Confirming Cosmic Expansion, Part 3 (of 4)
Although written thousands of years ago, the Bible’s scientific information was so far ahead of its time that advances in astronomy and cosmology didn’t catch up to it until the big bang theory emerged in the twentieth century. Since then, evidence supporting the biblical big bang creation model continues piling up, including determinations of the cosmic expansion rate.
Continual cosmic expansion under fixed physical laws from an actual beginning of matter, energy, space, and time is the key to this particular creation model. This series of articles is dedicated to outlining the efforts to calculate the cosmic expansion rate via accurate direct distance measuring to near and far objects. Part 1 discussed the distance ladder method, which uses direct distance measurements on nearby objects to calibrate indirect methods for far away objects. Part 2 introduced two newer, more accurate techniques of direct distance measuring: measurements of the expanding shock fronts of supernova eruptions; and observations of water maser sources orbiting around the center of the host galaxy. The former method provides direct distance values for galaxies within 20 million light-years and the latter for galaxies within 200 million light-years.
This article briefly explains the third technique, measured time delays of gravitational lenses, which gives precise values for galaxies up to several billion light-years away.
Time delays of gravitational lenses
A galaxy situated in the line of sight between an observer’s telescope and a distant quasar is an example of a strong gravitational lens system. Einstein’s theory of general relativity states that the intervening galaxy will act as a lens by bending the light from the distant quasar. If the galaxy is exactly in the line of sight, the image of the quasar will be transformed from its actual point image into a small ring. In the much more common case where the galaxy is slightly off the line of sight, the quasar’s point image becomes lensed into two or more point images.
Almost all quasars experience large, frequent variations in their light output. Such variations allow astronomers to determine how rapidly the universe expands at the epoch corresponding to the light-travel time to the quasar. Here is how the technique works:
A variation in the light output of the quasar also will show up in the lensed image of the quasar. But, typically, different parts of the lens will be situated at different distances relative to the observer, causing the light to reach the observer’s telescope at different times. Knowing the velocity of light, astronomers can translate the light arrival times into distance differentials in kilometers and then use plane geometry theorems to determine the distance to the lens in kilometers by measuring the angles separating the different components of the lens. Measuring the redshift of the spectral lines in the lensed image tells astronomers how rapidly the lens is moving away from us. The expansion rate of the universe for the lensing galaxy’s light travel time epoch is the galaxy’s velocity divided by its distance. (For a more detailed description of the technique complete with diagrams of the relevant geometry see here.)
In this manner astronomers can use gravitational lenses over a wide variety of cosmic distances to determine how rapidly the universe expands at different distances relative to Earth.
In the March 1, 2010 issue of the Astrophysical Journal, a team of eight astronomers published the most accurate measurement to date of the cosmic expansion rate (also known as the Hubble constant) founded on time delays of a gravitational lens.1 Based on their latest measurements of the gravitational lens system B1608+656 (the distance of the four lensing galaxies ranges from 3 to 8 billion light-years) the team determined that the universe is expanding at the rate of 70.6 ± 3.1 kilometers per second per megaparsec (one megaparsec = 3.26 million light-years). This measurement represents an increase in precision that is nearly a factor of three times superior to previous attempts.
The same Astrophysical Journal published work from four other astronomers describing results they achieved from their measurements on the gravitational lens system Q0957+561 (the distance of the lensing galaxy = 3.7 billion light-years).2 They calculated the cosmic expansion rate to be 79.3 ± 7.6 kilometers per second per megaparsec. Previous determinations, one based on sixteen published time delay quasars3 and a second based on four different gravitational lens systems,4 found the universe to be expanding at a rate of 72 ± 8 and 74 ± 8 kilometers per second per megaparsec respectively.
All of these measurements are consistent within their stated errors. The latest and best measurement (70.6 ± 3.1 kilometers per second per megaparsec) is a factor of almost three times more precise than the traditional gold standard for indirect determinations of the cosmic expansion rate, namely the Hubble Space Telescope (HST) Key Project’s final value of 72 ± 8 kilometers per second per megaparsec.5 However, the HST Key Project’s value is still completely consistent with the best gravitational lens measurements.
The best value for the cosmic expansion rate determined by a gravitational lens is also consistent with the latest refurbished indirect calculations. A research team, led by astronomer Adam Riess, thoroughly improved and updated the HST Key Project. The update yielded a cosmic expansion rate of 74.2 ± 3.6 kilometers per second per megaparsec.6 Meanwhile, combined results from the Wilkinson Microwave Anisotropy Probe five-year database of the temperature fluctuations in the cosmic microwave background radiation, the distribution of galaxies seen in the Sloan Digital Sky Survey, and the measurements of Type Ia supernovae gave an expansion rate of 70.5 ± 1.3 kilometers per second per megaparsec (see here.)7
It is remarkable how well the most accurate determinations of the cosmic expansion rate agree. This is especially comforting to proponents of the big bang creation model, but it should cause alarm among its dissenters. Next week, the fourth and final installment in this series will review the philosophical implications of the results achieved through the three new direct distance measuring techniques.
|Part 1 | Part 2 | Part 3 | Part 4|
- S. H. Suyu et al., “Dissecting the Gravitational Lens B1608+656. II. Precision Measurements of the Hubble Constant, Spatial Curvature, and the Dark Energy Equation of State,” Astrophysical Journal 711 (March 1, 2010): 201–21.
- R. Fadely et al., “Improved Constraints on the Gravitational Lens Q0957+561. II. Strong Lensing,” Astrophysical Journal 711 (March 1, 2010): 246–67.
- Masamune Oguri, “Gravitational Lens Time Delays: A Statistical Assessment of Lens Model Dependences and Implications for the Global Hubble Constant,” Astrophysical Journal 660 (May 1, 2007): 1–15.
- L. V. E. Koopmans and C. D. Fassnacht, “A Determination of H0 with the CLASS Gravitational Lens B1608+656. II. Mass Models and the Hubble Constant From Lensing,” Astrophysical Journal 527 (December 20, 1999): 513–24.
- Wendy L. Freedman et al., “Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant,” Astrophysical Journal, 553 (May 20, 2001): 47–72.
- Adam G. Riess et al., “A Redetermination of the Hubble Constant with the Hubble Space Telescope From a Differential Distance Ladder,” Astrophysical Journal 699 (July 1, 2009): 539–63.
- E. Komatsu et al., “Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation,” Astrophysical Journal Supplement Series 180 (February 2009): 330–76.