Astronomy Cast 4.2: String Theory, Time Travel, White Holes, Warp Speed, Multiple Dimensions, and Before the Big Bang (Episode 31)

This podcast discusses some theoretical concepts that people constantly ask about:
String Theory - According to string theory, our Universe is composed of more than three spacial dimensions and time, and that at the subatomic level, what we’re seeing is just one aspect of a particle that is a string if you’re able to see it in the multiple different dimensions.  One problem with this theory is that since it's a mathematical one, it can be tweaked to fit different circumstances and, as a result, there are multiple versions of it.  Also, because there a many outputs for every input, string theory is untestable.
Time Travel -  Since time is dimensional, it is only possible to move forward, rather than backward too.  To travel forward in time, we would have to go really fast, possibly 80-90% the speed of light.  Even though we can travel back in time when looking at a mathematical model, time only moves forward, so it's not possible.
White Hole - White holes are theoretical objects that, if they were to exist, would be spewing light and energy out of them.  The problem with this is that it goes against the Second Law of Thermodynamics.  White holes are a mathematical invention of what happens if you look at all the geometry of a black hole and get rid of the mass in the center.  They're not possible in our current universe because there is no way for a star to collapse and not have mass in it.  Also, since white holes have no mass, as soon as any atom gets near it, it would turn into a black hole anyway.
Warp Speed - Theoretically, if one were to slow down the light waves, and move more quickly than them, then they could travel long distances more quickly.  So in theory, you can shoot a light beam through some sort of media that causes it to slow down and walk beside the media going faster than the speed of light. But you and light can’t go the exact same speed in the exact same media.  Now warp speed it moving quickly, but not faster than the speed of light.  It's bending the fabric of the universe in order to travel a distance.  However, for this to be possible, one would need to line up a bunch of black holes, and would require huge amounts of energy.
Multiple Dimensions - There are different ways to look at this theory: one is the thought of multiple universes; another is that there are multiple spatial dimensions of which we are simply confined to the three dimensions that we experience.  However, all those other dimensions are either compressed such that we can’t see them or we’re simply confined to the dimensions that we’re within and we have no way of getting out of those dimensions to experience the others.  This also brings about the idea of an infinite number of possible universes, where our current timeline branched off and changed on little thing.
Before the Big Bang - From what we understand, if you have something before the Big Bang, you have something before time came into existence.  People constantly want to know what caused the Big Bang, and what existed before it, but science can't explain that, and it doesn't even matter, really.