When We Learned Our Universe Is Speeding Up

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OhToday, almost thirty years ago, our view of our cosmic neighborhood changed forever. Our universe appears to be growing over time at an increasing rate, two groups of scientists announced at a 1998 meeting of the American Astronomical Society.

These teams studied distant supernovae, or massive explosions of dying stars, in hopes of learning how quickly the expansion of the universe was coming to an end. By comparing the intrinsic brightness of supernovae with the observed brightness, scientists can estimate their distance from Earth and learn more about the growth of the universe. That’s when they noticed something strange: These explosions, known as Type 1a supernovae, were fainter than expected. Such supernovae are usually quite bright, so something contributes to their surprisingly dark appearance.

Scientists realized that these supernovae were not as close as they had thought and had therefore moved away from Earth faster than expected. “These observations led scientists to conclude that the universe itself must be expanding more rapidly over time,” according to NASA.

Since then, a growing body of evidence from distant supernovae and other space spectacles has supported this theory. But what mysterious force lies behind the accelerated expansion of our universe?

Read more: »These physicists want to abandon dark energy»

Researchers use the term “dark energy” to describe whatever is responsible for this phenomenon, but they don’t have a clear idea of ​​what it actually is. However, there are many assumptions so far. For example, seemingly empty parts of space could generate so-called vacuum energy, which is thought to push the universe outward.

Vacuum energy, also known as the cosmological constant, comes from Albert Einstein’s theory of general relativity. He put this arbitrary component into his equations to ensure that the universe remained static – this was the dominant understanding of our cosmic realm at the time. He then abandoned the cosmological constant when astronomer Edwin Hubble demonstrated that the universe is in fact expanding. Einstein called this “his greatest mistake.”

But his work was not in vain. Today, scientists studying the strange field of quantum mechanics think vacuum energy can be explained by pairs of particles and antiparticles that appear and disappear quickly after colliding. “The effect of all these particles flowing in and out of being is a buzzing ‘vacuum energy’ that fills the cosmos and spreads out into space itself,” wrote Clara Moskowitz for Scientific American.

This is just one possible explanation for dark energy, which scientists can’t even glimpse directly and which makes up about 70% of the universe. To make matters even more complicated, recent discoveries suggest that the expansion of the universe may actually be slowing down.

Fortunately, high-tech tools like the Dark Energy Spectroscopic Instrument, which is currently surveying tens of millions of galaxies to learn more about the effects of dark energy on the growth of our universe, could help put the pieces of this cosmic puzzle together.

Until then, we will continue to be tiny specks within a vast kingdom, transforming at a pace unknown to us.

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Main image: NASA/CXC/U.Texas

• Molly Glick

  Published on January 9, 2026

  Molly Glick is the newsletter editor of Nautilus.