New Simulation Shows How the Universe Evolved

Bolshoi Simulation

How has the universe evolved over time? A new supercomputer simulation has provided what scientists say is the most accurate and detailed large cosmological model of the evolution of the large-scale structure of the universe. Called the Bolshoi simulation, and it gives physicists and astronomers a powerful new tool for understanding cosmic mysteries such as galaxy formation, dark matter, and dark energy.

If the simulation is right, it is showing that the standard cosmological model is fairly spot-on.

“These huge cosmological simulations are essential for interpreting the results of ongoing astronomical observations and for planning the new large surveys of the universe that are expected to help determine the nature of the mysterious dark energy,” said Anatoly Klypin, from New Mexico State University, who wrote the computer code for the simulation, which was run on the Pleiades supercomputer at NASA Ames Research Center.

The simulation traces the evolution of the large-scale structure of the universe, including the evolution and distribution of the dark matter halos in which galaxies coalesced and grew. Initial studies show good agreement between the simulation’s predictions and astronomers’ observations.

“In one sense, you might think the initial results are a little boring, because they basically show that our standard cosmological model works,” said co-leader Joel Primack, from the University of California, Santa Cruz. “What’s exciting is that we now have this highly accurate simulation that will provide the basis for lots of important new studies in the months and years to come.”

The simulation is based on data from the WMAP mission that has been mapping the light of the Big Bang in the entire sky. A comparison of the Bolshoi predictions with galaxy observations from the Sloan Digital Sky Survey showed very good agreement, said Primack.

The standard explanation for how the universe evolved after the Big Bang is known as the Lambda Cold Dark Matter model, and it is the theoretical basis for the Bolshoi simulation. According to this model, gravity acted initially on slight density fluctuations present shortly after the Big Bang to pull together the first clumps of dark matter. These grew into larger and larger clumps through the hierarchical merging of smaller progenitors. Although the nature of dark matter remains a mystery, it accounts for about 82 percent of the matter in the universe. As a result, the evolution of structure in the universe has been driven by the gravitational interactions of dark matter. The ordinary matter that forms stars and planets has fallen into the “gravitational wells” created by clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.

A series of papers has been put out from the Bolshoi simulation, including one that looks at the characteristics of the dark matter halos and another that looks at the abundance and properties of galaxies predicted by the Bolshoi simulation of dark matter.

See more at the Bolshoi Simulation website.

4 Replies to “New Simulation Shows How the Universe Evolved”

  1. Superb article of journalism Nancy, wondered why it was called “Bolshoi” and assumed it was named after the famous theatre, on the FAQ of the Bolshoi Simulation website they explain Bolshoi means: Big/grand/or great in Russian language.

  2. This video looks like a portion of the SDSS survey with filaments. From what I can see initially they start out with a set of initial conditions that have some anisotropy, or lumpiness, and evolve these conditions with a spacetime that is stretching out.

    Bolsoi = Big, po ruskii


  3. It is interesting how these filaments of dark matter and galaxies behave as if they are rubber bands. This behavior can be understood with just Newtonian gravity. The Newton’s force of gravity is

    F = -GMm/r^2.

    The potential on a mass m due to M is ? = -GMm/r. The Newton force law for gravity is derived from F = -?? . The mass M may be due to a distribution of matter with some density ?, where for some volume V the mass M is M = ?V or more generally M = ?dV ?. The volume of consideration is V = r^3, say we are thinking of a cube, and inside the cubic volume the potential is

    ? = -G?mr^2

    And the Newton force law of gravity is

    F = -2G?mr.

    These cubic units of volume may be summed together to make larger volumes. However, this force law is that of a spring. Hence these filaments tend to hold together and have a tension.


  4. It is easy to note since IIRC already the press releases did it that the new Bolshoi-simulation [read: mega-simulation] is more of the same but different. It looks similar but is as Primack claimed “highly accurate” since it uses the new parameter set that differs significantly from the old.

    From the 1st paper on the Bolshoi website [“Halos and galaxies in the standard cosmological model: results from the Bolshoi simulation”, A. Klypin, S. Trujillo-Gomez, J. Primack]:

    “Formally, the value of σ8 used in the Millennium simulations [the old but still gold ones] is more than 3σ away from theWMAP5+BAO+SN value and nearly 4σ away from the WMAP7+BAO+H0 value. However, the difference is even larger on galaxy scales because the Millennium simulations also used a larger tilt n = 1 for the power spectrum.”

    Clearly the standard cosmology is robust, and as described recently here, now capable to predict all large scale phenomena (from, say, galaxies and up) better than any alternatives. o(^_^o) (o^_^o) (o^_^)o

    [Added in posting: dunno why the HTML subscript doesn’t work, I believe it worked fine earlier. Kept for comprehension.]

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