Edwin Hubble DID NOT say that Universe is expanding.
Let us see what he actually said in year 1929. Following is link to his original 1929 paper:
Title of the paper is: “A relation between distance and radial velocity among extra-galactic nebulae.”
Here “radial velocity” means “redshift”.
From 1912 onwards, scientists had been noticing redshifts in far off galaxies (then thought of spiral nebulae). Naturally by that time those redshifts were interpreted in terms of Doppler’s Effect. Due to Doppler’s interpretation, those redshifts were also called “radial velocities”.
Here in the title of his paper, Hubble has used common term “radial velocity” for “redshift”.
But to determine what he actually wants to say, we must very carefully study the first paragraph of 1929 paper. Following is the first paragraph:
“Determinations of the motion of the sun with respect to the extra-galactic nebulae have involved a K term of several hundred kilometers which appears to be variable. Explanations of this paradox have been sought in a correlation between apparent radial velocities and distances, but so far the results have not been convincing. The present paper is a re-examination of the question, based on only those nebular distances which are believed to be fairly reliable.”
Here it is also true that he starts his paper with sentence “Determinations of the motion of the sun with respect to the extra-galactic nebulae”.
But … in the very first paragraph … he is pointing something perplexing for which he is using word ‘paradox’ and after pointing out this ‘paradox’, now he is using term apparent velocities instead of velocities.
Following is relevant sentence in the first paragraph:
“Explanations of this paradox have been sought in a correlation between apparent radial velocities and distances, but so far the results have not been convincing.”
Here is the point. In Doppler’s Shift, there is no redshift-distance relationship but what Hubble was observing was a redshift-distance relationship. Therefore with this paper, he was seeking explanations for this ‘paradox’.
From whom he was seeking explanation?
He wrote this question in a public paper so he asked it from wise community. But he asked for this explanation from particular people of his choice also. Furthermore, he has skeptically concluded this paper with following words:
“In the de Sitter cosmology, displacements of the spectra arise from two sources, an apparent slowing down of atomic vibrations and a general tendency of material particles to scatter. The latter involves an acceleration and hence introduces the element of time. The relative importance of these two effects should determine the form of the relation between distances and observed velocities; and in this connection it may be emphasized that the linear relation found in the present discussion is a first approximation representing a restricted range in distance.”
In the letter to de-Sitter, he writes:
“Mr. Humason and I are both deeply sensible of your gracious appreciation of the papers on velocities and distances of nebulae. We use the term ‘apparent’ velocities to emphasize the empirical features of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority.[i]”
Thus ‘apparently’ redshifts seemed like velocities but for Hubble, the actual interpretation of redshifts was unresolved question. With this, he actually rightly recognized the fact that redshift involved in extra galactic nebulae was of a different kind than to the usual Doppler’s Shift.
With his 1929 paper, Hubble not only did not suggest ‘expansion of universe’, he also almost denied that meaning of ‘redshifts’ was ‘velocities’. He used term ‘apparent velocities’ and he even looked for such reasons of redshift as apparent slowing down of atomic vibrations and a general tendency of material particles to scatter.
The usage of term ‘apparent’ for velocities and then looking for explanation of redshifts in such reasons as apparent slowing down of atomic vibrations and a general tendency of material particles to scatter indicates that for Edwin Hubble, ‘velocities’ was not the final meaning for redshifts. The term ‘apparent’ points to the determination of meaning of redshifts as indeterminate.
But soon Robertson and Walker were going to give him an undue gift of literal meaning of ‘apparent velocities’. FLRW metric (Friedmann-Lemaître-Robertson-Walker) was declared to be the only possible interpretation of cosmological redshifts. In this so-called metric, ‘apparent velocities’ of galaxies literally became ‘apparent velocities’ such that there was no actual velocity but ‘space’ was expanding thus galaxies were ‘apparently’ receding away from our solar system.
Whatever FLRW metric says but point of this blog post is only to show that Edwin Hubble himself did not suggest expansion of universe and neither did he took redshifts of galaxies as actual receding velocities of those galaxies.
After having seen what Hubble exactly told us in year 1929, now we should guess the level of misinformation in general public about Hubble’s finding when NASA itself is also gravely misinformed. Following is a quote from NASA website:
“The Big Bang model was a natural outcome of Einstein’s General Relativity as applied to a homogeneous universe. However, in 1917, the idea that the universe was expanding was thought to be absurd. So Einstein invented the cosmological constant as a term in his General Relativity theory that allowed for a static universe. In 1929, Edwin Hubble announced that his observations of galaxies outside our own Milky Way showed that they were systematically moving away from us with a speed that was proportional to their distance from us. The more distant the galaxy, the faster it was receding from us. The universe was expanding after all, just as General Relativity originally predicted! Hubble observed that the light from a given galaxy was shifted further toward the red end of the light spectrum the further that galaxy was from our galaxy.”
For heaven’s sake NASA – Hubble DID NOT say that galaxies are ‘moving away’. At the most he said that galaxies are APPARENTLY moving away.
Please see the book A Philosophical Rejection of The Big Bang Theory for further in-depth analysis.