Ask Ethan: How Far Is The Edge Of The Universe From The Farthest Galaxy?
“If our current best theories are correct, the first true galaxies will have formed at some point between around 120 and 210 million years of age. That corresponds to a distance from us of between 37 and 35 billion light years, placing the distance from the farthest galaxy of all to the edge of the observable Universe at 9-to-11 billion light years today. That’s incredibly far, and points to one incredible fact: the Universe was expanding extremely rapidly in the early stages, and expands at a much slower rate today. That first 1% of the Universe’s age is responsible for approximately 20% of the Universe’s total expansion!”
When we look to the deepest reaches of space, we can look for the “first” of any type of object. The first galaxy, the first star, the first light from the CMB, or even the first signals from the Big Bang, like gravitational waves. Yet these signals all have very different redshifts from one another, and perhaps more puzzlingly, lie at extraordinarily different cosmic distances from us. The reason for this is the intricate relationship between the expansion of the Universe and the contents of what’s in it, and how that changes over time. When the Universe was hotter and denser in the past, it was also expanding much faster. It expanded so much faster in the past that looking back to the edge of the observable Universe (when the big bang occurred) versus looking to the cosmic microwave background (380,000 years later) corresponds to a 900 million light year difference today!