The "third" dimension is the one we experience day-to-day. An example of the "second" dimension is the shadow of a three-dimensional object. How do we describe the "first" dimension? What would be an example of matter in the first dimension?
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Something like the height or really any dimension of an object. Do any length measurement – ClassicStyle Aug 27 '14 at 03:58
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The number of dimensions is simply the number of independent (not necessarily orthogonal) directions an object can move along. Everything macroscopic in this universe can move in three different directions. In some physical systems the movement in one or two of these directions is sufficiently restricted, to treat the system APPROXIMATELY as two or one dimensional, and sometimes, we are treating objects, that essentially can't move, at all, in zero dimensions. – CuriousOne Aug 27 '14 at 04:42
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You say:
The "third" dimension is the one we experience day-to-day
but this is not so. We experience three (spatial) dimensions, but there is no distinction between the first, second and third dimensions. For example I might choose the first, $x$, and second, $y$, dimensions to be horizontal and the third $z$, dimension to be vertical. I live in the UK, but suppose a friend in the US does the same, our dimensions would be different:
My first, $x$, dimension isn't the same as my friend's $x$ dimension. So which of us is correct? Well, neither of us. There isn't a unique first dimension; we can arrange our dimensions at whatever angles we want - it doesn't make sense to talk about a first, second and third dimension because the distinction is a matter of choice. All we can be sure of is that there will be three dimensions.
An example of the "second" dimension is the shadow of a three-dimensional object.
We can image a plane cutting through our three dimensional space, and this plane would be a two dimensional object. However our 2D plane is a purely mathematical construct and no 2D objects really exist.
How do we describe the "first" dimension?
If instead of a plane I draw a line, then the line is a 1D object. However, like the 2D plane, this is just a mathematical construct.
What would be an example of matter in the first dimension?
The point I've attempted to make above is that the universe and everything in it is three dimensional, so it doesn't make physical sense to talk about matter constrained to lie in one dimension.
John Rennie
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I did not know exactly how to word the "matter in the first dimension" part of my question. I understood that in (x,y,z), z denotes an object would be in three dimensions, dimensions x, y, and z. Knowing that, it makes sense to say x would be the first dimension and y the second. x,y,z are of course arbitrary and only have meaning from a mathematical stand point. – math and mountains Aug 27 '14 at 18:08