I'm going to write about a difficult topic today, about our 4-dimensional spacetime. "4 dimensional spacetime" means that there are 3 dimensions for the space(x,y,and z axis) and 1 for "time". but the four dimensional space we live in, is twisted in another dimension other than the ones I mentioned about before.
for example, think about Earth. the surface of our planet is 2-D(2-D as in space, not spacetime). but the planet itself is a 3-d sphere. if you started from-say- Rome and went westwards and westwards, you'd eventually get back to Rome.
then add another dimension to it. get the idea? this means that if he traveled space in 1 direction for a very long time, we'd get back to Earth. the universe is like the Earth, but only a LOT more confusing.
funnily, this reminds me of a question solved centuries ago-"what's the edge of earth like?" people thought that the edge of our world(which turned out to be earth) had waterfalls and high mountains and the like. but then Magellan went around the world during the 1500s, to prove it was a sphere. the universe is a similar thing. except that there is no Magellan to prove it physically.