Is the cosmic web a web because cosmic voids don't have access to time?

Dec 23, 2019
Cosmic voids don't have black holes, so is it reasonable to assume black holes are the cause of Time? Does Dark Matter have access to time?
Mar 4, 2020
If you believe in space-time, how can there be a void? What is in a void?

Did space come with the BB, and replace a void? How fast does light travel thru a void?
I'm puzzled here as to the defintion of a cosmic void. Is this just space?

A long time ago (around 13.8 billion years before now), there was no comic web. There were, of course, no galaxies and no stars. There were only the fundamental components of the universe: dark matter, hydrogen, helium and a little sprinkling of lithium just for flavor. All this stuff was as homogenous as the milk you buy at the grocery store: pretty much evenly spread throughout the nascent universe.

But there were tiny mass differences here and there. Some spots had more density. Some areas had less. And the denser locales had slightly more gravitational attraction than the less dense ones. So those heavier spots would pull on their neighbors, grow larger and develop even stronger gravity — and the process would continue over time.

Over the course of hundreds of millions of years, the rich got richer and the poor got poorer. Matter flowed into the dense pockets, where it eventually coalesced into the first stars, galaxies and clusters. That matter had to come from somewhere, so as the cosmic web grew and evolved, the voids emptied out.

Of course, the voids are not entirely empty. There are some dim, scattered dwarf galaxies floating around inside these mostly empty areas. And dark matter and some hydrogen managed to cling to life inside those empty, parched stretches. But by and large, the voids really are void. And because of this emptiness, ironically, the voids are filled with one thing: dark energy

This is the name we give to the accelerated expansion of the universe, as well as for whatever's causing it. We don't really know what dark energy is, but our best current guess is that it has something to do with the vacuum of space-time itself; where there's this vacuum, there's dark energy. So, there's dark energy in the rooms we're in right now, hanging out in all the little pockets of vacuum between and within atoms. But dark energy isn't very strong, so it's easily masked by the presence of pretty much anything else — matter, radiation, dirty socks in the laundry basket, you name it.

You don't get to experience dark energy, because your environment is too full of matter. But the voids? They're almost empty except for the virtual particles which pop in and out of existence from the vacuum energy.
cosmic voids.jpg
This simulated view of the large-scale structure of the universe shows the vast cosmic web of galaxies, as well as the dark, empty expanses of the cosmic voids in between.
(Image: © Nico Hamaus, Universitäts-Sternwarte München, courtesy of The Ohio State University)

There's nothing there to compete with dark energy, which means these areas are exactly where dark energy gets to play its game.

The accelerated expansion of our universe happens in the voids themselves, and these voids literally push on their surroundings, driving apart the galaxies and dissolving the great cosmic web that took billions of years to construct.

Simulations of the cosmic web showing the filaments connecting structures. Credit: Illustris Simulation

14 March 2017 10:04

Astronomers have sampled 40,000 distant galaxies to better understand how galaxies like our own Milky Way have formed and evolved across cosmic time.

Dr David Sobral from Lancaster University is a member of an international team led by a joint collaboration between the California Institute of Technology (Caltech) and the University of California, Riverside.
The team looked at the COSMOS field (where CR7* was also discovered), a large patch of sky with deep enough data to look at galaxies very far away, and with accurate distance measurements to individual galaxies.
Dr Sobral said: "We have studied over 40 thousand galaxies and catalogued the cosmic web in large scales into its main components within the COSMOS field: clusters, filaments, and sparse regions devoid of any object. It’s remarkable how state-of-the-art data and methods now allow us to extend our analysis into a much younger universe, and probe such structures up to 8 billion years back in time.”
The galaxies were then divided into those that are central to their local environment (the centre of gravity) and those that roam around in their host environments (satellites).
The scaffolding that holds the large-scale structure of the universe constitutes galaxies, dark matter and gas (from which stars are forming), organized in complex networks known as the cosmic web.
This network comprises dense regions known as galaxy clusters and groups that are woven together through thread-like structures known as filaments. These filaments form the backbone of the cosmic web and host a large fraction of the mass in the universe, as well as sites of star formation activity.
While there is ample evidence that environments shape and direct the evolution of galaxies, it is not clear how galaxies behave in the larger, global cosmic web and in particular in the more extended environment of filaments.
Behnam Darvish a postdoctoral scholar at Caltech who is the lead author on the paper, said: “What makes this study unique is the observation of thousands of galaxies in different filaments spanning a significant fraction of the age of the Universe”.
Other authors include Nick Scoville and Shoubaneh Hemmati of Caltech, Andra Stroe of the European Southern Observatory, and Jeyhan Kartaltepe of the Rochester Institute of Technology.
The research in the Astrophysical Journal was funded by NASA.

* cr7 - Cosmos Redshift 7 (also known as COSMOS Redshift 7, Galaxy Cosmos Redshift 7, GalaxyCR7 or CR7) is a high-redshift Lyman-alpha emitter galaxy. At a redshift z = 6.6, the galaxy is observed as it was about 800 million years after the Big Bang, during the epoch of reionisation**. With a light travel time of 12.9 billion years, it is one of the oldest, most distant galaxies known.

** The Epoch of Reionization marks the first time in our cosmic history that baryonic matter (gas and stars) shaped the entire Universe around them.


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Cosmic voids don't have black holes, so is it reasonable to assume black holes are the cause of Time? Does Dark Matter have access to time?

Cosmic voids are spaces millions of light years across that contain fewer and more sparsely distributed galaxies than the average. Found between voids are galaxy clusters, the largest known structures formed in the universe, as heavy as 1 million billion solar masses. Gravity controls how quickly galaxy clusters grow, as well as their density.

In recent years astronomical mappings of the cosmos have become so large and detailed that scientists have begun to compile large catalogs of cosmic voids. This discovery is providing new opportunities to study dark energy and gravity using the future large-scale mappings planned for next-generation satellites and telescopes.

Major projects like the Euclid satellite, the 4MOST telescope, the Large Synoptic Survey Telescope, and the gigantic Square Kilometre Array radio telescope will be able to map millions of voids and clusters in the next decade, up to 10 billion years into the past. Researchers at Uppsala University, in Sweden, are involved in the work with 4MOST, the Square Kilometre Array, and Euclid.

The space-time geometry is determined by the energy-momentum tensor of all the matter field, by virtue of Einstein's equation in general relativity. If the Higgs field is zero in a region, then all particles (fermions + bosons) would have zero rest mass as predicted by the Standard Model. Therefore, according to
Patrick Das Gupta of the University of Delhi, the space-time geometry in this region will be determined by the energy-momentum tensors of zero rest mass particles as well as that of the Higgs field potential. This geometry will be fundamentally different from the case when the Higgs field has acquired the vacuum expectation value due to the spontaneous symmetry breaking, because of which fermions and gauge bosons (except for photons and gluons) acquire masses. Thus, space-time geometry is indeed linked with the dynamics of the Higgs field.

The mysterious 'aether' that was long ago supposed to permeate the void may now be making a comeback with the latest research into the 'Higgs field'. We now know that the vacuum is far from being 'nothing' - it seethes with virtual particles and antiparticles that erupt spontaneously into being and then disappear, and it also may contain hidden dimensions that we were previously unaware of.

Now, cosmic voids are acting as probes for modified gravity theories, evolution of cosmological density perturbations, etc. Various observational surveys aim to reveal the characteristics of the voids, the distributions of their spatial scales, underdensity parameter, as their knowledge is of particular importance for the reconstruction of the spectrum of the density perturbations and the formation of the large scale Universe.

Cosmic Microwave Background (CMB) provided another window to trace the presence of the voids, along with the traditional galaxy surveys. For example, the Cold Spot, a remarkable non-Gaussian feature* known in the CMB sky was shown to reveal properties of a void, as supported also with galactic survey.
During the study of the Cold Spot the hyperbolicity** property of voids was used, especially, the deviation of the photon trajectories, i.e. of null geodesics due to the decreased density of the void. The deviation of geodesic flows is known to be a property of negatively curved spaces as studied in the theory of dynamical systems. Regarding the voids, it was shown that the low-density spatial regions can induce hyperbolicity even in conditions of globally flat or positively curved Universe.

The hyperbolicity of the photon beams caused by observed parameters of underdense regions, voids, were shown to be compatible with the elongation of the excursion sets in temperature maps of CMB sky maps obtained by WMAP satellite. The signature of the deviation of the photon beams in voids was shown to fit the Kolmogorov stochasticity parameter map*** obtained for CMB temperature data in the Cold Spot region.

Another effect in which the described hyperbolicity can contribute is the distortion of the redshift-space in the galactic surveys defined by the correlation function of the separations of galaxies in line-of-sight and tangential directions. That effect is attributed to the peculiar velocities of the galaxies within the galactic groups, clusters and superclusters, including the infall of galaxies to the cluster center (Kaiser effect), as well as to the gravitational shift - blue or red - due to the potential well of the particular structure and its peculiar motion with respect to us. As an illustration, let us consider the survey of 10,000 galaxies in 300 Mpc distance (i.e. at redshift z = 0.8) for which the distortion β ≃ 0.7 has been reported. That distortion if attributed mainly to the tangential component of galactic separation, would correspond to a cumulative effect of e.g. N = 6 line-of-sight voids of mean diameter D = 50M pc and mean density parameters of the walls (of 4 Mpc mean diameter) and voids , δWall = 10 , δVoid = −0.8, respectively. Quantitatively, the tangential distortion due to hyperbolicity depends on the angular distribution of the photon beams as shown in Fig. 1. At even slightly anisotropic beams the distortion can occur both at negative and positive matter mean densities.

Fig. 1. Tangential distortion at isotropic (σ = 0) and non-isotropic (σ = 0.1) distribution of photon beams.

* A typical application of non-Gaussian modeling is the smoothing of a time series that has mean value function with both abrupt and gradual changes. Simple Gaussian state—space modeling is not adequate for this situation. Here the model with small system noise variance cannot detect jump, whereas the one with large system noise variance yields unfavorable wiggle. To work out this problem within the ordinary linear Gaussian model framework, sophisticated treatment of outliers is required. But by the use of an appropriate non-Gaussian model for system noise, it is possible to reproduce both abrupt and gradual change of the mean without any special treatment.

** hyperbolic
  1. Of or pertaining to a hyperbola. quotations ▼
  2. Indicates that the specified function is a hyperbolic function rather than a trigonometric function.The hyperbolic cosine of zero is one.
  3. (mathematics, of a metric space or a geometry) Having negative curvature or sectional curvature. quotations ▼
  4. (geometry, topology, of an automorphism) Whose domain has two (possibly ideal) fixed points joined by a line mapped to itself by translation. quotations ▼
  5. (topology) Of, pertaining to or in a hyperbolic space (a space having negative curvature or sectional curvature). quotations ▼
*** The Kolmogorov stochasticity parameter (KSP) is applied to quantify the degree of randomness (stochasticity) in the temperature maps of the Cosmic Microwave Background radiation maps. It is shown that the KSP for the WMAP5 maps is about twice as high as that of the simulated maps for the concordance ΛCDM cosmological model, implying that a randomizing effect exists that has not been taken into account by the model. Less dense regions in the large scale matter distributions, i.e. the voids, possess hyperbolic and, hence, randomizing properties. The degree of randomness for the Cold Spot appears to be about twice as high as the average of the mean temperature level spots in the sky, which supports the void nature of the Cold Spot. Kolmogorov's parameter then acts as a quantitative tracer of the voids by means of the CMB.




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The definition depends on the speaker, because there are no definitions

Instead of individual galaxies, we see huge walls and tendrils containing thousands of galaxies; filaments of galaxies connect in nodes. These structures are huge; hundreds of millions of light-years across, containing thousands of galaxies. But the voids between these clusters can be even larger.

Astronomers first started thinking about these voids back in the 1970s, when the first large-scale surveys of the Universe were being made. By measuring the redshift of galaxies, and determining how fast they were speeding away from us, astronomers started to realize that the distribution of galaxies wasn’t even.

Some galaxies were relatively close, but then there were huge gaps in distance, and then another cluster of galaxies collected together.

Over the last few decades, astronomers have built sophisticated 3-dimensional models that map out the Universe in the largest scales. The Sloan Digital Sky Survey, updated in 2009, has provided the most accurate map so far. The Large Synoptic Survey Telescope, destined for first light in a few years will take this to the next level.

The largest void that we currently know of is known as the Giant Void, and it’s located about 1.5 billion light-year away. It has a diameter of 1 billion to 1.3 billion light-years across.

To be fair, these regions aren’t really completely empty. They just have less density than the regions with galaxies. In general, they’ve got about a tenth the density of matter that’s average for the Universe.

Galaxy MCG+01-02-015 is so isolated that if our galaxy, the Milky Way, were to be situated in the same way, we would not have known of the existence of other galaxies until the 1960s Credit: ESA/Hubble & NASA and N. Gorin (STScI). Acknowledgement: Judy Schmidt
Galaxy MCG+01-02-015 is so isolated that if our galaxy, the Milky Way, were to be situated in the same way, we would not have known of the existence of other galaxies until the 1960s. Credit: ESA/Hubble & NASA and N. Gorin (STScI). Acknowledgement: Judy Schmidt

Which means that there’s still gas and dust in these regions, as well as dark matter. There will still be stars and galaxies out in the middle of those voids. Even the Giant Void has 17 separate galaxy clusters inside it.
You might imagine continuing to scale outward. Maybe you’re wondering if the this spongy distribution of matter is actually just the next step to an even larger structure, and so on, and so on. In fact, astronomers call this “the End of Greatness”, because it doesn’t seem like there’s any larger structure in the Universe than these giant galactic structures and the associated galactic voids.

We are in this tiny corner of the Local Group, which is part of the Virgo Supercluster, which is perched on the precipice of vast cosmic voids.

The voids are enormous spans existing between the lattice work of galaxies, but they are not completely empty. Nothing is.

Voids are seen as vast spaces between filaments (the largest-scale structures in the universe), which contain very few or no galaxies. Voids typically have a diameter of 10 to 100 megaparsecs; particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids. They have less than one tenth of the average density of matter abundance that is considered typical for the observable universe. They were first discovered in 1978 in a pioneering study by Stephen Gregory and Laird A. Thompon at the Kitt Peak National Observatory.

Voids are believed to have been formed by baryon acoustic oscillations in the Big Bang, collapses of mass followed by implosions of the compressed baryonic matter. Starting from initially small anisotropies from quantum fluctuations in the early universe, the anisotropies grew larger in scale over time. Regions of higher density collapsed more rapidly under gravity, eventually resulting in the large-scale, foam-like structure or "cosmic web" of voids and galaxy filaments seen today. Voids located in high-density environments are smaller than voids situated in low-density spaces of the universe.

Voids appear to correlate with the observed temperature of the cosmic microwave background (CMB) because of the Sachs–Wolfe effect*. Colder regions correlate with voids and hotter regions correlate with filaments because of gravitational redshifting. As the Sachs–Wolfe effect is only significant if the universe is dominated by radiation or dark energy, the existence of voids is significant in providing physical evidence for dark energy.

* Sachs-Wolfe effect: On large angular scales, the most important of various physical processes by which the primordial density fluctuations should have left their imprint on the cosmic microwave background radiation in the form of small variations in the temperature of this radiation in different directions on the sky. It is named after Rainer Kurt Sachs (1932- ) and Arthur Michael Wolfe (1939- ). The effect is essentially gravitational in origin. Photons travelling from the last scattering surface to an observer encounter variations in the metric which correspond to variations in the gravitational potential in Newtonian gravity. These fluctuations are caused by variations in the matter density
from place to place. A concentration of matter, in other words an upward fluctuation of the matter density, generates a gravitational potential well. According to general relativity, photons climbing out of a potential well will suffer a gravitational redshift which tends to make the region from which they come appear colder. There is another effect, however, which arises because the perturbation to the metric also induces a time-dilation effect: we see the photon as coming from a different spatial hypersurface (labelled by a different value of the cosmic scale factor a(t) describing the expansion of the Universe).

For a fluctuation
in the gravitational potential, the effect of gravitational redshift is to cause a fractional variation of the temperature
T/T =
/ c2, where c is the speed of light. The time dilation effect contributes
T/T = -
a/a (i.e. the fractional perturbation to the scale factor). The relative contributions of these two terms depend on the behaviour of a(t) for a particular cosmological model. In the simplest case of a flat universe described by a matter-dominated Friedmann model**, the second effect is just -2/3 times the first one. The net effect is therefore given by
T/T =
/3c2. This relates the observed temperature anisotropy to the size of the fluctuations of the gravitational potential on the last scattering surface.

It is now generally accepted that the famous ripples seen by the Cosmic Background Explorer (COBE) satellite were caused by the Sachs-Wolfe effect. This has important consequences for theories of cosmological structure formation, because it fixes the amplitude of the initial power spectrum of the primordial density fluctuations that are needed to start off the gravitational Jeans instability*** on which these theories are based.

Any kind of fluctuation of the metric, including gravitational waves of very long wavelength, will produce a Sachs-Wolfe effect. If the primordial density fluctuations were produced in the inflationary Universe, we would expect at least part of the COBE signal to be due to the very-long-wavelength gravitational waves produced by quantum fluctuations in the scalar field driving inflation.

Sachs, R.K. and Wolfe, A.M., `Perturbations of a cosmological model and angular variations of the cosmic microwave background', Astrophysical Journal, 1967, 147, 73.

** Friedmann Model: Friedmann model universe was developed in 1922 by the Russian meteorologist and mathematician Aleksandr Friedmann (1888–1925). He believed that Albert Einstein’s general theory of relativity required a theory of the universe in motion, as opposed to the static universe that scientists until then had proposed. He hypothesized a big bang followed by expansion, then contraction and an eventual big crunch. This model supposes a closed universe, but he also proposed similar solutions involving an open universe (which expands infinitely) or a flat universe (in which expansion continues infinitely but gradually approaches a rate of zero). See also Edwin P. Hubble.

*** Jeans Instability: Is the instability of a self-gravitating, thermally supported interstellar cloud that is thought to be responsible for the collapse of parts of the cloud larger than a scale size which becomes unstable, eventually fragmenting and forming stars.