The Center of the Universe

[Chattiestspike2]

I have heard a few times that the universe doesn't particularly have a center because of how it expands. I'm sure people who study cosmology and astronomy might have cringed at how I worded that sentence, so I appologize for that.

First off, the universe is expanding. Great. Now is it expanding from a certain point? What I mean by that is that all the galaxies are getting father away from each other, but even with the famous balloon example, all of the little gallaxies drawn on the balloon ARE getting farther apart when the balloon is inflated, but they are essentially growing apart from each other from one central point- the center of the balloon. Is this just a flaw in the analogy? Or is it not a flaw and therefore the universe does in fact have a center in which all the matter is spreading away from?

I hope this makes sense. I don't mean to come across as asking a stupid question, but this is just something I have been wondering for quite a while. Thanks in advance for any answer I get.

 

[monitoradiation]

I'm no physicist, but...

If I'm understanding you correctly, you're asking whether or not there's a "center" aside from one that would normally be prescribed to a location in 3D space. But rather, you're asking, essentially, where the location of the center of the expansion was if the balloon analogy were to hold.

Since everything is being expanded uniformly at an accelerated rate, you will see from every location in space that each item is moving away from you, regardless of where you are. This means that there is no "center" in 3D space, and going from the balloon analogy basically you're asking where that "center" is in the other dimensions, so to speak. My gut feeling from what little I know about the M-theory and stuff like that is that that might just be trying to carry the metaphor too far...

 

[Chattiestspike2]

Actually that makes sense. I'm not sure if it was your intent (probably was) but I got another understanding of the balloon analogy. Sort of like those gravity diagrams that look like big sheets of graph paper with big indendations in them when a sphere over it to show the gravitational pull or whatever (if my explanation of that makes any sense)- the outside of the balloon would represent 3D space and (just like the graph paper gravity analogy thing) and as it expands, the center of the balloon would make no difference because it's not apart of the "3D" space which is exclusively on the outside of the balloon. And anything off the 3D space would be, as you put it, in a different dimention. .. And a center of the universe being in a different dimention doesn't make any sense really.

So thank you for sharing your insight. It did help.

 

[Commander Eagle]

I have heard a few times that the universe doesn't particularly have a center because of how it expands. I'm sure people who study cosmology and astronomy might have cringed at how I worded that sentence, so I appologize for that.

First off, the universe is expanding. Great. Now is it expanding from a certain point?

No.

The universe is expanding, yes, but it is expanding in all directions from all points. Every point in the universe sees every other point in the universe as accelerating away from it. There is no center; everything is retreating from everything else in all directions.

This is because it isn't just that the galaxies are moving away from one another. Space itself is expanding. Take a set of coordinate axes, then stretch it in every direction simultaneously. Every point on the coordinate system will see every other point moving away from it in all directions. That's what's happening to our universe.

 

[monitoradiation]

Actually that makes sense. I'm not sure if it was your intent (probably was) but I got another understanding of the balloon analogy. Sort of like those gravity diagrams that look like big sheets of graph paper with big indendations in them when a sphere over it to show the gravitational pull or whatever (if my explanation of that makes any sense)- the outside of the balloon would represent 3D space and (just like the graph paper gravity analogy thing) and as it expands, the center of the balloon would make no difference because it's not apart of the "3D" space which is exclusively on the outside of the balloon. And anything off the 3D space would be, as you put it, in a different dimention. .. And a center of the universe being in a different dimention doesn't make any sense really.

So thank you for sharing your insight. It did help.

Glad to be of help; I would recommend "The Elegant Universe" By Brian Greene, its a layman's book and quite easy to follow on the low-down on quantum mechanics, relativity, all the way up to string and M-theory. I found it enjoyable.

 

[JustBusiness17]

 

[Netheralian]

... but even with the famous balloon example, all of the little gallaxies drawn on the balloon ARE getting farther apart when the balloon is inflated, but they are essentially growing apart from each other from one central point- the center of the balloon. Is this just a flaw in the analogy?

Its a flaw. You should be looking at the surface of the balloon only (which is obviously a poor representation because it is a surface and not a volume.) The centre volume of the balloon is not analogous with anything in the universe.

 

[AllMakesCombined]

I always held the opinion that a damp, compressed, round, sponge illustrated a better example than a balloon.

Or, even better, sticking a marshmallow in the microwave. :mrgreen:

 

[Nelson]

The balloon analogy is tricky as you have to jump up an extra dimension, and our brains can't visualize 4 dimensions. If you instead imagine a universe with 2 spatial dimensions and 1 temporal dimension then you can come up with a fitting analogy.

Pretend we have a solid balloon, or just a sphere. The surface of this sphere, or any spherical shell within the sphere can be considered 2-dimensional space, where the radial dimension represents time. As you can see, there is no center on any of these concentric shells, but there does appear to be a center when you consider the temporal dimension as well. In this universe with 2 spatial dimensions and one temporal dimension, the center can be considered to be EVERYWHERE on each 2-d surface, but the true center only exists when considering time, and it is positioned at time zero (the center of the sphere).

Generalizing to our 4-dimensional universe, the center can again be considered to be everywhere in our 3 spatial dimensions, but only at the instant before/during/after/whatever the big bang does the 4-dimensional center exist. As we run the clock backwards everything in the universe approaches the center in 4-dimensions.

 

[Schmoikel]

Glad to be of help; I would recommend "The Elegant Universe" By Brian Greene, its a layman's book and quite easy to follow on the low-down on quantum mechanics, relativity, all the way up to string and M-theory. I found it enjoyable.

While waiting for your order of "The Elegant Universe" to be shipped, you could start with this.

http://www.youtube.com/watch?v=ULlR_pkHjUQ&feature=related

...sorry, can't quite figure out how to imbed the actual video.

 

[Demojen]

There ya go bud

 

[DeathofSpeech]

I always held the opinion that a damp, compressed, round, sponge illustrated a better example than a balloon.

Or, even better, sticking a marshmallow in the microwave. :mrgreen:

Peeps wrapped in aluminized tinsel makes a great model for... err actually not much of anything errr sorry, don't mind me.

 

[AndromedasWake]

Generalizing to our 4-dimensional universe, the center can again be considered to be everywhere in our 3 spatial dimensions, but only at the instant before/during/after/whatever the big bang does the 4-dimensional center exist. As we run the clock backwards everything in the universe approaches the center in 4-dimensions.

It's a handy way to 'run the clock' mentally. Simply inflate the balloon and you notice that the surface moves to intersect future time, deflate to intersect past time. It's also great for Inflation, if your balloon is durable enough!

I also like to use it to illustrate the 'Closed universe so big it appears flat' scenario.

 

[Nelson]

I also like to use it to illustrate the 'Closed universe so big it appears flat' scenario.

The balloon analogy really is quite useful.

I've actually supervised an undergraduate lab that used this exact sort of experiment to demonstrate how you could measure the curvature of the universe on large scales. It was an astronomy course for non-science majors (to explain why such a simple experiment was used). The idea is to take an object of known physical dimensions, and to measure the angular size as a function of distance on the surface of the balloon. On small scales the angle decreases with distance as would be expected in a flat space, but on very large scales (the other side of the balloon in this case) the angular size will begin to increase at larger distances, demonstrating how a space can appear flat on small scales even though it is actually curved.

 

[Chattiestspike2]

I also like to use it to illustrate the 'Closed universe so big it appears flat' scenario.

The balloon analogy really is quite useful.

I've actually supervised an undergraduate lab that used this exact sort of experiment to demonstrate how you could measure the curvature of the universe on large scales. It was an astronomy course for non-science majors (to explain why such a simple experiment was used). The idea is to take an object of known physical dimensions, and to measure the angular size as a function of distance on the surface of the balloon. On small scales the angle decreases with distance as would be expected in a flat space, but on very large scales (the other side of the balloon in this case) the angular size will begin to increase at larger distances, demonstrating how a space can appear flat on small scales even though it is actually curved.

So which one is our universe? Flat or Closed?

 

[Nelson]

So which one is our universe? Flat or Closed?

Well, WMAP measurements indicate that our universe is very likely flat, and I would guess Planck will confirm this. But, as Andromedaswake pointed out, we can always have an open or closed universe that has such a large radius of curvature that the deviation from a flat universe is essentially undetectable. If the curvature is small enough (corresponding to a large radius) the universe would appear flat even all the way out to the horizon.

 

[Chattiestspike2]

So which one is our universe? Flat or Closed?

Well, WMAP measurements indicate that our universe is very likely flat, and I would guess Planck will confirm this. But, as Andromedaswake pointed out, we can always have an open or closed universe that has such a large radius of curvature that the deviation from a flat universe is essentially undetectable. If the curvature is small enough (corresponding to a large radius) the universe would appear flat even all the way out to the horizon.

Ok that makes sense. I remember the first time I heard of a "flat universe" was from a creationist I debated in person in the middle of a festival. He said that scientists figured out that the universe was flat and this correlated with the scriptures because somewhere in the bible, it says something like "god rolled out everything as a scroll" or something like that. The guy said that the unvierse was literally flat as in a big disk or something. He actually said disk. Sigh...

 

[monitoradiation]

Ok that makes sense. I remember the first time I heard of a "flat universe" was from a creationist I debated in person in the middle of a festival. He said that scientists figured out that the universe was flat and this correlated with the scriptures because somewhere in the bible, it says something like "god rolled out everything as a scroll" or something like that. The guy said that the unvierse was literally flat as in a big disk or something. He actually said disk. Sigh...

I'm always amused by how desperately creationists want their religious views to mesh with current science that they'll try to make things fit. But when it so happens that it absolutely conflicts, science is, of course, obviously wrong.

 

[DeathofSpeech]

Well, WMAP measurements indicate that our universe is very likely flat, and I would guess Planck will confirm this. But, as Andromedaswake pointed out, we can always have an open or closed universe that has such a large radius of curvature that the deviation from a flat universe is essentially undetectable. If the curvature is small enough (corresponding to a large radius) the universe would appear flat even all the way out to the horizon.

Ok that makes sense. I remember the first time I heard of a "flat universe" was from a creationist I debated in person in the middle of a festival. He said that scientists figured out that the universe was flat and this correlated with the scriptures because somewhere in the bible, it says something like "god rolled out everything as a scroll" or something like that. The guy said that the unvierse was literally flat as in a big disk or something. He actually said disk. Sigh...

Yes well, if correctly interpreted (correct interpretation requiring a half dozen peyote buttons, half a gram of LSD, and a six pack of Mike's Hard Lemonade) one can clearly see that the bible confirms this.

 

[RichardMNixon]

Just so we're clear, flat in this context only means Euclidean, correct? Space is flat, but there are galaxies (flatly) in all three dimensions from us? It's not like galaxies are all arranged in a plane?

I think that's what the creationists are claiming. When I heard it, it was from the Koran.