When astronomers use the word “universe”, they mean space and all the heavenly bodies contained in it. It is impossible for human imagination really to grasp what this involves.
Just to give you an idea, a light year equals about six billion miles. Our own galaxy, the Milky Way, is about 100,000 light years in length. There are millions of other galaxies, and one of the nearest to us is about 2,000,000 light years away. The most distant ones are billions of light years away. And all this is only that part of the universe that we know about. There may be more that we have not detected yet.
When astronomers try to answer a question like this, they become involved with the nature of space itself. According to the present theory, space curves around on itself. This means that you can never get “outside” space because your path will always curve around and lead you back again.
For example, when a plane flies from New York to San Francisco, it does not really fly in a straight line. Since the earth is curved, if the plane flew in a straight line, by the time it was over San Francisco it would be several thousand miles up in the air.
So in flying from New York to San Francisco, a plane follows a curved path. And if the plane continued in that same curved path, it would eventually come back to New York. Astronomers believe that space curves around in a special way. not as simple as earth’s curving. A picture of it cannot be drawn on paper nor can a model be made of it. But it can be figured out by using complicated mathematics.