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| Final frontier: Sir Roger Penrose (above) and an image of a galaxy formation after the Big Bang |
Is that the way the universe began, not with a bang but with a whimper? Sir Roger Penrose, Emeritus Rouse Ball professor of mathematics at the University of Oxford, did not go to the extent of saying “yes” in his lecture arranged by the British Council at the Indian Association for the Cultivation of Science, but he certainly challenged the conventional view of the Big Bang.
In the standard Big Bang model, the question ‘What came before the Big Bang?’ is not allowed. This is reminiscent of the following question-answer sequence in St Augustine’s Confessions:
Q. What was God doing before He created the Universe?
A. Before he created Heaven and Earth, God created hell as the refuge for people who ask this kind of question.
In his lecture, Sir Roger made bold to ask, “What happened before the Big Bang?” and also proposed an answer.
It’s worth recalling the history of the last hundred years when the Big Bang model arrived and entrenched itself in the scientific community. The first theory of the universe was due to Albert Einstein who obtained a static unchanging universe only after he had reluctantly put in a cosmological constant, designed to defy gravity. Alexander Friedman, a Russian mathematician at St Petersburg, thought that the cosmological constant was ugly and decided to solve Einstein’s equation without it. The result was a dynamic or evolving model of the universe, which Friedman published in 1922. Friedman died prematurely in 1925 but a Belgian priest and cosmologist, George Lemaitre, independently discovered the same dynamic solution that led to an expanding universe. Lemaitre carried the idea further by arguing that if the universe is expanding today, it must have been a tiny compact primeval particle at some point in the past. At the moment this particle exploded and ejected its fragments, the history of our universe began — a point of time described in Lemaitre’s words as “a day without a yesterday”.
Edwin Hubble’s observation of receding galaxies (like raisins on the rising surface of a cake being baked) in 1929 boosted Lemaitre’s observations. By the middle of the century, US physicists Ralph Alpher and Robert Herman had a reasonably clear picture of the evolution process. An hour after creation, the universe was a plasma soup of simple nuclei and free electrons, accompanied by a lot of light that kept scattering off the charged particles in the plasma. As the universe expanded and cooled down to about 3,000 degrees centigrade, the transition from plasma to atoms happened for hydrogen and helium. It was estimated that the universe would take about 3,00,000 years to cool to such temperatures. As atoms started getting formed, the light that existed in that era had few targets to interact with (light does not interact easily with neutral objects like atoms) and Alpher and Herman predicted that that light would still be around today. Alpher and Herman estimated that today the wavelength of that Big Bang leftover light would be one millimetre. This is not in the visible part of the spectrum, but is located in the so-called microwave region.
This cosmic microwave background (CMB) radiation was detected accidentally by Arno Penzias and Robert Wilson, two scientists working with the Bell Telephone Laboratories, in the mid-1960s. Finally Nasa’s Cosmic Background Explorer Satellite (COBE) found definitive proof of the existence of a tiny variation (one part in hundred thousand) in CMB radiation coming from different parts of the sky. This indicated the existence of density variation in the early universe, which would have seeded the formation of galaxies. The triumph of the Big Bang model was complete.
Interestingly enough, it is this most impressive triumph of the Big Bang model that Sir Roger used, to contend that the question “What happened before the Big Bang?” is meaningful.
To probe a possible weakness of the standard Big Bang scenario, Sir Roger took recourse to thermodynamics — the most robust of all sciences as evidenced by its happy surviving of the relativity and quantum revolutions. Thermodynamics thrives on a somewhat esoteric object called the entropy — a measure of the amount of randomness in a system. The second law of thermodynamics can be cast as the catchy statement “the entropy of an isolated system always increases with time”. In addition, there is the concept of equilibrium. Equilibrium is generally defined as a state that does not change with time. If entropy always increases and equilibrium implies no change, then the equilibrium state must be one of maximum entropy.
Sir Roger argued that if we look at the early stages of the universe, we get, on the basis of the Big Bang model, essentially a black body radiation curve; meaning that the universe was in a state of equilibrium and hence in a state of maximum entropy from its very beginning. This is in conflict with the second law that requires entropy to increase. This creates a paradox. Prof. Penrose went on to explain that this paradox can be resolved if we can lower the entropy in the initial stages of the universe. To do this, one has to suppress the matter contribution to entropy in the beginning of time. This can be done because the gravity contribution is initially negligible. As time progressed, different parts of the universe started clumping together and gravity, which was not a part of the thermal equilibrium, started to become part of it. As the role of gravity increased, so did the entropy.
Accepting the picture of an ever-expanding universe, Sir Roger looked to the remote future where much of the matter clumps into black holes. The limitless expansion of the universe cools it below the Hawking temperature of the black holes which then evaporate and all that is left behind is radiation. Turning to the past from the future, the extremely low entropy of the initial state, forced on us by the second law of thermodynamics, makes Prof. Penrose conjecture that in the initial stages, the Weyl curvature, which is a measure of the gravitational irregularities, is zero. This is consistent with the fact that at the very high energies of the initial state, the rest masses of particles are negligible and hence it is all radiation. The remote future is thus equivalent to another Big Bang!
The early beginning and the remote future having the same form, it is possible, argued Sir Roger, to device a mathematical trick to go from the present to the early stages without encountering a singularity. Standing at the edge of creation, looking forward and looking back presents the same view and thus one does not have the sinking feeling that space and time have ceased to exist. The immediate fallout on the scientific community is not apparent but atheists may sleep in peace — the concept of creation which a singularity entails, may after all be shelved.
The author works in the theoretical physics department of the Indian Association for the Cultivation of Science (IACS), Calcutta
