Christian Doppler
Christian Doppler | |
|---|---|
| Born | 29 November 1803 Salzburg, Austria |
| Died | 17 March 1853 (aged 49) Venice |
| Nationality | Austrian |
| Known for | The Doppler effect |
| Scientific career | |
| Fields | Physics, Mathematics, Astronomy |
| Institutions | Prague Polytechnic; Vienna Polytechnic; University of Vienna |
Christian Andreas Doppler (29 November 1803 – 17 March 1853) was an Austrian mathematician and physicist who showed that the frequency of a wave measured by an observer depends on the relative motion of source and observer — the Doppler effect, on which nearly all of observational cosmology now rests.
Doppler struggled for years to find an academic post, and at one point had made arrangements to emigrate to America. He obtained a chair at the Prague Polytechnic, and it was there, on 25 May 1842, that he read the paper "Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels" ("On the coloured light of double stars and certain other stars of the heavens") to the Royal Bohemian Society of Sciences. He later moved to Vienna and in 1850 became the first director of the Institute of Physics at the University of Vienna, where Gregor Mendel was briefly among his students. He died of tuberculosis in Venice at the age of 49.
The relation he derived is elementary: an approaching source crowds its wavefronts and raises the observed frequency, a receding source stretches them and lowers it. What made the paper important was the claim that this applies to light from stars.
What Doppler got wrong, and what survived
Doppler's own application was mistaken. He proposed that the observed colours of binary stars were caused by their orbital motion. This does not work: stellar velocities are far too small to produce a visible colour change, and shifting a continuous blackbody spectrum does not simply redden or blue it in the way he supposed.
The effect itself was confirmed acoustically in 1845 by C. H. D. Buys Ballot, who stationed trumpeters on an open railway carriage near Utrecht and listeners beside the track — while explicitly rejecting Doppler's stellar argument. In 1848 Fizeau, working independently, identified the correct optical application: the shift is to be measured not in overall colour but in the positions of spectral lines. Doppler shifts of spectral lines became the foundation of stellar radial-velocity measurement, of binary and exoplanet detection, and — when Hubble found the linear relation between galaxy redshift and distance — of expanding-universe cosmology.
It is worth being precise about the standard position: modern cosmology does not treat cosmological redshift as a Doppler shift. In the general relativistic account it is attributed to the expansion of space during the light's transit, and the two are only approximately equivalent at small distances. The Doppler interpretation of cosmological redshift is a textbook simplification rather than the formal claim.
On this wiki
The Doppler interpretation of redshift is one of the most contested points on this wiki. The argument takes several forms; see Category:Redshift and the Doppler Effect and Redshift pages.
That cosmological redshift is not motion at all. Paul Marmet's "A New Non-Doppler Redshift" (Physics Essays, 1988) proposes inelastic scattering of light by interstellar gas producing a shift that follows the same Δν/ν = constant law as a Doppler shift and is therefore indistinguishable from it except near resonances. This is the wiki's most fully worked tired-light mechanism. Paul Schroeder argues for a gravitational origin in "Cosmological Redshift is Caused by Gravitation, Not Doppler Motion" (2008), and Viraj Fernando for photon–field interaction in "Doppler Phenomena Determined by Photon-Cosmic Field Interactions" (2012). Halton C Arp's anomalous-redshift observations are the wiki's standing empirical challenge to reading redshift as recession velocity.
That the relativistic transverse Doppler shift is not observed. Hartwig Wolfgang Thim's "Absence of the Relativistic Transverse Doppler Shift at Microwave Frequencies" (2003) reports a null result where special relativity predicts a second-order shift; A I A Adey ("A Note on Transverse Doppler Effects", Galilean Electrodynamics, 1996) and Randy Reukauf ("A Particle Explanation of the Transverse Doppler Effect", 2006) treat the same case from theory.
That Doppler analysis can replace relativity rather than depend on it. Neil E Munch argues in "Critical Flaws in Special Relativity and Its Possible Replacement by Doppler Concepts" (2002) that the Lorentz transformation is better understood as a Doppler relation; Yuri I Petrov derives it that way in "Lorentz Transformation as a Consequence of the Doppler Effect" (2008), and Ken H Seto builds a full alternative in "Doppler Relativity Theory" (Galilean Electrodynamics, 2001).
A related curiosity catalogued here is the inverse Doppler effect — a shortened wavelength on reflection from a receding boundary — discussed by Leslee A Kulba in "Inverse Doppler Effect" (Electric Spacecraft Journal, 2004).