Scientific Revolutions: Copernicus, Newton, Einstein
What is a Scientific Theory?
A scientific theory is a set of ideas or hypotheses (assumptions) that satisfies two conditions: it must align with observations or recorded data, and it must not contradict fundamental concepts.
The Copernican Revolution: Sun-Centered Universe
For about 2,000 years, from the time of Aristotle until after Columbus’s voyages to the New World, it was believed that the Earth was the center of the universe (the geocentric theory). The shift to the Copernican heliocentric theory, which proposed the Sun as the center around which the Earth revolves, is known as the Copernican Revolution.
The development and acceptance of Copernicus’s astronomical model, focusing on the Sun, did not happen quickly; it took about 150 years for it to become established. Its seeds grew and developed through the works of Galileo and Kepler, while Newton ultimately shaped it, contributing to what is known as the Scientific Revolution. The heliocentric theory proved successful partly because it was adaptable. For instance, Kepler incorporated the concept of elliptical orbits without undermining the core idea of Copernicus’s heliocentric model.
Newton’s Laws: Gravity and Cosmic Mechanics
The Englishman Isaac Newton proposed that the solar system operates as a mechanism governed by his law of universal gravitation:
The motion of matter is determined by the force of gravity, which acts as the fundamental principle of cosmic mechanics. Newton also postulated the existence of an absolute space and time (often associated with the idea of a ‘cosmic ether’), providing fixed frames of reference against which the positions, moments, and motion of bodies could be known with absolute precision. Physics became the preeminent science, and Newton’s laws were considered a monumental achievement of human intellect.
Energy Conservation and The Rise of Entropy
Physics states that the universe operates based on energy. Energy appears in various forms (e.g., gravitational potential, kinetic energy, electrical energy) that can be converted from one form to another. Similar to how there’s a finite amount of money, there’s a finite amount of energy, expressed by the principle of conservation of energy: Energy is neither created nor destroyed; it merely transforms from one form to another during interactions and can be dissipated.
The spontaneity of a transformation within a material system is characterized by entropy, a measure of the system’s disorder. Natural material systems tend to evolve from more orderly states to more disordered states, reflecting the tendency of constituent particles towards a random distribution. Systems and processes in nature typically evolve in a way that increases their entropy. This increase is governed by principles similar to the laws of probability and statistics.
Einstein’s Relativity: Space, Time, and Gravity
In the latter half of the 19th century, the Scottish physicist James Clerk Maxwell explained that light is electromagnetic radiation propagating at approximately 300,000 km/s. This led to questioning the existence of the ‘cosmic ether’ as an absolute frame of reference.
Special Relativity: Light Speed and E=mc²
In 1905, Albert Einstein published his Special Theory of Relativity. It was based on the principle that the speed of light in a vacuum is a finite, universal constant (approximately 300,000 km/s) and rejected the hypothesis of a cosmic ether providing an absolute frame of reference. The main consequences of the Special Theory of Relativity include:
- Time dilation: Time passes differently for observers moving relative to each other at speeds approaching the speed of light.
- Length contraction: The length of an object appears shorter when measured by an observer moving relative to it at near light speed.
- Mass-energy equivalence: Mass (m) and energy (E) are equivalent and interconvertible, described by the famous equation E=mc², where c is the speed of light. This has profound implications, particularly in nuclear physics, where small decreases in mass release large amounts of energy.
After publishing the Special Theory, Einstein developed the General Theory of Relativity to account for accelerating systems and gravity.