Universe in the Red
I
AN acquaintance, whose experience with affairs gives him the lingo of business, described the shaky condition of a near-bankrupt as ‘deep in the red.’ I had forgotten this color scheme of accountancy, by which profits are recorded in black ink and losses in red. It gives a chromatic effect to bookkeeping. The Bank of the United States was ‘in the red’ — so it ‘folded up,’ to borrow another of my neighbor’s Wall Street terms. Ivar Kreuger was ‘in the red’ — so he ventured what Cato did and Addison approved. Great Britain was ‘in the red’ — so it went off the gold standard. ‘In the red’ becomes a label for depletion, debts, deficits. The history of the worldwide economic depression may be epitomized as a shifting of material values into the red.
Now, the strangest upturn in modern science — perhaps the deepest mystery of astronomy — is the recent discovery that the whole stellar universe is partaking of a persistent shifting into the red. In astrophysics, to be sure, the phrase has a different meaning technically from its meaning in finance; and yet, when these meanings are analyzed and interpreted, their implications are not far different. For just as the shifting of bookkeeping accounts into the red measures disintegrating, scattering, dissipating financial resources, so the shifting of starlight into the red indicates disintegrating, scattering, dissipating physical resources. It says that the universe is running down, the atomic clock is ticking off suns and planets along with its radioactive particles, matter is dispersing into space and dissipating into radiation, the stupendous pocketbook of the cosmos is emptying itself irrevocably, taking its cash and letting its credit go — at least, so it seems on the most probable hypothesis.
II
The physical world is complex, but for the purpose of this paper it may be viewed, I think, as consisting of two parts: (1) our own stellar system, the Galaxy or Milky Way, in which the sun is one speeding orb among millions, including all the stars that one can see with the unaided eye; and (2) the stellar systems outside our Galaxy, sometime known as the spiral nebulæ, or extragalactic nebulæ, or ‘island universes.’ Originally these outside objects were thought to be clouds of accumulated star dust and so were called nebulæ; but as telescopes of greater power were built and turned on the nearer of them, the clouds were resolved into individual stars, and it was seen that a spiral nebula is a counterpart of the Milky Way. From this we infer that our Milky Way is also a spiral nebula, gigantic, perhaps larger than any of the outside systems, but still of their nature and form — a vast whirling pinwheel of stars.
A few years ago Dr. V. M. Slipher, of the Lowell Observatory in Arizona, began a study of these outside galaxies. The only way he could make such a study was by observing or photographing their light — for, except for a few sporadic high-speed meteorites, all that we know of the world outside the solar system comes by the grace of light. Stars have been weighed, their diameters measured, their density felt, their temperature taken, their chemical elements identified, their age determined, their distances, motions, and velocities recorded; all these and even more intimate details have been ascertained by means of that delicate, fragile, feeble medium — the vibrant light of a star.
When starlight is spread out into its spectrum, or rainbow pattern, thousands of parallel lines are seen crossing the bands of color. They are the identifying marks of the elements burning in the star. There are certain lines which mean iron, hundreds of them; other lines mean hydrogen; and so with all of the sixty chemical elements that have been sighted in that nearest of the stars, the sun: each element has its telltale lines arranged in immutable series, as individual as thumb prints. Though more than 20,000 spectral lines have been found, each has its fixed position relative to the other lines, some in the violet band, some in the blue, some in the green, some in the yellow, and some in the red.
Dr. Slipher, in his study of the outside galaxies, discovered that almost all of them showed a shifting of their lines toward the red end of the spectrum. Out of forty-one galaxies examined, he found only five in which the lines were not displaced in that direction.
Beginning about 1928, Dr. Edwin Hubble, of Mount Wilson Observatory, took up a similar study, and with the aid of the great 100-inch telescope was able to penetrate deeper into space and to obtain spectra of even more remote galaxies. By the spring of 1932, Dr. Hubble and his associate, Dr. Milton L. Humason, had photographed fortyeight other galaxies; and they found precisely what Dr. Slipher had discovered: that, almost all of these faint far-away patches of starlight showed their spectral lines shifted predominantly toward the red.
Pondering this strange one-sidedness of extragalactic light, Dr. Hubble noticed another point. He found that when he listed the galaxies in a series according to the extent of their shift, beginning with the one which showed the least displacement, going on to the one next in order of displacement, and so on, until he had put at the bottom of his list the object showing the largest shift — he found that his list also corresponded to the order of distance of the galaxies. In other words, the nearer objects showed the slighter shift toward the red, the farthest showed the greatest shift. Observations on even more distant objects during the last year have confirmed the conclusion, and the relationship is now generally accepted as a fact.
This, then, is how the matter stands at the end of 1932: —
A total of ninety-one outside galaxies has been observed and photographed.
Of these, eighty-four show unmistakably their lines shifted toward the red.
Of the remaining seven, two show an opposite shift so slight that the probable error of measurement exceeds the degree of their apparent displacement — which therefore may be toward, rather than away from, the red.
Of the eighty-four, all whose distances it has been possible to approximate show the operation of that strange relationship found by Hubble — the more remote the galaxy, the more pronounced is the lurch of its light toward the red. Curious!
‘Curiouser and curiouser!’ cried Alice, when she found herself shifting up, up, up, away from her feet, opening out like the largest telescope that ever was. ‘Good-bye, feet!’ For when she looked down at her feet they seemed to be almost out of sight, they were getting so far off. ... ‘Oh dear, what nonsense I’m talking!’ Just at this moment her head struck against the roof of the hall.
None of the astrophysical heads has yet bumped the roof—but what is happening Out There in the deep abyss of space is ‘curiouser’ and more ‘nonsensical ’ than anything ever gasped at down in the rabbit hole.
III
Three explanations have been proposed to account for this strange propensity of extragalactic light for the red. The cause lies in the lengthening of the wave length, for red rays represent the vibrations of lowest frequency and longest wave length. The length of a red ray’s wave is about double that of a violet ray’s, and theoretically it is possible to change blue light into red by decreasing its frequency. But by what alchemy is this transmutation wrought in the long journey through space? What are the agencies that may operate to lengthen the wave in a degree strictly proportionate to the number of millions of years that the ray has traveled?
Dr. F. Zwicky, of the California Institute of Technology, says it is a gravitational drag that causes the shift. As light vibrates through space it passes innumerable particles of matter, random atoms, wandering electrons, the tenuous débris of stars. Collision with one of these particles absorbs or deflects the light; but, even if they do not collide, the gravitational attraction between the particle of matter and the photon, or particle of light, subtracts something of the photon’s momentum and energy, and thereby decreases its frequency. Obviously, the farther the ray of light travels, the more particles it must pass and the more times it will be preyed upon by these gravitational forces. Professor Zwicky has computed the probable effect from the estimated density of space, and arrives at a value approximately in agreement with Hubble’s observations of the shift-distance relationship.
Dr. W. D. MacMillan, of the University of Chicago, offers a different hypothesis in a communication to the British weekly, Nature. His idea is that the photon loses energy in its long journey of millions of years — a loss attributable, not to collisions with matter, but to collisions with other photons or perhaps to the inherent instability of the particle of light. On this hypothesis, light ceases to be the dependable, inviolable messenger that physics has long taken it to be, and becomes a chameleon changing its hue progressively with the operation of time and by virtue of its shifting nature.
Both of these suggested explanations involve a re-inventory of many of the data of astrophysics. One of the urgent practical problems of pure science is to determine the degree to which space is transparent and light immutable. It is well known that certain patches of the sky — such as the Coalsack in the region of the Southern Cross, for example — are closed to our inquiry by reason of dense concentrations of dark matter. It is also known that a cloud, in which calcium atoms predominate, seems to permeate interstellar space. Dr. Harlan T. Stetson tells me that one of the tasks to which he will put the great 69-inch telescope of Perkins Observatory, in Ohio, this year, will be this problem of the interstellar cloud. He will seek to measure more precisely than has yet been done the extent, distribution, and nature of the diffuse matter. When that survey is completed (and it will take many years and the coöperation of many observers), we may be able to calculate more accurately than is possible to-day the degree to which starlight is absorbed, dragged upon, pulled out of its original path and pattern, slowed into lower frequencies, evaporated, and distorted by reason of its journey through time and space.
The third hypothesis offered to explain the redward trend of extragalactic light involves paradoxes inexplicable. Indeed, this explanation seems to dictate an entirely new world picture — upsetting in its drastic curtailment of the time scale, and breath-taking in its dramatic portrayal of a universe unstable, in flight, in dispersal.
This hypothesis is based on a wellknown physical effect which any passing locomotive whistle will demonstrate. As the locomotive approaches, we hear the whistle at a higher screech than that of the sound waves emitted at its mouth. This is because the speed of the oncoming locomotive crowds the sound waves upon one another, shortening their wave length; the ear receives more waves per second than it would from a stationary whistle. As the locomotive passes, its speed of recession has the opposite effect: the sound waves are dragged into longer wave lengths, and the pitch drops to a low bass.
Exactly the same process operates with light. A star that is approaching at a speed of many miles a second presses its light waves upon one another; they are thereby shortened, shifted toward the soprano end of the spectrum — the violet. A receding star pulls its waves out, lengthens them, and the pitch of its light takes on a bass note — that is, it shifts toward the red. This optical phenomenon, called, from the name of its discoverer, the Doppler effect, has long been known and used in astronomy. By measuring the direction and extent of the line shift in the spectrum, the rotation of the sun on its axis has been measured, the varying rotations of Saturn’s rings, the approach of oncoming stars like Vega, and the recession of departing stars.
The effect has been checked and rechecked in numerous observations within the solar system and on the nearer stars, and there is no speedometer better accredited and more confidently used by the astronomer. Yet, when Drs. Slipher, Hubble, and Humason first announced their measurements of the red shift in the distant galaxies, the tendency was to account for the phenomenon on grounds other than that of the Doppler effect. It was suggested that the red shift in these spectra was a relativity effect, an apparent crumpling of space, the result of some mysterious process operating out in the great curve of the universe to slow down the atomic clock. No one in authority came out boldly and announced that the outside galaxies were actually receding, as the Doppler effect would indicate them to be.
Why? Well, for one thing, because it seemed incredible that the bodies could be moving outward with such unanimity. According to the generally accepted theory of relativity, space is finite, the universe is a sphere of fixed radius. To entertain this preposterous idea of all these massive star systems racing outward was to accept a radically new picture of the cosmos — a universe in expansion, a vast bubble blowing, distending, scattering, thinning out into gossamer, losing itself. The snug, tight, stable world of Einstein had room for no such flights. To accept this astronomical bolshevism meant scrapping the accepted time scale, scrapping the whole concept of stability on which both Einstein and De Sitter had built their beautifully reasoned cosmologies.
And yet, this is precisely what many of the deep thinkers in science have done. They have come to the conclusion that the evidence cannot be sidetracked into a special interpretation, that the red shift of extragalactic light means what the red shift of sunlight means — namely, a motion of recession on the part of the light source. Such a conception, carried to the development which it has received at the hands of Sir Arthur Eddington, portrays this outward flight of the galaxies — our Milky Way included — as a perpetual process. ‘About every 1500 million years it [the universe] will double its radius, and its size will go on expanding in this way in geometrical progression forever.’
An eternally exploding universe? . . .
IV
The distinction of being the first to work out an acceptable model of the universe accounting for this runaway flight of the galaxies rests on a young priest of the Roman Catholic Church, the Abbé George Henry Joseph Edward Lemaître, of the University of Louvain. In the fall of 1924 he arrived in Cardinal O’Connell’s archdiocese of Boston, crossed the river to Cambridge, and called at the Harvard College Observatory, where he had arranged to have access to its voluminous store of astronomical data. A room was assigned him in the west wing of the old building, and for some months he labored here with pencil and paper, working out complicated equations. At intervals he had a conference with Dr. Shapley, but for the most part his work at the Observatory was pursued in solitude. Certain studies in physics were also made at the near-by Massachusetts Institute of Technology. Leaving Cambridge in February 1925, Lemaître visited observatories on the Pacific coast. He returned to Belgium, and two years later published a paper in the Annals of the Scientific Society of Brussels. The title of this paper advertised the revolutionary content of its subject matter: ‘A Homogeneous Universe of Constant Mass and Increasing Radius accounting for the Radial Velocity of Extragalactic Nebulæ,’ but no one seems to have noticed it. At that time, in 1927, the red shift had not yet become a matter of serious concern in astronomical meetings, and Lemaître’s paper was soon buried in the continually growing mountain heap of relativity literature.
But by 1930 the subject was dominant. Wherever two or three astronomers were gathered together, their talk was almost certain to drift around to the findings of Slipher, Hubble, and Humason. Eddington, speaking at the May meeting of the Royal Astronomical Society that year, publicly expressed his belief that the red shift was evidence of the expansion of the universe — and at the same time called attention to the need of a mathematical solution which would account for the phenomenon. Then it was that Lemaître’s unknown paper was called to his attention — by Lemaître himself.
Lemaître was formerly a student under Eddington, and doubtless there was more than intellectual satisfaction in the Cambridge professor’s reading of this treatise of his young disciple. Immediately he ‘recognized the elegance and completeness of Lemaître’s work,’ and called De Sitter’s attention to it. They heralded it to others. The Royal Astronomical Society translated the paper into English and gave it circulation in the Society’s Monthly Notices.
Thus was a new world concept brought forward — to devastate many accepted notions of time and space, and to electrify the interest of the entire astronomical fraternity. To-day the Belgian’s bubble universe holds the centre of the cosmological stage.
V
If we accept Lemaître’s world as real, we must admit some amazing speed contrasts. Thus, in the constellation Hunting Dogs is the famous Whirlpool nebula, first of the spirals to be identified. It is a comparatively near neighbor, since its light takes only about two million years to reach us. The red shift clocks its speed as relatively slow, only 175 miles a second.
The most remote objects yet measured are two faint galaxies discovered at Mount Wilson in January 1932. They are 135 million light years distant; and, according to the red shift, they are outward bound at the rate of 15,000 miles a second.
Between these extremes the record shows a wide range of velocities, and in every instance the velocity increases as the remoteness of the object increases. From the full data Dr. Hubble computes that for every million light years of distance the rate of recession increases about 100 miles a second. If this relationship holds throughout time and space, it provides a basis for estimating the size and age of the universe — since we can reckon back from their present velocities the time that has elapsed since the galaxies left their starting point.
What was the starting point? The speculations are many. Lemaître has suggested that the beginning may have been a single quantum, a unique atom into which was packed all the mass of the universe, and its present state represents a development of that first unit.
Another suggestion is that the universe may have begun large and then shrunk to smaller size, from which it is now expanding. Dr. R. C. Tolman, of the California Institute of Technology, is the author of an oscillating model in which the universe performs a succession of alternate expansions and contractions of increasing amplitude without ever reaching the cold death which certain other cosmologists predict as inevitable.
De Sitter estimates that the original radius of the universe was 1000 million light years, and the present radius 3000 million light years, though, he adds, ‘ it may be much larger.’ If, as Eddington says, it doubles in size every 1500 million years, then it would seem (using De Sitter’s figures) that the age of the universe is of the order of a little more than 2000 million years — which is preposterously brief.
For where is there time — in 2000 million years or in ten or even fifty times that scale — for the stars to evolve, the planets to form, the earth to cool, and life to emerge?
The earth itself is at least 2000 million years old, according to the testimony of the radioactive rocks. The sun must have been in existence millions of millions of years before there occurred that supposed encounter with a passing star which caused (we believe) the solar disruptions that eventually hardened into planets and moons. An old star like the sun or Alpha Centauri must be at least 70 million million years old, according to astrophysical data; even a young star like Betelgeuse is rated as around a million million years old.
The intrinsic evidence of the stars, says Sir James Jeans, makes it ‘very difficult to believe that the universe can be such an ephemeral concern as the apparent speeds of recession of the nebulae would suggest.’
Eddington attacked the problem by a different approach. He computed from atomic theory, from the wave equation of the electron, what the rate of cosmic expansion should be. He arrived at a figure not far from that observed by Hubble — a confirmation of observation by theory that seems significant.
Dr. Harlow Shapley suggests that final interpretation of the red shift may have to await t he development of new means of research. ‘Man may need to invent a new set of mathematical tools and a new system of mechanics before he can grasp the strange seeming paradox of a universe in expansion. So far as our present tools permit us to measure distances and so far as our present census of the metagalaxy goes, the total number of star systems and the radius of space may both be infinite.’
VI
We are building a 200-inch telescope, and when that is attained we shall probably build a larger. Can we not eventually, if we build an eye big enough, see the whole breadth of space?
No, answers Abbé Lemaître, for, as telescopes probe deeper, the light from the yet more distant galaxies will be shifted farther into the red, until finally the rays disappear in the infrared to which eyes and photographic plates are insensitive. Thus, ‘the largest part of the universe is forever out of our reach,’ concludes the Abbé. For us it is already ‘Good-bye, feet!’ and probably ‘Good-bye, knees.’ We can never hope to see around the vast growing curve of our bubble, because the light with which we see will have degenerated into invisible rays before it reaches us.
A weird world: a world in which the parts seem older than the whole which produced them, in which the child outdates its parent, in which repulsion overrules the familiar laws of attraction. But the testimony of the most ponderous physical bodies that exist seems to say that the picture is a true one — that the universe in the red truly signifies the universe in disruption.
Fleeting, evanescent, evaporating into light, which in turn is fading into invisibility — that is our solid physical world of suns, and planets, and skyscrapers, and gold, and flesh. ‘Look upon the world as a bubble,’ said Buddha, ‘look upon it as a mirage: the king of death does not see him who thus looks down upon the world.’