This is another snippet from my Cosmology lecture, based on Dr. Barbara Ryden's textbook "Introduction to Cosmology" Vol 2. Galilean Relativity: All inertial frames are equal and observe the same laws of physics. Newton’s Laws of Motion: Three laws describing the relationship between a body and the forces acting upon it, and its motion in response. Law of Inertia: An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Newton’s Philosophy: Newton’s mechanics were based on the concepts of absolute time and space, assuming an absolute reference frame for both. Galileo’s Relativity: Galileo’s relativity, while assuming absolute time, did not delve into the nature of absolute space and posited that no experiment could determine an absolute reference frame. Newton’s Rotating Bucket Thought Experiment: Newton used the example of a rotating bucket of water to illustrate the concept of absolute space, noting the difference in water surface shape between a spinning and a stationary bucket. Newton’s Explanation: The shape of the water’s surface in a spinning bucket is determined by its motion relative to absolute space. Alternative Explanation: The difference in water surface shape is solely due to the relative motion of the water within the bucket. Newton’s First Law and Inertial Frames: In an inertial frame, an object with no forces acting on it moves at a constant velocity relative to absolute space. Mach’s Inertial Frame: Defined as at rest with respect to distant fixed stars, rejecting the need for absolute space. Mach’s View on Spinning Objects: Inertial frame is ‘at rest or close enough to’ with respect to distant stars, applicable only in universes with many stars. Newton’s Laws and Absolute Space: Newton’s Laws apply to Galileo’s relativity but introduced the concept of absolute space and time.