The Dark and Bright Sides of Cosmology
Astrophysics has its ironies. Here’s one: Studies of the brightest galaxies in the universe led to the discovery that 99 percent of all matter is “dark matter”.1 But matter is only part of the universe (about a fourth). The rest is energy. Adding irony to irony, research focusing on the brightest stars in the universe shows that “dark energy” is far more abundant than dark matter, making up most of the rest of the universe. Despite its often negative connotation, this “darkness” is not a bad thing.
Under the influence of dark energy (the self-stretching property of the cosmic space surface), the universe now expands at an accelerating rate. As astronomers today look far away (thus back in time), they can observe the most ancient stars in the universe, the first stars to form out of the cosmic creation event. They also observe that cosmic expansion is pushing those stars away from us faster and faster, at a rate (right now) just slightly slower than the speed of light. But that accelerating rate will one day exceed light’s velocity. And when it does, those earliest-formed stars will cease to be visible to us.
In an award-winning essay, physicists Lawrence Krauss and Robert Scherrer announced that because of dark energy, astronomers will one day be unable to ascertain any of the universe’s important features.2 Eventually, no one living anywhere within the universe will be able to determine whether the universe had a beginning or how the elements originated. In other words, the scientific discipline of cosmology (the study of the universe’s history and structure) will come to an end.
The existence of dark energy implies that the later we human observers arrive on the cosmic scene-after about 14 billion years from the moment of creation-the smaller the fraction of cosmic history remains visible. An earlier arrival would also present problems. For someone arriving and researching much before the human era, the light from those earliest stars would not yet have reached our telescopes. However, right before and up to that dark-energy limit, the older the universe, the greater the span of cosmic history we can see. The universe is now at that just-right age-the moment when astronomers can directly view and analyze 99.9972 percent of cosmic history.
From an astronomer’s viewpoint, both the past and future look dark for cosmology. The present, however, is ideal. There’s no better time than now to investigate and comprehend our surroundings. What are the odds that we humans would appear on the cosmic scene at the best possible time to witness the sweep of cosmic history, to study the universe’s beginning and attributes? Given that we humans also occupy the best possible location for viewing all of cosmic history (unblinded by the light of nearby nebulae, star clusters, galaxies, and our own galactic core and protected from multiple other cosmic hazards), it seems reasonable to conclude that the Creator intended for us to be here and to make Himself known.
- Ordinary dark matter is comprised of protons, neutrons, and electrons; exotic dark matter is composed of particles that do not strongly interact with photons.
- Lawrence M. Krauss and Rebert J. Scherrer, “The Return of a Static Universe and the End of Cosmology,” eprint arXiv0704.0221, fifth prize 2007 Gravity Research Foundation Essay Competition, to appear in General Relativity and Gravitation, October 2007.