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General relativity (1915), as I've heard it explained, describes a universe that is either shrinking or expanding. By adding a cosmological constant it can describe a universe in eternal steady state, which was favored at the time.

Were there published suggestions, or otherwise discussed, that the universe could be expanding before Edwin Hubble observed that more distant galaxies indeed have higher redshift (1929)? Was Hubble deliberately looking for an expanding universe in the intergalactic space he had discovered in 1923?

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  • $\begingroup$ @RoryDaulton Of course, yes! While typing it I did have a shadow of a thought about how his biggest blunder came into this. I've now changed the question accordingly to not distract further from the question's core. $\endgroup$ – LocalFluff May 3 '17 at 10:57
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Were there published suggestions, or otherwise discussed, that the universe could be expanding before Edwin Hubble observed that more distant galaxies indeed have higher redshift (1929)?

Yes. De Sitter published expanding cosmological models in March 1917 in which there was a cosmological constant. Friedman published his models in 1922. People didn't take this sort of stuff very seriously at the time. This kind of speculation was not considered mainstream science.

The first Doppler shift of a galaxy was discovered in 1912: a blueshift for the Andromeda galaxy. By 1914 Slipher had realized that most galaxies had red shifts. His work was greeted with extreme skepticism initially. The Shapley-Curtis debate on the nature of the spiral nebulae didn't take place until 1920. Mount Wilson undertook a large-scale campaign of observing spiral nebulae in 1919, and the picture of them as galaxies wasn't really solidly confirmed until about 1924.

The Cepheid distance scale dates to about 1924, so de Sitter and Friedman's models considerably predated the Hubble law. Lemaitre synthesized the various ideas and predicted in the Hubble law in 1925. Hubble confirmed it observationally in 1927.

So basically the theory and observations were developed side by side over a period of about 15 years. Hubble certainly was aware of the relevant ideas before he undertook the program of observation which, as one of its results, demonstrated the Hubble law empirically.

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This is an extended comment to Ben Crowell's answer. Friedmann proved that without the "cosmological term" the universe cannot be stationary: has either to expand or contract. As a result of this Einstein introduced the cosmological term to his equations, the thing which he later called "the greatest blunder" in his life. The correct logical conclusion from Friedmann's theorem was that the universe is not stationary.

Remark. Wikipedia spells him as Friedmann, but the exact transliteration from Russian will be Fridman.

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  • $\begingroup$ Are you sure this is right? Einstein published his static universe solution in 1917. Friedman published his models in 1922. Maybe I'm oversimplifying or misunderstanding something, or I have my facts wrong, but it appears to me that you have the chronology reversed. $\endgroup$ – Ben Crowell May 3 '17 at 21:36
  • $\begingroup$ @Ben Crowell: adsabs.harvard.edu/abs/2011AcHA...43..268J $\endgroup$ – Alexandre Eremenko May 3 '17 at 22:56
  • $\begingroup$ I don't see anything in the abstract you linked to that contradicts my previous understanding of the chronology. Am I missing something? $\endgroup$ – Ben Crowell May 4 '17 at 2:21

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