The universe meaning everything in our world, our galaxy, and all of outer-space for as far as we can see and not see is pretty darn big. In fact, it's so big that scientists usually divide it up into two parts:
The visible universe (which is everything we can see and measure, either directly or indirectly) and the non-visible (which we can neither see nor measure). While there some things we know about the size of the visible universe (including that it's really, really, really BIG!), we have no way of knowing what (if anything) lies beyond its border in the non-visible portion. The non-visible universe is so far away that it's beyond our range of evaluation, so it's hard for scientists to make a lot of conclusions about it.
What it is, how big it is, and whether or not it is "endless" is something with many ideas and theories, but no single answer... scientists are still constantly investigating and trying to figure it out! (And most grown-ups struggle to understand it.) But as science and technology continue to advance, new discoveries will surely be made!
by Brian Griffith (Whyzz writer)
What's out there?
It can be very hard to imagine an endless universe, or even one so big that we can't see its end. Does it make your imagination run wild with possibilities??
Draw a picture or write a story about something in this enormous universe that intrigues you. For example, you could tell the tale of a great scientist trying to make discoveries about the shape and size of the universe, or draw a picture of an astronaut who travels to another galaxy!
Scientists often measure really far distances in "light years," which refers to how far light would travel in one year. Turn on a lamp and notice how quickly you can see the light that it shines! The reason it happens so quickly is that light travels at a speed faster than anything else we're familiar with: 186,000 miles per second! So if light can travel 186,000 miles in just one second, think about how far it must go in an entire year! Scientists use this unit of a "light year" to measure things in outer-space because the distances they need to describe are so huge that a unit this size makes sense!
There are some things we know about the size of the visible universe: It's believed that the visible universe is about 13.7 billion years old. Therefore, our first clue about its size is that any light or waves of energy reaching us from the furthest out distances of the universe must be at least 13.7 billion light years away!
But, because the current most widely accepted theory about the universe says that the universe has been expanding over time, that far away light has also had to travel the distance of the expansion, meaning that it's actually even further than 13.7 billion light years! According to calculations made based on the rate of expansion, some scientists now estimate that the width of the visible universe is probably at least 156 billion light years wide!