I can hardly imagine a more mind stretching experience than to find that reality is not what we always perceived it to be. Yet the purpose of science is to open our eyes to the true nature of the universe. There are many things we take for granted. The so-called arrow of time, the apparent directionality in the way things happen, remains one of the deepest mysteries in science. In everyday life we don’t ask why eggs break but do not unbreak, why the pieces of a broken glass do not miraculously come together again or why people age but do not get younger. These asymmetries rule our daily lives; if it were different the world around us would be unrecognizable. To many it would seem to be an exercise in futility to even try to find out why a broken glass does not unbreak. But in science we want to understand. That is why we ask the question: “Where does the time-asymmetry come from, what determine this most basic property of science?” The puzzle deepens even further when we consider that in the known laws of physics there is no such asymmetry; all directions, backward, forward are all treated the same. And that is a big puzzle; the laws of physics seem to be at odds with our daily experience.
So far we have concentrated on everyday issues, but there are cosmological issues such as the cosmological principles of homogeneity (when viewed on large scales matter seems evenly distributed in the universe) and isotropy (at large distances the universe looks the same in every direction) and the problem of why the temperature of the microwave background radiation appears so uniform across the sky. These perceived mysteries cannot be explained by Einstein’s version of how the universe began the Big Bang theory. To find an answer to these questions we have to go to the most difficult of all events – the birth of the universe. The questions are: “Why is the universe so uniform in all directions? “Why is the temperature of the microwave background radiation so uniform across the sky?” It was these issues and others that inspired the inflationary universe theory, also known as inflationary cosmology in the late 1970’s and early 1980’s. The Big Bang theory was modified by the insertion of a brief period of rapid expansion; the universe increased by a factor of larger than a million trillion trillion in less than a millionth of a trillionth of a trillionth of a second.* This theory went a long way to explain the gaps in the Big Bang theory.
This explained why we had a highly ordered universe in the beginning that was a prerequisite for the physicist Ludwig Boltzmann’s statistical laws and that explain why there appears to be directionality in the way things happen, never the reverse. Any irregularities that may have existed in the very early universe were ‘ironed’ out in the exponential expansion of the very early universe and the fact that the universe is still expanding, indicates a direction in the unfolding of events. Thus the universe is aging (in trillions of years there will be no more hydrogen to form stars and the universe will become a very cold place due to its continuous expansion) people are aging; stars die never the reverse. This tells us something very important; the entropy (disorder) of any system will only increase, never decrease. This is the so-called second law of thermodynamics.
It is rumoured that the eminent British scientist, Sir Arthur Eddington said that if your theory is contrary to the second law of thermodynamics, then your theory must be discarded.
Despite its successes there is a very big problem with inflationary cosmology because it rests on Einstein’s general relativity equations. Scientists know that Einstein’s equations are in conflict with the study of quantum objects such as the very early universe. If you apply Einstein’s equations to a quantum object everything goes haywire; all answers are infinite which is nonsensical. We can therefore not use general relativity to find out if conditions in the very early universe really explain times arrow. This is a real dilemma. And this is what scientists are currently trying to achieve; to unite Einstein’s general relativity with quantum mechanics. To complicate matters further the conditions of extreme temperature, density and gravity in the very early universe were so extreme that it cannot be recreated on earth. The study of black holes went some way to understand conditions at the birth of the universe, but scientists hope to find a theory of quantum gravity; the only theory which will enable scientists to study gravitational effects at the quantum level. We had a glimpse of what such a theory may look like when Stephen Hawking proved that a black hole behaves like any black body; it radiates thermal energy.
* This is very well explained by Brian Greene in his book ”The Fabric of the Cosmos”
Frikkie de Bruyn