<p>C. S. Lewis's book <em>The Discarded Image</em> is about how to understand and how not to misunderstand medieval literature. In some parts he explicitly contrasts medieval with modern culture. In one of those he writes about the transition from Ptolemaic astronomy to heliocentric theories.</p>
<p>He asserts that the replacement of the former by the latter did <b>not</b> result from empirical discoveries that could not be explained within the Ptolemaic theory, but rather from the discovery that observations could be explained with fewer complications in the heliocentric theory.</p>
<p>Was he right?</p>
<p><strong>quote from Lewis's book:</strong></p>
<blockquote>
<p>The old astronomy was not, in any exact sense, 'refuted' by the telescope. The scarred surface of the Moon and the satellites of Jupiter can, if one wants, be fitted into a geocentric scheme. Even the enormous, and enormously different, distances of the stars can be accomodated if you are prepared to make their 'sphere', the <em>stellatum</em>, of a vast thickness. The old scheme, 'with Centric and Eccentric scribl'd o're', had been tinkered a good deal to keep up with observations. How far, by endless tinkerings, it could have kept up with them till even now, I do not know. But the human mind will not long endure such ever-increasing complications if once it has seen that some simpler conception can 'save the appearances'. Neither theological prejudice nor vested interests can permanently keep in favour a Model which is seen to be grossly uneconomical. The new astronomy triumphed not because the case for the old became desperate, but because the new was a better tool; once this was grasped, our ingrained conviction that Nature herself is thrifty did the rest.</p>
</blockquote>

CC BY-SA 4.0
2022-01-24T01:06:46.197Z
This sounds like a better fit for this history of science SE than astronomy SE. Also, "was he right" is not optimal for this kind of site, since it the answer is a matter of degree and consensus. (I think he had a good point, but the story is more complex with e.g. Tycho's star giving evidence for change in the supralunar sphere that undermined the overall framework...)
Anders Sandberg
CC BY-SA 4.0
2022-01-24T01:13:15.340Z
@AndersSandberg : Actually Lewis mentions the nova in that book, and that it refuted the belief in immutability of stars, but seems to give some reason why that is not a big problem for the older theory.
Michael Hardy
CC BY-SA 4.0
2022-01-24T02:50:51.773Z
This interesting question would be much improved with a relevant direct quote from C.S. Lewis, so we aren't fighting a strawman.  Also, it is a pretty bold assertion that empirical evidence played no part in changing the widely accepted model.  For example, Galileo's discovery of Jupiter's Moons was clear empirical evidence in contradiction to the existing Ptolomeic model that everything orbited the Earth.  No one was swayed by this discovery? I think not...
Connor Garcia
CC BY-SA 4.0
2022-01-24T10:56:50.853Z
Galileo’s observations of the phases of Venus (verified by other astronomers within a few months) very clearly ruled out Ptolemy’s model. (It did not rule out some alternate geocentric models, such as Tycho Brahe’s.)
Peter Erwin
CC BY-SA 4.0
2022-01-24T15:39:07.223Z
I’m voting to close this question because this is low-quality philosophy and has nothing to do with astronomy
Carl Witthoft
CC BY-SA 4.0
2022-01-24T20:29:01.117Z
@ConnorGarcia : He didn't say empirical evidence played no role in changing it. He said new empirical evidence was explained with fewer complications in the heliocentric model than in the Ptolemaic model, as opposed to empirical evidence actually contradicting the Ptolemaic model.
Michael Hardy
CC BY-SA 4.0
2022-01-24T20:42:46.880Z
@ConnorGarcia : I've added the quote from the book. $\qquad$
Michael Hardy
CC BY-SA 4.0
2022-01-24T20:51:17.773Z
Does this answer your question? [Was the Geocentric Model correct at all?](https://astronomy.stackexchange.com/questions/38927/was-the-geocentric-model-correct-at-all)
ProfRob
CC BY-SA 4.0
2022-01-24T20:55:18.560Z
Then you have your answer, if observations are adequately predicted (that isn't of course what that answer says) then a model cannot be falsified.
ProfRob
CC BY-SA 4.0
2022-01-24T20:58:16.533Z
@ProfRob : So a question is whether the things that the old model "failed to explain" could be explained within the old model by "tinkering" that makes the model "uneconomical" (i.e. complicated). The answer says the old model failed to explain those things, but is it possible that the answer's author, being impressed by the simplicity with which the new model explains those things, fails to notice that by "tinkering" that further complicates the old model, the old model might still explain the observations, even if nowhere near as economically.
Michael Hardy
CC BY-SA 4.0
2022-01-24T20:59:24.290Z
@ProfRob : So a question is: How often does it happen that an old theory is discarded not because of outright falsification but because a new theory is found to explain the observations much more simply?
Michael Hardy
CC BY-SA 4.0
2022-01-24T21:11:21.200Z
@MichaelHardy I can't think of one off-hand. There are usually observational discrepancies, often small, that lead to a complete paradigm overhaul (e.g. General Relativity). Ptolemy's model doesn't explain why Jupiter's moons orbit Jupiter, but then it didn't explain anything, it was just a (successful) prediction tool - a model, rather than a theory. You can just say the moons orbit Jupiter by magic if that's what you mean by tinkering. Lewis has a valid point in that heliocentrism was adopted as a *model* before Newtonian gravity gave a more impressive theory.
ProfRob
CC BY-SA 4.0
2022-01-29T11:50:32.070Z
I’m voting to close this question because its is not specifically about astronomy and is more suited for History of Science and Mathematics Stack Exchange
GrapefruitIsAwesome
<history>
Empirical findings, Occam's razor, and the replacement of Ptolemaism by heliocentrism
Michael Hardy
# Empirical findings, Occam's razor, and the replacement of Ptolemaism by heliocentrism

(Asked by: username_0 on 2022-01-24)

C. S. Lewis's book *The Discarded Image* is about how to understand and how not to misunderstand medieval literature. In some parts he explicitly contrasts medieval with modern culture. In one of those he writes about the transition from Ptolemaic astronomy to heliocentric theories.

He asserts that the replacement of the former by the latter did **not** result from empirical discoveries that could not be explained within the Ptolemaic theory, but rather from the discovery that observations could be explained with fewer complications in the heliocentric theory.

Was he right?

**quote from Lewis's book:**

> The old astronomy was not, in any exact sense, 'refuted' by the telescope. The scarred surface of the Moon and the satellites of Jupiter can, if one wants, be fitted into a geocentric scheme. Even the enormous, and enormously different, distances of the stars can be accomodated if you are prepared to make their 'sphere', the *stellatum*, of a vast thickness. The old scheme, 'with Centric and Eccentric scribl'd o're', had been tinkered a good deal to keep up with observations. How far, by endless tinkerings, it could have kept up with them till even now, I do not know. But the human mind will not long endure such ever-increasing complications if once it has seen that some simpler conception can 'save the appearances'. Neither theological prejudice nor vested interests can permanently keep in favour a Model which is seen to be grossly uneconomical. The new astronomy triumphed not because the case for the old became desperate, but because the new was a better tool; once this was grasped, our ingrained conviction that Nature herself is thrifty did the rest.

**Tags:** history

> **Comments:**
> **username_1**: This sounds like a better fit for this history of science SE than astronomy SE. Also, "was he right" is not optimal for this kind of site, since it the answer is a matter of degree and consensus. (I think he had a good point, but the story is more complex with e.g. Tycho's star giving evidence for change in the supralunar sphere that undermined the overall framework...)  
> **username_0**: @username_1 : Actually Lewis mentions the nova in that book, and that it refuted the belief in immutability of stars, but seems to give some reason why that is not a big problem for the older theory.  
> **username_2**: This interesting question would be much improved with a relevant direct quote from C.S. Lewis, so we aren't fighting a strawman.  Also, it is a pretty bold assertion that empirical evidence played no part in changing the widely accepted model.  For example, Galileo's discovery of Jupiter's Moons was clear empirical evidence in contradiction to the existing Ptolomeic model that everything orbited the Earth.  No one was swayed by this discovery? I think not...  
> **username_3**: Galileo’s observations of the phases of Venus (verified by other astronomers within a few months) very clearly ruled out Ptolemy’s model. (It did not rule out some alternate geocentric models, such as Tycho Brahe’s.)  
> **username_4**: I’m voting to close this question because this is low-quality philosophy and has nothing to do with astronomy  
> **username_0**: @username_2 : He didn't say empirical evidence played no role in changing it. He said new empirical evidence was explained with fewer complications in the heliocentric model than in the Ptolemaic model, as opposed to empirical evidence actually contradicting the Ptolemaic model.  
> **username_0**: @username_2 : I've added the quote from the book. $\qquad$  
> **username_5**: Does this answer your question? [Was the Geocentric Model correct at all?](https://astronomy.stackexchange.com/questions/38927/was-the-geocentric-model-correct-at-all)  
> **username_5**: Then you have your answer, if observations are adequately predicted (that isn't of course what that answer says) then a model cannot be falsified.  
> **username_0**: @username_5 : So a question is whether the things that the old model "failed to explain" could be explained within the old model by "tinkering" that makes the model "uneconomical" (i.e. complicated). The answer says the old model failed to explain those things, but is it possible that the answer's author, being impressed by the simplicity with which the new model explains those things, fails to notice that by "tinkering" that further complicates the old model, the old model might still explain the observations, even if nowhere near as economically.  
> **username_0**: @username_5 : So a question is: How often does it happen that an old theory is discarded not because of outright falsification but because a new theory is found to explain the observations much more simply?  
> **username_5**: @username_0 I can't think of one off-hand. There are usually observational discrepancies, often small, that lead to a complete paradigm overhaul (e.g. General Relativity). Ptolemy's model doesn't explain why Jupiter's moons orbit Jupiter, but then it didn't explain anything, it was just a (successful) prediction tool - a model, rather than a theory. You can just say the moons orbit Jupiter by magic if that's what you mean by tinkering. Lewis has a valid point in that heliocentrism was adopted as a *model* before Newtonian gravity gave a more impressive theory.  
> **username_6**: I’m voting to close this question because its is not specifically about astronomy and is more suited for History of Science and Mathematics Stack Exchange  

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## 0 answers

