What’s the matter with Matter? This is a line that caught my attention in Charles Seife’s highly engaging book, entitled “Alpha and Omega: The search for the beginning and the end of the universe” (Doubleday, Trans world Publishers, UK, 2003). I thought that it would be an apt title to discuss some aspects of matter and energy in the context of particle physics and cosmology. Although there is no consensus definition for it, matter can be regarded as anything that occupies space and has rest mass (or invariant mass). Typically, matter includes atoms and other particles which have mass, and normally exists in the form of solids, liquids and gases. We all know from Einstein’s work that mass and energy are actually different states of a single energy-matter continuum, and that wave-particle duality is a well manifested phenomenon by light. Quantum theorists have since extended the wave-particle duality to include all matter. The atoms that compose ordinary matter have their associated electrons closely tied to the atoms; occasionally, an electron gets knocked free, but it quickly attaches itself to another nucleus. But in the early universe, within a tiny fraction of a second after the Big Bang, this was not the case. The Big Bang was a massive explosion that created all the mass and energy in the universe, as well as its space-time fabric, fourteen billion years ago. What started the big bang still remains unfathomable, but it has been hypothesized that the space-time fabric inflated incredibly rapidly after the cataclysm, and before it ended some 10-32 seconds later, the universe was a seething soup of primitive matter in the form of quarks, gluons and leptons (dominantly the electrons), and radiation, the so-called quark-gluon plasma. Within a millionth of a second, the soup cooled to ten trillion degrees, and the quarks succumbing to the pull of the gluons tripled up to form the baryons (neutrons and protons) and some doubled up with antiquarks to form mesons which did not survive as long. The neutrons and protons thus formed were highly energetic and collided with one another randomly and violently, sticking together and then breaking apart, but as the universe cooled they coalesced forming atomic nuclei. This is the era of nucleosynthesis which lasted for a mere 3 minutes and it was incomplete. Most of the protons in the universe remained unbound; the remainder coalesced with neutrons forming deuterium, helium-3 and helium-4 rand other heavier species. This explains why hydrogen constitutes the bulk (about 75%) of the matter found in primordial gas clouds, with helium being about 25%. As described by Seife, the electrons still remained untied to the nuclei during this period, and this plasma state being opaque to light resulted in scattering and re-scattering of photons trapping it in a cage of matter that cooled for thousands of years. All of a sudden, 400,000 years after the big bang, recombination hit. The electrons and the nuclei settled down together forming atoms, the opaque universe became clear, and the trapped photons were released from their cage of matter. This is the cosmic microwave background which fills the observable universe almost uniformly and carries a wealth of information that cosmologists still continue to analyse. One piece of information that cosmologists have been able to discern from this cosmic background radiation coupled with analysis of supernova data is the value of Ω, the density of stuff in the universe that includes both matter and energy. This density parameter Ω is related to the shape and fate of the universe and is now thought to equal approximately 1. The inflationary universe is favoured by most cosmologists, including Stephen Hawking, because “it solves more problems than it creates”. The inflationary burst would have smoothed out all the matter in the early universe to a density that would have allowed the universe to expand as long as ours has. If it had been densely packed with matter at its very start, it could simply have collapsed on itself, like a black hole. If the matter had been spread out too thin in the rapidly growing universe, then it might not have been clumpy enough to form galaxies and it would have drifted away into space. Clearly, the inflationary burst starting from 10-35 seconds and ending at 10-32 seconds was critical in determining the structure of our universe. There are also a number of other factors which are delicately balanced that have ensured that our universe exists as it does. If the strong nuclear force (vide infra) were any weaker, elements other than hydrogen would not exist; if the strong nuclear force were just a bit stronger than the electromagnetic force, then a di-proton nucleus would be the only stable entity in the universe and hydrogen, the source of evolution of our stars and galaxies, would not exist. If the constant of gravity, which is 1038 times weaker than the strong nuclear force, were any stronger, our universe would be small and swift and the mass and lifetime of the average star would be so small as to deny the development of complex biological systems. On the other hand, if gravity was less powerful than it is, matter would not have congealed into stars and galaxies. Then there is also the factor called entropy, which has its origins in the second law of thermodynamics. According to this concept, systems in nature tend to evolve from order to disorder, from complexity to simplicity, with passage of time, and entropy is a measure of this disorder or randomness. We see evidence of increasing entropy all around us – Ice melting in a warm room, cars rusting, people becoming old, mountains eroding, economies going into disarray, conflicts becoming too frequent, the ecosystem increasingly coming under stress and our lives becoming ever more hectic and uncertain. Entropy always goes up with increasing disorder. The entropy of a closed system (isolated such that no matter/energy enters or leaves the system; our universe is an ultimate example of this), always increases. This is the Second Law of Thermodynamics. The entropy of an open system, on the other hand, can increase or decrease, but if it decreases, the entropy of its total environment must increase such that the entropy of the universe increases. Biological systems are open systems for the reason that they can decrease their entropy. Entropy has also found a conceptual application in information theory where it is used as a measure of unpredictability or uncertainty associated with a random variable. For a given context, entropy is a measure of the order or disorder in a sequence that can be regarded as information. Since its first introduction by Shannon (1948), entropy in the information sense has taken on many forms, namely topological, metric, Kolmogorov-Sinai and Renyi. These definitions have been applied, for example, to estimating DNA sequence entropy (of introns and exons) with varying levels of success. Left to its own devices, entropy goes up as time passes. As a matter of fact, natural decay and the general tendency toward greater disorder are so universal that the second law of thermodynamics has been appropriately dubbed "time's arrow", pointing from past to future. From the standpoint of entropy, the primordial gas of hydrogen and helium that was uniformly spread out in the nascent universe would have constituted a high entropy physical state, but this state existed only for a time as gravity intervened causing the formation of orderly clumps. It is believed that clouds of gas initially began clumping together due to the accumulation of primordial fluctuations, which were small changes of the density in certain parts of the early Universe. Through gravity, gas was then drawn towards these denser regions of the Universe along with a girdling mass of hypothetical dark matter (vide infra). Gravity continued to wield its critical influence unabated for billions of years turning the clumps into stars and galaxies, “with some lighter clumps forming planets (like the earth), with a nearby star (like the sun) that provided a relatively low- entropy source of energy that allowed low-entropy life-forms to evolve”, to quote Brian Greene (“The Fabric of the Cosmos”; Penguin Books, 2004). As elucidated by Greene, the Big Bang started the universe off in a state of low entropy; this generation of order was more than compensated by the generation of disorder by the heat generated as the gas compressed, and, ultimately, by the enormous amount of heat and light when nuclear processes began to take place. Still awaiting a consensus explanation though is why matter rather than anti-matter prevailed when the universe was created. There is no experimental evidence for an imbalance in their creation and equal amounts of these would have annihilated each other with no matter to show. An explanation that is currently in vogue is that some reactions specifically involving the weak nuclear force do allow for charge-parity violations, tilting the balance in favour of matter over anti-matter. Another possibility quoted in Wikipedia (http://en.wikipedia.org/wiki/Baryon_asymmetry) is that there may be “antimatter dominated regions exist within the universe, but outside our observable universe” and ”radiation from the boundary of matter and antimatter dominated regions may simply still ‘be on its way’ to Earth, and so cannot be observed.” Cosmologists tallying up all the matter they could see in all the visible stars and galaxies using the most powerful telescopes have come to accept the fact there is insufficient matter to make Ω = 1; the value they obtained is woefully short at about 0.5% of Ω.