For far too long, humanity has been content with unquestioned faith in subjective knowledge passed down from generation to generation. This has been especially true on issues regarding the origins of our species and, indeed, the universe. However, in the last 100 years, a new culture has emerged. A culture rooted in the ideals espoused by such trailblazers as Bertrand Russell; a belief in scientific understanding of the world we live in and veneration of acquisition of knowledge. The human race is no longer content with fables and fairy tales. We want to know how, when and why our universe came into existence. We want to know where we are coming from and where we are going. And we have had much progress to that end.
The defining moment in this quest came in 1927 when physicist, civil engineer and Roman Catholic priest of Belgian origin, Georges Lemaitre, hypothesized the origin of the universe. This hypothesis was later named by the scientific community as the Big Bang theory and is undoubtedly the most accurate attempt at explaining the origin of the universe. The theory has undergone major modifications since it was conceived in light of emerging developments of science, notably in the field of quantum mechanics. But its basics remain more or less fixed.
The theory claims that 13.7 billion years ago, at the moment we call the Big Bang, an infinitely dense state characterized by indescribably high temperature and pressure expanded exponentially forming the universe. In this early universe, a fraction of a second old, there were high temperatures and particle movements were ostensibly random with particles being created and destroyed at equally high rates.
Using Einstein’s theory of general relativity in tracing the expansion of the universe in reverse order with respect to time, one arrives at the conclusion that, indeed, the universe originated from a singularity. However, general relativity becomes inadequate in explaining this early universe beyond the singularity since general relativity is suited for explanation of macroscopic phenomena. Commander Stephen Hawking and Penrose have come up with an ostensible solution to this problem by claiming that the singularity should be analysed using quantum mechanics, that we should treat the singularity as some sub-atomic particle. If they have their way – and it seems they do – then the universe will be explained by a mathematical model incorporating both classical and quantum mechanics. The string (or M) set of theories is a frontrunner in this respect.
Research is ongoing and we will certainly in time unravel the mysteries of our universe and thus “know the mind of God” as Hawking once aptly put it.
Nucleosynthesis at the Beginning of the Universe
Nucleosynthesis is the process by which elements are formed. The primordial nucleosynthesis or Big Bang Nucleosynthesis thus describes the process by which the nuclei of certain light elements were produced in the young universe. Some acceptably accurate estimates claim that this process began some one hundred seconds after the event of the big bang. Nucleosynthesis was preceded by baryogenesis which puzzlingly resulted in the universe being composed of matter as opposed to antimatter. By this time, the universe had cooled considerably and the environment could then permit the existence of particles. This phase is often referred to as the nucleosynthesis epoch in the history of the universe. As already intimated, the epoch began approximately one hundred seconds after the big bang and ended within three minutes after the bang. After this time, the density and temperature of the universe had dropped to such levels that could not support nuclear fusion thus formation of atomic nuclei. The big bang nucleosynthesis made use of primordial protons and neutrons.
At this time the universe’s temperature was in the region of one billion Kelvin and its density was about 1.3 Kg/m3. The conditions precipitated the combination of these primordial protons and neutrons leading to formation of the nuclei of helium and deuterium. However, a large fraction of the protons did not combine and retained as hydrogen nuclei.
We thus see that the conditions in the nucleosynthesis phase were such that only light elements were formed. Heavier elements could not be formed because they tend to be unstable under the thermal and barometric conditions in which nucleosynthesis takes place. It follows that by the end of this epoch, the atomic nuclei that had formed were majorly those of deuterium, hydrogen-1 and helium. Lithium and beryllium had also formed but in very minute quantities.
For over 300 000 years after nucleosynthesis, no major changes took place in particle composition of the universe. Later, when conditions permitted and temperatures had dropped to about 300K, the nuclei combined with electrons to form atoms, notably hydrogen. Much heavier particles, like carbon, were created much later by nuclear fusion processes that take place in stars. Explosion of huge stars (supernova) saw to it that the heavy elements got scattered across the entire universe.
Artificial Helium Nucleosynthesis
At the scale of the universe, helium is certainly one of the most common elements. Yet, at the level of planet earth, it is a rare element whose extraction from the atmosphere would prove uneconomical. Helium for commercial use is thus extracted from natural gas by refining it.
For artificial nucleosynthesis of helium, certain conditions have to be met. As we have already seen, the nuclei of helium in the early universe were produced by fusion of hydrogen nuclei under intense conditions. For artificial nucleosynthesis, these conditions ought to be set and met. To achieve the characteristic rapid proton-capture process (rp-process) that is known to be the cause of generation of energy and nucleosynthesis processes in stellar systems we have to have conditions of such high temperatures and pressures that defined the young universe.
Like in the young universe, artificial nucleosynthesis of helium is achieved by the fusion of deuterons, 2H. For nuclear fusion to be attained, the nuclei need to be near enough to each so that the repulsive forces of their like charges is overcome. Thus nuclear fusion is particularly more practical with light elements like hydrogen whose nuclear charges are smaller.
Practically, nuclear fusion is attained by raising the temperature of deuterium gas to some millions of degrees thus leading to their fusion. Usually, the temperatures are raised by sending immensely heavy electrical discharges through the gas deuterium gas. This process of course leads to production of nuclear energy as well.
Asplund M., Grevesse N., and Sauval A. J. Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis. 2005.
Stephen Hawking, The Universe in a Nutshell
Stephen Hawking and Leonard Mlodinow, The Grand Design, 2010
Bradley S. Meyer and Ernst Zinner, Nucleosynthesis
A. M. Amthor Rp-process Nucleosynthesis in X-ray Bursts, 2005