What Is the Universe Made Of

Short answer

• The universe is made of three main ingredients, measured as shares of its total mass and energy. Ordinary matter, the atoms that make up stars, planets, gas, and people, accounts for about 5 percent. Dark matter, an invisible form of matter detected only through gravity, accounts for about 27 percent. Dark energy, a mysterious influence that speeds up the expansion of space, accounts for about 68 percent. Radiation, including light and neutrinos, makes up far less than 1 percent of the present day total. Those figures are the rounded results of the Planck satellite mission, published in its final 2018 analysis and summarized by NASA and in the OpenStax Astronomy textbook. The European Space Agency rounds the same data slightly differently, as about 5 percent ordinary matter, about 26 percent dark matter, and about 69 percent dark energy. They describe the present day universe, not the early universe, and they are estimates inside a model called Lambda-CDM, not a direct count of objects on a scale. The two dark ingredients are inferred from their effects, not seen directly, which is why this article labels measured results separately from inferences throughout.

The Recipe at a Glance

The precise Planck 2018 figures behind those round numbers are 4.9 percent ordinary matter, about 26.6 percent dark matter (derived as total matter 31.5 percent minus ordinary matter 4.9 percent), and about 68.5 percent dark energy, with total matter at about 31.5 percent. An earlier Planck release in 2013 gave 4.9 percent, 26.8 percent, and 68.3 percent. The small shifts between releases reflect better calibration and more complete sky maps, not a change in the basic picture. Whenever you see slightly different figures in other articles, check which Planck release they cite or how the figures were rounded, because one of those two is usually the reason for the difference.

A useful way to picture the result is to imagine a pie cut into one hundred slices. Five slices are everything you have ever touched or seen through a telescope. Twenty seven slices are matter that no telescope has ever imaged, yet whose gravity holds galaxies together. Sixty eight slices are not matter at all, but an energy tied to space itself that pushes the expansion of the universe faster. The surprise is not only that the familiar stuff is the smallest share. It is that the two largest shares are things scientists have never directly observed.

How Scientists Measured the Recipe

Nobody weighed the universe on a scale. The recipe comes from reading the oldest light in the sky, the cosmic microwave background, and combining it with other observations. That background is the cooled leftover glow from the time the young universe first became transparent, about 380,000 years after the Big Bang, when atoms first formed and light could finally travel freely. NASA describes it as the oldest light we can observe in the universe.

The European Space Agency launched the Planck satellite in 2009 to map that glow across the whole sky in finer detail than any earlier mission. Tiny temperature differences in the map, variations of only a few millionths of a degree, record how much ordinary matter, dark matter, and dark energy were present, because each ingredient shaped the early universe in a slightly different way. Fitting a model to the full map gives the composition figures quoted above. Planck released its final data in July 2018, and the results strongly supported the standard cosmological model, known as Lambda-CDM.

Two other lines of evidence back up the same recipe. The pattern of galaxies across the sky, and the way light from distant objects is bent by gravity, both depend on how much matter is present and how it is distributed. The brightness of distant exploding stars, used to measure how fast the universe has expanded over time, points to the same dark energy share. No single measurement carries the whole case. The recipe is trusted because several independent kinds of observation agree on it, within their uncertainties.

It also matters what the numbers mean. The percentages are shares of the critical density, the density a flat universe needs for its geometry to be flat on the largest scales. They describe the average contents of the universe as a whole, not the contents of any one place. Your own body is made entirely of ordinary matter, and so is the Sun. The dark shares only show up when you average over enormous volumes of space.

Ordinary Matter: The 5 Percent We Know

Ordinary matter is also called baryonic matter, after baryons, the family of particles that includes protons and neutrons. Everything familiar is built from it: stars, planets, moons, asteroids, comets, clouds of gas and dust, and every living thing. If you can touch it, see it, or detect it with a telescope, it is ordinary matter.

At the smallest scale, ordinary matter is built from elementary particles described by the Standard Model of particle physics. CERN, the European particle physics laboratory, explains that all matter around us is made of two types of elementary particle, quarks and leptons, arranged in three generations. The lightest and most stable particles form the first generation, and those are the ones that build everyday matter. Up quarks and down quarks combine to make protons and neutrons. A proton is two up quarks and one down quark. A neutron is one up quark and two down quarks. Electrons, the third member of the first generation, orbit atomic nuclei and take part in chemistry.

Only the first generation matters for the universe we live in. The heavier quarks and leptons of the second and third generations are unstable and decay quickly, so they appear only in high energy settings such as particle accelerators or cosmic ray collisions, not in stars or people. The Standard Model also includes force carrying particles: photons carry the electromagnetic force, gluons carry the strong force, and the W and Z bosons carry the weak force. Gravity is not part of the Standard Model, a gap CERN states openly, and the Standard Model on its own describes only about 4 percent of the known universe, which is a reminder of how much of the cosmic recipe lies outside particle physics as currently understood.

Atoms form when protons, neutrons, and electrons combine. A hydrogen atom is one proton and one electron. A helium atom is two protons, two neutrons, and two electrons. Every heavier element is built the same way, with more protons and neutrons in the nucleus and more electrons around it. The periodic table lists 118 known elements, but the universe uses them very unevenly.

Most ordinary matter is hydrogen and helium. In the first few minutes after the Big Bang, when the universe was hot and dense, protons and neutrons fused into the lightest atomic nuclei in a stage called Big Bang nucleosynthesis. NASA describes how, after five minutes, most of the helium that exists today had already formed, and further element formation had stopped as the universe expanded and cooled. Models of that early fusion predict a primordial mix of about 75 percent hydrogen and 25 percent helium by mass, with only traces of lithium, and observations of the oldest gas clouds match that prediction. Every heavier element, from the carbon in your body to the iron in the Earth, was made much later, inside stars and in stellar explosions.

That history explains a useful distinction. The hydrogen and helium in the universe are mostly ancient, made in the first minutes. The heavier elements are mostly young, made in stars over billions of years. When astronomers say ordinary matter is about 5 percent of the universe, most of that 5 percent is still hydrogen and helium, much of it floating as gas between the stars and between galaxies rather than locked inside stars.

Where the Ordinary Matter Lives

Only a small part of ordinary matter shines. Stars and galaxies together hold less than 1 percent of the critical density, about one half of 1 percent by the estimate summarized in the OpenStax Astronomy textbook. The rest of the ordinary matter, about 4 percent of the critical density, is mostly hydrogen and helium gas in the space between stars and between galaxies. In other words, most of the visible kind of matter is not visible at all in the usual sense: it is thin, cold gas that glows too faintly to see with the eye, though telescopes can detect it by the light it absorbs or emits.

Galaxies are the largest structures that ordinary matter builds, and they are far more numerous than early astronomers imagined. For the current best estimates of how many galaxies exist, and how those estimates changed as telescopes improved, see How Many Galaxies Are There. Each galaxy is a collection of stars, gas, dust, and dark matter held together by gravity, and the gas between galaxies in a cluster can outweigh all the stars in the cluster combined.

Black holes are also part of the ordinary matter story, in the sense that they form from collapsed stars and gas, which are ordinary matter. They hold only a tiny share of the total mass budget, and their importance is gravitational, not numerical. For how they form and what they are, see What Is a Black Hole?.

Planets, moons, and people are an even smaller rounding error in the cosmic budget. All the solid material in the universe, every rock and every ocean and every living thing, is a tiny fraction of the ordinary matter total, which is itself only about 5 percent of everything. That is not a statement about importance. It is a statement about mass. The universe is mostly gas, dark matter, and dark energy, with solid objects as a rare special case.

Dark Matter: The 27 Percent We Infer From Gravity

Dark matter is the name for matter that does not emit, absorb, or reflect light, and does not appear to be made of any known particle. It is not dark in the sense of being dim, like a lump of coal. It is dark in the sense of being invisible to every telescope, in every kind of light, while still pulling on other matter through gravity. Its existence is inferred, not observed, and the inference is strong enough that it is part of the standard model of cosmology, even though no dark matter particle has ever been detected in a laboratory.

The first hint came in 1933, when Swiss astronomer Fritz Zwicky studied the Coma cluster of galaxies and found that the galaxies inside it were moving too fast to be held together by the gravity of the visible matter alone. He proposed that unseen matter must supply the missing gravity. His estimate of how much extra matter was needed was far too large by modern standards, but the basic observation, that clusters behave as if they contain much more mass than their stars provide, has held up.

The evidence became much harder to dismiss in the 1970s, when Vera Rubin and her colleagues measured how fast stars orbit inside spiral galaxies. If only visible matter were present, stars far from a galaxy center should orbit more slowly, in the way planets farther from the Sun orbit more slowly. Instead, the outer stars moved about as fast as the inner ones. The simplest explanation is that each galaxy sits inside a large halo of unseen matter whose gravity keeps the outer stars moving fast. Later work extended the same result to many galaxies.

Gravitational lensing adds a third, independent line of evidence. Massive objects bend the path of light from more distant objects, and the amount of bending reveals how much mass is doing the bending. In galaxy clusters, the bending is far stronger than the visible matter can explain, and maps of the bending show mass spread well beyond the visible galaxies. The pattern matches a dark matter halo, not a misunderstanding of the visible matter.

A fourth line comes from the cosmic microwave background itself. The tiny temperature variations in that early light show how matter was distributed when the universe was about 380,000 years old, and they show dark matter already clumped and shaping the structures that later became galaxies. Without dark matter, the ordinary matter alone could not have formed galaxies as fast as observations show they formed.

What could dark matter be? That is still unknown. Leading ideas propose new particles that interact hardly at all with ordinary matter, which is why laboratory searches have not yet found them. One candidate family is called WIMPs, weakly interacting massive particles, and another is axions, extremely light particles proposed for other reasons in particle physics. Both remain hypotheses. Other ideas, including changes to the law of gravity itself, have been explored, but they struggle to explain all four lines of evidence at once, especially the lensing maps and the microwave background pattern. Until a particle is detected or a better explanation covers the same evidence, dark matter stays on the list as an inferred ingredient with an unknown identity.

A common confusion is worth clearing up. Dark matter is not the same as antimatter, and it is not the same as ordinary matter hidden in dim stars or black holes. Astronomers have counted those possibilities, and they cannot supply the missing mass. Dark matter is also not the same as dark energy, despite the shared word dark. Dark matter pulls things together through gravity, like ordinary matter does. Dark energy does the opposite, pushing the expansion of the universe faster.

Dark Energy: The 68 Percent That Pushes Outward

Dark energy is the largest share of the universe and the least understood. It is the name given to whatever is causing the expansion of the universe to speed up. It is not a kind of matter, and it is not located in particular objects. In the leading picture, it is a property of space itself, present everywhere, with an energy density that stays roughly constant as space expands. That last point is what makes it different from matter, which thins out as the universe grows.

The discovery came in 1998, and it surprised everyone. Two teams of astronomers were studying distant Type Ia supernovae, exploding stars that act as standard candles because their intrinsic brightness is known. They expected to find that the expansion of the universe was slowing down under the pull of gravity. Instead, the supernovae were fainter than expected, meaning they were farther away than their redshifts suggested. The only consistent explanation was that the expansion had sped up over time, carrying the supernovae farther than a slowing expansion would have. The team leaders, Adam Riess, Saul Perlmutter, and Brian Schmidt, won the 2011 Nobel Prize in Physics for this work. NASA states the result plainly: about nine billion years after the universe began, its expansion started to speed up, driven by an unknown force that scientists have named dark energy.

The leading candidate for dark energy is the cosmological constant, an idea Einstein introduced into his equations of general relativity and later set aside. In this picture, empty space itself carries a small, constant energy that pushes space apart. It fits the observations so far, which is why it is the default assumption in the Lambda-CDM model, where the Greek letter lambda stands for it. But it is a candidate, not a confirmed identity, and the value it would need is far smaller than simple quantum physics estimates suggest, a mismatch that physicists call one of the biggest unsolved problems in the field.

Other ideas remain live. Dark energy could be a changing field, sometimes called quintessence, whose strength varies over time. It could be a sign that general relativity needs a correction on the largest scales. Observations from the Euclid space telescope, launched in 2023, and from the Nancy Grace Roman Space Telescope are designed to test these possibilities by mapping how dark energy has shaped the growth of cosmic structure over time. Until those measurements separate the candidates, the honest statement is that dark energy makes up about 68 percent of the present energy budget, its effect is measured, and its nature is unknown.

Dark energy also decides the broad fate of the universe. Because it speeds up expansion, and because its density does not thin out as space grows, current observations point toward continued expansion. The detailed future, whether expansion continues at the same rate, speeds up further, or changes character, depends on the true nature of dark energy, which is exactly the part we do not yet know. For the history of the expansion itself, from the early hot universe to the present acceleration, see Big Bang Theory of Universe.

Radiation and Neutrinos: The Tiny Remainder

Radiation is the fourth ingredient in the full accounting, and today it is a small one. The cosmic microwave background fills all of space, and starlight fills galaxies, but together with neutrinos, these forms of energy contribute far less than 1 percent of the present mass and energy budget. They are listed separately here because they mattered far more in the past.

In the early universe, radiation dominated. For the first tens of thousands of years, light and fast moving particles carried more of the energy budget than matter did, and their pressure held back the formation of structures. As the universe expanded and cooled, radiation thinned out faster than matter, because its energy is stretched by the expansion itself. By the time the universe was about 380,000 years old and the microwave background was released, matter had already taken over as the dominant ingredient.

Neutrinos deserve a brief note because they are easy to confuse with dark matter. Neutrinos are real particles in the Standard Model, produced in huge numbers by the Sun and by the early universe, and they pass through ordinary matter almost without interacting. They do have a tiny mass, and they do contribute to the energy budget, but their total share is small, and they move too fast to clump into the halos that dark matter forms. They are part of the ordinary particle story, not a candidate for most of the dark matter.

Antimatter is another small entry in the ledger. The early universe produced matter and antimatter in nearly equal amounts, and most of it annihilated, leaving a small excess of ordinary matter behind. That leftover excess is the ordinary matter in the recipe. Antimatter still appears in cosmic rays and in particle collisions, but it is rare today, and it is not a separate large ingredient.

What the Universe Is Not Made Of

A few popular ideas do not survive the evidence. The universe is not made mostly of stars. Stars are less than 1 percent of the total, and even galaxies as a whole are a minority of ordinary matter, most of which is gas. The universe is not made of ether, the invisible substance once proposed to carry light waves. Experiments in the late nineteenth century found no sign of it, and modern physics has no need for it. The universe is not made of a single element or a single particle. Even the ordinary 5 percent needs quarks, leptons, and force carrying particles working together, and the remaining 95 percent needs two ingredients whose identities are still unknown.

The universe is also not mostly empty in the way the word empty suggests. Space between galaxies contains thin gas, background radiation, and the dark energy that fills every volume. A cubic meter of intergalactic space holds very few atoms, but it is not nothing, and on the scale of the whole universe those sparse contents add up to the recipe above.

How the Pieces Fit: The Lambda-CDM Model

The full recipe has a name: Lambda-CDM, short for Lambda Cold Dark Matter. Lambda stands for dark energy in the form of the cosmological constant, and CDM stands for cold dark matter, meaning dark matter made of slow moving particles that clump under gravity. Together with ordinary matter, radiation, and the known laws of physics, this model describes the expansion history of the universe, the pattern of the microwave background, the abundances of light elements, and the large scale distribution of galaxies, all with the same small set of numbers.

The model is called the standard model of cosmology because it fits so much evidence, not because it is complete. It does not explain what dark matter particles are, what dark energy is, or what set the initial conditions of the universe. Physicists also know of tensions inside it, including a disagreement about the current expansion rate when measured from the early universe versus from nearby objects. Those tensions are active research topics, and they may point to new physics or to measurement problems that are not yet resolved. Either way, the composition figures in this article are the best current estimates inside that model, and they are presented here with their date and their source so that a reader can check them against future updates.

One practical consequence follows from the recipe. Because dark energy dominates and its density does not thin out, the ordinary matter share will fall further over time as the universe expands. In the far future, the same pie chart will look even more lopsided: galaxies will be more isolated, the background radiation will be colder, and the dark energy share will be larger still. The recipe in this article is a snapshot of today, about 13.8 billion years into the history of the universe.

What We Still Do Not Know

The honest summary is that scientists have measured the amounts of the ingredients far better than they understand what two of them are. The amounts are known to within a percent or so. The identities are open questions, and they are among the largest open questions in science.

Three questions matter most. First, what is dark matter made of? No particle has been detected, and the leading candidates remain hypotheses until an experiment finds one. Second, what is dark energy? The cosmological constant fits the data, but its expected size disagrees wildly with theory, and other explanations have not been ruled out. Third, why do the ingredients have the amounts they do? Nothing in current physics explains why ordinary matter is about 5 percent rather than 50 percent, or why dark energy became dominant only in the last few billion years. Until those questions are answered, the recipe is a precise measurement of a partly unknown mixture.

That uncertainty is not a weakness of the science. It is the reason the measurements matter. Knowing that 95 percent of the universe is dark, and knowing it to within a percent, tells researchers exactly how big the unknown is and where to look next.

Frequently Asked Questions

What is the universe mostly made of?

Dark energy, at about 68 percent of the present mass and energy budget. Dark matter is next at about 27 percent. Ordinary matter, everything made of atoms, is only about 5 percent. The figures are the rounded Planck 2018 results, published in the final analysis of the Planck satellite mission and summarized by NASA and in the OpenStax Astronomy textbook.

Is dark matter real if nobody has seen it?

Dark matter has never been directly detected, and no dark matter particle has been found in a laboratory. It is treated as real because several independent observations point to the same conclusion: galaxy rotation speeds, the motions of galaxies in clusters, gravitational lensing maps, and the pattern of the cosmic microwave background all behave as if extra, invisible mass is present. A single observation could be a mistake. Four independent kinds of observation agreeing is much harder to dismiss, which is why dark matter is part of the standard model of cosmology while its identity remains unknown.

What is the difference between dark matter and dark energy?

Dark matter is matter. It has gravity, it clumps into halos around galaxies, and it pulls things together. Dark energy is not matter. It does not clump, and its effect is to speed up the expansion of space. The two share only the word dark, which in both cases means unknown rather than literally black. Confusing them is common, and it is the most frequent misunderstanding about the composition of the universe.

What are atoms made of?

Atoms are made of protons, neutrons, and electrons. Protons and neutrons are themselves made of quarks: a proton is two up quarks and one down quark, and a neutron is one up quark and two down quarks. Electrons are leptons, a different family of elementary particle. The Standard Model of particle physics, maintained by CERN, describes these particles and the forces between them, and it explains all ordinary matter, though it does not include gravity and does not describe dark matter or dark energy.

How much of the universe is hydrogen?

By mass, ordinary matter is about 75 percent hydrogen and 25 percent helium, with only traces of heavier elements, according to models of Big Bang nucleosynthesis that match observations of the oldest gas clouds. Hydrogen is therefore the most common element in the universe by a large margin, and helium is second. But remember the scale: all ordinary matter is only about 5 percent of the total mass and energy budget, so hydrogen is about three quarters of a small slice, not three quarters of the universe.

Does the composition of the universe change over time?

Yes. In the early universe, radiation carried a larger share of the energy budget than matter. As the universe expanded and cooled, matter took over, and later dark energy became the largest share, starting about nine billion years after the universe began, according to NASA. The figures in this article describe the present day universe. In the far future, the dark energy share will be larger still.

Will scientists ever find out what dark matter and dark energy are?

That is the goal of several major projects, including the Euclid space telescope and the Nancy Grace Roman Space Telescope, along with underground particle detectors searching for dark matter directly. There is no guarantee of success, and no date can honestly be promised. What can be said is that the questions are precise, the evidence is strong, and the search is active.

Sources & references

• European Space Agency, Cosmic energy budget page, opened and read 5 Nov 2026. According to Planck, normal matter contributes about 5 percent of the universe's mass and energy inventory, dark matter occupies about 26 percent, and dark energy accounts for the remaining 69 percent. Page dated 29 October 2019.
• NASA Jet Propulsion Laboratory, Refining the Ingredients of Our Universe, opened and read 5 Nov 2026. Planck's map of the oldest light allowed the most precise inventory of the universe's ingredients to date: normal matter 4.9 percent, dark matter 26.8 percent, dark energy 68.3 percent. Planck is a European Space Agency mission with significant NASA participation.
• NASA Science, The Universe's History overview, opened and read 5 Nov 2026. The universe expanded through cosmic inflation around 13.8 billion years ago; one second after the Big Bang the universe was an extremely hot primordial soup of light and particles; nucleosynthesis produced hydrogen, helium, and traces of lithium and beryllium, with most of today's helium formed after five minutes; recombination occurred around 380,000 years after the Big Bang, releasing the cosmic microwave background; the first stars were 30 to 300 times more massive than the Sun; in 1998 astronomers found distant supernovae fainter than expected, pointing to accelerating expansion driven by dark energy.
• NASA Science, What is Dark Energy? Inside Our Accelerating, Expanding Universe, opened and read 5 Nov 2026. Nine billion years after the universe began, its expansion started to speed up; dark energy makes up approximately 68.3 to 70 percent of the universe; the acceleration was discovered in 1998 from distant Type Ia supernovae, and the team leaders Adam Riess, Saul Perlmutter, and Brian Schmidt won the 2011 Nobel Prize in Physics; the ESA Euclid mission, launched in 2023, maps how dark energy has pulled matter apart over time.
• CERN, The Standard Model, opened and read 5 Nov 2026. Everything in the universe is made from a few basic building blocks called fundamental particles, governed by four fundamental forces; matter particles are quarks and leptons in two groups of six, arranged in three generations; the strong force is carried by the gluon, the electromagnetic force by the photon, and the weak force by the W and Z bosons; gravity is not part of the Standard Model; the Standard Model describes only about 4 percent of the known universe.
• OpenStax Astronomy, section 29.5, What Is the Universe Really Made Of?, opened and read 5 Nov 2026. Luminous matter in stars and galaxies and neutrinos contribute about 1 percent of the critical density; hydrogen and helium in interstellar and intergalactic space contribute another 4 percent; dark matter accounts for about 27 percent; dark energy supplies the remaining 68 percent; only about one half of 1 percent of the critical density is found in stars.
• Planck Collaboration, 2018 results VI, Cosmological parameters, arXiv:1807.06209, checked against the arXiv abstract 5 Nov 2026. The final full-mission Planck analysis gives a matter density parameter of 0.315, a baryon density of 0.0224, and a Hubble constant of 67.4 km/s/Mpc. The precise figures are ordinary matter 4.9 percent, total matter 31.5 percent, and dark energy 68.5 percent, with dark matter 26.6 percent derived as total matter minus ordinary matter.
• Planck Collaboration final results, 2018, as summarized by the Grenoble Observatory press release, opened and read 5 Nov 2026. The full and final Planck data and associated articles were published on 17 July 2018; the data support a model of ordinary matter, cold dark matter, and dark energy, with an inflation phase at the beginning; 95 percent of the universe is made up of dark matter and dark energy whose nature is not known.