Hawking's Model-Dependent Realism

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This is a soft question, but I am reading Hawking's "The Grand Design" and he mentions that "Although it is not uncommon for people to say that Copernicus proved Ptolemy wrong, that is not true ... One can use either picture as a model of the universe." He goes on to say that we hold the heliocentric model to be true because it is the simpler of the two.

This is my question: How is the heliocentric model not "actually" more correct the geocentric model? With modern technology (as well as with the theory of gravitation) isn't it clear that the heliocentric model is objectively true? Could someone play devil's advocate and somehow fudge together a consistent description of the universe in today's world that uses Ptolemy's geocentric model?
 

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  • #2
Borek
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I guess what he meant was that the choice of the "main" point is arbitrary. Math necessary to describe the kinematics of the Solar system is much easier if you put its center where the mass center is, but in general you can use any other point for that.

Actually sometimes you have no choice but to use an "inconvenient" point as the center. Simulating Jupiter moons is much easier when you assume they revolve around Jupiter, but it becomes problematic when you want to deal with whole Solar system at once.
 
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I guess what he meant was that the choice of the "main" point is arbitrary. Math necessary to describe the kinematics of the Solar system is much easier if you put its center where the mass center is, but in general you can use any other point for that.

Actually sometimes you have no choice but to use an "inconvenient" point as the center. Simulating Jupiter moons is much easier when you assume they revolve around Jupiter, but it becomes problematic when you want to deal with whole Solar system at once.
But is he not saying that one is completely equivalent to the other from a "realness" point of view (not considering mathematical complexity)? I don't understand how that could be so, if clearly the earth revolves around the sun because of gravitation. Doesn't this mean that the heliocentric model is "more true" than the geocentric model in a real sense?
 
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Borek
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clearly the earth revolves around the sun
It doesn't. It revolves around the mass center of the system.

"More true", "real sense"" in such contexts are very poorly defined. You may think they are, but when you try to analyze them you will soon learn what you though was intuitively obvious evades precise understanding.

Let's get back to the Jupiter example. Imagine living on the Ganymede. Which system - the one centered on Ganymede, the one centered on Jupiter, the one centered on Sun - is the "real one"? But this hierarchy of center points doesn't end here, what about the center of our Galaxy? Center of the local group of galaxies?

Or perhaps - once you realize the choice is arbitrary - choice of the center point doesn't actually matter?
 
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This is my question: How is the heliocentric model not "actually" more correct the geocentric model?
The 'truth' of the models are always matter of measurement accuracy. At the accuracy available by the 'modern technology' it is 'evident' that the heliocentric model is the better, but for 'not modern technology' it is actually quite taxing to find the problems with the geocentric model, and at that level there are no advantages in using the heliocentric one.

According to that, the geocentric model is not 'wrong'. It is just ... well, out of its relevance range if somebody brings it up now.

It might be better to check it out on a less absurd example. Is Newton 'wrong'? We already has better models and math available...
 
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