222 ANlSrUAL REPORT SMITHSONIAN INSTITUTION, 1955 



In any case, the present evidence is inconclusive as to the reality of 

 the space-reddening effect. Some residual reddening from absorption 

 by intergalactic matter may exist. The question may be decided by 

 two-color observations in yellow and red, avoiding the unreliable 

 violet-blue spectral regions. 



ALTERNATIVE HYPOTHESES 



It has been repeatedly stressed that the nebular red shift may not 

 indicate recession, and alternative suggestions have been made recently 

 (Freundlich, Shelton). It is difficult to imagine a collisional process 

 of reddening without simultaneous blurring of the nebular images 

 (67). Further, the nonexpanding universe will be unstable and will 

 end in collapse ; or in expansion, if the cosmological repulsion is intro- 

 duced. Thus, the present state would be exceptional, the normal state 

 being one of Doppler shifts corresponding to real approach or reces- 

 sion. It does not seem advisable to sacrifice the solid concept of reces- 

 sion to a piling up of od hoc new laws and improbable states. 



Continuous creation of matter under various aspects (Kapp, Jordan, 

 Bondi, Gold, Hoyle) is another alternative which would dispense with 

 a finite age for the universe. It requires the retention of the cosmo- 

 logical constant (repulsion), or a pulsating variety of it (Kapp). 

 For reasons similar to those given above these theories can at present 

 be assessed only from the standpoint of their esthetic value. It is not 

 easy to image observational criteria for them which cannot be ex- 

 plained away. 



Perhaps the distribution of masses of the galaxies can provide the 

 least objectionable proof. In Hoyle's expanding universe galaxies 

 will continually grow by accretion, especially large ones with gaseous 

 envelopes firmly bound by gravitation ; the envelopes will act as nets 

 catching atoms from interglactic space, or incorporating whole gase- 

 ous envelopes of smaller galaxies which happen to be in their way 

 (43) . They will grow almost indefinitely with time. Their frequency 

 per unit volume in Hoyle's universe will vary inversely as the cube 

 of age, thus more or less as the cube of mass, too ; when selected by 

 apparent magnitude, there will be no upper limit of mass and almost 

 no correlation of distance with magnitude. The available evidence 

 implies a frequency of nebulae in space decreasing with the 4/3 power 

 of mass (68, 69) , a definite upper limit of mass (66) , and a correlation 

 of distance with apparent magnitude. Wliat evidence there is, is 

 definitely negative. 



CONCLUSION 



The rate of irreversible processes in different physical complexes — 

 the radioactive elements, the earth and the solar system, the stars, stel- 

 lar systems, the galaxy, the observable portion of the extragalactic 



