300 
THE SOURCE OF STELLAR ENERGY 
and over-stability seems to be very narrow. We have seen that there is 
one way of meeting it. We can suppose that the dependence of the libera 
tion of energy on density and temperature is not immediate but deferred ; 
that is to say, active material is formed at a rate depending on tempera 
ture and density, but it has a life of at least several years and yields up its 
energy at a rate independent of temperature and density. In that case 
the liberation of heat will not vary during short period oscillations but 
will respond to long continued changes of temperature. 
But the grave objection to a critical temperature—especially a critical 
temperature so low as 40,000,000°—is that there is nothing in our current 
physical knowledge of atoms and electrons and radiation to render it 
probable. In particular the radiation at this temperature consists of X rays 
of a very ordinary kind and the electrons have speeds such as are common 
in laboratory experiments. Only after a very exhaustive elimination of 
alternatives would we venture to recommend so revolutionary a hypothesis. 
Physical Difficulties. 
209. If the astronomical evidence afforded more definite guidance for 
a formulation of the laws of liberation of subatomic energy, we should 
still, I suppose, have to submit the resulting theories to the censorship 
of the mathematical physicist. It may save waste of time in looking in 
hopeless directions if we know in advance the kind of theory which the 
physicist would condemn as intolerable. But his own position contains 
difficulties and contradictions and it is doubtful if he is justified in exer 
cising any rigid censorship. 
The difficulty is that from the physicist’s point of view the temperature 
of the stars is absurdly low. He regards the stars as practically at absolute 
zero, because in regard to nuclear processes 40 million degrees is a small 
quantity which it is scarcely worth while to take notice of. If liberation 
of subatomic energy occurs freely on the stars, why not on the earth? 
As regards laboratory conditions, electrons and ions of far higher 
energy than would correspond to 40 million degrees can be studied. If 
concentration of energy is required, the stars have the advantage ; never 
theless a concentration equivalent to 1| million degrees has been reached 
by Kapitza and by Anderson. It is to be remarked, however, that the 
radiation released by the subatomic processes would be extremely pene 
trating, and even if released in the laboratory would be difficult to catch 
and measure. 
The absence of release in the interior of the earth could perhaps be 
explained by the comparative fixity of the electrons. Yet there must be 
considerable numbers of free electrons, as is shown by the thermoelectric 
emission from hot metals.