Edwin Hubble... and the myth that he discovered an expanding universe
By Vincent Sauvé This supplementary essay is for those who may be asking if Edwin Hubble was consistent in his work. On my main page I cited a quote from Hubble that is at odds with the myth that Hubble discovered an expanding universe. To my knowledge, Hubble’s major contribution was the discovery of Cepheid variables in nearby galaxies, “thus demonstrating to the satisfaction of almost all astronomers the extra galactic nature of the spirals,” so writes Robert W. Smith, author of The Expanding Universe: Astronomy’s ‘Great Debate’ 1900-1931, (Cambridge University Press, 1982), who also informs us in his “The Origins of the Velocity-Distance Relation” (Science History Publications, 1979):
We shall argue that Hubble did not claim that he had found a linear velocity-distance relation, since he was unsure of the cause of a galaxy’s redshift. Also, Hubble, as he himself acknowledged, was working within a well-defined problem area, and before 1929 other astronomers had considered the existence of a redshift-distance relation. Hubble’s success was not to “discover” a relation; rather, it was to convince his colleagues that the relation was linear.
Most of todays’ astronomers/cosmologists have ignored and/or abandoned Hubble. This indicates that Hubble has not succeeded. For Hubble found that the observational data best fit a linear relation between redshift and distance. But to Hubble a linear relation did not mean an expanding universe. Before I explain the above statement further, let’s take a look at how Hubble considered the interpretation of redshifts as being velocity-shifts. From The Realm of the Nebulae, (In the early 20th century galaxies were referred to as nebulae.):
This explanation interprets red-shifts as Doppler effects, that is to say, as velocity-shifts, indicating actual motion of recession. It may be stated with some confidence that red-shifts are velocity-shifts or else they represent some hitherto unrecognized principle in physics. [...]
Meanwhile, red-shifts may be expressed on a scale of velocities as a matter of convenience. They behave as velocity-shifts behave and they are very simply represented on the same familiar scale, regardless of the ultimate interpretation. The term “apparent velocity” may be used in carefully considered statements, and the adjective always implied where it is omitted in general usage. --pp. 122-123
Because it was known that receding motion in the line of sight will produce a redshift (a blueshift if approaching) and because no other satisfactory understanding was available of how a redshift might be produced, the popular interpretation was to view redshifts as Doppler effects. In Hubble’s paper, “The Problem of the Expanding Universe,” as well as in many other of his writings, one can see his reasons for skepticism regarding the Doppler interpretation for galactic redshifts. In the section “The Interpretation of the Red Shifts,” Hubble writes:
The investigations were designed to determine whether or not red shifts represent actual recession. In principle, the problem can be solved; a rapidly receding light source appears fainter than a similar but stationary source at the same momentary distance....
For velocities of a few miles or a few hundred miles per second, the dimming factor is negligible. But for the extremely distant nebulae, where the apparent recessions reach tens of thousands of miles per second, the effects are large enough to be readily observed and measured. Hence, if the distances of the nebulae were known quite accurately we could measure their apparent faintness and tell at once whether or not they are receding at the rates indicated by red shifts.
Unfortunately, the problem is not so simple. The only general criterion of great distances is the very apparent faintness of the nebulae which we wish to test. Therefore, the proposed test involves a vicious circle, and the dimming factor merely leads to an error in distance. However, a possible escape from the vicious circle is found in the following procedure. Since the intrinsic luminosities of nebulae are known, their apparent faintness furnishes two scales of distance, depending upon whether we assume the nebulae to be stationary or receding. If, then, we analyze our data, if we map the observable region, using first one scale and then the other, we may find that the wrong scale leads to contradictions or at least to grave difficulties. Such attempts have been made and one scale does lead to trouble. It is the scale which includes the dimming factors of recession, which assumes that the universe is expanding. --pp. 108-109.
As to the question I opened with: Yes, Hubble was consistent. He, I believe, would have strongly challenged as totally unfounded statements like this one by Allan R. Sandage (Sandage is said to have taken over the work of Hubble): “The expansion of the entire universe is the most important single hard scientific fact of cosmology” (from The Hammond Barnhart Dictionary of Science, Barnhart Books, 1986, under the word cosmology). This is particularly curious coming from someone who in his closing sentence in his introduction to Hubble’s The Realm of the Nebulae (Dover, 1958) writes: “Hubble’s original approach to observational cosmology remains." Yet, obviously it doesn't with astronomers like Allan Sandage. Hubble’s approach was one of caution, even skepticism, regarding the expanding universe idea. From the conclusion of Hubble’s “The Problem of the Expanding Universe”:
Thus the use of dimming corrections leads to a particular kind of universe, but one which most students are likely to reject as highly improbable. Furthermore, the strange features of this universe are merely the dimming corrections expressed in different terms. Omit the dimming factors, and the oddities vanish. We are left with the simple, even familiar concept of a sensibly infinite universe. All the difficulties are transferred to the interpretation of red shifts which cannot then be the familiar velocity shifts. [...]
Meanwhile, on the basis of the evidence now available, apparent discrepancies between theory and observation must be recognized. A choice is presented, as once before in the days of Copernicus, between a strangely small, finite universe and a sensibly infinite universe plus a new principle of nature.
It is not unusual to find astronomy and cosmology books that credit Hubble with the discovery of the expansion of the universe. As we now see this is inaccurate. Such talk doesn't square very well with Hubble’s repeated declarations that “for a stationary universe, the law of red shifts is sensibly linear." And “The results may be stated simply. If the nebulae are stationary, the law of red shifts is sensibly linear; red shifts are a constant multiple of distances. In other words, each unit of light path contributes the same amount of red shift." 1
It is frequently said that 1929 is the year Hubble discovered that our universe is expanding. Yet, six years later in the abstract of a paper he co-authored with Richard Tolman, they wrote that the data is “not yet sufficient to permit a decision between recessional or other causes for the red-shift." 2 To the best of my knowledge Hubble’s 1929 paper 3 is the only published paper where the reader is left with the view by Hubble, and now apparently universally adopted, that the linear law of redshifts applies only as a velocity-distance relation. It is no wonder that this is the paper that is usually cited by itself in astronomy textbooks. Big Bang critic, and radio astronomy pioneer Grote Reber desires to make it known that Hubble expressed “grave doubts about red shifts being caused by relative motion.” Reber asks us to see pages 2, 21, 26, 31, 43, 44, 54, 63 and 66 of Hubble’s 1937 book The Observational Approach to Cosmology. This book is excellent in showing Hubble’s doubts about redshifts being due to the Doppler effect. In a 1934 lecture with the title "Red-Shifts in the Spectra of Nebulae," Hubble writes:
The field is new, but it offers rather definite prospects not only of testing the form of the velocity-distance relation beyond the reach of the spectrograph, but even of critically testing the very interpretation of red-shifts as due to motion. With this possibility in view, the cautious observer refrains from committing himself to the present interpretation and prefers the colourless term “apparent velocity.” 4
The field was still young, but not so new by the time Hubble died in 1953, so perhaps Hubble dropped his doubts by then. Yet even in 1953, in his last lecture before he died, Hubble still treated the linear velocity-distance relation as an apparent velocity-distance relation. In his George Darwin Lecture of 1953 with the title “The Law of Red-Shifts,” a graph is provided showing a linear relation of several galaxy groups. On the bottom corner of the graph are the words “NO RECESSION FACTOR." In other words, if the dimming factor for recession of the galaxies is not used, the relation between redshift (usually expressed as velocity) and apparent magnitude will be linear. And in Hubble’s words from the same lecture: “When no recession factors are included, the law will represent approximately a linear relation between red-shifts and distance." 5
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1. Edwin Hubble, “The Problem of the Expanding Universe,” American Scientist, Vol. 30, No. 2, April 1942, (p.111), pp. 99-115.
2. Edwin Hubble and Richard Tolman, “Two Methods of Investigating the Nature of the Nebular Red-Shift,” Astro-Phys. J., 82:302-37, 1935. 3. Edwin Hubble, “A Relation Between Distance and Radial Velocity Among Extra-Galactic Nebulae,” Proc. N.A.S., Vol. 15, 1929, pp. 168-173. 4. Edwin Hubble, "Red-Shifts in the Spectra of Nebulae," being The Halley Lecture, delivered on 8 May 1934 (Oxford: at the Clarendon Press, 1934), (p.14), (17 page booklet). 5. Edwin Hubble, “The Law of Red-Shifts,” George Darwin Lecture, delivered May 1953.
For an image displaying Hubble's Law of Redshifts diagrams click here.
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