# B What is the center of the universe?

1. Jul 2, 2015

### KylieVegas

I read in a book that there is no center of the universe because for example, you put dots around a balloon, and when you put air into the ballon, the dots will seperate from each other, and each dot will see themselves as the center of the balloon, depending on the dots' perspective. That only applies if our universe is spherical, like a balloon. But the accepted shape of our universe is flat, in that case, what is the center of our universe? Please tell me if i miss out something, and i am open to any other theories/facts. Thank you and have a nice day!:)

2. Jul 2, 2015

### Staff: Mentor

There is no center of the universe that we know of.

3. Jul 3, 2015

### jaormsby

There is no definitive center of the Universe. The only center we can define is the center of the observable Universe but the Universe itself extends far beyond that. Exactly how far can't be determined.

4. Jul 3, 2015

### Chronos

The 'center' of the universe is an observer dependent illusion, just like the 'edge' of the universe. Wherever you may be in the universe it appears you are both at its 'center' and at its most ancient point. See any logical disconnects with that?

5. Jul 3, 2015

6. Jul 4, 2015

### tfr000

The balloon thing is meant to be a 3-d model of 4-d space. In other words, the inhabitants of the balloon universe are trapped in the thin skin of the balloon. If they go in any direction, they end up back where they started, hence, no center that they can detect. Extrapolate to the real universe...

7. Jul 4, 2015

### phinds

No, it is essentially a 2D model of 3D space. We don't live in 4D space. I suggest that you too read the link in my signature.

8. Jul 8, 2015

### SteamKing

Staff Emeritus
Everybody knows it's Boston, Massachusetts. After all, Boston is nicknamed "The Hub", as in "the Hub of the Universe".

https://en.wikipedia.org/wiki/Boston_nicknames

9. Jul 8, 2015

### newjerseyrunner

How would you define the center? If you are on a line, the center would be defined as the point where you have the exact same amount of distance in front of you and behind you. If both ends go off to infinity, no matter at what point in the line you are, you always have infinity in front and behind you, therefore you can not define a location where you have the same distance in front and behind you. infinity does not equal itself.

10. Jul 8, 2015

### KylieVegas

Thanks for the reply guys! I did some research and i understand it now :)

11. Jul 8, 2015

### KylieVegas

You don't have to be rude, i asked because i didn't understand :)

12. Jul 8, 2015

### phinds

I agree. Just so you know, if you object to a post, you can report it using the report button that exists in each post. The moderators have a low tolerance for rude behavior, as I know very well 'cause I get called on the carpet every now and then when I forget to bite my tongue

EDIT: sometimes people come here and ask very basic questions, clearly without having made the slightest attempt to figure things out for themselves. This can be annoying, but you clearly did not do that (and even if you had, the moderators still ban rudeness).

13. Jul 9, 2015

### Chronos

Phinds, don't be put off by naive questions - we all have suffered that disorder. Cosmology is complicated. I like them, they are the easiest to answer with any sense of confidence.

14. Jul 9, 2015

### phinds

Oh, I have NO problem with naive questions. I was full of them when I first decided a few years back to start learning a bit about cosmology and quantum mechanics. What I object to is people who make no effort on their own. The OP had clearly made an attempt to figure it out and was understandably puzzled, which is the perfect time to come here to PF for help.

15. Jul 10, 2015

### Joe Ciancimino

Not exactly accepted theory, but I tend to think of the center of the universe as the past and the universe expands into the future. Works well in a 4D model, even better in a 5D model of Hugh Everett's many worlds interpretation so long as the universe is not flat.

16. Jul 10, 2015

### Staff: Mentor

Unfortunately this is likely to cause even more confusion than the standard analogies.

17. Jul 29, 2015

### DHF

I had similar questions on the Center of the universe a while back. I found it difficult to grasp the concept of no center but then someone here (I am sorry I cant remember who posted) asked "where is the center of the surface of the Earth?" That helped me get my head around the idea that there is no center to the universe.

18. Jul 30, 2015

### nuwanda

OK, perhaps you could share your understanding since your beginner perspective would help someone like me. Others here may join in, of course.

I have this image of a starting point expanding outwards in the form of the ballooning surface. At that moment a center ceases to exist and becomes a surface with the matter of the original center on it, each bit of that matter expanding away from each other as the surface of the balloon expands.

If that's not a reasonable image, albeit simplistic, by what description can the universe be said to have had a starting point from which matter originated?

Further, does this mean that, in the balloon model, that the balloon is empty and all that exists is on the surface?

Further again, I may be having a problem with this idea that a void, an emptiness, now exists within this balloon upon which the surface rests, and a void into which the surface is expanding. I guess this goes to the perhaps mistaken idea that something existed outside the origin into which things are expanding.

By the way, if there's a beginner's forum I should use, please let me know.

Last edited: Jul 30, 2015
19. Jul 30, 2015

### Staff: Mentor

It can't be said to have a starting point at all. That's the entire point (pun not intended).

20. Jul 30, 2015

### Bandersnatch

@nuwanda it's easier to start from the present time and go backwards, rather than the other way around.
Working some more with the analogy at hand, if you have this balloon's surface, and start deflating the balloon, then the surface will become more and more compact, and points on it closer and closer together, but no matter how small you'll make the balloon, it'll never stop having a surface and will not turn into a point.
Even an infinitely small balloon is still a balloon.

21. Jul 30, 2015

### nuwanda

Certainly we can say that a thing compressed will always be a smaller version of itself. But at a certain point, conceptually, is that the singularity from which the universe originated?

Conceptually it's easy to imagine infinitely small versions of a thing. Just as it's easy to consider an infinitely long series of numbers. But that's not what I'm asking. Going to the discussion point of a center I can see that a balloon surface expanding means that the matter on the surface of the balloon has no center, although it certainly seems to have an origin within the balloon from which it expanded.

Is it a matter of confusing the terms origin (singularity) and center? Because I can certainly see that our current position on the surface of the balloon in relation to other locations on that surface doesn't need any reference to an original origin point.

22. Jul 30, 2015

### Bandersnatch

The balloon analogy requires you to discard the concept of anything beyond its 2-dimensional surface. The 3D 'centre' of the balloon is not supposed to represent anything about our universe.

You're right, the singularity shouldn't be confused with the centre. The singularity is what you get when you do try and get the 'balloon' to an infinitely small size. Much like with a function of the form $1/x$, if you try to get it to zero, it stops being defined. I.e.: the function has a singularity at x=0, same as the BB theory ends up with a singularity at scale factor a=0 (scale factor is the fraction of current distances, so at a=0 everything is on top of everything).

The singularity is commonly taken to mean that the theory is unfit to describe a regime where it appears, not that it represents anything physical.

23. Jul 30, 2015

### nuwanda

OK, I may need to reset here.

In what way is our universe different than a firework that has exploded, we the sparks, and the original firework no longer in existence?

We have a singularity, conceptually, the origin of our universe. Is the term expansion invalid? That is, what did matter and energy expand into? And if expansion is valid as a cosmological term, then the expansion must have occurred away from something and into something else.

I think I'm reasonably good at abstractions being a programmer by trade. But analogies help when concepts are too abstract. Are there more helpful analogies than the expanding balloon?

24. Jul 30, 2015

### Bandersnatch

25. Jul 30, 2015

### nuwanda

OK. My idea of expanding into something is not right. I get that. I was wrong to suggest something out there existed.

But the idea of expanding away from an origin surely must be valid. I think that's what most amateurs conceive as a center.