The Universe is getting bigger!
But then, we knew this. We’ve known it for a long time! The reason you know Edwin Hubble’s name at all is because in the 1920s he was critical in figuring out the Universe was expanding. He and many other people did this by looking at a specific kind of star, called Cepheid variables. These stars literally pulsate, getting brighter and dimmer on a regular schedule. As it happens, how much they change in brightness depends on their actual brightness… and that means if you measure how much they change, and how bright they appear in our sky, you can figure out how far away they are. And if they are in other galaxies, then you can tell how far away those galaxies are.
Boom! You can measure the size of the Universe. And more.
Using this method (which I explain in more detail in an earlier post, if you want details), they figured out the Universe was expanding – the farther away a galaxy is, the faster it appears to recede away from us. This is what led to the Big Bang ...