|MLA Citation:||Bloomfield, Louis A. "Question 817"|
How Everything Works 18 Jan 2018. 18 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=817>.
To understand these effects, suppose that there was an observer who was stationary at the creation and watched the earth and galaxy head off in opposite directions at almost the speed of light. From that observer's perspective, the two objects are heading away from one another at almost twice the speed of light. After 15 billion years, this observer sees the galaxy as almost 30 billion light years away from the earth.
Now suppose that there was another observer who was on the earth at the creation. From this person's perspective, the galaxy recedes from the earth at almost the speed of light, but no more. Nothing can move faster than speed of light! After 15 billion years, this observer sees galaxy as almost 15 billion light years away from the earth.
These two observations don't seem to agree. The problem lies in how the two observers perceive time and space. According to special relativity, observers who are moving relative to one another don't perceive time and space in the same way. Their perceptions will be so different that they will not even agree about just when 15 billion years has passed.
With this long introduction, here is the answer to your question: no distant galaxy in the observable universe can ever be farther from us than the distance light has traveled since the creation of the universe. Since that creation was about 15 billion years ago, the most distant possible galaxy is almost 15 billion light years away.