Major Scientific Discoveries

Why This Matters

Scientific discoveries don't happen in isolation—they build on each other, challenge existing paradigms, and reshape how we understand everything from the smallest particles to the entire universe. You're being tested on more than just names and dates; exams want you to understand how scientific knowledge develops, why certain discoveries were revolutionary, and what principles they established that still govern our understanding today.

These breakthroughs demonstrate core concepts like empirical observation, theory revision, reductionism vs. systems thinking, and the unification of seemingly unrelated phenomena. Whether you're tackling questions about the nature of matter, the mechanisms of life, or the structure of the cosmos, don't just memorize who discovered what—know what conceptual shift each discovery represents and how it connects to the broader scientific enterprise.

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Foundational Theories of Matter and Energy

These discoveries answered the fundamental question: what is everything made of, and how does it behave? They moved science from philosophical speculation to testable, mathematical frameworks.

Atomic Theory

• Matter consists of indivisible atoms—John Dalton's 1803 proposal that elements are made of identical atoms that combine in fixed ratios to form compounds
• Subatomic structure was later discovered, revealing that atoms contain protons, neutrons, and electrons arranged in specific configurations
• Foundation of modern chemistry—explains chemical reactions, bonding, and why elements have distinct properties

Periodic Table of Elements

• Organized elements by atomic number and recurring properties—Dmitri Mendeleev's 1869 arrangement predicted undiscovered elements based on gaps in the pattern
• Electron configuration determines an element's chemical behavior, explaining why elements in the same column share similar reactivity
• Essential predictive tool—allows scientists to anticipate how elements will bond, react, and behave in compounds

Laws of Thermodynamics

• Energy cannot be created or destroyed—the First Law establishes conservation of energy as a universal principle: $\Delta U = Q - W$
• Entropy always increases in isolated systems (Second Law), explaining why heat flows from hot to cold and why perpetual motion machines are impossible
• Governs everything from engines to ecosystems—these laws set fundamental limits on energy conversion efficiency and biological processes

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Revolutions in Physics: Motion, Gravity, and Spacetime

These discoveries describe how objects move and interact across scales—from falling apples to orbiting galaxies. Each built upon or overturned its predecessors.

Heliocentric Model of the Solar System

• Sun-centered solar system—Copernicus's 1543 model displaced Earth from the cosmic center, fundamentally challenging the geocentric worldview
• Supported by observation—Galileo's telescope observations and Kepler's laws of planetary motion provided empirical evidence
• Paradigm shift in scientific thinking—demonstrated that accepted truths could be overturned by evidence, establishing a model for scientific revolution

Laws of Motion and Universal Gravitation

• Three laws describe all classical motion—Newton's framework explains inertia, $F = ma$, and action-reaction pairs governing how objects move
• Universal gravitation states every mass attracts every other mass: $F = G\frac{m_1 m_2}{r^2}$, unifying terrestrial and celestial mechanics
• Foundation of classical physics—enabled prediction of planetary orbits, tides, and projectile motion; remained unchallenged for over 200 years

Theory of General Relativity

• Gravity is the curvature of spacetime—Einstein's 1915 theory redefined gravity not as a force but as mass bending the fabric of space and time
• Predicts extreme phenomena including black holes, gravitational lensing (light bending around massive objects), and gravitational waves
• Confirmed repeatedly—from Mercury's orbital precession to LIGO's detection of gravitational waves, validating predictions classical physics couldn't explain

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The Quantum Revolution

Quantum mechanics revealed that the subatomic world operates by fundamentally different rules than the macroscopic world we experience—probability replaces certainty, and observation affects outcomes.

Quantum Mechanics

• Wave-particle duality—matter and energy exhibit both wave and particle properties depending on how they're observed
• Heisenberg's uncertainty principle states you cannot simultaneously know a particle's exact position and momentum: $\Delta x \cdot \Delta p \geq \frac{\hbar}{2}$
• Enables modern technology—semiconductors, lasers, MRI machines, and emerging quantum computers all depend on quantum principles

Theory of Electromagnetism

• Unified electricity and magnetism—Maxwell's equations (1860s) showed these are two aspects of a single electromagnetic force
• Light is an electromagnetic wave—this insight connected optics to electricity and predicted the entire electromagnetic spectrum
• Foundation for modern technology—radio, television, wireless communication, and electronics all derive from electromagnetic theory

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Understanding Life: Biology's Core Principles

These discoveries established what life is, how it works, and how it changes over time—moving biology from description to mechanistic explanation.

Cell Theory

• All living things are made of cells—established by Schleiden, Schwann, and Virchow in the 1830s-50s as biology's fundamental organizing principle
• Cells arise only from pre-existing cells (omnis cellula e cellula), explaining the continuity of life through reproduction
• Unifies all biology—from bacteria to whales, cellular structure provides a common framework for understanding life processes

Discovery of DNA Structure

• Double helix structure—Watson and Crick's 1953 model (built on Rosalind Franklin's X-ray crystallography) revealed how genetic information is physically encoded
• Base pairing explains heredity—adenine pairs with thymine, guanine with cytosine, showing how DNA replicates and transmits information
• Launched molecular biology—enabled genetic engineering, genomics, CRISPR, forensic DNA analysis, and personalized medicine

Theory of Evolution by Natural Selection

• Species change over time through differential reproduction—Darwin's 1859 theory explains how organisms with advantageous traits survive and pass those traits on
• Natural selection is the mechanism—environmental pressures "select" beneficial variations, driving adaptation without conscious design
• Unifies all of biology—explains biodiversity, extinction, antibiotic resistance, and the relationships among all living things

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Medicine and Public Health Breakthroughs

These discoveries transformed medicine from guesswork to science, dramatically extending human lifespan and establishing evidence-based treatment.

Germ Theory of Disease

• Microorganisms cause infectious disease—Pasteur and Koch's work (1860s-80s) overturned the "miasma" theory that blamed bad air for illness
• Koch's postulates established criteria for proving a specific microbe causes a specific disease, creating a rigorous methodology
• Revolutionized public health—led to antiseptic surgery, pasteurization, water treatment, and vaccination programs

Discovery of Penicillin

• First true antibiotic—Fleming's 1928 accidental discovery that Penicillium mold killed bacteria launched the antibiotic era
• Dramatically reduced mortality from bacterial infections—previously fatal conditions like pneumonia and infected wounds became treatable
• Model for drug discovery—spurred systematic searches for other antibiotics, though overuse has created the current antibiotic resistance crisis

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Cosmic Scale: Understanding the Universe

These discoveries address the biggest questions: where did everything come from, and how is it structured?

Big Bang Theory

• Universe began 13.8 billion years ago from an extremely hot, dense state and has been expanding ever since
• Supported by multiple evidence lines—cosmic microwave background radiation (the "afterglow"), redshift of distant galaxies, and abundance of light elements
• Explains cosmic evolution—describes how the universe cooled to form atoms, then stars, galaxies, and eventually planets and life

Plate Tectonics

• Earth's lithosphere consists of moving plates—their interactions cause earthquakes, volcanoes, mountain formation, and continental drift
• Explains geological patterns—why earthquakes cluster along plate boundaries, why continents fit together like puzzle pieces, why ocean floors are younger than continents
• Unifies Earth science—connects geology, paleontology (fossil distribution), and climate history into a coherent framework

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Quick Reference Table

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Self-Check Questions

1. Which two discoveries both involved unifying previously separate phenomena into a single framework? What did each unify?

2. Compare Newton's Laws of Motion with Einstein's General Relativity: under what conditions does each theory apply, and why did physics need both?

3. How does the discovery of DNA structure build upon and extend Cell Theory? What new questions could be answered after 1953 that couldn't be answered before?

4. Identify two discoveries that fundamentally changed medical practice. Explain how one is explanatory (tells us why disease happens) and the other is interventional (tells us how to treat it).

5. If an FRQ asked you to explain how scientific knowledge develops over time using specific examples, which three discoveries would you choose to show paradigm shifts, accumulation of evidence, and technological application? Justify your choices.