You will find truth more quickly through delight than gravity. Let out a little more string on your kite. ~ Alan Cohen!
They are however, if not impossible, extremely hard to reconcile and the main obstacle has to do with renormalizability. In a nutshell, unlike all other particles, whether in a first or second-quantizational context, the graviton does not respond to charge directly: it is massless, because the gravitational force theoretically has unlimited range and must be a