Summary
Highlights
In 2016, the Hubble Space Telescope captured an image of GN-z11, the most distant galaxy ever observed. This raises the question of whether there's a final galaxy or an end to the universe. However, there's a limit to how far we can see, which is determined by the speed of light and the age of the universe. Light travels at a finite speed, meaning it takes time for light from distant objects to reach us.
Even light from our sun takes 8 minutes to reach us. For stars and galaxies, distances are measured in light-years, representing the time it takes for their light to travel to Earth. The light from GN-z11 was emitted 13.4 billion years ago. Since the universe is only 13.8 billion years old, we cannot see much farther, as it takes time for galaxies to even form. This establishes a hard limit to the edge of the universe we can observe.
GN-z11 formed early in the universe's history, just 400 million years after the Big Bang. Before that, there were no stars or galaxies, only a very hot gas. This hot gas, now cooled and expanded, forms a "shell" around us known as the cosmic microwave background (CMB). The CMB is the oldest light in the universe, an echo of the Big Bang, and represents the furthest thing we can see, the edge of our observable universe.
The observable universe is simply the part of the universe we can see. It can be thought of as a spotlight centered on our location; we can see to its edge but not beyond. This spotlight moves with us. For inhabitants of GN-z11, a completely different part of the universe would be observable, meaning they are at the edge of our observable universe, and we are at the edge of theirs.
Despite light from GN-z11 taking 13.4 billion years to reach us, measurements indicate it is currently 32 billion light-years away, three times further than initially thought possible. This discrepancy arises because the universe is expanding. The expansion of space itself stretches the distances between objects, meaning that while the light traveled for 13.4 billion years, the galaxy itself has moved much further away during that time. This expansion adds another layer of complexity to understanding the true edge of the universe.