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3.2.Cosmological Aspects of the Problem
It is on this basic data coupled with other astronomical and cosmological knowledge that theories have been propounded as to the origin of cosmic rays and how they get their energy.
A discussion of current theories of cosmology is beyond the scope of this paper, but it might be useful if we reviewed those aspects applicable to cosmic ray production.
There are several theories put forward to explain the origin and relative abundance of the elements, but none so far presented are without serious difficulties. On a recent survey Alpher and Herman (1953) divide the theories into two main classes—equilibrium theories and non-equilibrium theories At present the theory of element formation principally by neutron capture reactions in an expanding universe seems to meet with the fewest difficulties. According to McCrea (1951) we have the spontaneous creation of neutrons and protons at the rate of 10-41 kg m-3 sec-1 to maintain a constant density of 10-24 kg m-3 at the present expansion rate. McCrea explains the matter created as the mass equivalent of the work done by stress in the energy momentum tensor in
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the universal expansion. Dirac (1937) prefers to think in terms of a time variation of the constant of gravitation.
Many of the cosmic ray particles are assumed (Fermi — 1949) to be injected into an accelerating system from stellar explosions where in some cases energy equivalent to the mass of the sun is radiated in a few weeks—1042 particles with energies up to 1 Bev. The number of novae occurring in our galaxy is about one per 100 years; the intermittent nature of the production process however presents no difficulties as the life-time of the primary cosmic ray protons has been estimated to be of the order of 107 years. Sunspots, stellar spots and other disturbances undoubtedly make some contribution—in fact a large number of sources contributing in a random manner to the total flux fits in well with the experimental data.