I try to arrive at my speaking events early. Not only do I want to check out the presentation technology, I also want to get a feel for the kind of audience I’ll be addressing.
No matter what the event, early arrivers consistently choose the most optimally located seats. They sit anywhere from about a third of the distance from the podium to the back of the auditorium. They get the best view of the projection screen and can see clearly all my table demonstrations.
As with early arrivals to an auditorium, astronomers have found that there is an ideal location for life in our Milky Way Galaxy (MWG). The high density of nearby stars and molecular gas clouds would gravitationally disturb a star born too close to the galactic center. Likewise, such a star would be exposed to many nearby gamma-ray burst events and supernova eruptions. That star would never develop a stable set of planets where one of the planets could sustain life. On the other hand, a star born too far away from the galactic center would lack the necessary heavy elements to form a possibly life-friendly system of planets.
For our MWG, a star would need to be born about one third of the way out from the galactic center in order for future life to be a possibility (see figure 1). Italian astronomer Lorenzo Iorio reported in the Monthly Notices of the Royal Astronomical Society that more than the ejection of the Sun from its birthing star cluster is responsible for moving the solar system to its present position.1 The value of the cosmological constant also impacted the solar system’s relocation. Additionally, the cosmological constant is astronomers’ leading candidate for explaining the existence of dark energy, which makes up 72 percent of all the stuff of the universe.
Figure 1: Habitable Zone for the Milky Way Galaxy
In developing a detailed map of the Milky Way’s structure, astronomers discovered that a planet with the capacity to support advanced life can exist only at a highly specified distance from the center of the galaxy.
Image credit: NASA/JPL-Caltech
Using the present position of the Sun, compared to where it must have been born (for advanced life to be presently possible on Earth), Iorio constrained the value of the cosmological constant. In so doing, he provided more evidence for the cosmological anthropic principle.2 (This principle states that the laws of physics and the features of the universe were exquisitely fine-tuned to make possible the future existence of life and human beings in particular.) Iorio demonstrated the need to fine-tune the cosmological constant to get the universe to expand at just-right rates throughout cosmic history so as to produce a galaxy, star, planetary system, and planet that make advanced life possible.
Iorio established that the cosmological constant affects the dynamics of a star so as to cause it to migrate inward from its birthing location toward the galactic center. Iorio demonstrated that the greater the value of the cosmological constant, the greater the amount of inward migration. In particular, he showed that for the Sun to end up at its present distance from the Milky Way’s center (26,600 light-years),3 its birth location would have been 64,000 light-years from the galactic center, assuming the cosmological constant = 10-55 per centimeter squared. The large distance of the Sun’s birth location from the galactic center would strongly rule out the possibility of the Sun producing a planet as rich in heavy elements as Earth. Thus, the cosmological constant’s value must be much less than 10-55 per centimeter squared. In fact, it must be at least a factor of ten times less.
If dark energy makes up seven tenths of all stuff of the cosmos, then the value of the cosmological constant = 10-56 per centimeter squared.4 A dark energy density = 0.7 is exactly what the best measurements of the cosmic expansion rates throughout cosmic history yield.5
Iorio also demonstrated that the cosmological constant must be fine-tuned so that the migration of the primordial solar system brings it to its present just-right location, namely slightly inside the Milky Way Galaxy’s co-rotation distance. The co-rotation distance is that radial distance from the galactic center where a star revolves around the center of the galaxy at exactly the same rate as the galaxy’s spiral structure. That’s the distance where a star and its planets would suffer the lowest rate of spiral arm crossings (crossing through a spiral arm would expose a planetary system to life-threatening radiation and gravitational disturbances from massive stars and molecular gas clouds). However, a planetary system situated exactly at the co-rotation distance would be subject to mean motion resonances. Such resonances would lead to catastrophic gravitational disturbances. Consequently, the best place to be is just slightly inside the co-rotation distance.
Such multifaceted and high degrees of fine-tuning of the cosmological constant demand nothing less than an all-knowing, purposeful, all-powerful, and all-loving Creator. Research on the cosmological constant shows yet again that the more astronomers learn about the universe, the more evidence they uncover that the God of the Bible exists and created the universe for the specific benefit of Earth’s life and human beings in particular.