Did famed American astronomer Edwin Hubble (or someone acting upon his behalf) conspire to deprive another astronomer of credit for a major discovery? Recent scholarship suggests not.

In 1927, Monsignor George Lemaître published an article^{1} in a little-known Belgian journal, *Annals of the Scientific Society of Brussels*. In the article, he proposed the concept that the universe is in a state of expansion. This conjecture was based upon the existing body of redshift measurements and calculations published by astronomers such as Vesto Slipher, Gustaf Strömberg, Edwin Hubble, and others. From General Relativity, Lemaître derived a linear formula for describing the expansion rate of the cosmos, and, making the faulty assumption that the absolute magnitude of a galaxy could be used as a “standard candle” for calculating the distances to galaxies, calculated an estimate for the expansion rate at 625 km/s/Mpc.

In 1929, Hubble published a paper^{2} in which he also derived a linear formula for describing cosmological expansion practically identical to the formula earlier devised by Lemaître, as well as computing a value for the expansion constant of 500 km/s/Mpc. The calculation was made using more refined estimates of galactic distances using the brightest stars in each galaxy as the standard candles for distance determination. (These days, Cepheid variable stars and the luminosity curves of Type 1a supernovae are typically used to provide more accurate distance determinations.) The relationship published by Hubble has come to be known as “Hubble’s law,” and serves to this day as the foundation (alongside the field equations from Einsteins Theory of General Relativity) of modern cosmology.

But what about Lemaître’s formula? Why don’t we call the expression describing the expansion of the cosmos Lemaître’s Law instead of Hubble’s Law?

Well, in 1931, an English translation of Lemaître’s 1927 paper was finally published.^{3} However, this translation was missing some rather significant portions, most notably the section where Lemaître derived the formula describing cosmological expansion. Recently, this omission has kicked off a firestorm of debate^{4,5,6,7,8} over the possibly that Lemaître’s results had been suppressed so that Hubble would get credit for the formula which now bears his name. So, who translated the paper? And who trimmed out the sections in question?

This controversy intrigued astronomer Mario Livio enough that he decided to get to the bottom of the issue.^{9} He actually managed to dig up the original correspondences between Lemaître and Dr. William Marshall Smart, then editor of the *Monthly Notices of the Royal Astronomical Society*. Among those letters, he found the following from Lemaître to Dr. Smart:

I highly appreciate the honour for me and for our society to have my 1927 paper reprinted by the Royal Astronomical Society. I send you a translation of the paper. I did not find advisable to reprint the provisional discussion of radial velocities which is clearly of no actual interest, and also the geometrical note, which could be replaced by a small bibliography of ancient and new papers on the subject. I join a french text with indication of the passages omitted in the translation. I made this translation as exact as I can, but I would be very glad if some of yours would be kind enough to read it and correct my english which am afraid is rather rough. Nor formula is changed, and even the final suggestion which is not confirmed by recent work of mine has not be modified. i did not write again the table which may be printed from the french text.

As regards to addition on the subject, I just obtained the equation of the expanding universe by a new method which makes clear the influence of the condensations and the possible causes of the expansion. I would be very glad to have them presented to your society as a separate paper.

So, it would seem that the person who censored Lemaître was Lemaître himself! He appeared to regard his derivation of the expansion relationship as being far too speculative and tentative, nor of any real interest to anyone in the wake of Hubble’s paper. He was far more interested in proceeding with the next step of his work, publishing papers^{10,11} in which he took his earlier speculation about cosmological expansion to its logical next step: the recognition that this expansion implies that the universe was once much hotter and denser in the past. Monsignor Lemaître was developing what Fred Hoyle would later derisively dub the “Big Bang Theory.”

Lemaître, it would seem, was not interested in establishing priority for credit for his discovery. Perhaps he recognized a fundamental truth of science that is all too easily disregarded: science is not done in isolation. It is a collaborative effort built upon the foundations of the work of others. Lemaître’s own work was built on observations and calculations done by many others, including Hubble and Einstein. (For a glimpse at the contributions of others, see the sidebar below on the history of redshift cosmology.) Einstein’s Theory of General Relativity was built on the work of Riemann and Hilbert. His Theory of Special Relativity was built on the work of Lorentz and Poincaré. Newton’s mechanics was built upon the work of Galileo and Kepler. As Newton himself observed (his spat with Gottfried Wilhelm Leibniz over credit for inventing the Calculus aside), *“If I have seen a little further it is by standing on the shoulders of Giants.*”

What counts is not the credit, but the results.

1. G. Lemaître, “Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extragalactiques”. *Annals of the Scientific Society of Brussels ***47A**: 41.(1927)

2. E. Hubble, “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae”. *Proceedings of the National Academy of Sciences*, **15**:168-173 (1929).

3. G. Lemaître, “A Homogeneous Universe of Constant Mass and Growing Radius Accounting for the Radial Velocity of Extragalactic Nebulae”. *Monthly Notices of the Royal Astronomical Society* **91**: 483–490. 1931.

4. Reich, E. S., “Edwin Hubble in translation trouble“, *Nature News* (2011).

5. John Farrell, “Why Hubble’s Law… Wasn’t Really Hubble’s“, Forbes Tech Blog.

6. Nussbaumer, H. & Bieri, L. “Who discovered the expanding universe?”, preprint at http://arxiv.org/abs/1107.2281 (2011).

7. Van den Bergh, S. “The Curious Case of Lemaitre’s Equation No. 24”, preprint at http://arxiv.org/abs/1106.1195 (2011).

8. Block, D. “A Hubble Eclipse: Lemaitre and Censorship”, preprint at http://arxiv.org/abs/1106.3928 (2011).

9. Mario Livio. “Lost in translation: Mystery of the missing text solved”. *Nature* **479**, 171–173 (10 November 2011) doi:10.1038/479171a

10. G. Lemaître. “The Expanding Universe”. *Monthly Notices of the Royal Astronomical Society* **91**, 490-501 (1931).

11. G. Lemaître. “The Evolution of the Universe: Discussion”. *Nature ***128**: 699–701. (1931) doi:10.1038/128704a0

### A Brief History of Redshift Cosmology

Vesto Slipher reported an anomalous redshift in observations of Andromeda in 1912, followed by another paper in 1915 in which he reported on 15 “spiral nebula” (galaxies), all but three of which seemed to have recessional velocities.

Slipher, Vesto (1912). “The radial velocity of the Andromeda Nebula”.

Lowell Observatory Bulletin1: 2.56–2.57. Bibcode1913LowOB…1b..56SSlipher, Vesto (1915). “Spectrographic Observations of Nebulae”.

Popular Astronomy23: 21–24. Bibcode1915PA…..23…21S

Also in 1915, Einstein presented his General Theory of Relativity to the Prussian Academy of Science. The following year, he published the paper laying out his theory. Not long thereafter, it became obvious that the solutions to his field equations implied a universe that was either expanding or contracting. Since this contradicted the then widely-held assumption of a static universe, Einstein added a correction term known as the Cosmological Constant to provide a static (albeit unstable) solution. Once astronomical observations made it clear that the universe was in fact expanding, Einstein came to regard his failure to predict cosmological expansion from his theories to be the biggest blunder of his career.

Alexander Friedman in 1922 found solutions for Einsteins field equations corresponding to an expanding universe which proved to be consistent with subsequent astronomical observations. His solutions are known as the Friedman equations.

Friedman, A. A. (1922). “Über die Krümmung des Raumes”.

Zeitschrift fur Physik10(1): 377–386. Bibcode 1922ZPhy…10..377F. doi:10.1007/BF01332580. English translation in Friedman, A. (1999).General Relativity and Gravitation31(12): 1991–2000. Bibcode 1999GReGr..31.1991F. doi:10.1023/A:1026751225741.)Friedman, A. (1924). “Über die Möglichkeit einer Welt mit konstanter negativer Krümmung des Raumes”.

Zeitschrift für Physik21(1): 326–332. doi:10.1007/BF01328280. English translation in: Friedmann, A. (1999). “On the Possibility of a World with Constant Negative Curvature of Space”.General Relativity and Gravitation31: 2001–2008. doi:10.1023/A:1026755309811

Carl Wilhelm Wirtz in 1922 published an analysis of redshift data indicating that more distant galaxies are moving away from us more quickly than nearer ones. In a 1924 paper, these results were confirmed by more precise results, which Wirtz further interpreted as a confirmation that ours is a de Sitter universe, which is to say one that obeys a specific solution to Einstein’s field equations found by Willem de Sitter. In his calculations, Wirtz used galaxy diameters as “standard rulers” for estimating their distances.

Wirtz, C. W. (1922). “Einiges zur Statistik der Radialbewegungen von Spiralnebeln und Kugelsternhaufen”.

Astronomische Nachrichten215(5153): 349–354. Bibcode 1922AN….215..349WWirtz, C. W. (1924). “De Sitters Kosmologie und die Radialbewegungen der Spiralnebel”.

Astronomische Nachrichten222(5306): 21–26. Bibcode 1924AN….222…21W.doi:10.1002/asna.19242220203

Knut Lundmark used a combination of galaxy diameter and absolute magnitude to estimate galaxy distances, as well as making use of supernovae and Cepheid variable stars as standard candles. His analysis yielded a rather complex polynomial relationship between redshift and distance.

K. Lundmark, 1924 “The determination of the curvature of space-time in de Sitter’s world“,

Monthly Notices of the Royal Astronomical Society, Vol. 84, p.747-770.K. Lundmark, 1925 “Nebulae, The motions and the distances of spiral“,

Monthly Notices of the Royal Astronomical Society, Vol. 85, p.865.

In 1925, Gustaf Strömberg, an astronomer at the Mount Wilson Observatory in California, published an article containing velocities of other galaxies measured by Vesto Melvin Slipher. In his analysis of Slipher’s observations, Strömberg assumed that the absolute magnitude of a galaxy was a valid “standard candle,” but found no correlation between distance and redshift. Both Hubble and Lemaître relied heavily upon Strömberg’s data in their subsequent work.

Strömberg, G. “Analysis of radial velocities of globular clusters and non-galactic nebulae”.

Astrophys. J.61, 353–362 (1925).E. Hubble, 1926 “Extragalactic nebulae“,

Astrophys. J., 64, 321-369

George Lemaître’s analysis of the data published by Strömberg assumed that the absolute magnitudes of galaxies could be used as standard candles. He made use of calibrations appearing in Hubble’s 1926 paper and found a linear relationship between distance and redshift. He calculated the expansion rate to be 625 km/s/Mpc.

G. Lemaître, “Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extragalactiques”.

Annals of the Scientific Society of Brussels47A: 41.(1927)

Edwin Hubble, acting on the assumption that the brightest stars in a given spiral galaxy could be used as standard candles, used seven nearby galaxies for calibration purposes, then found a linear relationship between distance and redshift. He calculated the expansion rate to be 500 km/s/Mpc.

E. Hubble, “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae”.

Proceedings of the National Academy of Sciences,15:168-173 (1929).

In 1931 came the English translations of Lemaître’s 1927 paper, followed shortly thereafter by his formulation of the Big Bang Theory (a name attributed to the model as a pejorative by Fred Hoyle, who clung to a steady-state model of the cosmos).

G. Lemaître, “A Homogeneous Universe of Constant Mass and Growing Radius Accounting for the Radial Velocity of Extragalactic Nebulae”.

Monthly Notices of the Royal Astronomical Society91: 483–490. 1931.G. Lemaître. “The Expanding Universe”.

Monthly Notices of the Royal Astronomical Society91, 490-501 (1931).G. Lemaître. “The Evolution of the Universe: Discussion”.

Nature128: 699–701. (1931) doi:10.1038/128704a0

Finally, in 1965, Arno Penzias and Robert Wilson detected the Cosmic Microwave Background radiation field, the “afterglow” of the Big Bang, providing definitive support for Lemaître’s theory.

For more recent developments, especially the 1998 discovery of the acceleration of cosmic expansion leading to the dark energy hypothesis and the resurrection of Einstein’s Cosmological Constant, see my article on 2011 Nobel Prize in Physics.

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