Questions Regarding the Expanding Universe

[hickboy]

All of the talk about finding a new distance record for farthest galaxy from us has fed my interest in the concept of universe expansion. I had three questions that hopefully someone here can help me understand.

First, because of the fact that all galaxies are moving away from each other, does that mean that some (those on the leading edge) galaxies are travelling faster than other galaxies?

Two, regarding the new farthest galaxy, is it further out than the center (at least the percieved center, but I'll get to that in my next question) from us or are astronomers looking back to the farther edge?

Finally, addressing the center of the universe - looking for information on this subject, I found this on the Bad Astronomy website

It looks as if we are at the center of a gigantic explosion that made all the galaxies blow outward from us. This is an illusion; any galaxy would see the same thing. They aren't really moving away from us; we are all moving away from each other. We're not really at the center (as a matter of fact, there wasn't any center, but this is complicated enough!).

can someone help me understand how there is no center?

Sorry, if my questions seem silly, sometimes I have a hard time conceptualizing that which I cannot see.

[Kaptain K]

1) Galaxies are not moving, space is expanding and dragging the galxies with it.
2) Not the farthest edge, but the earliest edge.
3) There is no center in the same way that there is no center to the surface of the Earth.

[Thumper]

[stupid question alert] I think I understand now how galaxies are not moving apart. The space is expanding in all directions making it appear from ANY given point that every other point is moving away from you. I've heard it said that this is over "large scale" distances as in those between galaxies. Does this expansion of space have a limit in terms of smaller distances? Is our galaxy itself expanding? Are the atoms in my desk slowly getting further apart?

If the amount of matter in the universe remains constant and the volume or space of the universe continues to expand, the average density of the universe is decreasing, right? Is the density of my desk also decreasing? If not, what is the limit where space ceases to be expanding?[/stupid question alert]

[Kaptain K]

Is our galaxy itself expanding? Are the atoms in my desk slowly getting further apart?

No...not yet! Maybe 30 billion years from now. Do a Google search for "big rip" for info on a possible "end of the universe" scenario.

[Thumper]

So then is there some point between galaxies where space ceases to expand?

[Tensor]

So then is there some point between galaxies where space ceases to expand?

It's not that space ceases to expand, it's that gravity is stronger than the expansion. The mass of our galaxy is enough to prevent (currently) our galaxy from expanding along with space. For an intergalactic example, in the local group, gravity is strong enough to cause M31 and our galaxy to approch each other.

[hickboy]

The universe is expanding in all directions, right? If so, isn't there a center, either with something or as a void?

[Pi Man]

Well, technically there is a center, but it would be outside of our universe. Think of our universe as being spherical. In fact, think of it as a large, expanding balloon. Our universe has an extra dimension, so our 3 dimensional space is contained on the surface of the 4 dimensional sphere. It's basically like an ant on the baloon observing it's 2 dimensional movement capability (foreward, back, left, right) and seeing that the distance to the next ant on the baloon was increasing and concluding that this expansion had to have a center. It does, but it's no longer accessable. The center is not part of the baloon, it's inside it. Just as in this analogy, the center of the universe is not accessable to anybody in the universe, but technically there is a center. I cannot point to where the universe is, but I can tell you that if you go in one of two different directions perpendicular (spelling?) to all of our three, you will eventually hit the center of our universe. However, this would be impossible to do without some technology we haven't discovered yet.

[JohnOwens]

Well, technically there is a center, but it would be outside of our universe. Think of our universe as being spherical. In fact, think of it as a large, expanding balloon. Our universe has an extra dimension, so our 3 dimensional space is contained on the surface of the 4 dimensional sphere. It's basically like an ant on the baloon observing it's 2 dimensional movement capability (foreward, back, left, right) and seeing that the distance to the next ant on the baloon was increasing and concluding that this expansion had to have a center. It does, but it's no longer accessable. The center is not part of the baloon, it's inside it. Just as in this analogy, the center of the universe is not accessable to anybody in the universe, but technically there is a center. I cannot point to where the universe is, but I can tell you that if you go in one of two different directions perpendicular (spelling?) to all of our three, you will eventually hit the center of our universe. However, this would be impossible to do without some technology we haven't discovered yet.

While I love to envision it this way myself, and was considering bringing up the example, is that true only of a closed topology universe? Or does an open universe have some way of having a center in higher dimensions as well? This is the kind of thing that gives me headaches whenever I hear more evidence mounting that the universe is negatively curved. #-o :P

[hickboy]

Thanks for the explanation, it makes a little more sense now. Kind of freaks me out to think about it though...

[Sam5]

Our universe has an extra dimension, so our 3 dimensional space is contained on the surface of the 4 dimensional sphere.

Uhh, what do you mean our universe has an “extra dimension”? You mean there is a “w” Cartesian coordinate of space, like in w, x, y, and z?

[Taibak]

Well, technically there is a center, but it would be outside of our universe. Think of our universe as being spherical. In fact, think of it as a large, expanding balloon. Our universe has an extra dimension, so our 3 dimensional space is contained on the surface of the 4 dimensional sphere. It's basically like an ant on the baloon observing it's 2 dimensional movement capability (foreward, back, left, right) and seeing that the distance to the next ant on the baloon was increasing and concluding that this expansion had to have a center. It does, but it's no longer accessable. The center is not part of the baloon, it's inside it. Just as in this analogy, the center of the universe is not accessable to anybody in the universe, but technically there is a center. I cannot point to where the universe is, but I can tell you that if you go in one of two different directions perpendicular (spelling?) to all of our three, you will eventually hit the center of our universe. However, this would be impossible to do without some technology we haven't discovered yet.

If you want to go that route, you're still a dimension short. You can't leave out time.

[Sam5]

1) Galaxies are not moving, space is expanding and dragging the galxies with it.

So space is “dragging” our own galaxy through... through what... space?

Does that mean that when I’m running away from a lamp post, I’m “moving”, but if someone puts me in a car, then the car “drags” me away from the post, but I’m not really “moving” relative to the post? The car is just “dragging” me along with it, but I’m “stationary”? What branch of physics is this?

Explain to us exactly how space “expands”. Do space particles get bigger, or what? Does “new space” fill in the gaps in the “old space”? Does the old space “stretch” or what?

You keep saying that “space expands”, but I want to know how space expands. What is the physical function of “space” that allows it to “expand”?

If we’ve got two rocks in front of us, and we move them apart, we see that the space between the rocks has “expanded”, but that’s because we moved the rocks. So how can the galaxies be moving away from us, thereby causing their light to redshift, yet you say they are “not moving”? Please explain in detail how that physically works.

[DJ]

here's a neato page i found on yahoo:
http://www.estfound.org/

[Thumper]

Thanks for the good explanations. I pretty much have lost the ability to learn new things (or perform new tricks) so thanks for being patient. I think I learned more in the last two days about the universe from reading this and the other thread. I hope to be able to peruse some of the links as well.

As for your questions Sam5, I'm not your man, I have no idea how it works. Don't even know if I could comprehend it if explained.

I'm with you hickboy, kind of freaks me out too and hurts my head if I try to think about it too hard. :-s

[Tobin Dax]

Pi Man, that's only for a closed universe only, isn't it? Since our universe is flat, it's center would be somwhere inside of it, if it has one. Would it even have a center if it's infinite in extent? If it did, it wouldn't be impossible to tell if you were there.

[John Kierein]

I wish BA would send all these guys who say that space is expanding and that the galaxies are not moving to the "against the mainstream" board. That is such a stupid, ridiculous idea and misconception. If space is expanding to explain the red shift, then why does it expand so much more for radio waves than for x rays? A radio wave at z = 1 expands to twice its wavelength which is several meters, but an x-ray at z = 1 only expands a few nanometers. If the red shift is doppler, of course more distant galaxies are moving away faster than more nearby ones.

[Kaptain K]

Explain to us exactly how space “expands”.

No! Several of us have tried (on several diferent threads that you have hijacked) until we were all blue in the face. I am sick and tired of banging my head against the wall of your obtuseness. I refuse to play your little game anymore.

[Kaptain K]

If space is expanding to explain the red shift, then why does it expand so much more for radio waves than for x rays? A radio wave at z - 1 expands to twice its wavelength which is several meters, but an x-ray at z = 1 only expands a few nanometers.

HUH!! Your point is?

A one meter radio wave emitted at z=1 expands to two meters. A billion 1 nanometer waves of X-rays (1 meter) expands to two meters (one billion 2 nanometer waves). What's the problem? :roll:

[George]

If space is expanding to explain the red shift, then why does it expand so much more for radio waves than for x rays? A radio wave at z - 1 expands to twice its wavelength which is several meters, but an x-ray at z = 1 only expands a few nanometers.

HUH!! Your point is?

A one meter radio wave emitted at z=1 expands to two meters. A billion 1 nanometer waves of X-rays (1 meter) expands to two meters (one billion 2 nanometer waves). What's the problem? :roll:

I think I see the confussion. The question seems t be...If z is the same for all wavelengths from a given object, and, it is the space that is expanding, then, wouldn't space have to expand more for the longer wavelength light vs. the shorter. Analogy - place a 1" long rubber band parallel to a 2" long rubber band, expand the space by 1 inch (z=1 for the 1" rubber band) but the 2" rubber band has only a z of 0.5 even though both saw the same amount of [space] expansion.

[TrAI]

Our universe has an extra dimension, so our 3 dimensional space is contained on the surface of the 4 dimensional sphere.

Uhh, what do you mean our universe has an "extra dimension"? You mean there is a "w" Cartesian coordinate of space, like in w, x, y, and z?

Hmmm... Maybe the 4th dimension needed in this hypothesis would be what we think of as time, that would be, time flows as the universe moves along this dimension... Then perhaps the overall expansion of the universe is fixed by this movement, but gravity could slow down local expansion, and maybe even time, at least for a distance... This might mean that space where there is farther between large mass clusters would expand faster to compensate for the areas that expands slower(the clusters themself)...

Or perhaps I should leave the thinking out crazy ideas about the universe to the professionals... :P

[JohnOwens]

Our universe has an extra dimension, so our 3 dimensional space is contained on the surface of the 4 dimensional sphere.

Uhh, what do you mean our universe has an "extra dimension"? You mean there is a "w" Cartesian coordinate of space, like in w, x, y, and z?

Hmmm... Maybe the 4th dimension needed in this hypothesis would be what we think of as time, that would be, time flows as the universe moves along this dimension... Then perhaps the overall expansion of the universe is fixed by this movement, but gravity could slow down local expansion, and maybe even time, at least for a distance... This might mean that space where there is farther between large mass clusters would expand faster to compensate for the areas that expands slower(the clusters themself)...

Or perhaps I should leave the thinking out crazy ideas about the universe to the professionals... :P

No, everything I know/have thought about this would indicate that time and the fourth dimension for the universe wrapping around itself would have to also be mutually perpendicular (in addition to perpendicular to x,y,z of course). I could be wrong, I haven't seen it explicitly mentioned, but I feel fairly confident about this.

P.S. On the other hand, I'm not one of "the professionals", either. :wink:

[TrAI]

No, everything I know/have thought about this would indicate that time and the fourth dimension for the universe wrapping around itself would have to also be mutually perpendicular (in addition to perpendicular to x,y,z of course). I could be wrong, I haven't seen it explicitly mentioned, but I feel fairly confident about this.

P.S. On the other hand, I'm not one of "the professionals", either. :wink:

Wrapping? I thought of the two as the same dimension, or, that time was, in a way, just one of the symptoms inside the universe of the movement along this dimension, so that when people talk about three space and one time dimension, the time dimension would realy be the movment from the point of the BB singularity(or what ever the universe was created in) along this dimension.

But perhaps you are right. It will be quite some time, if ever, before time and such things are understood, but it can be fun just thinking about it. I guess people have thought about this kind of things as long as there have been thinking people...

[Cougar]

The center is not part of the baloon, it's inside it. Just as in this analogy, the center of the universe is not accessable to anybody in the universe, but technically there is a center.

I'm not sure how accurate this analogy is. The balloon analogy is helpful, but once you start considering anything other than the 2-dimensional surface of the balloon, I think the analogy loses its accuracy. I hesitate to refer to places that are outside our universe since their existence can never be supported or falsified. I think the common explanation is that there simply is no center, or equivalently, since everything started jammed together in essentially the same, single place, then everyplace was at "the center" and still is.

So space is “dragging” our own galaxy through... through what... space?

I think the raisin bread analogy works very well here. As the bread rises or expands, each raisin gets farther and farther from every other raisin. The bread (space) expands between each raisin (galaxy), and in a sense, the raisins get "carried along" with the expanding bread.

What branch of physics is this?

Classical physics?

Explain to us exactly how space “expands”. Do space particles get bigger, or what? Does “new space” fill in the gaps in the “old space”? Does the old space “stretch” or what?

I don't think this is exactly known. There's a lot about the natural world and universe that hasn't been figured out yet. But scientists have to base their theories on observations, and all indications lead to the conclusion that the universe is expanding.

If we’ve got two rocks in front of us, and we move them apart, we see that the space between the rocks has “expanded”, but that’s because we moved the rocks. So how can the galaxies be moving away from us, thereby causing their light to redshift, yet you say they are “not moving”? Please explain in detail how that physically works.

I'm sorry if science has not advanced to a level that meets your satisfaction, but instead of moving two rocks, consider two raisins in a rising loaf of bread. The appearance and reality is that they are separating, but the raisins are not moving through the bread. The bread between them is expanding. As I said, I don't know if the actual mechanism for this phenomenon is known, but then, we don't know the actual mechanism for gravity either.

I wish BA would send all these guys who say that space is expanding and that the galaxies are not moving to the "against the mainstream" board. That is such a stupid, ridiculous idea and misconception.

When you have to claim that 99% of the scientific community is stupid and ridiculous, you might start to think about whether it is you who has the misconception.

[Sam5]

...but instead of moving two rocks, consider two raisins in a rising loaf of bread. The appearance and reality is that they are separating, but the raisins are not moving through the bread.

No, but they are moving through space.

And our universe is not made up of bread dough with yeast in it. Your analogy doesn’t have anything to do with “space” or the real universe. Your “cosmic muffin” model doesn’t work.

The galaxies aren’t being “carried along” by bread dough.

I used an analogy earlier.... I’m running away from you at 5 mph, so I’m “moving through space” away from you. Then I get into a car and it carries me away from you at 60 mph. I’m being “carried along” by the car, but I’m still "moving away from you" at 60 mph.

The best model of the universe, based on what we can see from inside it, is Lemaitre’s expanding “fireworks” model. If you look at a big “star burst” fireworks display on the 4th of July, you will see and expanding sphere of bright dots, all moving outward from a “point”. The ones that are most distant from the point are moving the fastest. The ones that are closest to the point are the slowest. The original point doesn’t move.

[Kaptain K]

Sam5, As you have been told many times, the fireworks analogy is not valid. The universe has no center. Or, equally valid, evey point in the universe is a center. The "raison bread" analogy and the "dots on a balloon" analogy are both more valid than your "fireworks".

[Chip]

...The best model of the universe, based on what we can see from inside it, is Lemaitre’s expanding “fireworks” model. If you look at a big “star burst” fireworks display on the 4th of July, you will see and expanding sphere of bright dots, all moving outward from a “point”. The ones that are most distant from the point are moving the fastest. The ones that are closest to the point are the slowest. The original point doesn’t move.

Lemaitre’s “fireworks” is not a "model". He was fond of poetic descriptions around his mathematics. He referred to space as "feux d'artifice" or "fireworks". His name for the "Big Bang" was "L'atome primitif" or "the primeval atom". He also called radiation "fumée" or "smoke". So if you want to create a revisionist history theory of the universe drawn from terms that Lemaitre used (without understanding what he meant,) then you’ll also need a conjure up a "smoke model" of radiation to attribute to Lemaitre, so as to explain radiation in an alternative unscientific fashion. And it will also amount to Diddly Squat.

That’s because these are analogies, not specific scientific theories. An analogy is something that draws a comparison in order to show a similarity. Its not the same as the object it is compared with. Lemaitre, Einstein and many others were fond of analogies and used then to illustrate concepts. The descriptions "its like fireworks" "its like raisins in bread dough" or "its like dots representing galaxies on the expanding surface of a balloon" are not scientific models, they are analogies serving as a representation to explain the gist of what is observed.

Based on what is observed, the cosmos on the largest scales seems to be an expanding, accelerating, geometrically flat boundless-yet-finite space-time manifold without a preferred center. It is not a balloon or fireworks display filling preexisting space.

On the local level, space can be curved as theorized by general relativity, and on larger, yet still local levels, such as galaxy clusters, gravitation attracts galaxies toward or around each other. While these processes are happening, on the very largest scales, the universe is expanding from everywhere.

In Lemaitre’s actual theory, the "fireworks" analogy precedes the big bang and expansion. During Lemaitre's lectures at Mt. Wilson observatory (which Einstein attended) Lemaitre stated: "In the beginning of everything we had fireworks of unimaginable beauty. Then there was the explosion, followed by the filling of the heavens with smoke."

This has been said many times but if the universe was just like a fireworks display it would look and behave very differently from what is observed. The expanding balloon with dots on it that move apart only represents the idea of space expanding with no single dot being the preferred center.

[Sam5]

The expanding balloon with dots on it that move apart only represents the idea of space expanding with no single dot being the preferred center.

In the balloon model:

All the galaxies get bigger as the balloon expands, the galaxies expand along with “space”.

All the galaxies are flat and curved in two dimensions like an inverted dinner plate.

All galaxies move apart at the same rate.

All the galaxies are the same age.

Light curves as it moves from galaxy to galaxy, and if it goes far enough, it returns to its point of origin.

The viewer is out in 3-D space looking at the surface of an expanding sphere.

The third D of our universal space is left out of the galaxies and the universe.

All beings in the galaxies would have to be flat and could not have round eyes.

The center of the balloon is inside the 3-D balloon, but all the galaxies are on the 2-D skin of the balloon.

Our universe does not look like the expanding 2-D surface of a balloon.

Our galaxies are not dots of black ink made on the spherical surface of a white rubber balloon.


Observation from our vantage point:

We are not on a curved “surface” of the universe looking “around”, we are at some point inside it looking out in three directions, not looking around it in just two directions.

There is no evidence the galaxies are “expanding”.

There is no evidence that the galaxies are flat or are shaped like dinner plates. The galaxies are 3-D just like the universe is, just like we are.

We have round eyes, not flat ones.

We see a 3-D universe, with the galaxies moving away from each other in 3-D space, not in “curved” 2-D space.

There is no evidence that all light beams are curved or that they always return to their point of origin.

The galaxies are points or blobs of glowing light. They aren’t dots made on rubber with a black magic marker.

[Kaptain K]

Are you being deliberately obtuse? :-?

[Chip]

In the balloon model:...galaxies get bigger...galaxies expand...space etc...galaxies are flat and curved...like an inverted dinner plate...move apart at the same rate...same age...returns to its point of origin...in 3-D...flat...not expanding 2-D...not dots of black ink on...a white rubber balloon. (Sam5's)Observation from our vantage point:...not on a curved surface...no evidence galaxies are expanding...galaxies are 3-D...We have round eyes...3-D universe...moving away from each other in 3-D space...galaxies are points or blobs of glowing light...etc...

Your "models" are wrong. (i.e. - Don't agree with observation.)

A more accurate description of the "Balloon analogy" is:

The density of outer space is at least less than, and at most equal to the cosmic critical density, so the Universe is expanding and there is no preferred central location.

That's it.

It has nothing to do with elastic coverings, 3D or 2D spaces, spheres, inverted dinner plates, curved surfaces, or galaxies defined (wrongly) as "points and blobs of glowing light." That's because its an analogy.

Note also that as galaxies are "moving away from each other in 3-D space" as you described, a "Fireworks model" of sparks and points of light flying away from a central point is not supported.