Galaxies move away from each other from "summary" of A Breif History of Time and the Universe in a Nutshell by Stephen Hawking
As we look out into the vast expanse of the universe, we can observe a curious phenomenon - galaxies seem to be moving away from each other. This observation, known as the expansion of the universe, has profound implications for our understanding of the cosmos. The concept of galaxies moving away from each other is not just a random occurrence, but rather a fundamental property of the universe itself. It is a consequence of the Big Bang, the event that marked the beginning of our universe. In the moments following the Big Bang, the universe was incredibly hot and dense, and as it expanded, it also cooled down. As the universe expanded and cooled, matter began to clump together under the influence of gravity, eventually forming galaxies. However, the expansion of the universe did not stop there. Instead, it continued to accelerate, causing galaxies to move away from each other at ever-increasing speeds. This phenomenon can be understood using the concept of space-time, the fabric of the universe in which all matter and energy exist. As space-time itself expands, it carries galaxies along with it, causing them to move away from each other. This expansion is not limited to a particular region of the universe but is happening everywhere, on a cosmic scale. The observation that galaxies are moving away from each other has been confirmed through various measurements, such as the redshift of light from distant galaxies. This redshift is a result of the Doppler effect, which causes light from objects moving away from us to be shifted towards longer wavelengths.- The concept of galaxies moving away from each other is a testament to the dynamic and ever-changing nature of the universe. It reminds us that we are just a tiny speck in the vast cosmic ocean, witnessing the grand spectacle of the cosmos unfolding before our eyes.
