B Can we identify the centre of the Universe?

[Nick tringali]

The center is where ever you are at that time.

 

[phinds]

The center is where ever you are at that time.

Which is exactly what Chronos said in post #28. My point it that it's a good idea to read a whole thread before responding, so that you don't just give the same answer that someone else has already given.

 

[ScottVal]

This discussion also begs the question of whether or not the universe is bounded in the sense of space (as opposed to time). I.e., does it go on forever, in all directions?
-Scott V.

 

[phinds]

This discussion also begs the question of whether or not the universe is bounded in the sense of space (as opposed to time). I.e., does it go on forever, in all directions?
-Scott V.

It is the consensus that it is either infinite or finite but unbounded and the significant trend these days seems to be a believe that it is most likely infinite. A bounded universe presents sever problems with cosmology and destroys that Cosmological Principle.

 

[Snerdguy]

Planets, solar systems, and asteroids can move in different directions relevant to one another because gravity influences their travel and holds solar systems and galaxies in one piece. But, space is expanding so that distance between things like stars and galaxies is getting bigger. We know this because the farther out we look toward the galaxies at the farthest edge of the visible universe, the greater the red shift is. Red shift is a Doppler effect indicating speed. Galaxies in general are red shifting away from us. But, the further away they gets from us, the faster they are moving away from us no matter which direction we look in. The Andromeda galaxy will likely be bumping into our galaxy in the future because gravitational forces are moving it faster toward us than the expansion. So space isn't expanding from a single point. It's expanding everywhere. An analogy would be the surface of a latex balloon. It doesn't just expand in one place when inflated. It expands all over. There is no center because the single point were started from is just getting bigger. The whole universe is the center of the universe.

 

[ScottVal]

phinds, thanks for the answer to my query. I guess it follows, if the universe has no center in terms of space, it also would have no "edge" in terms of space. The microwave background is like a spherical wall around us, with a radius of 14 billion light years. This gives credence to the idea of the "celestial sphere" as being almost literal. A billion years from now, the radius will be 15 billion light years. I.e., we'll never "run out of space." It also follows that you could never measure the total mass of the universe (it is infinite), but you could measure its density. It gets less dense as it expands.
-Scott V.

 

[phinds]

phinds, thanks for the answer to my query. I guess it follows, if the universe has no center in terms of space, it also would have no "edge" in terms of space. The microwave background is like a spherical wall around us, with a radius of 14 billion light years. This gives credence to the idea of the "celestial sphere" as being almost literal. A billion years from now, the radius will be 15 billion light years. I.e., we'll never "run out of space." It also follows that you could never measure the total mass of the universe (it is infinite), but you could measure its density. It gets less dense as it expands.
-Scott V.

The radius at the moment is about 47billion light years, not 14billion. We don't know if it's infinite or not, so do not make a categorical statement that it is. Matter density gets smaller but with energy included it's not changing much ("dark energy" density remains the same).

 

[mathman]

You have drawn inferences unsupported by facts. Galactic clusters, like individual galaxies, are also known to collide. This is possible because clusters have their own peculiar motion, also just like individual galaxies. Such collisions were more common in the early universe because the average density of the universe was greater than it is at present. For discussion see http://arxiv.org/abs/1502.01339, The merger rate of galaxies in the Illustris Simulation: a comparison with observations and semi-empirical models. As far as the OP question is concerned, welcome to the apparent center of the universe! Given that distant galaxies are receeding at velocities proportionate to their distance from earth. It is a fairly simple matter to deduce Earth is located at the center of the observable universe. If that sounds like a highly improbable coincidence, welcome to the non-intuitive science of cosmology.

We are at the center of our observable universe, but so is everything else (center of its observable universe)! Surface of an expanding balloon is the 2 dimensional analog.

 

[Alexandra Fabiello]

So basically, unless we could somehow see the whole universe, we could never tell where it's center is, if it has one (if it's a sphere, it has one; if it's like the skin of a blown up balloon, the surface area still has a center if you 'popped the balloon' and flattened it out). But the universe didn't necessarily start from one spot; it may have started from many spots at once, but we just don't know.

 

[russ_watters]

So basically, unless we could somehow see the whole universe, we could never tell where it's center is, if it has one...

No. If it had one, we'd be able to tell where it is, regardless of how much of the universe we see: it does not and cannot have one. The geometry that is observed and "motion" of the galaxies do not allow for a center.

 

[phinds]

So basically, unless we could somehow see the whole universe, we could never tell where it's center is, if it has one (if it's a sphere, it has one; if it's like the skin of a blown up balloon, the surface area still has a center if you 'popped the balloon' and flattened it out).

No, that's not correct.

But the universe didn't necessarily start from one spot; it may have started from many spots at once, but we just don't know.

That's even less correct, if possible.

The evidence against a center is overwhelming. Google "the Cosmological Principle"

 

[Alexandra Fabiello]

No, that's not correct.

That's even less correct, if possible.

The evidence against a center is overwhelming. Google "the Cosmological Principle"

That just involves what we can observe from our bit of the universe as a whole, both observable and unobservable. Since we obviously know nothing of the unobservable universe (we assume it follows the same laws as the observable universe, but that's about it), we can't ever tell where the middle of it is in 3D space, especially if it looks the same from wherever in the universe you look from.

If there is a finite amount of matter in this universe, then there is conceivably a point in space where there is no more matter because it hasn't gone any farther yet. If you drew an imaginary line wall thing connecting all of the bits of matter that have no matter further from it (for a certain value of further; where no matter exists in at least one direction from the matter particle), you would get the 3D shape of the universe's matter. Consider that the universe; the universe is it's matter. If you want to measure energy too, like light, then use where there is no more light particles existing in at least one direction from that particle. So the universe is matter and energy for this purpose. In 3D space, it MUST have an area (amoeba shaped as it may be) that is equidistant from the edges of the matter/energy thing, and this would be its center. There wouldn't necessarily be a particular POINT, unless you went to the center of that area, and the center of that, and the center of that, and so on into infinity, but there would be an area.

Unless 3D space means something completely different now. Even if it's bent or curved (and we know it is), the 'center' would be measured from the flattened out version, 'cause that's what we see, more or less. If it has no true center because of other dimensions and how they work, fine, but that's irrelevant to us that can't perceive them.

As for the start of the universe, well it had to start somewhere. It's either one area or many. Whatever the singularity manifested itself as from our 3D perspective.

And isn't a black hole considered a singularity? Or is that just in sci-fi?

 

[davenn]

As for the start of the universe, well it had to start somewhere. It's either one area or many. Whatever the singularity manifested itself as from our 3D perspective.

And isn't a black hole considered a singularity?

I suspect you still don't understand the meaning of the term singularity in these contexts'

Chronos covered it in post #2

 

[russ_watters]

...we can't ever tell where the middle of it is in 3D space, especially if it looks the same from wherever in the universe you look from.

That just plain isn't true. I'm sorry, but at this point you are simply choosing to believe what you want to believe and ignoring the explanations people are giving you.

I'll say it again: the observed distribution of galaxies can't possibly be from a spherical universe with a center. I'll explain: anyone not at the center would be able to detect the direction of the center of such a galaxy from interpreting the distribution of the galaxies. Our universe is so large that galaxies at right angles to the axis of expansion would be moving away from us much slower than galaxies along the axis of expansion.

 

[Alexandra Fabiello]

A singularity is 'a point at which a function takes an infinite value, especially in space-time when matter is infinitely dense, as at the center of a black hole'. If stuff stops making sense at that point, fine, but the results DO make sense, and if the 'explosion' (note the single quotes) threw out a bunch of matter from that infinitely dense area thing (like the center of a black hole, except outwards; a 'white hole' as such things have been called, even if it's only theoretical at this point), then it should theoretically be possible to find the source area of that matter, unless it literally appeared everywhere at once and somehow still gained the energy to move in different directions from one another (unless we're all going the same direction and don't know it or are spinning around each other due to gravity and stuff like that).

The math doesn't work anymore, but reality and math are clearly in conflict at this point, probably because we don't know the right math to make it work. Maybe quantum physicists will give us a better answer at some point. Or whatever comes after quantum physics, like if they ever figure out string theory.

 

[Alexandra Fabiello]

And when did I say the universe had to be spherical? The universe could be a formless blob of matter from an outside perspective for all we know.

 

[russ_watters]

And when did I say the universe had to be spherical? The universe could be a formless blob of matter from an outside perspective for all we know.

I assumed you at least accepted that it was expanding from a Big Bang. "Formless blob" isn't an option that fits anything anywhere close to a Big Bang; not even the common misunderstandings of the Big Bang. So to be frank, I guess I'm just not sure how far away from reality your belief is. Just FYI though, we do have a requirement on this site that discussions be grounded in reality.

 

[Alexandra Fabiello]

I assumed you at least accepted that it was expanding from a Big Bang. "Formless blob" isn't an option that fits anything anywhere close to a Big Bang; not even the common misunderstandings of the Big Bang. So to be frank, I guess I'm just not sure how far away from reality your belief is. Just FYI though, we do have a requirement on this site that discussions be grounded in reality.

I know that, but it was said in these posts that the common misunderstanding of the Big Bang was that it exploded from one spot, more or less, so clearly if that's wrong, then a whole bunch of other stuff stops making sense. I say 'formless blob' meaning more 'having a shape that doesn't have a name'. If the Big Bang happened like most people assume it did, from one spot of infinitely dense matter going boom and flinging matter everywhere, then yeah, a somewhat spherical universe would make sense. If it didn't, then we have to go by what happened once things started making sense. Did matter move away from a certain area? Did it move away from several areas? Did it just pop into the third dimension and start floating in one direction rather fast and gravity ended up changing the shape of the eventual bunch of matter due to changing the direction things moved ever so slightly? Something must have happened from a 3D perspective once matter appeared in it and started moving. If it is NOT a formless blob and actually has a 3D shape, then it MUST have an area equidistant from the edges of that shape and therefore has a center! If it IS a formless blob in 3D, it STILL has such an area! If it doesn't have a 3D shape... that makes no sense if we can perceive it as such.

 

[russ_watters]

I know that, but it was said in these posts that the common misunderstanding of the Big Bang was that it exploded from one spot, more or less, so clearly if that's wrong, then a whole bunch of other stuff stops making sense. I say 'formless blob' meaning more 'having a shape that doesn't have a name'. If the Big Bang happened like most people assume it did, from one spot of infinitely dense matter going boom and flinging matter everywhere, then yeah, a somewhat spherical universe would make sense. If it didn't, then we have to go by what happened once things started making sense. Did matter move away from a certain area? Did it move away from several areas? Did it just pop into the third dimension and start floating in one direction rather fast and gravity ended up changing the shape of the eventual bunch of matter due to changing the direction things moved ever so slightly? Something must have happened from a 3D perspective once matter appeared in it and started moving. If it is NOT a formless blob and actually has a 3D shape, then it MUST have an area equidistant from the edges of that shape and therefore has a center! If it IS a formless blob in 3D, it STILL has such an area! If it doesn't have a 3D shape... that makes no sense if we can perceive it as such.

I don't know what else to tell you. You've been told how the shape works, but you aren't accepting it and you are making things up that don't fit the reality of what is observed. I don't know what you are hoping to hear instead, but again, you really need to stop with the idle speculation and just start trying to understand what people are telling you.

 

[davenn]

If the Big Bang happened like most people assume it did, from one spot of infinitely dense matter going boom and flinging matter everywhere, then yeah, a somewhat spherical universe would make sense.

Sorry, you really have to get away from this point source explosion belief, it is incorrect ... Most scientists DONT believe that
only laypersons lead astray by poor pop-science TV programs.

To quote phinds from another thread in the cosmology section of the forum

First, it was NOT an infinitely dense point. That is popularization nonsense that you see everywhere on TV but nowhere in physics books. The big bang is a theory that discusses the expansion of the universe from a hot dense state without ever saying what it was like at t=0 except that it was NOT a point. You may hear the term "singularity" but this does not mean point, it just means "place where the math models break down".

You really need to change your line of thinking if you want to move on in this topic
You keep restating the same thing over and over and then get told that it isn't correctregards
Dave

 

[davenn]

I don't know what else to tell you. You've been told how the shape works, but you aren't accepting it and you are making things up that don't fit the reality of what is observed. I don't know what you are hoping to hear instead, but again, you really need to stop with the idle speculation and just start trying to understand what people are telling you.

snap

 

[Alexandra Fabiello]

I don't know what else to tell you. You've been told how the shape works, but you aren't accepting it and you are making things up that don't fit the reality of what is observed. I don't know what you are hoping to hear instead, but again, you really need to stop with the idle speculation and just start trying to understand what people are telling you.

I am trying. Clearly I'm not understanding yet. So try again, in one shot; how does the shape work? In 3D please. As perceived.

EDIT: I am aware that the universe exists in more than three dimensions. It's just rather irrelevant to the topic when we can only perceive three.

 

[russ_watters]

I am trying. Clearly I'm not understanding yet. So try again, in one shot; how does the shape work? In 3D please. As perceived.

EDIT: I am aware that the universe exists in more than three dimensions. It's just rather irrelevant to the topic when we can only perceive three.

It can't even be perceived in 3D. That's why the 2D analogy of the surface of a sphere is used. It really is pretty straightforward even if it is difficult to believe:

1. At the Big Bang, the entire universe was (or nearly was) contained in a single point, and began expanding from there.
2. All points are moving away from each other at a rate roughly proportional to their distance from each other.
3. There is no edge and no center. The only way for this to be possible is for the universe to be curved, so that traveling in one direction leads you back to where you started. You cannot visualize this in 3D: you must use a 2D analogy such as a curved plane. A plane that is curved in a 3rd dimension so that every direction of travel on that plane leads you back where you started is a sphere. The universe works the same way, but in 3D instead of 2D.

It should be easy to see that on the surface of an expanding balloon, all points are moving away from each other and none of the points on the surface of the balloon can claim to be at the center of the surface.

FYI, though, your post #39 was an attempt to rationalize a "we don't know" (which wasn't correct) into a "there still could be a center". You will need to work harder at letting the idea go and trying to understand the reality instead of trying to find ways to avoid reality and hold on to your preference that there be a center.

 

[Alexandra Fabiello]

It can't even be perceived in 3D. That's why the 2D analogy of the surface of a sphere is used. It really is pretty straightforward even if it is difficult to believe:

1. At the Big Bang, the entire universe was (or nearly was) contained in a single point, and began expanding from there.
2. All points are moving away from each other at a rate roughly proportional to their distance from each other.
3. There is no edge and no center. The only way for this to be possible is for the universe to be curved, so that traveling in one direction leads you back to where you started. You cannot visualize this in 3D: you must use a 2D analogy such as a curved plane. A plane that is curved in a 3rd dimension so that every direction of travel on that plane leads you back where you started is a sphere. The universe works the same way, but in 3D instead of 2D.

It should be easy to see that on the surface of an expanding balloon, all points are moving away from each other and none of the points on the surface of the balloon can claim to be at the center of the surface.

FYI, though, your post #39 was an attempt to rationalize a "we don't know" (which wasn't correct) into a "there still could be a center". You will need to work harder at letting the idea go and trying to understand the reality instead of trying to find ways to avoid reality and hold on to your preference that there be a center.

1. You literally just said that the Big Bang isn't a single point. Now you're saying it is. No wait, I think I get it, more or less...
2. Okay.
3. Oddly enough, I actually get the balloon thing, sort of. Though since there IS a start point to the expansion, while technically not a 'center' anymore by the balloon imagery, I think that's basically what the original poster was asking if we could find, just with the wrong term. However, we can't see the universe from outside the balloon, just from our surface of the balloon.

So from our perspective from the surface, what would it look like if we went towards the original expansion point? Where would that be? Would things still look like they're moving away regardless, even as you move 'against the grain' so to speak? I'm starting to think of it as the Earth and flat maps, except in balloon form.

When you say 3D and curve here, it seems less 3D and more higher Ds at that point. Now I'm imagining a rectangular prism curving in on itself and touching its ends together, except from the perspective of the beings inside the thing, they see around the curve as if it were a straight line.

 

[russ_watters]

1. You literally just said that the Big Bang isn't a single point.

Where did I say that? Please quote me.

3. Oddly enough, I actually get the balloon thing, sort of. Though since there IS a start point to the expansion, while technically not a 'center' anymore by the balloon imagery, I think that's basically what the original poster was asking if we could find, just with the wrong term. However, we can't see the universe from outside the balloon, just from our surface of the balloon.

Basically, yes.

So from our perspective from the surface, what would it look like if we went towards the original expansion point? Where would that be?

T=0, everywhere? I don't think there is any other way to describe it. We can only move in 3D space, so we can't move towards the point - it doesn't exist in our space (and I'm not sure it actually exists in any other space).

When you say 3D and curve here, it seems less 3D and more higher Ds at that point.

The universe we observe has 3 spatial dimensions and one time dimension. I'm not sure the curvature can or even needs to be described in terms of additional spatial dimensions.

 

[Alexandra Fabiello]

Where did I say that? Please quote me.

Basically, yes.

T=0, everywhere? I don't think there is any other way to describe it. We can only move in 3D space, so we can't move towards the point - it doesn't exist in our space (and I'm not sure it actually exists in any other space).

The universe we observe has 3 spatial dimensions and one time dimension. I'm not sure the curvature can or even needs to be described in terms of additional spatial dimensions.

Oops, someone else said that, not you. About the Big Bang not starting from one point like the common view is. Sorry.

If we went constantly in one direction in the correct direction, wouldn't we eventually get to the bottom of the 'balloon'? The point where everything is moving away from? That would be more like the 'center of the universe' for the simple fact that we probably wouldn't be able to go through it along the curve to the other side.

 

[Drakkith]

If we went constantly in one direction in the correct direction, wouldn't we eventually get to the bottom of the 'balloon'? The point where everything is moving away from? That would be more like the 'center of the universe' for the simple fact that we probably wouldn't be able to go through it along the curve to the other side.

Which is why the analogy is just an analogy. Imagine a spherical balloon which simply expands. There is no opening. No air needs to be pumped in. This is obviously not possible, but it doesn't matter. The idea is to understand what is going on with the surface of an expanding sphere like this. In such a case, there is nothing on the surface which could be taken as the "center". Wherever you are, you will observe other points on the surface moving away from you, with the speed proportional to the distance.

 

[Frost Dragon]

From what I understand the evidence suggests that the universe is flat which means it's infinite, side note: does this mean infinite mater? Or am I missing something. The way I had to think of this to make sense is using the balloon analogy but in a flat infinite universe. So a piece of rubber that is flat and infinite can stretch and all the dots on that rubber will get farther away. Infinite getting bigger seems impossible but from what I understand it isn't. That's what I remember learning anyway.

 

[Drakkith]

does this mean infinite mater? Or am I missing something.

An infinite universe probably has an infinite amount of matter.

 

[Alexandra Fabiello]

Which is why the analogy is just an analogy. Imagine a spherical balloon which simply expands. There is no opening. No air needs to be pumped in. This is obviously not possible, but it doesn't matter. The idea is to understand what is going on with the surface of an expanding sphere like this. In such a case, there is nothing on the surface which could be taken as the "center". Wherever you are, you will observe other points on the surface moving away from you, with the speed proportional to the distance.

Oh. That's actually pretty cool, but pretty weird as well.