The quantum @mindhunter
I started writing a huge hypothesis post about my impression of the dimensions before I realized that it was literally 'Relativity Theory'. I believe that all dimensions are spatial though, so if time is a dimension then it almost certainly follows that there are multiple/parallel universes.
The way humans perceive time, t, is essentially along an x-axis. It goes from 0 - infinity, running in one direction only. If it exists as a spatial dimension though (it can move anywhere along the x-axis), it follows that time travel is possible, events in the present can influence the past, etc. That much is obvious.
But if it can exist at different y-points, then that surely is a sign of a multiple universe or existence. Because at the same time along the x-axis of time, there is a different event occurring at another y-point of time. I'm assuming then, that the z-axis represents the x/y's parallel.
Time is not a dimension
The other thought is that time isn't a dimension at all, but a construct. In this scenario, there is a spatial plane/s (4th dimension +) which we are unable to experience. The way I imagine this scenario is that every dimension exists as the entire space outside of the previous dimension.
So if the 0th dimension is a singularity, then every space outside it is a straight line. The 1st dimension is a singular line, so every space outside it is a line going in another direction. In the second dimension, everything is a flat surface. Every space outside that flat surface is depth - the 3rd dimension.
So now we have the finite cube. A tri-axial shape. According to my hypothesis, everything that exists outside these dimensions is the 4th dimension. To put it very simplistically, the 4th dimension is a void outside of this cube.
Try it yourself, just draw a cube on a piece of paper and imagine the rest of the paper as the 4th dimension. Or perhaps, roll the paper into a cylinder, and watch the dimensions bend. That could be the 4th dimension. Maybe that's why light bends around objects with large gravity?
The way I imagine it is like magnetism; if you are standing at the North Pole, everywhere else is south. If you are experiencing the 3rd dimension, everywhere else is the 4th dimension.
Think about it on the scale of a tiny creature, like an ant. They have no use for the 3rd dimension, because they are so small that forwards, backwards, left and right are the only directions that matter. They exist within the 3rd dimension, but they only use 2. In that same way, we exist in the 4th dimension but are too small to really comprehend it.
In this scenario I don't really doubt that there are infinite dimensions, but we have no way of possibly accessing the 5th dimension and above.
I've only just started thinking about dimensions, so these are very raw hypotheses. There is every chance that this has been well hashed out over the course of history, but I just thought of it in the last 12 hours or so.