Most Precise Tests of Dark Energy and Cosmic Expansion Yet Confirm the Model of a Spatially Flat Universe

Energy Density Matter Dark Energy

A section of the three-dimensional map of galaxies Sloan Digital Sky Survey used in this analysis. The rectangle on the far left shows a patch of the sky containing nearly 120,000 galaxies (a small fraction of the total survey). The center and right images show the 3D map created from these data: brighter regions correspond to the regions of the Universe with more galaxies, and darker regions to voids. Credit: Jeremy Tinker and the SDSS-III collaboration

A new paper has shown how large structures in the distribution of galaxies in the Universe provide the most precise tests of dark energy and cosmic expansion yet.

“This result shows the power of galaxy surveys to pin down the amount of dark energy and how it evolved over the last billion years.” — Dr Seshadri Nadathur, Research fellow

The study uses a new method based on a combination of cosmic voids – large expanding bubbles of space containing very few galaxies – and the faint imprint of sound waves in the very early Universe, known as baryon acoustic oscillations (BAO), that can be seen in the distribution of galaxies. This provides a precise ruler to measure the direct effects of dark energy driving the accelerated expansion of the Universe.

This new method gives much more precise results than the technique based on the observation of exploding massive stars, or supernovae, which has long been the standard method for measuring the direct effects of dark energy.

The research was led by the University of Portsmouth, and is published in Physical Review Letters.

The study makes use of data from over a million galaxies and quasars gathered over more than a decade of operations by the Sloan Digital Sky Survey.

The results confirm the model of a cosmological constant dark energy and spatially flat Universe to unprecedented accuracy, and strongly disfavor recent suggestions of positive spatial curvature inferred from measurements of the cosmic microwave background (CMB) by the Planck satellite.

3D Map of Galaxies

The values of the energy density of matter (Ω_m) and dark energy (Ω_Λ) in the Universe measured from different cosmological data. Credit: Seshadri Nadathur

Lead author Dr. Seshadri Nadathur, research fellow at the University’s Institute of Cosmology and Gravitation (ICG), said: “This result shows the power of galaxy surveys to pin down the amount of dark energy and how it evolved over the last billion years. We’re making really precise measurements now and the data is going to get even better with new surveys coming online very soon.”

Dr. Florian Beutler, a senior research fellow at the ICG, who was also involved in the work, said that the study also reported a new precise measurement of the Hubble constant, the value of which has recently been the subject of intense debate among astronomers.

He said: “We see tentative evidence that data from relatively nearby voids and BAO favor the high Hubble rate seen from other low-redshift methods, but including data from more distant quasar absorption lines brings it in better agreement with the value inferred from Planck CMB data.”

Reference: “Testing Low-Redshift Cosmic Acceleration with Large-Scale Structure” by Seshadri Nadathur, Will J. Percival, Florian Beutler and Hans A. Winther, 2 June 2020, Physical Review Letters.
DOI: 10.1103/PhysRevLett.124.221301

7 Comments on "Most Precise Tests of Dark Energy and Cosmic Expansion Yet Confirm the Model of a Spatially Flat Universe"

  1. Torbjörn Larsson | June 8, 2020 at 5:57 am | Reply

    [The images has been combined with the wrong captions.]

    Very nice result, which may pinpoint the expansion rate [“H0” below] and explain some of the problems with other methods!

    Inherently voids and BAO starts out close to the distance ladder based results. But as other observations – even fairly nearby galaxies at half the universe age (or z ~ 2) – are included the result converges naturally to a CMB consistent expansion rate […1044.pdf ; Fig. 3].

    “Thus, the final joint constraint we obtain is H0 = 69.0±1.2 km s^-1 Mpc^-1, (all BAO + voids + BBN).

    This represents a 1.7% ‘early-type’ measurement of H0 from LSS, independent of the CMB. The final joint value is consistent with Planck and in ~2.7 sigma tension with the local distance ladder.”

    The new result has a < 2 % imprecision!

    That it is consistent with both Planck and in tension with the local distance ladder – but statistically insignificant so – points to the problem as being related to the ladder. That ladder has 5 – 20 % imprecision [ ]. But we'll see when more measurements are collated.

    Meanwhile, a H0 of <= 70 km s^-1 Mpc^-1 would mean no new physics needed, IIRC the Planck collaboration papers.

  2. Howard Jeffrey Bender | June 8, 2020 at 6:06 am | Reply

    This article suggests that the distribution of galaxies implies the existence of Dark Energy and the concept of a flat universe.

    Another way to explain Dark Energy is suggested by String Theory. All matter and energy, including photons (light), have vibrating strings as their basis.

    String and anti-string pairs are speculated to be created in the quantum foam, a roiling energy field suggested by quantum mechanics, and they immediately annihilate each other. If light passes near these string/anti-string annihilations, perhaps some of that annihilation energy is absorbed by the string in the light. Then the Fraunhofer lines in that light will move a bit towards the blue and away from the red shift. As this continues in an expanding universe we get the same curve displayed by Perlmutter and colleagues at their Nobel Prize lecture, without the need for Dark Energy.

    This speculation has the universe behaving in a much more direct way. Specifics can be found in my YouTube

    While it’s true the distribution of galaxies implies a flat universe, String Theory may also suggest a continuous Big Bang/Big Crunch scenario beyond galaxy distribution. Surely you didn’t think all of the matter and energy we see now was stuffed in a single Big Bang! As you may know, quantum mechanics proposes a roiling quantum foam energy field everywhere in the universe, and the right kind of energy spikes creates string/anti-string pairs. These pairs immediately annihilate each other, but I suggest a process similar to Hawking radiation that form permanent strings that are the basis of all the matter and energy we have. This is a Big Bang/Big Crunch cycle, over and over. Interestingly, this same process can be used to form the galaxies we see. Gravity is far too weak to cause anything to combine rather than flying apart from the enormous force of the Big Bang. Specifics for the physical creation of the universe and the galaxies are shown in my YouTube

    • Torbjörn Larsson | June 9, 2020 at 12:18 pm | Reply

      There is no need for string theory, “quantum foam” or cycling universes in the current Lambda-Cold Dark Matter [LCDM] models for a flat universe.

      The quantum fields vacuum energy constitutes the dark energy, and the “virtual particle” particle-antiparticle fluctuations they suggest are not real particles (are non-resonant, imaginary mass fluctuations). They don’t need to “foam” the geometry of flat space. Nor – as a vacuum – do they interact with traveling light (since, I think, Feynman diagrams describe particle interactions). As we can see in multimessenger astronomy – gravitons, neutrinos and photons arrive near enough simultaneously from various multimessenger observations.

      String theory is in dire straights, since natural superstring particles don’t turn up in particle accelerators or in electron sphericity experiments and natural axion like particles also don’t turn up in search. Add to that recent conjectures that the AdS swampland is all “swamp” (unphysical) in flat space (as approximation of dS space).

      Cycling universes have an inherent problem with space flatness and entropy increase – why is space flat and why is it initially zero entropy? Only LCDM inflation can explain that.

      “Surely you didn’t think all of the matter and energy we see now was stuffed in a single* Big Bang!”

      This seems to both misinterpret the standard Big Bang models who never described a big bang as a small volume and with flat space certainly can’t, as well as that flat space means energy density is on average zero. (Positive and negative contributions are canceling on large enough observed volumes, again explained by inflation.)

      I’ll put a link to a short video based on an astrophysicist manuscript that explains the modern inflationary big bang (LCDM) universe in a separate comment, since the link will mean it is held for moderation. It does not cover mechanisms, but I suggest cosmological MOOCs for that (where Susskind’s free Stanford lectures still rank among the best, I think).

      * Flat space is a straightforward observation in the cosmic background spatial spectra, the main peak is spot on where it should be in that case. But the 2018 Planck cosmology parameter summary succeeded in something less straightforward. At that time they had managed to model and subtract dust noise in a verifiable way as well as added data from Antarctica telescopes, and they could extract parameters from both the spots amplitudes and orientation (polarization) for the first time. Each were testing inflation well on its own and in combination, and for the first time they could observe – without any source for degeneracy – that inflation is slow roll.

      There is no good reason why a slow roll wouldn’t make a zero energy, zero entropy, and eternally inflating universe with an infinite number of big bang local universes – a multiverse – since that is its natural physics and statistically speaking its most likely outcome (least constraint).

    • Torbjörn Larsson | June 9, 2020 at 12:20 pm | Reply

      The The Big Bang is Probably Not What You Think It Is: .

    • Torbjörn Larsson | June 9, 2020 at 12:21 pm | Reply

      Ah, comments with one [1] link is not held for moderation!


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