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The answer is just that the light didn't happen to start at the edge of the universe going outward. If the Sun suddenly became transparent to light, as our universe did, then parts of the Sun's north pole would after some finite time see light emitted from the parts of the Sun's south pole, because that light isn't purely directed outwards but is omnidirectional.
Now, you might have instead believed that the light from the ancient universe would have "passed us by, by now" -- in other words, that the universe was/is very small. So, the Sun as our example, after a minute or two (if the Sun stops radiating more), the light from the south pole should no longer reach its north pole because it should be several planets away from the Sun by now. That makes this an interesting question, where before it was a little simplistic.
The answer now is that we must not be able to see all of the universe just yet. The universe must be larger than 13.7 billion light years in diameter! (The universe was once, but space has been expanding as this light has been traveling along.) We say that the universe is believed to be larger than the visible universe. We can only see this small 13.7 billion light year ball at various stages of its development; but the universe was bigger at that in the time when the universe became transparent to light.
There is another interesting question: being outside of this "bubble" (called a "light cone" in relativity) means that the separation between us and those parts of the universe is "spacelike" and no causal influences can cross the distance. The problem here is that the cosmic microwave background is *highly homogeneous*, to around one part in 100,000; and it is the most perfect thermal spectrum ("blackbody radiation") ever seen in nature. Why would causally-unconnected bits be in good thermal equilibrium with each other? The answer is one of the most important parts of Big Bang cosmology, called "cosmic inflation". The idea is that the very earliest bits of the universe's life were dominated by a not-so-well-understood expansion where space actually expanded faster than light, "ripping apart" the small thermal-equilibrium universe into domains that aren't causally connected.
This sort of "rip" is akin to the Big Rip, which you might have heard about elsewhere.
Now, you might have instead believed that the light from the ancient universe would have "passed us by, by now" -- in other words, that the universe was/is very small. So, the Sun as our example, after a minute or two (if the Sun stops radiating more), the light from the south pole should no longer reach its north pole because it should be several planets away from the Sun by now. That makes this an interesting question, where before it was a little simplistic.
The answer now is that we must not be able to see all of the universe just yet. The universe must be larger than 13.7 billion light years in diameter! (The universe was once, but space has been expanding as this light has been traveling along.) We say that the universe is believed to be larger than the visible universe. We can only see this small 13.7 billion light year ball at various stages of its development; but the universe was bigger at that in the time when the universe became transparent to light.
There is another interesting question: being outside of this "bubble" (called a "light cone" in relativity) means that the separation between us and those parts of the universe is "spacelike" and no causal influences can cross the distance. The problem here is that the cosmic microwave background is *highly homogeneous*, to around one part in 100,000; and it is the most perfect thermal spectrum ("blackbody radiation") ever seen in nature. Why would causally-unconnected bits be in good thermal equilibrium with each other? The answer is one of the most important parts of Big Bang cosmology, called "cosmic inflation". The idea is that the very earliest bits of the universe's life were dominated by a not-so-well-understood expansion where space actually expanded faster than light, "ripping apart" the small thermal-equilibrium universe into domains that aren't causally connected.
This sort of "rip" is akin to the Big Rip, which you might have heard about elsewhere.