Science is rarely a linear progression of understanding

Scientific progress works toward absolute truth, but can never reach it

Through the acquisition of scientific knowledge, scientists construct explanations of the world, which are rigorously tested and verified until they narrow down to a leading theory of the natural world. However, because of how science works, these ideas will never become factual, as they must always remain open to be iteratively revision based on new data.

Each scientific study adds incremental knowledge to existing understanding

On its own, no study serves as a source of truth or solves an existing problem indefinitely, though many can be analyzed collectively in a systematic review to build more confidence—the result of more data—in a conclusion. Studies can explore knowledge gaps or test an existing theory, which is always subject to refinement and improvement.

Learn why modern scientific patterns have been described as theories rather than laws

After confirming that the accuracy of some laws of physics is limited to certain domains, science became more hesitant to categorize identified mathematical relationships, such as quantum mechanics, as unchanging laws. Instead, these recent, complex frameworks are designated as theories to acknowledge that they are conditional and may be part of a larger, more complete future framework.

How upheavals in accepted scientific theories helped popularize the term 'paradigm'

When Thomas Kuhn published "The Structure of Scientific Revolutions" in 1962, he described the history of science as comprising periods of "normal science" where these accepted frameworks—paradigms—gradually accumulate anomalies until they cannot describe nature. Revolutionary science, such as the development of a new theory, results in a paradigm shift, another term Kuhn helped popularize. (Some readers may experience a paywall.)

How facts, hypotheses, theories, and laws in science differ from everyday language

Facts are observations of the world, and they can be pooled together for a given phenomenon to develop a hypothesis—a proposed explanation consistent with observations that requires further investigation. Experiments and additional data can rule out many hypotheses or graduate a proposed explanation into a widely accepted and validated theory.

Discoveries in electromagnetism, which suggested that light traveled at a single speed, became the catalyst for overturning Isaac Newton's view that all speeds are relative and could appear to change based on one's perspective.

The mystery of the expanding universe

One of the most surprising discoveries about our universe over the past century is that it's expanding. Even more surprising is that it’s speeding up, and scientists aren’t entirely sure why. The rate should be roughly dependent on the total energy contained in the universe, but calculations keep coming up short. Explore the so-called “Hubble Tension,” along with potential candidates to solve the riddle.

Distinguishing between scientific theories and laws, and why both are on equal footing

Scientific laws describe outcomes of specific conditions, and scientific theories explain why those outcomes occur. Both are supported by observational and experimental data and can each inform one another, but neither can become the other. Instead, additional data can improve each towards more accurate descriptions and explanations of reality.

New ways of seeing the cosmos have redrawn the map of human identity

From Galileo’s crude spyglass to the James Webb Space Telescope, each technological leap has expanded our observational reach and redefined philosophical and moral conceptions of our place in the universe. Identifying signs of life through the study of exoplanet atmospheres would represent the next great revolution.

Scientists are experimenting with ways to probe the multiverse theory

Researchers are simulating vacuum bubbles—the theorized starting points of universes—using quantum computers, digital models, and exotic lab setups to study how they form, expand, and possibly collide. One experiment aims to "blow" artificial universe-like bubbles inside ultra-cold quantum gases, potentially capturing real-time glimpses of cosmic birth processes in a lab.

Because some models of the universe do not incorporate time, it may be an emergent property born from our limited perception of the universe, rather than a fundamental property of reality.

Humans experience the world subjectively. What does that mean for scientific research?

When you close your eyes, do you see static or colorful patterns or an "intrinsic grey" known as Eigengrau in German? This variation of our internal experiences is just the tip of the iceberg, one that scientists are increasingly studying and...

The breakthrough that changed our perception of the universe

In the 1920s, the Hooker Telescope helped Edwin Hubble make a discovery that forever changed how we see the universe. Building on the work of astronomers like Henrietta Leavitt and Harlow Shapley, Hubble used the telescope to prove that galaxies exist beyond the Milky Way—revealing a vast and expanding universe.

English chemist Rosalind Franklin (1920 - 1958) on the importance of science

"Science and everyday life cannot and should not be separated. Science, for me, gives a partial explanation of life."

How do scientists study far away stars?

Astronomy is the only science that is purely observational: meaning, scientists can't study stars in a lab. Here's a breakdown of how modern researchers use new tools to understand objects billions of light years away. As it turns out, the rules of science allow us to identify, categorize, and experiment with phenomena light years away.

Explore a series of interdisciplinary explainers on climate science

From animations on the quantum mechanics of greenhouse gases to a photo essay on how scientists acquire climate data, this collection provides detailed explorations of how different branches of science have contributed to our understanding of climatology.

The weakening of dark energy suggests a dynamic universe with evolving forces

The discovery, which came from analyzing extensive data from a major cosmological survey, challenges the assumed constancy of dark energy in modern physics. Understanding dark energy's behavior is crucial for predicting the universe's long-term evolution.

'The urge to explore has propelled evolution since the first water creatures reconnoitered the land. Like all living systems, cultures cannot remain static; they evolve or decline. They explore or expire.'

- Astronaut Buzz Aldrin (1930-present)

The finite speed of light means we can only perceive the world's past

When objects emit or reflect light, it takes time for the light to reach an observer and be detected. During the travel time, the object may have changed, limiting detections to describing the conditions of the object when the light was first emitted or reflected, before it was detected.

Emergent quantum phenomena can produce nonfundamental quasiparticles

While physicists have discovered new particles by colliding known ones at high speeds, placing known particles in extreme environments or configurations can allow quantum mechanics to produce bizarre behaviors, making them seem like new types of matter.

A quote by scientist Nikola Tesla

"The scientific man does not aim at an immediate result ... His duty is to lay the foundation for those who are to come, and point the way."

Understanding how and when time began requires a theory of quantum gravity

Rewinding the universe to the big bang compresses all matter, energy, space, and time into a single point, necessitating a model that combines general relativity with quantum mechanics. Although physicists understand time to have begun when the universe did, a clear understanding of the mechanisms involved remains unclear.

View an historical mural depicting the NSF's impact across seven decades

From 1950 to 2020, the National Science Foundation supported discovery-based, exploratory research that led to numerous breakthroughs, including the development of supercomputing centers, 3D printing technologies, biometric identification systems, an understanding of vector-borne illnesses, a DNA amplification technique, mobile meteorology units, and scientific education and literacy programming.

Scientists have determined the properties of cosmic rays by analyzing their trajectories in bubble chambers—containers filled with a vapor that clings to charged particles.

Why being able to disprove explanations distinguishes scientific theories from pseudoscience

Introduced by philosopher Karl Popper, falsifiability holds that a scientific theory must make predictions that could be proven inaccurate by future observations. Explanations that cannot make such predictions are not scientific theories. It is scientists' jobs to seek out data to poke holes in scientific theories, thereby potentially strengthening them if they hold up to scrutiny.

The universe's expansion is accelerating due to a mysterious force called dark energy

Astronomers discovered in the late 1990s that galaxies move apart faster over time, contradicting expectations that gravity should slow cosmic expansion. This prompted the revival of the "cosmological constant," a form of repulsive gravity first proposed by Albert Einstein.

Science communicator Bill Nye (1955 - ) on science

"Science is the key to our future, and if you don’t believe in science, then you’re holding everybody back."

Observations of colliding neutron stars by the Laser Interferometer Gravitational-Wave Observatory in 2017 confirmed that gravity travels at the speed of light.

There are statistically significant discrepancies in measured universal expansion

Using data from the cosmic microwave background, which allows astronomers to model the universe's conditions since its earliest moments, yields a rate of expansion—the Hubble constant—lower than values obtained from multiple techniques measured locally at more recent timescales. Reconciling the discrepancy, known as the Hubble tension, will require a third independent measurement method between the two scales

The wave nature of matter can produce phenomena like negative time and retrocausality

Within quantum mechanics, matter simultaneously exists as both fixed particles and extended waves, allowing it to emerge across barriers—just as sound travels through walls—before it fully enters the obstacle. The resulting measurements can show that particles spent negative time within a barrier, with the future occurring before the past.

The 2011 Nobel Prize in physics was awarded for the discovery of dark energy

Through the use of standard candles—objects whose brightness is well-known—astronomers can determine distances by recognizing that the same phenomena will dim in predictable ways with increasing distance. By observing the same type of bright stellar explosion at various locations, Saul Perlmutter, Brian Schmidt, and Adam Riess identified that the universe's expansion was increasing.

Expanding special relativity to accelerated motion led to general relativity

The specialized theory postulates the speed of light is the same for all observers and the laws of physics are identical in all settings where velocity is constant. These established the concept of spacetime, whose flexibility became even greater when used to explain gravity.

Experimenting with space-time

Einstein's theory of general relativity—that mass literally bends space and time—can be difficult for the human brain to imagine. This interactive resource lets you create celestial objects, imagine their effect on space-time, and see how they interact with each other (best viewed on desktop).

The universe expands by stretching space itself, not into anything beyond it

Thanks to Einstein’s relativity and Hubble’s observations, scientists understand that space stretches, like rising bread dough between raisins, with no "outside" to expand into. Some theories suggest our universe might be just one "bubble" in a vast multiverse, possibly floating on a higher-dimensional surface called a brane.

Under a model of quintessence, the strength of dark energy should change over time

The theory suggests that dark energy permeates space and may drive the universe to expand or contract throughout its history. The model's flexibility allows it to fit every possible observed behavior of the universe's expansion, rendering it unfalsifiable and untestable.

Within quantum physics, the order of events across time may not follow causality

Although time is considered a fixed, ordered mapping of events, where the past affects the future, quantum superposition breaks down causality, suggesting that future events can occur simultaneously with past ones. Within the quantum model, the notion of cause and effect is not a fundamental feature of our universe.

An early burst of dark energy may resolve discrepancies in the universe's measured expansion

The Hubble tension refers to mismatches in the calculated rate of expansion of the universe derived from different methods, such as supernova data and the cosmic microwave background. By allowing dark energy to become active at a different time, models of the universe on which some of these methods depend are revised, altering the calculated values.