Scientists Say: Dark Energy

This mysterious force is driving the universe to expand at an ever-faster rate

Dark energy works against the force of gravity to drive matter in the universe farther apart — including the galaxies seen in this telescope image.

Dana Berry/ Scientific Visualization Studio/NASA

Dark Energy (noun, “Dark EN-er-jee”)

Dark energy is a mysterious force causing the universe to expand faster and faster. No one knows exactly what it is. But if it keeps stretching out space, it may someday tear the cosmos to shreds.

The universe has been expanding ever since the Big Bang, about 14 billion years ago. But scientists long thought that gravity would rein in this expansion. Perhaps the universe would keep swelling, but more slowly. Or someday gravity might cause the universe to collapse back in on itself. That doomsday scenario is called the “Big Crunch.”

In 1998, though, those predictions were upended. Astronomers had been peering at supernovae — the explosions of distant stars. Measuring the distances to those explosions let scientists calculate how fast the universe was expanding. And the results shocked them. The universe appeared to be flying apart faster than ever before. Even now, scientists can’t explain why. But they have dubbed the phantom force pushing the cosmos apart “dark energy.”

Learn more about what we don’t know about dark energy (and dark matter) yet how we still know that each exists. This video offers a fun exploration into what appear to be the biggest mysteries of our universe.

Dark energy can’t be measured directly. But scientists can estimate how much there is based on how fast the universe is expanding. Dark energy makes up about 70 percent of all the contents of the universe. (Those contents include both matter and energy.) Another 25 percent the total stuff in the universe is an invisible substance called dark matter. The rest — a measly 5 percent — is normal matter. That’s the stuff that makes up all visible objects in the universe.

The nature of dark energy is one of science’s greatest mysteries. Maybe it is a property of empty space. Maybe it’s some kind of energy fluid or field that fills space. Some theorists have dubbed that cosmic broth “quintessence.” Others think the expanding universe could be explained by a new theory of gravity.

Since we don’t know what dark energy is, it’s hard to predict how it will behave. Far in the future, perhaps dark energy will overcome the forces holding the universe together. The universe would then tear itself apart. Such runaway expansion is called the “Big Rip.” So dark energy is key not just for understanding the cosmos today. It’s also key to understanding the ultimate fate of the universe.

In a sentence

Observations made by the recently launched James Webb Space Telescope could offer new clues into the nature of dark energy.

Check out the full list of Scientists Say.

Maria Temming is the assistant editor at Science News for Students. She has bachelor's degrees in physics and English, and a master's in science writing.

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