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A NASA Ames scientist sets up an experiment using sand and green lasers.

What is science—and why does it matter?

Questions, questions. Why this...? Why that...? How does this...? How come that...? If you're the sort of person who's always seeking answers, maybe you're a scientist of sorts without knowing it? Knowing, in fact, is what science is all about: the term "science" is linked to Latin words like scire ("to know") and scientia ("knowledge"), so it's the process of finding answers to how and why the world works as it does. From why the sky's blue to how your nose smells, from why boats float on water to what makes us happy or sad, you can seek answers—and enlightenment— in all kinds of ways: you can ask your friends their opinion, pray to a god, paint pictures, write songs, or meditate on a mountain, scratching your head. What makes science so different from these other ways of thinking about things—and why does it matter?

Photo: Experiments are the "fuel" of science: they provide the evidence that confirms or disproves our ideas (hypotheses and theories) of how the world works. Photo courtesy of NASA Ames Research Center.


  1. What is science?
  2. Types of science
  3. Science and its rivals
  4. The very short story of science
  5. Find out more

What is science?

What makes science different is that it's a very systematic way of building up knowledge. It uses logical thinking to explain why things work or how things happen based on evidence gathered through observation and experiment. Slowly and surely, science comes up with coherent explanations called theories that mesh with bigger theories to make ever more comprehensive accounts of what's going on around us. So, for example, Isaac Newton's comprehensive, "universal" theory of gravity was built on smaller theories like Galileo's observations of how falling objects hurtle toward Earth and Johannes Kepler's ideas about the planets sweeping through space, themselves based on earlier science dating back to ancient times. Newton's ideas, in turn, became part of a wider explanation of gravity, known as the general theory of relativity, which Albert Einstein put forward in the early 20th century. Science is a jigsaw puzzle, the theories are the pieces, and as different theories gradually lock together, they give us an ever-expanding picture of how our world works.

The scientific method

The important thing is not to stop questioning.

Albert Einstein

Why's the sky blue? If you don't know the actual explanation, you could probably guess at all sorts of answers—and so could everyone else. If we just asked people what they thought, we could easily end up with 50 or 500 possible accounts. How do we figure out which of these is the right one?

Scientists use an approach called the scientific method. First, they observe or measure something (the sky being blue, for example) very carefully and systematically, which is known as gathering data. (When is it blue? Precisely what shade of blue? Is it ever other colors? When?) From this, they come up with a tentative, logical explanation known as a hypothesis. (It could be something like: the sky is blue because there's water in the air.) The hypothesis should suggest ways in which it can be tested, which are known as experiments. (Is the sky blue on cloudy days, when there's apparently more water in the sky, or dry days, when it's sunnier?) By carrying out experiments, a scientist can test a hypothesis to see if it's a good explanation that accounts for all the evidence.

Experiment exposing organisms to blue excitation lighting

Photo: Which of Earth's many lifeforms can survive on other planets or in space stations? It's something we need to test with experiments like this one, which looks at how different genes are turned "on" or "off" in space. Photo courtesy of NASA.

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Although experiments can be quick and simple, they can also be intricate and complex. Most experiments compare a situation where we've deliberately changed something (say, doing more exercise to see if we feel better) with another situation where we haven't. That's called a controlled experiment and it allows us to see whether the thing we change makes any difference. (We can do other experiments that change other things, one at a time, and see what difference that makes instead.) Experiments that come up with mathematical results also have to prove that those results couldn't have happened purely by chance. There are ways of testing experimental data using math and if the data is better than a chance result, we say it's statistically significant.

If a hypothesis can't be tested by experiment, it's usually rejected as bad science from the start. So if your idea of why the sky is blue is that Martians got out their paint pots when you weren't looking, that's essentially untestable: there's no evidence and no obvious way of getting any, so the hypothesis is a non-starter. That doesn't mean a hypothesis has to be tested immediately: sometimes it takes quite a while to devise just the right experiment. Albert Einstein first put forward his general theory of relativity in 1915. But he had to wait four years before another physicist, Sir Arthur Eddington, was able to confirm it, with the help of a famous solar eclipse.

Science is a method to keep yourself from kidding yourself.

Edwin Land

Why is evidence so important to science? Medicine is probably the best example. If you're sick, you want an effective treatment that makes you better; if you're dying, you want a cure. It's perfectly possible that quack cures will sometimes help people get better, either through pure chance or the very intriguing (and very real) placebo effect. But to come up with medical treatments that consistently improve people's lives, we need to carry out experiments and build up evidence that those treatments really do work, consistently, and in all the different groups of people who might try them; we also need to be sure they don't do more harm than good. Science stops us falling into the trap of gullibility—of believing specious ideas (things that sound right that are actually wrong). As Edwin Land, the physicist inventor of the Polaroid camera once said: "Science is a method to keep yourself from kidding yourself."

What is a theory?

If there's good evidence, a tentative and very fluid hypothesis starts to solidify into a more formal, generally accepted explanation of something, which is called a theory. In other words, a theory is a hypothesis confirmed by experimental evidence or other observations. The more and better the evidence, the stronger the theory—and the more things a theory can explain, the better it is. Importantly, evidence for a theory has to come from more than one person or group: in other words, the results of one team's work has to be replicated (repeated) by others. Theories also have to be published and discussed by the wider scientific community (usually in reputable scientific journals) in a process known as peer review, which gives other people the opportunity to spot flaws in your theory or the methods you used to test it. If any evidence contradicts a theory, the theory is either wrong or incomplete, which means a better theory is needed. Sometimes wrong theories come from bad experiments that supply incorrect data or other kinds of misleading evidence. It's important to try to disprove theories ("If we see this happening, the theory must be wrong") and not just confirm them ("If we see this happening, it agrees with our theory"), though it's a sign of a good theory if it can be properly defended against criticism.

A good theory will also make predictions that go beyond things scientists have already seen or observed. A great example of this is the Periodic Table, Dmitri Mendeleev's explanation of how different atoms relate to one another. When he drew up the table, there were various gaps in his diagram that predicted the existence of elements (such as gallium and germanium) that had not yet been discovered. When those elements were discovered later, it helped to confirm Mendeleev's ideas. (It's also important to note that Mendeleev's theory predicted elements that were never found, so it wasn't a perfect theory.)

The periodic table of elements with key groups highlighted in color.

Artwork: The Periodic Table is part of a brilliant theory that explains why different chemical elements have similar properties.

Some science is very complex and the process of rigorously testing theories can be even more challenging than devising them in the first place. There could be all kinds of alternative explanations for why certain people, living in a certain place at a certain time, suddenly develop a certain kind of sickness. Is it air pollution from a nearby industrial plant... something in the water... radioactive rocks underground... or just a statistical fluke? It can be very difficult to isolate the single most important variable when there are lots of factors could be responsible.

The best theories—things like the theory of evolution—have "evolved" (if you'll excuse the pun) over decades or centuries, supported by many different kinds of evidence involving thousands of experiments and studies by many different scientists from all sorts of fields. It can take a long time for an excellent theory like this to be accepted. In much the same way, wrong-headed theories will sometimes take a long time to disappear. For example, it was originally believed that Earth was the center of the universe and the Sun and planets revolved around it. Known as the geocentric theory (literally, "Earth-centered" theory), that was widely accepted in ancient times, but evidence slowly emerged that it was wrong. To get around this, early scientists could simply have thrown that theory away and come up with a totally new one. Instead, what they did was come up with increasingly tortuous fudges to account for the discrepancies. Eventually, scientists like Kepler, Galileo, and Copernicus developed a rival heliocentric theory, in which the Sun sits at the center of things, which is what people believe today. Another commonly believed explanation that lasted a very long time was the miasma theory—the idea that diseases were passed on by bad air. It persisted as a plausible explanation of disease from ancient times right up until the late 19th century, when growing evidence led to a much better explanation known as the germ theory (the idea that bacteria and viruses cause diseases).

Albert Einstein in later life with white frizzy hair

Photo: Albert Einstein's theory of relativity wasn't just his throwaway "opinion": it was a explanation designed to account for all the facts Einstein knew about things like light, gravity, and motion. Photo courtesy of US Library of Congress.

It's important to realize that calling something "a theory" doesn't mean it's flaky, speculative, or just an opinion. The theory of evolution is supported by a huge mass of very different evidence and, though there are still gaps in our understanding of how it works, it's generally accepted as the best explanation of how the modern pattern of humans and other living creatures came to arrive on Earth. In other words, it's the best explanation for all the facts that we have. Einstein's original, "special" theory of relativity was also supported by evidence, but there were various things it couldn't explain. That was why Einstein soon developed a deeper, more comprehensive explanation in the shape of his "general" theory of relativity. This, too, has gaps and is by no means a perfect theory (for example, it's an ongoing challenge to reconcile Einstein's ideas with quantum theory, the currently favored explanation of how the atomic world works). Crucially, no scientific theory can ever be proved completely correct: someone could always come up with new evidence tomorrow that disproves it. But that doesn't mean every theory is automatically suspect. If a theory has been around a long time and it's supported by a huge body of different evidence (like the theory of evolution), we can be reasonably confident that it's right. Even so, as the heliocentric theory shows, we can never be complacent: as scientists, our minds should always be open. The key point is that science is a work in progress; it's like a vast jigsaw puzzle that will never be complete.

Some claim that evolution is just a theory, as if it were merely an opinion. The theory of evolution—like the theory of gravity—is a scientific fact.

Richard Dawkins

Types of science

If science is a method—a way of building knowledge about the world—that suggests it's a kind of tool we can apply to all kinds of things. From physics and chemistry to medicine and sociology, scientific methods have been used to study every aspect of our world. Different sciences are very different from one another and range from the highly abstract, mathematical ideas of theoretical physics to the very concrete ideas of medical science, which are firmly grounded in biological observations of how our bodies work.

Sciences are sometimes divided into pure and applied. Pure sciences (like theoretical physics) are mostly concerned with studying things to find answers, whether that's obviously or immediately useful or not. Applied sciences (like materials science) are geared towards more practical, everyday problems and are closely related to technology (developing practical things, like inventions, that make life better).

Three women scientists practice weightlessness by swimming in a flotation tank

Photo: Much of space science is applied physics—ordinary physics theories applied to the problems of space travel or living in microgravity. Here, three of NASA's women scientists are practicing weightlessness in a flotation tank at Marshall Space Flight Center. Photo courtesy of NASA.

There's no hard distinction between pure and applied science, however. A scientific discovery might seem rather abstract and "pure" initially—like the idea that two different metals can make a frog's leg twitch. What possible use is that? Sooner or later, however, a finding like that could lead to a highly practical bit of science (a way of making electricity whenever you need it for laboratory experiments)—namely, the invention of the battery. And that, in turn, could lead to all kinds of interesting technological applications. In the same way, applied scientific work designed to develop very practical inventions can often lead to new, "pure" scientific discoveries. Often, pure and applied science weave in and out of one another. Heinrich Hertz's demonstration of waves in his laboratory led to the very practical science of radio, but it also led to pure research into things like the ionosphere (a part of Earth's atmosphere that helps to bounce radio signals around our planet).

Science and its rivals

The scientific method—and the fundamental importance of evidence—is the big difference between science and other ways of thinking about our place in the world, including myths, superstitions, art, religion, and things like astrology. You might be a superstitious kind of person who doesn't walk on the cracks in the pavement, but there's no evidence that walking on cracks is either bad or good for you in any way—and no obvious mechanism by which it ever might be. Myths and superstitions may be fascinating and fun, but they're not credible explanations that can compete with science.

Green cress-like plant shoots and leaves growing in a plastic box in a NASA experiment

Photo: Science tells us plants are green because of the chloroplasts inside them, which capture the Sun's energy a bit like miniature solar cells. Can religion, art, or myth explain things like this? Osiris, the ancient Egyptian god of agriculture and fertility, had green skin, hinting at a connection with vegetation, but that's hardly an explanation! Photograph courtesy of NASA.

Science versus religion?

What about religion? It's perfectly fine to have religious beliefs about why we see colors in the sky or to paint a picture that shows a rainbow forming, but art and religion are a world away from scientific explanations. They might even be based on meticulous observations, but they still lack the logical rigor of scientific theories. You might say "Well, a religious miracle is evidence for [such and such]," but that's hardly a scientific explanation. Miracles aren't testable, they're not repeatable, and they generally have other, more scientific explanations behind them. That's not to say that religion has no value; the value it has as a coherent belief system, which helps people to live morally good, spiritually enriched, happy and fulfilled lives, is very different from the value of science. You can pray, if you have lung cancer, and it could help you in all kinds of ways—but medical treatments, based on years of evidence-based research, are much more likely to cure you.

Science and art

To develop a complete mind: Study the science of art; Study the art of science. Learn how to see. Realize that everything connects to everything else.

Leonardo da Vinci

When people are studying in schools and colleges, they often think of themselves as "arty" or "sciencey," as though there's a sharp line between the two. Arts subjects are meant to be more human, creative, poetic, emotional, and romantic; sciences are considered more logical, rational, methodical, prosaic, and perhaps even a bit plodding and boring. Of course, that's all a matter of opinion: it's hard to think of anything more human than medicine, for example, which is quintessentially scientific.

It's never really clear why people want to build high walls between the arts and sciences. A genius like Leonardo da Vinci obviously straddled the divide; modern artists and scientists also work on similar or overlapping problems. You could argue, for example, that, with their pursuit of cubism, artists like Cezanne, Braque, and Picasso were studying very similar problems to scientists like Einstein. Bridget Riley's op-art clearly has much in common with a branch of psychology called psychophysics (which studies how the eyes and brain perceive light, colors, and patterns). Artist Josef Albers was just as much a scientist of color as Isaac Newton or Thomas Young. Less obviously, a sculptor like Rodin was arguably just as preoccupied with gravity (in his own way) as a scientist like Galileo or Newton.

The very short story of science

How did humans come up with the idea of science? What was wrong with myths, superstitions... and all those earlier, older, and often more magically enchanting ways of explaining? Science, ultimately, turned out to be a more successful intellectual engine for powering civilization. It had better answers and more useful explanations; it soon pulled ahead of the pack.

It's easy to see why with an example. In hindsight, it's clear how a growing scientific understanding of electricity and magnetism in the 18th and 19th centuries enabled the development of a superb new way of harnessing, storing, and using energy that's been revolutionizing our world ever science. By contrast, it's hard to see how mystical, mythical, religious, or superstitious ways of explaining things like static electricity, lightning, or sparks could ever have spawned such fabulously useful technologies as electric cars or computers. They might be very comforting to people, as self-contained explanations of a kind, but they offer no real value going forward.

Before science

Early civilizations had systematic knowledge—astronomy and math were their strongest suits—but they didn't have what we now regard as science. People certainly made discoveries—fire, for example—and they came up with world-beating inventions like the wheel and axle. They could see those things were effective, but they didn't understand how or why (how a fire burst to life or exactly why a wheel made it easier to push a cart). Nor did they appreciate how one discovery could couple with another to make a third that was even more useful (how a fire could be used to drive a wheel—which was the thinking behind steam engines). Early people knew how to extract metals like gold and silver from the Earth and how to refine them, but they didn't understand the relationship between different elements or the chemistry of how they combine, which is why they got sidetracked by absurd ideas like alchemy. Knowledge, such as it existed, tended to be practical rather than theoretical and very much more fragmented.

Ancient science

Statue of Thales of Miletus with lightning bolts

Photo: Thales: the ancient Greek father of modern electrical science. Credit: Photographs in the Carol M. Highsmith Archive, courtesy of Library of Congress, Prints and Photographs Division.

Science was really born in ancient times, with the Sumerians, Egyptians, and Greeks like Thales, Pythagoras, Anaximander, Aristotle, Archimedes, and Eratosthenes. Infatuated with logical reasoning and mathematics, they had both qualitative ("wordy") and quantitative ("numbery") explanations for things. The scientific foundations of physics, botany, zoology, anatomy, physiology, engineering, and medicine were all laid down in ancient times. The Romans who followed the Greeks were, by contrast, more practical and applied scientists, making huge leaps in architecture and engineering.

Dark and Golden science

Arabic science throughout its golden age was inextricably linked to religion; indeed, it was driven by the need of early scholars to interpret the Qur'an.

Jim Al-Khalili

Following the collapse of the Roman Empire, scientific progress stalled in the west, in a time known as the Dark Ages, while the baton of progress passed to the Islamic world in a glorious period of science history now known as the Islamic Golden Age. Al-Khwarizmi (who gave his name to algorithms) developed algebra, Avicenna advanced medicine, Alhazen pioneered modern optics, and Al-Jazari developed ingenious machines. In the Arabic world, the best ideas from Egypt, Greece, China, India, and elsewhere fused and burned like the fuel in a modern-day rocket, before drifting back to Europe at the end of the Middle Ages. Science, in the Golden Age, helped to illuminate religion. And from then on, religious and philosophical ideas slowly started to merge with scientific ones thanks to the enlightened open minds of scholars like Peter Abelard, Thomas Aquinas, Hildegard of Bingen, and Roger Bacon.

The science revolution

True science probably began at the point where the world's best thinkers started to toss aside ancient ideas. Leonardo da Vinci blurred the boundaries between art and science, as never before or science. Another defining figure was Nicolaus Copernicus, who, as we've already seen, challenged the long-held (and religiously defended) idea that God's Earth anchored a "geocentric" Universe. Meanwhile, Belgian Andreas Vesalius published a detailed anatomical textbook superseding the ancient, out-of-date medical ideas of Galen and Avicenna. And Francis Bacon helped to formalize the scientific method.

Copernicus paved the way for Kepler and Galileo, who, in turn, opened the door for Isaac Newton and his insightful theories of gravity, motion, light, and a superb mathematical tool known as calculus (developed in parallel by German polymath Gottfried Leibniz). Meanwhile, Robert Hooke studied plants, animals, and living cells under the microscope, while William Harvey built on Vesalius's work with a pioneering theory of how blood circulates around our bodies and hugely influential ideas about magnetism. Another Robert, Robert Boyle, kick-started the systematic, experimental study of chemistry.

Galileo Galilei

Artwork: Galileo Galilei—student of motion and gravity, and pioneer of telescopes. Photo courtesy of US Library of Congress.

Modern science

In physics, thanks to a steady stream of pioneers from Benjamin Franklin to Michael Faraday, the 18th and 19th centuries were the age of electricity and energy, a fusion of practical and applied ideas, science spawning technology. Over in chemistry, magical ideas like alchemy (which even Newton had toyed with) gave way to more realistic, systematic explanations based on a gradual understanding of the chemical elements as fundamental building blocks of our world. Two key figures here were Frenchman Antoine Laurent Lavoisier, who figured out the logic of how elements fused together in reactions, and Englishman John Dalton, who sketched out the beginnings of our modern atomic theory (the idea that everything is ultimately made of atoms). Their ideas would help Dmitri Mendeleev to figure out how elements related to one another in a theoretical diagram he drew up known as the Periodic Table.

Meanwhile in biology, a Swedish botanist named Carl Linnaeus studied the similarities and differences between plants and animals and worked out a neat, hierarchical system of classifying species that we still use to this day. A little later, Gregor Mendel pioneered genetics (the idea that plants and animals inherit important characteristics from their parents). The work of Linnaeus and Mendel held the door wide for Charles Darwin and his life-explaining theory of evolution by "natural selection."

These seeds of modern biology spawned amazing new advances in the 20th century, most notably with Francis Crick and James Watson's discovery of the structure of DNA in 1953, and Frederick Sanger's pioneering work on DNA sequencing. But the 20th century saw many other huge advances, from Einstein's world-bending theory of relativity to Edwin Hubble's idea of the ever-expanding universe. The biggest, most revolutionary advances arguably came with a much deeper understanding of the atomic theory, with discovery piled upon discovery by such brilliant physicists as Ernest Rutherford, Niels Bohr, Lise Meitner, Enrico Fermi, Richard Feynman, and many others. Practical spin-offs of this work included everything from nuclear power plants to superconductors and supercomputers.

The power of science

George Washington Carver

Photo: Not all famous scientists are "dead white guys." African-American scientist George Washington Carver (1864?–1943) was a pioneer of 20th-century biotechnology. Born to parents who were slaves in Missouri, he discovered that he loved learning and worked hard to educate himself. Photo courtesy of US Library of Congress.

And this is how the story of science moves forward. Each theory builds on older theories, adjusts them, improves them, or kicks them entirely aside. Theories interlock with other theories, making bigger, better, and more comprehensive explanations. We learn more and more about the world and our place in it, how to solve pressing problems, how to do things better, quicker, or in less environmentally destructive ways. Time moves on, the world moves with it. But thanks to the power of science, humans always move forward, to a better place.

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