The “Uniformity” Problem

The “Uniformity” Problem

The “uniformity” problem has to do with the incredible degree of uniformity of the Cosmic
Microwave Background Radiation at 2.726 degrees Kelvin [22]. Even though the slight
“ripples” have been found to agree with the level needed to explain galaxy formation, there is
another problem even more serious. It is known that the universe was expanding at such an
incredible rate during its most early period, prior to the radiation being released, that it could not
have had any opportunity to come into thermal equilibrium. Not even light could have had time
to travel between separated regions of the expanding universe to allow the same uniform
temperature to be reached in all parts of the universe. Thus the highly uniform radiation
temperature is either simply an extremely arbitrary initial condition of the expansion or some
mechanism existed to allow the universe to thermalize prior to the expansion. It is important
here to note that scientists by nature do not wish to accept extremely arbitrary initial conditions
as an explanation, since that ends the search for any other explanations, of which there may be a
good one. A good explanation is also one that may indeed be correct, as borne out by further
investigation.
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In this case, a good explanation does exist. It is good for several reasons. It resolves not only
the “uniformity” problem, but it also the “flatness” problem, which we shall address next.
Another argument in its favor is that it agrees with our understanding of the fundamental forces
of nature. However, it requires that we go back very close to the start of the universal expansion,
to when all of the fundamental particles were swarming in an extremely hot, dense mixture that
formed the entire universe. At this earliest time, there were no galaxies, stars, or even protons or
neutrons. Everything is broken down into the smallest constituent particles in the universe. The
fundamental forces responsible for electromagnetism and the nuclear strong and weak
interactions were essentially all identical at this extreme temperature. This expected unification
of the fundamental forces of physics is itself a remarkable leap in understanding, since it arose
from the study of particles and fields, independent of cosmology. But the only time the
fundamental forces in nature were identical was during the moment right after the creation of the
universe. We cannot achieve a high enough temperature to simulate these conditions today, and
thus it remains somewhat speculative. The time is within an extremely small fraction of a
second, approximately 10-35 seconds after the start of the universal expansion, which began in an
exceedingly hot state. As the universe expands it cools in this brief time, until it is cool enough
for the nuclear strong force to become distinct from the other forces. As this transition takes
place, an enormous amount of energy is released and a tremendous effect occurs. The energy
released serves as a repulsive force, overpowering the gravitational attraction. The universe
undergoes an extremely short and rapid expansion called “inflation”, analogous to a phase
transition when a liquid becomes a gas. This inflationary period was proposed by physicist Alan
Guth in 1981 to resolve the uniformity problem [23].

The rapid expansion balloons the universe from an extremely small dot too little for our eyes to
see, into a universe roughly 50 orders of magnitude larger within an extremely small fraction of a
second. Then the universe continues to expand in a much more milder fashion, although still
quite impressively such that the universal expansion is too fast to allow light enough time to
travel from one part of it to another quite distant part as it expands. We know that the universe
has expanded faster than light can traverse its extent, since we are presently observing events at
the “edge” of the visible universe with our most sensitive telescopes. At the “edge” of the visible
universe, objects now coming into view have previously been too far removed from us for the
light, traveling at the speed of 186,000 miles each second, to have arrived to us since the
universe began. This problem has also been referred to as the “horizon” problem, since most of
the universe has been beyond the horizon limited by the travel of light [24].
Inflation resolves the “uniformity” or “horizon” problem in the following way. Prior to the
inflationary expansion, the universe was extremely tiny, small enough that even in the small
fraction of a second prior to inflation, light could easily traverse the universe. Thus thermal
equilibrium is reached quite thoroughly before inflation takes place. That equilibrium is then
preserved during the rapid inflation of the universe. After the rapid expansion, the uniform
temperature everywhere is simply because of the previously very close proximity of everything,
when the universe was able to come into equilibrium. Even though vast regions of the universe
are now separated beyond what even light could traverse during vast ages of the universe, these
regions were already “causally” connected, and thus at very nearly the same temperature. The
very rapid inflation of the universe served to smooth out irregularities even more, resulting in a
cosmic microwave background radiation today at a very uniform temperature everywhere. But

without any such inflationary period, the universal expansion does not allow the vastly separated
regions to ever be “causally” connected by light.