Universe expanding since Big Bang from "summary" of A Breif History of Time and the Universe in a Nutshell by Stephen Hawking
The idea that the universe has been expanding ever since the Big Bang is a central concept in modern cosmology. When we look out into space, we see that galaxies are moving away from us in all directions. This observation led scientists to conclude that the universe must be getting bigger. But what does it mean for the universe to be expanding? One way to think about it is to imagine the universe as a balloon being inflated. As the balloon expands, every point on its surface moves away from every other point. In the same way, as the universe expands, galaxies move away from each other. The expansion of the universe has important implications for our understanding of its past and future. If we run the clock backwards, we can infer that the universe was much smaller and denser in the past. Eventually, we reach a point where everything in the universe was packed into an incredibly hot and dense state, which we call the Big Bang. The concept of the expanding universe is supported by a wealth of observational evidence. For example, astronomers have measured the redshift of light from distant galaxies, which is a telltale sign of cosmic expansion. Additionally, the cosmic microwave background radiation, a relic of the early universe, shows patterns consistent with an expanding cosmos. One of the most fascinating aspects of the expanding universe is the fact that it is not expanding into anything. This might sound counterintuitive, but it is a consequence of the nature of space itself. Rather than expanding into pre-existing space, the universe is stretching and creating new space as it grows.- The idea of the universe expanding since the Big Bang is a cornerstone of modern cosmology. It provides a framework for understanding the history and evolution of the cosmos, from its hot and dense beginnings to its vast and ever-expanding present. The concept challenges our intuitions about space and time, but it also opens up new avenues for exploration and discovery in the field of astrophysics.
