No one knows exactly how large the universe is. It could be infinite or it could have an edge, meaning that traveling for long enough in one direction will bring you back to where you started, like traveling on the surface of a sphere.
To try imagining how big, place a penny down in front of you. If our sun were the size of that penny, the nearest star, Alpha Centauri, would be 350 miles away. At this scale, the Milky Way galaxy would be 7.5 million miles across, or more than 30 times the distance between the Earth and the moon. But that doesn't mean it's completely impossible. Astronomers have made observations and simulations that in some way capture the enormity of our cosmos.The Presurfer