Reasons to Believe

Gravity Wave Energy Density Nothing to Worry About

Image: LIGO Control Room during Advanced LIGO’s First Observing Run. Image credit: Amber Stuver

The world’s largest gravity wave telescope (see figures 1 and 2 below), the Laser Interferometer Gravitational-Wave Observatory (LIGO), just received a major upgrade. Now, the LIGO Scientific Collaboration team has announced results from the first observing run of Advanced LIGO. In a preprint1 posted just days ago on the arXiv site, the team reported that they had measured the energy density of gravitational waves with 33 times more sensitivity than all previous attempts.

Figure 1: Western Leg of LIGO Interferometer at Hanford, Washington

Figure 2: Northern Leg of LIGO Interferometer at Hanford, Washington

The LIGO Scientific Collaboration team did not actually detect the energy density of gravitational waves. However, they did establish a highly constrained upper limit on the maximum possible contribution that gravity waves make to the total density, or “stuff,” that comprises the universe.

The holy grail of cosmology is to measure the total density of the universe and the component parts that make up that density. The value of the universe’s total density reveals important insights on the origin of the universe. It also determines the geometry of the universe and the fate of the universe.

Only four factors can possibly contribute to the total cosmic density: mass density (ordinary matter + exotic dark matter), Ωm; relativistic particle density (photons and neutrinos), Ωr; gravity wave energy density, Ωgw; and dark energy density, ΩΛ. Astronomers prefer to measure these four cosmic density contributions as ratios relative to the total cosmic density that would make the geometry of the universe perfectly flat. For a geometrically perfectly flat universe, the total cosmic density parameter, Ωtotal is set at exactly 1.0. Astronomers have also established a cosmic spatial curvature parameter, Ωk. Ωk = 0 for a perfectly flat universe. For a curved geometry universe, Ωtotal = 1.0 – the measured value for Ωk. In terms of its component parts, Ωtotal = Ωm + ΩΛ + Ωr + Ωgw – Ωk.

With 95 percent confidence, the LIGO Scientific Collaboration team says they’ve established an upper limit for Ωgw < 1.7 x 10–7. This very tiny maximum possible value means that the gravity wave energy density has no meaningful impact on the total cosmic density or the dynamics of the universe. That is, it plays no significant role either in the early history of the universe or in its future. It is one less thing we human beings need to worry about.

Knowing that Ωgw has a trivial value helps astronomers in their quest for the holy grail—density. Thanks to detailed maps of the cosmic background radiation (the radiation remaining from the cosmic creation event) and detailed maps of galaxies and galaxy clusters, they already know that the geometry of the universe is either flat or very close to flat. Four sets of measurements yield Ωk = –0.0005±0.0012.2 They also know that Ωr has a very small value. Analysis of the Wilkinson Microwave Anisotropy Probe (WMAP) map of the cosmic background radiation yields Ωr = 8.52 x 10–5.3. These measurements mean that astronomers need focus only on Ωm and ΩΛ to determine which cosmic creation model is correct.

As I mentioned in a previous blog article, astronomers possess multiple independent observational tools for directly measuring  ΩΛ.4 These direct measuring tools leave no doubt that dark energy is the dominant contributor to Ωtotal. However, the most accurate measure of ΩΛ comes from the simple subtraction: ΩΛ = 1.0 – Ωm – Ωk. An arithmetic mean of 12 recent independent measurements of Ωm yields Ωm = 0.293±0.011.5 Therefore, ΩΛ = 0.708±0.012.

For more than two decades many atheists and virtually all young-earth creationists have been adamant in denying the existence of dark energy. Atheists do not like dark energy because it implies a relatively recent cosmic beginning. It implies a beginning so recent as to defy a naturalistic explanation for the origin of life and a history of life that makes possible the origin and existence of human beings who attain a global high-technology civilization.

Another reason they do not like dark energy is the fine-tuning design it implies. Philip Ball, an atheist physicist and former senior editor for the British journal Nature, in an interview he conducted with three theoretical physicists about a paper they had just written, quoted the three theoretical physicists as saying in regard to dark energy, “Arranging the cosmos as we think it is arranged would have required a miracle.”6 In the same interview the three physicists said that the existence of dark energy would imply that an “unknown agent intervened in the evolution [of the universe] for reasons of its own.”7 The three physicists concluded their paper with these words, “Perhaps the only reasonable conclusion is that we do not live in a world with a true cosmological constant.”8 Cosmological constant is another term for dark energy.

Young-earth creationists, too, wish that dark energy would go away. They wish it, however, for a reason opposite to atheist scientists. If dark energy is real, it makes the universe too old for their interpretation of the Genesis 1 creation days and the Genesis 5 and 11 genealogies.

Like it or not, dark energy is real. With a measure as accurate as ΩΛ = 0.708±0.012 there no longer is any rational basis for doubting its existence. In fact, it makes up more than two-thirds of the universe. And, those of us who believe in the God of the Bible should really like it. It implies that the universe has a beginning in finite time just like the Bible repeatedly declares. Furthermore, the fine-tuning design it implies means that a known Agent who can operate from beyond space and time has miraculously intervened in the history of universe for reasons of his own. Aren’t you glad you are alive in the twenty-first century to witness such amazing revelations from the book of nature (Psalm 97:6)?

Endnotes

  1. LIGO Scientific Collaboration and the Virgo Collaboration, “Upper Limits on the Stochastic Gravitational-Wave Background from Advanced LIGO’s First Observing Run,” preprint, submitted December 6, 2016, https://arxiv.org/abs/1612.02029.
  2. Gary Hinshaw et al., “Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results,” Astrophysical Journal Supplement Series 208 (October 2013): 1, id. 19, doi:10.1088/0067-0049/208/2/19; Planck Collaboration, “Planck 2013 Results. XVI. Cosmological Parameters,” Astronomy & Astrophysics 571 (November 2014): 40, id. A16, doi:10.1051/0004-6361/201321591; Shadab Alam et al., “The Clustering of Galaxies in the Completed SDSS-III Baryon Oscillation Spectroscopic Survey: Cosmological Analysis of the DR12 Galaxy Sample,” preprint, submitted July 11, 2016, https://arxiv.org/abs/1607.03155; Ariel Sánchez et al., “The Clustering of Galaxies in the Completed SDSS-III Baryon Oscillation Spectroscopic Survey: Cosmological Implications of the Configuration-Space Clustering Wedges,” Monthly Notices of the Royal Astronomical Society 464 (January 2017), 1640–58, doi:10.1093/mnras/stw2443.
  3. E. Komatsu et al., “Five-Year Wilkinson Microwave Anisotropy Probe Observations: Cosmological Interpretation,” Astrophysical Journal Supplement Series 180 (February 2009): 333–35, doi:10.1088/0067-0049/180/2/330; Hinshaw et al., “Nine-Year Wilkinson,” 9–15.
  4. Hugh Ross, “Cosmic Acceleration: Is It Real?” Today’s New Reason to Believe (blog), Reasons to Believe, November 28, 2016, http://www.reasons.org/blogs/todays-new-reason-to-believe/cosmic-acceleration–is-it-real.
  5. Hinshaw et al., “Nine-Year Wilkinson,” 9–11; Planck Collaboration, “Planck 2013 Results,” 1; Alam et al., “Clustering of Galaxies”; Éric Aubourg et al., “Cosmological Implications of Baryon Acoustic Oscillation Measurements,” Physical Review D 92 (December 2015): 1, id. 123576, doi:10.1103/PhysRevD.92.123516; G. S. Sharov and E. G. Vorontsova, “Parameters of Cosmological Models and Recent Astronomical Observations,” Journal of Cosmology and Astroparticle Physics 2014 (October 2014): id. o57, doi:10.1088/1475-7516/2014/10/057T. de Haan et al., “Cosmological Constraints from Galaxy Clusters in the 2500 Square-Degree SPT-SZ Survey,” Astrophysical Journal 832 (November 2016), 1, id. 95, doi:10.3847/0004-637X/832/1/95; Chia-Hsun Chuang et al., “The Clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Single-Probe Measurements from CMASS Anisotropic Galaxy Clustering,” Monthly Notices of the Royal Astronomical Society 461 (October 2016): 3781, doi:10.1093/mnras/stw1535; Xiao-Dong Li et al., “Cosmological Constraints from the Redshift Dependence of the Alcock-Paczynski Effect: Application to the SDSS-III Boss DR12 Galaxies,” Astrophysical Journal 832 (December 2016): 1, id. 103, doi:10.3847/0004-637X/832/2/103; M. Betoule et al., “Improved Cosmological Constraints from a Joint Analysis of the SDSS-II and SNLS Supernova Samples,” Astronomy & Astrophysics 568 (August 2014): 1, id. A22, doi:10.1051/0004-6361/201423413; Nico Hamaus et al., “Constraints on Cosmology and Gravity from the Dynamics of Voids,” Physical Review Letters 117 (August 2016): 1, id. 091302, doi:10.1103/PhysRevLett.117.091302; Raul E. Angulo and Stefan Hilbert, “Cosmological Constraints from the CFHTLenS Shear Measurements Using a New, Accurate, and Flexible Way of Predicting Non-Linear Mass Clustering,” Monthly Notices of the Royal Astronomical Society 448 (March 2015): 364, doi:10.1093/mnras/stv050; David Spergel, Raphael Flauger, and Renée Hložek, “Planck Data Reconsidered,” Physical Review D 91 (January 2015): 1, id. 023518, doi:10.1103/PhysRevD.91.023518.
  6. “Is Physics Watching Over Us?” Philip Ball, Nature News (blog), Nature, August 13, 2002, http://www.nature.com/news/2002/020812/full/news020812-2.html
  7. Ibid.
  8. Lisa Dyson, Matthew Kleban, and Leonard Susskind, “Disturbing Implications of a Cosmological Constant,” Journal of High Energy Physics 2002 (November 2002): 17, id. 011, doi:10.1088/1126-6708/2002/10/011.

Subjects: Cosmic Expansion, Cosmology, Dark Energy & Dark Matter, Inflation, Universe Design