Expanding space & embedded objects qestion.

[Blue Fire]

Okay, I guess I have identified a gaping hole in my knowlege and understanding of the expansion of space. If our universe is expanding due to the fact that the fabric of space itself is expanding rather than objects simply moving away from each other "through" space, then what about any objects embedded in that space? Do those objects (galaxies, stars, planets, molecules, atoms, etc.) themselves expand due to expanding space within them? Or is expanding space rather like pennies glued to a balloon's surface wherein the surface of the balloon expands but the pennies experience no expansion themselves?

[Dragon Star]

This belongs in Astronomy Q&A.

As of now this is one of the unanswered questions...space it's self seems to have no qualities at all as far as we know to cause everything to move away from everything else. There actually is no "fabric", we just use that as a coordinate system of measurement for rationalization, space is essentially nothing, but we try to turn it into something all the time.

Keep in mind that gravity, space, and time are all constructs of the human mind used to help us quantify the behavior we see, and nothing else. It is subject to change as we don't fully understand the universe, how can we fully understand out rationalization of it?

We have much to learn.

[Blue Fire]

Originally Posted by Dragon Star

This belongs in Astronomy Q&A.
. . .

Ooops, yeah, sorry about that. I must be blind! Moderator, feel free to move this now. (Oh but he's away now, right? )

As of now this is one of the unanswered questions...space it's self seems to have no qualities at all as far as we know to cause everything to move away from everything else. There actually is no "fabric", we just use that as a coordinate system of measurement for rationalization, space is essentially nothing, but we try to turn it into something all the time.

Keep in mind that gravity, space, and time are all constructs of the human mind used to help us quantify the behavior we see, and nothing else. It is subject to change as we don't fully understand the universe, how can we fully understand out rationalization of it?

We have much to learn.

Well, that almost makes me feel better that I'm not alone in not understanding.
In any case, my question was sparked by some reading I've been doing from Brian Greene's The Fabric Of The Universe wherein he attempt to tackle current Theory as it relates to the possible "makeup" of spacetime itself and what "qualities" it might have to allow it too essentially stretch. One implication would be that space is actually a "something". Further down the road within this particular interpretation of space, it is possible that there is a smallest "chunk" of space, and a smallest chunk of time. But I have not found where he addresses the specifics of expanding spacetime elsewhere than between galaxies. Thus my question.

You make a good point though - that if a theory is not yet fully developed and verifiable, how can we pretend to fully explain/comprehend some specific thing Within that theory?

Thanks for the response!

[Dragon Star]

Originally Posted by Blue Fire

One implication would be that space is actually a "something".

Yea, well it has to be a something, or everything we know about the universe would fall apart. Without it being something Mass would not be able to warp it, which would change so much we know about the universe. The fact of the matter is that their are things we are wrong about, and lots of changes are going to be made about lots of our current theories, and some/most of the theories we have are bogus-much like using training wheels and saying you learned how to ride you're bicycle. Not quite.

We will know much more about space when we finally define much more about Dark Energy and Dark Matter...lots of the stories the universe has to tell lie within the "Darkness".

You make a good point though - that if a theory is not yet fully developed and verifiable, how can we pretend to fully explain/comprehend some specific thing Within that theory?

The problem arises when you take into consideration as to when something is developed and verifiable in the essence that it is indeed true throughout the universe...because that moment never happens until all the secrets of the universe are revealed to humanity for everything to work as it should. Because although the puzzle looks complete, what if the last piece doesn't fit?

[stuart]

My understanding is the classic raisin bread analogy: The universe (the bread) expands (as the bread expands while baking in the oven). This expansion carries along with it the objects (the raisins) that are embedded within the bread, spreading them apart from each other. However, the raisins themselves do not expand because their chemical bonds (or self-gravity, for astronomical objects) hold them together within the expansion. You have to get on very large scales for the expansion to dominate over gravity at the present epoch in our Universe.

[Dragon Star]

Thing is...if space has embedded objects, that should suggest that nothing could travel in space, earth would not orbit the sun, moon would not orbit Earth...and their would be no special motions (ex:Milky-Way and Andromeda)

So how can we say that space has any affect once so ever on objects? What if their is some mysterious force in space that is causing all of this but not space it's self?

If it were something that is in space instead of space it's self, then that means it could be clumped or thicker in some spots then others, and provides a better explanation to help solve problems with special motions and perhaps other observations yet unexplained in the universe.

Just a thought...

[stuart]

Okay, to expand on what I said before (no pun intended) - and remember this is just what I'm remembering from undergraduate classes - the idea is that the "fabric of space" can be thought of as a 3-D cartesian (let's ignore hyperbolic and parabolic geometries for now) grid. This grid is iteself expanding. So, let's say our group of galaxies were placed at the origin, point (0, 0, 0). Let's say that another group of galaxies is placed at point (1, 1, 1). The physical distance between those two points is found to be 1 Mpc (mega parsec). Many years later, the relative velocities between the two objects were not enough to alter their positions on the grid, so they are still at (0, 0, 0) and (1, 1, 1). However, the expansion of the grid itself has made that physical distance be 2 Mpc.

That's the situation I'm describing. That's why Earth still orbits the Sun, the Sun the Galaxy, and so on. As to what the "fabric of space" actually is and how objects are "attached" to a given location in it, that's where I get fuzzy and it could be what you were saying above, with it being an incommplete theory and more of a construct for how stuff works.

[Dragon Star]

Originally Posted by stuart

Okay, to expand on what I said before (no pun intended) - and remember this is just what I'm remembering from undergraduate classes - the idea is that the "fabric of space" can be thought of as a 3-D cartesian (let's ignore hyperbolic and parabolic geometries for now) grid. This grid is iteself expanding. So, let's say our group of galaxies were placed at the origin, point (0, 0, 0). Let's say that another group of galaxies is placed at point (1, 1, 1). The physical distance between those two points is found to be 1 Mpc (mega parsec). Many years later, the relative velocities between the two objects were not enough to alter their positions on the grid, so they are still at (0, 0, 0) and (1, 1, 1). However, the expansion of the grid itself has made that physical distance be 2 Mpc.

That's the situation I'm describing. That's why Earth still orbits the Sun, the Sun the Galaxy, and so on. As to what the "fabric of space" actually is and how objects are "attached" to a given location in it, that's where I get fuzzy and it could be what you were saying above, with it being an incommplete theory and more of a construct for how stuff works.

You are describing objects that are not moving relative to one another though, but just that the space between them is increasing. That still doesn't explain how a body moves through space at any given time, as the space between it and other objects isn't the point, but that it stays the same distance from an object but is still moving relative to other objects such as Earth to Sun.

Thus it can be concluded from my POV that their is not physical attachment to objects/bodies to space, but that a force is the cause for action of observation between bodies in space. Perhaps this force propagates at different speeds throughout space which gives it separate amounts of force on objects, e.g special motions. As we have no detection of it yet it may have propagated much faster in our "neck of the woods" so to speak then others making it very weak but still explaining expansion. Of course everyone reading this should note that this is purely speculation, as we know as much about space as why light travels at C in space.

I may be missing something big here, if I am speak up and let me know...sometimes I bottle neck my thought patterns.

[Blue Fire]

Originally Posted by stuart

However, the raisins themselves do not expand because their chemical bonds (or self-gravity, for astronomical objects) hold them together within the expansion. You have to get on very large scales for the expansion to dominate over gravity at the present epoch in our Universe.

Okay, I guess this gets at the heart of my question. I'd forgotten the raisinbread analogy and that local bonds/gravity predominate in areas of space that contain significant mass like that inside a galaxy. Thanks!

Regarding the nature of the "fabric" of spacetime, I remember reading somewhere that if indeed space is actually a something (related to the idea that the vacuum is teaming with qauntum fluctuations, zero-point energy, etc.), then it just might turn out that there really is an aether-like quality to spacetime that might just provide the ultimate reference point/frame for everything else.

On the other hand, maybe guys like Liebnitz (sp?) are right - they consider space and time to be nothing more than convenient ways to summarize the relationships between objects, and have no discrete exisitence in and of themselves.

[Dragon Star]

We just don't know until we figure out if their is A force causing observations or not, at that point then we can try to explain what is going on with expansion/space relations.