The Modern Scientific Worldview

V. Akhri.

I.

We are now experiencing one of the greatest crises; all our thinking, all ethics, all life, all our spiritual and moral existence are in a state of a certain intellectual ferment; those immutable laws and even principles upon which our entire worldview and all our life were built are being reconsidered, cast aside, and in their place a new system is growing up—more general, broader—which is to become the guiding doctrine for many decades and even centuries.

These new principles will have to direct the whole of our intellectual and moral life onto a new path, along which humanity will come somewhat closer to the knowledge of truth and to the increase of happiness on earth, along which, in other words, a certain progress will be achieved. The peculiarity of human thought consists in the fact that it always strives to construct a system of the world, as harmonious as possible, which would encompass all the phenomena of nature, would foresee them, would provide explanations for everything that occurs, and would serve as the guiding thread for all human actions. In this striving to construct a harmonious system of worldview, man tries to reduce all phenomena of nature to the minimal number of general principles, from which all human actions, both moral and spiritual, would be logically derived.

If we trace the development of human thought from ancient times to our own days, we may note the following principal stages: 1) the period before Aristotle; 2) from Aristotle to the sixteenth century; 3) from Galileo, Descartes, and Newton to the beginning of the twentieth century; and finally, 4) the crisis now being experienced, whose cause is Einstein’s physics.

II.

To give the first fundamental laws of logical thought; to establish the concepts of matter, form, substance, force, motion, time, space, active and potential action; to construct a series of basic laws to which all natural phenomena are reduced; and finally to give a theory of the structure of the universe, of its motions, of its origin and its future—all this was the creation of one of the greatest minds that humanity has seen up to the present day: Aristotle, who lived two thousand years ago.

The power of this doctrine explains the enormous influence it had on the further study of nature. Indeed, all the endless treatises, doctrines, debates, and trials ending in the burning at the stake of those who denied Aristotle’s principles, the whole distinctive cultural life of the Middle Ages, had as their chief center Aristotle’s teaching. A whole series of fundamental questions were posed by Aristotle: these questions, in their generality and significance, are so important that they have remained to this day the cornerstones on which our entire scientific worldview is built.

The first question concerns the existence of absolute laws of nature.

When we observe some phenomenon and try to derive the laws according to which it proceeds, we are observing this phenomenon under certain conditions—for example, on the earth—and we ask whether the laws we derive are not relative, so that, if we were transferred to other conditions, we would obtain different laws. Thus, for instance, can we consider that natural phenomena obey one and the same laws on the earth, on Jupiter, on the Sun, and on some star, say Sirius?

Aristotle answers this question in the affirmative. The same affirmative answer to it was given by all scholars and philosophers up to the present time. And this question seemed not to present any particular difficulties. The universality of the laws of motion, attraction, heat, electricity, magnetism, and the radiation of bodies is recognized by all, as the basis that makes it possible to create a coherent system of the structure and origin of the world.

However, upon a more careful analysis of this question, one very serious difficulty arose. We know that light propagates at a definite speed, equal to three hundred thousand kilometers per second, so that it would circle the earth in \(1/8\) of a second; from the sun to the earth light travels in eight minutes; from the nearest stars it reaches us in several years, and from more distant stars in several thousand

is; and from the recently discovered enormous spiral nebulae, which constitute an entire system of universes, it is several million years.

But this speed of light was determined on the earth, and the earth itself moves around the sun at a speed of 30 kilometers per second. At first glance this speed is very small in comparison with the speed of light, but the methods of astronomy and physics are so precise that they require taking into account even such comparatively slow motions. One therefore asks whether the speed of light which we measure on the earth is not a relative quantity, i.e. one dependent on the speed of the earth’s motion. Very careful experiments on the speed of propagation of light on the earth, both parallel to the earth’s motion and perpendicular to that direction, have shown that the speed of light is exactly the same in all cases; this is the essence of the famous experiments of Michelson and Morley; these attempts were begun as early as 1881 and were carried out under various conditions until 1905.

Thus experience has shown that the speed of propagation of light in a vacuum is an absolutely constant quantity; that is, under whatever conditions we measure it, whether on a moving object or on an immobile one, we shall always find one and the same value. Let us imagine, for example, that from the Ivan the Great Bell Tower in Moscow a light signal is given, and all people located at some distance are told to note the moment when it reaches them. The question is: how will all those people who simultaneously see the given signal be situated with respect to the Ivan the Great Bell Tower? Since the earth moves around the sun at a speed of 30 km per second; besides that, it rotates about its axis at a speed of almost half a kilometer per second, it would therefore seem obvious that those people who are carried by the earth toward the signal coming to them will see it earlier than those who are carried by the earth in the same direction as the light ray sent from Ivan the Great.

However, it turns out that all those whom the light signal reaches simultaneously will be located on a circle whose center will be the Ivan the Great Bell Tower. In this result we sense something incomprehensible, contradicting our ordinary logical thinking. For when an express train, traveling at a speed of 90 versts per hour, overtakes a passenger train traveling at a speed of 50 versts, it seems to the people sitting in the passenger train that the express overtaking them is moving at a speed equal to 90 minus 50, i.e. 40 versts per hour; this constitutes the essence of the principle of relativity of motion, which was introduced by Galileo and which is obvious to everyone.

But if we are riding in a train, or rushing along in an aeroplane, or in a ядро, at any speed whatsoever, and a light signal is sent after us in pursuit, then it overtakes us, and its speed relative to us is co-

exactly the same as if we were not moving. Even if we were traveling 290 thousand kilometers per second and a beam of light were sent after us, it would overtake us, since its speed is equal to 300 thousand kilometers per second; and it would seem to us that the speed of the beam of light relative to us is not 300—290, i.e. 10 thousand kilometers per second, as the principle of the relativity of motions requires, but that this beam travels with the same speed as it would if we were not moving.

There is some contradiction here.

III.

According to the principle, already accepted by Aristotle and underlying all doctrines up to the present time, the laws of nature have the same significance regardless of the conditions under which they are observed; thus, on the one hand, the law of the relativity of velocities, derived by Galileo for motion, and, on the other hand, the law of the constancy of the speed of light, constitute quite general laws of nature; and it turns out that between these two fundamental laws there exists a contradiction. What, then, is the matter here? How are these two laws to be reconciled with one another? This is the problem that arose at the beginning of the twentieth century and that has now received a perfectly rigorous and unshakable solution, representing a scientific investigation as beautiful and harmonious as the finest works of classical art.

To resolve this question we shall again turn to Aristotle. Aristotle devotes a large part of his physics to clarifying the concepts of time, space, and motion. He shows that these three concepts are interconnected. We judge motion by time and, conversely, reduce time to some motion; likewise, in order to judge space, for example the length of some line, we make use either of motion or note the position occupied simultaneously by both ends of this line, i.e. we subordinate space either to motion, which occupies a certain time, or to the concept of the simultaneity of two events. But if we determine time by motion, then the question arises whether the measurement of time will depend on the state of more or less rapid motion. And to this fundamental question Aristotle answers in detail that “for motions occurring simultaneously, time is measured in the same way, independently of the velocities of these motions, even if one body is at rest and another is moving.”

This fundamental principle—that the duration of any phenomenon does not depend on the state of rest or motion of the body on which it is observed—

This motion, was made the foundation by all teachings from Aristotle, Galileo, Descartes, Newton down to modern scholars—Helmholtz, Kelvin, Poincaré, and others.

Upon it rested all mechanics and the entire conception of the laws of nature. This was regarded as the most general principle of the worldview.

Thus we have three principles: the constancy of the measurement of time, the relativity of velocities, and the constancy of the speed of light. We saw above that if one accepts the independence of the measurement of time from the state of motion of bodies, then a contradiction arises between the principle of the relativity of velocities and the constancy of the speed of light.

It is asked: is the constancy of time really an obligatory principle, or can one renounce it and thereby reconcile the relativity of velocities with the constancy of the speed of light? Such is the first question that was posed by the famous German physicist Einstein in 1905, when he was barely 28 years old. He resolutely declared that we must renounce the principle of the constancy of time and replace it with a more general one, namely the principle of the relativity of time itself.

Since all phenomena of nature proceed in time, this change entails a revision of absolutely all the laws of nature and leads to the construction of an entirely new worldview.

The necessity of applying the principle of relativity to time follows directly from strictly logical reasoning. Indeed, let us imagine that we have a long train of one hundred cars, moving very rapidly along a railway track; in what way could we establish precisely that some phenomenon occurs simultaneously in the first and in the last car?

The most exact method consists in having this phenomenon produce an optical signal, for example a bright spark, both in the first and in the hundredth car, and in our observing these signals while located in the middle of the train; then we shall say that both phenomena occurred simultaneously if, at the middle of the train, we receive simultaneously the rays of light from the first and from the last car. But an entirely different conclusion concerning the simultaneity of these two phenomena will be drawn by an observer standing motionless on the railway track, exactly opposite the middle of the train, at the moment when the signals are given in the first and last cars. To this observer the spark in the first car will appear to flash later than the spark in the hundredth car. Indeed, the observer located in the train is moving toward the ray of light coming from the first car; he therefore sees it somewhat earlier than does the observer at rest on the railway track.

Thus, two phenomena occurring in different places will be considered either simultaneous, or the first as preceding the second,

or conversely, depending on the state of motion or rest of the observer or of the recording instrument.

Consequently, when we say of some phenomenon taking place far from us that it occurs at such-and-such a moment, this determination of time depends on the state of motion or rest both of the observer and of the body on which this phenomenon occurs.

The measurement of time is thus a relative quantity. And since the distance between two points is directly connected with the measurement of time, it is evident that the measurement of length will also depend on the state of rest or motion. Thus, for example, if someone traveling in a train compares the length of some ruler lying on the railway track, he will find that his ruler is shorter than the stationary one.

It is easy, for example, to calculate that if an observer moves with a speed equal to 135 thousand kilometers per second, then a ruler one meter long will, for him, in comparison with a stationary ruler, be equal to 90 centimeters, and his clock will show 60 seconds while the stationary clock shows 67 seconds. Another, more vivid example may be furnished by Jules Verne’s shell. Let us imagine that a shell containing a man has been fired from a gigantic cannon, and that the speed of the shell’s flight is slightly less than the speed of light and is equal to 299990 kilometers per second; the man flies and after a year arrives at some star, from which he is sent back to earth. Again it seems to him that he is flying for a year; his clock, all his vital sensations, everything proceeds in such a way that it appears to him that his journey lasted two years. And yet, having returned to earth, he recognizes nothing, because during this time not two years have passed on earth, but two hundred years.

One involuntarily asks whether such results can have any real significance. Are there really cases in which the actual measurements of time and space change because a body is moving? Is this not merely an abstract doctrine, constructed only in order to reconcile two principles with one another?

We can answer with certainty that these new views of space and time not only have enormous significance for explaining various phenomena of nature, but have made it possible to predict a whole series of new phenomena and have given the possibility of constructing a harmonious system of the world in which the number of laws is reduced to a minimum.

IV.

In his physics, Aristotle, for the study of the motion of bodies, gives a series of principles which formed the foundations of all the mechanics of the Middle Ages.

for centuries, to deny which was considered a heresy persecuted by the Church. Here are the chief of these laws: a body moves only when a force acts upon it; under the influence of a constant force a body moves with constant velocity; if any force is applied to a given body, it will cause the body to move only if the magnitude of this force exceeds a certain minimum; bodies fall with different velocities, depending on their weight; a vacuum is impossible, because in a vacuum bodies would fall with infinite velocity. It is clear to us what incredible efforts it cost Galileo, Descartes, Newton, and others to overthrow all these principles, on which generations had been brought up and on which all the scientific thinking of their contemporaries was built. Indeed, Giordano Bruno, who gave lectures in Paris in which he protested against the principles of Aristotle, was burned at the stake in Rome in 1600; Galileo narrowly escaped the same fate; Descartes prudently remained in Holland and did not dare publish his treatise on the world.

Galileo’s principle of inertia, according to which a body not subjected to the influence of external forces continues to move rectilinearly with constant velocity; the uniformly accelerated motion under the influence of a constant force proved by Galileo; the setting in motion of a given body under the influence of any force, however weak it may be; the equal velocity of fall of all bodies, independent of their weight; the realization of empty space and, finally, the discovery of the attraction of bodies—all these conquests of seventeenth-century science led to an entirely new worldview, which found its fullest and most universal form in Newton’s teaching.

And now we are again experiencing a new crisis in all the sciences. One of the fundamental quantities on which all mechanics is built, namely the mass of some body, which until now was regarded as something immutable, turns out to be capable of undergoing changes under the influence of radiation on the one hand, and under the influence of motion on the other. And this change is not only a conclusion of the theory of relativity of time, but is a fact derived from direct experiments on the motion of the smallest particles of matter, called electrons, which are emitted by radioactive bodies, incandescent bodies, and especially by the Sun with very great velocity. These same particles, which the Sun sends us in enormous quantities, on entering the upper layers of the Earth’s atmosphere at a height of 100 versts, produce a strong luminescence of gases, which we observe in the form of the northern lights; they also cause electrical storms on Earth. The magnitude or mass of these particles can be measured, as can their velocity, and so it turns out that their mass changes with the velocity of motion. This change in quan—

qualitatively coincides with what Einstein’s theory of relativity predicts.

In connection with the mass of a body there is the force of attraction directly associated with it, as was shown by Newton, and we must therefore expect that the laws of motion of bodies under the influence of attraction will likewise depend on Einstein’s principle of relativity.

In this case the question is extraordinarily complex, since we are dealing with accelerated motions and the force of attraction varies with distance; thus, in order to approach the solution of this complex question, Einstein had to overcome an enormous mathematical difficulty, in which he extended the principle of relativity, applying it to all cases of motion under the influence of forces acting non-uniformly. Assuming that the speed of propagation of the force of attraction is equal to the speed of light, Einstein shows that in all cases—uniform, non-uniform, and even rotational motion—we must regard time, space, and mass as quantities depending on the velocity of motion. This strictly mathematical dependence introduces a correction into all the equations of celestial mechanics, i.e. it compels astronomers to revise all their calculations concerning the motion of heavenly bodies.

One case was recalculated by Einstein himself: the motion of the smallest planet, Mercury. According to Einstein’s theory, this motion takes place along an elliptical orbit which, in turn, rotates around the Sun while remaining in the same plane. This peculiarity had long been noticed, and all astronomers, beginning with Leverrier, diligently sought an explanation for this complex motion of Mercury; however, it is not only qualitatively explained by Einstein’s theory, but even agrees quantitatively with exactness: indeed, the calculated displacement of Mercury’s perihelion is 42.9 seconds per century, whereas the observed value is 43 seconds.

Thus, the mass of every body depends on the state of its motion; on the other hand, we know that the kinetic energy of a moving body is equal to the product of half its mass and the square of its velocity; consequently, we can easily imagine that mass in general is the expression of a certain energy, which changes when the body moves. Any radiation, visible or invisible, represents a certain loss of energy; consequently, Einstein’s principle of relativity tells us that the mass of some body emitting thermal, visible, or ultraviolet rays decreases. If, therefore, we suppose that at some remote time various elements—nitrogen, oxygen, copper, lead, gold, and so on—were formed from compounds of elementary atoms of hydrogen and helium, then since that time there has occurred

the constant emission of energy, and the mass of these elements should have decreased; that is why the atomic weights of different elements are not exactly equal to whole numbers. From the atomic weight we can learn the history of the origin of the elements.

This hypothesis of the origin of the elements, constructed by the celebrated French physicist Langevin, has this year received remarkable confirmation in the experiments of the English physicist Rutherford, who succeeded in showing that, under the influence of α-rays, nitrogen decomposes and releases hydrogen.

The development of the theory of gravitation, founded on the principle of relativity, led Einstein to the result that light, which is one of the forms of energy, when propagating near some mass, does not travel in a straight line but describes a certain curve, so that the principle of the rectilinear propagation of light must also be rejected and replaced by a more general one. This result could be tested by observations during the solar eclipse of May 29, 1919. As early as 1914 Einstein had derived from his theory that, if during a solar eclipse one observes stars lying behind the sun (so that their ray passes very close to the sun), then the apparent position of these stars will be shifted because the ray, passing by such a large body as the sun, will be attracted by it and therefore will describe a certain curve. It was proposed to send an expedition to observe the solar eclipse in August 1914. But the war stopped everything, and only on May 29, 1919 was it possible to carry out the measurements. Two expeditions were organized by English astronomers from Greenwich and Cambridge: one to northern Brazil, to Sobral, the other to the island of Principe, off the coast of Africa in the Gulf of Guinea. The eclipse was very favorable for such measurements, since the region of the sky lying behind the sun was very rich in stars—there were about twenty of them, situated around the very disk of the sun. The photographs showed the existence of a deflection of rays in passing by the sun; this deflection was, for the observations in Brazil, 1.98 seconds, and on the island of Principe, 1.6 seconds, which gives an average deflection of 1.79 seconds, i.e. a number that coincides quite exactly with the deflection calculated by Einstein.

Thus the principle of the relativity of time made it possible, as a result of a rigorous logical construction, to predict the existence of an entirely new general phenomenon and thereby to connect Newton’s force of attraction of bodies with light, and consequently with electricity and magnetism.

Until now the force of attraction had stood entirely apart, and in constructing the laws of nature it had been necessary to treat separately the laws of mechanics and astronomy, the laws of heat, and finally the laws.

chemical transformations; now, thanks to the all-embracing, generalizing principle of relativity, it has become possible to connect mass with energy, light with attraction, heat with light, so that it becomes possible to build one general system encompassing all the phenomena of nature and subordinating them to several fundamental universal laws.

The beauty of such a construction is so great that our spiritual life finds in it such enormous delight and satisfaction that this gives strength and faith for the struggle against all adversities and compels us to be optimists, since creative work leads to happiness, while criticism and destruction lead to pessimism.

But what has been done from this vast system of the world? We are at the beginning of an enormous movement and development. We have been given new methods, we have been given proofs of the solidity of the foundations on which, in all directions, each in his own specialty, we can build the edifice of science.

The study of the phenomena of radioactivity led to the conclusion of the unity of matter. Spectral analysis and the study of Roentgen rays made it possible to provide a very complete theory of the structure of atoms, and the application of the theory of relativity to the motions occurring within atoms made it possible to predict quantitatively a whole series of features of the spectrum of the elements. The application of new methods of optics made it possible to observe directly the motions of molecules, to determine their number and magnitude. The laws of statistics, as applied to physical and chemical phenomena, made it possible to connect the phenomenon of heat with light and led to the fundamental conclusion that, just as matter consists of the smallest particles called atoms and electrons, so energy too must be regarded as consisting of small elementary particles called quanta. The application of the principle of relativity in its general modern form to the study of the heat released by chemical reactions shows that this heat depends on the force of attraction, so that, for example, one and the same reaction releases more heat on the sun than on the earth. In the field of biology, no less important paths are opening before the investigator: the laws of the evolution of organisms are being replaced by the laws of mutations, i.e., leaps. The development of cells and tissues can occur outside the organism; for example, if one takes a tiny piece of a chick’s heart and places it in a certain liquid, it grows, gives off fibers, and begins to contract. Irritation of the nerves, and in particular our vision, can be precisely reduced to purely physico-chemical processes and calculated in advance. In general, we are penetrating more and more deeply into the understanding of the laws of the world, and before us opens a glorious future, when the harmony of all fields will be achieved.

In this cooperative work Russian scientists have played a very great role.

guiding role; Lebedev, Mendeleev, Lyapunov, and Mechnikov—these are four great creators who laid the foundations of physics, chemistry, celestial mechanics, and biology, on which the scientists of the whole world rely.

And we know that nothing and no one can crush or halt scientific creativity and genius, since it believes in the great ethical significance of the search for truth.

Paris. January 1920.