ETHER AND MATTER
THE MECHANICAL NECESSITY FOR A CONTINUOUS
MEDIUM FILLING SPACE
In this chapter I propose to summarise in simple and consecutive form
most of the arguments already used. Thirty years ago Clerk Maxwell
gave to the Royal Institution of Great Britain a remarkable address on
"Action at a Distance." It is reported in the Journal R.I., Vol. VII,
and to it I would direct attention. Most natural philosophers hold,
and have held, that action at a distance across empty space is
impossible; in other words, that matter cannot act where it is not,
but only where it is. The question "Where is it?" is a further
question that may demand attention and require more than a superficial
answer. For it can be argued on the hydrodynamic or vortex theory of
matter, as well as on the electrical theory, that every atom of matter
has a universal though nearly infinitesimal prevalence, and extends
everywhere; since there is no definite sharp boundary or limiting
periphery to the region disturbed by its existence. The lines of force
of an isolated electric charge extend throughout illimitable space.
And though a charge of opposite sign will curve and concentrate them,
yet it is possible to deal with both charges, by the method of
superposition, as if they each existed separately without the other.
In that case, therefore, however far they reach, such nuclei clearly
exert no "action at a distance" in the technical sense.
Some philosophers have reason to suppose that mind can act directly on
mind without intervening mechanism,--and sometimes that has been
spoken of as genuine action at a distance; but no proper conception or
physical model can be made of such a process, nor is it clear that
"space" and "distance" have any particular meaning in the region of
psychology. The links between mind and mind may be something quite
other than physical proximity; and in denying action at a distance
across empty space I am not denying telepathy or other activities of a
non-physical kind. For although brain disturbance is certainly
physical, and is an essential concomitant of mental action whether of
the sending or receiving variety, yet we know from the case of heat
that a material movement can be excited in one place at the expense of
corresponding movement in another, without any similar kind of
transmission or material connexion between the two places: the thing
that travels across vacuum is not heat.
In all cases where physical motion is involved, however, I would have
a medium sought for. It may not be matter, but it must be something;
there must be a connecting link of some kind, or the transference
cannot occur. There can be no attraction across really empty space.
And even when a material link exists, so that the connexion is
obvious, the explanation is not complete; for when the mechanism of
attraction is understood, it will be found that a body really only
moves because it is pushed by something from behind. The essential
force in nature is the _vis a tergo_. So when we have found the
"traces," or discovered the connecting thread, we still run up against
the word "cohesion"; and we ought to be exercised in our minds as to
its ultimate meaning. Why the whole of a rod should follow, when one
end is pulled, is a matter requiring explanation; and the only
explanation that can be given involves, in some form or other, a
continuous medium connecting the discrete and separated particles or
atoms of matter.
When a steel spring is bent or distorted, what is it that is really
strained? Not the atoms--the atoms are only displaced; it is the
connecting links that are strained--the connecting medium--the ether.
Distortion of a spring is really distortion of the ether. All stress
exists in the ether. Matter can only be moved. Contact does not exist
between the atoms of matter as we know them; it is doubtful if a
piece of matter ever touches another piece, any more than a comet
touches the sun when it appears to rebound from it; but the atoms are
connected, as the comet and the sun are connected, by a continuous
_plenum_ without break or discontinuity of any kind. Matter acts on
matter only through the ether. But whether matter is a thing utterly
distinct and separate from the ether, or whether it is a specifically
modified portion of it--modified in such a way as to be susceptible of
locomotion and yet continuous with all the rest of the ether, which
can be said to extend everywhere far beyond the bounds of the modified
and tangible portion--are questions demanding, and I may say in
process of receiving, answers.
Every such answer involves some view of the universal and possibly
infinite uniform omnipresent connecting medium, the Ether of space.
It has been said, somewhat sarcastically, that the ether was made in
England. The statement is only an exaggeration of the truth. I might
even urge that it has been largely constructed in the Royal
Institution; for, I will summarise now the chief lines of evidence on
which its existence is believed in, and our knowledge of it is based.
First of all, Newton recognised the need of a medium for explaining
gravitation. In his "Optical Queries" he shows that if the pressure of
this medium is less in the neighbourhood of dense bodies than at
great distances from them, dense bodies will be driven towards each
other; and that if the diminution of pressure is inversely as the
distance from the dense body, the law of force will be the inverse
square law of gravitation.
All that is required, therefore, to explain gravity, is a diminution
of pressure, or increase of tension, caused by the formation of a
matter unit--that is to say of an electron or corpuscle. And although
we do not yet know what an electron is--whether it be a strain centre,
or what kind of singularity in the ether it may be--there is no
difficulty in supposing that a slight, almost infinitesimal, strain or
attempted rarefaction should be produced in the ether whenever an
electron comes into being--to be relaxed again only on its resolution
and destruction. Strictly speaking it is not a real _strain_, but only
a "stress"; since there can be no actual _yield_, but only a pull or
tension, extending in all directions towards infinity.
The tension required per unit of matter is almost ludicrously small,
and yet in the aggregate, near such a body as a planet, it becomes
enormous.
The force with which the moon is held in its orbit would be great
enough to tear asunder a steel rod four hundred miles thick, with a
tenacity of 30 tons per square inch; so that if the moon and earth
were connected by steel instead of by gravity, a forest of pillars
would be necessary to whirl the system once a month round their
common centre of gravity. Such a force necessarily implies enormous
tension or pressure in the medium. Maxwell calculates that the
gravitational stress near the earth, which we must suppose to exist in
the invisible medium, is 3000 times greater than what the strongest
steel could stand; and near the sun it should be 2500 times as great
as that.
The question has arisen in my mind, whether, if the whole sensible
universe--estimated by Lord Kelvin as equivalent to about a thousand
million suns--were all concentrated in one body of specifiable
density,[7] the stress would not be so great as to produce a tendency
towards etherial disruption; which would result in a disintegrating
explosion, and a scattering of the particles once more as an enormous
nebula and other fragments into the depths of space. For the tension
would be a maximum in the interior of such a mass; and, if it rose to
the value 10³³ dynes per square centimetre, something would have to
happen. I do not suppose that this can be the reason, but one would
think there must be _some_ reason, for the scattered condition of
gravitative matter.
Too little is known, however, about the mechanism of gravitation to
enable us to adduce it as the strongest argument in support of the
existence of an ether. The oldest valid and conclusive requisition of
an ethereous medium depends on the wave theory of light, one of the
founders of which was the Royal Institution Professor of Natural
Philosophy at the beginning of last century, Dr. Thomas Young.
No ordinary matter is capable of transmitting the undulations or
tremors that we call light. The speed at which they go, the kind of
undulation, and the facility with which they go through vacuum, forbid
this.
So clearly and universally has it been perceived that waves must be
waves of something--something distinct from ordinary matter--that Lord
Salisbury, in his presidential address to the British Association at
Oxford, criticised the ether as little more than a nominative case to
the verb to undulate. It is truly _that_, though it is also truly more
than that; but to illustrate that luminiferous aspect of it, I will
quote a paragraph from the lecture of Clerk Maxwell's to which I have
already referred:--
"The vast interplanetary and interstellar regions will no longer be
regarded as waste places in the universe, which the Creator has not
seen fit to fill with the symbols of the manifold order of His
kingdom. We shall find them to be already full of this wonderful
medium; so full, that no human power can remove it from the smallest
portion of space, or produce the slightest flaw in its infinite
continuity. It extends unbroken from star to star; and when a molecule
of hydrogen vibrates in the dog-star, the medium receives the impulses
of these vibrations, and after carrying them in its immense bosom for
several years, delivers them, in due course, regular order, and full
tale, into the spectroscope of Mr. Huggins, at Tulse Hill."
This will suffice to emphasise the fact that the eye is truly an
etherial sense-organ--the only one which we possess, the only mode by
which the ether is enabled to appeal to us; and that the detection of
tremors in this medium--the perception of the direction in which they
go, and some inference as to the quality of the object which has
emitted them--cover all that we mean by "sight" and "seeing."
I pass then to another function, the electric and magnetic phenomena
displayed by the ether; and on this I will only permit myself a very
short quotation from the writings of Faraday, whose whole life may be
said to have been directed towards a better understanding of these
ethereous phenomena. Indeed the statue in the entrance hall of the
Royal Institution, Albemarle Street, may be considered as the statue
of the discoverer of the electric and magnetic properties of the Ether
of space.
Faraday conjectured that the same medium which is concerned in the
propagation of light might also be the agent in electromagnetic
phenomena. "For my own part," he says, "considering the relation of a
vacuum to the magnetic force, and the general character of magnetic
phenomena external to the magnet, I am much more inclined to the
notion that in the transmission of the force there is such an action,
external to the magnet, than that the effects are merely attraction
and repulsion at a distance. Such an action may be a function of the
æther; for it is not unlikely that, if there be an æther, it should
have other uses than simply the conveyance of radiation."
This conjecture has been amply strengthened by subsequent
investigations.
One more function is now being discovered; the ether is being found to
constitute matter--an immensely interesting topic, on which there are
many active workers at the present time. I will make a brief quotation
from Professor Sir J.J. Thomson, where he summarises the conclusion
which we all see looming before us, though it has not yet been
completely attained, and would not by all be similarly expressed:--
"The _whole_ mass of any body is just the mass of ether surrounding
the body which is carried along by the Faraday tubes associated with
the atoms of the body. In fact, all mass is mass of the ether; all
momentum, momentum of the ether; and all kinetic energy, kinetic
energy of the ether. This view, it should be said, requires the
density of the ether to be immensely greater than that of any known
substance."
Yes, far denser--so dense that matter by comparison is like gossamer,
or a filmy imperceptible mist, or a milky way. Not unreal or
unimportant,--a cobweb is not unreal, nor to certain creatures is it
unimportant, but it cannot be said to be massive or dense; and matter,
even platinum, is not dense when compared with the ether. Not till
last year, however, did I realise what the density of the ether must
really be,[8] compared with that modification of it which appeals to
our senses as matter, and which for that reason engrosses our
attention.
Is there any other function possessed by the ether, which, though not
yet discovered, may lie within the bounds of possibility for future
discovery? I believe there is, but it is too speculative to refer to,
beyond saying that it has been urged as probable by the authors of
_The Unseen Universe_, and has been thus tentatively referred to by
Clerk Maxwell:--
"Whether this vast homogeneous expanse of isotropic matter is fitted
not only to be a medium of physical interaction between distant
bodies, and to fulfil other physical functions of which, perhaps, we
have as yet no conception, but also ... to constitute the material
organism of beings exercising functions of life and mind as high or
higher than ours are at present--is a question far transcending the
limits of physical speculation."
And there for the present I leave that aspect of the subject.
_Ether and Matter._
I shall now attempt to illustrate some relations between ether and
matter.
The question is often asked, is ether material? This is largely a
question of words and convenience. Undoubtedly, the ether belongs to
the material or physical universe, but it is not ordinary matter. I
should prefer to say it is not "matter" at all. It may be the
substance or substratum or material of which matter is composed, but
it would be confusing and inconvenient not to be able to discriminate
between matter on the one hand, and ether on the other. If you tie a
knot on a bit of string, the knot is composed of string, but the
string is not composed of knots. If you have a smoke or vortex-ring in
the air, the vortex-ring is made of air, but the atmosphere is not a
vortex-ring; and it would be only confusing to say that it was.
The essential distinction between matter and ether is that matter
_moves_, in the sense that it has the property of locomotion and can
effect impact and bombardment; while ether is _strained_, and has the
property of exerting stress and recoil. All potential energy exists in
the ether. It may vibrate, and it may rotate, but as regards
locomotion it is stationary--the most stationary body we know:
absolutely stationary, so to speak; our standard of rest.
All that we ourselves can effect, in the material universe, is to
alter the motion and configuration of masses of matter; we can move
matter, by our muscles, and that is all we can do directly: everything
else is indirect.
But now comes the question, how is it possible for matter to be
composed of ether? How is it possible for a solid to be made out of
fluid? A solid possesses the properties of rigidity, impenetrability,
elasticity, and such-like; how can these be imitated by a perfect
fluid such as the ether must be?
The answer is, they can be imitated by a _fluid in motion_; a
statement which we make with confidence as the result of a great part
of Lord Kelvin's work.
It may be illustrated by a few experiments.
A wheel of spokes, transparent or permeable when stationary, becomes
opaque when revolving, so that a ball thrown against it does not go
through, but rebounds. The motion only affects permeability to matter;
transparency to light is unaffected.
A silk cord hanging from a pulley becomes rigid and viscous when put
into rapid motion; and pulses or waves which may be generated on the
cord travel along it with a speed equal to its own velocity, whatever
that velocity may be, so that they appear to stand still. This is a
genuine case of kinetic rigidity; and the fact that the
wave-transmission velocity is equal to the rotatory speed of the
material, is typical and important,--for in all cases of kinetic
elasticity these two velocities are of the same order of magnitude.
A flexible chain, set spinning, can stand up on end while the motion
continues.
A jet of water at sufficient speed can be struck with a hammer, and
resists being cut with a sword.
A spinning disk of paper becomes elastic like flexible metal, and can
act like a circular saw. Sir William White tells me that in naval
construction steel plates are cut by a rapidly revolving disk of soft
iron.
A vortex-ring, ejected from an elliptical orifice, oscillates about
the stable circular form, as an india-rubber ring would do; thus
furnishing a beautiful example of kinetic elasticity, and showing us
clearly a fluid displaying some of the properties of a solid.
A still further example is Lord Kelvin's model of a spring balance,
made of nothing but rigid bodies in spinning motion.[9] This
arrangement utilises the processional movement of balanced
gyrostats--concealed in a case and supporting a book--to imitate the
behaviour of a spiral spring, if it were used to support the same
book.
If the ether can be set spinning, therefore, we may have some hope of
making it imitate the properties of matter, or even of constructing
matter by its aid. But _how_ are we to spin the ether? Matter alone
seems to have no grip of it. As already described, I have spun steel
disks, a yard in diameter, 4000 times a minute, have sent light round
and round between them, and tested carefully for the slightest effect
on the ether. Not the slightest effect was perceptible. We cannot spin
ether mechanically.
But we can vibrate it electrically; and every source of radiation does
that. An electrical charge, in sufficiently rapid vibration, is the
only source of ether-waves that we know; and if an electric charge is
suddenly stopped, it generates the pulses known as X-rays, as the
result of the collision. Not speed, but sudden change of speed, is the
necessary condition for generating waves in the ether by electricity.
We can also infer some kind of rotary motion in the ether; though we
have no such obvious means of detecting the spin as is furnished by
vision for detecting some kinds of vibration. Rotation is supposed to
exist whenever we put a charge into the neighbourhood of a magnetic
pole. Round the line joining the two, the ether is spinning like a
top. I do not say it is spinning fast: that is a question of its
density; it is in fact spinning with excessive slowness, but it is
spinning with a definite moment of momentum. J.J. Thomson's theory
makes its moment of momentum exactly equal to _e m_, the product of
_charge_ and _pole_; the charge being measured electrostatically and
the pole magnetically.
How can this be shown experimentally? Suppose we had a spinning top
enclosed in a case, so that the spin was unrecognisable by ordinary
means--it could be detected by its gyrostatic behaviour to force. If
allowed to "precess" it will respond by moving perpendicularly to a
deflecting force. So it is with the charge and the magnetic pole. Try
to move the charge suddenly, and it immediately sets off at right
angles. A moving charge is a current, and the pole and the current try
to revolve round one another;--a fact which may be regarded as
exhibiting a true gyrostatic action due to the otherwise
unrecognisable etherial spin. The fact of such magnetic rotation was
discovered by Faraday.
I know that it is usually worked out in another way, in terms of lines
of force and the rest of the circuit; but I am thinking of a current
as a stream of projected charges; and no one way of regarding such a
matter is likely to exhaust the truth, or to exclude other modes which
are equally valid. Anyhow, in whatever way it is regarded, it is an
example of the three rectangular vectors.
The three vectors at right angles to each other, which may be labelled
Current, Magnetism, and Motion respectively, or more generally E, H,
and V, represent the quite fundamental relation between ether and
matter, and constitute the link between Electricity, Magnetism, and
Mechanics. Where any two of these are present, the third is a
necessary consequence. This principle is the basis of all dynamos, of
electric motors, of light, of telegraphy, and of most other things.
Indeed, it is a question whether it does not underlie everything that
we know in the whole of the physical sciences; and whether it is not
the basis of our conception of the three dimensions of space.
Lastly, we have the fundamental property of matter called _inertia_,
which can, to a certain extent, be explained electromagnetically,
provided the ethereous density is granted as of the order 10¹²
grammes per cubic centimetre. The elasticity of the ether would then
have to be of the order 10³³ c.g.s.; and if this is due to
intrinsic turbulence, the speed of the whirling or rotational
elasticity must be of the same order as the velocity of light. This
follows hydrodynamically; in the same sort of way as the speed at
which a pulse travels on a flexible running endless cord, whose
tension is entirely due to the centrifugal force of the motion, is
precisely equal to the velocity of the cord itself. And so, on our
present view, the intrinsic energy of constitution of the ether is
incredibly and portentously great; every cubic millimetre of space
possessing what, if it were matter, would be a mass of a thousand
tons, and an energy equivalent to the output of a million-horse-power
station for 40 million years.
The universe we are living in is an extraordinary one; and our
investigation of it has only just begun. We know that matter has a
psychical significance, since it can constitute _brain_, which links
together the physical and the psychical worlds. If any one thinks that
the ether, with all its massiveness and energy, has probably no
psychical significance, I find myself unable to agree with him.
FOOTNOTES:
[7] On doing the arithmetic, however, I find the necessary
concentration absurdly great, showing that such a mass is quite
insufficient. (See Appendix 1.)
[8] See Lodge, _Philosophical Magazine_, April, 1907. Also Appendix 2
below.
[9] Address to Section A of British Association at Montreal, 1884.