was no center point. Observation says galaxies are moving awy from each other not diverging from a central point.

No matter what observational point you pick the belie is the observation will be the same. Things are spreading out from each other.

And that expansion rate is increasing.

Years ago I made the suggestion that our Universe is a bubble, that most of the matter is not floating around inside the bubble but is the bubble itself. As matter inside the bubble gets closer to the outside it accelerates due to gravity and some interaction with the curvature, like foam in a cup of coffee heads toward the edge where the cup meets the surface of the coffee.

Can't explain dark matter though.

 

[steve_bank]

Does the BB actually yield a finite size?

At the time of the event there was no center point. Observation says galaxies are moving awy from each other not diverging from a central point.

No matter what observational point you pick the belie is the observation will be the same. Things are spreading out from each other.

And that expansion rate is increasing.

Years ago I made the suggestion that our Universe is a bubble, that most of the matter is not floating around inside the bubble but is the bubble itself. As matter inside the bubble gets closer to the outside it accelerates due to gravity and some interaction with the curvature, like foam in a cup of coffee heads toward the edge where the cup meets the surface of the coffee.

Can't explain dark matter though.

It was discovered observational details did not match the model based on our science. To correct the model dark matter was coined to compensate. What dark matter 'is' is unknown. It is seen as an effect.

I understand the metaphors, but the idea of being inside and outside the universe makes no sense to me. The bubble concept to me implies a bubble within a greater universe.

 

[SLD]

I vote for an infinite/eternal multiverse.

I do too, but that’s a different debate.

SLD

Well, if what we call the universe is actually a part of a far larger system, a multiverse...our universe is not a universe at all. It is the multiverse that is the universe and our little part of it is merely an infinitesimal bubble.

Fair enough, but my question relates to the size of our little bubble. The multiverse is indeed infinite, but that’s not my question. I’m trying to understand the present size of all the matter that came out of the Big Bang 13.6 billion years ago. Not other big bangs.

https://www.space.com/24073-how-big-is-the-universe.html

This article says it’s at least 250 times the observable universe, or 7 trillion light years in diameter. Or it could be 10^23 light years in diameter. And it only appears flat because it’s so much bigger than the observable universe. That’s quite a range. I would think that if the universe were merely 7 trillion light years, we could detect at least some definite curvature.

SLD

 

[Jokodo]

Well, if what we call the universe is actually a part of a far larger system, a multiverse...our universe is not a universe at all. It is the multiverse that is the universe and our little part of it is merely an infinitesimal bubble.

Fair enough, but my question relates to the size of our little bubble. The multiverse is indeed infinite, but that’s not my question. I’m trying to understand the present size of all the matter that came out of the Big Bang 13.6 billion years ago. Not other big bangs.

And once again, there is no knowing that it is finite.

https://www.space.com/24073-how-big-is-the-universe.html

This article says it’s at least 250 times the observable universe, or 7 trillion light years in diameter. Or it could be 10^23 light years in diameter.

Or it could be infinite

And it only appears flat because it’s so much bigger than the observable universe. That’s quite a range. I would think that if the universe were merely 7 trillion light years, we could detect at least some definite curvature.

And how do you suggest we do that?

Detecting the curvature of the earth is easy: With a curved 2d surface in 3d space, there's one direction (up/down) that's very much not like the others, and all you have to do is find that different places' "up" are not parallel. I don't see any analogous and comparably easy way to detect the curvature of space in a universe where all directions are equal.

 

[SLD]

And once again, there is no knowing that it is finite.

https://www.space.com/24073-how-big-is-the-universe.html

This article says it’s at least 250 times the observable universe, or 7 trillion light years in diameter. Or it could be 10^23 light years in diameter.

Or it could be infinite

And it only appears flat because it’s so much bigger than the observable universe. That’s quite a range. I would think that if the universe were merely 7 trillion light years, we could detect at least some definite curvature.

And how do you suggest we do that?

Detecting the curvature of the earth is easy: With a curved 2d surface in 3d space, there's one direction (up/down) that's very much not like the others, and all you have to do is find that different places' "up" are not parallel. I don't see any analogous and comparably easy way to detect the curvature of space in a universe where all directions are equal.

The typical way is by looking at the CMB. Here’s one article suggesting a positive curvature from Planck data. https://arxiv.org/abs/1502.01589

And yes, it could be infinite, but I’m skeptical.

SLD

 

[Jokodo]

And once again, there is no knowing that it is finite.



Or it could be infinite



And how do you suggest we do that?

Detecting the curvature of the earth is easy: With a curved 2d surface in 3d space, there's one direction (up/down) that's very much not like the others, and all you have to do is find that different places' "up" are not parallel. I don't see any analogous and comparably easy way to detect the curvature of space in a universe where all directions are equal.

The typical way is by looking at the CMB. Here’s one article suggesting a positive curvature from Planck data. https://arxiv.org/abs/1502.01589

That's not what the article suggests. Quite the contrary: They find that their best estimate for the curvature is 0.000 ± 0.005, it even says so in the abstract: "Spatial curvature is found to be |Omega_K| < 0.005"

 

[DrZoidberg]

I vote for an infinite/eternal multiverse.

Why? Why bother having an opinion on something nobody could possibly know? We all know you're just guessing. Anybody having an opinion is just having a more or less qualified guess, with a massive error margin. But we're all just guessing.

My money is on that the answer will be mind-bendingly weird. So weird nobody could even begin to imagine it accurately. If we ever get an answer.

 

[DBT]

I vote for an infinite/eternal multiverse.

Why? Why bother having an opinion on something nobody could possibly know? We all know you're just guessing. Anybody having an opinion is just having a more or less qualified guess, with a massive error margin. But we're all just guessing.

My money is on that the answer will be mind-bendingly weird. So weird nobody could even begin to imagine it accurately. If we ever get an answer.

Nobody is claiming to know, except theists...they are adamant the universe is created. As for me, I am merely guessing. Which is not a fixed position, just an idea. Like you say, speculation. Not fattening, illegal or bad for your health.

 

[steve_bank]

It is enjoyable to think and talk about it. That's all.

There is always the chance scientists will stumble on something new, serendipity is always a part of the progress of science. That is why research needs to go on.

My only problem is when the extrapolations in cosmology are presented as fact, which is common in pop science and science shows. An article proclaiming science has proven xxx...

 

[SLD]

And once again, there is no knowing that it is finite.



Or it could be infinite



And how do you suggest we do that?

Detecting the curvature of the earth is easy: With a curved 2d surface in 3d space, there's one direction (up/down) that's very much not like the others, and all you have to do is find that different places' "up" are not parallel. I don't see any analogous and comparably easy way to detect the curvature of space in a universe where all directions are equal.

The typical way is by looking at the CMB. Here’s one article suggesting a positive curvature from Planck data. https://arxiv.org/abs/1502.01589

That's not what the article suggests. Quite the contrary: They find that their best estimate for the curvature is 0.000 ± 0.005, it even says so in the abstract: "Spatial curvature is found to be |Omega_K| < 0.005"

Another article linking this indicated the actual full article indicated a possible positive curvature, but regardless, curvature is measured by the CMB. It can be and is measured by Astronomers. Hence the main question, as we measure no curvature, just like we can’t detect it on the earth's surface, how big is the universe?

Given that all models I have read about the Big Bang have indicated that ALL matter was condensed in an extremely sub atomic size out of which it expanded, then it stands to reason that the size is still finite.

SLD

 

[steve_bank]

That's not what the article suggests. Quite the contrary: They find that their best estimate for the curvature is 0.000 ± 0.005, it even says so in the abstract: "Spatial curvature is found to be |Omega_K| < 0.005"

Another article linking this indicated the actual full article indicated a possible positive curvature, but regardless, curvature is measured by the CMB. It can be and is measured by Astronomers. Hence the main question, as we measure no curvature, just like we can’t detect it on the earth's surface, how big is the universe?

Given that all models I have read about the Big Bang have indicated that ALL matter was condensed in an extremely sub atomic size out of which it expanded, then it stands to reason that the size is still finite.

SLD

How did the initial conditions come to be?

 

[Jokodo]

That's not what the article suggests. Quite the contrary: They find that their best estimate for the curvature is 0.000 ± 0.005, it even says so in the abstract: "Spatial curvature is found to be |Omega_K| < 0.005"

Another article linking this indicated the actual full article indicated a possible positive curvature,

If that's what you got from that mythical "other article", than one of two things must be the case: The "other article" misinterpreted or misquoted this article, or you misinterpret or misremember the "other article". Without identifying the "other article" and thus without knowing its reliability, we cannot even make an educated guess which it is.This article very clearly states no evidence for curvature positive or negative (and I did read, or rather scan for curvature, the full text). We

but regardless, curvature is measured by the CMB. It can be and is measured by Astronomers. Hence the main question, as we measure no curvature, just like we can’t detect it on the earth's surface, how big is the universe?

A question that might very well be meaningless.

Given that all models I have read about the Big Bang have indicated that ALL matter was condensed in an extremely sub atomic size out of which it expanded, then it stands to reason that the size is still finite.

Given that we do not know the universe's current size, any text that talks about the universe being this or that (absolute) size at this or that stage of its development when it had this or that density necessarily talks about today's visible universe, whether making it explicit or not (or it's just talking shit). Not knowing the universe's size today implies not knowing the universe's size when its density was 10^120 times (or whatever other figure) what it is today.

 

[SLD]

That's not what the article suggests. Quite the contrary: They find that their best estimate for the curvature is 0.000 ± 0.005, it even says so in the abstract: "Spatial curvature is found to be |Omega_K| < 0.005"

Another article linking this indicated the actual full article indicated a possible positive curvature, but regardless, curvature is measured by the CMB. It can be and is measured by Astronomers. Hence the main question, as we measure no curvature, just like we can’t detect it on the earth's surface, how big is the universe?

Given that all models I have read about the Big Bang have indicated that ALL matter was condensed in an extremely sub atomic size out of which it expanded, then it stands to reason that the size is still finite.

SLD

How did the initial conditions come to be?

That’s a very different question and one unanswered by science at this time.

SLD

 

[Jokodo]

How did the initial conditions come to be?

That’s a very different question and one unanswered by science at this time.

SLD

Just as "unanswered by science" is the question whether the universe has a finite size. If anything, the evidence suggests it doesn't.

 

[skepticalbip]

That's not what the article suggests. Quite the contrary: They find that their best estimate for the curvature is 0.000 ± 0.005, it even says so in the abstract: "Spatial curvature is found to be |Omega_K| < 0.005"

Another article linking this indicated the actual full article indicated a possible positive curvature, but regardless, curvature is measured by the CMB. It can be and is measured by Astronomers. Hence the main question, as we measure no curvature, just like we can’t detect it on the earth's surface, how big is the universe?

Given that all models I have read about the Big Bang have indicated that ALL matter was condensed in an extremely sub atomic size out of which it expanded, then it stands to reason that the size is still finite.

SLD

How did the initial conditions come to be?

That question assumes that only a couple of the cosmological models could be true. Many cosmological models do not have a beginning so the term, 'initial conditions', would be a non sequitur for those models.

 

[steve_bank]

How did the initial conditions come to be?

That’s a very different question and one unanswered by science at this time.

SLD

It was a leading question. BB is predicated on the initial conditions accepted without proof or demonstration.

If all matter was condensed to a colure less than an atom what surrounded the mass? Was there a center to the mass?

The start of the BB model is a bit nevbulous, but mathematical consistent. I can create an electrical circuit which is mathematically consent, mathematically simulate it, and for which can never be built in reality.

That is why I accept the BB as a good model. That is certainly an understatement considering the complicity, time, and man hours that went into it. That being said there is nothing to say that the beginning of the model must be true.

Geometry is based on a point being massless and infinitely small, and a line comprised of points. Physically impossible. But the abstract constructs over laid on reality can provide useful analysis. That is how I look at the BB and the initial conditions.

There are other examples of useful mathematical constricts in modeling. In EM and antennas the principle of Method Of Images.

 

[Sarpedon]

I disagree that the BB is without proof or demonstration. The cosmic background radiation and observed recession of distant bodies clearly demonstrates that expansion has occurred.

 

[skepticalbip]

I disagree that the BB is without proof or demonstration. The cosmic background radiation and observed recession of distant bodies clearly demonstrates that expansion has occurred.

Yes, the universe is expanding. And that is essentially what the BB theory and the other cosmological theories describe. However, the extrapolation from current observations to the universe 'beginning' at a point presents some serious problems. The proposed solution for one of those problems was an inflationary period to account for the uniformity but this 'solution' creates more problems to be answered than the one it addressed. The BB theory is widely accepted by cosmologists but the 'BB plus Inflation model' has significant number of detractor cosmologists who see 'inflation' as analogous to the epicycles of the geocentric universe model - an inflationary period would solve the uniformity problem as the epicycles solved the reversal of planet motion for the geocentric model but the physics of how either could happen is left unanswered.

 

[steve_bank]

I disagree that the BB is without proof or demonstration. The cosmic background radiation and observed recession of distant bodies clearly demonstrates that expansion has occurred.

Mu response to that is correlation is not necessarily causation. You take 1000 data points and fit a curve to the points. The mathematical function fit tom the data is predictive , it will accurately predict results between measures data points. You can extrapolate past the endpoints.

I look at the BB as a sophisticated curve fit to a narrow set of observational data. The originating event is extrapolation.

There are conceptual problems for me. There was no center at the BB and there is now no center. However a speherical boundary of some kind implies a center. What led to the initial conditions?

Imagine a nuclear explosion. As the event progresses a civilization evolves on a particle from the explosion. Astronomers on the particle see everything moving away, an apparent expansion. They may deduce there was an originating cataclysmic event. They can deduce nothing outside of their limits of observation.