Explain how Edwin Hubble discovered how all galaxies are expanding away from each other and us (hint: think back light waves and perhaps evensong waves)

Edwin Hubble, an American astronomer, made a groundbreaking discovery in the early 20th century that revolutionized our understanding of the universe. His work primarily focused on the behavior of galaxies and their movement. Hubble's discovery that all galaxies are expanding away from each other and from us was based on his observations of light waves.Hubble used a powerful telescope to observe distant galaxies and measured the light they emitted. He noticed that the light from these galaxies was shifted towards the red end of the spectrum, a phenomenon known as the redshift. This redshift indicated that the galaxies were moving away from us, and the farther away a galaxy was, the faster it was moving away.Hubble's observations led him to propose the idea that the universe is expanding, and this expansion is happening uniformly in all directions. This concept is now known as Hubble's Law. The idea that the universe is expanding is also supported by the theory of general relativity, which suggests that space itself is expanding, causing galaxies to move away from each other.It's important to note that Hubble's discovery was not based on sound waves or any other type of wave, but rather on the behavior of light waves emitted by galaxies.