Does the Universe have a Center of Gravity? Where is it?

[Chris Peterson]

I absolutely understand what you mean, charlieo3. It's just that this beautiful lettering makes the words horribly difficult for me to read!!!

The written form of Danish doesn't help. Although this reads almost perfectly as modern Danish, it was written before the modern spelling conventions were adopted- so it looks a bit odd, even after the font is puzzled out.

[geckzilla]

At least at the time that the script was written people had advanced past uncials.

Would you believe that at some point in history there was no punctuation clearly guiding us from one sentence to the next and all letters were capital? Oh yeah, and all the words were connected, as well. Compared to that, this is a breeze!

[ErnieM]

I watched this video titled "How Large Is the Universe" http://www.youtube.com/watch?feature=pl ... EQouX5U0fc

In it, it is estimated that the whole universe is so large that my original questions "Does the Universe have a Center of Gravity" Where is It?" that opened this thread, I now admit, is irrelevant, meaningless and nonsense.

However, I am not sorry I asked because it sparked my imagination and started me on a trail leading to this point.

Thank you for all the replies.

[Chris Peterson]

I watched this video titled "How Large Is the Universe" http://www.youtube.com/watch?feature=pl ... EQouX5U0fc

In it, it is estimated that the whole universe is so large that my original questions "Does the Universe have a Center of Gravity" Where is It?" that opened this thread, I now admit, is irrelevant, meaningless and nonsense.

While I do think that the Universe cannot have a center of gravity in three dimensions, I don't see what the size of the Universe has to do with the question. Any massive three-dimensional structure of less than infinite size has a center of gravity. The reason the Universe doesn't have a center of gravity in the usual sense is because it isn't a three-dimensional structure, not because it is spatially large.

[neufer]

I watched this video titled "How Large Is the Universe" http://www.youtube.com/watch?feature=pl ... EQouX5U0fc

In it, it is estimated that the whole universe is so large that my original questions
"Does the Universe have a Center of Gravity" Where is It?"
that opened this thread, I now admit, is irrelevant, meaningless and nonsense.

• To perform the experiment: get yourself two eagles ....

[b][color=#0000FF]The omphalos in museum of Delphi.[/color][/b]

---

<<An omphalos (ὀμφαλός) is an ancient religious stone artifact, or baetylus. In Greek, the word omphalos means "navel." According to the ancient Greeks, Zeus sent out two eagles to fly across the world to meet at its center, the "navel" of the world. Omphalos stones used to denote this point were erected in several areas surrounding the Mediterranean Sea; the most famous of those was at the oracle in Delphi. It is also the name of the stone given to Cronus in Zeus' place in Greek mythology.

Most accounts locate the Omphalos in the temple adyton near the Pythia. The stone itself (which may have been a copy) has a carving of a knotted net covering its surface, and has a hollow centre, which widens towards its base.

The Omphalos at Delphi came to be identified as the stone which Rhea wrapped in swaddling clothes, pretending it was Zeus. This was to deceive Cronus, his father, who swallowed his children so they could not grow up and depose him as he had deposed his own father, Uranus.

Omphalos stones were said to allow direct communication with the gods. Leicester Holland (1933) has suggested that the stone was hollow to channel intoxicating vapours breathed by the Oracle. Erwin Rohde wrote that the Python at Delphi was an earth spirit, who was conquered by Apollo, and buried under the Omphalos, and that it is a case of one god setting up his temple on the grave of another.

Christian destruction of the site in the fourth century at the order of Emperors Theodosius I and Arcadius makes all suggestions about its use tentative.>>

[ErnieM]

Chris wrote:

While I do think that the Universe cannot have a center of gravity in three dimensions, I don't see what the size of the Universe has to do with the question. Any massive three-dimensional structure of less than infinite size has a center of gravity. The reason the Universe doesn't have a center of gravity in the usual sense is because it isn't a three-dimensional structure, not because it is spatially large.

When astronomers say "The expansion of Space is accelerating", how many dimensions of Space are they referring to? What do you mean with "because it isn't a three-dimensional structure"? Is the holographic 2D Universe universally accepted now?

I see this expansion making the already large Universe larger and the gravitational hold between galaxy structures weakening to inconsequential.

[Chris Peterson]

When astronomers say "The expansion of Space is accelerating", how many dimensions of Space are they referring to?

They are generally referring to the three spatial dimensions.

What do you mean with "because it isn't a three-dimensional structure"?

The Universe is a four-dimensional structure. Its geometric center contains t=0, a point that we can't observe. If the Universe if finite, its geometric center of mass will also be a four-dimensional point, which will not lie on the three-dimensional manifold we can observe.

I see this expansion making the already large Universe larger and the gravitational hold between galaxy structures weakening to inconsequential.

Gravity is a weak force to begin with. Certainly, its influence between points that are very far apart (but still causally connected) is likely to be very tiny. But not zero. Any bounded region of the Universe will have a center of mass.

[lpearcy]

Since we don't know how large the Universe is, if it is even bounded, I don't think we can answer this.

However, from the perspective of some point, some relative frame of reference, like standing on the surface of Earth, gravity waves from the entire Universe do not reach us, but in a sphere around us gravity waves from the edge of the Observable Universe and closer reach us. Since nothing appears to block, bend, or modify gravity waves, we should then be able to calculate (if we knew enough information to) what the gravitational center the entire Observable Universe has upon that relative frame of reference in question.

More over, even though a person standing on Earth's surface clearly has a different frame of reference from the Sun and from Pluto, if we were to calculate for each of them their relative gravitational center of the Observable Universe that is effecting them, each relative gravitational center would be virtually the same because of the size of the Observable Universe versus to distances of the differing relative frames of reference. Thus, I would argue that this relative gravitational center of the Observable Universe for a system of relative frames ends up being virtually an Absolute Nonmoving Frame for the system... even though it is not exactly Nonmoving, but because of the scales involved it is effectively nonmoving.

Well, that is my thought. Not sure if it is correct.

[Chris Peterson]

Since we don't know how large the Universe is, if it is even bounded, I don't think we can answer this.

However, from the perspective of some point, some relative frame of reference, like standing on the surface of Earth, gravity waves from the entire Universe do not reach us, but in a sphere around us gravity waves from the edge of the Observable Universe and closer reach us. Since nothing appears to block, bend, or modify gravity waves, we should then be able to calculate (if we knew enough information to) what the gravitational center the entire Observable Universe has upon that relative frame of reference in question.

More over, even though a person standing on Earth's surface clearly has a different frame of reference from the Sun and from Pluto, if we were to calculate for each of them their relative gravitational center of the Observable Universe that is effecting them, each relative gravitational center would be virtually the same because of the size of the Observable Universe versus to distances of the differing relative frames of reference. Thus, I would argue that this relative gravitational center of the Observable Universe for a system of relative frames ends up being virtually an Absolute Nonmoving Frame for the system... even though it is not exactly Nonmoving, but because of the scales involved it is effectively nonmoving.

Well, that is my thought. Not sure if it is correct.

I'd say that every point in the Universe has very nearly the same amount of mass surrounding it... both in the observable universe and the Universe as a whole. That is, just as every point can be treated as the geometric center of the 3D universe, so to can it be treated as very close to the center of mass of the Universe. The ability to answer the question lies in our ability to know the topology of the Universe, which appears to be discoverable.

[neufer]

I'd say that every point in the Universe has very nearly the same amount of mass surrounding it... both in the observable universe and the Universe as a whole. That is, just as every point can be treated as the geometric center of the 3D universe, so to can it be treated as very close to the center of mass of the Universe. The ability to answer the question lies in our ability to know the topology of the Universe, which appears to be discoverable.

The center of mass of the Universe is at "the Big Bang singularity" in which
space & time lose all meaning because they are just coming into existence.

Russell's paradox:
Does the set of all those sets that do not contain themselves contain itself?

[Chris Peterson]

I'd say that every point in the Universe has very nearly the same amount of mass surrounding it... both in the observable universe and the Universe as a whole. That is, just as every point can be treated as the geometric center of the 3D universe, so to can it be treated as very close to the center of mass of the Universe. The ability to answer the question lies in our ability to know the topology of the Universe, which appears to be discoverable.

The center of mass of the Universe is at "the Big Bang singularity" in which
space & time lose all meaning because they are just coming into existence.

The "singularity" you speak of is not a singularity dimensionally at all. It is a physical point in the Universe, defined by (0,0,0,0). It is not, however, accessible to us. Which is why I specifically referred to the center of mass of the 3D universe, where (assuming a topologically closed universe... a point that remains unsettled) it is reasonable to treat every 3D point as the center of mass.

[Fred the Cat]

If everywhere is the center of the universe, how far from Earth have we accurately measured the force of gravity? Seems a difficult thing to do.

[Chris Peterson]

If everywhere is the center of the universe, how far from Earth have we accurately measured the force of gravity? Seems a difficult thing to do. :?

We can see nearly to the edge of the observable universe (to the CMB, although the actual edge is slightly farther), and everywhere in that space that we've observed gravity operates, to the limits of our ability to measure it, exactly as it does here.

[neufer]

If everywhere is the center of the universe, how far from Earth have we accurately measured the force of gravity? Seems a difficult thing to do.

We can see nearly to the edge of the observable universe (to the CMB, although the actual edge is slightly farther), and everywhere in that space that we've observed gravity operates, to the limits of our ability to measure it, exactly as it does here.

• Assuming, of course, that dark matter & dark energy actually exist.

[Chris Peterson]

If everywhere is the center of the universe, how far from Earth have we accurately measured the force of gravity? Seems a difficult thing to do. :?

We can see nearly to the edge of the observable universe (to the CMB, although the actual edge is slightly farther), and everywhere in that space that we've observed gravity operates, to the limits of our ability to measure it, exactly as it does here.

• Assuming, of course, that dark matter & dark energy actually exist.

Yes. A reasonable assumption, whatever their underlying mechanisms, however.

[neufer]

I'd say that every point in the Universe has very nearly the same amount of mass surrounding it... both in the observable universe and the Universe as a whole. That is, just as every point can be treated as the geometric center of the 3D universe, so to can it be treated as very close to the center of mass of the Universe. The ability to answer the question lies in our ability to know the topology of the Universe, which appears to be discoverable.

The center of mass of the Universe is at "the Big Bang singularity" in which
space & time lose all meaning because they are just coming into existence.

The "singularity" you speak of is not a singularity dimensionally at all. It is a physical point in the Universe, defined by (0,0,0,0). It is not, however, accessible to us. Which is why I specifically referred to the center of mass of the 3D universe, where (assuming a topologically closed universe... a point that remains unsettled) it is reasonable to treat every 3D point as the center of mass.

Due to light speed time delays of gravitational forces: that (0,0,0,0) physical point in the Universe (along with all the mass & energy between it & us) is the only Universe accessible to us. We observe either gravitational decelerations & accelerations with respect to that very (0,0,0,0) physical point (and not any other distant "center of mass").

Note, however, there has also been a natural physical attraction to Shapley Supercluster local mass concentration:

<<The cosmic microwave background (CMB) dipole moment could also be interpreted as the peculiar motion of the Earth toward the CMB. From the CMB data, it is seen that the Sun appears to be moving at 368 ± 2 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB). The Local Group — the galaxy group that includes our own Milky Way galaxy — appears to be moving at 627 ± 22 km/s in the direction of galactic longitude ℓ = 276° ± 3°, b = 30° ± 3°. This motion results in an anisotropy of the data (CMB appearing slightly warmer in the direction of movement than in the opposite direction). The standard interpretation of this temperature variation is a simple velocity red shift and blue shift due to motion relative to the CMB.>>

Panoramic view of the entire near-infrared sky. Norma & the Great Attractor is shown with the long blue arrow at bottom right.

---

<<The Great Attractor is a gravitational anomaly in intergalactic space and the apparent central gravitational point of the Laniakea Supercluster. The observed anomalies suggest a localized concentration of mass millions of times more massive than the Milky Way. However, it is inconveniently obscured by our own Milky Way's galactic plane, lying behind the Zone of Avoidance (ZOA), so that, in visible light wavelengths, the Great Attractor is difficult to observe directly.

The anomaly is observable by its effect on the motion of galaxies and their associated clusters over a region of hundreds of millions of light-years across the universe. These galaxies are observable above and below the ZOA; all are redshifted in accordance with the Hubble Flow, indicating that they are receding relative to us and to each other, but the variations in their redshifts are large enough and regular enough to reveal that they are slightly drawn towards the anomaly. The variations in their redshifts are known as peculiar velocities, and cover a range from about +700 km/s to −700 km/s, depending on the angular deviation from the direction to the Great Attractor. The Great Attractor itself is moving towards the Shapley Supercluster.>>

Shapley Supercluster with its galaxy members and its intergalactic dark matter halo

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<<The Shapley Supercluster or Shapley Concentration (SCl 124) is the largest concentration of galaxies in our nearby universe that forms a gravitationally interacting unit, thereby pulling itself together instead of expanding with the universe. It appears as a striking overdensity in the distribution of galaxies in the constellation of Centaurus. It is 650 million light-years away (z=0.046).

The Shapley Supercluster lies very close to the direction in which the Local Group of galaxies (including our galaxy) is moving with respect to the cosmic microwave background (CMB) frame of reference. This has led many to speculate that the Shapley Supercluster may indeed be one of the major causes of our galaxy's peculiar motion—the Great Attractor may be another—and has led to a surge of interest in this supercluster. It has been found that the Great Attractor and all the galaxies in our region of the universe (including our galaxy, the Milky Way) are moving toward the Shapley Supercluster.

In 2017 it was proposed that the movement towards attractors like the Shapley Supercluster attractor creates a relative movement away from underdense areas, that may be visualized as a virtual repeller. This approach enables new ways of understanding and modelling variations in galactic movements. The nearest large underdense area has been labelled the dipole repeller.>>

[Chris Peterson]

The center of mass of the Universe is at "the Big Bang singularity" in which
space & time lose all meaning because they are just coming into existence.

The "singularity" you speak of is not a singularity dimensionally at all. It is a physical point in the Universe, defined by (0,0,0,0). It is not, however, accessible to us. Which is why I specifically referred to the center of mass of the 3D universe, where (assuming a topologically closed universe... a point that remains unsettled) it is reasonable to treat every 3D point as the center of mass.

Due to light speed time delays of gravitational forces: that (0,0,0,0) physical point in the Universe (along with all the mass & energy between it & us) is the only Universe accessible to us. We observe either gravitational decelerations & accelerations with respect to that very (0,0,0,0) physical point (and not any other distant "center of mass").

I disagree. Every point that we can observe in the universe has t>0.

[neufer]

The "singularity" you speak of is not a singularity dimensionally at all. It is a physical point in the Universe, defined by (0,0,0,0). It is not, however, accessible to us. Which is why I specifically referred to the center of mass of the 3D universe, where (assuming a topologically closed universe... a point that remains unsettled) it is reasonable to treat every 3D point as the center of mass.

Due to light speed time delays of gravitational forces: that (0,0,0,0) physical point in the Universe (along with all the mass & energy between it & us) is the only Universe accessible to us. We observe either gravitational decelerations & accelerations with respect to that very (0,0,0,0) physical point (and not any other distant "center of mass").

I disagree.

Every point that we can observe in the universe has t>0.

• So we DON'T disagree, then.
  
  (Note: Every point in the universe has t>0.)

[Chris Peterson]

Due to light speed time delays of gravitational forces: that (0,0,0,0) physical point in the Universe (along with all the mass & energy between it & us) is the only Universe accessible to us. We observe either gravitational decelerations & accelerations with respect to that very (0,0,0,0) physical point (and not any other distant "center of mass").

I disagree.

Every point that we can observe in the universe has t>0.

• So we DON'T disagree, then.
  
  (Note: Every point in the universe has t>0.)

Every point in the Universe has t=now. Every point in the Universe that we can theoretically observe has t>=0.

[neufer]

Every point that we can observe in the universe has t>0.

• So we DON'T disagree, then.
  (Note: Every point in the universe has t>0.)

Every point in the Universe has t=now.
Every point in the Universe that we can theoretically observe has t>=0.

• So we DON'T disagree, then.

O.K. ...

• I'm talking about the center of mass of the observable universe.
  You're talking about the center of mass of the t=now universe.

It was a silly question in any event.

[Fred the Cat]

Accumulations of dark matter are written about from planets to galaxy-sized objects and beyond. It was pinpointing its location, to warrant looking for deviations in gravity, that fostered my original question.

It may be repulsive to some and attractive to others but interesting to all of us trying to center our understanding - close to home.

[anellaportland]

No, the universe does not have a single center of gravity in the way that a massive object like Earth or a galaxy does. The concept of a center of gravity applies to objects with mass that can exert gravitational forces on other objects. In the case of the universe, it consists of countless galaxies, galaxy clusters, and dark matter distributed throughout space on a vast cosmic scale.

The distribution of matter in the universe is not uniform, and it is governed by the gravitational interactions between all the objects within it. The universe is thought to be homogeneous and isotropic on large scales, meaning that, on average, it looks roughly the same in all directions. However, there is no single point or region in the universe that can be identified as its center of gravity.

The concept of a "center" for the universe can be misleading because the universe does not have a well-defined boundary or center in the way that a finite object does. Instead, it is a space that extends infinitely in all directions, and its large-scale structure is influenced by the distribution of matter and the expansion of space. It's important to note that our understanding of the universe's large-scale structure and its dynamics is based on the principles of cosmology, which continue to be refined through observations and scientific research.