# I There must be a center of the universe...?

1. Nov 25, 2015

### thetexan

I am going to state the few assumptions I am making as I ask this question.

1. The big bang was an expansion of space/time rather than a physical explosion, although the general effects seem similar.
2. The universe is not infinite and cannot be if #1 is true.
3. The observable universe is but a small visible subset of the actual entire universe. How much the ratio is I don't know.
4. Expansion and recession makes each observable object in the universe seem to be moving away from us, the observer. The resulting conclusion that we are at the center of the universe is therefore unfounded when it is based solely on this visual appearance.
5. If there is a center to the universe we can not know where it is.

Now here are my assertions based on these assumptions.

1. A few femtoseconds after the big expansion began the universe was maybe 100 feet across. (I am aware of the ridiculousness of this measurement due to relativity but go with me for a minute).
2. If I could stand off from this 100 foot sphere I could point to it and say to my friend, "Joe, there is the entire universe and it fits into a sphere 'that' big (however you want to describe 'that' big...I am using 100 feet across).
3. Since the entire universe fits into an observable sphere of 'that' big then we can say that the extents of the universe fit into a observable if not measurable geometric sphere.
4. Even if the sphere or whatever shape it is is irregular we can say that it is a finite object with a 3 dimensional shape observable by me and Joe.

Here is my point...

5. That observable shape which contains the universe has a geometric center if not an effectual center. By that I mean the center from which all expansion is expanding from. Which means...
6. That there will be some mathematical point that is not part of the expansion because it is dead center to it.
7. And unless there is some future disturbance to the overall space/time in that region containing that point, it will remain at its original point in the expanding universe.

This is a long way to ask my question but I wanted to show how I am arriving at my notions that generate this question. Here it is...

Even though we can not know where the center of the expansion is, theoretically, must there not be one somewhere? Isn't there a theoretical center to the sphere that contains the entire universe?

I know we are talking about big numbers here but if one can build a sphere around the actual physical extents of the universe isn't it a simple geometry question?
tex

2. Nov 25, 2015

### Orodruin

Staff Emeritus
This is wrong. The universe is possibly infinite and has been infinite all the time (the time $t=0$ is a singularity which is not part of the Big Bang). What goes to zero as $t\to 0$ is the scale factor $a(t)$.

Even if the universe is finite, it does not need to have a center.

3. Nov 25, 2015

### phinds

And I would add that your statements about "standing off" from the universe do not make any sense. The universe is now, and always has been, everything there is and there IS no place from which you can "stand off" because there is no place that is not part of the universe. This is not semantics, it is fundamental to the physics. You cannot (legitimately) say "if I suspend the laws of physics, what do the laws of physics have to say about <insert nonsense of your choice>".

4. Nov 25, 2015

### thetexan

I'm trying a thought experiment here. It's not nonsensical to imagine being able to visualize the universe from afar. I see pictures in science mags all the time of multi universes where they are drawn as individual and distinct objects as if observed from afar. This is no more imaginary than my illustration. And I don't believe this convolutes any discussion about my question.

Is the universe containable within a large enough sphere. This should be a simple yes or no. And if no there should be a good reason why not. Don't mistake this a argumentative. My understanding is limited and I know it's difficult to explain this kind of stuff to non-physicists. It seems to me after everything I've read that the universe is not infinite in the sense that if it can continue to expand then it can annex more of whatever stuff it has been annexing. AND I UNDERSTAND that even this statement implies that there is a relationship between the expanding universe and whatever 'stuff' is beyond meaning that the 'stuff' itself is existent and therefore part of the universe. In that sense the universe in infinite in that all that there is or can be is already a part of the universe.

I get all of that. But to my point, the universe expanded from a point to a bigger 'something'. I think the something has a general shape...spherical or something and if so has a center.

And what I would like is someone to explain how my neophyte analogy is incorrect...in a way I can understand.

This brings up an interesting definition question. Let's consider what is beyond the universe which is nothing. Not even nothing...it is a nonexistent nothing where even space/time doesn't exist. What makes it something? As the universe expands space/time is expanding but into what. Doesn't the use of the word expand imply expanding into something. Otherwise the term is meaningless. We hypothesize that the universe is expanding and has expanded. The only term of reference seems to be based on the relationship of objects to one another within the universe. Not the size of the universe to some huge ruler outside of the universe. And expansion includes the implication of a size change relative to something else.

Doesn't it.

tex

Last edited: Nov 25, 2015
5. Nov 25, 2015

### phinds

Yes, popular science is wonderfully misleading and often has nothing to do with actual physics.

No.

This is incorrect. Infinite can continue to be added to. Google the Hilbert Hotel.

Wrong again. It MAY have expanded from a finite size or it may have been infinite to start with. We don't know. Current experimental evidence points toward an infinite universe but that's not conclusive.

Wrong again. Finite shapes do not have to have a center.

No. You are making the common mistake of assuming infinity can be treated algebraically like a number. It can in some forms of math but not in this case. Google "Hilbert Hotel".

By the way, this topic is discussed here with great regularity. If you would like to see the answers we gave you repeated over and over (and often expanded on) just do a forum search.

A good place to start is the 5 links at the bottom of this thread.

Last edited: Nov 25, 2015
6. Nov 25, 2015

### nikkkom

#2 is wrong. Universe can be infinite. However, let's assume that it is finite...

I'm sure you have played "pacman" game. Now imagine yourself in some magic office building which has properties of "pacman field": namely, you can go through rooms and corridors and they never end (there is no "outside"); however, even if you go into one direction (IOW: not in circles), you notice that you eventually enter a room you already been through.

Where is the center of this "magic office building"?

7. Nov 25, 2015

### Lino

Thetexan, Maybe I could just add one more thing that helps me ... It is not the entire universe that fits in to an observable sphere, it is the entire OBSERVABLE (caps only for emphasis, not a shout :) ) universe that fits in to an observable sphere.

If you could step outside our observable universe, then you could talk about the expanding sphere of that observable universe, with its geometric centre ... but you are still in the overall universe, which maybe infinite / closed / flat / ... or not, and does not need to have a centre

Other corrections that have already been highlighted, what you are saying is correct for the observable universe, not the overall universe.

Regards,

Noel.

8. Nov 25, 2015

### Staff: Mentor

People have already pointed out that #2 is wrong, but didn't connect it to #1: #2 is wrong because of the gloss-over you did with #1, saying that "the general effects seem similar". Right: #2 only follows from #1 if the effects really are similar. They aren't. The Big Bang has virtually nothing in common with an explosion. Superficially you could say both involve an expansion, but the geometry of the expansion is very different.

9. Nov 30, 2015

### Hellmut1956

I have seen once a picture, sadly I do not remember where, that was claimed to be closer to what our current understanding of the universe is. Imagine, just for the purpose to keep it imaginable, that the universe consists of a 3D-Matrix of locations. The universe expansion is just that the distance between those nodes increases. So very early in the universe all those nodes in this 3D-Matrix all those infinite number of nodes where there. So it doesn't matter next to which node you were or are, the other nodes of this matrix are all increasing their distance to the neighbouring nodes! An Indication of this is that independent in which direction or from which location you look at the background radiation, it will always look the same!
The other aspect the initiator of this thread should make clear to himself, is that the view is dependent from the viewer. The photon behaviour when going through the 2 slits is either like a particle or like a wave dependent on how the viewer observes. It is not independent of the viewer, another indication that the only way to really grasp physical concepts is by using the only language we know of that can grasp, describe, calculate issues in physics that are counter intuitive, is mathematics. I am just studying the course from Keith Devlin, professor at the Stanford University, Introduction to Mathematical Thinking, as part of my efforts to learn that language!

10. Nov 30, 2015

### curious Tom

thetexan has a good point. Ten Billion years ago, the universe was considerably smaller than it is now, so something must have been 'outside the borders' of the universe then; five billion years after that the universe, though still considerably smaller than it is now, had expanded into that area which had previously been beyond its borders and so therefore was considerably larger than it used to be. The best guess is that it will continue that way forever (or will as long as dark energy propels it). Consequently, whatever was beyond the borders before either (a) has been incorporated into the present universe after being engulfed by it or (b) been simply pushed further away from where it used to be by the inexorable force of expansion. Curious Tom

11. Nov 30, 2015

### phinds

Absolutely incorrect. There IS no "border". The universe has no center and no edge.

It was larger, but it did not expand "into" anything. I recommend you study some basic cosmology.

again, there IS no "border" and no "outside".

Google "metric expansion" and "the Hilbert Hotel".

12. Nov 30, 2015

### QST

If space/time is a true continuum then the universe is infinite no matter what "size" it is. The universe could only be finite if space/time were digital.

13. Nov 30, 2015

### phinds

Incorrect. What makes you think this?

HUH? that doesn't seem to make any sense. What does it even MEAN for the universe to be digital?

14. Nov 30, 2015

### Staff: Mentor

Sorry, but that's just a re-statement of the same wrong understanding thetexan had. I know it is hard to envision something else being true, but you are going to have to let that go. I'm not sure what else to say except to suggest you read some of the other posts in the thread.

15. Nov 30, 2015

### PeroK

Instead of considering the universe, let's just consider the question of shapes and geometry.

In two dimensions: a disc (the area within a circle) has a centre that is part of the disc, but the centre of a circle is not part of the circle. If you were compelled to live on a circle, there would be no centre that you could visit.

In three dimensions, you have the same situation with a solid sphere (the centre is part of the sphere) and a spherical surface (its centre is not part of itself).

In higher dimensions, you have similarly the concept of a hypersurface.

To begin with, you could expand your knowledge of shapes and geometry. Then use this knowledge to understand what people are saying about the universe.

16. Nov 30, 2015

### QST

If you try to impose a coordinate grid upon a space/time that were digital then there would be only a finite number of possibilities. I realize it is hard to imagine space/time being digital.

17. Nov 30, 2015

### phinds

I still have no idea what you are talking about.

18. Nov 30, 2015

### JJNic

I think he means that GR is a continuum field theory and that R^n is an uncountable set? by "being digital" i think he actually means 'discrete' (to overcome the uncountability). Anyway, QST, thats not always problematic (n-volume integrals over R^n can still be finite), but can be (like UV divergences in QFT) when not taken care of properly.

19. Nov 30, 2015

### curious Tom

If the 'expanding balloon' explanation is correct, then thetexan and I have to be on the right track. From what the staff said, this and other diagramable conventions are actually incorrect. On the other hand, neither thetexan nor I invented them -- these were invented and drawn by physicists and/or their illustrators to explain concepts that were difficult to put into words. However, these weren't just some guys off the street from Disney making diagrams in their spare time, but include regular contributors to Scientific American and Discover magazines. The concept is even used by Steven Hawking himself in A Brief History Of Time, especially at pages 36 and 148-181. Hawking speaks in terms of the light cone of an event: a particle which is traveling at or below the speed of light is said to be in the future of P. That which is in the past is able to reach event P by traveling at or below the speed of light and is said to be in the past. The events that do nor lie in the future or past of P are said to lie in the elsewhere of P. When the event P is the universe itself -- either at the time of the big bang or at various times (like now, for instance) during the expansion of the universe, what exactly is 'the elsewhere'? Numerous illustrations regarding time cones show the elsewhere to be the space into which the universe is expanding. If these and all the other illustrations that physicists and popularizers of science use are false, isn't what you're really saying to me and thetexan: "Fools, how could you possibly be gullible enough to believe what we told you last time?" Curious Tom

20. Nov 30, 2015

### Staff: Mentor

Sorry: still no.

21. Nov 30, 2015

### Orodruin

Staff Emeritus
No, you are not, you are misinterpreting the analogy. The analogy is quite fine, but your interpretation of it is not.

22. Nov 30, 2015

### rootone

What is often misunderstood about the balloon analogy is that it applies to the surface of a balloon.
The surface only, air inside the balloon or outside of the balloon (invisible extra dimensions) is no part of it at all.

23. Nov 30, 2015

### phinds

24. Nov 30, 2015

### Chronos

Drawing from GR, it would be not be inappropriate to deduce that 'finiteness' is strictly local in a sense similar to that of the relativity of simultaneity. A universe that originated with finite boundaries can never grow to infinite proportions. Neither can a universe that originated in an unbounded state ever shrink to finite proportions. The observable universe does not conflict with these principles. It is widely agreed the observable universe has always been bounded, hence finite and could in priciple be quantized. There is, however, no compelling evidence suggesting an absolute lower limit on the size of any such fundamental units. Our best guess is that quantization could emerge somewhere around the planck scale. But, this remains little more than conjecture. We do not, and most likely will never have technology sufficient to validate this hunch. Quantization is merely a mathematical trick useful for managing the divergencies that appear to arise when we approach the realm of the infinitesimal. Just because it works does not prove the universe is inherently discrete or finite. The laws of physics have always been scale dependent. The laws of gravity are extremely well represented by our modern theories of gravitation. Yet most scientists would agree they appear to be incomplete at sufficiently small and possibly at sufficiently large scales. Would a working quantum gravity theory be the ultimate end all theory of gravity? I would guess it is merely another layer in an unending layer cake. Surely, GR has taught us that the universe abhors absolutes.

25. Nov 30, 2015

### Bandersnatch

The 'elsewhere' are the places in the universe from which light did not have the time to reach the observer at P, or which could not yet observe P.
You can draw lightcones in any universe, regardless of its expansion status, and there will always be events that lie outside past lightcones of other events.

Lightcones do not represent any sort of event horizons, but merely show which past events had the chance to interact with event P (or, which events event P will be able to interact with in the future). This is nothing else than expressing what is the extent of what you can see, when the time light had to travel and reach you is finite.

Since lightcones are drawn in space-time coordinates, they naturally 'expand' as you move forward in time (their 'peak' moves up the time axis together with you, the observer). This is unrelated to the expansion of the universe, and just represents the passage of time, and that you get to see farther and farther as time passes.

So, for example of a (future) lightcone, if the event P is you reading this, the 'elsewhere' at the time of P is everywhere in the universe, including e.g. your next door neighbour, or an alien sitting on Mars, as at the precise time of P there is no other place in space that could have seen the event but the place collocated with P. As the time passes, and light from the event spreads out, the 'elsewhere' shrinks as more and more observers get to see the light.