CHAPTER III

_Time in Astronomy and Physics_

The real discrepancy between the world of physics and that of life lies in the fact that physics has never recognized the irreversibility of time, while this is fundamental to life. We may even feel a doubt if the ‘t’ of physics has the same significance as the time of biology, evolution, history, and human experience. The physical conception of time arose from the practical utility of clocks for describing natural processes, and finally took the form of defining astronomical time in terms of the rotation of the earth. The day was in fact taken as an absolute measure of time, and this remained quite satisfactory so long as the laws of physics were found to take a simple form with reference to the time so defined.

But then a complication arose. The study of the moon’s motion suggested to astronomers that the earth’s rotation was slowing down, i.e. to account for the apparent motion of the moon they had to assume that the day was increasing in length. The theory of the tides revealed a possible cause for this slowing down in the tidal friction on the bottom of shallow water basins, for instance the rush of the Atlantic tides into the Irish Sea provides an appreciable frictional force retarding the spin of the earth. In addition to this slowing down there appears to be a very slow periodic variation in the length of the day such as would be accounted for by a rhythmic expansion and contraction of the earth’s crust.

The astronomers declare that our old measure of time is not only getting slower and slower, it is even varying rhythmically! It is clear that they have thrown over the earth as their definition of equal time intervals and have surreptitiously substituted something else. Yet one cannot discover any formal announcement of this, or find out if they realize that by doing this they have altered the theoretical significance of all physical measurements. In earlier days physics defined time in terms of a selected clock, and then set about finding the laws of nature. But the old ways aren’t good enough for the modern astronomer who gives us our time and sets the clocks of our physical laboratories. He has reasons for disapproving of the earth, and has almost reversed the procedure. In order to save the laws of inertia and gravitation in connection with the moon’s motion--and to a lesser degree in the cases of the planets and the sun--he has made these laws his standard of equal time intervals in place of the earth’s rotation.

It is a curious situation, especially in view of the fact that Einstein’s law, which has superseded Newton’s, is not very suitable for use as an astronomical clock, as has been pointed out by Larmor. Perhaps the physicist will soon be able to use the atom as the theoretical clock for physics, and we can go on using the corrected rotation of the earth as our practical standard. There is a faint chance, for instance, that if physics can invent some way of measuring the minute time intervals along the track of an electron, then electrons might be used as giving the fundamental measure of time. Thus if the velocity of an electron were first measured by some indirect method the electron itself might then be used as a clock. But in the meantime the astronomers should make a formal announcement to the Royal Society of what they have been up to. It then might be found necessary to appoint a commission to discover exactly what physics is now doing. For by using an astronomical clock of the new type it is assuming classical laws while researching on processes which are already known to undermine the absolute validity of these laws. Theoretical physics cannot hope to clear up its fundamental problems until it has considered exactly what is involved in this suspicious procedure.

Like most professions, physics includes a good deal of bluff, but unlike the others physics is now occupied on a campaign to get rid of all pretence. For instance, physical text-books have been filled for twenty years with phrases of this kind: “an electron with a velocity of so many cms per sec.” Yet the professors omitted to tell their students the awful secret that this hypothesis of electron velocities is one that has never yet received direct experimental confirmation. To-day a reaction has set in and the demand is being made that physical theory shall not make use of conceptions that do not correspond to directly observed quantities. Thus the latest theories of the atom have eliminated the idea of electron orbits because it was realized that these were nothing more than a mathematical trick for calculating something quite different: the wave-length of the light an atom can emit. In place of the orbits it is hoped to substitute something which only makes use of the directly-observed features of the atom, but this new picture is not complete.

Yet physics still makes use of ideas that have not been adequately justified. For though the idea of moving electrons has been removed from the latest atomic model, no substitute for it has yet been proposed for the case of electrons outside the atom. It therefore becomes very important for the experimental physicist to discover whether he can measure the distance travelled by an electron in a measured fraction of a second. As yet we have no proof that nature has not confused us by making electrons behave rather like moving particles, though really they are something different. In fact we have not yet made enough direct experiments to know even whether the dimensional system which is used for electrons is correct. Since no electron velocity has ever been directly measured we cannot be sure that the dimensions of the new constant ‘h’--called Planck’s constant--are really what we suppose, energy multiplied by time. Until a way has been invented of making a direct measurement of some _time_ involved in electronic motions, it is impossible for physical theory to know how it should deal with the quantum processes.

When we realize how uncertain are the conceptions on which the whole of electron theory is based, we may wonder what is really known about the atom itself. Yet it is possible that we know more about the atom than we think, and that what are talked about as facts concerning electrons and radiation may really be better viewed as information about individual atoms and the way in which they influence one another. The emission of light is an atomic process, and we only know about light when it has reached some atom and been at least partially absorbed. Some un-understood change of condition occurs in an atom when it radiates and passes this changed condition on to another atom. The absorbed energy may cause chemical change, as on a photographic plate. But if a human mind is to become aware of this change of condition, then sooner or later, directly or indirectly, its influence must be passed on to an atom in the retina. We know very little about this change of atomic condition, and though it is usually called a change of the internal electrical energy of the atom this supposes more than we really know until some electron velocity has been directly measured. The dimensions of electrical energy are taken as those of kinetic energy, i.e. mass times square of velocity, but we do not yet know if this describes atomic changes correctly. Since no one has ever measured a _time_ involved in an electronic process, the scale of time in the atom might be quite different from that given by our calculations.

Our ignorance of what this change of atomic condition really signifies is so profound that some writers have begun to treat the atom as though it were an organism, alive when the atom is excited, and dead when in a state of minimum energy. Thus Whitehead proposes that we should call the atom an organism, though this of course may only muddle us since we know even less about life than we do about the atom.

Yet we do know one very interesting thing about this change which happens to atoms but cannot be reduced to a change of structure. When light reaches an atom in the retina, an electrical stimulus passes up a nerve and alters the condition of the protoplasm somewhere in the brain. This change in brain condition is known to us directly as the perception of colour. Therefore in one sense we know more about this change of atomic condition than we ever did about ‘electric fields’ or ‘gravitational potential’ or any other of the mathematical conveniences used by physics in correlating observed quantities. The change in a sodium atom when we put salt in a flame is not a change in the consciousness of the sodium atom, because it is not part of a complex nervous system with the same high co-ordination as is found in the human being, and therefore the atom has no consciousness. But when an atom in the brain undergoes the same change we may become conscious of it, and the changes in matter which occur when light is absorbed are undoubtedly associated with the problem of consciousness.

Thus we are led to ask: how are single atoms built up into complex systems which have the characteristics of life, and finally into still more complex systems which have human consciousness?