The answer comes from a relic originating just 380,000 years post–Big Bang and stretching across 93 billion light-years. The farthest thing we’ve detected in space isn’t a star or galaxy—it’s the Cosmic Microwave Background, or CMB. The discovery of the CMB in 1965 was a pivotal moment, offering strong support for the Big Bang model. This is essentially the afterglow of the universe’s birth, captured in the microwave band of light.
The farthest thing in the universe isn’t a place: it’s a time.
We’re looking at light that began its journey just 380,000 years after the universe became transparent. By measuring its redshift, scientists estimate the CMB is currently about 46.5 billion light-years away from us in every direction. This implies the observable universe has a diameter of about 93 billion light-years.
Importantly, this is not thought to be the edge of the universe—only the edge of what we can observe. Estimating beyond the CMB requires modeling. Two broad possibilities are often discussed: an open or flat universe and a closed universe. If the universe is open (or flat), it may be infinite. If it is closed, current conservative estimates suggest it could be at least six times larger than the observable universe—on the order of 600 billion light-years across.