Reasons to Believe

A "House of Cards" Gets a Foundation

Measurement of the universe's expansion (essential for knowing its size and age) critically depends on what astronomers call the cosmic distance scale. Distances to the farthest objects in the heavens cannot be measured directly but must be built up through a sequence of steps that some people have characterized as a "house of cards"-so dubbed because if the shorter distances are proven incorrect then the whole distance scale falls apart.

In such a sequence, distances of about a hundred light years can be measured directly using a triangulation method called parallax.1 Greater distances, however, must rely on "standard candles." These objects possess some property (like the cycle of variability in their intensity) that can be tied to their absolute brightness. This property allows astronomers to use the difference between the object's apparent and absolute brightness to estimate a distance to the object. An example of a standard candle is a star called a Cepheid variable,2 which provides distance estimates to about 10 million light years. Its accuracy depends on the accuracy of the closer distances-the foundation of the house of cards-measured by parallax being correct.

Type Ia supernovae3 comprise another example of a standard candle. These exploding stars allow for distance measurements from about 10 million light years out to the edge of the universe at 13 billion light years. Again, the accuracy of these distances depends critically on the correctness of the closer distances.

Though astronomers have been fairly confident of the correctness of the cosmic distance scale, relatively recent VLBI (Very Long Baseline Interferometry)4 measurements have strengthened that confidence and given the "house of cards" a secure foundation. VLBI makes use of a network of antennas strategically placed around the world and equipped with ultrasensitive receiving systems. Using VLBI in a sort of reverse parallax, radio astronomers have been able to measure the very small proper motions (angular motions across the line of sight) of compact regions in the galaxy NGC 4258.5 Based on some simple assumptions about the geometry of the galaxy, they have been able to estimate the distance corresponding to this proper motion and thereby derive the distance to the object independent of any other measuring technique. Previous estimates of the galaxy's distance ranged from about 11 million to nearly 23 million light years. These VLBI observations yield a distance of 23.5 +/- 0.9 million light years.

This vast improvement in the cosmic distance scale will allow astronomers-and interested nonastronomers-to peer into the reaches of the universe and verify two of its key attributes: that the universe had a beginning and continues to expand. Such characteristics, which are features of RTB's cosmic creation model, were first revealed as long as 3500 years ago by the authors of the Bible.6

References

  1. Learn more about parallax here:
    http://www-spof.gsfc.nasa.gov/stargaze/Sparalax.htm.
  2. Learn more about Cepheid variables here:
    http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/cepheid.html.
  3. Learn more about supernovae here:
    http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html.
  4. Learn more about this technique at:
    http://dsnscience.jpl.nasa.gov/vlbi.html.
  5. J. R. Herrnstein et al., "A Geometric Distance to the Galaxy NGC4258 from Orbital Motions in a Nuclear Gas Disk," Nature 400 (1999): 539-41.
  6. Hugh Ross, A Matter of Days (Colorado Springs, CO: NavPress, 2003), 139-48.

Subjects: Instrumentation

Dr. David Rogstad

Dr. Dave Rogstad received his PhD in physics from Caltech and worked over 30 years for NASA’s Jet Propulsion Laboratory. Though now retired, Dave continues to serve as an RTB board member and participates regularly in several RTB podcasts.