Imaging the Early Universe
Every image I take holds light that has been traveling for a very different length of time. Some of it left a few years ago. Some of it left before the Sun existed. Scroll from the scale of home to the oldest light I have captured.
A light-year is the distance light travels in one year.
Light covers about 186,000 miles every second. Keep that pace for a full year and you have gone one light-year. Every size and distance on this page uses that single unit, from the width of Earth to the most distant quasar. Small numbers keep their leading zeros and large numbers keep every digit, so you can watch them grow.
The oldest light in my photographs left when the universe was about 1,800,000,000 years old.
Light is not instant. Every photo on this page is a picture of the past. Here is the whole history of the universe, 13,800,000,000 years, as one line. Each mark shows when the light in one of my photographs set out.
Earth, the Solar System, every Milky Way nebula and every nearby galaxy on this page fit inside the small gold box at the left end, next to now. The quasars are what carry the journey back across most of cosmic history.
Three numbers that are easy to mix up.
12,000,000,000 light-years is how far the final quasar's light traveled, measured as travel time. That is the number used throughout this journey.
About 22,700,000,000 light-years is where that quasar is today. Space kept expanding while the light was in transit, so the source is now much farther away than the light's travel time suggests.
About 46,200,000,000 light-years is the radius of the observable universe today. It is larger than 13,800,000,000 for the same reason: expansion. Age and present-day size are different measurements.
Planck 2018 cosmology.
87% of cosmic history.
The part of cosmic history before my oldest light. The oldest light anyone can detect, the cosmic microwave background, left about 380,000 years after the Big Bang.