MODERN CONCEPTIONS OF THE UNIVERSE. fil 
experiments, being satisfied that the grand agents of nature are, 
by the Creator’s fiat, indestructible.”* 
§ 11. The Beginning and End of the Universe—The modern 
conception of the universe sets before us a wonderful system 
working in a manner so regular and so orderly that we are 
almost tempted to believe that this regular working has con- 
tinued not merely for many centuries or for many millions of 
millions of years, but that there never was a time when the 
universe was not guided by the same laws, neither more nor 
less, aS are in operation to-day. This temptation must, 
however, be resisted, for if we yield to it we abandon the 
conclusion that the universe was created, since to assert that 
there never was a time when matter did not exist is equivalent 
to saying that it is self-existent. 
If the universe consisted merely of the ether and of a single 
sphere of matter without any motion either of its centre or of 
the parts of its molecules, we could set no limit to its age, 
because no changes could occur in it. But the universe is not 
of this character; on the contrary, it contains matter in very 
vigorous motion—both in bulk, as seen in the earth’s motion 
round the sun, and in detail, as seen in the molecular vibrations 
which give rise to light. Hence the state of the universe to-day 
differs from its state yesterday, and so on. We might, of course, 
conceive that all these motions are periodic, and that any 
particular state of the universe recurs continually, though 
perhaps at long intervals, and, apart from the ditticulty of 
accounting for them, we might suppose that these periodic 
changes had occurred regularly for an infinite time, and that 
they would continue for an infinite time. But modern 
investigations prove such a view to be untenable. For they 
have shown that, while the total amount of energy remains 
unchanged, there is at present a progressive diminution in its 
availability, and they point remorselessly to a time when the 
energy will be so distributed that further redistribution will be 
impossible. The meaning of availability may be illustrated by 
reference to water in a reservoir on a mountain near the sea. 
‘The water in the reservoir represents available gravitational 
energy, and in its descent to the sea-level may be made to drive 
machinery and to produce electrical or other energy, but as 
soon as the water reaches the sea-level it ceases to be available 
for doing work. 
When the further redistribution of energy ceases to be 
* Joule’s Sctentific Papers, vol. i, p. 157. 
