If you ask the question of how large the universe is, absent qualifiers, that is a question that we are incapable of answering. Anything further than the absolute horizon imposed on us by the speed of light and the age of the universe is invisible to us; all we can do is speculate about what, if anything, lies beyond. In actuality, we cannot even see back to the earliest moments of the universe since it is believed that the very early universe was opaque to electromagnetic radiation and, obviously, stars did not form until sometime after the Big Bang.
As the universe gets older and continues to expand, the portion of matter in the universe that lies within our visible horizon will continue to shrink until we are alone in the visible universe. This does not keep us from investigating where these boundaries lie. In this regard, telescopes such as the Hubble Space Telescope have helped us immeasurably and will continue to do so in the future.
The farthest object found in the heavens to date is a gamma ray burst, traditionally associated with the collapse of massive stars into black holes. The final death throes of such a star release a massive amount of energy, and such bursts were even more common in the early universe, since the nebulae that formed these older stars lacked the heavy elements synthesized by generations of supernovae and, thus could burn hotter and grow larger than stars like our own sun; these stars, termed Population III stars, represent the first generation of star formation in our universe. Observations have supported this theory, as gamma ray bursts become much more common as one looks out into the cosmos and, thus, backwards in time. The record-holding burst, GRB 090423, has a redshift of 8.2, or 820 %, which corresponds with a distance of 13.1 billion light-years - only a little more than half a billion years younger than the universe itself and within 200 million years of the formation of the very first stars.
Study of such stars has much to teach us about where we come from, since the matter synthesis and radiation emitted by the birth and death of those early stars both literally and figuratively set the stage for the birth of our own sun as well as life here on Earth.
Image courtesy of the National Science Foundation