Because you're a fucking ponce, too stupid to travel through time and not get stuck and you spend all your time on this website. You're not from our time but you're using up our resources and fucking up history as you go.
I spend very little of my time here on this website. For now, I am just using it as a break.
My time machine will hopefully be repaired too. I made many trips safely, it was just damaged in some bad weather before my last journey.
Do tell what theories are accepted in the future you are allegedly from.
The string theory that exists in this time is highly incomplete, I suspect. From what I have heard, it also has not been unified or reconciled with other areas of science. Twenty six dimensions are required in order to fully describe behavior. Honestly, I can't give the full justification for that: I knew it at one time, but it is far too complex to recount completely by memory.
The basic idea is that it is impossible to move in just one dimension. Everything exists in all twenty six dimensions, and if it exists in a dimension, then it has mass. (Clearly we exist in the time dimension: we may not control our movement there, but if we did not exist in it, we could not move along through it). We move in all the dimensions we exist in: there is no way to be perfectly still. If you examine something closely, however, very closely, then its movement will be like a fractal: constant, tiny adjustments. However, on an arbitrarily small scale, especially in time, you may be able to find a straight line of movement.
That is where quantum behavior comes in. Light has what is called a quantum mass: it exists, but it exists in the smallest possible amount in each dimension. That makes it appear to have 'lost' a dimension: whatever fraction of it exists is negligible. Waves bear a great many similarities to lower-dimensional objects, as entities that only exist with a medium to disperse them in higher dimensions: light takes on a property similar to this when examined, though it is only close to being a wave. Similarly, such small objects act the same.
That's complex, but that's a very very simple explanation of how the theories were unified.
I'm not sure what relevance brains are: to my knowledge they are simply the organs where we think. You may mean brane, as in membrane, that was an archaic term used in this topic.
The idea of the higher dimensions being curled up aids imagining the theory, but does not fully work in practise. They would appear curled up from our perspective because we do not understand motion in those dimensions. They are simply other possible directions of movement. In a singularity, space and time are warped: that's four of the twenty six dimensions. As gravity affects all twenty six, the other twenty two are warped within the singularity as well: that which radiates from a black hole does so in every dimension. It's referred to as the Clarke Effect (or occasionally the Technical Error, I think that term's a relic).
We are primarily concerned with the '3-brane', as you call it, as those are the dimensions where we primarily exist.
On a side note, a hypothesis in my time states that there are in fact two time dimensions. This is pure speculation at this stage, it has been neither proven nor disproven, but it is interesting nonetheless. A corollary to the worldline model would allow for there to be 'hypertime', the time dimension along which time itself progresses. What this would give is, rather than a timeline, a time-square.
You have multiple horizontal lines, each one a simple timeline. The horizontal direction is classical time, the vertical is hypertime. We then get a diagonal line as we move forward in both dimensions.
This model of time is partly based on a pre-worldline model, which explained how time could change. It is impossible to cross the diagonal line, the 'moving present', but you may travel to it. This would mean I came from some point horizontally past the moving present, and I am now continuing diagonally on, with the hope the horizontal line I end with, will be different to the one I started on.
Some horizontal lines are different worldlines, but not all.
It's an archaic theory, but it had a brief resurgence in popularity before I left.