Is there a center in the middle of the universe?

Answer

We will never be able to point to that famous center: you imagine the big bang as an explosion in an already existing empty space. That is not correct. The big bang was not an explosion at a certain point in a pre-existing empty space, a point from which all matter then flies away. The space itself was also created during the big bang.
Compare it to a spherical surface on which 2-dimensional beings live. That surface is their world, so they have absolutely no awareness of below and above. Only from forward and backward, and from left and right. Their world has no boundaries either, they can walk around on it forever without also coming to an edge. Their world has no center either, for every point on the spherical surface is equally important or unimportant in that regard.
But suppose you slowly inflate that spherical surface. Then they see their “universe” expanding just as we see it.
Even if two beings stand still, they will see that they are being widened from each other, not because they move, but because space itself expands. They might also reason, “Hey, look, that means our universe may have originated from 1 point in the distant past, let’s call that event the big bang”.
You see, they cannot answer the question where their big bang took place in their current universe, but their own space did arise from that one point.