Vesto Melvin Slipher (1875 - 1969)


This page is motivated by a feeling I have held for some years: that a very large share of the credit for the discovery of the expanding universe is due to Slipher, and yet he tends to take very much second place to Hubble in most accounts. In 2004, I tried and failed to discover electronic versions of Slipher's seminal papers anywhere on the web. This is a disgrace; since ROE is fortunate enough to possess an outstanding collection of historical journals, I was able to track down the originals, and they are made available below. Since then, I am proud to say that my complaints to ADS have had an effect: not only are Slipher's main papers all now listed (the 1917 masterpiece wasn't even in the database), but you can also find the scans I made through ADS.

Reading these papers only confirmed my impression that Slipher's work is badly under-valued. They are confidently argued, and make some points that are astonishingly perceptive with the aid of 21st-century hindsight.

Further details

Slipher's pioneering work was the subject of a conference in Flagstaff Arizona, held in September 2012 to mark the 100th anniversary of Slipher's first successful observation of M31. My paper from that meeting gives more details of the above arguments, as well as a full statistical re-analysis of Slipher's data. An interesting point emerges from this concerning what can be said about expansion on the basis of what was known in 1917. Slipher did not claim that velocities had a general tendency to be redshifts because he was able to reduce the mean redshift very significantly by removing the dipole signal due to the motion of the Sun. But in fact the remaining mean redshift is significantly positive (at 8sigma; rising to 14sigma with the expanded data that Slipher gave to Eddington in 1923). Thus Slipher had in his possession clear evidence for a general recession of the nebulae, the best part of a decade before Hubble came on the scene.