DESTINY OF THE STELLAR SYSTEM
We have said that the evolutionary processes depend primarily upon
the loss of heat. This is to the best of our knowledge a genuine loss,
except as some of the heat rays happen to strike other celestial bodies.
The flow of heat energy from a star must be essentially continuous,
always in one direction from hotter bodies to colder bodies, or into
so-called unending and heatless space. Temperatures throughout the
universe are apparently moving toward uniformity, at the level of
absolute
zero. Now, this uniformity would mean universal stagnation
and death. It is possible to have life and to do work only when there
are differences of temperature between the bodies concerned: work is
done or accompanied by a flow of heat, always from the hotter to the
colder body. We are not aware that any compensating principle exists.
Several students of the subject, notably Arrhenius, have searched for
such a principle, a fountain of youth so to speak, in accordance with
which the vigor of stellar life should maintain itself from the beginning
of time to the end of time; but I think that nothing approaching a
satisfactory theory has yet been formulated. The stellar universe seems,
from our present point of view, to be slowly "running down.'' The
processes will not end, however, when all the heat generable
within the stars shall have been radiated into an endless space.
Every body within the universe, it is conceivable, could have cooled down to
absolute zero, but the system might still be in its youth. So long as the
stars, whether intensely hot or free from all heat, are rotating rapidly
on their axes or are rushing through space with high speeds, the system
will remain
very much alive. Collisions or very close approaches of
two stars are bound to occur sooner or later, whether the stars are hot
or cold, and in all such cases a large share of the kinetic energy—the
energy of motion—of the two bodies will be converted into heat. A
collision, under average stellar conditions, should convert the two stars
into a luminous gaseous nebula, or two or more nebulæ, which would
require hundreds or thousands of millions of years to evolve again into
young stars, middle-aged stars, old stars, and stars absolutely cold. So
long as any of these bodies retain motion with reference to other bodies,
they retain the power of rebirth and another life. Not to go too far
into speculative detail, the general effect of these processes would be
the destruction of relative motions and the gradual decrease in the
number of separate bodies, through coalescence. Assume further, however,
that all existing bodies, widely scattered through the stellar system,
are absolutely cold and absolutely at rest with reference to each
other: the system might even then be only middle-aged. The mutual
gravitations of the bodies would still be operative. They would pass
each other closely, or collide, under high generated velocities: there
would be new nebulæ, and new and vigorous stellar life to continue
through other long ages. The system would not run down until all
the kinetic energy had been converted into heat, and all the heat generable
had been dissipated. This would not occur until all material in
the universe had been combined into one body, or into two bodies in
mutual revolution. However, if there are those who say that the universe
in action is eternal, through the operation of compensating principles
as yet undiscovered, no man of science is at present equipped
to prove the contrary.
