Imagine you’re a slug. For many of us that won’t be too difficult. You spend your life crawling in straight lines along flat surfaces, such as rotting planks and gravel. Your vision is limited to impressions of light and shadow and objects straight ahead or beside you. At night you crawl along the ground in curls.
Your universe as a slug is for all intents and purposes flat. There is no up or down, really, because a slug cannot go or even see in those directions. The flat path might turn out to be a plant stalk, but a slug’s experience of it is in the range of “more toilsome” rather than “up.” A robin swooping down to snatch the slug is coming from nowhere, as far as the slug is concerned. The slug lives in two dimensions.
The robin, though, clearly lives in the three dimensions – length, width and depth – where we do. In our case, we’re also aware of time, which physicists have established is a fourth dimension. Whether a robin is aware of time is not known. The robin certainly lives in time with us, the same way a slug without knowing it lives in the third dimension with us and the robin. Maybe a robin has a vague, unconscious experience of time the way a slug has a vague, unconscious experience of “up.”
This is all conjecture, of course, because we do not know what slugs and robins experience. We do know that while we have a definite fix on the three spatial dimensions, our understanding of time is quite limited. We experience it as an impervious flow forward even though it’s not a flow; it’s a dimension that is nonetheless impossible to visualize.
Two kinds of evidence indicate time is a dimension: 1. experiments that show a time interval can vary from clock to clock according to speed or proximity to gravity; and 2. mathematical equations.
Now, watch out for robins: A good many physicists are convinced by the mathematical equations that there is a fifth dimension. Some of them are pretty sure there are 10 or 11 dimensions, and a few think there may be 26. All here, now, with us, but unseen, the way the third dimension is with the slug and time is with the robin.
The reason the physicists think so is actually pretty simple. The math (which apparently is correct) that represents behaviors of light in quantum physics and the math (also correct) that represents behaviors of gravity in relativity physics, do not jibe. That is, they do not jibe when calculated in the four dimensions where we live. However, when the calculations are made on the assumption there are 11 dimensions, most all the math falls neatly into place. In other words, according to the math – and since no equations have been found that solve the problems in four-dimensions – there have to be higher dimensions. In fact, the equations imply that light is generated by ripples in the fifth dimension.
I wonder if our perception of fifth-dimensional light is as limited as a slug’s perception of three-dimensional light. Our eyes, after all, pick up only a small range of all the wavelengths of light.
Anyway, if there is a fifth dimension, where is it? The physicists’ answer to this question is: It is too small to see.
What could this mean? When you rise through the three spatial dimensions, they get staggeringly larger. One dimension is a line. Pull that into two dimensions, and you get a plane, which in area is like the difference between the road to Bangor and the Earth’s surface. Pull a plane into three dimensions and you get a cube, or the difference between the surface of Earth and all the rest of space out to the quasars.
Pull a cube into four dimensions and you get – what? Well, you’d get the fifth dimension which is described as the fourth spatial dimension, since time is not spatial but instead temporal (meaning related to our experience of time rather than our experience of space). The physicists call a cube pulled into the fourth spatial dimension a “tesseract.”
What could the fourth spatial dimension look like, from our three-dimensional slug-eye view of the universe?
It turns out that, according to the mathematics, the higher dimensions are very large in surface area, but very small in volume. A higher dimension is akin to the whole surface of the Earth rolled up into a tiny tube. If you could somehow see it, it would look like a hair or a pencil at a distance, but inside is a vast surface curled up on itself.
The physicists who work on “string theory,” whose math solves a great many physics problems that are so far intractable if the universe is only four-dimensional, believe the visible universe develops out of the vibration of subatomic strings in these other dimensions. They think we may be living on the surface of one of these dimensions, and all space and time are just a thin membrane among 10 or 11 “branes.”
I don’t know what this means either. I think we have intellectual and psychic perceptions going for us that slugs and robins don’t. But how much more we see of all that’s actually going on around here, I have my doubts.
Read more on the nature of space-time:
“Time, it’s even stranger than you think”
“Trapped in the fourth dimension”
“Time travel: What’s holding us back?”
Amateur Naturalist archive
More Naturalist writings on outer space and environs: