Cosmology is the study of how the universe we live in came into being, why it looks and behaves as it does, and what its ultimate fate is. Building on the work of Albert Einstein, cosmologists have come up with a new account of the origin of the universe, the so-called big-bang cosmology. Over the past three decades a series of observational developments and refinements to the theory have led to its wider acceptance. For the present, there are no fundamental challenges to the big bang theory, although there are certainly unresolved issues with the theory itself. Astronomers are not sure, for example, how the galaxies were formed, but it is questionable whether there is a reason not to think the process did not occur within the framework of the big bang. Indeed, the predictions of the theory have survived all tests to date.
Nevertheless, we should always bear in mind that present-day science is not the last word, and perhaps Einstein’s theories, and the big-bang cosmology, will in turn be superseded.
Our present knowledge of the universe is restricted to a handful of observational facts. The expansion of the universe, indicated by the law relating the red shift in light from astronomical objects to their distance, was disÂ¬covered by Edwin Hubble in the early part of this century. The existence of the microwave background radiation corresponding to a temperature of 2.7K, and the cosmological abundance of helium are more recent discoveries. Together, these three observations suggest that the universe was born in a hot fireball from a very dense state-the big bang. Not just matter was created in the big bang, but space-time as well. There was nothing outside for the big bang to explode into-and this nothing means not even empty space.
Cosmologists today do not claim to know exactly what made the universe explode into existence from a state of zero volume and infinite density-a space-time singularity-but they do claim to be able to describe in great detail how a hot fireball of matter and radiation has evolved from a fraction of a second after the instant of creation over about 15 billion years to produce the cool, dark spread of empty space, dotted with galaxies made up of stars, gas, dust and planets, that we see about us now.
The laws of nature as we currently understand them allow us to trace the observed expansion of the universe back billions of years to what would be a true beginning, a moment when the universe was infinitely hot and dense. Although, theorists are now pushing back their speculations about what happened in the first 10-35 seconds after the big bang, with less confidence, the modern cosmological world view begins at a time when the universe had cooled to only 1012K, about 10-5 seconds after the instant creation. At these extreme conditions, the laws of physics as deduced here on earth can be applied to produce the story of everything that ha happened since. At a temperature of 1012K, particles and radiation would be interchangeable, as the mass equivalent of energy in the radiation would be ample to produce particles like protons, neutrons, and electrons, not out of thin air but out of thick radiation, in line with the rules E=mc2 for a particle of mass m and E=hv for radiation with frequency v (h is Planck’s constant). Here higher black body temperature of radiation corresponds to bigger v, that is bigger energy E, and therefore to more massive particle equivalents.
So, one-hundred-thousandth of a second after it began, the universe would have been a seething mass of particles and radiation, a swirling soup in which particle/antiparticle pairs were constantly being created out of energetic photons, and constantly annihilating with one another to produce other energetic photons. Overall though, the total mass/energy of the whole system was constant. For every E/c2 of mass created or destroyed an exactly equivalent E/h of radiation is destroyed or created.
Things began to get more orderly at 1011, still within the first 0.1 seconds after the big bang, as the universe expanded so that the density of radiation at any point was no longer enough to produce the more exotic particles. Only electron/positron pairs, and the massless photons and neutrino/antineutrino pairs, were light enough to have a continuing involvement in the matter/radiation balance.
About 14 seconds after the big bang, the temperature of the universe had dropped to around 3xl09K, and even electrons and positrons needed too much energy for the weakening radiation to create them. As the universe conÂ¬tinued to expand and cool, creation became slower than annihilation, and almost all the particles and antiparticles disappeared. But for some unknown reason, a small proportion of electrons, protons and neutrons were left over. It is this early excess of matter over anÂ¬timatter that survived to form light atomic nuclei a few minutes later, then (after about a million years) to form atoms and, still later, to be cooked to heavier elements in stars, ultimately to provide the material out of which life would arise. The reason for this predominance of matter over antimatter remains a mystery and has been a source of concern to modern cosmology. It is, nevertheless, one of the key initial conditions that determined the future development of the universe.
As the temperature dropped to 109K-about 70 times the temperature in the heart of the sun today-many protons and neutrons fused into helium nuclei, and by the end of first four minutes no free neutrons were left. Some 75% of the mass of the visible universe had been processed into protons plus electrons (ultimately to be bound into hydrogen atoms) while rather more than 25% mass of the universe had been processed into helium. The abundance of these elements in the universe is detectable today, and provides a constraint on the range of allowable models.
Another 700,000 years later, the expanding universe cooled to the point where electrons can bind to helium and hydrogen nuclei to make atoms, at a temperature of around 5000K. This signalled the end of the last remaining links between matter and radiation on a cosmic scale. Although free electrons and atomic nuclei, being electrically charged, interact strongly with radiation, electrically neutral atoms do not. From then on, the background radiation had nothing left to do but spread thinner in the expanding and cooling universe, to become the faint hiss we now detect at temperature equivalent of 2.7K. The very high degree of uniformity of the microwave background today is a strong indication that uniform, isotropic models provide a good description of the universe.
After the first thousand million years or so, with matter firmly established and radiation playing only a minor and decreasing role, the story of the universe can be taken up in terms of gravity, left as the dominating force because of its long range and its independence of electric charge. Gravitational forces then shaped the galaxies by holding stars and planets together.
However, our grasp of the conditions that prevailed in the early universe does not translate into a full understanding of how galaxies formed. Many scientists believe that the hydrogen and helium gases that filled the universe must have been pulled into concentrations by gravity. But there are problems with this explanation: for, what could cause large, diffuse gas clouds to collapse, even with the aid of gravity, while the universe as a whole is expanding?
Having established that the universe began in a hot big bang, and being tolerably happy with a rough understanding of how galaxies formed, the truly cosmological question remaining for astronomers to puzzle over is whether the universe is open (will it expand forever) or closed (will it one day collapse into a new fireball)?
The answer lies in its density. The symbol used for the mass density of the universe is Omega. If Omega, is less than 1, the universe will expand forever, so that, eventually, all the galaxies and stars will grow dark and cold. The alternative to this ‘big chill’ is a ‘big crunch.’ If Omega is more than 1, gravity will eventually reverse the expansion, and all matter and energy will be reunited. For the present, since we are not sure how galaxies formed, the value of Omega is uncertain-most astronomers put it somewhere between 0.1 and 1.
While eternal expansion is the generally favoured hypothesis; there may be enough of the unseen matter in the universe to produce a gravitational pull capable of halting the expansion and eventually producing a recollapse. Though the case is not yet proven, one current idea is that neutrinos, once believed to be massless particles, may have a rest mass less than 1/10000 of an electron. As neutrinos are thought to be as numerous as photons, their aggregate mass could suffice to close the universe. The fact that we cannot see enough matter to close the universe does not mean that it is not there.
During the next decade, as techniques for measuring the mass of the universe improve, we may learn whether the present expansion is headed toward a big chill or a big crunch. What happens then? Just as we do not know how everything could appear from nothing in the big bang if space-time did not exist, we do not know what happens to the universe at this stage; the laws of physics are inadequate to describe such extreme conditions. If there is ever to be a solution to the mystery of the origin and end of the universe, it must await a substantial increase in our understanding of the quantum nature of gravity-the big bang account of creation has forged an unlikely marriage between cosmology, the science of the very large, and particle physics, the science of the very small.
In any event, the universe we inhabit seems to be very improbable. Random processes and statistical fluctuations on cosmological time scales could easily have made it quite inhospitable to life. Are we just lucky? Or is there some deep significance to the fact that we live in a universe just right for us?
For all its violence-including the possibility of a black hole resident at the centre of our own galaxy-the universe seems to be an ideal place for man. Everywhere we look in the universe, from far flung galaxies to the deepest recesses of the atom, we encounter order. The laws of physics can explain beautifully the analytic structure of nature, the behaviour of individual particles and fields, but tell us nothing about the collective, collaborative organization of matter: that is, how the world is put together.
Why is the world the way it is and not otherwise? This is not the type of question scientists normally ask. The customary approach to scientific inquiry is to discuss what we see, not what we might see. Nevertheless, the universe is such a remarkable place, and we, as observers, are perhaps the most remarkable feature, it seems worth while ascertaining just how probable or improbable the present arrangement is.
For example, we do not understand why the fundamental constants of nature have the values they do. Einstein captured its essence when he said: ‘What really interests me is whether God had any choice in the creation of the world.’ Very slight changes in the physical constants of nature could have made the universe unfold in a completely different manner.
Most of the features of the everyday world and the astronomical scene are determined by a few basic physical laws and constants, such as the masses of the elementary particles and the relative strengths of the basic forces that operate between them. In many cases, a rather delicate balance seems to prevail. For example, if the nuclear forces were slightly stronger then they actually are, compared with electromagnetism, the di-proton-an atomic nucleus containing just two protons and no other particle-would be stable; ordinary hydrogen would not exist, and stars would evolve very differently. If nuclear forces were slightly weaker, no chemical elements other than hydrogen would be stable, and chemistry would be dull indeed. In either case, we would not be here to ponder such matters.
Or suppose the constant of gravity were stronger and the gravitational force were, say 1030 times weaker than the electromagnetic force instead of a factor of 1040 weaker. Then we would have a small-scale, speeded-up universe, in which stars-gravitationally bound fusion redactors-had only 10-15 times the sun’s mass, and lived for about a year. This might not allow time for complex systems-such as life forms-to evolve. The question-Was the relative strength of electromagnetic force over the gravitational force there from the beginning of time or is it an accident of today? -remains intractable.
These mysteries are heightened when we reflect how surprising it is that the laws of nature and the initial conditions of the universe should allow for the existence of beings who could observe it. Life as we know it would be impossible if any of several physical quantities had slightly different values. The best known of these quantities is the energy of one of the excited states of the carbon-12 nucleus. There is an essential step in the chain of nuclear reactions that build up heavy elements in stars. In this step, two helium nuclei join together to form the unstable nucleus of beryllium-8, which sometimes before fissioning absorbs another helium nucleus, forming carbon-12 in this excited state. The carbon-12 nucleus then emits a photon and decays into the stable state of lowest energy. In subsequent nuclear reactions carbon is built up into oxygen and nitrogen and the other heavy elements necessary for life. If the energy of the excited state of carbon-12 were just a little higher, the rate of its formation would be much less, so that almost all the beryllium-8 nuclei would fission into helium nuclei before carbon could be formed. The universe would then consist almost entirely of hydrogen and helium, without the ingredients for life.
Moreover, if the proton and neutron masses were equal, then neutrons and protons could not bind to form deuterium and heavy nuclei, and nuclear burning in stars and, consequently, life would be impossible.
The most ubiquitous examples of orderliness in the universe are the stars. They represent an extreme departure from thermodynamic equilibrium because they burn brightly in a cold, dark space. The source of starlight is the nuclear furnace at the core of the star, where the chief nuclear reaction is the fusion of hydrogen to helium. This is a downhill process, leading to nuclei of greater stability, and the cost paid for achieving it is the redistribution of nuclear energy into the surrounding space in the form of heat and light. This particular orderliness, and with it most familiar examples of terrestrial organization, leads to the question: Is the present structure of the universe-which is made mainly of hydrogen and not helium or heavier elements-just luck, a coincidence? Because, if the universe were made of, say, iron (the most stable element) there would be no stars like the sun.
Also, the structure of our world depends vitally not only on the availability of free hydrogen, but also on the reasonably smooth distribution of the primeval matter. If the big bang had only coughed out black holes-the ultimate triumph of gravity-in which everything is completely obliterated and disappears, no life would have been possible.
Can all these peculiar ‘coincidences’ be understood in terms of some self-evolutionary mechanism?
In its standard form, the big bang theory assumes that all parts of the universe began expanding simultaneously. Observations confirmed this assumption and showed that the expansion is remarkably uniform in all directions. This would seem to imply a collaboration between widely separated regions of the cosmos to expand at the same rate everywhere. Such highly organized behaviour leads us to ask how all the different parts of the universe could synchronize the beginning of their expansion?
Where does the energy that makes the universe expand come from? What could be a permanent, decidedly nonzero source of energy in the universe, with cosmic consequences? Could it be vacuum-as the source of everything yet itself nothing? This is one of the hottest topics in contemporary physics and lies at the heart of perhaps the most important new concept in cosmology of the past decade. If it is correct, could the creation of being out of nothingness occur without the mediation of a Creator?
There are many such peculiar ‘coincidences’ in the universe. Is it just our luck that they have worked out that way, or is there a deeper explanation? One understanding would be that the world is the way it is because it is the creation of a Creator who wills it to be capable of fruitful process: His command, when He desires a thing, is to say to it ‘Be!’, and it is (Ya Sin, 36.82). Without an Organizer, chaos can never be transformed into cosmos. This explanation is not a temporary sop to satisfy our curiosity about phenomena for which we cannot yet work out a satisfactory physical explanation; rather, it is a step guiding us towards a better understanding of the real world.
That does not mean that these mysteries constitute a barrier beyond which science cannot pass. As in the past, we may reasonably expect that, in the future, deeper understanding will be achieved and a more profound pattern discerned at the basis of physical reality, in a new, perhaps new kind, of explanatory theory. It may be some version of supergravity or it may be the novel theory of ‘superstrings’. Or some other theory that we have not yet thought of.
However, we should bear in mind that both our growing knowledge about the universe, and the need, alongside it, to revise it continually, is clear evidence for the inconclusiveness of science and the limitation of its methods.
In addition, the finititude of man’s existence (in this very small part of a vast universe) and the limitations of his senses mean that all our efforts must be considered ‘relative.’ The results of pure and experimental sciences are a limited portion of reality as man can grasp it from his location in the universe and within the very limited time allotted to him, and not the truth itself. There is of course, a great difference between being aware of things and knowing their actual truth. The former is limited to sensible events only, while the latter lies beyond the capacity of our senses.
No inquiry into the nature of creation or any part of it can be closed and concluded. The patterns of God in creation are infinite: there will always be more of them to discover. As we strive to do so, understand more and more about nature, the scientist’s sense of wonder will not diminish but become sharper, more narrowly focused on the mysteries that still remain. The worth of science lies in its commitment to understanding the Divine handiwork. The comprehensibility of the reality around us is among the greatest of God’s favours to us. Einstein remarked this: ‘The most incomprehensible thing about the universe is that it is comprehensible.’
The Qur’an contains many scientifically accurate statements, some of them still relevant to cosmology; it does not contain any statements which are in conflict with the findings of man’s scientific research nor open to criticism from modern science. Many of its verses allude to, and urge, reflection upon the reality around us as a form of worship, as a way to draw nearer to the Creator. I shall conclude by citing (in translation) a verse which draws our attention to the fact that, in a general sense, the future will be the age of knowledge and information, and that as a natural consequence of this, it will be an age of faith and belief:
Soon We shall show them Our signs on the furthest horizons, and in their own souls, until it becomes manifest to them that this is truth. Is it not enough that your Lord witnesses all things? (Fussilat, 41.53)
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