Would finding the centre of the Universe help us understand our place in the Cosmos? In a previous article, I talked about the problem of trying to measure speeds in space. Because there are no fixed positions in the universe, there can be no such thing as an absolute, “real” speed. Even the ground beneath your feet is attached to a planet hurtling through space!. The very idea of speed simply means “The distance traveled, divided by the time it took to get there”, but if there are no fixed points, how can you be sure what the actual distance was? If you just look locally, it’s easy to measure, but on a universal scale? Relativity means that those distances suddenly aren’t as real as you thought!
But a comment on the article raised an interesting point. What if, the commenter wanted to know, we just find the spot where the Big Bang happened, and use that as the ultimate reference point? After all, since the Universe is expanding, and has been ever since the Big Bang, it must be expanding from the centre of the Universe. If we find the centre, we can measure all positions relative to that spot.
The Big Bang
But there’s a problem with that idea: The Universe has no centre, and the Big Bang did not happen anywhere. Or rather, it happened everywhere at once. This probably won’t make sense to you at first, because most people don’t have a clear idea of what the Big Bang actually was.
When we try to imagine it, we usually remember the animations from popular science shows. There’s a black screen, space is completely empty. All you see is a tiny, dense speck of something floating around: the infant Universe. The speck explodes with a mighty roar, the screen glows white, and the glow fades to reveal hundreds of galaxies spreading out and filling the universe.
But that image is wrong, and stems from the early 20th century. Astronomers had just begun to notice that all the furthest galaxies in the universe are speeding away from us, but had no idea why. These days we know that it was not just the things in the Universe that came from the Big Bang, but the actual space and time that the Universe itself is made from. Before the Big Bang, there was no space, and no time. It was truly the beginning of everything.
The actual Big Bang
That means that it’s not just the galaxies that are flying apart, but that the fabric of space and time itself is growing and stretching. The Universe isn’t expanding into existing space, but rather it is making more space for the physical stuff to move into. And if all of space itself was once confined to that infinitely dense point that birthed the Big Bang, then every place, every spot in the universe was also in that point. The Big Bang did not happen in any one place in our Universe, it happened everywhere at once, because there was only one tiny point for everywhere to be.
If this is an easy idea for you, then you probably haven’t really thought about it. Go take a break, sit under a tree, close your eyes and try to really imagine this. Feel free to say “woah”. I’ll wait.
Back? Good. Let’s move on to the next point.
It wouldn’t actually help
Even if it existed, the centre of the Universe still wouldn’t help us solve the speed problem. Part of the reason is that you could never actually find the centre. From our vantage point on Earth, we see that all distant galaxies are retreating away from us. The further they are, the faster they’re running away, and we see this no matter what direction we look. So at first you might think that, since everything is rushing away from Earth, then Earth must be at the centre of the Universe. But in fact you can go anywhere in the Universe at all and you’d still see everything rushing away from that point. Why?
Imagine a baker making a loaf of raisin bread. The raisins have been mixed in, and the dough is busy rising. As it expands, the dough carries the raisins further apart from each other. But the interesting thing, even in this limited analogy, is that there is nowhere that the raisins start to clump up – all raisins are moved further away from all the other raisins. Whichever raisin you measure from, the distance to each and every other raisin increases over time. And if you were a tiny microbe living on a raisin, somehow able to see through the dough, it would look to you as if you were at the centre of the loaf, with everything expanding away from you, wherever you might actually be.
This leads us to one of the basic principles of cosmology: that if you look on a big enough scale, the Universe looks pretty much the same, wherever you are and in whichever direction you look. Even if there was a centre to the Universe, how would you recognise it if there’s no way to tell it from the other areas?
What does all this mean?
This is what I meant when, in the Speed article, I mentioned that there is no frame of reference for an “absolute speed”. The entire Universe is in a state of constant motion. Widely separated areas move at very high speeds relative to each other, while nearby regions move less quickly. You can point at any single location and declare that it is the centre of the Universe, and that it is not moving and that everything else is moving relative to it. And you would be right because a) that is certainly what you would see through your telescope and b) that place was once inside the Big Bang so it is quite literally where it happened.
So what’s the short answer? The centre of the Universe is everywhere, and nowhere. And that’s the literal truth.