390-392] Life and the Universe 421 
392. The cinematograph film which we set out to construct exhibits 
the universe as a mass of matter slowly but inexorably dissolving away into 
intangible radiation. The stars may be compared to icebergs which have broken 
away from the main ice-packs—the extra-galactic nebulae—and are drifting 
into warmer seas and extinction. Nothing stands, everything melts away, 
except for the few permanent atoms which, like the rocks or stones of the 
iceberg, are destined to survive after all else has dissolved. We have esti 
mated (§ 126) the average duration of the present matter of the universe to 
be of the order of 10 12 years only. After some such period the main mass of 
matter now in existence will have been transformed into radiation. If all 
matter were completely annihilated, the estimated present mass-density of 
15 x 10 ~ 31 grammes per cubic centimetre would produce a mass-density of 
radiation of T35 x 10 ~ 10 ergs per cubic centimetre and this is the density of 
radiation at a temperature of 1T5 degrees absolute. But we cannot say how 
far this radiation may be diluted through invading parts of space in which no 
matter exists. 
While the far end of the film of pictures is fairly clear, the beginning is 
veiled in obscurity. We have been able to form an estimate of the time during 
which the stars have existed as stars, but we cannot say for how long their 
electrons and protons have existed, since, before they formed stars at all, they 
may have existed in completely dissociated form, immune from annihilation, in 
the central regions of the great nebulae. Thus the five to ten millions of millions 
of years which we have estimated as the average age of the stars only provides 
a sort of lower limit to the ages of the atoms, and so to the age of the 
universe. We can estimate the future life of the present matter of the 
universe from the rate at which it is transforming itself into radiation, but we 
can only fix a lower limit to its past life. Even so, this lower limit is so long 
as to create a suspicion that we may have appeared on the scene rather late 
in the history of the universe; possibly the main drama of the universe is 
over, and our lot is merely to watch the unwanted ends of lighted candles 
burning themselves out on an empty stage. 
An alternative view is that there may be neither beginning nor end, so 
that we may speak of the ages of the stars but not of the age of the universe. 
It is difficult, but not impossible, to believe that matter can be continuously in 
process of creation, or possibly of re-creation out of stray radiation. If, how 
ever, this obvious initial difficulty is disregarded, we are free to think of stars 
and other astronomical bodies as passing in an endless steady stream from 
creation to extinction, just as human beings pass from birth to the grave, 
with a new generation always ready to step into the place vacated by the old, 
Observation cannot finally decide between these two possibilities, but rather 
frowns upon the view just stated. If the number of objects in the various 
stages of development had proved to be roughly proportional to the times 
taken to pass through these stages, this being the characteristic of a steady