Giordano Bruno. He was one of the first disciples of Copernicus, and,
having accepted the doctrine that the earth travels round the sun as one
among his family of planets, was led very naturally to the belief that
the other planets are inhabited. He went farther, and maintained that as
the earth is not the only inhabited world in the solar system, so the
sun is not the only centre of a system of inhabited worlds, but each
star a sun like him, about which many planets revolve. This was one of
the many heresies for which Bruno was burned at the stake. It is easy,
also, to recognise in the doctrine of many worlds as the natural sequel
of the Copernican theory, rather than in the features of this theory
itself, the cause of the hostility with which theologians regarded it,
until, finding it proved, they discovered that it is directly taught in
the books which they interpret for us so variously. The Copernican
theory was not rejected--nay, it was even countenanced--until this
particular consequence of the theory was recognised. But within a few
years from the persecution of Bruno, Galileo was imprisoned, and the
last years of his life made miserable, because it had become clear that
in setting the earth adrift from its position as centre of the
universe, he and his brother Copernicans were sanctioning the belief in
other worlds than ours. Again and again, in the attacks made by
clericals and theologians upon the Copernican theory, this lamentable
consequence was insisted upon. Unconscious that they were advancing the
most damaging argument which could be conceived for the cause they had
at heart, they maintained, honestly but unfortunately, that with the new
theory came the manifest inference that our earth is not the only and by
no means the most important world in the universe--a doctrine manifestly
inconsistent (so they said) with the teachings of the Scriptures.
It was naturally only by a slow progression that men were able to
advance into the domain spread before them by the Copernican theory, and
to recognise the real minuteness of the earth both in space and time.
They more quickly recognised the earth's insignificance in space,
because the new theory absolutely forced this fact upon them. If the
earth, whose globe they knew to be minute compared with her distance
from the sun, is really circling around the sun in a mighty orbit many
millions of miles in diameter, it follows of necessity that the fixed
stars must lie so far away that even the span of the earth's orbit is
reduced to nothing by comparison with the vast depths beyond which lie
even the nearest of those suns. This was Tycho Brahe's famous and
perfectly sound argument against the Copernican theory. 'The stars
remain fixed in apparent position all the time, yet the Copernicans tell
us that the earth from which we view the stars is circling once a year
in an orbit many millions of miles in diameter; how is it that from so
widely ranging a point of view we do not see widely different celestial
scenery? Who can believe that the stars are so remote that by comparison
the span of the earth's path is a mere point?' Tycho's argument was of
course valid.[31] Of two things one. Either the earth does not travel
round the sun, or the stars are much farther away than men had conceived
possible in Tycho's time. His mistake lay in rejecting the correct
conclusion because simply it made the visible universe seem many
millions of times vaster than he had supposed. Yet the universe, even as
thus enlarged, was but a point to the universe visible in our day, which
in turn will dwindle to a point compared with the universe as men will
see it a few centuries hence; while that or the utmost range of space
over which men can ever extend their survey is doubtless as nothing to
the real universe of occupied space.
Such has been the progression of our ideas as to the position of the
earth in space. Forced by the discoveries of Copernicus to regard our
earth as a mere point compared with the distances of the nearest fixed
stars, men gradually learned to recognise those distances which at first
had seemed infinite as in their turn evanescent even by comparison with
that mere point of space over which man is able by instrumental means to
extend his survey.
Though there has been a similar progression in men's ideas as to the
earth's position in time, that progression has not been carried to a
corresponding extent. Men have not been so bold in widening their
conceptions of time as in widening their conceptions of space. It is
here and thus that, in my judgment, the subject of life in other worlds
has been hitherto incorrectly dealt with. Men have given up as utterly
idle the idea that the existence of worlds is to be limited to the
special domain of space to which our earth belongs; but they are content
to retain the conception that the domain of time to which our earth's
history belongs, 'this bank and shoal of time' on which the life of the
earth is cast, is the period to which the existence of other worlds than
ours should be referred.
This, which is to be noticed in nearly all our ordinary treatises on
astronomy, appears as a characteristic peculiarity of works advocating
the theory of the plurality of worlds. Brewster and Dick and Chalmers,
all in fact who have taken that doctrine under their special protection,
reason respecting other worlds as though, if they failed to prove that
other orbs are inhabited _now_, or are at least _now_ supporting life in
some way or other, they failed of their purpose altogether. The idea
does not seem to have occurred to them that there is room and verge
enough in eternity of time not only for activity but for rest. They must
have all the orbs of space busy at once in the one work which they seem
able to conceive as the possible purpose of those bodies--the support of
life. The argument from analogy, which they had found effective in
establishing the general theory of the plurality of worlds, is forgotten
when its application to details would suggest that not _all_ orbs are
_at all times_ either the abode of life or in some way subserving the
purposes of life.
We find, in all the forms of life with which we are acquainted, three
characteristic periods--first the time of preparation for the purposes
of life; next, the time of fitness for those purposes; and thirdly, the
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
may float with the Nereids upon the deep, or mount upon wings as eagles,
or rise upon the pinions of the dove, that he may flee away and be at
rest,' with much more in the same fanciful vein. We now know that there
can be no cavities more than a few miles below the crust of a planet,
simply because, under the enormous pressures which would exist, the most
solid matter would be perfectly plastic. But while Whewell's general
objection to the theory that Jupiter or Saturn is in the same condition
as our earth thus acquires new force, the particular explanation which
he gave of the planet's small density is open to precisely the same
general objection. For he assumes that, because the planet's mean
density is little greater than that of water, the planet is probably a
world of water and ice with a cindery nucleus, or in fact just such a
world as would be formed if a sufficient quantity of water in the same
condition as the water of our seas were placed at Jupiter's greater
distance from the sun, around a nucleus of earthy or cindery matter
large enough to make the density of the entire planet thus formed equal
to that of Jupiter, or about one-third greater than the density of
water. In this argument there are in reality two assumptions, of
precisely the same nature as those which Whewell set himself to combat.
It is first assumed that some material existing on a large scale in our
earth, and nearly of the same density as Jupiter, must constitute the
chief bulk of that planet, and secondly that the temperature of
Jupiter's globe must be that which a globe of such material would have
if placed where Jupiter is. The possibility that Jupiter may be in an
entirely different stage of planetary life--or, in other words, that the
youth, middle life, and old age of that planet may belong to quite
different eras from the corresponding periods of our earth's life--is
entirely overlooked. Rather, indeed, it may be said that the extreme
probability of this, on any hypothesis respecting the origin of the
solar system, and its absolute certainty on the hypothesis of the
development of that system, are entirely overlooked.
A fair illustration of the erroneous nature of the arguments which have
been used, not only in advocating rival theories respecting the
plurality of worlds, but also in dealing with subordinate points, may be
presented as follows:
Imagine a wide extent of country covered with scattered trees of various
size, and with plants and shrubs, flowers and herbs, down to the
minutest known. Let us suppose a race of tiny creatures to subsist on
one of the fruits of a tree of moderate size, their existence as a race
depending entirely on the existence of the fruit on which they subsist,
while the existence of the individuals of their race lasts but for a few
minutes. Furthermore, let there be no regular fruit season either on
their tree or in their region of vegetable life, but fruits forming,
growing, and decaying all the time.
Let us next conceive these creatures to be possessed of a power of
reasoning respecting themselves, their fruit world, the tree on which it
hangs, and to some degree even respecting such other trees, plants,
flowers, and so forth, as the limited range of their vision might be
supposed to include. It would be a natural thought with them, when first
they began to exercise this power of reasoning, that their fruit home
was the most important object in existence, and themselves the chief and
noblest of living beings. It would also be very natural that they should
suppose the formation of their world to correspond with the beginning of
time, and the formation of their race to have followed the formation of
their world by but a few seconds. They would conclude that a Supreme
Being had fashioned their world and themselves by special creative acts,
and that what they saw outside their fruit world had been also specially
created, doubtless to subserve their wants.
Let us now imagine that gradually, by becoming more closely observant
than they had been, by combining together to make more complete
observations, and above all by preserving the records of observations
made by successive generations, these creatures began to obtain clearer
ideas respecting their world and the surrounding regions of space. They
would find evidence that the fruit on which they lived had not been
formed precisely as they knew it, but had undergone processes of
development. The distressing discovery would be made that this
development could not possibly have taken place in a few seconds, but
must have required many hours, nay, even several of those enormous
periods called by us days.
This, however, would only be the beginning of their troubles. Gradually
the more advanced thinkers and the closest observers would perceive that
not only had their world undergone processes of development, but that
its entire mass had been formed by such processes--that in fact it had
not been created at all, in the sense in which they had understood the
word, but had _grown_. This would be very dreadful to these creatures,
because they would not readily be able to dispossess their minds of the
notion that they were the most important beings in the universe, their
domain of space coextensive with the universe, the duration of their
world coextensive with time.