Reasons to Believe

Dark Energy and Gravity Withstand Tests

In the life sciences, researchers are discouraged from challenging certain reigning paradigms, such as the evolutionary explanation for the origin of humans. The opposite is the case in the astrophysical sciences. Astrophysicists are encouraged to critique and test even the best established facts, principles, and laws of physics and astronomy. An example of such a critique and test, one that has enormous implications for our biblical cosmic creation model, was announced just days ago.

It is hard to think of anything better established in physics than the law of gravity. In the other sciences, gravity often is used as an analogy for certainty. Yet, the astrophysical community has been busy trying to build a case for an alternate theory of gravity, one that does away with the need for dark energy.

Dark energy, the self-stretching property of the space surface of the universe, also is a well-established concept in astrophysics. For several decades astronomers insisted that dark energy had to exist to explain a variety of observations of the gross features of the universe. In 1998 and 1999 two teams of astronomers actually observed the cosmic space surface expanding at a progressively faster rate—a clear signature of dark energy. The dark energy signature that they and subsequent observers have measured amounts to about 3/4 of all the stuff that makes up the universe. This discovery won the Nobel Prize for the leaders of the two teams.

Einstein’s theory of general relativity is the most exhaustively tested and best proven principle in the disciplines of astronomy and physics. Some tests of general relativity have proven its reliability to predict the future positions of massive bodies to better than 15 places of the decimal. Yet, it is this very theory of general relativity that many physicists and astronomers are calling into question.

The most seriously proposed alternative to general relativity is something called f(R) theory. In f(R) theory, in addition to the bending or warping of space-time in the vicinity of mass and energy as predicted by general relativity, there is an extra gravity-like force that either attracts or repels. This extra force is referred to as a scalar field or a fifth fundamental force of physics.

In 2007, two theoretical physicists showed that with the just-right choice of the function f(R), the measured expansion history of the universe (a slight deceleration for the first half of cosmic history followed by a slight, ever-increasing acceleration during the second half of cosmic history) could be explained without invoking dark energy.1 Not until 2015 did anyone attempt to put this special f(R) theory to the test.2 A large team of astronomers and physicists first determined that this version of f(R) theory predicted that galaxy clusters would form faster and be more numerous than would be the case in the standard cosmological model with dark energy and gravity governed strictly by general relativity. In analyzing the then current databases on galaxy clusters, the team noted that the data favored dark energy and disfavored f(R) theory. However, the galaxy cluster data was neither extensive enough nor of sufficient observational quality to make their deduction conclusive. In particular, the team lacked precision measurements of the total masses of the galaxy clusters.

Now, a team of astronomers led by Xiangkun Liu has taken advantage of weak gravitational lensing to directly and fairly accurately measure the masses of numerous galaxy clusters.3 Gravity from a very massive object, or a dense cluster of massive objects, will distort the images of more distant galaxies directly behind it in our line of sight. The featured image for this article shows a nearly complete ring of blue light around a central giant spherical galaxy. The blue ring is the distorted image of a more distant galaxy. The size of the ring and the degree of distortion reveals the mass of the foreground giant galaxy.

The research team led by Liu used observations of 5.5 million galaxies produced by other astronomers using the Canada-France-Hawaii Telescope to develop a catalog of weak gravitational lensing galaxies. Analysis of this catalog strongly agreed with the predictions of dark energy and contradicted the predictions of f(R) theories. In the words of Lui et al.,

Our fits are consistent with general relativity, not requiring a fifth force.4

This new result, though devastating to f(R) theory, does not entirely kill it. To settle the issue once and for all will require the Large Synoptic Survey Telescope, currently under construction in Chile. This instrument will increase the database of weak gravitational lensing galaxies by a factor of about 130 times greater than that achieved by the Canada-France-Hawaii Telescope.

The bottom line is that general relativity and dark energy have passed yet another milestone test. The theological implication of this passed test is that general relativity is the basis for the space-time theorems that prove that the universe has a beginning that includes the beginning of space and time itself. This space-time beginning implies that the Cause of the universe must be an Agent that operates beyond the universe who possesses the power to create space-time dimensions at will. As for dark energy, it ranks by far as the most highly fine-tuned known parameter of the universe in terms of fine-tuning design needed to make the existence of life and humans possible. Therefore, dark energy implies that the Causal Agent who created the universe is a personal Being.5

Before a high fidelity test of f(R) theory was possible, because of numerous other tests of general relativity and dark energy, we had a very high degree of scientific certainty that a God beyond space and time created the universe and personally designed it for the benefit of human beings. Now, thanks to the recent precision test of f(R) theory, we possess even greater scientific certainty. When the Large Synoptic Survey Telescope begins accumulating observations, we will gain the opportunity to develop still greater scientific certainty. As the Bible repeatedly infers, the more we study the realm of nature, the more evidence we will accumulate for the handiwork of God.

 

Endnotes

  1. Wayne Hu and Ignacy Sawicki, “Models of f(R) Cosmic Acceleration that Evade Solar System Tests,” Physical Review D 76 (September 2007): id. 064004, doi:10.1103/PhysRevD.76.064004.
  2. Harry Wilcox et al., “The XMM Cluster Survey: Testing Chameleon Gravity Using the Profiles of Clusters,” Monthly Notices of the Royal Astronomical Society 452 (September 2015): 1171–83, doi:10.1093/mnras/stv1366
  3. Xiangkun Liu et al., “Constraining f(R) Gravity Theory Using CFHTLenS Weak Lensing Peak Statistics,” preprint, Physical Review Letters, submitted July 1, 2016.
  4. Wilcox, “XMM Cluster Survey,” 1171.
  5. For more on the implications of the personal nature of the universe’s Causal Agent, see my book Why the Universe Is the Way It Is (Grand Rapids: Baker, 2010), 38–41, 9293, 230n17.

Subjects: Cosmic Expansion, Cosmology, Dark Energy & Dark Matter, Laws of Physics, Origin of the Universe, Universe Design