Expansion Methods

[Buffy]

everything seems to be expanding away from you evenly in all directions.

 

Isotropically,

Buffy

Is it really evenly? I mean hubble's law...which seems to valable at least on sub-horizon scales...

 

Homogenousically,

Sanctus

"evenly" does not mean the same thing as "at the same speed." Seems you got my joke though: The Isotropic part of the Cosmological Principle is that the universe looks the same in all directions: if there were a center of course, given that we observe Isotropy, the only explanations are that either there is no center or we are at the exact center.

 

jackson33: this has nothing to do with the observable universe, because we would be able to perceive differences in large scale velocity of objects in different directions from our location even *within* the observable universe.

 

Further, the *local* motion of the earth within the Milky Way would be enough to cause parallax in these observations, so you'd not only have to say that our galaxy is in the exact center, but that our current location in our orbit is currently in the exact center too, and in a few hundred thousand years we would finally start to see some large scale anisotropy from our new location. Even Mr. Spock would have a hard time calculating the odds of that, so the accepted explanation is that the universe is indeed homogeneous and isotropic, and therefore there is no center.

 

The Steady State model also predicts/explains expansion, but it too holds to the Cosmological Principle and says there is no center. There is no single "origin" of creation of matter. Thus, it does not matter which theory you hold to, expansion works, and its not the "inside of a balloon": you have to think in multiple dimensions to get it.

 

Big Crunch,

Buffy

[jackson33]

The size of the Universe may not matter but it's an easier way to understand what I'm trying to explain.

 

So Buffy tried to explain the expansion method but I'm darn confused as to what Buffy means when she talks about many interpretations of each dimension. Whatd dimension is the Universe then, I'll work from there?

 

" The Universe is not an enclosed sphere "

 

At the time I specified, what is it?

 

are you suggesting the universe is evolving along with another universe in an unseen dimension or many dimensions, another time or maybe outside visual concept.

 

dimensions we live in and see are length-width and distance. if something exist in dimensions we cannot see, then anythings possible. if your thinking dual or coexistence, it gets complicated.

[LJP07]

So what position do we actually hold, we imagine ourselves to be inside a sphere yet the idea of living on a surface eg. Balloon still arises, which one and why the comparison with the other.

[Buffy]

So what position do we actually hold, we imagine ourselves to be inside a sphere yet the idea of living on a surface eg. Balloon still arises, which one and why the comparison with the other.

The balloon analogy only works if you are a two dimensional being. You don't know about "up" or "down", you only know left/right/forward/back. You can't perceive the notion of a "center of the balloon". But when you walk around on the balloon, as it expands, it looks the same everywhere and everything is always moving away from you.

 

Now switch to being a three dimensional being. You perceive the universe (observable) as a sphere, but no matter where you go, it always looks like you're at the center and everything is always moving away from you. This is just as hard for you to understand as the balloon is to the 2-d person, but its pretty much the same explanation.

 

The "raisins in a loaf" description that Tormod mentions above tries to get this across in 3-d, but it still is misleading because a loaf has an "outside the loaf" and as he also said, in reality, there is no "outside" of the universe that we are "expanding into". If there are other universes, "outside" is not quite adequate to explain the actual physics, and since we can't observe them anyway, its all conjecture for now.

 

Blowing stuff up,

Buffy

[jackson33]

Buffy; i understand expansion is possible under any theory. my problem is understanding need, reasons for what we see (random movements at high speeds) or how such direction was motivated. matter just doesn't tend away from other matter and empty space gives should offer no incentive. ie. why would or how could a galaxy stray away w/o cause...

 

as to center; all matter should extend out from some point, even if always there and with indeterminate times. even if a football shape, a box shape or pencil shape and a center (not original or implied original) should exist.

[Buffy]

i understand expansion is possible under any theory. my problem is understanding need, reasons for what we see (random movements at high speeds) or how such direction was motivated.

At large scales, we BB'ers say it was the BB, but on small scales, gravity dominates, and that's why you see neighbor galaxies colliding all the time: they're literally orbiting each other in very complex ways within galaxy clusters.

 

That's the funky thing about the definition of the Cosmological Principle: its true "on large scales", on small scales, its the Roller Derby....

as to center; all matter should extend out from some point, even if always there and with indeterminate times. even if a football shape, a box shape or pencil shape and a center (not original or implied original) should exist.

You're still trapped in 3-d world. You've got to try to perceive it in 4-d. That's why we keep refering to the 2-d analogy of the surface of a balloon: its very, very, very hard to understand this because its way outside the way we are used to having physical objects operate. The 2-d example gives you an idea, but when you're looking at that surface of the balloon, its similarly hard to "get" what it is like to be "a 2-d being", but at least its a start.

 

When the moon is in the seventh house, ;)

Buffy

[TheFaithfulStone]

The best part is that if you walk around the balloon you end up right back where you started.

 

Where do we go now but nowhere? ;)

 

TFS

[imitation is the sincerest form of flattery]

[Buffy]

The best part is that if you walk around the balloon you end up right back where you started.

My fave: and for a simpler version of this, read Dr. Seuss' "The Big Brag" in "Yertle the Turtle and Other Stories http://www.amazon.com/Yertle-Turtle-Other-Stories-Seuss/dp/0394800877/sr=8-1/qid=1167862497"

 

How far can you see,

Buffy

[LJP07]

How can we visualize 4-D, I'm not sure what 4-D is amazingly at least not to imagine it concurring with the Universe?

 

Let me consider each dimension:

 

2-D : A piece of paper is 2d

3-D : A solid cube is 3-D that's physical to touch and not drawn.

4-D : not sure.

 

From 2-d and 3-d, does this not imply that dimensions have shape, so if these have shape, then what Dimension does the Universe have, I'm not referring to the one in relation to us, but what actual dimension is it and if it's constantly expanding, then it will never have a definite shape, does this then imply it doesn't have a dimension.

[sanctus]

Prolu, to answer your question about what is an universe a prof of mine gave a good definition: it's the set of points where events take place.

 

You can't visualize 4-d, but ou can improve your guessing and intuition by taking lower dimensionals examples. So if you take the balloon example understand it in 2-d and then tell yourself that it is the same in higher dimensions...

[Tormod]

It's not really that hard. While we say "4d" it really means space-time, which implies that we need to factor in time when talking about space. The two are not separable when we talk about the shape and size of the universe.

 

Thus, whether the universe is 10 seconds old and has the shape of a starfish, or whether it is 13,7 billion years old and has the shape of a trumpet - it won't matter because the laws of physics are the same and according to the standard theory the universe does not grow "out" of something, nor "into" something. It simply expands. The expansion takes place in intergalactic space and is why the galaxies appear to be receding (or in some cases, pushed closer to each other). It's like a big ocean with things moving in it - if the ocean slowly grows, the islands don't necessarily move but they will appear to move relative to each other.

 

Over time the shape and size of the universe changes, but the laws of physics remain more or less the same. To try to understand the shape of the universe from inside it is perhaps possible - we might never (I'd argue we will never) be able to see it from the outside. And if it does indeed reside inside another universe, it would be a place of very different laws of physics, so that the laws would be different "outside" than "inside". :)

 

Someone said I should not talk about the observable universe because *everyone* would be at the centre of it. That was in fact my point. The observable universe is a confusing entity because 1. it is not the entire universe and 2. it is remarkable homogenous. Yet it is very interesting because by observing the observable universe we can study the evolution of the known universe and infer a lot of things about it.

 

However, we cannot *know* that the universe will look the same no matter where (or when) you are. We do not know if there are places in the universe where you actually see the "end of the universe" (there might be a restaurant there). What is the end? Is it a place where time stops, or is it a physical barrier? Who knows?

[jackson33]

At large scales, we BB'ers say it was the BB, but on small scales, gravity dominates, and that's why you see neighbor galaxies colliding all the time: they're literally orbiting each other in very complex ways within galaxy clusters.

 

That's the funky thing about the definition of the Cosmological Principle: its true "on large scales", on small scales, its the Roller Derby....

You're still trapped in 3-d world. You've got to try to perceive it in 4-d. That's why we keep refering to the 2-d analogy of the surface of a balloon: its very, very, very hard to understand this because its way outside the way we are used to having physical objects operate. The 2-d example gives you an idea, but when you're looking at that surface of the balloon, its similarly hard to "get" what it is like to be "a 2-d being", but at least its a start.

 

When the moon is in the seventh house, :doh:

Buffy

 

there is no reason to consider what we see clearly, what we think we see thats not clear or that beyond what is seem should act in any different manner. therefore to me what we see locally is much of what should be to the limits of whatever are in this Universe.

 

i also don't think gravity is essentially what we think it is. it may be an end result of something and explanations seem to conform to this final result. that is a galaxy on a course will collide with anything on that course, but not change this course for another galaxy. to think this would give question to what keeps all the members in the galaxy from effects of what ever you think that could draw a galaxy to its gravity.

 

frankly i think there are many dimensions not considered, with regards to understanding of virtually anything. however we are privy to only three and our concepts are limited to even those. we can assume anything outside these understandings, but this should be in some manner to what we do know or if you prefer, with logic.

 

the raisin bread, balloon idea, were used to explain BB and if someday i give in to this idea they could make sense. as to expansion there remains no apparent reason or even a way, for this to be. since your coming at me from BB, a principle i find unacteptable (tho accepted by science) we could not agree on many things.

[blue69]

Can there be a center?

 

When you blow a breath of air on a cold day, where is the center?

 

Why does or would the universe expand equally? Why would it spread out evenly?

[Buffy]

therefore to me what we see locally is much of what should be to the limits of whatever are in this Universe.

Cool!

i also don't think gravity is essentially what we think it is. it may be an end result of something and explanations seem to conform to this final result.

A lot of physicists would *agree* that we *don't* know what it is at all. Newton merely described its effects, and Einstein explained it more completely as being the *result* of the curvature of space-time, but he didn't say *what caused* space-time. In some of your other posts I know you posit some interesting ideas, but they're kinda vague and you might want to explain yourself a little more completely if you want to discuss them.

that is a galaxy on a course will collide with anything on that course, but not change this course for another galaxy. to think this would give question to what keeps all the members in the galaxy from effects of what ever you think that could draw a galaxy to its gravity.

Except for the need to identify Dark Matter and Energy, local motions of galaxies behave exactly as would be predicted by Einstein's General Relativity, so there's not really any strange behavior out there. There's increasing evidence that dark matter does exist and behaves as the theory predicts, but we don't know *what* it is yet.

 

As with most scientific theory, its not *complete*, but that doesn't prove its "wrong." Other theories are certainly possible, but its necessary to specify them completely and address all of the known data to show there are none that refute the theory. And there's a *lot* of data these days!

frankly i think there are many dimensions not considered, with regards to understanding of virtually anything. however we are privy to only three and our concepts are limited to even those.

On the contrary, string theory and even some of its alternates do indeed work extensively with dimensions beyond 4. With algebraic geometry, there is no need to be able to "visualize" multiple dimensions at all in order to find important laws and relationships and quite frankly, mathematicians have been doing it for several hundred years (e.g. matrix algebra and topology). "Visualization" and the approximations suggested here are useful for learning, but they are not a foundation for the theories.

we can assume anything outside these understandings, but this should be in some manner to what we do know or if you prefer, with logic.

Logic is cool! So is advanced mathematics! I highly recommend studying both!

the raisin bread, balloon idea, were used to explain BB and if someday i give in to this idea they could make sense. as to expansion there remains no apparent reason or even a way, for this to be. since your coming at me from BB, a principle i find unacteptable (tho accepted by science) we could not agree on many things.

Well, the "why" of expansion is a little hard to address, because there is no current method of getting any data about "before t=0", or if you prefer the steady state theory, its simply always been expanding. Thus why is a metaphysical question, but it really doesn't have any bearing on the fact that expansion is an observable phenomenon, and it does indeed work the way its being described here whether you are into BB or SS.

 

A lot of physics and cosmology does not seem to "make sense" when compared to what our eyes see and ears hear, but the behavior is definitely observable and the theories that we're touching on here have survived much scrutiny. That's not to say they won't be expanded one day by the next Einstein to come down the pike, but if you want to propose an alternate theory, it does have to run the same gauntlet that Prof. Einstein had to navigate.

 

Ya find one in every car, you'll see, :doh:

Buffy

[jackson33]

Can there be a center?

 

When you blow a breath of air on a cold day, where is the center?

 

Why does or would the universe expand equally? Why would it spread out evenly?

 

there is always a center. it may be different at any given time, such as when you exhale, until it dissipates. all this means is at some point equal matter or material is from that central point. it is easy to show in a circle but is in all things. by the way this central point need not be in that item, such as a donut.

 

since i see no reason for expansion in the universe and can find no reason other then BB for a cause, i would say its not expanding in all areas. understand the scientific accepted theory of universal creation is BB. expansion and many other current theory are based from this one thought.

if your going to come back with red shift or blue, please know i have read most of the interpretations of findings as well as the equal number of those that believe these finding actually disprove BB. i just happen to find logic in SS over those of BB.

 

also; few think we see the edges of the universe, movements with in the universe are accepted as random. some things are moving one direction, others the opposite. Andromeda and Milky Way, galaxy just one example.

[Tormod]

if your going to come back with red shift or blue, please know i have read most of the interpretations of findings as well as the equal number of those that believe these finding actually disprove BB.

 

Good. Take that into one of the redshift threads. Especially your examples of those who use redshift to disprove BB.

[jackson33]

Buffy;

 

if the total mass of one galaxy could attract the total mass of another, i assume you would agree both would head for a central point. my point is if this could be theory, what keeps these little bitty stars from having long been in a position. anything that can effect something a billion times larger, should have the power to effect 1/billion. since we know they do occasionally (not often) collide, it will be because they are in the same paths.

 

on dark matter, i personally think there are lots of things we cannot see. but again i have to refer to whats observed. is there more or less around large or small galaxy? since total mass controls gravity, there would need to be quite a bit...

 

SS does not require expansion. i have often said it's not material to the idea, but if it were in expansion and from eternity, i would think something must be creating new matter. since i don't buy that i prefer to think its been about the same size as it has been.

 

on dimensions my thought are more along concepts. if we saw in two dimension, we would have to think everything was painted in the sky and wonder who or what was painting those silly little dots. if we saw only in black and white, there would be no blue sky to question why. when i address an issue, in my mind anyway, i try to figure an extreme and back off to a point where it could add up. this is hard to explain but since i clean sewers for a living i find the idea compelling to that of instant acceptance.

 

at this point in a discussion i usually get hit with my grammar. so I'll accept my math knowledge and look forward to the grammar.