The universe (Latin: universus) is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.While the spatial size of the entire universe is unknown, it is possible to measure the size of the observable universe, which is currently estimated to be 93 billion light-years in diameter. The universe is currently estimated at roughly 13.8 billion years old, give or take 130 million years. Our solar system formed about 5 billion years ago when the Universe was about 65% of its present size (Figure 5a-2). The present day diameter using the ‘particle horizon’ and the proper distance definition is about 93 billion light-years, so it would have been 46 billion light-years roughly.
As the Universe expanded, matter began to coalesce into gas clouds, and then stars and planets. According to a study published Wednesday in the journal Nature, the 12.5 billion-year-old rotating galactic disk formed much earlier than astronomers thought possible for a galaxy of its size… In comparison, the solar system is only about 4.6 billion years old. When the universe was one thousandth its present size (roughly 500,000 years after the Big Bang), the density of matter in the region of space that now contains the Milky Way, our home galaxy, was perhaps 0.5% higher than in adjacent regions. It appears to be an infant galaxy similar in size to its grown-up counterpart, our own Milky Way, and dates to a time when the universe was only 1.5 billion years old, one-tenth its current age. If we’re willing to go back to when the Universe was just 0.092% its present size, we’ll find a Universe that’s 1089 times hotter than it is today: around 3000 K. When the cosmic microwave background was emitted at z = 1100 the diameter was … Today, the Universe continues to expand. Because its density was higher, this region of space expanded more slowly than surrounding regions. The diameter of the Milky Way is 100,000 light years; the observable Universe had this as its radius when it was approximately 3 years old. The size of the universe depends a great deal on its shape.