In the vast universe, whenever night falls, countless stars dot the dark sky, and their light travels through a long time and space to reach our sight. The reason why these stars appear so small is that they are so far away from us, and their light often takes hundreds or even tens of thousands of years to reach Earth.
With the help of cutting-edge observation equipment, scientists are able to glimpse the stars farther away, some of which took 15 billion years to reach our eyes. This can't help but amaze people that the speed of light is already extreme in the universe, but it still seems so insignificant on such a vast cosmic scale.
Light, as the fastest speed in the universe, is unimaginably fast. Imagine that in just one second, light is able to fly seven and a half times around the Earth. At this rate, the distance that light can cover in a year is as high as 9.5 trillion kilometers, a distance that would take 120 million years for an ordinary express train.
Astronomers often use the unit "light year" to measure the distance between stars in the universe. For example, Proxima Centauri, our closest star, is about 4.2 light-years away, and our Milky Way is a staggering 80,000 light-years in diameter. These numbers give a more intuitive understanding of the vastness of the universe.
However, although we already have a considerable understanding of the universe, the question of the boundaries of the universe is still an unsolved mystery. Is the universe boundless? This question has puzzled countless scientists and philosophers. In mathematics, we can imagine the concept of infinity, but in the physical world, how can a universe made of actual matter have no boundaries?
With the advancement of science and technology, human beings are constantly exploring the mysteries of the universe. We already know that the solar system is a vast system in which planets orbit the sun. The solar system is only a part of the Milky Way, which contains hundreds of billions of stars. However, when we expand our horizons to the entire universe, the Milky Way is just a drop in the ocean.
On the question of the boundaries of the universe, scientists have put forward various theories and conjectures. Newton once used a paradoxical metaphor to describe the universe: it resembles a large box without borders, with stars evenly distributed inside. Einstein, on the other hand, believed that the universe was "unbounded and finite" and "finite and closed". These theories, though esoteric, attempt to answer the fundamental question of whether the universe has boundaries.
However, since we are in the universe and cannot look beyond the universe to see the whole picture, we may never find a definite answer to the question of the boundaries of the universe. We can only treat the universe as an imaginary model with a starting point in time and a limit in space. As for the questions of "what the universe was like before its birth" and "where is the boundary of the universe", we may always be left with endless reverie and exploration.