You are trapped in space. Seriously. You're captured, cornered, mired. You're totally stuck and there's not a damn thing you can do about it.
You're trapped in space and what that really means is you're trapped in three dimensions.
To get a gist of what I'm talking about, imagine for a moment you're walking through the woods and a bear magically appears in front of you.
To escape this angry bear, which direction would you run?
You could bolt to the left or to right. That would be a good idea. You could also run straight ahead into the bear (that would be dumb) or you could run straight away in the other direction.
If there were a cliff nearby, you could jump off it and escape by falling downward. And, finally, if you had a jet-pack you could fly straight upward (which would be totally awesome).
So, there we go: left/right, forward/back, up/down. For physicists, each of these pairs constitutes a dimension.
Now, let's get really simple for a moment to really see what this idea of dimensions really means.
If forward and back were all that existed, you'd be living in a 1-dimensional world. In a 1-D universe, everyone lives along a single line. But if you added left and right to the line, suddenly everyone gets more room. There would, literally, be more space to inhabit. This expanded 2-D world would be planar like an infinite sheet of paper.
But "up" and "down" still wouldn't exist for inhabitants of this 2-D world. In fact, it would take a pretty creative 2-D citizen to even imagine the possibility of a third dimension.
So can you see where I am going with this?
We, of course, know about up and down because we inhabit a 3-D world. For us moving in three dimensions — forward/back, left/right and up/down — is obvious.
But who's to say there can't be a forth, fifth or even sixth dimension to travel in? Maybe, just like those 2-D planar creatures, we're trapped in our 3-D space and can't even picture the other directions.
Albert Einstein showed us that time can be thought of as a fourth dimension. Just like you can drive from east to west along Interstate 80, all of us are constantly traveling from the past to the future through time. Of course, the weird thing about time as a dimension is you can only travel one way. You can drive back west along I-80, but you can't go backwards in time.
These days, a lot of physicists are going beyond Einstein in their thinking that there might be extra dimensions of space that we just don't experience. One of the great frontiers of physics is pushing the boundaries of experiments to find evidence of these extra dimensions.
That would be pretty cool.
If we found them, suddenly there would be extra directions to travel in — and more space to fill.
But for now, we're all just stuck in 3-D.
Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described "evangelist of science." You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4.