Trying to understand the size of the universe is hard, really because it cannot be measured.  So when a child asks, “How big is the universe?”, parents often say, no one knows. But the truth is that we do know a little. What we do think, is that the universe has been constantly growing for 13.8 billion years. While the universe is expanding, recent research has begun to suggest that it accelerating as it expands. Current estimates peg the size of the universe at 93 billion light years, but that is hard to understand. Which is where we start talking about toilets.

England’s Royal Observatory Greenwich has this explainer to help us explain it to our kids.

there really is no way to know how big the universe is

Since light travels at a finite speed, even if we had the means to measure the size, we might not be able to. One of the problems we encounter is that the universe may even be expanding at the speed of light, so if we had a transmitter on one edge of the universe and a receiver at the other end. We could use the transmitter to shoot a laser, or a message off to the receiver. Since we know how fast light travels, all we have to do is use the time that it takes to receive the message along to calculate with the speed of light and we would know precisely how big the universe is (however, we would have to leave it up to out robotic descendants, because humanity will be long gone by then). However, we run into a problem.

However, we run into a problem. Since the receiver and the transmitter are moving away from each other at (probably, sometimes) the speed of light, our laser beam simply will never, ever, ever reach the receiver. So, we can’t actually know how big the universe is.

Just think in time it took you to watch the video and read this article, the universe grew massively, on a scale that is hard to understand. To learn more about how to picture the size of the universe, check out this article from Wired.com.