---
title: "Eddington experiment"
chunk: 4/5
source: "https://en.wikipedia.org/wiki/Eddington_experiment"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:39:05.943562+00:00"
instance: "kb-cron"
---

The presentation of the results at the joint 6 November 1919 session of Royal Society and Royal Astronomical Society led to intensive press coverage first in Great Britain and a few days later in the US press, notably in The New York Times, and some days later still in the German press. While Einstein had been a moderately famous public figure in Germany for a few years by that time, the articles in question marked the beginning of his international celebrity status. A notable exception was Belgium, where the Eddington results were given the cold shoulder – partly because Einstein was seen as representing Germany, with the suffering of Belgium in World War I still very present in the country. The sudden popularity of Einstein's theories led to an "Einstein boom" of popular science books.
While there is a later anecdote describing Einstein as unimpressed about the experimental results, and sure of his theory even in the absence of evidence (stating, when asked what he would have said if the results had been otherwise, "Then I would feel sorry for the dear Lord. The theory is correct anyway.") the evidence of Einstein's letters to other scientists indicates, on the contrary, that he was both impressed and moved by the new results, and regarded them as an important success.
The 1919 results were also used as part of the systematic efforts by the Nobel laureate Philipp Lenard to discredit Einstein, whom Lenard, himself an avid national socialist and exponent of what he saw as "German physics", saw as a dangerous exponent of unnatural "Jewish physics". Lenard pointed to the 1801 prediction that Johann Georg von Soldner had derived from Newtonian gravity for starlight bending around a massive object, which corresponds to half the general-relativistic prediction derived by Einstein in 1915, and thus to Einstein's own earlier derivation of 1911, and claimed that it proved Einstein to be a plagiarist, and that von Soldner deserved to be given credit for the 1919 result.
Both the 1919 results themselves and Eddington's textbook on general relativity, whose second edition including the results saw numerous translations as interest in Einstein's theory grew, played important roles in the reception of Einstein's theory in the scientific community. It is notable that while the Eddington results were seen as a confirmation of Einstein's prediction, and in that capacity soon found their way into general relativity text books, among other astronomers there followed a decade-long discussion of the quantitative values of light deflection, with the precise results in contention even after several expeditions had repeated Eddington's observations on the occasion of subsequent eclipses. The discussion concerned both the data analysis – such as the different weight assigned to different stars in the 1922 and 1929 eclipse expeditions – and the question of specific systematic effects that could skew the results.
All in all, eclipse measurements of this kind, using visible light, retained considerable uncertainty, and it was only radio-astronomical measurements in the late 1960s that definitively showed that the amount of deflection was the full value predicted by general relativity, and not half that number as predicted by a "Newtonian" calculation. Those measurements and their successors are nowadays an important part of the so-called post-Newtonian tests of gravity, the systematic way of parametrizing the predictions of general relativity and other theories in terms of ten adjustable parameters in the context of the parameterized post-Newtonian formalism, where each parameter represents a possible departure from Newton's law of universal gravitation. The earliest parameterizations of the post-Newtonian approximation were performed by Eddington (1922). The parameter concerned with the amount of deflection of light by a gravitational source is the so-called Eddington parameter (γ), and it is currently the best-constrained of the ten post-Newtonian parameters.
At about the time of the last serious photo-plate eclipse measurements, by a University of Texas expedition observing in Mauritania in 1973, doubts began to surface about whether or not the original Eddington measurements were sufficient to vindicate Einstein's prediction, or whether biased analysis by Eddington and his colleagues had skewed the results. Similar concerns about systematic errors and possibly confirmation bias were raised in the science history community and gained more prominence as part of the popular book The Golem by Trevor Pinch and Harry Collins. A modern reanalysis of the dataset, though, suggests that Eddington's analysis was accurate, and in fact less afflicted by bias than some of the analyses of solar eclipse data that followed. Part of the vindication comes from a 1979 reanalysis of the plates from the two Sobral instruments, using a much more modern plate-measuring machine than was available in 1919, which supports Eddington's results.
The Eddington Experiment was crucial for inspiring Karl Popper's theory of falsifiability, the central idea of The Logic of Scientific Discovery and a core part of the scientific method. The concept of falsifiability says that all scientific theories, to count as scientific, must have an associated scientific experiment or experiments which could, in principle, prove the theory wrong. Popper cites Albert Einstein's theory of general relativity as an example of good science because it is falsifiable, and the Eddington Experiment is an example of an experiment which could have falsified the theory but didn't. Popper contrasts this with Sigmund Freud's psychoanalysis, which he claims cannot be tested by experiment, meaning that psychoanalysis is unfalsifiable and therefore pseudoscience.

== In popular culture ==
The experiment was central to the plot of the 2008 BBC television film Einstein and Eddington, with David Tennant in the role of Eddington.

== See also ==

Tests of general relativity
Einstein and Eddington

== Notes ==

== References ==