About current scientific speculations there is one characteristic,
subtle, perhaps, but profound and far-reaching, which distinguishes
them from the scientific speculations of the Victorian age. We can
best isolate this characteristic by considering it as a particular
manifestation of something which is met with in nearly every
phase of contemporary life--something which may fairly be called
the _Zeitgeist_ of our time. This spirit is chiefly a sense
of unlimited possibilities, a sense that the radically new and
unprecedented may be upon us; with this feeling comes a recrudescence
of the spirit of adventure; there are unknown paths leading to vague
but--probably--splendid goals. In the Victorian age the main lines of
everything were settled; the chief features of the universe were known.
There were matter and energy, and there was, of course, the æther.
The astronomical and geological scales were known in broad outline,
and a first survey of the march from amœba to man had been taken. The
work of future ages was to fill in the details. The universe of the
Victorians was a large and rather grand affair, but it was sombre.
Those emotional barometers, the poets, in so far as they were aware
of the scientific outlook, either “transcended” it or were crushed by
it. Jules Laforge furnishes an excellent example of the effect of the
Victorian scientific outlook on an intelligent and sensitive mind.
His reaction was to compose funereal dirges on the death of the earth
and the extinction of mankind. The universe of the Victorians was
objective, indifferent, tracing a purposeless pattern in obedience to
“iron” laws. It was a universe which held no great surprises.
It is obvious that a very different spirit is abroad to-day. At the
present time the general consciousness seems to hold that almost
anything is possible. In part this may be accounted for, as in other
ages, by credulity based on ignorance, but there is also a credulity
based on knowledge, and it is this aspect of the general attitude which
deserves attention. The two kinds of credulity may be observed in
different believers of the same statements. Spiritualism, for instance,
has its followers amongst those who are unfamiliar with investigations
in the subject and amongst those whose belief has been compelled by
their very knowledge of the investigations. And disbelievers form
two exactly similar classes. There is also a credulity--the most
common kind--based on neither ignorance nor knowledge, but on partial
knowledge. Thus knowledge, but incomplete knowledge, of such phenomena
as wireless telegraphy or telephony, seems to predispose many people
to believe “wonders” which have no real connection with those
phenomena, but which are merely as inexplicable by partial knowledge.
Undoubtedly the recent developments in science are responsible for much
of this kind of credulity. But the new indulgence of possibilities,
as exhibited by the man of science, is dependent on quite different
considerations. To the student of physics, at any rate, the work of
the last two or three decades has been peculiarly disturbing. He has
been called upon, not merely to revise and extend his knowledge, but to
alter his assumptions. It is in this respect that the physics of our
own day chiefly differs from Victorian physics.
The distinctively modern epoch began with the promulgation of the
Electron Theory. That “matter” could be “electrified” was easily
granted. The fact that the famous question, What is electricity? could
not be answered was no difficulty in admitting the fact that, as a
result of certain processes, matter could be made to exhibit certain
phenomena which could conveniently be referred to the fact that it
possessed an “electric charge.” And the discovery of particles very
much smaller than a hydrogen atom presented no conceptual difficulties.
The fact that the ultimate particles of matter were smaller than had
been supposed could easily be granted; the new assumption was of the
same kind as the old one. And, further, to admit that each of these
particles possessed an electric charge made no unfamiliar demands on
the imagination. But the next step, that these particles consisted
of nothing but an electric charge--that was a very different thing.
The early popularisations of the idea show something of the mental
confusion it caused. “Disembodied charges of electricity” was a
favourite descriptive phrase; many physicists fought hard to retain
even a nucleus of “ordinary matter” on which this charge could be
supposed to be lodged. That an electric charge could exist apart from
matter seemed to many people as difficult to conceive as motion without
anything which moved. But the conception speedily became familiar; that
useful entity, the æther, soon made things easier. For the disembodied
charge, the electron, could be conceived as a local distortion of
some kind in the æther, and, by endowing the æther with some sort of
substantiality, the hypothesis that matter was in some way built up
out of this primitive substance could be tolerated. But the general
effect of the theory was to give a more philosophical tinge to science.
The gross, easy assumptions of everyday thinking about “matter” had
to be revised; articles were written showing that matter was really
immaterial, and materialism was conjectured to have received a severe
set-back.
The mind had barely become accustomed to the new assumptions before it
was again profoundly disturbed by the publication of Planck’s Quantum
Theory. The theory, which was invented to explain certain radiation
phenomena, asserted, briefly, that energy was atomic. One’s most
intimate assumptions were disturbed. Men of science are not usually
accustomed to philosophic exercises, and the idea that energy, which
they regarded as necessarily continuous, had an atomic structure seemed
at first almost meaningless. If we consider, for instance, the energy
possessed by a moving body, it seems natural to suppose that this
energy can be increased or diminished in a continuous manner; the idea
that its energy can only increase or decrease by finite jumps was a
very strange idea, and led again to a scrutiny of assumptions which
had appeared fundamental in science. Here, again, objections to the
new theory were sometimes the outcome purely of mental inertia, of an
inability to examine and discard a way of thinking which seemed almost
a necessary consequence of the structure of the mind. The last great
_bouleversement_ of one’s fundamental assumptions has been, of
course, Einstein’s generalised theory of relativity. Here we are asked
to revise our most deep-rooted assumptions--so deep-rooted that we are,
for the most part, unconscious of them--our assumptions regarding space
and time.
It is this thorough overhauling of primary assumptions which
distinguishes the modern progress in physics from all the progress of
the Victorian age. Physics has not merely been extended, it has become
a radically new thing, and there are very good reasons for supposing
that it is going to change still more. A certain sense of unknown
possibilities is therefore natural, even if it be the product merely of
bewilderment. The total effect of the new ideas is to make the universe
of physics less objective; to an unsuspected extent this indifferent
universe, with its iron laws, is a product of our own minds. To some
extent this fact was always recognised, particularly by the Continental
physicists, but as a general persuasion it is comparatively recent.
We cannot escape the structure of our own minds, it is true, but we
do not yet know what that structure is; we do not know what barriers
are breakable; we do not know what thoughts are thinkable by man. A
universe in whose construction so plastic and mysterious an entity as
the mind of man collaborates, may very well hold great surprises.