ISLAND GALAXIES DOUGLAS 199 



He then evaluates the radius of curvature of space time, which, accord- 

 ing to Einstein, depends only upon this average density and t^yo 

 constants, the velocity of light and the gravitational constant. This 

 radius comes out to be 5,000 million million astronomical units 

 (5X10^^ times the sun-earth distance). This value is a thousand 

 times greater than that calculated by Silberstein from other relations 

 and other data available three years ago. Here, perhaps, in reality, 

 as ahvaj's metapliorically, the horizon recedes as knowledge increases. 



What then is the total amount of matter distributed as stars and 

 nebulae, in clusters and in galaxies, throughout this vast yet finite 

 universe? To express these figures in words is far too cumbersome, 

 and so Ave set them forth in the elegant shorthand used always by 

 the physicist and the astronomer : If M be the total mass of matter 

 in the Einstein universe, then 



J/ -1.8X10" gms. 

 = 9.0X10^2 suns 

 = 3.5X10^^ normal galaxies 

 In other words, there are about 10'^ tons of matter, and were this to 

 consist only of hydrogen there Avould be 10*^ atoms. 



How much real value these stupendous figures have it is impossible 

 to say. Firstly, they involve the Einstein conception of the uni- 

 verse, not yet indisputably established.^ Secondly, assuming that 

 the Einstein universe has a real significance, these figures are con- 

 clusions regarding a universe not one ten-millionth of whose volume 

 can be explored by even the giant telescope at Mount Wilson Ob- 

 servatory. If the distance of a galaxy exceed only one six-hundredth 

 of the radius of curvature above mentioned, no telescope yet con- 

 structed can detect it. But a- man will judge the world of humanity, 

 rheir habits and characteristics, their comings and goings, by his 

 knowledge of a few score individuals and his passing glimpses of a 

 few thousand, and his conclusions will not be entirely valueless. So, 

 too, the astronomer, with reliable knowledge of hundreds of stars 

 and many nebulae, and glimpses of thousands yet more distant, will 

 not refrain from speculation regarding the vast regions as yet 

 beyond his ken — the ocean of spacetime studded with 1,000 million 

 million glorious island galaxies. 



' Indeed there are many who reject the Einstein cosmology in favor of the modifications 

 proposed by de Sitter, modifications which obviate some of the difliculties inherent in 

 Einstein's cosmology. Doctor Silberstein, for example, denies any reality to the above 

 figures, retaining confidence in his own value of the radius of curvature based upon his 

 deductions from the de Sitter equations. 



