Many people use quantum gravity as a loophole for avoiding the conclusion that a Creator must have intervened from beyond space and time to create the universe. (There are excellent theoretical rebuttals to such speculations that I will report on in future articles.) A recent breakthrough shows the possibility of observational testing in this area. Thanks to new observations of distant quasars and blazers at short wavelengths, astronomers have placed strong constraints on quantum gravity speculations.
What Is Quantum Gravity?
Everything we can know and measure about the universe from the present all the way back to when the universe was just 10-35 seconds old reveals that gravity dominates the dynamics of the universe. Physicists are designing theories to cope with conditions before the universe was even 10-43 seconds old (less than a quadrillionth-quadrillionth-trillionth second). At 10-43 seconds, the force of gravity within the universe becomes comparable to the strong nuclear force. (The strong nuclear force holds protons and neutrons together in the nucleus of the atom.) Before this epoch in the history of the universe, gravity may possibly be modified by quantum mechanical effects. Hence this early stage of the universe is called the quantum gravity era.
Since the energy densities that exist during the quantum gravity era lie far beyond the capabilities of even the most powerful particle accelerators (a particle accelerator longer than 50 times the distance to the most distant galaxy in the universe is needed), many theoreticians have presumed, therefore, that they are free to speculate any physical conditions, or, for that matter, any physical laws they desire. However, since such physics is obviously beyond “the possibility of observational verification,” it would by definition fall outside the realm of science and into the realm of metaphysics.
Observational Constraints on Quantum Gravity Speculations
Even though the energies during the quantum gravity era are far beyond current experimental physics, a powerful observational check does exist—the present universe in which we live. If a quantum gravity theory cannot explain how the present universe developed from the initial quantum state, it must be incorrect. By this means, a number of quantum gravity theories can be ruled out.
Astronomers can rule out many more quantum gravity theories through observations of distant quasars and gamma-ray sources. In quantum gravity models the foaminess of space-time is a consequence of the energy uncertainty principle. While the individual space-time fluctuations (foam) are infinitesimally small, depending on the particular quantum gravity model, the fluctuations accumulate (become more frothy) over long path lengths. This accumulation can blur the images of the most distantly observed sources. The blurring effect is most pronounced at short wavelengths.
For some quantum gravity models, the blurring effect makes the detection of distant quasars and gamma-ray burst sources impossible.1 These models clearly are eliminated by astronomers’ successful observations of these sources. Constraints on the blurring of the images of distant quasars, blazers, and gamma-burst objects rule out random walk (randomly varying quantum foam) quantum gravity models2 and also rule out holographic quantum gravity models.3 (Holographic cosmic models are an outcome of string theories that suggest the entire universe may be seen as two-dimensional information on a cosmological horizon beyond our field of view.) As four European astrophysicists concluded, “All the main QG [quantum gravity] scenarios are excluded.”4
The next generation of ground-based and space telescopes will have the capability of observing the blurring, or lack thereof, of images of quasars, blazers, and gamma-ray burst sources at greater distances and shorter wavelengths. These future observations will yield much stronger constraints on quantum gravity and string theories.
Already, the observed lack of blurred images of objects at great distances establishes that the universe’s space-time fabric is smooth to a high degree out to great distances and deep into the quantum gravity realm. This smoothness implies the likely ubiquitous application of both the theories of special relativity and general relativity. This ubiquitous application means that the space-time theorems proving that a Causal Agent beyond space and time created the universe5 are unlikely to be overturned by some exotic physics operating during the quantum gravity era. It also yields by far the strongest constraint on possible variations in the velocity of light. It establishes that the velocity of light in a vacuum cannot vary by more than a few parts in 100 million trillion trillion (1032).6
The lack of observed image blurring has implications beyond the validity of the space-time theorems. Many physicists, in their attempts to avoid the varied theological implications of big bang cosmology, speculate that the laws of physics break down previous to 10-43 seconds after the cosmic creation event. The observed lack of blurred images of distant sources means that if such a breakdown does occur, the physical laws cannot break down by very much.