Question

Why does the observable universe have an edge?

1) because there are so many galaxies in the universe that every line of sight eventually hits a galaxy, stopping us from seeing any farther
2) because the density of neutrinos at the "edge" is so large that photons cannot pass through, preventing us from seeing beyond this point
3) because absorbing matter prevents us from seeing out past a certain distance
4) because we cannot see any farther than the distance that light has traveled over the lifetime of the universe

Answer 1

The 'edge' of the observable universe is the limit of what we can see based on the distance light has traveled since the birth of the universe, about 13.8 billion years ago. It is not a physical boundary but a limitation on the information that can reach us due to the finite age of the universe and its continual expansion.

Step-by-step explanation:

The observable universe has an 'edge' primarily because we cannot see any farther than the distance that light has traveled over the lifetime of the universe. This limitation is not due to an actual physical boundary but is rather a restriction on the information that can reach us because the universe has a finite age. According to the standard Big Bang model, light has had only about 13.8 billion years to travel since the beginning of the universe, which defines our observable universe's horizon.

It's important to understand that the 'edge' is not an actual edge but a limitation on visibility. Due to the expansion of the universe, all galaxies outside of our local cluster appear to be moving away from us, and the light from galaxies beyond a certain distance hasn't had enough time to reach us. Consequently, the observable universe is a sphere centered on the observer, with a radius equal to the distance light can travel in the universe's age—nothing can be observed beyond this horizon