Complete Science Guide 2026: Physics to Climate

Science is a way of finding out what is true about nature by testing ideas against evidence and keeping only the ones that survive. Physics describes matter, energy, space and time. Chemistry explains how atoms join and react. Earth and climate science tracks how the planet's air, oceans and ice behave and how people are changing them. Materials science turns all of that into things we can build.

This page covers the main ideas in each of those fields, the open questions, and the habits of thought that make science work. Each section links to the deep-dive article that covers its subtopic best.

---

What Science Actually Is

Science isn't a fixed set of facts. It's a procedure: observe something, propose an explanation, work out what that explanation predicts, then check whether the prediction holds. The body of "scientific knowledge" is the accumulated result: claims that have survived repeated attempts to prove them wrong. The scientific method and how evidence becomes knowledge walks through each step with historical examples.

What makes a claim scientific:

1. Falsifiability. It must be testable in principle. If no possible observation could count against it, it is not a scientific claim.
2. Reproducibility. Independent groups following the same method should get the same result.
3. Peer review. Other experts check the methods and reasoning before a result is published. Review catches many errors, though not all of them.
4. Revision with evidence. Claims change when better data arrives. Changing is how the system works, not a sign that it failed.

These rules explain why science differs from opinion. A scientific claim is always conditional: it holds as long as the evidence supports it. Isaac Newton's mechanics worked for two centuries until precise measurements of fast motion and strong gravity showed where it broke down. The replacement, relativity, did not discard Newton. It explained why his laws work so well at everyday speeds and where they stop working. Most scientific progress looks like that: a theory gets wrapped in a broader one rather than thrown away.

Experiments are the engine of this process. Some confirm a prediction that no one could have guessed in advance. Others kill an attractive idea. The complete guide to landmark science experiments collects the most important of both kinds by field, and many of them appear in the sections below.

---

The Major Branches at a Glance

Scientific fields overlap. A chemist modelling a battery uses quantum physics; a climate scientist uses fluid dynamics and chemistry. The table below shows how the main physical sciences divide the work.

Branch	What it studies	Key question	Start here
Physics	Matter, energy, forces, space and time	What are the basic rules everything obeys?	Four fundamental forces
Chemistry	Atoms, bonds and reactions	Why do substances combine and change the way they do?	Linus Pauling and the chemical bond
Earth science	Rock, ocean, atmosphere and interior	How does the planet work as a system?	Earth's internal layers
Climate science	Long-term behaviour of the atmosphere and oceans	How do energy flows set Earth's temperature?	The water cycle
Materials science	How structure produces properties	How do we design matter for a job?	Superconductivity
Mathematics	Logical structure and quantity	What follows necessarily from a set of assumptions?	Chaos and the butterfly effect

Physics supplies the rules; the other fields apply them at larger scales and to more specific systems.

---

Physics

Physics is the study of matter, energy, space and time. Everything else in the natural sciences rests on it, because chemical bonds, weather and living cells all obey physical law.

Classical physics covers the world we see directly: falling objects, orbits, heat, sound, light and electricity. Newton's laws of motion and gravitation, published in 1687, still put spacecraft into orbit. James Clerk Maxwell's equations of the 1860s unified electricity, magnetism and light into a single theory, and the biography of James Clerk Maxwell shows how that unification came about.

Quantum mechanics covers the very small: atoms, electrons, photons. It is counterintuitive but extremely accurate, and it underpins semiconductors, lasers and MRI scanners.

Relativity covers the very fast and the very massive. Special relativity (1905) joined space and time into spacetime; general relativity (1915) explained gravity as the curvature of spacetime.

All known interactions reduce to four forces: gravity, electromagnetism, the strong nuclear force and the weak nuclear force. Three of them fit into one framework, the Standard Model of particle physics. Gravity does not, and reconciling quantum mechanics with general relativity remains the largest open problem in physics.

Energy, Heat and Thermodynamics

Thermodynamics explains why heat flows from hot to cold, why engines can never be perfectly efficient, and why perpetual motion machines fail. Its first law says energy is conserved. Its second law says the total entropy of an isolated system does not decrease, which is why a broken egg doesn't reassemble and why time seems to have a direction. Thermodynamics and entropy covers both laws in detail.

The idea that heat is a form of energy rather than a fluid was settled by experiment. Count Rumford noticed that boring cannon barrels produced heat without limit, which made no sense if heat were a substance being used up. James Joule later measured how much mechanical work produces a given amount of heating, using a falling weight to turn a paddle wheel in water. Everyday technology still runs on this physics: a refrigerator uses work to push heat from a cold space into a warmer room, and how a refrigerator works traces the cycle step by step.

Electricity, Magnetism and Light

Electricity and magnetism are two faces of one force. Hans Christian Oersted showed in 1820 that an electric current deflects a compass needle; Michael Faraday then showed that a moving magnet induces a current, the principle behind every generator. Maxwell's equations predicted that oscillating electric and magnetic fields travel as waves at the speed of light, and that light itself is such a wave. Heinrich Hertz produced and detected those waves in the lab in the late 1880s, as described in Hertz's radio wave experiments. Microwave ovens are an everyday example; see how microwaves work.

Light behaves as a wave in some experiments and as a stream of particles in others. Thomas Young's interference fringes in the early 1800s supported the wave view. The photoelectric effect, which Albert Einstein explained in 1905, showed that light delivers energy in discrete packets called photons. What a photon is explains how both descriptions can be true at once. For the day-to-day side of magnetism, from fridge magnets to Earth's magnetic field, see how magnetism works.

Quantum Mechanics

Quantum mechanics describes how matter and energy behave at atomic scales. Three ideas do most of the work:

• Quantisation. Energy comes in discrete steps. Max Planck introduced the idea in 1900 to explain the spectrum of heated objects.
• Superposition and probability. Before measurement, a quantum system is described by a wavefunction that gives probabilities for each outcome.
• Entanglement. Two particles can share a single quantum state, so measuring one constrains what you will find for the other, however far apart they are.

The clearest single demonstration is the double-slit experiment: fire electrons one at a time at two slits and an interference pattern still builds up, as if each electron passed through both. The double-slit experiment covers both the classic version and its modern variants. For a structured introduction to the theory as a whole, quantum mechanics foundations covers waves, uncertainty and entanglement in order.

Entanglement troubled Einstein, who suspected hidden variables lay underneath. In 1964 John Bell showed that hidden-variable theories of the kind Einstein favoured make predictions that differ measurably from quantum mechanics. Experiments since then, including Alain Aspect's in the early 1980s, have sided with quantum mechanics; the Aspect Bell test explains the setup. Quantum effects are also the basis of new machines: how quantum computers actually work explains qubits, error correction and what these devices can and cannot yet do.

Relativity

Einstein's two theories changed how physicists think about space, time and gravity.

Special relativity (1905) starts from two assumptions: the laws of physics are the same for all observers moving at constant speed, and light in a vacuum travels at the same speed for all of them. From those follow time dilation (moving clocks run slow), length contraction, and the equivalence of mass and energy, E = mc².

General relativity (1915) treats gravity not as a force but as the curvature of spacetime by mass and energy. Objects follow the straightest possible paths through curved spacetime, and those paths look to us like orbits and falls. Einstein's relativity explained covers both theories, and the Albert Einstein biography places them in the context of his life.

The predictions have passed every test so far:

• Light bending. The 1919 solar eclipse expeditions measured starlight bending around the Sun by close to the amount general relativity predicted; see the Eddington eclipse expedition.
• Gravitational time dilation. Clocks higher in a gravitational field run faster. GPS satellites must correct for both special and general relativistic effects or positioning errors would build up quickly, as how GPS uses Einstein's relativity explains.
• Gravitational waves. The LIGO detectors recorded ripples in spacetime from two merging black holes on 14 September 2015, announced in February 2016. The first gravitational wave detection covers how instruments measured a distortion far smaller than an atomic nucleus.

Particle Physics and the Standard Model

The Standard Model lists the known fundamental particles (six quarks, six leptons, the force-carrying bosons and the Higgs boson) and describes three of the four forces. It is one of the most precisely tested theories in science.

Its last missing piece was found at CERN. On 4 July 2012, the ATLAS and CMS experiments at the Large Hadron Collider announced a new particle with a mass of about 125 GeV, consistent with the Higgs boson. The Higgs field is what gives many elementary particles their mass; the Higgs boson explained describes how. Earlier steps toward the Standard Model came from smaller experiments: Ernest Rutherford's gold-foil scattering revealed the atomic nucleus, and the Rutherford gold foil experiment shows how an unexpected result overturned the prevailing model of the atom.

The Standard Model is known to be incomplete. It does not include gravity. It does not explain dark matter or dark energy, which according to the Planck satellite's 2013 results make up roughly 27% and 68% of the universe's mass-energy, leaving about 5% for ordinary matter. It also had to be patched after neutrino oscillation experiments showed neutrinos have mass. The neutrino detection and solar neutrino problem tells that story.

---

Chemistry

Chemistry studies how atoms combine into molecules and how those molecules react. It connects physics, which explains atomic structure, to biology, which runs on chemical reactions.

Main branches:

• Inorganic chemistry: metals, minerals, salts and most elements other than carbon.
• Organic chemistry: carbon-based compounds, including fuels, plastics and drugs.
• Biochemistry: the chemistry of living systems.
• Physical chemistry: the physics of reactions, including energy changes and rates.
• Analytical chemistry: working out what a sample contains and how much.

Modern chemistry dates to the late 1700s, when Antoine Lavoisier used careful weighing to show that combustion is combination with oxygen, not the release of a substance called phlogiston. Lavoisier's combustion experiments explain why that closed balance sheet of mass mattered so much.

The Periodic Table

The periodic table arranges the elements by atomic number, so that elements with similar chemical behaviour fall into the same columns. Dmitri Mendeleev's 1869 version left gaps for elements not yet discovered and predicted their properties; several were found later with properties close to his predictions. The Dmitri Mendeleev profile covers how he built it.

The table currently has 118 confirmed elements. The last four to be named were nihonium (113), moscovium (115), tennessine (117) and oganesson (118), whose names IUPAC approved on 28 November 2016. That completed the seventh row. The heaviest elements are made in particle accelerators and decay in fractions of a second.

Bonds, Reactions and Rates

Atoms bond by sharing or transferring electrons. The type of bond explains a great deal: ionic salts dissolve in water and conduct when molten, covalent molecules form gases, liquids and plastics, and metallic bonding gives metals their shine and conductivity. Quantum mechanics is what ultimately explains bonding, which is why the two fields became so closely tied in the twentieth century.

Many reactions that release energy still need a push to get started. A catalyst lowers that barrier without being used up, so the reaction runs faster at lower temperatures. Enzymes are biological catalysts; catalytic converters and oil refineries depend on metal catalysts. How catalysts speed up reactions is the main article on this. The most consequential industrial example is the Haber-Bosch process, which combines nitrogen from the air with hydrogen to make ammonia for fertiliser; the Haber-Bosch process covers its chemistry and its effect on world food supply.

Gases follow simple relationships between pressure, volume, temperature and amount, which Robert Boyle, Jacques Charles and Amedeo Avogadro worked out separately and which combine into the ideal gas law. The gas laws of Boyle, Charles and Avogadro shows how the pieces fit together.

Acids, Bases and pH

The pH scale measures how acidic or basic a water-based solution is. Values below 7 are acidic and values above 7 are basic. Because the scale is logarithmic, each whole-number step is a tenfold change in hydrogen ion concentration, so pH 3 is a hundred times more acidic than pH 5.

Living systems are sensitive to pH. Human blood is held between about 7.35 and 7.45; values outside that range indicate acidosis or alkalosis, which are medical problems. Acid-base chemistry and the pH scale explains buffers, indicators and why ocean acidification matters.

Electrochemistry

Electrochemistry links chemical reactions with electric current. Alessandro Volta's stack of metal discs separated by brine-soaked cloth, built around 1800, was the first battery to produce a steady current; Volta's battery and early electrochemistry covers it. Running the process in reverse uses electricity to drive a reaction that would not happen on its own. How electrolysis splits water explains the version behind "green hydrogen" proposals.

---

Earth and Climate Science

Earth science studies the planet as a set of connected systems: solid rock, oceans, atmosphere, ice and living things. Climate science is the part that deals with long-term patterns in temperature, rainfall and circulation, and with how human activity is changing them.

Inside the Planet

Nobody has drilled through the crust, so knowledge of Earth's interior comes mostly from earthquake waves. Seismic waves change speed and direction as they pass through layers of different density and state. Some types cannot travel through liquid, which revealed that the outer core is molten. How scientists know what is inside Earth explains the evidence.

The surface is broken into plates that move a few centimetres a year. Alfred Wegener proposed continental drift in 1912 from matching coastlines, rocks and fossils, but he had no mechanism and the idea was largely rejected for decades. Seafloor mapping in the 1950s and 1960s, including Marie Tharp's maps of the mid-Atlantic ridge, supplied the evidence that turned drift into plate tectonics. The Alfred Wegener biography is a good case study in how a correct idea can wait for evidence. Plate boundaries are where most earthquakes and volcanoes occur; how earthquakes work explains faults, waves and magnitude scales.

How Climate Works

Earth's climate is set by an energy balance. Sunlight arrives, some is reflected by clouds, ice and bright surfaces, and the rest warms the land and oceans. The warm surface radiates infrared energy back toward space. Certain gases, mainly water vapour, carbon dioxide and methane, absorb some of that infrared and re-emit it in all directions, including back down. That is the greenhouse effect, and without it Earth's surface would be far colder.

Other parts of the system move heat around rather than trap it. Ocean currents carry heat from the tropics toward the poles. Evaporation and condensation move large amounts of energy through the atmosphere, which is why the water cycle is central to both weather and climate. Storms are the atmosphere releasing that energy; how hurricanes form shows why they need warm ocean water.

Climate Change: What the Evidence Shows

The basic physics has a long history. In 1859 John Tyndall measured how strongly different gases absorb infrared radiation at the Royal Institution. He found that nitrogen and oxygen are nearly transparent to it, while water vapour and carbon dioxide absorb it strongly, as described by NASA's Earth Observatory and the Royal Institution.

Since then, measurements have filled in the rest:

Indicator	Value	Source
Pre-industrial CO2 concentration	about 280 ppm	NOAA Global Monitoring Laboratory
Global mean CO2, 2024	422.7 ppm	NOAA Global Monitoring Laboratory
CO2 increase during 2024	3.75 ppm, the largest annual rise in NOAA's record	NOAA Global Monitoring Laboratory
Global surface temperature, 2024	about 1.55 °C (±0.13 °C) above the 1850–1900 average, the warmest year on record	World Meteorological Organization, January 2025
Projected sea level rise by 2100 (likely range, relative to 1995–2014)	0.28–0.55 m under very low emissions; 0.63–1.01 m under very high emissions	IPCC Sixth Assessment Report

Concentrations, temperatures and sea level are all moving in the direction the physics predicts.

Two points are often misread. First, a single year above 1.5 °C does not mean the Paris Agreement limit has been crossed; the WMO notes that the target refers to warming averaged over decades. Part of 2024's heat came from an El Niño that lasted from mid-2023 into 2024. Second, scientific disagreement today is not about whether human emissions are warming the planet. It is about how fast particular changes will happen, how they will play out regionally, and which responses work best.

Ice and Sea Level

The Greenland ice sheet holds enough water to raise global sea level by about 7.4 metres if it melted completely, and the Antarctic ice sheet about 58 metres, based on recent bed-topography (BedMachine) estimates. Neither will melt completely on human timescales, but even partial loss matters for coastal cities. The IPCC's likely ranges above exclude low-likelihood, high-impact ice-sheet processes because confidence in them is low; a faster Antarctic collapse cannot be ruled out.

Dating the Past

Climate science depends on knowing what happened before instruments existed: ice cores, ocean sediments, tree rings and rocks record past conditions. Putting dates on those records relies on radioactive decay, which proceeds at a known rate. How radiocarbon dating works covers the carbon-14 method used for organic material up to tens of thousands of years old, and how scientists measure the age of Earth explains the uranium-lead methods used for billions of years.

---

Materials Science

Materials science asks how the arrangement of atoms and molecules in a substance determines its properties, and how to engineer that arrangement. Why does glass shatter while steel bends? Why does copper conduct and rubber insulate? The answers come from crystal structure, bonding and defects at the atomic scale. New materials have often set the pace of new technology.

Semiconductors and Light

Semiconductors conduct electricity better than insulators but worse than metals, and their conductivity can be precisely controlled by adding small amounts of other elements. Silicon dominates electronics; modern chips contain billions of transistors. The same physics produces light-emitting diodes, in which electrons dropping across an energy gap emit photons of a specific colour. How LED lights work explains why blue LEDs were so hard to make and why their invention earned a Nobel Prize. Lasers use related principles to produce light in which every wave is in step; see how lasers work.

Superconductors

Some materials, cooled far enough, conduct electricity with zero resistance and expel magnetic fields. Superconductors already run MRI magnets and particle accelerators, but most need cooling with liquid helium or liquid nitrogen. A material that superconducts at room temperature and ordinary pressure would change power grids and electronics, and claims of one appear regularly; none has been confirmed. The superconductivity deep dive linked in the table above covers the physics and why the search is so hard.

Glass, Crystals, Polymers and Smart Materials

Not every solid is a crystal. Glass is an amorphous solid whose atoms are frozen into a disordered arrangement, and why glass is not a normal solid clears up the popular myth that old windows flow. Crystals, by contrast, grow by adding atoms or molecules in a repeating pattern, which how crystals grow from solutions demonstrates.

Polymers are long chains of repeating units. Natural examples include DNA, proteins and cellulose; synthetic ones include nylon, polyethylene and rubber. The discovery of how to link small molecules into chains on purpose created the plastics industry; polymerisation and synthetic materials tells that history. Some alloys and polymers can be deformed and then return to a stored shape when heated, a property used in medical stents and eyeglass frames; why some materials remember their shape explains the crystal-structure switch behind it.

Energy Materials

Batteries, solar cells and fuel cells are materials problems. Lithium-ion batteries dominate portable electronics and electric vehicles; research aims at higher energy density, better safety, lower cost and less reliance on scarce metals. Solid-state batteries replace the liquid electrolyte with a solid one. Silicon dominates commercial solar panels, while perovskite cells offer cheaper production but still face durability problems. Fusion power is also a materials challenge: reactor walls must survive intense heat and neutron bombardment. Nuclear fusion energy explained covers the physics and the engineering obstacles.

---

Mathematics: The Language of Science

Mathematics is not a natural science in the usual sense. It discovers what follows logically from assumptions rather than facts about the physical world. Yet physical laws are written in it, and that fit is still something of a puzzle.

One important lesson from mathematics is that simple, fully deterministic rules can produce behaviour that is unpredictable in practice. In chaotic systems, tiny differences in starting conditions grow exponentially, so long-range forecasts fail even with perfect equations. That is why weather forecasts lose skill after about a week or two, while climate projections, which concern averages rather than specific days, remain possible. The chaos theory article linked in the branches table explains the distinction.

---

Scientists Who Shaped These Fields

Behind each idea above are people who argued, made mistakes and sometimes waited decades for recognition. A few profiles are especially useful companions to this page:

• Isaac Newton unified motion on Earth and in the heavens with three laws and universal gravitation. The Isaac Newton profile covers his physics, optics and mathematics.
• Marie Curie discovered polonium and radium and was the first person to win Nobel Prizes in two sciences, physics (1903) and chemistry (1911). See the Marie Curie biography.
• Michael Faraday discovered electromagnetic induction with little formal mathematics; the Michael Faraday profile shows how careful experiment can lead theory.
• Niels Bohr built the first quantum model of the atom and argued with Einstein for decades about what quantum mechanics means. Read the Niels Bohr profile.
• Chien-Shiung Wu showed in 1956–57 that the weak force does not respect mirror symmetry, a result that surprised much of the physics community; see Chien-Shiung Wu.
• Richard Feynman helped build quantum electrodynamics and was known for explaining physics plainly; the Richard Feynman profile covers both.

---

Major Open Questions

What science does not yet know in 2026:

Physics and cosmology. What is dark matter? What is dark energy? Why is there more matter than antimatter? How can quantum mechanics and general relativity be combined into one theory? Candidate approaches such as string theory make few predictions that current experiments can test.

Chemistry and materials. Can a superconductor work at room temperature and normal pressure? Can computers reliably predict a new material's properties before anyone makes it?

Earth and climate. How fast will the West Antarctic and Greenland ice sheets lose mass? At what levels of warming do tipping points, such as changes in major ocean circulation, become likely? How much warming follows from a doubling of CO2? The IPCC's Sixth Assessment Report narrowed that range considerably, but it is still a range.

Mathematics. Why does mathematics describe nature so well, and what are the limits of what can be proven?

These are not embarrassments for science. They are where research is happening, and the answers will become future textbook material.

---

How to Think Like a Scientist

Scientific thinking is a set of habits more than a body of facts:

1. Separate observations from interpretations. Data is what you measured. A theory is how you explain it.
2. Ask what would prove you wrong. A theory that can explain any outcome predicts nothing.
3. Put numbers on uncertainty. "Probably" is more useful with a rough probability attached.
4. Update when evidence changes. Holding a belief against contrary evidence is the opposite of science.
5. Be specific. "The climate is changing" is weaker than "2024 averaged about 1.55 °C above the 1850–1900 baseline."
6. Distinguish cause from correlation. Two things happening together do not show that one caused the other.
7. Wait for replication. A single study is a lead, not a conclusion.

A practical way to test your own understanding is to explain an idea in plain words to someone else and notice where you get stuck. The Feynman technique turns that into a learning method.

---

FAQ

Q: Is science always right? A: No. Individual studies can be wrong, and even well-established theories have limits, as Newton's mechanics turned out to have at very high speeds. What science offers is a process that finds and corrects errors over time. Claims that have survived decades of testing by independent groups are the most reliable knowledge we have, though still open to revision.

Q: What is the difference between a scientific theory and a law? A: Less than people often think. A law is usually a concise description of a pattern, often an equation, such as the ideal gas law. A theory is an explanation of why patterns occur, such as general relativity. Both are well tested. A guess that has not yet been tested is a hypothesis, not a theory.

Q: How do we know rising CO2 is warming the planet? A: Laboratory measurements since Tyndall's work in 1859 show that CO2 absorbs infrared radiation. NOAA records show CO2 rising from about 280 ppm before industrialisation to 422.7 ppm in 2024, and the WMO reports 2024 as the warmest year on record. Physics predicts the warming, and observations confirm it.

Q: Why can't physicists combine quantum mechanics and general relativity? A: Each works extremely well in its own domain, but they describe space and time in incompatible ways. Quantum theory treats spacetime as a fixed background, while general relativity makes spacetime dynamic. The conflict only matters at extreme conditions, such as the centre of a black hole or the very early universe, where neither theory alone can be trusted and experiments are currently impossible.

Q: Why is the periodic table arranged the way it is? A: Elements are ordered by atomic number, the number of protons in the nucleus. Columns group elements whose outer electrons are arranged similarly, which is why elements in the same column behave alike chemically. Quantum mechanics explains why electron shells fill in the order that produces this repeating pattern.

Q: What does materials science actually do? A: It links atomic structure to useful properties and designs new materials for specific jobs. Examples include semiconductors for chips, LEDs for lighting, polymers for packaging and medicine, shape-memory alloys for stents, and superconductors for MRI magnets. Many technologies wait on a materials advance before they become practical.

---

Bottom Line

Science is the most reliable method people have found for working out how the natural world behaves. Physics provides the basic rules, chemistry shows how atoms build everything we touch, earth and climate science explains the planet we live on and how we are changing it, and materials science turns that knowledge into technology. None of it is infallible. Its strength is that it checks itself, so judge claims by the soundness of the method behind them, not only by their conclusions.

Last verified: October 2026