Scientific theory

A scientific theory is an explanation of an aspect of the natural world that has been repeatedly tested and has corroborating evidence using the scientific method. Theories are tested through observation, measurement, and evaluation of results, often in controlled experiment settings. Even when experiments aren't possible, theories are checked using abductive reasoning. Strong theories have faced many tests and still explain what we see.

A scientific theory is different from a scientific fact. A fact is something we observe, like seeing leaves fall from a tree. A theory connects many facts and explains why they happen. For example, gravity explains why leaves fall. Theories can also make predictions about things we haven't observed yet. Stephen Jay Gould said facts and theories are different, not one better than the other. Facts are the data, and theories help us understand those data.

In everyday language, people might use "theory" to mean a wild guess. But in science, a theory is an idea that has been tested a lot and is trusted. The best theories explain many different things simply and clearly. Sometimes, as we learn more, a theory might need changes or even be replaced by a better one. But some theories, like evolution or the heliocentric theory, are so strong they are unlikely to change much.

Scientific theories help us understand the universe. They explain things like electricity, chemistry, and the stars. Theories let scientists make predictions and help create new technology and medicine. While scientists can never fully prove a theory, they can show that the evidence supports it. This process helps us learn more about the world around us.

Types

Albert Einstein talked about two kinds of scientific theories. One kind is called "constructive theories." These help us understand how things happen, like how tiny parts move in a theory about heat. The other kind is called "principle theories." These are general ideas that come from watching and measuring things, such as the rules that explain how objects move.

Characteristics

A scientific theory is a way to explain something in nature that has been tested many times and has strong evidence to support it. Theories help us understand the world better by making predictions that can be checked through experiments and observations.

For a theory to be accepted, it must make predictions that can be tested and proven wrong, which helps scientists learn new things. Good theories are supported by lots of evidence and fit with what we already know. They should also be simple and easy to test, making it easier for scientists to use them to discover more about the world.

Formation

The first observation of cells, by Robert Hooke, using an early microscope. This led to the development of cell theory.

The scientific method is a way scientists use to test ideas called hypotheses. They make guesses about what will happen and then do experiments to check if those guesses are right. If the guesses match the experiments, scientists might build a bigger explanation called a theory.

When scientists have done many experiments about a certain topic, they can create a theory. This theory tries to explain what they have seen. Even if a theory isn’t perfect, it can still be very helpful. For example, some ideas work very well for everyday things but might not be right for very fast or special situations. Scientists keep testing theories to make sure they stay accurate. A theory that many scientists agree on is considered the best explanation we have right now.

Modification and improvement

When experiments show results that don't match a theory's predictions, scientists check if the experiment was done right. If it was, they try to improve the theory. Sometimes small changes work, and sometimes bigger ones are needed. Over time, theories get better and can predict things more accurately.

Sometimes, a whole new theory is needed if the old one can't explain the new results. Even then, the old theory might still be useful for other things. For example, Newton's ideas about gravity worked well for a long time, even though they didn't explain everything.

Unification

In quantum mechanics, the electrons of an atom occupy orbitals around the nucleus. This image shows the orbitals of a hydrogen atom (s, p, d) at three different energy levels (1, 2, 3). Brighter areas correspond to higher probability density.

Sometimes, scientists find that two theories are actually parts of one bigger theory. For example, we now know that electricity and magnetism are two sides of the same thing called electromagnetism.

Example: Relativity

In 1905, Albert Einstein created the theory of special relativity. He combined ideas from physics and showed that the speed of light stays the same no matter how things move. This led to new ideas like time changing speed and things seeming shorter when moving fast. Later, Einstein expanded this to include gravity, creating general relativity. This shows how space and time can bend because of gravity. Even though general relativity explains more, scientists still use Newton's simpler ideas for many calculations.

Theories and laws

About theories

Theories as axioms

Logical positivists thought of scientific theories like statements in a special kind of language. This language included not just theories, but also simple observations like "the sun rises in the east," definitions, and math facts. Things we can't see directly, like atoms or radio waves, were treated as ideas that help explain what we observe. In this view, theories work like starting points from which we can figure out what should happen, much like solving problems in geometry. These ideas are then checked against real life to see if they work well.

Theories as models

Main article: Scientific model

Today, many scientists think of theories as models that represent how the real world works, similar to how a map shows a city. A model is a way to picture reality, even if it isn't the real thing itself. For example, a model of the Solar System might use simple objects to stand for the Sun and planets, with rules about how they move. By testing these models, scientists can see if they match what actually happens in space. Most of the time, older models work well, but sometimes newer, more detailed models are needed for better accuracy.

Differences between theory and model

Main article: Conceptual model

Some thinkers say that theories not only describe what happens but also explain why it happens, while models mainly describe things. This helps scientists create ideas to test.

Assumptions in formulating theories

When creating theories, scientists sometimes start with ideas that haven't been proven yet. These starting points help build the theory, and later tests can show if they match reality. For example, some theories work only under certain conditions, and new theories might fix problems with older ones.

Descriptions

From philosophers of science

Karl Popper explained what makes a scientific theory special in several ways:

It’s easy to find things that seem to support any theory, but real support comes from tests that could have shown the theory wrong.
A good theory tells us what cannot happen. The more it rules out, the better it is.
A theory must be able to be tested and possibly shown wrong. This ability to be tested is what makes it scientific.
When we test a theory, we are trying to prove it wrong. Only when these tests fail to show it wrong do we say the theory is supported.

Stephen Hawking added that a good theory must explain many observations using just a few ideas, and it should make clear predictions about what we will see in the future.

Some thinkers argue that theories also need to be creative and bring new ideas, not just rules that can be tested.

Analogies and metaphors

People have used many ways to describe what a scientific theory is like. One idea is that a theory is like a detailed map that helps us understand the world.

Galileo Galilei said that the universe is like a book written in the language of mathematics, with shapes and numbers that we must learn to read.

Another thinker compared nature to a large library where each book gives us special ways to understand different parts of the world, even though the books may seem to disagree with each other.

In physics

In physics, a theory is a set of ideas that help scientists make predictions about how things will behave in experiments. These ideas come from a few basic rules, like saying all places in space are the same or that all electrons are identical. A good example is classical electromagnetism, which uses a few important equations known as Maxwell's equations to explain how electric and magnetic forces work. These equations have been tested many times and work very well.

Within electromagnetism, scientists also have many ideas about how it works in different situations. Some of these ideas have been tested a lot, while others are still being studied. For example, there is an idea called the radiation reaction force. We can see its effects in big machines called synchrotrons, but usually only when we look at them over a long time. Some scientists are now trying to see these effects happen right away, not just over time.

Examples

Many areas of study don’t have a single named theory, but they still have strong ideas backed by lots of evidence. Theories often pull information from many different fields.

Some well-known theories include:

Explanatory notes

A scientific theory is an explanation about how nature works. It is supported by many tests and evidence that follow strict scientific methods. These methods include careful observation, measuring results, and checking findings.

When possible, theories are tested in controlled experiments. In cases where experiments are not possible, theories are examined using logical reasoning.