Increasingly accurate measures of the rate and constancy of cosmic expansion also put the dispute between old- and young-universe creationism to a more rigorous test.2 One such breakthrough comes from a team of American and Canadian radio astronomers whose work buttresses the current method for measuring cosmic expansion.
Until just a few years ago, the only reliable method for determining the expansion rate of the universe relied on the “distance ladder” method. (Even today, this method is still considered one of the pillars for determining the expansion history of the universe because it offers insights into the expansion rate at multiple cosmic epochs.)
Using direct distance measurements to nearby objects, astronomers calibrate the indirect distance methods and then use the indirect methods to determine the distance to more-distant objects. Indirect methods make certain assumptions about the properties of the observed objects. The direct methods are assumption free.
Direct distance measurements rely upon the plane geometry theorems students learn in high school. Traditionally, the diameter of Earth’s orbit becomes the base of the triangle for these calculations. But because that base of 186 million miles is comparatively small, the nearly perpendicular side angles and extremely narrow vertex angle of the triangle for stars located more than a thousand light-years away seriously limit the precision of such measurements.
In the July 2, 2007 edition of Today’s New Reason To Believe I reported on recent measurements made on microwave maser sources orbiting around the super-giant black hole residing in the center of the galaxy NGC 4258.The spectra of the maser sources yielded the orbital velocities of the sources about the black holes. Newton’s laws of motion translated those velocities into measured diameters for the orbits. A different radio astronomy research team then used electronically linked radio telescopes all over the world to create an instrument with an angular resolving power a thousand times better than the biggest ground-based optical telescope and a hundred times superior to the Hubble Space Telescope. With accurate measures of the angles subtended by the orbits combined with precise measures of the diameters of the orbits in kilometers, the team used geometry theorems to calculate the distance to NGC 4258.3 This technique pushed accurate direct distance measurements out to 25 million light-years and it confirmed that the indirect distance measuring methods were reliable.
Now, radio astronomers have developed another method, independent of the one used on NGC 4258, to determine a direct distance measurement to a galaxy millions of light-years away. In 1993, astronomers observed the beginning of a supernova eruption in the spiral galaxy, M81. Since then, astronomers have measured the growth of an expanding shock front emanating from the supernova. By studying spectral measurements of the light at the leading edges of the shock front, astronomers deduced its rate of growth in kilometers per second. This information led to the discovery of the width in kilometers of the shock front at various epochs in its expansion. Using a global network of radio telescopes, the American-Canadian radio astronomy team provided precise measurements of the angles subtended by the shock front at those same epochs.4 As with the maser sources in NGC 4258, high school geometry theorems gave the team an accurate direct distance measurement to M81.
The American-Canadian team determined the distance to M81 to be 12.9 million light-years ± 0.9 million light-years. Though slightly higher than the best indirect distance determination, this distance measure was consistent given the measuring errors. Therefore, astronomers now possess two independent direct distance determination methods on two different galaxies that confirm the reliability of the indirect methods. Such confirmations allow us to enjoy a more certain picture of the universe’s expansion history and a more accurate calculation of the time back to the cosmic creation event—the event of which Moses wrote in Genesis 1:1.