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    Dark matter and dark energy, explained

    Dark matter and dark energy are the two unknown ingredients that, by CERN's figures, make up about 27% and 68% of the universe; ordinary matter is about 5%.[1] As of October 2026 no dark matter particle has been detected, and DESI's hint that dark energy changes over time, at 2.8 to 4.2 sigma, awaits its full five-year dataset in 2027.[2][3][4]

    Editor reviewedUpdated Particle physics and cosmologyPhysicsScience

    The invisible 95%

    Stars, planets, gas and people together make up only about 5% of what is in the universe. Scientists think about 27% is dark matter and 68% is dark energy.[1] These are two different mysteries. Dark matter pulls things together. Dark energy pushes the universe apart faster and faster.[5][6]

    In the standard cosmological model, Lambda-CDM, the universe contains cold dark matter plus a cosmological constant (Lambda), the simplest form of dark energy.[7] The model fits the cosmic microwave background well. ACT’s final 2025 analysis found the CMB spectra described by Lambda-CDM.[8] The open questions are what the dark components are, and whether Lambda is really constant.

    Dark matter does not interact with light, so it is inferred only from its gravity. Galaxies spin faster than their visible matter could hold together.[5] Theories beyond the Standard Model, such as supersymmetry, predict particles that could be dark matter.[9]

    There are two main ways to search:

    • Direct detection waits for a dark matter particle to bump into an atom in a shielded underground detector. The LZ experiment, nearly a mile underground in South Dakota, reported 417 live days of data in December 2025 with no sign of WIMPs (weakly interacting massive particles).[10][2] The detector is now sensitive enough to pick up neutrinos from the Sun’s core, which it saw at 4.5 sigma.[11]
    • Collider production. If the large-hadron-collider made dark matter particles, they would escape unseen, but would show up as missing energy and momentum.[12]

    LZ plans to run through 2028 and its team is designing a larger successor, XLZD.[13]

    Dark energy: the accelerating universe

    In 1998 two teams measured exploding stars, called Type Ia supernovae, and found them dimmer than expected. That meant the universe’s expansion is speeding up, not slowing down. The discovery won the 2011 Nobel Prize in Physics.[6] “Dark energy” is the name for whatever causes this. NASA says plainly that we do not know what it is.[14]

    Candidate explanations include vacuum energy (a cosmological constant), a dynamical field such as quintessence, and modified gravity.[14] Surveys test these with standard rulers. Baryon acoustic oscillations imprint a characteristic scale in galaxy clustering, and how that scale’s apparent size changes across cosmic time traces the expansion history.[15] DESI’s 2025 analysis favoured models with w0 > -1 and wa < 0, a dark energy whose effect weakens over time. Combined with CMB and supernova data, the preference reached 2.8 to 4.2 sigma, depending on the supernova sample.[16][3]

    The cosmic microwave background

    Much of what we know about the universe’s contents comes from the cosmic microwave background. This leftover radiation from the Big Bang was released about 380,000 years after the beginning and is now at 2.7 kelvin.[17] ESA’s Planck satellite mapped its temperature differences, as small as a few millionths of a degree, across the whole sky.[18] A planned US successor, CMB-S4, lost DOE and NSF support in July 2025.[19]

    What to watch

    The DESI survey finished its planned five-year map in April 2026, and dark energy results from the full dataset are expected in 2027.[20][4] Those results should show whether the evolving-dark-energy hint grows or fades.[4] Two other surveys now attack the same question. Rubin Observatory began its 10-year survey of the southern sky in mid-2026, and NASA’s Roman Space Telescope, launched in August 2026, will use Type Ia supernovae, the same exploding stars that revealed cosmic acceleration.[21][22][23]

    Questions readers ask

    What is dark matter made of?

    Nobody knows. It is detected only through its gravity. Proposed candidates include particles predicted by theories beyond the Standard Model, but searches such as LZ have not found them.[5][9][2]

    How do we know dark energy exists?

    In 1998 astronomers found distant supernovae dimmer than expected, showing the universe's expansion is speeding up. Dark energy is the name for whatever drives that acceleration.[6][14]

    Is dark energy changing over time?

    Possibly. DESI's 2025 analysis preferred evolving dark energy at 2.8 to 4.2 sigma, short of the 5-sigma discovery standard.[3]

    What is the cosmic microwave background?

    Leftover radiation from the Big Bang, released about 380,000 years after the universe began and now at 2.7 kelvin.[17]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      According to CERN, ordinary matter makes up about 5% of the universe's content, dark matter about 27% and dark energy about 68%. confirmedas of 2026-10-10

    2. [2]

      In December 2025 the LZ experiment reported 417 live days of data taken from March 2023 to April 2025 with no sign of WIMP dark matter, including a first search of the 3 to 9 GeV mass range. confirmedas of 2025-12-08

    3. [3]

      On 19 March 2025 DESI released baryon acoustic oscillation results from three years of data covering about 14 to 15 million galaxies and quasars; combined with other data they preferred evolving dark energy over a cosmological constant at 2.8 to 4.2 sigma, short of the 5-sigma discovery standard. confirmedas of 2025-03-19

    4. [4]

      DESI will keep observing through 2028, expanding its map from 14,000 to about 17,000 square degrees, and its first dark energy results from the full five-year dataset are expected in 2027. confirmedas of 2026-04-15

    5. [5]

      Dark matter does not interact with the electromagnetic force and is inferred only from its gravitational effect on visible matter, for example galaxies rotating faster than their visible matter could hold together. confirmedas of 2026-10-10

    6. [6]

      In 1998 astronomers found that distant Type Ia supernovae were dimmer than expected, showing that the universe's expansion is accelerating; the discovery won the 2011 Nobel Prize in Physics. confirmedas of 2026-10-10

    7. [7]

      The standard cosmological model, Lambda-CDM, combines cold dark matter with Lambda, the simplest form of dark energy, which acts as a cosmological constant. confirmedas of 2025-03-19

    8. [8]

      The Atacama Cosmology Telescope's final (DR6) analysis in March 2025 found the CMB described by Lambda-CDM and, combined with Planck, CMB lensing and DESI, a Hubble constant of 68.22 ± 0.36 km/s/Mpc (68.43 ± 0.27 with DESI DR2). confirmedas of 2025-03-18

    9. [9]

      Hypothesised particles from theories beyond the Standard Model, such as supersymmetric partners of known particles, are among the proposed dark matter candidates. confirmedas of 2026-10-10

    10. [10]

      LZ is run by about 250 scientists and engineers from 37 institutions and sits nearly a mile underground at the Sanford Underground Research Facility in South Dakota. confirmedas of 2025-12-08

    11. [11]

      LZ detected boron-8 solar neutrinos scattering off xenon nuclei with 4.5-sigma significance, above the 3-sigma evidence threshold. confirmedas of 2025-12-08

    12. [12]

      Dark matter particles produced at the LHC would escape the detectors unseen, but physicists could infer them from energy and momentum missing after a collision. confirmedas of 2026-10-10

    13. [13]

      LZ plans to run through 2028 to collect more than 1,000 live days, and its team is developing a larger next-generation detector, XLZD. confirmedas of 2025-12-08

    14. [14]

      NASA states that scientists do not know what dark energy is; candidate explanations include vacuum energy (a cosmological constant), a varying field called quintessence, and modified gravity. confirmedas of 2026-10-10

    15. [15]

      Baryon acoustic oscillations leave a pattern in the distribution of galaxies that acts as a standard ruler, whose size at different times depends on how the universe was expanding. confirmedas of 2025-03-19

    16. [16]

      The DESI 2025 analysis favours dark energy models with w0 greater than -1 and wa less than 0, meaning dark energy whose strength changes over time. confirmedas of 2025-03-19

    17. [17]

      The cosmic microwave background is leftover radiation from the Big Bang, released about 380,000 years after the universe began and now at an effective temperature of 2.7 kelvin. confirmedas of 2026-10-10

    18. [18]

      ESA's Planck satellite mapped temperature variations in the cosmic microwave background as small as a few millionths of a degree across the whole sky. confirmedas of 2026-10-10

    19. [19]

      In July 2025 the US Department of Energy and National Science Foundation said they could no longer support CMB-S4, an estimated $900 million project to search the cosmic microwave background for primordial gravitational waves from inflation. confirmedas of 2025-07-23

    20. [20]

      In April 2026 DESI completed its planned five-year survey ahead of schedule, having observed more than 47 million galaxies and quasars, against an original target of 34 million, plus more than 20 million stars. confirmedas of 2026-04-15

    21. [21]

      NSF NOIRLab, which operates Rubin with SLAC, announced on June 30, 2026 that the 10-year Legacy Survey of Space and Time had officially started after a period of system optimization and an operational readiness review; Rubin Observatory's own website dates the start of the survey to July 2026. confirmedas of 2026-10-10

    22. [22]

      The NSF-DOE Vera C. Rubin Observatory on Cerro Pachón in Chile, named after the astronomer Vera Rubin and aimed at questions including dark energy and dark matter, uses the 8.4-meter Simonyi Survey Telescope and the LSST Camera, the largest digital camera ever built, and is operated by NSF NOIRLab and SLAC. confirmedas of 2026-10-10

    23. [23]

      Roman is expected to find many more Type Ia supernovae, the exploding stars used to discover dark energy, to test the standard cosmological model, and its catalogues will be available to everyone rather than only to academics. reportedas of 2026-08-28

    Revision history (2)
    1. Page created.
    2. Linked the Rubin and Roman dark energy surveys.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "Dark matter and dark energy, explained." ContentLora, updated Oct 10, 2026. https://contentlora.com/explain/dark-matter-and-dark-energy-explained

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