This might be a bit much for eli5, but I find any googling yields results far too complex for me to understand. Ive heard that there are up to 11 dimensions. If up/down, left/right, and forward/back are the 3 spatial dimensions, what are the others? And what of time being a dimension itself?
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In recent years it’s become popular in scientific circles to refer to our universe as having 3.5 or 3+1 dimensions because although it’s useful to treat time like a dimension in a mathematical construct, time is not actually a dimension. And our universe only has 11 dimensions — none of which represent time — if string theory holds true, but there’s no evidence of that. Our intuition is however bound to 3-dimensions so beyond that it’s difficult to understand without analogies or through pure math. Having said that, it’s worth mentioning that complex systems of information can be sometimes be better navigated or understood when it’s formatted in more than 3 dimensions, so 5- or 6-dimensional (or more) math is still useful even if it doesn’t represent the spatial dimensions of our universe.
Freddy_guy, I think the point is we are unable to perceive the “line” of boxes, and the “box” of boxes, because they’ exist in a set of dimensions outside of those which we are able to experience. We can see things in terms of 3 dimensions, but extend those dimensions beyond that – in the same way we can extend perception beyond 1 dimension, or 2 dimensions, to 3, and we have no frame of reference to compare it to. My question is: that’s really cool, but why does it extend to 10 or 11 (depending on who you ask) and why that number, not more or fewer? That’s the eli5 bit
We (i.e. pretty much any human) can’t visualise more that 3D space.
So don’t bother trying to understand “what it would look like”. It’s futile.
Instead, let’s try to understand “what it does”. A dimension is an INDEPENDENT axis/variable. If you have 3D space represented as three axis, all 90 degrees to eachother, you can draw a random line in that space. The problem is, this line is not independent, it will be some combination of the original three.
This is best understood by length of lines. In 1D, the length of a line is the line. In 2D, the length of a line is a combination of its perpendicular x and y components according to Pythagoras, c = sqrt ( x^2 + y^2 ). This holds in every higher dimension. In 3D, every line will have a length r = sqrt ( x^2 + y^2 + z^2 ). The direction in which it’s pointing can be expressed as angles from these axes.
So to get a new dimension, you need a new axis that is perpendicular to the other three, like z is to x and y. As in, r = sqrt ( x^2 + y^2 + z^2 + w^2 ). An independent axis. You can’t visualise it. Don’t bother. The point is that the math works the same for this new axis as it did for z when you went from 2 to 3. So basically, you say “this is a new independent axis because I’m giving it the properties of an independent axis”.
Now, to understand where the others of the 11 dimensions of string theory are hiding, the physicists declared that they are, in fact… Hiding. That their axes aren’t (apparently) straight lines like our three spatial dimensions. Those extra dimensions are all curled up on themselves really tightly, too small to interact with anything we perceive aside from gravity.
I can’t remember if they’re literally meant to be closed loops, so finite and repeating, or are they meant to be infinitely long but wound into coils. Maybe either, depending on the theory. It honestly doesn’t matter, because string theory is currently unprovable anyway, so it’s splitting hairs.
It’s important to understand that these dimensions are just hypothetical. There’s no evidence that they actually exist. Something called string theory requires these extra dimensions to work, but there’s no evidence that string theory is correct or that these dimensions actually exist. Our universe is demonstrably one of 4 dimensions – 3 of space and one of time. Anything beyond that is speculative.
As for how these dimensions exist, in string theory, they’re “compactified.” It’s hard to eli5 but the best way to understand it is that they exist on scales too small for us to notice or interact with. Maybe this example will help: A human hair to use might as well be 1-dimensional line, right? We can only interact with it in that manner. But now imagine that you’re a tiny mite that lives on your scalp. At that scale, an individual human hair would be much larger, and as a mite, you could interact with it in all 3 dimensions. You could walk up and down it, across it, and around it.
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