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What is dimension and how many types of dimensions are there in the universe? I mean how many total dimensions are there? I have only heard about 2d and 3d. Other than these two, are there any other dimensions. If yes than please explain each of them clearly.

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  • $\begingroup$ There are three spatial dimensions (left-right, front-back, up-down) and one time-like dimension (past-future) in the universe. Beyond that it's all speculation. Strictly speaking even the time-like dimension is probably not a dimension like the spatial ones, but on the level of general relativity we treat it like one, anyway. $\endgroup$ – CuriousOne Jan 2 '15 at 4:09
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In the mathematics used for physics dimensions are independent mathematical fields on which a variable can be assigned . Independent means that in the algebra used each projected on the other gives zero, is orthogonal. The example is the three dimensions we live in which are assigned orthogonal directions and the field is the real numbers on the axis.

So classical physics uses these three dimensions to model mathematically all observations on macroscopic scales, and in this formulation time is a parameter.

For very large energies it was experimentally found that the mathematics was most efficient by assigning a dimension to time and treating it as the fourth dimension whose mathematical field is an imaginary number, i.e. the real mathematical field multiplied by the square root of minus one. Thus there are four verified space dimensions as far as physics goes.

In the quantum regime, where the size of the items under observation is very small, new theories are proposed in trying to formulate an overall theory. These may have many extra space dimensions and some even time dimensions. String theories as an example. Until they are validated experimentally it is a moot question whether their extra dimensions are observable in our physical reality.

Thus, as far as physics goes, there are four dimensions over all at the moment, three of space and one of time.

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