Myths and Marvels of Astronomy
time of decadence tending gradually to death. We see among all objects
which exist in numbers, examples of all these stages existing at the
same time. In every race of living creatures there are the young as yet
unfit for work, the workers, and those past work; in every forest there
are saplings, seed-bearing trees, and trees long past the seed-bearing
period. We know that planets, or rather, speaking more generally, the
orbs which people space, pass through various stages of development,
during some only of which they can reasonably be regarded as the abode
of life or supporting life; yet the eager champion of the theory of many
worlds will have them all in these life-bearing or life-supporting
stages, none in any of the stages of preparation, none in any of the
stages of decrepitude or death.
This has probably had its origin in no small degree from the disfavour
with which in former years the theory of the growth and development of
planets and systems of planets was regarded. Until the evidence became
too strong to be resisted, the doctrine that our earth was once a baby
world, with many millions of years to pass through before it could be
the abode of life, was one which only the professed atheist (so said too
many divines) could for a moment entertain; while the doctrine that not
the earth alone, but the whole of the solar system, had developed from a
condition utterly unlike that through which it is now passing, could
have had its origin only in the suggestions of the Evil One. Both
doctrines were pronounced to be so manifestly opposed to the teachings
of Moses, and not only so, but so manifestly inconsistent with the
belief in a Supreme Being, that--that further argument was unnecessary,
and denunciation only was required. So confident were divines on these
points, that it would not have been very wonderful if some few students
of science had mistaken assertion for proof, and so concluded that the
doctrines towards which science was unmistakably leading them really
were inconsistent with what they had been taught to regard as the Word
of God. Whether multiplied experiences taught men of science to wait
before thus deciding, or however matters fell out, it certainly befell
before very long that the terrible doctrine of cosmical development was
supported by such powerful evidence, astronomical and terrestrial, as to
appear wholly irresistible. Then, not only was the doctrine accepted by
divines, but shown to be manifestly implied in the sacred narrative of
the formation of the earth and heavens, sun, and moon, and stars; while
upon those unfortunate students of science who had not changed front in
good time, and were found still arguing on the mistaken assumption that
the development of our system was not accordant with that ancient
narrative, freshly forged bolts were flung from the Olympus of
orthodoxy.
So far as the other argument--from the inconsistency of the development
theory with belief in a Supreme Being--was concerned, the student of
science was independent of the interpretations which divines claim the
sole right of assigning to the ancient books. Science has done so much
more than divinity (which in fact has done nothing) to widen our
conceptions of space and time, that she may justly claim full right to
deal with any difficulties arising from such enlargement of our ideas.
With the theological difficulty science would not care to deal at all,
were she not urged to do so by the denunciations of divines; and when,
so urged, she touches that difficulty, she is quickly told that the
difficulty is insuperable, and not long after that it has no existence,
and (on both accounts) that it should have been left alone. But with the
difficulty arising from the widening of our ideas respecting space and
time, science may claim good, almost sole, right to deal. The path to a
solution of the problem is not difficult to find. At a first view, it
does seem to those whose vision had been limited to a contracted field,
that the wide domain of time and space in which processes of development
are found to take place is the universe itself, that to deny the
formation of our earth by a special creative act is to deny the
existence of a Creator, that to regard the beginning of our earth as a
process of development is to assert that development has been in
operation from the beginning of all things. But when we recognise
clearly that vastness and minuteness, prolonged and brief duration, are
merely relative, we perceive that in considering our earth's history we
have to deal only with small parts of space and brief periods of time,
by comparison with all space and all time. Our earth is very large
compared with a tree or an animal, but very small compared with the
solar system, a mere point compared with the system of stars to which
the sun belongs, and absolutely as nothing compared with the universe of
space; and in like manner, while the periods of her growth and
development occupy periods very long-lasting compared with those
required for the growth and development of a tree or an animal, they are
doubtless but brief compared with the eras of the development of our
solar system, a mere instant compared with the eras of the development
of star-systems, and absolutely evanescent compared with eternity. We
have no more reason for rejecting the belief in a Creator because our
earth or the solar system is found to have developed to its present
condition from an embryonic primordial state, than we have had ever
since men first found that animals and trees are developed from the
germ. The region of development is larger, the period of development
lasts longer, but neither the one nor the other is infinite; and being
finite, both one and the other are simply nothing by comparison with
infinity. It is a startling thought, doubtless, that periods of time
compared with which the life of a man, the existence of a nation, nay,
the duration of the human race itself, sink into insignificance, should
themselves in turn be dwarfed into nothingness by comparison with
periods of a still higher order. But the thought is not more startling
than that other thought which we have been compelled to admit--the
thought that the earth on which we live, and the solar system to which
it belongs, though each so vast that all known material objects are as
nothing by comparison, are in turn as nothing compared with the depths
of space separating us from even the nearest among the fixed stars. One
thought, as I have said, we have been compelled to admit, the other has
not as yet been absolutely forced upon us. Though men have long since
given up the idea that the earth and heavens have endured but a few
thousand years, it is still possible to believe that the birth of our
solar system, whether by creative act or by the beginning of processes
of development, belongs to the beginning of all time. But this view
cannot be regarded as even probable. Although it has never been proved
that any definite relation must subsist between time (occupied by
events) and space (occupied by matter), the mind naturally accepts the
belief that such a relation exists. As we find the universe enlarging
under the survey of science, our conceptions of the duration of the
universe enlarge also. When the earth was supposed to be the most
important object in creation, men might reasonably assign to time itself
(regarded as the interval between the beginning of the earth and the
consummation of all things when the earth should perish) a moderate
duration; but it is equally reasonable that, as the insignificance of
the earth's domain in space is recognised, men should recognise also the
presumable insignificance of the earth's existence in time.
In this respect, although we have nothing like the direct evidence
afforded by the measurement of space, we yet have evidence which can
scarcely be called in question. We find in the structure of our earth
the signs of its former condition. We see clearly that it was once
intensely hot! and we know from experimental researches on the cooling
of various earths that many millions of years must have been required by
the earth in cooling down from its former igneous condition. We may
doubt whether Bischoff's researches can be relied upon in details, and
so be unwilling to assign with him a period of 350 millions of years to
a single stage of the process of cooling. But that the entire process
lasted tens of millions and probably hundreds of millions of years
cannot be doubted. Recognising such enormous periods as these in the
development of one of the smallest fruits of the great solar tree of
life, we cannot but admit at least the reasonableness of believing that
the larger fruits (Jupiter, for instance, with 340 times as much matter,
and Saturn with 100 times) must require periods still vaster, probably
many times larger. Indeed, science shows not only that this view is
reasonable, but that no other view is possible. For the mighty root of
the tree of life, the great orb of the sun, containing 340 _thousand_
times as much matter as the earth, yet mightier periods would be needed.
The growth and development of these, the parts of the great system, must
of necessity require much shorter time-intervals than the growth and
development of the system regarded as a whole. The enormous period when
the germs only of the sun and planets existed as yet, when the chaotic
substance of the system had not yet blossomed into worlds, the mighty
period which is to follow the death of the last surviving member of the
system, when the whole scheme will remain as the dead trunk of a tree
remains after the last leaf has fallen, after the last movement of sap
within the trunk--these periods must be infinite compared with those
which measure the duration of even the mightiest separate members of the
system.
But all this has been left unnoticed by those who have argued in support
of the Brewsterian doctrine of a plurality of worlds. They argue as if
it had never been shown that every member of the solar system, as of
all other such systems in space, has to pass through an enormously long
period of preparation before becoming fit to be the abode of life, and
that after being fit for life (for a period very long to our
conceptions, but by comparison with the other exceedingly short) it must
for countless ages remain as an extinct world. Or else they reason as
though it had been proved that the relatively short life-bearing periods
in the existence of the several planets must of necessity synchronise,
instead of all the probabilities lying overwhelmingly the other way.
While this has been (in my judgment) a defect in what may be called the
Brewsterian theory of other worlds, a defect not altogether dissimilar
has characterised the opposite or Whewellite theory. Very useful service
was rendered to astronomy by Whewell's treatise upon, or rather against,
the plurality of worlds, calling attention as it did to the utter
feebleness of the arguments on which men had been content to accept the
belief that other planets and other systems are inhabited. But some
among the most powerfully urged arguments against that belief tacitly
relied on the assumption of a similarity of general condition among the
members of the solar system. For instance, the small mean density of
Jupiter and Saturn had, on the Brewsterian theory, been explained as
probably due to vast hollow spaces in those planets' interiors--an
explanation which (if it could be admitted) would leave us free to
believe that Jupiter and Saturn may be made of the same materials as our
own earth. With this was pleasantly intermixed the conception that the
inhabitant of these planets may have his 'home in subterranean cities
warmed by central fires, or in crystal caves cooled by ocean tides, or