Here’s another way of thinking about the size of the natural world.

Imagine you’re a slug. For some people, this will not be too difficult. All you do is crawl along surfaces. On rotting planks. On gravel. Sometimes you perceive light, sometimes dark. Sometimes the dark is sudden, and when that happens you might be aware there’s danger.

But you don’t know where the danger comes from because you have practically no sense of up or down. You only creep front, back and sideways. The idea that a robin might swoop from the sky and swallow you is too specific for you to understand, even though it happens. Robins are out of your range of understanding because your world is a flat surface.

In other words, slugs live in two dimensions. And not only do they have no idea where robins live – up – they have no idea about the world of humans and the complexities that inhabit it, such as cars. Even if slugs somehow could understand concepts they can’t visualize, such as “up in the nest” or “Let’s drive to Betts Bookstore,” they have no way of understanding, or even perceiving, anything found in those places.

Of course, the third dimension – up – still exists even though slugs don’t know it, and they still live in it. Birds and humans are fully aware of the three dimensions of space: forward and back; sideways; and up and down.

And even though birds probably don’t know it, humans understand – since Einstein showed us – that we all live in four dimensions. The fourth dimension is invisible to us, the way the third dimension is invisible to slugs. And like slugs, we experience it anyway: It’s time. Space and time are not separate; they are one continuum Einstein called space-time. The difference between the three spatial dimensions and the one time dimension is that space seems fixed, while time is perceived as a kind of motion.

Now, physicists and mathematicians have figured out a lot about how nature works, but they have not figured out everything. For example, 96 percent of the matter in the universe has never been seen or detected. We know it exists, though, because mathematical equations and their accurate predictions of certain activities of light have verified it.

Mathematicians also have shown it is likely – though not verified – that at least six dimensions beyond space-time exist, even though they never have been seen or detected. Like the slug on its plank, we can’t perceive them. But they can be imagined by thinking upward: First dimension is a line; second dimension extends from the line to a plane; third dimension extends from the plane into space; fourth dimension is time; fifth dimension is another extension that no one has visualized. And so on.

Some physicists refer to these unvisualized dimensions as “hyperspace.” They think it likely that light results from vibrations in hyperspace.

Like the slug on its plank, detecting light and dark, here we are on the ground picking up photons with our eyes but unaware of their places of origin.

It seems likely that the universe is larger than us in the same way the contents of the books at Betts are larger than the slug.

– DANA WILDE, DWILDE@BANGORDAILYNEWS.NET