How do astronomers know the universe is expanding? All known elements emit and absorb particular wavelengths of light, which is part of the electromagnetic spectrum.

This observation, known as Hubble's law, combined with the observation that the universe at the largest scales is homogeneous (the same everywhere) and isotropic (the same in all …

Dec 13, 2024 · Then, in 1998, scientists discovered the universe’s rate of expansion is accelerating. In the years since, researchers using the Hubble Space Telescope have …

Apr 22, 2025 · How can we know the universe is expanding? Using theories and measurements about light coming from distant stars, multiple astronomers in the early 1900’s suggested that …

Aug 8, 2025 · Hubble observations, along with those of ground-based observatories, surprised astronomers by revealing that the universe is not just expanding but accelerating – a discovery …

Dec 9, 2024 · Scientists know the universe is expanding because they can track other galaxies as they move away from ours. They define expansion using the rate that other galaxies move …

Dec 18, 2024 · Scientists know the universe is expanding because they observe galaxies drifting away from the Milky Way. They define expansion by how fast these galaxies move apart.

For much of the 20th century, it was an open question whether the universe is open (of infinite extent in space) or closed (of finite extent) and whether the universe in the future will continue …

May 4, 2025 · At the moment of the Big Bang, about 13.8 billion years ago, the universe began expanding from an almost unimaginably dense state. In the first fractions of a second, space …

Jan 11, 2025 · This article gives a short explanation of how the expanding and accelerating universe was discovered and the related and unsolved mysteries of dark energy and dark matter.