I just got a condenser mic that uses phantom power and I connect this to both of my inputs (using xlr female to 2 xlr male y-Cable) on my scarlet 2i2 audio interface. I needed to do this to record in quicktime (which only records in stereo). This works good so far. But I was wondering if phantom power's powering it twice might it blow up my microphone or something?
It won't blow it up, because the +48V is the same voltage source, via some resistors of typically a few kilohms. So all you are really doing is decreasing the value of the resistors. They aren't critical and the mic should work fine.
But it's really not a good idea, because you are also shorting the inputs of the two mic amps together, and they just are not designed to work like that. At best you might get a degradation in noise performance and so on, at worst things might start to oscillate or do odd things, possibly at frequencies that you will not hear. I mean - it might seem to work, but things are a bit unpredictable and you could run into all kinds of odd problems.
The way to do this (analogue domain) is first put the mic into a preamp, and then connect the preamp out to two line inputs (L+R).
But there is a much easier way - just record a mono track and then use Audacity or similar to duplicate the recording into both channels of a stereo wav file. This is the way to do it with digital perfection.
(Of course, there is such thing as a mono wav file - are you sure you need a stereo one with identical L and R channels?)