system
Given the following post, respond as if you're commenting on Reddit:
human
If we cannot receive light from objects more than 14 billion lightyears away (Hubble length), then how do we know the radius of the universe?

The radius of the universe is said by WolframAlpha to be predicted at a value of 93 billion lightyears, about seven times this, but how do we know if no light reaches us from farther than 14 billion lightyears?
gpt
Firstly, it is important to note that this is not the radius of the *entire* Universe. This is the radius of the *observable* Universe, that is the part of the Universe where light has had a chance to reach us.

So, if the Universe is only ~14 billion years old, how is it that we can see out to about 93 billion light-years? Well, that's because the Universe is expanding! After a distant galaxy released some light that began its 14 billion year journey, the space between us and that galaxy grew. Once the light finally reached us, that galaxy is now 93 billion light-years away. So we can actually "see" much farther than just 14 billion light-years!