system
Given the following post, respond as if you're commenting on Reddit:
human
How is the universe 93 billion light-years across if it has only existed for 13.4 billion years?

I've searched on google for this and found no answer so here I am.

If the edges of the universe are expanding away from each other at the speed of light for 13.4 billion years you would think they would be 26.8 billion light-years apart by now.

I know inflation was a period that where universe expanded much faster than the speed of light. Is that what made the universe so big? Did inflation (which according to google only lasted 32 seconds) cause the universe to expand 66.2 billion light-years? (93-26.8)

Would love to understand this.
gpt
First, the inflationary epoch did not last 32 seconds, but rather a tiny fraction of a second (1/10^32 of a second). This is 0.(31 zeros)1 seconds long.

Next, the universe itself is also much larger than 93 billion light years across. This is the size of the universe which *we can see.* It would be extraordinarily unlikely that there is no universe outside our horizon.

Putting these two facts together, no, the inflationary epoch is not the reason the observable universe is larger than 26.8 billion light years. The farthest we can see is 93 billion light years, and looking 93 billion light years in any direction you will see the same thing: the Cosmic Microwave Background. This is a remnant of when the universe was about 350,000 years old, and before that the universe was too highly energetic to actually allow light to travel. So this is the farthest back in time we can, even theoretically, ever see.

What caused the observable universe to swell to 93 billion light years in size in only 13.4 billion years is dark energy, which is what's driving the accelerated expansion of the universe. Clearly, objects 93 billion light years away are being separated from us faster than the speed of light.

This does not violate relativity because those objects aren't actually moving *through* space, but rather the space between us and those objects is itself expanding.

Since all space expands at an equal rate, the farther we are from an object, the faster it will be expanding away from us. There are many many things which we can see which we can never, ever, ever reach, even if we could travel at 99.9999% the speed of light.