The Light Course
29 December 1919, Stuttgart
My dear Friends,
In our last lecture we were going into certain matters of principle which I will now try to explain more fully. For if we start from the experiences we can gain in the realm of light, it will also help us observe and understand other natural phenomena which we shall presently be studying. I will therefore begin today with these more theoretical reflections and put off the experimental part until tomorrow. We must determine still more exactly the method of our procedure. It is the task of Science to discern and truly to set forth the facts in the phenomena of Nature. Problems of method which this task involves can best be illustrated in the realm of Light.
Men began studying the phenomena of light in rather recent times, historically speaking. Nay, the whole way of thinking about the phenomena of Physics, presented in the schools today, reaches hardly any farther back than the 16th century. The way men thought of such phenomena before the 16th century was radically different. Today at school we get so saturated with the present way of thought that if you have been through this kind of schooling it is extremely difficult for you to find your way back to the pure facts. You must first cultivate the habit of feeling the pure facts as such; please do not take my words in a too trivial meaning. You have to learn to sense the facts, and this takes time and trouble.
I will now take my start from a particular instance wherein we may compare the way of thought prevailing in the schools today with that which can be gained by following the facts straightforwardly. Suppose this were a plate of glass, seen in cross-section (Figure VIa). Through it you look at a luminous object. As I am drawing it diagrammatically, let me represent the latter simply by a light circle. Cast your mind back to what you learned in your school days. What did they teach you of the phenomenon you see when you observe the luminous object, — with your eye, say, here — looking through the glass? You were no doubt told that rays of light proceed from the luminous object. (We are imagining the eye to be looking in this particular direction, — see the Figure). Rays, you were told, proceed from the shining object. In the direction of the “ray” I am now drawing, the light was said to penetrate from a more tenuous into a denser medium. Simply by looking through the glass and comparing what you see with what you saw before the plate of glass was there, you do indeed perceive the thing displaced. It appears at a different place than without the glass. Now this is said to be due to the light being “refracted”. This is how they are wont to put it: — When the light passes from a more tenuous into a denser medium, to find the direction in which the light will be refracted, you must draw the so-called “normal at the point of incidence”. If the light went on its way without being hindered by a denser medium, it would go on in this direction. But, they now say, the light is “refracted” — in this case, towards the normal, i.e. towards the perpendicular to the glass surface at the point of incidence. Now it goes out again, — out of the glass. (All this is said, you will remember, in tracing how the “ray of light” is seen through the denser medium.) Here then again, at the point of exit from the glass, you will have to erect the normal. If the light went straight on it would go thus: but at this second surface it is again refracted — this time, away from the normal — refracted just enough to make it go on parallel to its original direction. And now the eye, looking as it is from here, is said to produce the final direction of the ray of light and thus to project the luminous object so much the higher up. This then is what we are asked to assume, if we be looking through such a plate of glass. Here, to begin with, the light impinges on the plate, then it is twice refracted — once towards the normal, a second time away from the normal. Then, inasmuch as the eye has the inner faculty to do so (.... or is it to the soul, or to some demon that you ascribe this faculty ....) the light is somehow projected out into space. It is projected moreover to a position different from where it would appear if we were not seeing it through a refracting medium; — so they describe the process.
The following should be observed to begin with, in this connection. Say we are looking at anything at all through the same denser medium, and we now try to discriminate, however delicately, between the darker and lighter portions of what we see. Not only the lighter parts, the darker too will appear shifted upward. The entire complex we are looking at is found to be displaced. Please take this well into account. Here is a darker part bordering on a lighter. The dark is shifted upward, and since one end of it is lighter we see this shifted too. Placing before us any such complex, consisting of a darker and a lighter part, we must admit the lighter part is displaced simply as the upper boundary of the darker. Instead, they speak in such a way as to abstract the one light patch from all the rest that is there. Mostly they speak as though the light patch alone were suffering displacement. Surely this is wrong. For even if I fix my gaze on this one patch of light, it is not true that it alone is shifted upward. The part below it, which I am treating as if it were just nothing when I describe it thus, is shifted upward too. In point of fact, what is displaced in these optical phenomena can never be thus abstractly confined. If therefore I repeat Newton's experiment — I let into the room a cone of light which then gets diverted by the prism — it simply is not true that the cone of light is diverted all alone. Whatever the cone of light is bordering on — above it and below — is diverted too. I really ought never to speak of rays of light or anything of that kind, but only of luminous pictures or spaces-of-light being diverted. In a particular instance I may perhaps want to refer to some isolated light, but even then I still ought not to speak of it in such a way as to build my whole theory of the phenomenon upon it. I still ought to speak in such a way as to refer at the same time to all that borders on the light. Only if we think in this way can we begin to feel what is really going on when the phenomena of colour comes into being before our eyes. Otherwise our very habit of thought begets the impression that in some way the colours spring from the light alone. For from the very outset we have it settled in our mind that the one and only reality we are dealing with is the light. Yet, what we have before us in reality is never simply light as such; it is always something light, bordered on one side or other by darkness. And if the lighter part — the space it occupies — is shifted, the darker part is shifted too. But now, what is this “dark”? You must take the dark seriously, — take it as something real. (The errors that have crept into modern Physics since about the 16th century were only able to creep in because these things were not observed spiritually at the same time. Only the semblance, as appearing to the outer senses, was taken note of; then, to explain this outer semblance, all kinds of theoretical inventions were added to it). You certainly will not deny that when you look at light the light is sometimes more and sometimes less intense. There can be stronger light and less strong. The point is now to understand: How is this light, which may be stronger or weaker related to darkness? The ordinary physicist of today thinks there is stronger light and less strong; he will admit every degree of intensity of light, but he will only admit one darkness — darkness which is simply there when there is no light. There is, as it were, only one way of being black. Yet as untrue as it would be to say that there is only one kind of lightness, just as untrue is it to say that there is only one kind of darkness. It is as one-sided as it would be to declare: “I know four men. One of them owns £25, another £50; he therefore owns more than the other. The third of them is £25 in debt, the fourth is £50 in debt. Yet why should I take note of any difference in their case? It is precisely the same; both are in debt. I will by all means distinguish between more and less property, but not between different degrees of debt. Debt is debt and that is all there is to it.” You see the fallacy at once in this example, for you know very well that the effect of being £25 in debt is less than that of being £50 in debt. But in the case of darkness this is how people think: Of light there are different degrees; darkness is simply darkness. It is this failure to progress to a qualitative way of thinking, which very largely prevents our discovering the bridge between the soul-and-spirit on the one hand, and the bodily realm on the other. When a space is filled with light it is always filled with light of a certain intensity; so likewise, when a space is filled with darkness, it is filled with darkness of a certain intensity. We must proceed from the notion of a merely abstract space to the kind of space that is not abstract but is in some specific way positively filled with light or negatively filled with darkness. Thus we may be confronting a space that is filled with light and we shall call it “qualitatively positive”. Or we may be confronting a space that is filled with darkness and we shall judge it “qualitatively negative” with respect to the realm of light. Moreover both to the one and to the other we shall be able to ascribe a certain degree of intensity, a certain strength. Now we may ask: How does the positive filling of space differ for our perception from the negative? As to the positive, we need only remember what it is like when we awaken from sleep and are surrounded by light, — how we unite our subjective experience with the light that floods and surges all around us. We need only compare this sensation with what we feel when surrounded by darkness, and we shall find — I beg you to take note of this very precisely — we shall find that for pure feeling and sensation there is an essential difference between being given up to a light-filled space and to a darkness-filled space. We must approach these things with the help of some comparison. Truly, we may compare the feeling we have, when given up to a light-filled space, with a kind of in-drawing of the light. It is as though our soul, our inner being, were to be sucking the light in. We feel a kind of enrichment when in a light-filled space. We draw the light into ourselves. How is it then with darkness? We have precisely the opposite feeling. We feel the darkness sucking at us. It sucks us out, we have to give away, — we have to give something of ourselves to the darkness. Thus we may say: the effect of light upon us is to communicate, to give; whilst the effect of darkness is to withdraw, to suck at us and take away. So too must we distinguish between the lighter and the darker colours. The light ones have a quality of coming towards us and imparting something to us; the dark colours on the other hand have a quality of drawing on us, sucking at us, making us give of ourselves. So at long last we are led to say: Something in our outer world communicates itself to us when we are under the influence of light; something is taken from us, we are somehow sucked out, when under the influence of darkness.
There is indeed another occasion in our life, when — as I said once before during these lectures — we are somehow sucked-out as to our consciousness; namely when we fall asleep. Consciousness ceases. It is a very similar phenomenon, like a cessation of consciousness, when from the lighter colours we draw near the darker ones, the blue and violet. And if you will recall what I said a few days ago about the relation of our life of soul to mass, — how we are put to sleep by mass, how it sucks-out our consciousness, — you will feel something very like this in the absorption of our consciousness by darkness. So then you will discern the deep inner kinship between the condition space is in when filled with darkness and on the other hand the filling of space which we call matter, which is expressed in “mass”.
Thus we shall have to seek the transition from the phenomena of light to the phenomena of material existence. We have indeed paved the way, in that we first looked for the fleeting phenomena of light — phosphorescence and fluorescence — and then the firm and fast phenomena of light, the enduring colours. We cannot treat all these things separately; rather let us begin by setting out the whole complex of these facts together.
Now we shall also need to recognize the following, When we are in a light-filled space we do in a way unite with this light-filled space. Something in us swings out into the light-filled space and unites with it. But we need only reflect a little on the facts and we shall recognize an immense difference between the way we thus unite with the light-flooded spaces of our immediate environment and on the other hand the way we become united with the warmth-conditions of our environment, — for with these too, as human beings, we do somehow unite.
We do indeed share very much in the condition of our environment as regards warmth; and as we do so, here once again we feel a kind of polarity prevailing, namely the polarity of warm and cold. Yet we must needs perceive an essential difference between the way we feel ourselves within the warmth-condition of our environment and the way we feel ourselves within the light-condition of our environment. Physics, since the 16th century, has quite lost hold of this difference. The open-mindedness to distinguish how we join with our environment in the experience of light upon the one hand and warmth upon the other has been completely lost; nay, the deliberate tendency has been, somehow to blur and wipe away such differences as these. Suppose however that you face the difference, quite obviously given in point of fact, between the way we experience and share in the conditions of our environment as regards warmth and light respectively. Then in the last resort you will be bound to recognize that the distinction is: we share in the warmth-conditions of our environment with our physical body and in the light-conditions, as we said just now, with our etheric body. This in effect — this proneness to confuse what we become aware of through our ether-body and what we become aware of through our physical body — has been the bane of Physics since the 16th century. In course of time all things have thus been blurred. Our scientists have lost the faculty of stating facts straightforwardly and directly. This has been so especially since Newton's influence came to be dominant, as it still is to a great extent today. There have indeed been individuals who have attempted from time to time to draw attention to the straightforward facts simply as they present themselves. Goethe of course was doing it all through, and Kirchhoff among others tried to do it in more theoretic ways. On the whole however, scientists have lost the faculty of focusing attention purely and simply on the given facts. The fact for instance that material bodies in the neighbourhood of other material bodies will under given conditions fall towards them, has been conceived entirely in Newton's sense, being attributed from the very outset to a force proceeding from the one and affecting the other body — a “force of gravity”. Yet ponder how you will, you will never be able to include among the given facts what is understood by the term “force of gravity”. If a stone falls to the Earth the fact is simply that it draws nearer to the Earth. We see it now at one place, now at another, now at a third and so on. If you then say “The Earth attracts the stone” you in your thoughts are adding something to the given fact; you are no longer purely and simply stating the phenomenon.
People have grown ever more unaccustomed to state the phenomena purely, yet upon this all depends. For if we do not state the phenomena purely and simply, but proceed at once to thought-out explanations, we can find manifold explanations of one and the same phenomenon. Suppose for example you have two heavenly bodies. You may then say: These two heavenly bodies attract one another, — send some mysterious force out into space and so attract each other (Figure VIb). But you need not say this. You can also say: “Here is the one body, here is the other, and here (Figure VIc) are a lot of other, tiny bodies — particles of ether, it may be — all around and in between the two heavenly bodies. The tiny particles are bombarding the two big ones — bombarding here, there and on all sides; — the ones between, as they fly hither and thither, bombard them too. Now the total area of attack will be bigger outside than in between. In the resultant therefore, there will be less bombardment inside than outside; hence the two bodies will approach each other. They are, in fact, driven towards each other by the difference between the number of impacts they receive in the space between them and outside them.”
There have in fact been people who have explained the force of gravity simply by saying: It is a force acting at a distance and attracts the bodies towards each other. Others have said that that is nonsense; according to them it is unthinkable for any force to act at a distance. They then invite us to assume that space is filled with “ether”, and to assume this bombardment too. The masses then are, so to speak, for ever being sprayed towards each other. To add to these explanations there are no doubt many others. It is a classical example of how they fail to look at the real phenomenon but at once add their thought-out explanations.
Now what is at the bottom of it all? This tendency to add to the phenomena in thought — to add all manner of unknown agencies and fancied energies, presumed to be doing this or that — saves one the need of doing something else. Needless to say, the impacts in the theory of Figure VIc have been gratuitously added, just as the forces acting at a distance have been in the other theory. These adventitious theories, however, relieve one of the need of making one fundamental assumption, from which the people of today seem to be very much averse. For in effect, if these are two independent heavenly bodies and they approach each other, or show that it is in their nature to approach each other, we cannot but look for some underlying reason why they do so; there must be some inner reason. Now it is simpler to add in thought some unknown forces than to admit that there is also another way, namely no longer to think of the heavenly bodies as independent of each other. If for example I put my hand to my forehead, I shall not dream of saying that my forehead “attracts” my hand, but I shall say: It is an inner deed done by the underlying soul-and-spirit. My hand is not independent of my forehead; they are not really separate entities. I shall regard the phenomenon rightly only by recognising myself as a single whole. I should have no reality in mind if I were to say: There is a head, there are two arms and hands, there is a trunk, there are two legs. There would be nothing complete in that; I only have something complete in mind if I describe the whole human body as a single entity, — if I describe the different items so that they belong together. My task is not merely to describe what I see; I have to ponder the reality of what I see. The mere fact that I see a thing does not make it real.
Often I have made the following remark, — for I have had to indicate these things in other lectures too. Take a crystal cube of rock-salt. It is in some respect a totality. (Everything will be so in some respect). The crystal cube can exist by virtue of what it is within the compass of its six faces. But if you look at a rose, cut from the shrub it grew on, this rose is no totality. It cannot, like the cube of rock-salt, exist by virtue of all that is contained within it. The rose can only have existence by being of the rose-bush. The cut rose therefore, though you can see it just as you can see the cube of rock-salt, is a real abstraction; you may not call it a reality by itself.
The implications of this, my dear Friends, are far-reaching. Namely, for every phenomenon, we must examine to what extent it is a reality in itself, or a mere section of some larger whole. If you consider Sun and Moon, or Sun and Earth, each by itself, you may of course invent and add to them a force of gravity, just as you might invent a force of gravity by means of which my forehead would attract my right hand. But in considering Sun and Earth and Moon thus separately, the things you have in mind are not totalities; they are but parts and members of the whole planetary system.
This then is the essential thing; observe to what extent a thing is whole, or but a section of a whole. How many errors arise by considering to be a whole what is in fact only a partial phenomenon within a larger whole! By thus considering only the partial phenomena and then inventing energies to add to these, our scientists have saved themselves the need of contemplating the inherent life of the planetary system. The tendency has been, first to regard as wholes those things in Nature which are only parts, and by mere theories then to construe the effects which arise in fact between them. This therefore, to sum up, is the essential point: For all that meets us in Nature we have to ask: What is the whole to which this thing belongs? Or is it in itself a whole? Even then, in the last resort, we shall find that things are wholes only in certain respects. Even the crystal cube of rock-salt is a totality only in some respect; it too cannot exist save at certain temperatures and under other requisite conditions. Given some other temperature, it could no longer be. Our need is therefore to give up looking at Nature in the fragmentary way which is so prevalent in our time.
Indeed it was only by looking at Nature in this fragmentary way that Science since the 16th century conceived this strange idea of universal, inorganic, lifeless Nature. There is indeed no such thing, just as in this sense there is no such thing as your bony system without your blood. Just as your bony system could only come into being by, as it were, crystallizing out of your living organism as a whole, so too this so-called inorganic Nature cannot exist without the whole of Nature — soul and Spirit-Nature — that underlies it. Lifeless Nature is the bony system, abstracted from Nature as a whole. It is impossible to study it alone, as they began doing ever since the 16th century and as is done in Newtonian Physics to this day.
It was the trend of Newtonian Physics to make as neat as possible an extract of this so-called inorganic Nature, treating it then as something self-contained. This “inorganic Nature” only exists however in the machines which we ourselves piece together from the parts of Nature. And here we come to something radically different. What we are wont to call “inorganic” in Nature herself, is placed in the totality of Nature in quite another way. The only really inorganic things are our machines, and even these are only so insofar as they are pieced together from sundry forces of Nature by ourselves. Only the “put-togetherness” of them is inorganic. Whatever else we may call inorganic only exists by abstraction. From this abstraction however present-day Physics has arisen. This Physics is an outcome of abstraction; it thinks that what it has abstracted is the real thing, and on this assumption sets out to explain whatever comes within its purview
As against this, the only thing we can legitimately do is to form our ideas and concepts in direct connection with what is given to us from the outer world — the details of the sense-world. Now there is one realm of phenomena for which a very convenient fact is indeed given. If you strike a bell and have some light and very mobile device in the immediate neighbourhood, you will be able to demonstrate that the particles of the sounding bell are vibrating. Or with a pipe playing a note, you will be able to show that the air inside it is vibrating. For the phenomena of sound and tone therefore, you have the demonstrable movement of the particles of air or of the bell; so you will ascertain that there is a connection between the vibrations executed by a body or by the air and our perceptions of tone or sound. For this field of phenomena it is quite patent: vibrations are going on around us when we hear sounds. We can say to ourselves that unless the air in our environment is vibrating we shall not hear any sounds. There is a genuine connection — and we shall speak of it again tomorrow — between the sounds and the vibrations of the air.
Now if we want to proceed very abstractly we may argue: “We perceive sound through our organs of hearing. The vibrations of the air beat on our organ of hearing, and when they do so we perceive the sound. Now the eye too is a sense-organ and through it we perceive the colours; so we may say: here something similar must be at work. Some kind of vibration must be beating on the eye. But we soon see it cannot be the air. So then it is the ether.” By a pure play of analogies one is thus led to the idea: When the air beats upon our ear and we have the sensation of a sound, there is an inner connection between the vibrating air and our sensation; so in like manner, when the hypothetical ether with its vibrations beats upon our eye, a sensation of light is produced by means of this vibrating ether. And as to how the ether should be vibrating: this they endeavour to ascertain by means of such phenomena as we have seen in our experiments during these lectures. Thus they think out an universal ether and try to calculate what they suppose must be going on in this ethereal ocean. Their calculations relate to an unknown entity which cannot of course be perceived but can at most be assumed theoretically.
Even the very trifling experiments we have been able to make will have revealed the extreme complication of what is going on in the world of light. Till the more recent developments set in, our physicists assumed that behind — or, should we rather say, within — all thus that lives and finds expression in light and colour there is the vibrating ether, a tenuous elastic substance. And since the laws of impact and recoil of elastic bodies are not so difficult to get to know, they could compute what these vibrating little cobolds must be up to in the ether. They only had to regard them as little elastic bodies, — imagining the ether as an inherently elastic substance. So they could even devise explanations of the phenomena we have been showing, — e.g. the forming of the spectrum. The explanation is that the different kinds of ether-vibrations are dispersed by the prism; these different kinds of vibrations then appear to us as different colours. By calculation one may even explain from the elasticity of the ether the extinction of the sodium line for example, which we perceived in our experiment the day before yesterday.
In more recent times however, other phenomena have been discovered. Thus we can make a spectrum, in which we either create or extinguish the sodium line (i.e., in the latter case, we generate the black sodium line). If then in addition we bring an electro-magnet to bear upon the cylinder of light in a certain way, the electro-magnet affects the phenomenon of light. The sodium line is extinguished in its old place and for example two other lines arise, purely by the effect of the electricity with which magnetic effects are always somehow associated. Here, then, what is described as “electric forces” proves to be not without effect upon those processes which we behold as phenomena of light and behind which one had supposed the mere elastic ether to be working. Such discoveries of the effect of electricity on the phenomena of light now led to the assumption that there must be some kinship between the phenomena of light and those of magnetism and electricity.
Thus in more recent times the old theories were rather shaken. Before these mutual effects had been perceived, one could lean back and rest content. Now one was forced to admit that the two realms must have to do with each other. As a result, very many physicists now include what radiates in the form of light among the electro-magnetic effects. They think it is really electro-magnetic rays passing through space.
Now think a moment what has happened. The scientists had been assuming that they knew what underlies the phenomena of light and colour: namely, undulations in the elastic ether. Now that they learned of the interaction between light and electricity, they feel obliged to regard, what is vibrating there, as electricity raying through space. Mark well what has taken place. First it is light and colour which they desire to explain, and they attribute them to the vibrating ether. Ether-vibrations are moving through space. They think they know what light is in reality, — it is vibrations in the elastic ether. Then comes the moment when they have to say: What we regarded as vibrations of the elastic ether are really vibrations of electro-magnetic force. They know still better now, what light is, than they did before. It is electro-magnetic streams of force. Only they do not know what these are! Such is the pretty round they have been. First a hypothesis is set up: something belonging to the sense-world is explained by an unknown super-sensible, the vibrating ether. Then by and by they are driven to refer this super-sensible once more to something of the sense-world, yet at the same time to confess that they do not know what the latter is. It is a highly interesting journey that has here been made; from the hypothetical search for an unknown to the explanation of this unknown by yet another unknown.
The physicist Kirchhoff was rather shattered and more or less admitted: It will be not at all easy for Physics if these more recent phenomena really oblige us no longer to believe in the undulating ether. And when Helmholtz got to know of the phenomenon, he said: Very well, we shall have to regard light as a kind of electro-magnetic radiation. It only means that we shall now have to explain these radiations themselves as vibrations in the elastic ether. In the last resort we shall get back to these, he said.
The essence of the matter is that a genuine phenomenon of undulation — namely the vibrating of the air when we perceive sounds — was transferred by pure analogy into a realm where in point of fact the whole assumption is hypothetical.
I had to go into these matters of principle today, to give the necessary background. In quick succession we will now go through the most important aspects of those phenomena which we still want to consider. In our remaining hours I propose to discuss the phenomena of sound, and those of warmth, and of electro-magnetics; also whatever explanations may emerge from these for our main theme — the phenomena of optics.