Space Wasn’t Always A Big Place
“It’s true that we don’t know how large the unobservable part of the Universe truly is; it may be infinite. It’s also true that we don’t know how long inflation endured for or what, if anything, came before it. But we do know that when the hot Big Bang began, all the matter and energy that we see in our visible Universe today all the stuff that extends for 46.1 billion light-years in all directions must have been concentrated into a volume of around the size of a soccer ball.
For at least a short period of time, the vast expanse of space that we look out and observe today was anything but big. All the matter making up entire massive galaxies would have fit into a region of space smaller than a pencil eraser. And yet, through 13.8 billion years of expansion, cooling, and gravitation, we arrive at the vast Universe we occupy a tiny corner of today. Space may be the biggest thing we know of, but the size of our observable Universe is a recent achievement. Space wasn’t always so big, and the evidence is written on the Universe for all of us to see.”
If you take stock of our Universe as we see it today, you’ll find that it’s 46.1 billion light-years to the limits of what’s observable. Contained in that vast volume are some 2 trillion galaxies, typically containing hundreds of billions of stars apiece. And yet, if you think about our picture of the Big Bang, its tells us that all of this must have been smaller, hotter, and denser in the distant past.