What is dark energy?

Dark energy is the name given to the invisible mechanism that has caused the universe to expand at an accelerated rate for the past 5 billion years. Rather than conventional kinetic energy—the energy of objects moving through space—dark energy causes space itself to stretch out, pushing otherwise stationary objects farther apart. Calculations of the prevalence of this repulsion reveal that approximately 70% of the universe is made of dark energy.

Astronomers have known the universe was expanding since Edwin Hubble observed galaxies moving away from Earth in 1929, which served as evidence for the Big Bang. However, cosmologists believed the mutual gravitational attraction of everything in the universe would slow this expansion. By 1998, two independent research teams used Type Ia supernovae—stellar remnants that reignite and undergo runaway thermonuclear explosions—to map the universe's expansion over time and discovered it was instead speeding up (learn more).

While the nature of dark energy remains unknown, Albert Einstein's equations of gravity once included a term that represented a uniform, repulsive energy filling space. This cosmological constant represents the leading candidate for what dark energy is, but that may be changing. Data from 2025 suggests that the density of dark energy is slowly decreasing with time, weakening its accelerating effect.

Learn even more by exploring all our findings on dark energy here.

Here's a sample of what we found ...

> About 97% of galaxies move faster than the speed of light due to dark energy. (Watch)

> Dark energy dominance represents the final known era of the universe. (Read)

> How quantum physics and dark energy led to "the worst theoretical prediction in the history of physics." (Watch)

> What happens to the universe if dark energy gets stronger? (Read)

Dark matter, explained

Dark matter is a type of matter that does not reflect or emit light, making its direct observation impossible. Like visible matter, it has mass and takes up space, allowing it to interact with its surroundings via gravity. Through these interactions, astronomers have inferred the existence of dark matter, which is more than five times more common than visible matter and is believed to have facilitated the formation of galaxies and other large-scale structures in the universe (view simulation).

In 1933, Fritz Zwicky's analysis of galaxies in the Coma Cluster revealed that they moved faster than expected given the gravitational pull from the visible galaxies alone. He theorized the presence of invisible mass—"dunkle Materie"—to enable this motion, but miscalculated how much. By the 1970s, Vera Rubin and Kent Ford's more precise observations showed that stars in their galaxies orbited their centers faster than expected. To account for this, they suggested galaxies reside in massive clouds of unseen material that contribute to their mass and gravity (watch explainer).

Subsequent observations, including light bending around galaxies and galaxy clusters, have strengthened the case for these clouds—dark matter halos—and ruled out models that claim the universe has no dark matter. As of 2026, scientists do not know what dark matter is made of, but candidates include primordial black holes and new types of particles.

Learn even more by exploring all our findings on dark matter here.

Here's a sample of what we found ... 

> The solar system is currently traveling through a "dark matter hurricane." (View)

> A cup of coffee on Earth contains about 100 proton masses worth of dark matter. (Listen)

> Replicate the work of astrophysicists and discover the distribution of dark matter in different galaxies in this simulation. (Explore)

> Can we create dark matter on Earth? (Watch)

NASA, 101

The National Aeronautics and Space Administration is the primary civilian space agency of the United States. Founded in 1958, NASA has more than 17,000 employees nationwide and an annual budget of $24.4B (view budget breakdown).

After World War II, the United States and the Soviet Union sought to develop rockets capable of launching satellites into low Earth orbit, marking the beginning of a nearly two-decade-long Space Race between the two powers. After the USSR took a decisive lead by launching the first satellite into orbit in 1957, President Dwight Eisenhower signed legislation establishing NASA the following year, which consolidated several existing programs (watch explainer).

In the decades that followed, NASA became the world's leading space program: landing the first humans on the moon, conducting early crewed lunar orbits and long-duration missions, deploying landmark space telescopes, and laying the groundwork for a permanent human presence in orbit through space stations (view timeline). NASA plans to return humans to the moon in the late 2020s through its Artemis program.

Learn even more by exploring all our findings on NASA here.

Here's a sample of what we found ...

> NASA once conceived launching rockets from the ocean. (Watch)

> From 1961 to 1965, NASA purchased about 60% of all microchips. (Read)

> The full broadcast of humanity's first walk on the moon. (Watch)

> How does NASA communicate with spacecraft billions of kilometers away? (Watch)

Science Spotlight

Like all great scientists, we love spending time researching the latest scientific breakthroughs, tech releases, engaging explainers, and the connections between science and society that are making headlines. Here's what we found this week.

> The first two weeks of the war in Iran have released 5 million metric tons of CO₂

The Guardian | Damien Gayle. An environmental analysis of the conflict estimated that attacks on fossil fuel infrastructure, military bases, civilian areas, and ships at sea, and their subsequent fires, have produced the same amount of carbon dioxide as is released in a year by the 84 lowest-emitting nations combined. (Read) | Learn about greenhouse gases like CO₂ by exploring our write-up and findings here.

> 'Failed stars' can shine brightly by teaming up

Caltech | Whitney Clavin. Searching through observations made by the Zwicky Transient Facility, scientists found a tight-knit pair of brown dwarfs—objects 13 to 80 times more massive than Jupiter but not massive enough to sustain nuclear fusion—with one siphoning material from the other. The brown dwarfs are expected to merge into a new star, or the siphoning star will become massive enough to ignite. (Read)

> Red-tailed bumblebees can serve as hosts for acute honeybee paralysis virus

Martin Luther University Halle-Wittenberg | Staff. Data from field trials at 32 locations in Germany suggest that these wild bees can contribute to viral infections in honeybees. While the virus appears to cause little harm to bumblebees, infection is usually fatal to honeybees and can lead to the rapid collapse of an entire colony. (Read) | Learn about pollinators by exploring our write-up and findings here.

> Researchers develop and test the world's first quantum battery prototype

The University of Melbourne | Staff. Instead of relying on chemical reactions, the proof-of-concept leverages quantum properties to absorb light in a single, rapid, massive, and scalable event. Findings showed that such batteries charge faster the larger they are and can store energy at room temperature, but only for nanoseconds. (Read) | Learn about batteries by exploring our write-up and findings here.

> Microorganisms facilitate the formation of ice on microplastics in clouds

Virginia Tech News | Courtney Sakry. Researchers found that the temperature at which tiny water droplets containing microplastics began freezing when cooled increased by about 6.5 degrees, allowing ice to form sooner. This shift, which may result from microbes forming a sticky biofilm on microplastics, may influence regional weather patterns by affecting how clouds form and precipitation occurs. (Read) | Learn about microplastics by exploring our write-up and findings here.

Best of the Week

We curate hundreds of resources into 1440 Topics each week. Here are some of our favorites from the world of science and technology.

Read:

> Scientists have tested storing data on cassettes using DNA tape.

> The theory that suggests the entire universe only has one electron.
> Rivers in the sky? Atmospheric rivers, explained.
> What makes something a "superfood?"

Listen:

> Where do magnets come from, and how did Earth become one?

> How paleontology dates fossils and other geological specimens.
> The chemical contaminations caused by urban wildfires and their impacts.

Watch:

> The organisms that, when lined up together, would span the length of the Milky Way galaxy.

> Why lithium has been called "white gold."

> Could life on Earth have come from somewhere else in space?

Thank you to our readers for inspiring us with their questions! Curious about something in science and technology? Tell us here.

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