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I wasn't sure if this might be better suited to History of Science and Mathematics SE, but I suppose it is a bit more 'science-y' than historical.

Apparently Newton believed in absolute space and absolute time, existing independently from anything else within the universe (these beliefs were supposedly laid down in the 'Scholium' of his Principia; see here).

However I was under the impression that Galilean relativity, although supporting the idea of absolute time, did away with absolute space. And yet Newton believed in Galilean relativity and his first law- a body remaining in a state of rest or uniform motion unless acted on by a net force- is essentially a statement of Galielean relativity.

How can it be so that Newton believed in absolute space and believed in Galilean relativity? In fact, in the link it suggests that Newton believed in absolute motion as well (which would be implied from his belief in the existence of absolute space and absolute time anyway).

Perhaps I am getting confused between the notions of 'relativity' and 'absolute space/time'...

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  • $\begingroup$ -1. What Newton believed - and even his interpretation of his own Laws of Motion - is history, not physics. $\endgroup$ – sammy gerbil Aug 2 '17 at 21:40
  • $\begingroup$ @sammygerbil: Such questions are actually quite relevant, since they make one rethink the physical theories and understand them and their relations to other theories, much deeper and better. $\endgroup$ – AlQuemist Aug 9 '17 at 8:04
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Newton's idea of absolute space simply appeared as an answer to the following question: What is an inertial system? Saying that an inertial system is one with constant velocity relative to another inertial system of course does not answer the question. To avoid such logical weakness in Newton's first law one has, at some point, to assume that there is a frame of reference, called absolute space, that - by definition - is inertial.

On the other hand Galilean relativity consists on transformations among inertial frames of reference and such relations do not forbid an absolute space. In fact, the idea is that we can use Galilean relativity transformations to relate any inertial frame to the absolute space.

Although the concept of absolute space can be removed by Mach's definition of inertial frame (given an isolated particle, there is a reference frame, called inertial, relative to which the particle has constant velocity), there is no contradiction between Galilean relativity and absolute space. Only Special Relativity can definitely rule out the existence of absolute space.

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Galilean relativity is Galileo's observation that the laws of physics are the same in all reference frames. Specifically, he noted that if a scientist and his laboratory move at constant speed in an unvarying straight path, the scientist will have no way of knowing his reference frame is in motion. In other words, unaccelerated motion of an object has meaning only in relation to another object.

Although Newton believed that there is an absolute space and an absolute time, he also believed that humans live in relative space and relative time. He defined absolute space as a mathematical construction existing "without regard to anything external" (in his own words). But he also postulated that all motion takes place in relative space, which we incorrectly perceive to be absolute space.

Newton did not deny Galileo's principle of relativity. He supplemented it by saying that relative motion exists in a theater of absolute space and time. The idea of absolute space is not necessary to explain the laws of Newtonian mechanics. Perhaps Newton's idea of absolute space provided a way for him to reconcile relativity with the existence of an absolute God.

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