Newtonian physics laid the groundwork for understanding motion and gravity. It introduced laws that explain how objects move and interact, from apples falling to planets orbiting the sun. These principles helped us grasp the mechanics of our universe.

However, Newtonian physics has its limits. It falls short in explaining phenomena like Mercury's orbit or the behavior of light near massive objects. This paved the way for Einstein's theories and our modern understanding of space and time.

Newtonian Physics and Gravitation

Key concepts of Newtonian physics

• Newton's first law of motion (law of inertia) states that an object at rest remains at rest and an object in motion continues moving at a constant velocity unless acted upon by an external net force (friction, gravity)
• Newton's second law of motion establishes a relationship between an object's mass, acceleration, and the applied force, expressed as $F = ma$, where $F$ is the net force, $m$ is the mass, and $a$ is the acceleration
• Newton's third law of motion asserts that for every action, there is an equal and opposite reaction, meaning that forces always occur in pairs (rocket propulsion, recoil of a gun)
• Law of universal gravitation describes the attraction between any two objects with mass, given by the equation $F = G \frac{m_1 m_2}{r^2}$, where $F$ is the gravitational force, $G$ is the gravitational constant, $m_1$ and $m_2$ are the masses of the objects, and $r$ is the distance between their centers

Mathematical framework for celestial motion

• Kepler's laws of planetary motion, based on empirical observations, describe the orbits of planets around the Sun and can be mathematically derived from Newton's laws (elliptical orbits, equal areas in equal times)
• Orbital mechanics explains the motion of celestial bodies as a result of the balance between gravitational force and inertia, leading to elliptical orbits where planets accelerate near the Sun and decelerate farther away (comets, asteroids)
• Tides on Earth are caused by the gravitational pull of the Moon and Sun on Earth's oceans, with the Moon having a more significant effect due to its proximity (high tide, low tide)
• Comets and asteroids follow different types of orbits depending on their velocity and distance from the Sun:
  1. Elliptical orbits have a closed path around the Sun (short-period comets)
  2. Parabolic orbits have an open path and escape the solar system (long-period comets)
  3. Hyperbolic orbits have an open path and approach the Sun only once (interstellar objects)

Implications for universal understanding

• Absolute space is a fixed, unchanging background against which motion occurs, independent of the objects within it, providing a universal reference frame (3D coordinate system)
• Absolute time flows uniformly without relation to anything external, meaning that simultaneous events occur at the same absolute time regardless of the observer's location or motion (synchronized clocks)
• Deterministic universe concept suggests that the future state of the universe can be precisely predicted from its current state using Newton's laws, implying a lack of randomness or free will (Laplace's demon)
• Clockwork universe analogy compares the universe to a well-ordered machine governed by immutable laws, like the gears in a clock, emphasizing the predictability and regularity of celestial motions (solar system model)

Limitations in astronomical explanations

• Precession of Mercury's orbit revealed a discrepancy between the observed and predicted orbit using Newtonian physics, which was later explained by Einstein's general theory of relativity (perihelion shift)
• Newtonian physics breaks down in high-speed and high-gravity regimes, such as when objects move at speeds close to the speed of light or in strong gravitational fields (black holes, neutron stars)
• Dark matter and dark energy are concepts introduced to account for observations of galaxies and the expansion of the universe that cannot be explained by Newtonian physics alone (galaxy rotation curves, accelerating universe)
  1. Dark matter is proposed to explain the missing mass in galaxies and galaxy clusters
  2. Dark energy is hypothesized to drive the accelerating expansion of the universe