Actually, it's a 3D volume curving into a 4 dimensional hypersphere, and no matter where you are in it you are at the center, so the term radius makes perfect sense. An analogy is the 2D surface of the earth, which curves into a 3D sphere. No matter where you are on the earth's surface, you are about 12500 miles from your antipodal point (not along a radius, but along a geodesic on the earth's surface). If you travel in ANY direction in a straight line you will eventially go through the antipodal point and finally return to where you started. So there is really no "center" of the earth's 2D surface like there is definitely a center of the earth's 3D volume.
But the radius of the universe is not known for a fact to be 13.7 billion ly (the age of the universe at the speed of light). It may be much bigger, even if it is finite in size. Which means there are parts of the universe we will never know anything about, no matter how good our telescopes get. Personally, I think it's too early to tell yet. We're only now starting to ask the right questions, and we are only now developing the technology to see out to the Red Limit.
Space/Science » in reply to Why are you using the word, radius?
re: Why are you using the word, radius?