The universe is very large and possibly infinite in volume; the observable matter is spread over a space at least 93 billion light years across. For comparison, the diameter of a typical galaxy is only 30,000 light-years,
and the typical distance between two neighboring galaxies is only 3 million light-years. As an example, our Milky Way galaxy is roughly 100,000 light years in diameter, and our nearest sister galaxy, the Andromeda Galaxy, is located roughly 2.5 million light years away.
The observable matter is spread uniformly (homogeneously) throughout the universe, when averaged over distances longer than 300 million light-years. However, on smaller length-scales, matter is observed to form "clumps", i.e., to cluster hierarchically; many atoms are condensed into stars, most stars into galaxies, most galaxies into clusters, superclusters and, finally, the largest-scale structures such as the Great Wall of galaxies. The observable matter of the universe is also spread isotropically, meaning that no direction of observation seems different from any other; each region of the sky has roughly the same content.
The universe is old and evolving. The most precise estimate of the universe's age is 13.7±0.2 billion years old, based on observations of the cosmic microwave background radiation. Independent estimates (based on measurements such as radioactive dating) agree, although they are less precise, ranging from 11-20 billions years to 13–15 billion years.
