A significant problem has troubled cosmologists—and the big bang model—for at least the past two decades, ever since astronomers first made precision measurements of the rate at which the universe expands. The problem is an apparent discrepancy in the value of the Hubble constant, H0, the rate at which the cosmos is expanding. Measurements taken by two different methods yield discrepant results. Astronomers label this problem “the Hubble constant tension.”
The value of H0 determined through observation of relatively local (in astronomical terms) Cepheid variable stars and type Ia supernovae appears to differ from the value obtained through analysis of the far distant cosmic microwave background radiation (CMBR), the radiation left over from the cosmic origin event, observed and mapped at the farthest reaches of the universe.
Both groups call into question the standard big bang model (actually, a set of big bang models) and claim that it requires significant revision, if not outright rejection. What’s more, given the close parallel between big bang model features and the biblical depiction of our cosmic origin and features, these groups thereby call into question the accuracy and reliability of the Scriptures.3
Hubble Constant Tension Clearly there is much at stake in the Hubble constant tension, not just scientifically but also theologically and ideologically. So, how problematic is the discrepancy?
In at least two recently posted articles about the tension, I presented three different astronomical approaches to resolving the discrepancy that, if combined, would require no appeal to new physics.4 When these articles appeared, the best value of H0 determined locally was 74.03 ± 1.42 kilometers/second/megaparsec (km/s/Mpc), where a megaparsec = 3.26156 million light-years, or 19.174 million trillion miles; and the best value of H0 determined from maps of the CMBR was 67.4 ± 0.5 km/s/Mpc. The 6.6 km/s/Mpc difference, which amounts to a 4.4 standard deviation discrepancy, implied that the disparity was most likely more than a statistical fluke.
More recently, the discrepancy shrank further. The best value of H0 determined locally from observations of Cepheid variable stars and type Ia supernovae is 73.01 ± 0.99 km/s/Mpc.5 The best value of H0 determined from maps of the CMBR and baryon acoustic oscillations is 67.66 ± 0.42 km/s/Mpc.6 However, because both measurements include calculations of statistical and systemic errors, the error bars associated with them grew smaller, making the discrepancy slightly larger, thus failing to alleviate the tension.
From a historical perspective, this difference in H0 value would seem insignificant. When I was a graduate student, one team of astronomers was claiming that H0 was about 50 km/s/Mpc, while another team seemed sure that H0 was about 100 km/s/Mpc. The professor in an observational cosmology course I took responded to the discrepancy with this comment: “What’s a factor of two among friends?” At the time, the combination of the statistical and systematic errors exceeded 30 km/s/Mpc. Clearly, the difference between determinations of H0 has grown vastly smaller—by a factor of ten—with time and advancing research, and yet the tension remained.
Is Modern Cosmology in Crisis? Popular literature has gone so far as to declare that cosmology is in crisis because of the Hubble constant tension. However, as I discussed in articles from three years ago, the fact that our Milky Way Galaxy (MWG) resides in an underdense region of the universe bumps up measurements of H0 based on local observations by at least 1–2%.
Meanwhile, astronomers have come to understand that in a universe dominated by dark energy and dark matter, as observations affirm, H0 will be 1% less at the cosmic beginning than it is today. Also, measurements (even prior to 2020) of the local cosmic expansion rate based on a distance indicator called tip of the red giant branch (TRGB) stars, rather than on Cepheid variable stars, showed the value of H0 as 69.8 ± 0.8 km/s/Mpc.7 Still more recent and comprehensive measurements of the local cosmic expansion rate based on TRGB stars has yielded values for H0 as 71.5 ± 1.8 km/s/Mpc8and 72.94 ± 1.98 km/s/Mpc,9 respectively.
Although most astronomers would agree that these adjustments helped to alleviate at least some of the Hubble constant tension, a certain unease lingered. However, this tension need no longer remain.
The Missing Time Dilation Factor In an article posted a few weeks ago, I explained how big bang models predict that clocks in the distant universe run more slowly than clocks in the MWG.10 Time, as measured by clocks moving at high velocities relative to Earth, will be elongated by a factor of 1 divided by the square root of (1 – v2/c2), where v is the velocity at which the clock itself is moving (relative to clocks on Earth) and c is the velocity of light. In an expanding universe, galaxies move away from Earth at velocities proportional to their distances. The article goes on to describe how astronomers developed the ability to use certain “clocks” located in quasars more than 12.8 billion light-years away to further test and affirm the validity of this effect and, thus, the big bang prediction.
More recently still, an astronomer and an engineer working independently of one another have pointed out in their published papers that a key systematic factor in determining the Hubble constant value has been overlooked.11 That factor is time dilation.
Because of time dilation, which is inherent to all big bang models, different starting times for the determination of H0 will inevitably produce slightly different measured values. In the case of H0 measurements based on maps of the CMBR, the direction of time points toward the future, right up to today, from the surface of last scattering. At that time the universe transitioned from being opaque to transparent, roughly 380,000 years after the cosmic creation event. In the case of H0 measurements determined locally via observations of Cepheid and TRGB stars and type Ia supernovae, the direction of time points backward from the present toward the time when the universe transitioned. In both cases, the H0 measurement includes the effect of cosmic time dilation.
For H0 determinations based on observations of local stars and galaxies, the time dilation effect increases the value of H0, adding about 5 km/s/Mpc. For determinations of H0 based on observations of CMBR maps and very distant galaxies, time dilation results in a decrease in the value of H0, a decrease equivalent to about 5 km/s/Mpc.
Both measured values of H0 are valid, and both are consistent with one another when time dilation, which the big bang predicts, is fully accounted for. Simply stated, time dilation removes the apparent discrepancy in the Hubble constant measurements. The tension has been relieved.
Theological/Ideological Implications Resolution of the Hubble constant tension represents good news for proponents of the standard big bang model. For proponents of a recent cosmic creation, it represents the opposite.12 Given that the Bible predicted some of the fundamental features of big bang cosmology long before astronomers discovered them, resolution of the Hubble constant tension helps affirm a cornerstone doctrine of Christianity—the supernatural inspiration and inerrancy of the Bible in alltopics it addresses.
Stephano Gariazzo et al., “Late-Time Interacting Cosmologies and the Hubble Constant Tension,” Physical Review D 106, no. 2 (July 2022): id. 023530, doi:10.1103/PhysRevD.106.023530; Rance Solomon, Garvita Agarwal, and Dejan Stojkovic, “Environment Dependent Electron Mass and the Hubble Constant Tension,” Physical Review D105, no. 10 (May 2022): id. 103536, doi:10.1103/PhysRevD.105.103536; Weiqiang Yang et al., “Emergent Dark Energy, Neutrinos and Cosmological Tensions,” Physics of the Dark Universe 31 (January 2021): id. 100762, doi:10.1016/j.dark.2020.100762; Xiaolei Li and Arman Shafieloo, “Evidence for Emergent Dark Energy,” Astrophysical Journal 902, no. 1 (October 10, 2020): id. 58, doi:10.3847/1538-4357/abb3d0; Maria G. Dainotti et al., “On the Hubble Constant Tension in the SNe Ia Pantheon Sample,” Astrophysical Journal 912, no. 2 (May 10, 2021): id. 150, doi:10.3847/1538-4357/abeb73;
Mauricio Cruz Reyes and Richard I. Anderson, “A 0.9% Calibration of the Galactic Cepheid Luminosity Scale Based on Gaia DR3 Data of Open Clusters and Cepheids,” Astronomy & Astrophysics 672 (April 2023): id. A85, doi:10.1051/0004-6361/202244775; Adam G. Riess et al., “A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s-1 Mpc-1 Uncertainty from the Hubble Space Telescope and the SH0ES Team,Astrophysical Journal Letters 934, no. 1 (July 20, 2022): id. L7, doi:10.3847/2042-8213/ac5c5b; Adam G. Riess et al., “Cluster Cepheids with High Precision Gaia Parallaxes, Low Zero-Point Uncertainties, and Hubble Space Telescope Photometry,” Astrophysical Journal 938, no. 1 (October 10, 2022): id. 36, doi:10.3847/1538-4357/ac8f24.
Planck Collaboration, N. Aghanim et al., “Planck 2018 Results. VI. Cosmological Parameters,” Astronomy & Astrophysics 641 (September 2020): id. A6, doi:10.1051/0004-6361/201833910.
Wendy L. Freedman et al., “The Carnegie-Chicago Hubble Program. VIII. An Independent Determination of the Hubble Constant Based on the Tip of the Red Giant Branch*,” Astrophysical Journal 882, no. 1 (September 1, 2019): id. 34, doi:10.3847/1538-4357/ab2f73.
Gagandeep S. Anand et al., “Comparing Tip of the Red Giant Branch Distance Scales: An Independent Reduction of the Carnegie-Chicago Hubble Program and the Value of the Hubble Constant,” Astrophysical Journal 932, no. 1 (June 10, 2022): id. 15, doi:10.3847/1538-4357/ac68df.
D. Scolnic et al., “CATS: The Hubble Constant from Standardized TRGB and Type Ia Supernova Measurements,” submitted to Astrophysical Journal Letters April 14, 2023, eprint arXiv:2304.06693, doi:10.48550/arXiv.2304.06693.
Hugh Ross, “New Test Reaffirms Big Bang,” Today’s New Reason to Believe (blog), Reasons to Believe, July 31, 2023.
Naser Mostaghel, “Effects of Time Dilation on the Measurements of the Hubble Constant,” International Journal of Astronomy and Astrophysics 8, no. 4 (December 2018): 339–346, doi:10.4236/ijaa.2018.84024; Richard I. Anderson, “Towards a 1% Measurement of the Hubble Constant: Accounting for Time Dilation in Variable-Star Light Curves,” Astronomy & Astrophysics 631 (November 2019): id. A165, doi:10.1051/0004-6361/201936585.
For an explanation of how cosmic time dilation refutes young-earth creationist models, see my book A Matter of Days, 2nd ed (Covina, CA: RTB Press, 2015), 166–169.
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