Extra dimensions

I learned in science class that there are actually more than four dimensions (and something to do with string?)  What are they?  And is there a way to see them?

Oh god.  I don't know much about this, so take this with big grains of salt, but...
The idea is that the universe is made up of tons and tons of tiny little loops (or strings) that are oscillating in interesting ways.  These things are smaller than quarks though, so way beyond what we can measure or see or interact with at all.  Therefore, this is kind of an untestable theory and despite being a nice theory, may yet prove to be total bullshit, so don't freak out about it too much okay?

For this so-called string-theory to work, I believe the strings have to exist inside of tiny little curled-up folds in space-time that have much higher dimensions.  Like 20 or something ridiculous like that.  Now bear in mind, this means that there could be other dimensions gibbering about at very small scales, but at this macroscopic scale, we can't see shit.

If this talk of dimensions excites and inflames your imagination, you should read a book called Flatland as it's pretty cool.

>>2
Good layman's explanation.

These mathematical models are just that... mathematical models. I wouldn't take them too literally nor think stuff like "extra dimensions" has any physical meaning.

If time is a dimension, that means we can theoretically travel along it.  You just have to believe.

>>5
It's quite obvious we can travel along the time dimension. The only remaining question is whether we can travel *backwards*.

>>6
No

>>6
no it's not obvious that time flows "forward"(into the future),remember that little thing called "spacetime"? Well basically it means time and space are together, meaning that time and space are the dimensions of the universe, so instead of thinking about time and space separately you should just see them as x1,...,x4 and when you plot the universe you get some shape in that space. Now a point on that surface can move on it and that's how time "flows", but this is separate from time as a dimension. (see flows on a manifold)
tldr, the point is that flows can go forward or backward on manifolds(high dimensional surface)

>>4
I agree.  I'm willing to believe if the math works out, but I'm not so inclined to believe that our world has all those extra dimensions.  How do we even define existence?  QFT can be modeled by virtual particles coming in and out of existence, but they can't be measured (hence "virtual"), so do they really exist?  I consider them a mathematical construct, and our world is not actually full of "virtual" crap.

>>8
That's sort of true.  Minkowski space (and most other metrics under consideration) are time orientable.  That means that we can choose one (arbitrary) direction to be positive time, and everybody will agree, regardless of reference frame.  The exceptions are crap like mobius strips and the like.

Before ppl get confused, faster than light travel =/= travel back in time.  Faster than light travel does imply that (some) other observers will see you traveling backwards in time, or going through space instantaneously, but that does not mean you're going back in time; some observers will see you going forwards in time.  However, it is the former possibility that breaks causality (not everybody will agree on what caused what).

tl;dr faster than light travel opens a can of worms, but isn't equal to traveling backwards in time

There are 11 dimensions

I am the 11th.

imo the universe is just a big ass fractal and although it has a certain fractal dimension, it goes forever "down" and "up", and it can be finite(has a boundary)