Why is it assumed the universe has no centre?

[Incendia]

Exactly what is in the title...

 

I am confused..How can it be possible for all galaxies to appear to move away from the one you are using as the point of view?

 

Looking from one galaxy it appears that the others move away but if you use many as your point of view how can they all move away from each other?

 

If you universe began from a singularity how can it not have a centre...everything must have expanded from that singularity...therefore everything must be expanding evenly from 1 central point.

Edited December 15, 2010 by ProcuratorIncendia

[Sisyphus]

Exactly what is in the title...

 

I am confusion...How can it be possible for all galaxies to appear to move away from the one you are using as the point of view?

 

Looking from one galaxy it appears that the others move away but if you use many as your point of view how can they all move away from each other?

 

It isn't possible for them to move that way. However, the expansion of the universe is not motion through space. It is an increase of the amount of space.

 

One common analogy is an inflating balloon with dots drawn on the surface. The surface area of the balloon represents space, the dots represent stars, galaxies, etc. As the balloon inflates, the surface area of the balloon increases, and the dots get farther apart. However, the dots are not changing position - there is just more and more "space" between them.

 

If you universe began from a singularity how can it not have a centre...everything must have expanded from that singularity...therefore everything must be expanding evenly from 1 central point.

 

The singularity would have been everywhere. It wouldn't be a point in space, it would be space, just with everything infinitely close together. Imagine instead the balloon is shrinking so that the dots get closer and closer together and the surface shrinks more and more, until finally it shrinks down to zero and there is zero distance between the dots. That is the singularity. It isn't a "where." It's a "when."

[ydoaPs]

The following video has a good visual to show it. If you don't have a lot of time, skip to about 9 minutes in.

 

[Incendia]

I saw that video...it doesn't help...[but I did only watch the first 25 minutes]

 

@Sisyphus: If there is more space...where did it come from?...and planets can move through space...they aren't fixed like dots on a bloon. Space isn't solid like rubber and planets are not fixed...space just phases through objects through the empty space in-between atoms.

 

Also it is the distance that increases not the space...

[Sisyphus]

 

 

@Sisyphus: If there is more space...where did it come from?...

 

Space is just the distances between objects. It doesn't have to come from anywhere. If you mean "why is it expanding," then that's a pretty complicated question that we still don't have a complete answer to, and which I don't particularly understand myself.

 

and planets can move through space...they aren't fixed like dots on a bloon.

 

Why does that matter? If you want, use ants walking around on it instead of dots drawn on it.

 

It's not supposed to be a perfect analogy for the actual universe. Just a way to get at the concept of getting farther apart without moving.

[Incendia]

...we don't have all the answers yet?

Topic closed methinks...[if there is no answer there is no point in me asking the question until someone finds the answer]

Edited December 16, 2010 by ProcuratorIncendia

[Sisyphus]

...If we don't have all the answers yet, why is Steven Hawking wasting his time? [in trying to create a theory of everything.] He should be trying to find the missing answers...

Topic closed methinks...[if there is no answer there is no point in me asking the question until someone finds the answer]

 

If we already had all the answers, people like Stephen Hawking would be out of a job.

 

Also, I said we don't have complete answers, not that we don't have any idea. (I also said I didn't really personally understand it.) Here's a quote from the Wikipedia article on metric expansion:

 

Until the theoretical developments in the 1980s no one had an explanation for why this seemed to be the case, but with the development of models of cosmic inflation, the expansion of the universe became a general feature resulting from vacuum decay. Accordingly, the question "why is the universe expanding?" is now answered by understanding the details of the inflation decay process which occurred in the first 10−32 seconds of the existence of our universe. It is suggested that in this time the metric itself changed exponentially, causing space to change from smaller than an atom to around 100 million light years across.

[ydoaPs]

I saw that video...it doesn't help...[but I did only watch the first 25 minutes]

The part with the dots didn't help you understand how all galaxies moving away from each other looks the same as all the galaxies moving away from you?

[zapatos]

...If we don't have all the answers yet, why is Steven Hawking wasting his time? [in trying to create a theory of everything.] He should be trying to find the missing answers...

Topic closed methinks...[if there is no answer there is no point in me asking the question until someone finds the answer]

He is trying to find the missing answers. I just don't think he checked with you yet on what the important questions are he should be spending his time on.

[Incendia]

The part with the dots didn't help you understand how all galaxies moving away from each other looks the same as all the galaxies moving away from you?

 

It prompted this topic...It said there is no centre or everywhere is the centre just because everything looks like the centre if you overlay the current universe onto the old one. He did it by overlaying 1 dot onto the same dot on the other image...I say thats the wrong way to find the centre...The centre is obviously the centre of the image...

There must still be a centre...even if the universe was everything that everything has now spread out and must have spread out from 1 [or more] point within itself...background radiation making everything appear to be the centre just shows us that background radiation is not good evidence to use because it causes an illusion. Galaxies don't just move away from each other...Good evidence for this is the Andromeda galaxy heading straight towards us.

The universe is spreading out in all directions but that doesn't mean it doesn't/never had a centre.

I found this more helpful;

Also, I said we don't have complete answers, not that we don't have any idea. (I also said I didn't really personally understand it.) Here's a quote from the Wikipedia article on metric expansion:

Edited December 16, 2010 by ProcuratorIncendia

[Mr Skeptic]

Alternately, you could say that the location of the big bang/center of the universe, is 15 billion years ago. After all, that is where it happened.

[CaptainPanic]

The part with the dots didn't help you understand how all galaxies moving away from each other looks the same as all the galaxies moving away from you?

The thread title is: "Why is it assumed the universe has no centre?"

 

The part with the 6x6 matrix of dots in the video (at around 9 min) explained why every point in the universe will seem to the observer to be the center of the universe.

 

However - in that 6x6 matrix, 4 dots are awfully close to the actual center of that universe. The observer on those dots has no way to know it... but that particular universe has an actual center.

 

The initial question, as far as I can see (with my layman's eyes), remains unanswered.

 

To have no center, it must either be a geometrical shape that has no center, or it must be truly infinite.

[ydoaPs]

The thread title is: "Why is it assumed the universe has no centre?"

 

The part with the 6x6 matrix of dots in the video (at around 9 min) explained why every point in the universe will seem to the observer to be the center of the universe.

THe video answered questions asked in the OP rather than the title of the thread.

[Incendia]

Well now it's time to answer the title question...The universe must have a centre...In order for it to not have a centre it must either be infinite [which it is not] or doughnut/bagel shaped...but that would mean that the universe has a hollow centre and therefore still has one.

[Sisyphus]

Well now it's time to answer the title question...The universe must have a centre...In order for it to not have a centre it must either be infinite [which it is not]

 

We don't know that it isn't infinite.

 

or doughnut/bagel shaped...but that would mean that the universe has a hollow centre and therefore still has one.

 

That isn't true. You can't think of the shape of the universe as some 3D object (like a donut) inside a larger space, because we're talking about the shape of space itself. In other words, that "hollow center" is part of the universe, too. There is no "outside," and there are no edges.

 

However, there are plenty of finite shapes with a finite volume but no center or edges. These aren't very difficult to describe mathematically, but can be very difficult to imagine if you're not used to it, as is the whole concept of curved space.

 

One example is a universe where if you travel in a straight line in any direction, you will eventually get back to where you started. This is similar to how if you walk in a straight line on the surface of a planet, you'll eventually get back to where you started, except the surface of a planet is 2 dimensions, and space is 3.

[HAL9000]

Well now it's time to answer the title question...The universe must have a centre...In order for it to not have a centre it must either be infinite [which it is not] or doughnut/bagel shaped...but that would mean that the universe has a hollow centre and therefore still has one.

 

 

 

No, you didn't give an answer, because you didn't formulate the question. And if you try to formulate one, then the question and all the attempted answers will be necessarily metaphysical, and thus meaningless.

 

The premise of a Big Bang (call it Creation if you like) is not a consequence of modern physical theories, it is their basis. This is the ultimate reason that justifies the validity of all the scientific inquiry that uses it as the main principle, and as such it does not explain anything. It is just rational to suppose that really everything, including space and time, came out of nothing. Because if you negate everything, it is always a good place to start to think about that very everything.

Observe, that you can't imagine the absence of space, because your intuition is already inevitably spacial. And without intuition you cannot provide any reasonable statement concerning the origin of space.

Although I am not completely sure whether we can consider any good analogy to this problem, but I would advise you to imagine that the universe, and hence space, began with your birth. Can you or anybody else locate a point or time instant where YOU came into (conscious) being? This is a typical example of a meaningless question.

Edited December 17, 2010 by HAL9000

[Incendia]

It is unlikely to be infinite...Why is there no outside? No edge? How about a surface?

And why would you end up back where you started if you were travelling through space?

Gives me the names of your centre-less shapes... [Many things form spheres in space so it too may be spherical. As it is spreading out equally in all directions it is likely to be a spherical shape IMO.]

 

You can use flying equipment to leave the surface of a planet...Why no a special kind of space-ship to leave the universe.

 

@Hal9000: I'm not a creationist...I don't like any religions...they all sound like nonsense.

 

It isn't possible for it to arise from nothing. It bounced back from the old universe...where that came from I do not know but there is no point speculating until information about it has been found which it never will...[see[google] big bounce theory]

 

I'm not asking where the centre is...I'm asking why it is assumed there is no centre...sure we might never find the centre but it doesn't mean there never was a centre.

[Sisyphus]

It is unlikely to be infinite...

 

Says who?

 

Why is there no outside? No edge? How about a surface?

 

Because the universe, by definition, is everything that exists. An edge is a boundary between things inside and things outside.

 

And why would you end up back where you started if you were travelling through space?

 

Because that's its shape. The same reason if you travel in a straight line on the surface of the Earth, you end up back where you started.

 

Gives me the names of your centre-less shapes...

 

Some of the various possibilities are given here:

http://en.wikipedia.org/wiki/Shape_of_the_Universe

 

The example I gave, the 3D analog to the 2D surface of a sphere, is called a3-sphere.

 

[Many things form spheres in space so it too may be spherical. As it is spreading out equally in all directions it is likely to be a spherical shape IMO.]

 

It is not spreading out through space, though. That's the whole point of this.

 

You can use flying equipment to leave the surface of a planet...Why no a special kind of space-ship to leave the universe.

 

In order to leave the surface of the planet, you have to enter the third spatial dimension. To similarly "leave" the universe, you would have to enter a 4th spatial dimension. There is no direction in space that will lead you out, just like you can't leave the Earth by walking.

[HAL9000]

It is unlikely to be infinite...Why is there no outside? No edge? How about a surface?

And why would you end up back where you started if you were travelling through space?

Gives me the names of your centre-less shapes... [Many things form spheres in space so it too may be spherical. As it is spreading out equally in all directions it is likely to be a spherical shape IMO.]

 

You can use flying equipment to leave the surface of a planet...Why no a special kind of space-ship to leave the universe.

 

@Hal9000: I'm not a creationist...I don't like any religions...they all sound like nonsense.

 

It isn't possible for it to arise from nothing. It bounced back from the old universe...where that came from I do not know but there is no point speculating until information about it has been found which it never will...[see[google] big bounce theory]

 

I'm not asking where the centre is...I'm asking why it is assumed there is no centre...sure we might never find the centre but it doesn't mean there never was a centre.

 

I'm not a creationist either, but I do believe that anybody, who asks questions about the origin of the universe, tells the same old story in modern verse, so that it is poetry at best and not science.

 

By asking, why it is assumed that the universe has no centre, you expect an answer from science. But science cannot enlighten you about its own assumptions, it can only provide consequences from these assumptions.

 

In my previous post the meaning of the word "locate" must have surely mislead you, just like the word "birth"...that is why I hold that any analogy expressed in common language is actually misleading here.

 

You claim that there must be the centre. So you can think of the possibility of a centre (that is what I meant by "locate"). But then you take pieces of scientific arguments and try to argue for the converse assumption analytically, on purely logical grounds, i.e. you try to generate a contradiction. For example here:

 

Well now it's time to answer the title question...The universe must have a centre...In order for it to not have a centre it must either be infinite [which it is not] or doughnut/bagel shaped...but that would mean that the universe has a hollow centre and therefore still has one.

 

But purely logical analysis of scientific arguments produces tautologies, because any scientific inquiry needs premises that evolve on reasonable grounds, not by logic. Otherwise you get rationalism, that leads once again to metaphysics.

 

You cannot argue for the assumption "there must be a centre" by using the evidence of the theories, which are based on the converse assumption. All that is left is the obligation to derive a consistent theory from your own premise. This is the only way to prove the validity of the converse assumption. And I bet that will be a task too tough to cope with!

[ydoaPs]

The universe is flat and probably unbounded(infinite).

 

It isn't possible for it to arise from nothing.

Yes, it is, because the universe is flat.

 

It bounced back from the old universe

Extremely unlikely since it is flat; it is either the the only universe or the last.

 

To see how we know it's flat, watch the video I embedded above.

Edited December 17, 2010 by ydoaPs

[Incendia]

I finally got the time to watch the entire video...

Edited December 17, 2010 by ProcuratorIncendia

[CaptainPanic]

LOL

The question whether the universe has a center is in fact the same question as what shape it is, or whether it is infinite.

 

Bottom line, as far as I know, is that we're not 100% sure. We don't know if there's a center or not. All we know is that we can not determine (for reasons explained in the video with the dots) if we are ourselves in the center. All we know is what we don't know.

 

Or, to use Donald Rumsfeld's words:

We know there are known knowns: there are things we know we know. We also know there are known unknowns: that is to say we know there are things we know we don't know. But there are also unknown unknowns — the ones we don't know we don't know." —Defense Secretary Donald Rumsfeld, Defense Department briefing, Fe. 12, 2002 (link to place where I found this)

 

Please don't use this quote to hijack the thread - it's meant as a funny footnote !