The Time Scale of Our Universe^ 



By E. J. Opik 



Armagh Observatory 

 Armagh, Northern Ireland 



INTRODUCTION AND HISTORY 



The average scientist of half a century ago did not ponder much 

 the question of the beginning and age of the universe. For lack of 

 observational approach this problem remained outside the realm of 

 exact science. It was generally felt that the universe should have 

 neither beginning nor end, a viewpoint which was more influenced by 

 opposition to former mythological or religious ideas of creation than 

 by impartial reasoning. 



Indeed, the second law of thermodynamics was well established at 

 that time. According to this law, the universe is steadily rumiing 

 down toward equalization of the energy content of its parts. The 

 ultimate state is that of universally constant temperature, "Warmetod" 

 or thermal death, where, in the absence of temperature differences, no 

 exchange of energy, no relative motion except that of molecules could 

 take place. Organic life, the metabolism of which consists in ex- 

 change of energy, could not exist then, even were the temperature 

 favorable for life — which, in all probability, it would not be. The 

 mere fact that temperature differences exist, that suns shine and planets 

 carry life in the face of the immensities of cold space (into which heat 

 energy is lost in the form of radiation) , would point to the youthf ulness 

 of our world, to a beginning a finite interval of time ago. 



Scientists of the beginning of this century preferred to ignore this 

 writing on the wall. There were some reasons or, rather, pretexts 

 which seemed to justify this eluding of the fundamental problem. 

 The second law of thermodynamics, or that of increasing "entropy," 

 determines only the direction, not the speed with which equalization 

 is approached. The speed, depending on a number of unknown 



' Armagh Observatory Leaflet No. 26. Reprinted, with some revision as of 

 July 1955, by permission from the Irish Astronomical Journal, vol. 3, No. 4, 

 December 1954. 



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