If the universe is 13.6 billion years old, how can astronomers see galaxies close to the Big Bang, which created the universe? That seems implausible and impossible — until you understand light.
Everything you see has already happened. Light travels at 186,282 miles per second (299,792 kilometers per second), which is fast but still means it takes time to reach your eyes. For a lamp, it’s a millisecond. The brain then takes 13 milliseconds to process it. About 14 milliseconds is not noticeable, but the fact remains — all light you see is old light. It happened in the past.
You see everything as it was, not as it is.
All Light Is Old Light
When you look up at the night sky, that matters. The light you see — whether sunlight, moonlight or starlight — is old light that has taken considerable time to reach your eyes.
Here are some examples:
- Moonlight takes 1.28 seconds to reach your eyes.
- Sunlight takes 8 minutes and 20 seconds to reach your eyes.
- Starlight from Sirius, the closest and brightest star visible from the northern hemisphere’s night sky, takes 8.6 light years to reach your eyes. See it tonight, rising in the southeast a few hours after dark, and you’re seeing it as it was in 2015.
(A light-year is the distance across space traveled by light at 186,282 miles per second in an Earth-year).
- Starlight from Dubhe in the Big Dipper takes 125 years to reach your eyes.
- Starlight from Polaris, The North Star, takes 433 years to reach your eyes.
- Galaxy-light from the Andromeda galaxy (M31) has taken 2.5 million light-years to reach your eyes.
Back then, Earth was in its Pleistocene Epoch and human’s distant, long-extinct species of archaic human, the tool-making Homo habilis, had emerged in East and South Africa.
Galactic Empire
That’s just our cosmic neighborhood, Andromeda being in the same Local Group as the Milky Way (the farthest object visible to the naked eye). Go farther out — using telescopes — and it’s possible to see things like galaxies M81 and M82, a pair about 11 million light-years away. Think that’s far? You’re now looking at light from a time when Earth was in the Miocene Epoch, when horses, camels, deer and elephants were evolving.
Beyond these nearby galaxies are billions of others, many of them billions of light-years in the background — those that astronomers are obsessed with. These galaxies exist close to the edge of the creation of the universe itself — and their light has taken the universe’s entire existence to reach us.
Expanding Universe
Astronomers can see about 46 billion light-years in any direction. How can that be if the universe is only 13.8 billion years old? Because the universe is expanding. All objects in the night sky are not only seen by us as they were in the past, but they’re also racing away from us. Astronomers can see 46 billion light-years in any direction due to the expansion of the universe — not because light has traveled for 46 billion years.
Distant galaxies appear red because their light is stretched (red light has longer wavelengths) by the expanding universe stretching it.
The Hubble Ultra Deep Field features about 100 small, red galaxies that are among the most distant known, existing when the universe was just 800 million years old. Cue the James Webb Space Telescope, which has sharper, more sensitive optics and can detect infrared light, meaning it can see through the dust and gas that dominate early galaxies as they form, which absorbs the light. The redder the light a telescope is sensitive to, the farther it will see towards the big bang. Its deepest image so far, known as Webb’s First Deep Field, was published in 2022 and revealed, among other things, galaxies existing just a billion years after the Big Bang. In May this year, it found a galaxy called JADES-GS-z14-0 that existed 300 million years after the Big Bang. Its light has been traveling for 13.5 billion years.
Next time you want to see into the past, just look up.
Wishing you clear skies and wide eyes.
