Sunday, May 14, 2017

Quantum Gravity and the Beginning of the Universe


General relativity is one of the most tested and confirmed scientific theories and requires that there be an absolute beginning to all space, matter, time, and energy.  We have an excellent understanding of what has happened since the Big Bang – except for the first tiny fraction of a second.  In this first miniscule amount of time, it is believed that all the fundamental forces are unified into one grand force.  The problem is that we haven’t been able to figure out how this happens with gravity.  We can unify electromagnetism and the strong and weak nuclear forces using quantum mechanics, but we can’t get gravity and quantum mechanics to mesh. We also don’t expect to be able to get observations to help us do this because the energy required to simulate this era of the universe is way too high for any current or foreseeable particle accelerator to study. At this point, there is no possibility of direct observational verification of the quantum gravity era.  Does this fact that we haven’t figured out what happened in the first 10-43 seconds of the universe mean we can’t say that the universe had an absolute beginning?

Because we can’t directly observe the conditions of the early universe, we have to fall back on theoretical mathematical models to try to determine what went on.  Many have been purposed, but because this falls into the unobservable area of physics, called meta-physics, it is difficult to say which one is correct.  Skeptics of an absolute beginning to the universe have used this fact, that the first 10-43 seconds of the universe lie in the meta-physical realm, to call into question the conclusions of general relativity.  They will say that it is just as likely that the universe is eternal and therefore can’t know if the universe had an absolute beginning.  We have enough evidence to make this skeptical position untenable.

In order to propose an eternal universe (one without an absolute beginning), you have to play some mathematical games, one of which is to propose that the energy of the universe is non-zero.  The problem with this is that we have very good reasons to believe that the energy of the universe is zero; all of our observations about how matter interacts and the fact that space is smooth and uniform help us to confirm this.  Light and matter (including antimatter) contain what physicists call “positive energy.” The gravitational energy that exists between all these particles is “negative energy.” This negative gravitational energy exactly cancels the positive energy, so the total energy of the universe is zero.  Even in the meta-physical realm, it is more reasonable to say that the universe began to exist.

As it turns out, though, we don’t have to play mathematical games to know that the universe had a beginning; we can rule out several of the mathematical quantum gravity proposals with direct observation 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. 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 models and also rule out holographic quantum gravity models. (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.”[1]

Hugh Ross continues:

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 universe 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).

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.[2]

Direct observational evidence has all but eliminated the likelihood of any quantum gravity model overturning the conclusions of general relativity that all space, matter, time, and energy had an absolute beginning.  The second premise of the cosmological argument is most reasonably true:  The universe began to exist!

If you are interested in a full mathematical treatment of this topic, go here:  http://www.wall.org/~aron/blog/did-the-universe-begin-iv-quantum-eternity-theorem/

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