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Thread: Ep. 499: What is the proposed Hubble-Lemaitre Law?

  1. #1
    Join Date
    Jul 2003

    Ep. 499: What is the proposed Hubble-Lemaitre Law?

    We started out Astronomy Cast with the controversal decision to de-planet Pluto. And here we are, more than a decade later, at the brink of recording our 500th episode when another big decision is coming down from the IAU: whose name goes on the concept that our Universe is expanding: Hubble or Lemaître? It's a big deal and Pamela knows all about it.


  2. #2
    Join Date
    Sep 2003
    Interesting podcast since it gives some insights into the IAU voting plans. [I like "Hubble-Lemaitre", btw. ]

    The following might help those interested in what label to use for the law. Most comes from a paper by Harry Nussbaumer (Inst. of Astronomy, Zurich)

    1912 – Vesto Slipher obtains some of the first redshifts for galaxies.

    1917 – Beginning of modern cosmology. Einstein publishes “Cosmological consideration on the general relativity). He applied GR to the entire universe. But he felt that theory should support the established Static Theory for the immutable universe. His cosmological constant was introduced to counter gravity.

    1917 – A few months later, Willem de Sitter published alternative model, also representing a static model. This was a simplified model that excluded matter, thus not acceptable to Einstein who in 1923 noted that two particles would rush apart from one another because of the cosmological constant, no doubt.

    1922 – Friedman publishes his “About the curvature of Space” based on GR. He held to Einstein’s isotropic view but made R, the radius, variable with time, unlike Einstein and de Sitter’s model. Density, would, therefore, also be variable.

    It is noteworthy the de Sitter had time varying throughout the universe, which explains his redshift result without motion. Einstein didn’t initially accept Friedman’s math due to an error on Einstein’s part, but he never accepted the physical significance of Friedman’s work. Thus, Friedman was taken as purely theoretical.

    1925 – Lemaitre showed that de Sitter’s model violated homogeneity, as held by Einstein and himself. Also, Lemaitre treated universe as Euclidian, apparently unbeknownst to Einstein in 1932. [Also, Friedman dies of Typhus.]

    1926 – Hubble determines distances to extragalactic nebulae, that he won't call "galaxies".

    1927 – Independently of Friedman, Lemaitre also had radius and density to vary with time. Unlike Friedman, however, he spotted the weakness of de Sitter’s model that lacked spatial homogeneity.

    Lemaitre concluded that extragalactic nebulae would exhibit redshifts in the form of v = H*d, though H wasn’t for Hubble but expansion, interestingly.

    He knew of Hubble’s distances and he had Slipher’s redshifts. Though the uncertainties were great, Lemaitre postulated an expanding universe.
    He published in 1927 in French and in a little known Belgian scientific journal.

    A few months later, at the Solvay congress, he gave a reprint to Einstein, who considered it to be abominable. But Lemaitre visited with Einstein in a taxi ride to a laboratory and realized Einstein wasn’t informed about the astronomical facts. This didn’t sway Einstein, however.

    I believe it was at this same conference where Hubble had time to visit with de Sitter and learn that redshift wasn't necessarily due to motion, at least in de Sitter's model from Einstein's field equations (but without mass).

    1929 -- Hubble published findings that there was probably a linear relationship between nebular distances and redshifts. Apparently, he wasn’t aware of Lemaitre’s prior claim of this. But note that Hubble is not calling for an expanding universe.

    1929 – Fritz Zwicky proposes the Tired Light explanation for redshift.

    1930 – de Sitter, at the RAS meeting, confirmed Hubble’s work. Eddington and de Sitter were at a loss on how to explain the evidence. [de Sitter has redshift with no expansion, no homogeneity and no mass; Einstein has homogeneity and mass but no explanation for redshift.] Lemaitre read the minutes of the meeting, including the puzzlement, and immediately sent two reprints of his 1927 paper to Eddington, requesting he send the other copy to de Sitter.

    Both Eddington and de Sitter quickly accepted Lemaitre’s model. Eddington publicly acknowledges this in 1930 in the Monthly Notices.

    1930 (June) – Einstein visits Eddington and likely became updated on the observational and theoretical status of cosmology.

    1931 – In Einstein’s trip to Pasadena, there is no mention of Hubble anywhere in his diary, though it is known they met. Einstein’s unifying field views seem to have been foremost on his mind. Seeing the spectral plates seems to have been more a tourist attraction for Einstein. Unlike Tolman, Hubble was not fluent in German and was also reluctant to talk theory. Hubble, in his letter to de Sitter, stated that interpretations “should be left to you and the very few others who are competent to discuss the matter (redshift and distance correlations) with authority.” Hubble avoided the cosmological implications of his findings.

    It seems Einstein was already up to date on Slipher’s and Hubble’s work and may have felt little need to hear it directly as it would be redundant, possibly.

    The age for the universe was approximated to about 10 billion years, but stars were soon determined to be about 100 times older than this; older than the universe. This added no encouragement for Einstein to fully accept any expanding model.

    Lemaitre proposed an early stagnation period followed by an accelerated expansion due to the cosmological term of Einstein which would have greater effect as the universe became less dense.

    1931 -- Hubble and Humason publish new results with 10x the amount of data.

    1931 (March) -- Lemaitre translates his Belgium (French) paper but, with Hubble's great data, he leaves out his expansion calculations. But why? Lemaitre could have corrected his calculations with the new data, but this would be a revision and not a simple translation. He may have elected to honor Hubble for his great achievement in redshift results, perhaps realizing that Hubble never in the 38 page paper mentions the word expansion, leaving room for credit to the theorists like him.

    1931 (March) – Einstein reviews Friedman work and, on the last pages, “Friedman presents his periodic model with lambda = 0. In addition, Lemaitre’s 1927 paper provided the connection between the increasing radius of curvature and the redshifts in the spectra.”

    1931 (June) – Joined with Tolman in a paper that lambda is unnecessary in an expanding universe. Tolman seemed to want to hold on to the cosmological constant, however, and both Eddington and Lemaitre agreed that this constant might be an important force in nature.

    1931 -- Hubble and Humason publish new results with 10x the amount of data.

    1931 (March) -- Lemaitre translates his Belgium (French) paper but, with Hubble's great data, he leaves out his expansion calculations.

    1932 – At the IAU, Eddington and Lemaitre opposed the banishment of lambda.
    Last edited by George; 2018-Sep-13 at 03:27 PM.
    We know time flies, we just can't see its wings.

  3. #3
    Join Date
    Oct 2018
    Interesting podcast, but filled with misinformation (some of it perpetrated by the IAU resolution itself - there is no positive evidence that Hubble ever talked to Lemaitre at the IAU general assembly in Leiden - see Kragh

    The first person to derive the velocity-distance relationship in an expanding universe (linear to first order) and to estimate the value of the slope from the extant data was Hermann Weyl in 1923 (Raum Zeit, Materie; Phys. Zeitschr, 24, 230). Where is the IAU resolution to honor his work?

    We mix together the empirical observation of a linear correlation between velocity and distance with the theoretical underpinning of an expanding universe. Hubble established the former, but he never believed in an expanding universe. Lemaitre was firmly convinced that an expanding universe was the correct explanation of the velocity-distance relation, but he contributed nothing to establishing it empirically. Even Weyl, who first derived the Hubble law in an expanding universe, was cautious enough to say that there might be other explanations for the empirical observation (1930, Phil. Mag., 9, 936.)

    Make no mistake - Lemaitre's 1927 paper was one of absolute sheer brilliance. However, its brilliance needs to be understood within the context of the state of the field in 1927, not today. By plucking out one piece of the paper and trying to elevate it to a "law", the IAU is committing an injustice to Lemaitre, notwithstanding any good intentions.

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