The New Physics and Its Evolution by Lucien Poincare

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When the electron is subjected to an acceleration, a transverse wave
is produced, and an electromagnetic radiation is generated, of which
the character may naturally change with the manner in which the speed
varies. If the electron has a sufficiently rapid periodical movement,
this wave is a light wave; while if the electron stops suddenly, a
kind of pulsation is transmitted through the ether, and thus we obtain
Roentgen rays.

Sec. 4. NEW VIEWS ON THE CONSTITUTION OF THE ETHER AND OF MATTER

New and valuable information is thus afforded us regarding the
properties of the ether, but will this enable us to construct a
material representation of this medium which fills the universe, and
so to solve a problem which has baffled, as we have seen, the
prolonged efforts of our predecessors?

Certain scholars seem to have cherished this hope. Dr. Larmor in
particular, as we have seen, has proposed a most ingenious image, but
one which is manifestly insufficient. The present tendency of
physicists rather tends to the opposite view; since they consider
matter as a very complex object, regarding which we wrongly imagine
ourselves to be well informed because we are so much accustomed to it,
and its singular properties end by seeming natural to us. But in all
probability the ether is, in its objective reality, much more simple,
and has a better right to be considered as fundamental.

We cannot therefore, without being very illogical, define the ether by
material properties, and it is useless labour, condemned beforehand to
sterility, to endeavour to determine it by other qualities than those
of which experiment gives us direct and exact knowledge.

The ether is defined when we know, in all its points, and in magnitude
and in direction, the two fields, electric and magnetic, which may
exist in it. These two fields may vary; we speak from habit of a
movement propagated in the ether, but the phenomenon within the reach
of experiment is the propagation of these variations.

Since the electrons, considered as a modification of the ether
symmetrically distributed round a point, perfectly counterfeit that
inertia which is the fundamental property of matter, it becomes very
tempting to suppose that matter itself is composed of a more or less
complex assemblage of electrified centres in motion.

This complexity is, in general, very great, as is demonstrated by the
examination of the luminous spectra produced by the atoms, and it is
precisely because of the compensations produced between the different
movements that the essential properties of matter--the law of the
conservation of inertia, for example--are not contrary to the
hypothesis.

The forces of cohesion thus would be due to the mutual attractions
which occur in the electric and magnetic fields produced in the
interior of bodies; and it is even conceivable that there may be
produced, under the influence of these actions, a tendency to
determine orientation, that is to say, that a reason can be seen why
matter may be crystallised.[50]

[Footnote 50: The reader should, however, be warned that a theory has
lately been put forth which attempts to account for crystallisation on
purely mechanical grounds. See Messrs Barlow and Pope's "Development
of the Atomic Theory" in the _Transactions of the Chemical Society_,
1906.--ED.]

All the experiments effected on the conductivity of gases or metals,
and on the radiations of active bodies, have induced us to regard the
atom as being constituted by a positively charged centre having
practically the same magnitude as the atom itself, round which the
electrons gravitate; and it might evidently be supposed that this
positive centre itself preserves the fundamental characteristics of
matter, and that it is the electrons alone which no longer possess any
but electromagnetic mass.

We have but little information concerning these positive particles,
though they are met with in an isolated condition, as we have seen, in
the canal rays or in the X rays.[51] It has not hitherto been possible
to study them so successfully as the electrons themselves; but that
their magnitude causes them to produce considerable perturbations in
the bodies on which they fall is manifest by the secondary emissions
which complicate and mask the primitive phenomenon. There are,
however, strong reasons for thinking that these positive centres are
not simple. Thus Professor Stark attributes to them, with experiments
in proof of his opinion, the emission of the spectra of the rays in
Geissler tubes, and the complexity of the spectrum discloses the
complexity of the centre. Besides, certain peculiarities in the
conductivity of metals cannot be explained without a supposition of
this kind. So that the atom, deprived of the cathode corpuscle, would
be still liable to decomposition into elements analogous to electrons
and positively charged. Consequently nothing prevents us supposing
that this centre likewise simulates inertia by its electromagnetic
properties, and is but a condition localised in the ether.

[Footnote 51: There is much reason for thinking that the canal rays do
not contain positive particles alone, but are accompanied by negative
electrons of slow velocity. The X rays are thought, as has been said
above, to contain neither negative nor positive particles, but to be
merely pulses in the ether.--ED.]

However this may be, the edifice thus constructed, being composed of
electrons in periodical motion, necessarily grows old. The electrons
become subject to accelerations which produce a radiation towards the
exterior of the atom; and certain of them may leave the body, while
the primitive stability is, in the end, no longer assured, and a new
arrangement tends to be formed. Matter thus seems to us to undergo
those transformations of which the radio-active bodies have given us
such remarkable examples.

We have already had, in fragments, these views on the constitution of
matter; a deeper study of the electron thus enables us to take up a
position from which we obtain a sharp, clear, and comprehensive grasp
of the whole and a glimpse of indefinite horizons.

It would be advantageous, however, in order to strengthen this
position, that a few objections which still menace it should be
removed. The instability of the electron is not yet sufficiently
demonstrated. How is it that its charge does not waste itself away,
and what bonds assure the permanence of its constitution?

On the other hand, the phenomena of gravitation remain a mystery.
Lorentz has endeavoured to build up a theory in which he explains
attraction by supposing that two charges of similar sign repel each
other in a slightly less degree than that in which two charges, equal
but of contrary sign, attract each other, the difference being,
however, according to the calculation, much too small to be directly
observed. He has also sought to explain gravitation by connecting it
with the pressures which may be produced on bodies by the vibratory
movements which form very penetrating rays. Recently M. Sutherland has
imagined that attraction is due to the difference of action in the
convection currents produced by the positive and negative corpuscles
which constitute the atoms of the stars, and are carried along by the
astronomical motions. But these hypotheses remain rather vague, and
many authors think, like M. Langevin, that gravitation must result
from some mode of activity of the ether totally different from the
electromagnetic mode.

CHAPTER XI

THE FUTURE OF PHYSICS

It would doubtless be exceedingly rash, and certainly very
presumptuous, to seek to predict the future which may be reserved for
physics. The role of prophet is not a scientific one, and the most
firmly established previsions of to-day may be overthrown by the
reality of to-morrow.

Nevertheless, the physicist does not shun an extrapolation of some
little scope when it is not too far from the realms of experiment; the
knowledge of the evolution accomplished of late years authorises a few
suppositions as to the direction in which progress may continue.

The reader who has deigned to follow me in the rapid excursion we have
just made through the domain of the science of Nature, will doubtless
bring back with him from his short journey the general impression that
the ancient limits to which the classic treatises still delight in
restricting the divers chapters of physics, are trampled down in all
directions.

The fine straight roads traced out by the masters of the last century,
and enlarged and levelled by the labour of such numbers of workmen,
are now joined together by a crowd of small paths which furrow the
field of physics. It is not only because they cover regions as yet
little explored where discoveries are more abundant and more easy,
that these cross-cuts are so frequent, but also because a higher hope
guides the seekers who engage in these new routes.

In spite of the repeated failures which have followed the numerous
attempts of past times, the idea has not been abandoned of one day
conquering the supreme principle which must command the whole of
physics.

Some physicists, no doubt, think such a synthesis to be impossible of
realisation, and that Nature is infinitely complex; but,
notwithstanding all the reserves they may make, from the philosophical
point of view, as to the legitimacy of the process, they do not
hesitate to construct general hypotheses which, in default of complete
mental satisfaction, at least furnish them with a highly convenient
means of grouping an immense number of facts till then scattered
abroad.

Their error, if error there be, is beneficial, for it is one of those
that Kant would have classed among the fruitful illusions which
engender the indefinite progress of science and lead to great and
important co-ordinations.

It is, naturally, by the study of the relations existing between
phenomena apparently of very different orders that there can be any
hope of reaching the goal; and it is this which justifies the peculiar
interest accorded to researches effected in the debatable land between
domains hitherto considered as separate.

Among all the theories lately proposed, that of the ions has taken a
preponderant place; ill understood at first by some, appearing
somewhat singular, and in any case useless, to others, it met at its
inception, in France at least, with only very moderate favour.

To-day things have greatly changed, and those even who ignored it have
been seduced by the curious way in which it adapts itself to the
interpretation of the most recent experiments on very different
subjects. A very natural reaction has set in; and I might almost say
that a question of fashion has led to some exaggerations.

The electron has conquered physics, and many adore the new idol rather
blindly. Certainly we can only bow before an hypothesis which enables
us to group in the same synthesis all the discoveries on electric
discharges and on radioactive substances, and which leads to a
satisfactory theory of optics and of electricity; while by the
intermediary of radiating heat it seems likely to embrace shortly the
principles of thermodynamics also. Certainly one must admire the power
of a creed which penetrates also into the domain of mechanics and
furnishes a simple representation of the essential properties of
matter; but it is right not to lose sight of the fact that an image
may be a well-founded appearance, but may not be capable of being
exactly superposed on the objective reality.

The conception of the atom of electricity, the foundation of the
material atoms, evidently enables us to penetrate further into
Nature's secrets than our predecessors; but we must not be satisfied
with words, and the mystery is not solved when, by a legitimate
artifice, the difficulty has simply been thrust further back. We have
transferred to an element ever smaller and smaller those physical
qualities which in antiquity were attributed to the whole of a
substance; and then we shifted them later to those chemical atoms
which, united together, constitute this whole. To-day we pass them on
to the electrons which compose these atoms. The indivisible is thus
rendered, in a way, smaller and smaller, but we are still unacquainted
with what its substance may be. The notion of an electric charge which
we substitute for that of a material mass will permit phenomena to be
united which we thought separate, but it cannot be considered a
definite explanation, or as the term at which science must stop. It is
probable, however, that for a few years still physics will not travel
beyond it. The present hypothesis suffices for grouping known facts,
and it will doubtless enable many more to be foreseen, while new
successes will further increase its possessions.

Then the day will arrive when, like all those which have shone before
it, this seductive hypothesis will lead to more errors than
discoveries. It will, however, have been improved, and it will have
become a very vast and very complete edifice which some will not
willingly abandon; for those who have made to themselves a comfortable
dwelling-place on the ruins of ancient monuments are often too loth to
leave it.

In that day the searchers who were in the van of the march after truth
will be caught up and even passed by others who will have followed a
longer, but perhaps surer road. We also have seen at work those
prudent physicists who dreaded too daring creeds, and who sought only
to collect all the documentary evidence possible, or only took for
their guide a few principles which were to them a simple
generalisation of facts established by experiments; and we have been
able to prove that they also were effecting good and highly useful
work.

Neither the former nor the latter, however, carry out their work in an
isolated way, and it should be noted that most of the remarkable
results of these last years are due to physicists who have known how
to combine their efforts and to direct their activity towards a common
object, while perhaps it may not be useless to observe also that
progress has been in proportion to the material resources of our
laboratories.

It is probable that in the future, as in the past, the greatest
discoveries, those which will suddenly reveal totally unknown regions,
and open up entirely new horizons, will be made by a few scholars of
genius who will carry on their patient labour in solitary meditation,
and who, in order to verify their boldest conceptions, will no doubt
content themselves with the most simple and least costly experimental
apparatus. Yet for their discoveries to yield their full harvest, for
the domain to be systematically worked and desirable results obtained,
there will be more and more required the association of willing minds,
the solidarity of intelligent scholars, and it will be also necessary
for these last to have at their disposal the most delicate as well as
the most powerful instruments. These are conditions paramount at the
present day for continuous progress in experimental science.

If, as has already happened, unfortunately, in the history of science,
these conditions are not complied with; if the freedoms of the workers
are trammelled, their unity disturbed, and if material facilities are
too parsimoniously afforded them,--evolution, at present so rapid, may
be retarded, and those retrogressions which, by-the-by, have been
known in all evolutions, may occur, although even then hope in the
future would not be abolished for ever.

There are no limits to progress, and the field of our investigations
has no boundaries. Evolution will continue with invincible force. What
we to-day call the unknowable, will retreat further and further before
science, which will never stay her onward march. Thus physics will
give greater and increasing satisfaction to the mind by furnishing new
interpretations of phenomena; but it will accomplish, for the whole of
society, more valuable work still, by rendering, by the improvements
it suggests, life every day more easy and more agreeable, and by
providing mankind with weapons against the hostile forces of Nature.

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