A little more than a month ago the internet and popular press were abuzz about a paper published by a team of astronomers led by Nobel laureate, Adam Riess. Riess and his team reported measurements that indicated that the universe might be a little more than a billion years younger than the date determined from analyzing a map of the cosmic background radiation—the radiation left over from the cosmic creation event.1 As one web article commented, the new measurements are “upending one of the few things scientists felt certain about”2 and consequently “the birth of the universe is shrouded in guesses and hypotheses.”3 Another web article stated that astronomers “lost track of time”4 and quoted Riess in saying that “we’re not passing this test [the age of the universe]—we’re failing the test!”5
Such publicity prompted the Institute for Creation Research to post an article in which young-earth creationist physicist Jake Hebert asserted that the apparent contradiction between the two measures of the age of the universe was more evidence that “problems with the Big Bang are legion” and that “secular astronomers have wasted, and continue to waste, who-knows-how-many millions (perhaps billions?) of taxpayer dollars attempting to prop up a failing cosmology.”6
Is the big bang creation model really in as much trouble as these article authors imply? Are astronomers confused or feeling that their certainty about big bang cosmology will be upended? Is there a contradiction between the two measurements of the cosmic expansion rate?
Why the Answer Is No
For a variety of reasons, the answer to all three questions is no. Here is the basis for the paper and web articles. Riess’s team observed 20 detached eclipsing binary stars and 70 Cepheid variable stars in the Large Magellanic Cloud galaxy that yielded a measure of the cosmic expansion rate equal to 74.03±1.42 kilometers/second/megaparsec. (A megaparsec = 3,261,560 light-years or 19.174 million trillion miles.) This measure is about 9 percent faster than the one derived from the Planck satellite map (see figure) of the cosmic microwave background radiation (the radiation remaining from the cosmic creation event) which was 67.3±1.2 kilometers/second/megaparsec. However, it is important to recognize that these two measures do not stand alone.
Figure: Final Planck Map of the Cosmic Microwave Background Radiation. Image credit: ESA, Planck Collaboration
Other astronomy research teams have also produced high-quality measurements of the cosmic expansion rate. They are listed together with these two in the table below.
Cosmic Expansion Rate Measurements
masers in NGC 4258 72.0±3.0
masers in 3 other more distant galaxies 67.6±6.0
Cepheids/type Ia supernovae (2017) 70.6±2.6
Cepheids/type Ia supernovae (2019) 74.0±1.4
cosmic microwave background (Planck) 67.3±1.2
cosmic microwave background (WMAP) 69.3±0.8
baryon acoustic oscillation 67.3±1.1
First, it is important to note that of the seven measurements in the table, the two mentioned above are the farthest apart from one another. The other measurements are not so discrepant.
Second, the first four measurements are cosmic expansion rates for the late universe (the recent history of the universe) while the last three measurements are cosmic expansion rates for the early universe (that part of cosmic history shortly after the beginning of the universe). Thanks to both the cosmic mass density and the cosmic dark energy density, the universe must expand at a slower rate when it is young than it does when it is older.
As the universe expands, its space surface gets larger. Dark energy’s power to accelerate the expansion of the universe is proportional to the size of the cosmic space surface. Hence, due to dark energy alone the universe should expand faster as it gets older.
The expansion of the universe implies that clumps of mass in the universe will move progressively farther apart from one another. Thus, the mutual gravitational attraction of the mass clumps will gradually decrease. That is, as the universe gets older, the mass clumps become progressively weaker in their capacity to slow down the expansion of the universe.
Accounting for Different Measures
Riess’s team pointed out the problem that the difference between their measurement of the cosmic expansion rate and the rate derived from the Planck map of the cosmic microwave background radiation, 6.7 kilometers/second/megaparsec, is too large to be explained by the simplest models for the nature of dark energy and dark matter. However, in their paper they argue that both their measurement and the measurement derived from the Planck map of the cosmic expansion rate are correct. Thus, they conclude that the discrepancy can be resolved by adjusting the currently standard big bang creation model, what is known as the ΛCDM model (a universe dominated by dark energy, Λ, and secondarily by cold dark matter, CDM), by including the effects of “exotic dark energy, a new relativistic particle, dark matter-radiation or neutrino-neutrino interactions, dark matter decay, or a small [cosmic] curvature, each producing a different-sized shift [in the cosmic expansion rate].”7
What Riess and his colleagues are proposing is not at all considered “upending” or an appeal to “guesses and hypotheses.” Astronomers already possess evidence that dark energy may be more complex than the explanation that it is governed by a single cosmological constant. They also have some evidence for dark matter decay and possible dark matter interactions.
While Riess and his team believe that the cosmic expansion rate discrepancy is real, it may not be as large as what they claim. An average of all four cosmic expansion rate measures in the above table, based on the late history of the universe, is 71.1 kilometers/second/megaparsec. An average of all three cosmic expansion rate measures in the above table, based on the early history of the universe, is 68.0 kilometers/second/megaparsec.
In this case, the discrepancy is a little less than half of what Riess’s team cites in their paper. It is low enough that, in view of the error bars on the measurements, there may be no need to appeal to the adjustments suggested by Riess and his colleagues. At the least, the lower discrepancy calls for a deeper study of systematic errors. Systematic errors are possible offsets or multipliers of measurements due to instrumental effects and possible failures to properly calibrate or account for other natural phenomena that could influence the outcomes of the measurements.
Examples of relevant possible systematic effects include: (1) if the measurement produced by Riess’s team featured a much-improved calibration of the wide-field camera infrared detector on the Hubble Space Telescope; and (2) if the earlier 2015 measurement in the above table—using the same method of observing eclipsing binary stars, Cepheid variable stars, and type Ia supernovae to determine the cosmic expansion measure—featured a correction for star formation bias.8 These two systematic effects and others may explain why the two measurements, both based on eclipsing binary stars, Cepheid variable stars, and type Ia supernovae, yielded a difference of 3.4 kilometers/second/megaparsec. Fortunately, as Riess and his colleagues point out, high-resolution imaging from the soon-to-be-launched James Webb Space Telescope and the largest ground-based telescopes with adaptive optics will likely reduce these systematic errors and others to much below 1 percent.
Personally, I do not think systematic errors alone will account for the 9 percent difference between the cosmic expansion rate determinations by Riess’s team and from the Planck map of the cosmic microwave background radiation. Nor do I believe that any one of the five adjustments suggested by Riess’s team by itself will resolve the difference. I am persuaded, based on the best currently available observations, that resolving the difference will likely require a combination of two or more of:
- improved understanding and determination of systematic effects,
- dark energy proving to be more complicated than being governed solely by the cosmological constant,
- dark matter radiation and/or particle interactions, and
- the decay of one or more dark matter particles.
In my opinion, measurements of the geometry of the universe rule out a small cosmic curvature influencing the cosmic expansion rate to any significant degree.
I also see little chance that the determined age of the universe will shrink from 13.8 to 12.6 billion years. There are just too many different observational methods, independent of the cosmic expansion rate, pointing to an age between 13.0 and 13.9 billion years.9
Current Status of the Big Bang
In light of these recent observations, what is the status of the big bang creation model and how should we respond to young-earth creationists? It seems like the acronym, ΛCDM, will need to be expanded. Young-earth creationists are correct in pointing out that the big bang model has been evolving. However, it has been evolving in a manner that proves the big bang creation model rather than negating it.
The model has progressed from a big bang model to a hot big bang model, to a hot inflationary big bang model, to a hot inflationary big bang model where the universe is dominated by dark energy and secondarily by cold dark matter, to now an even more detailed big bang creation model. Young-earth creationists have cited each of these adjustments as failures for the model. However, none of these adjustments required an abandonment or major alteration in the big bang model. Rather, each provided additional evidence for its veracity.
No scientific model is or ever will be complete. There is always more to learn. Scientists affirm that a model is very likely correct when it extends their knowledge and understanding about some aspect of the natural realm and they are able to make the model progressively more detailed and comprehensive in its explanatory power. By these yardsticks, the big bang creation model is a spectacular success, and the paper published by Riess and his colleagues adds to that success. I look forward to one or two letters being added to the ΛCDM acronym.
I also look forward to scientists and laypeople who are not yet followers of Jesus Christ (and to young-earth creationists) recognizing that astronomers were not the first to conceive of the big bang creation model. Six Old Testament authors scooped astronomers by 2,500 years and more. For over two millennia the Bible stood alone as the only book declaring the fundamental features of big bang cosmology.10 This outstanding prediction is powerful evidence for the inspiration, inerrancy, and divine authority of the Bible. Now, we have even more scientific evidence that the Bible is the inspired, inerrant, authoritative Word of God.
Featured image: The Large Magellanic Cloud with Inset of Star Cluster Studied by Riess et al. Image credit: NASA/ESA, A. Riess (STScI/JHU), and Palomar Digitized Sky Survey