Not the centre of the universe.

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In summary: I read that a year ago or something. I'm not sure I quite remember. :P) then it is still infinite. Like the positive and negative numbers, there are an infinite number of points in the universe. But there can be a center of expansion. It's just that every point in the universe was once in this point.Not sure if that was a typo or not, but it is believed that space is unbounded yet finite, meaning that it doesn't have an edge but there is a finite amount of space. And I think I understand what you're saying about the center of expansion, but it still seems like a meaningless point because there is no way to physically determine or locate it. In summary,
  • #1
icvotria
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I'm having trouble getting my head around the universe not having a centre, can anyone maybe explain it to me or give me a good analogy or something? I need another "Ahhh, I geddit!" moment (better than sex. Sometimes o:) ). I can feel it teetering just on the edge of my mind... BTW, I wasn't really sure where to post this topic, sorry if this is the wrong place for it.
 
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  • #2
Ok. It was once said tht the universe is infinitly big. If this is so then it is impossible to define a centre. Thats just one theory
 
  • #3
the general acceptance of time and the universe, now, is that they are finite but have no "barrier". So, maybe there's no center of the universe because it just isn't like how we imagen it: like a round circular ball. maybe it's open, flat, curved...
 
  • #4
Hmmmm... But still...Nope, it's blagging my 'ed. Is it even possible for me to be able to conceptualise this? Or is it something that'll take a lot of studying for me to grasp?
 
  • #5
I don't know how closely the two are related, but do we know where the big bang might have taken place?
 
  • #6
drcrabs said:
Ok. It was once said tht the universe is infinitly big. If this is so then it is impossible to define a centre. Thats just one theory
I don't know if that's a good way of explaining it. There are an infanite amount of positive and negative numbers, but we can define a middle, zero
 
  • #7
But there's no "negative" universe.
 
  • #8
How do we know what's negative and what isn't? "negative" numbers are a way of explaining other numbers than the normal ones.
 
  • #9
theres nothing abnormal about a negative number though. Also, unless we can define what a negative universe is, there's no way of figuring out where the negative and positive universe converge like we do with numbers.
 
  • #10
icvotria said:
I'm having trouble getting my head around the universe not having a centre

I can settle that for you very simply: of course, the universe has a center: I am the center of the universe!
 
  • #11
HallsofIvy said:
I can settle that for you very simply: of course, the universe has a center: I am the center of the universe!
:rofl: :rofl: I so badly wanted to make that joke but I was worried it might make the question look like an elaborate set-up!
 
  • #12
its prolly a GR reference...every frame is moving except the Empty space frame...but then some people don't believe there exists this empty space so no center of universe =]
 
  • #13
Do you mean there is no center of expansion? There is a common balloon analogy which is nice (of course, like most analogies, if don't read too much into it). Have you heard it? Edit: Oh, there is another 3D analogy with raisins in dough.
http://curious.astro.cornell.edu/question.php?number=274 looks like a good explanation.
 
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  • #14
It should be: There is no center of expansion.


There is probably a center of the universe. But it is a meaningless point in space. But space is also too big to find it so no one cares. And with relativity it is even harder to find it because time (dilation) makes everything very confusing.
 
  • #15
Daevren said:
There is probably a center of the universe. But it is a meaningless point in space. But space is also too big to find it so no one cares. And with relativity it is even harder to find it because time (dilation) makes everything very confusing.
I ain't saying you're wrong, but that is very contrary to everything I've ever read. The universe is expanding from a point, and as such, every point in the universe was once in this point.
Einstein believed space to be infinite but bounded... if you could head in a straight line for long enough you may end up back where you started. I don't think everyone agrees on this.
The balloon analogy, as long as you don't take it too literally, is still the best I reckon. A balloon's surface expands as you blow it up - but where is the centre of the balloon's surface? Nowhere - every given distance on the surface balloon is expanding at the same rate as any other equal distance.
I used to transfer this analogy to the universe and think that the universe is expanding into a fourth spatial dimension, but apparently I was very wrong. Then I thought it was expanding into the time dimension but that's probably no better. That's no doubt why they say not to take the balloon analogy seriously.
 
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  • #16
Daevren said:
There is probably a center of the universe. But it is a meaningless point in space. But space is also too big to find it so no one cares. And with relativity it is even harder to find it because time (dilation) makes everything very confusing.
If you suspect the center of the universe probably exists, would you share your definition of it? For instance, the center of a line segment is the point equidistant from its endpoints.
El Hombre Invisible said:
I ain't saying you're wrong, but that is very contrary to everything I've ever read. The universe is expanding from a point, and as such, every point in the universe was once in this point.
Wouldn't that point then be the center of expansion? As I understand things, galaxies are not moving through space as pieces from an explosion would move through the air. Rather, the space between galaxies is itself expanding. But I'm not a physicist, astronomer, or cosmologist, and there are plenty of them around here to straighten it out.
I think most confusion about the balloon analogy results from it being a 2D model of a 3D concept. People forget or don't realize this and think the center of the 3D balloon would be the center of the universe or other such extrapolations.
 
  • #17
El Hombre Invisible said:
I ain't saying you're wrong, but that is very contrary to everything I've ever read.

I wonder what you read or if you misunderstood me. If space is unbounded and finite (so the other way you think Einstein claimed it is, because that doesn't make sense to me. I think you flipped them around.) it is 3d surface on a 3d object. Like a 2d surface on the 3d sphere(ballon).

The universe is expanding from a point, and as such, every point in the universe was once in this point.

This is incorrect. It didn't expand from a point, the point itself expanded.

The balloon analogy, as long as you don't take it too literally, is still the best I reckon.
You can take it quite literally.


Now about expanding. When the universe is expanding no object is moving in space. The universe as a whole is changing. All the universe is stretched. The space inbetween the galaxies grows bigger because of this stretching. You could say the universe is the same shape as before the big bang, only bigger. So the universe isn't expanding, its being stretched. (Except, it will not snap back.)

An inflating balloon does not expand from a point. Every point on the balloon itself expands.

Then I thought it was expanding into the time dimension.

I am not sure what you mean by this. Unless an object is frozen in time(its own time, not some other frame of reference its time), which has never been observed, it is already moving in the time dimension.

About the center of the universe. Since we do not know the shape of the universe we do not know if it has a center. It might have, but its pretty meaningless in itself. It has no function. Its just a point in empty cold dead space.
 
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  • #18
Daevren said:
I wonder what you read or if you misunderstood me. If space is unbounded and finite (so the other way you think Einstein claimed it is, because that doesn't make sense to me. I think you flipped them around.) it is 3d surface on a 3d object. Like a 2d surface on the 3d sphere(ballon).
Mmm. Did I get my words mixed up? Whichever is akin to a line on a circle. I thought that was infinite (you can go on and on forever) but bounded (you may come back to where you started). In what way is a 3D surface on a 3D object like a 2D surface on a 3D object?

Daevren said:
This is incorrect. It didn't expand from a point, the point itself expanded.
Okay, I think we mean the same thing, but perhaps saying them in ways that make sense to us. A singularity is dimensionless, so it has no dimensions to expand, hence I put it the way I did. But I think we have the same picture in our heads.

Daevren said:
You can take it quite literally.
Dammit, can I or can't I? I get different answers from different people. Last thing I was told is that the balloon analogy can't be taken too literally as its 2D surface is wrapped around a 3D volume. If the analogy held, the universe would be a 3D space volume wrapped around a 4D space... (what's the word for 4D spaces?). I was told this was incorrect, and that there is no fourth spatial dimension that we are expanding into or around. Harrumph!

Daevren said:
Now about expanding. When the universe is expanding no object is moving in space. The universe as a whole is changing. All the universe is stretched. The space inbetween the galaxies grows bigger because of this stretching. You could say the universe is the same shape as before the big bang, only bigger. So the universe isn't expanding, its being stretched. (Except, it will not snap back.)
Okay, this is getting a little far-fetched. The universe isn't expanding? Are you sure that's the consensus? I have not heard of the stretch model of the universe. Also, saying the universe, a 3D volume, is the same shape as the singularity, a 0D point, would not to me seem logical. Furthermore, "before the big bang"? What before is there? I think you're kind of going out on a limb here.

Daevren said:
About the center of the universe. Since we do not know the shape of the universe we do not know if it has a center. It might have, but its pretty meaningless in itself. It has no function. Its just a point in empty cold dead space.
I don't get it... you say the balloon analogy holds, but the surface of the balloon does not have a centre. Then you say the universe may have a centre.
 
  • #19
I'm not quite sure this has been posted before but the way I learned the universe has no centre is like ths:

It's basicly all down to special relativity. Saying that you cannot ever be sure of the fact that you are standing still, since there's always another reference frame in witch you are moving. Now, if there would be a centre of the universe it would be perfectly standing still, simply because a centre of anybody could ofcourse never be moving around, even not when the body itself is expanding. Second of all, if it was possible to actualy stand inside this centre it would be possible for you to determine if something is, or is not moving because your view from the centre of the universe would be something like an absolute reference frame of the universe. Einstein says this is not possible. If you would be flying around in your spaceship and you would get to what you think is the centre of the universe you would not be able to tell wether it is you who is moving or that it is the centre of the universe that is moving. But since the centre of the universe cannot be moving, and can never be sure of your own movement, this problem cannot be solved.

So if you accept special relativity you must accept that there can be no such thing as a centre of the universe.
 
  • #20
does the euclidean plane have a center? does it bother you?
 
  • #21
center

The way the big bang supposedly happened, I don't believe there can be a center.
As far as the edge, again I don't see how there could be one. If you think you found the edge, what is on the other side of it? What is 100 miles past the edge? The universe is everything, so even beyond the end of space & time is something. It expands as you observe it. You couldn't see the end because there is always room for more. It is dynamic. With no edge how could there be a center?
The starting point of the big bang seems like it should be easy to find, but it has not.
Roy
 
  • #22
The balloon analogy is perfect for this kind of thing!

A dozen ants are sitting on the surface of a small balloon. (It is an ideal balloon, having no "nipple" for inflation. It expands when the gas inside is heated, so there!)

Each ant is standing one inch from his immediate neighbours - and can see his neighbour's neighbours an inch beyond them.

The balloon expands and triples in size. All ants see their immediate neighbours moving away from them until they are 3 inches away. They see their neighbour's neighbours move away until they are 6 inches away.

Every ant sees the same thing: they see every other ant moving away. Immediate neighbours move away at speed x while distant neighbours move away at a speed proportional to their initial distance (ants twice as far away move away at speed 2x.) At all times, every ant sees the rest of the ants moving away from him, while he appears to be stationary at the centre.

Q Which ant was actually standing at the centre of expansion?
A: They all were!
 
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  • #23
mathwonk said:
does the euclidean plane have a center? does it bother you?
(Well... the Euclidean plane is a mathematical construct. It is does not have a physical existence. It is the physical things we have difficulty imagining without end.)
 

What does it mean that we are not the centre of the universe?

It means that Earth is not the literal physical centre of the universe, and that other celestial bodies and systems exist beyond our planet.

How was it discovered that Earth is not the centre of the universe?

The concept of Earth not being the centre of the universe was first proposed by ancient Greek philosophers, and later supported by scientific discoveries such as the heliocentric model of the solar system and the expansion of the universe.

Does this mean that Earth is insignificant?

No, although Earth may not be the centre of the universe, it is still a unique and important planet that supports life and has a complex and diverse ecosystem.

What implications does this have for our understanding of the universe?

The realization that Earth is not the centre of the universe has led to a shift in our perspective and understanding of the vastness and complexity of the universe. It has also opened up new avenues for scientific research and exploration.

How does this affect our place in the universe?

While we may not be physically at the centre of the universe, our existence and consciousness allow us to contemplate and appreciate the beauty and wonder of the universe, making our place in it significant in a different way.

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