Two US Scientists John Mather and George Smooth have shared this year's Nobel prize in Physics for their contribution to the Big Bang theory of the origin of the universe. The observed Anisotopy of the cosmic microwave background(CMB) is the afterglow of the radiation left over from the Big Bang, writes Professor Farooq Ahmad
In the nature of things it is delicate undertaking to try to discern the general structure and features of a universe which stretches out farther than we see. For less than a century both the theoreticians and the observers of the cosmos have been making exciting discoveries, but the points of contact between the discoveries have been few. Edwin Hobble's most remarkable and important discovery that universe is expanding and very distant galaxies are rushing away the fastest. This discovery surely ranks as one of the outstanding achievements of modern Physics. The progress in our understanding is intimately linked with the development in technology. The revolution in space technology and wealth of observational data, hence, available has stimulated renewed enthusiasm in understanding the large scale structure of the universe. In this direction US space agency NASA launched a satellite in late eighties for mapping the Universe and to know how is the detectable matter and radiation in the Universe organized on the largest distant scales. These results were quite revolutionalizing and added immense knowledge of understanding of Universe, which led to winning of Nobel prize for Physics this year announced in October 2006.
The 2006 Nobel Prize for Physics has been awarded to two US scientists John Mather and George Smooth for their contribution to Big Bang theory of the origin of the Universe. The significance of two scientists achievement is reflected in the swiftness with which the Swedish Academy chose to recognize it , Nobel Prizes are typically awarded decades after the work that they commemorate, but Prizes awarded this year were for the research completed in the last 15 years. Mather, 60 , is a senor Astrophysicist at US space agency NASA Goddard Space Flight in Maryland and Smooth , 61 , is a Professor of Physics at the University of California at Berkeley. They have been honoured for "their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation (CBM)". The pair worked as chief architects of NASA satellite observatory for Cosmic Background Explorer (COBE) launched in 1989, the space craft measured feeble remnants of light that originated early in the history of the Universe, about 380,000 years after the Big Bang. Before that time, the Universe would have been so hot that matter and radiation would have been "coupled"- it would have been opaque to light, making impossible to directly observe anything older. The CBM is the "oldest light" in the Universe and is all round us and comes from a time 380,000 years after Big Bang , which corresponds to matter and radiation "decoupled" phase. The matter went on to form stars and galaxies; the radiation spread out and cooled . This radiation called "CBM" now shines at week radio (microwave) wavelengths. It is interesting that COBE showed the CBM's profile to a predicted distribution – a so called black body curve. The measurements also revealed tiny ripples in the light's intensity, representing "lumps" no more than 0.001 per cent richer in matter than space around them. From those humble origins arose massive galaxies and galactic Super Clusters hundred of millions of light years across. The COBE also inspired even more detailed studies that made increasingly accurate estimates of age, history and composition of the Universe, revolutionalizing what had been a frustrating vague and theoretical field. Smooth's announcement in 1992 that his team had observed the long-sought variations in CBM – and therefore in the early Universe – shock the scientific community. The work was highly appreciated by the scientific community in general and even by world renowed British Astrophysicist Stephen Hawking called it "discovery of the century if not of all time". The COBE mapped tiny temperature fluctuations of the Universe in CBM. These fluctuations (anisotropy) correspond to the early distribution of matter. The discovery of these ripples and wrinkles in the very fabric of space time are believed to be the primordial seeds of modern-day structures in our Universe such as galaxies, clusters of galaxies and so on. The CBM satellite measured the temperature of this background radiation and found to be a frigid 2.725 degrees above absolute zero; it shines in the microwave portion of electromagnetic spectrum. Further, COBE results showed that CBM , temperature profile to follow a very precise pattern in the energy spectrum of so- called back body curve. The existence of such a profile was a major prediction of Big Bang theory.
Ever since the dawn of human life on this planet, man has always sought to understand nature, his own place in the scheme of creation. The creation of the Universe is explained by Astrophysicist in a widely accepted phenomenon popularly known as to "Big Bang". A part of science concerned with the structure and evolution of the Universe on the largest scales of space and time is known as Cosmology. The Gravity governs the structure of the Universe on these scales and determines its evolution. The Big Bang model of Cosmology rests on two key ideas: general theory of relatively and cosmological principle. The cosmological principle states that for any given cosmic time, the Universe is homogenous and Isotropic on the largest scales. One can use Einstein's general relatively to compute the corresponding gravitational effects of that matter. In physical cosmology, the Big Bang is the scientific theory of how Universe emerged from a tremendously dense and hot state about 13.7 billion years ago. The theory is based on the astronomical observations indicating the expansion of space as predicted by the Hubble's red shift of distant galaxies taken together with cosmological principle. Extrapolated into the past, these observation show that the Universe expanded from a state in which all the matter and energy in the Universe was at an immense temperature and infinite density – the cosmic singularity. The term Big Bang is used both in a narrow sense to refer to a point in time when the observed expansion of Universe began. The early Universe was filled homogeneously and Isotropically with an incredibly high energy density and concomitantly huge temperatures and pressures. It expanded and cooled, going through phase transitions analogous to the condensation of steam or freezing of mater as it cools, but related to elementary particles. Approximately one trillion trillion trillionth of a second after the Big Bang a phase transition caused the Universe to experience exponential growth during a period called cosmic inflation. After inflation stopped, the material components of the Universe were in the term of quark- gluon plasma in which the constituent particles were all moving with externally high velocity known as radiation phase. As the Universe continued growing size , the temperature dropped and producing protons and neutrons on the scene. Further decrease in temperature (about 5000 Kelvin) in a time scale of 380,000 years after Big Bang gave the birth of matter, mostly Hydrogen atoms. This relic radiation is the cosmic microwave background (CMB). One of the strongest protagonists of the Big Bang theory was George Gamow a brilliant Nuclear Physicists, who predicted that if the Universe had a hot phase soon after Big Bang , it should now possess a cooled-down relic radiation background. From this model Gamow was able to predict at least qualitatively, the existence of cosmic microwave background radiation having temperature of 7 Kelvin. Over the time, the slightly denser regions of nearly uniformly distributed mater gravitationally attracted nearby matter and thus grew denser, forming gas clouds, stars galaxies and the other astronomical structures observable today.
In the year 1964, Arno Penzias and Robert Wilson while conducting a series of diagnostic observations using a new microwave receiver owned by Bell laboratories, discovered cosmic back ground radiation and futher validated the Big Bang theory over its chief rival, steady state theory. Their discovery provided substantial confirmation of the general CMB predictions- the radiation was found to be Isotropic and consistent with black body spectrum of about 3.5 Kelvin- and it pitched the balance of opinion in favour of Big Bang hypothesis. Penzias and Wilson were awarded Nobel prize for their discovery in 1978 . To check the true black body character of radiation, it is necessary to have detectors above Earth's atmosphere. There were several early attempts using balloons and rockets. However, many of these reported results departured from black body radiation spectrum that turned out to be false alarms. The COBE measurements give a very precise Planckian Spectrum with black body temperature. The early developments in the post combination era imprint their signature on the radiation back ground, imprints that are expected to survive to this day.
The Big Bang model admits exotic physical phenomena that include dark matter, dark energy and Cosmic inflation which rely on certain conditions and Physics of which have not yet been observed in terrestrial laboratory experiments. In order to understand this phenomena, NASA has launched another probe, the Wilkinson Microwave anisotropy Probe (WMAP), which is examining minute variations in the CMB in even greater details and has provided strong evidence for a Universe dominated by mysterious dark matter and dark energy. There is a strong observational evidence to show that there is not sufficient visible matter in the Universe to account for apparent strength of gravitational forces within and between galaxies. This led to the conclusion that upto 90% of the matter is not normal but a dark matter, while no such matter has ever been directly observed in any laboratory. On the other hand, dark energy is a truly bizarre form of matter or perhaps property of the vacuum itself that is characterized by a large negative pressure. This is the only form of matter that can cause the expansion of Universe to accelerate or speed up. The August 2006 results of WMAP indicate that Universe has 74% dark energy, 22% dark matter and only 4% of regular matter which we see. This is a remarkable result which is a great challenge to the Cosmology, and is current problem for Cosmologists to interpret in physical laws. It is expected that future model of Universe will depend on how to discover remaining 96 % of unseen dark matter and dark energy.
(The author is an Astrophysicist and is a Professor of Physics in the Department of Physics, University of Kashmir, Srinagar)