‘What exactly does the Big Bang theory explain? A theory should be able to explain phenomenon, otherwise it is a conjecture only.’

‘The most important contribution of Big Bang theory is interpreting the abundance of different elements in the universe.’

FORMATION OF THE UNIVERSE>THERMONUCLEAR DETONATION>NUCLEOSYNTHESIS

The early universe behaved much like a fusion bomb, although then no atomic-trigger analogue of the atom bomb was needed to produce a high enough temperature for fusion to occur. At first, the neutrons remained free; the radiation held was so intense that it instantaneously destroyed the first nucleosynthetic products that might have formed. Only after about a minute, when the temperature had fallen to a billion degrees Kelvin, did the reactions commence. First, a neutron captured a proton to make a nucleus of deuterium (heavy hydrogen). Deuterium readily absorbs neutrons, Heavy water (HDO), in which one of the hydrogen atoms in H₂O is replaced by a deuterium atom, is commonly used in nuclear reactors because of its high absorptivity for neutrons. The deuterium next captured another neutron to make tritium; finally, the tritium reacted with a proton to make helium. Almost all the neutrons ended up in helium nuclei. Since each helium nucleus contains two neutrons and two protons, the result was one helium nucleus for every ten hydrogen nuclei. The big bang had created helium. The predicted ratio of helium to hydrogen can he changed, but only by severely modifying the big hang theory. We shall refer to this uniform and isotropic big bang as the standard model.

There are radical alternatives to the standard model. One alternative postulates enormous amounts of turbulence present during the nucleosynthetic era. Another alternative postulates that the gravitational force was much larger in the past. In either case, the effect would have been to accelerate the rate of expansion of the early universe and not to allow enough time for the neutrons to react effectively before they decayed. Thus, essentially no helium would have been produced. A more modest acceleration of the expansion would actually have increased the production efficiency at which the neutrons initially formed, thereby raising the predicted helium abundance.