AskScience: What do we call what holds multiple dimensions?
In science we attempt to classify everything. And everything seems to be a subset of something else. Planet is a part of a solar system, solar system is a part of a galaxy, galaxy is part of the universe, universe is a part of our dimension, etc.
Obviously there are exceptions to this, rogue planets, but we still consider them contained.
I understand the idea of multidimensions is theoretical, but if they exist, do we have a name or even a theory what might contain them?
My layman understanding is probably incorrect, but it was my understanding that multiple dimensions coexist in the same universe. If there are multiple universes, each universe would have its own dimensions.
Interestinf. Thank you!
(Caveat: this is kinda outside my normal field, some part of this is probably wrong or misleading in some way.)
This is the wrong way to think about this, for kind of a subtle reason. So generally when we talk about dimensions in science we mean one of two things:
The kind of units something has (so if a quantity can be measured in seconds/years/etc it has time dimensions, if it can me measured in meters/inches/etc it has length dimensions, and so on). That's clearly not the kind of dimension you're asking about.
How many numbers you need to describe a particular system (so a particle in space needs three dimensions to describe it's location – or four if we want to consider time – and we can approximate the position of a pendulum in a clock to a system that can be described in one dimension: how far along we are in one swing cycle). I believe you're talking about this kind of dimension: extra directions that we could, in theory, travel in: ie, an extra fifth (sixth, seventh, eighth, etc) number beyond the normal four we have in "everyday" spacetime.
Consider a sphere. It's two dimensional and both dimensions are unbounded (no edges), finite, and curved (convex in this case). Now, you're probably imaging a sphere in 3D space, because that's what our brains are wired to do. But this is a mathematical sort of object, and it turns out that the third spatial dimension is completely unneeded: you only need two numbers to describe where you are on a sphere (for example, latitude and longitude). In this case, the sphere doesn't need to be contained in anything! We can just toss out that third number, it's an extra. The sphere just is.
Likewise, our four dimensions of spacetime don't need to be contained in anything else. Their topology is different, sure. The space dimensions are, as far as we can tell, unbounded (no edges), infinite, and basically flat; time is more complicated. But just like you can use three numbers to describe your position on a sphere but only need two, you can use a fifth number to describe your position in spacetime but it's an extra. And, just like the sphere, the dimensions don't need to be in anything, they just are.
Now, you could say: "What if we assume that we do actually need five numbers, and the four we normally use are actually just a simplification?" That's a valid thing to do (although hard or impossible to prove), but in that case you can play the same game by adding a sixth number. That number is extra and not actually needed to contain the five dimensions in our new theory.
So tl;dr dimensions don't need to be inside of anything. You can embed different kinds of spaces into higher dimensional ones by adding an extra number, but even in that case you don't need anything to "hold" the extra number. Dimensions just are.
I hope this is more helpful than it is confusing! (Physicists/mathematicians: feel free to correct me if I got anything egregiously wrong here.)
That was amazing. I think maybe I've misclassified what I meant though maybe. I'm talking about mirrored realities or multiverse or whatever it's called copies of this reality.
Like string theory I think indicated there are other dimensions.
Basically thinking of the old tv show Sliders.
I really honestly appreciate that very informative and easy to digest post! Thank you very much for taking your to explain all of that. That is great. 😁
No problem! I was worried it might end up a bit of a word salad lol, so I'm glad you found it informative and easy to digest!
The extra dimensions in string theory are actually spatial dimensions, as far as I know, they're just "compact." So, for analogy, consider the surface of an infinitely long pencil (or straw or other cylinder). It's two dimensional. One of its dimensions is pretty large: the one along the length of the infinite pencil. It's unbounded, infinite, and flat. The other spatial dimension is the one that goes around the pencil: it's unbounded, but finite and curved (convex, like the dimensions on a sphere). That one that goes around is more like what string theorists are taking about, I think.
I also don't put that much stock in string theory, for whatever my opinion is worth (and it shouldn't be worth too much, because again I'm not a physicist). Mainly because we can't actually test it, and I think testability is important.
This I know much less about, unfortunately. I've seen this idea come up in, eg, the many worlds interpretation of quantum mechanics, but my sketchy understanding is that what they're actually talking about is something very different from the sort of multiverse as portrayed on TV and in novels. I have a bit of a suspicion that the answer might be the same (they're not contained in anything), but I really don't know for sure.
The term "Dimension" is a math term. It only applies to theories of multiple universes in comic books and sci Fi shows.
Also it's a mistake to suggest that the goal of science is to classify everything. Science seeks explanations that have explanatory and predictive power. Classification is simply a tool to achieve those goals, not a goal in itself.
I feel like the term you're searching for is 'multiverse.' To me, it's a literary term, I don't know if physicists would use it in relation to the Many Worlds theory.
How are you using a keyboard as a 1-dimensional being? 😛
In all seriousness, I understand your question is more about alternate universes? In that case, I guess the term is Multiverse
Edit: Speaking of 1-dimensional beings, I just remembered a really cool video with Carl Sagan about dimensions, maybe it's interesting for somebody reading this!
I mean I've been called 1 dimensional before. Lol definitely going to watch that when I can. Thank you!
Maybe this was already said, but to be clear, they do not have to be in anything. There are a lot of theories regarding universe, multiverse, and stuff, but this is separate from dimensions of our universe and of those being in anything as far as I know.
As far as dimensions I think is is more about how they relate to each other, what shape they have, and to what extent we have access them, etc.
@ozoned
Not familiar with this concept of dimension tbh. I think that when one talks about something bigger than the Universe, they have a specific theory in mind, with its specific definition of what the universe is. Which theory do you take this notion of dimension from?
They are using the scifi-concept of dimension which has nothing to do with the mathematical or physical concept of dimension.
@PinkOwls
I thought "dimension" in scifi was meant as "universe", like a parallel dimension is a parallel universe. What is the difference between the two?
It sounds like you got it basically right, but now think about the sentence "the universe is a part of our dimension" which would mean "the universe is a part of our universe".
The scifi "dimension" is as meaningless as "plane of existence"; it just sounds nice when you want to explain things away in scifi. I mean, it seems to be easier in scifi to travel between those "dimensions" than between the Milky Way and any other galaxy in the visible universe.
Does not sound too meaningless to me, but I'm used to calling that a universe 😁
I'm trying ahah. But if you call the universe a dimension, which subpart of it do you call a universe? The observable universe maybe? I mean it makes sense to say that the observable universe is part of our universe. Still sounds strange the way it is presented by OP.
@PinkOwls
The math/physical concept of dimension does sometimes appear in scifi though, think about hyperspace.
Well my understanding was that according to string theory, we're existing in one of many different dimensions that all kind of mirror each other.
As someone pointed out earlier, I'm not talking like 2D vs 3D vs 4D. But actually mirrored realities.
@ozoned I see, but if you call a "reality" a dimension, what is it that you call a universe?