# What is in the center of the universe?

If the universe has formed & originated by a Big Bang Explosion, then there must be empty space left in the center of the explosion site, as all the matter is travelling at tremendous speeds away from the center, and there must be more matter, stars, galaxies and dust, etc near the present periphery or circumference or horizon of the present universe. As that big explosion has taken place about 13.7 billion years back, then the outer boundaries of our universe are 13.7 billion light years away from the centre of the explosion of Big Bang.

Have our astronomers discovered hollowness or emptiness anywhere in the centre of the universe or not?

• Similar questions on Phys.SE: physics.stackexchange.com/q/25591/2451 and links therein. Jan 4 '14 at 17:46
• I am. And I have indeed discovered some hollowness. This is all subjectively proven beyond doubt. Nov 12 '16 at 20:24
• The universe is scraping foetus off the wheel, we dont know the nature of it's juices, nor the direction from which it came. it just hit us. we thought... UH? and that was the extent of all scientific knowledge. we don't have it's number plate, we dont know if there was a roofrack on the vehicle, it could have even be a jumbo. the only thing we know is, it was fast. Dec 22 '16 at 8:01

I think your question is on topic, but @RhysW has linked a very helpful post in understanding why your question is a common misconception about the Big Bang.

No Center

There is no 'center' to the universe. At any point, a local observer will claim that they are at the center of the universe by the way galaxies move away from them. How can we possibly know this? The universe appears to be both homogeneous (has the same structure everywhere) and isotropic (there is no preferred direction). If these are indeed properties of the universe, then the expansion of the universe must be the same at all other locations (See: The cosmological principle).

How the Big Bang and Explosions Differ

Additionally, the Big Bang is different from an explosion in the following ways:

1) Particles involved in an explosion slow down eventually due to frictional forces. Think of fireworks (http://www.youtube.com/watch?v=qn_tkJDFG3s). Particles are moving the fastest at the instant of explosion, and slow monotonically with time. The expansion of the early universe does not follow this trend, though sometimes people use the word 'explosion' to describe the enormous volumetric increase (an increase by a factor of $\sim10^{76}$) which occurred between $10^{-36}- 10^{-32}$ seconds after the Big Bang, which is aptly named inflation.

2) An explosion implies the existence of space. For an explosion to take place, particles (whether we're talking about matter or light) must have space to explode into. Strictly speaking the inflation of the universe is an expansion of space-time coordinates, and so the word explosion cannot really apply since there was nothing for space-time to explode into.

Your are misunderstanding the expansion of the Universe. The Big-Bang is not an explosion: this is the moment in time when the Universe had an (near) infinite density. So there is no center in the Universe as there is no center of the SURFACE of the earth (this is the most popular 2-dimensional analog).

Since this primordial ultra-high density state, the Universe is expanding, atoms have formed, stars and galaxies have formed and now, at very large scale, the distance between two clusters of galaxies continue to increase with time due to the expansion.

In one sense any point you choose is at "the centre" of the universe and at any point in the universe, at a large scale, the universe looks the same as at any other point. This is not the same as saying the universe is infinite, though (but it could be). The analogy with an explosion is a poor one, as explosions expand into existing space. With the Big Bang space itself expands. But by definition space does not have an edge (if it did then there would be a "meta space" which would be the real space and so on) and so everywhere is the centre and/or nowhere is.

The universe doesn't expand away from any centre perse. All the distances are expanding uniformly throughout the universe. This causes such an effect that for each individual observer, it looks as if the entire universe moves away from them. It can be demonstrated using this figure (from google):

$A$ represents the universe at one moment, $B$ represents the universe at a later time. You can notice (barely) that $B$ is scaled up by a small amount. This represents the expansion of the universe. Now, suppose you put $B$ over $A$ as shown in $C$, then it looks like the universe expanded away from $X$. But if you place them as shown in $D$ then it looks like the entire universe is expanding from another point! This is all due to the homogenous expansion of the universe.

What is in the center of the universe?

This question over at Physics.SE: "Did the Big Bang happen at a point?", which has an answer with over 300 UpVotes, explains:

"The simple answer is that no, the Big Bang did not happen at a point. Instead it happened everywhere in the universe at the same time. Consequences of this include:

• The universe doesn't have a centre: the Big Bang didn't happen at a point so there is no central point in the universe that it is expanding from."

• The universe isn't expanding into anything: because the universe isn't expanding like a ball of fire, there is no space outside the universe that it is expanding into.

We are less than a spec in our supercluster:

There is a Wikipedia webpage: "History of the Center of the Universe - The nonexistence of a center of the Universe" which explains:

"A homogeneous, isotropic universe does not have a center." - Source: Livio, Mario (2001). The Accelerating Universe: Infinite Expansion, the Cosmological Constant, and the Beauty of the Cosmos. John Wiley and Sons. p. 53. Retrieved 31 March 2012.

See also this CalTech video: "Where is the center of the universe?".

If the universe has formed & originated by a Big Bang Explosion, then there must be empty space left in the center of the explosion site, as all the matter is travelling at tremendous speeds away from the center, and there must be more matter, stars, galaxies and dust, etc near the present periphery or circumference or horizon of the present universe. As that big explosion has taken place about 13.7 billion years back, then the outer boundaries of our universe are 13.7 billion light years away from the centre of the explosion of Big Bang.

Have our astronomers discovered hollowness or emptiness anywhere in the centre of the universe or not?

Zooming in to the Milky Way (center of this image, but not the center of the universe) we see:

The blue areas near us are the local void, while the area to the left is the great attractor.

The shape of the universe, that we can detect/see, is complicated - it not a simple sphere or football shaped, radiating from a central point. The current measurement of the age of the universe is 13.799±0.021 billion ($$10^9$$) years within the Lambda-CDM concordance model. We can only see and measure so far, and during the past nearly 14 billion year parts of the universe have grown denser and parts have spread apart.

See these Wikipedia webpages: "Observable universe" and "Observational cosmology", this is from "Size and regions":

The size of the Universe is somewhat difficult to define. According to the general theory of relativity, some regions of space may never interact with ours even in the lifetime of the Universe due to the finite speed of light and the ongoing expansion of space. For example, radio messages sent from Earth may never reach some regions of space, even if the Universe were to exist forever: space may expand faster than light can traverse it.

Distant regions of space are assumed to exist and to be part of reality as much as we are, even though we can never interact with them. The spatial region that we can affect and be affected by is the observable universe.

The observable universe depends on the location of the observer. By traveling, an observer can come into contact with a greater region of spacetime than an observer who remains still. Nevertheless, even the most rapid traveler will not be able to interact with all of space. Typically, the observable universe is taken to mean the portion of the Universe that is observable from our vantage point in the Milky Way.

The proper distance—the distance as would be measured at a specific time, including the present—between Earth and the edge of the observable universe is 46 billion light-years (14 billion parsecs), making the diameter of the observable universe about 91 billion light-years ($$28×10^9$$ pc). The distance the light from the edge of the observable universe has travelled is very close to the age of the Universe times the speed of light, 13.8 billion light-years ($$4.2×10^9$$ parsecs), but this does not represent the distance at any given time because the edge of the observable universe and the Earth have since moved further apart. For comparison, the diameter of a typical galaxy is 30,000 light-years (9,198 parsecs), and the typical distance between two neighboring galaxies is 3 million light-years (919.8 kiloparsecs). As an example, the Milky Way is roughly 100,000–180,000 light years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light years away.

Because we cannot observe space beyond the edge of the observable universe, it is unknown whether the size of the Universe in its totality is finite or infinite.

Estimates for the total size of the universe, if finite, reach as high as $$10^{{10}^{{10}^{122}}}$$ megaparsecs, implied by one resolution of the No-Boundary Proposal.

According to the proposal Hartle–Hawking state: "The universe has no initial boundaries in time nor space".

Dr. Brent Tulley published an article: "The Laniakea supercluster of galaxies" (free arXiv preprint) and associated supplimentary video, along with Dr. Daniel Pomarède's Vimeo directory, specifically this video: Cosmography of the Local Universe (FullHD version) from which these images were drawn, which shows the shape of part of the universe as we know it:

• Take the WMAP data and project all galaxies within 8K km/s (1:18 on the video) onto a 3D space:

Click image to animate

A close up of our location shows the large local void:

The amorphous geometry of the Universe is currently being studied, and the large scale distribution of the galaxies is similar to a sponge. The measure in the middle of the image represents 1.5 billion light years. light travels in every direction, and at the time of the big bang, there was no light to travel anywhere, and early in the theory of the big bang, there were no 3D directions that we can conceive, no definition of straightness and edge, no distance in between anything in a know geometry, in 3D, 4D, 5D, 12D superstring theory. So to find the geometry you need, Mathematics can become 12D/28D and is confusing to us, the notion of center is different in 12/20 dimensions. The Big Bang high temperature predates atoms, light, subatomic particles, matter, gravity, it predates the existence of known geometry, its contents exceeds any geometrical or finite measure, the only focal point is time, so to measure it you need to invent many new dimensions and geometry models.

The number of voids in the sponge could be well over trillion times more numerous than the number of atoms in the ocean. There could be a Googolplex MPC's as a mote of the total. So where is the center of that? When will time end?

The big bang was amorphous from our viewpoint, and in that sense you could say it is "amassive" It's cosmic, space and physical properties are incommensurate (it's a nice word to say unmeasurable/unrelated).

If you imagine that our view of the cosmic background radiation(13.8bn LY) has the diameter of an atom in the sea. The big bang perhaps also happened in another atom on the other side of the sea, so the geometry doesn't have a gradation of measurement that can be defined within observation. If the big universe has a different appearance a Googolplex cubed trillion light years away, you will have a hard time finding out about it.

An object without symmetry or measurement and without a boundary cannot have a center. It has a cubic googolplex measurement rather than a single center.

You are therefore asking a geometric question similar to "where is the center on the surface of a sphere, and a hoop"?

• Everything in the universe is a component of a superstructure, just as galaxies are contained in a sponge distribution, the sponge is inside a larger, unknown, structure. If you extend the picture in it's given scale by a few kilometers or a few light years, to the end of the galaxy or to a distant galaxy, a new, larger structure would appear. That is something more likely than to search for it's center, it's to search for it's larger containing form. Dec 22 '16 at 14:42
• Furthermore, the universe could be infinite and the big bang would not have occurred at a point. Dec 25 '16 at 11:42

That's not actually how explosions work. When nitroglycerin detonates, it does not leave a hole in the centre. Just like an explosion, the big bang does not work that way either. In any valid frame of reference, the universe started expanding at the speed of light without leaving a hole in the centre and the centre is not a special place. Because of strange laws of the universe, there isn't only one valid frame of reference.

The universe follows general relativity which simplifies to special relativity in the absence of a gravitational field and in the absence of objects with an escape velocity that's a significant fraction of the speed of light, very closely follows a version of special relativity where gravity is a real force that does not bend space-time. See https://physics.stackexchange.com/questions/19937/time-dilation-as-an-observer-in-special-relativity/384547#384547 to learn how special relativity works.

According to special relativity, the universe has no centre. Any nonrotating object travelling at any constant velocity slower than the speed of light is a valid frame of reference and in its frame of reference, the centre of the universe is the place where the big bang has occurred. There is no timelike line that all observers agree is the centre of the universe. In any frame of reference, the centre of the universe in that frame of reference can't be a special place because it's not the centre in another frame of reference. When we look at galaxies near the edge of the universe, we see ones similar to those that occured near the beginning of the universe but we're really only looking back at galaxies from when when they were about half the age of our universe in our frame of reference. They're like much younger galaxies only because of their own time dilation and in their own frame of reference, are actually much younger. In any frame of reference, what happens if you're near the edge of the universe and stationary? You see yourself as being near the edge. In another frame of reference, you're in the center of the universe and moving and the aberration of light you observe makes you perceive yourself as not being in the center.

That's just what special relativity predicts but in reality, the universe doesn't follow special relativity but some of the results I already mentioned are still true. The universe is accelerating so galaxies will eventually recede from us faster than light because space itself is dragging them away faster than light. We probably live in a De Sitter universe. Our cosmic horizon, the region of space that's moving away from us at the speed of light in our frame of reference behaves just like a black hole in the sense that we will see galaxies exponentially approach the cosmic horizon without ever quite reaching it and getting more red shifted without bound as it gets closer.

• There's a few problems with this answer: 1) this is not something you can use special relativity to look at, specifically generally FLRW spacetime has different symmetries to Minkowski spacetime and performing a local Lorentz boost on an observer will lead that observer to observe anistropies (indeed we observe anistropies in the CMBR on Earth because we are Lorentz boosted in relation to the CMBR rest frame) Dec 20 '16 at 21:23
• 2) the sphere where objects recede at c is called the Hubble sphere, this is a different surface from the cosmic event horizon and they only coincide for the de Sitter Universe (for example in our Universe the cosmic horizon would be slightly beyond the Hubble sphere). The limit to how far we can see is called the particle horizon, which in our Universe is far beyond the cosmic event horizon and galaxies are necessarily getting further away from the particle horizon. The de Sitter Universe does not have a particle horizon, so there is no limit to how far you can see in such a Universe. Dec 20 '16 at 21:29
• We don't live in a De Sitter universe; we live in a universe where the energy densities of matter and dark energy are comparable. Dec 25 '16 at 11:41
• I just edited the answer in the link so I thought I better mention it. I just got 10 reputation points for this answer. That brought me to the attention of my answer that I linked. Now that I have better judgement, I realized I hadn't written my answer that I linked very well so I fixed it up. Jan 11 '20 at 4:51