Though the need for a quantum theory that includes gravity is clear, the route to such a theory is far from clear. Major contenders are the models based on the use of "strings" and "branes", and from a separate direction those models base on "loop space". Not desiring to get involved in the increasingly partisan debates on these issues, a more productive line of endeavour is to continue to investigate semi-classical quantum gravity.
- Whatever the ultimate nature of "quantum gravity", it is clear (from direct observation of the universe around us) that there will be some semi-classical limit in which it makes sense to think of gravity classically, and to quantize all the matter that resides in the universe.
- There is still an awful lot of interesting physics hiding in the semi-classical approximation.
- Furthermore, exploring what happens when you push this approximation to the point of breakdown might provide interesting hints for the "quantum gravity" programme.
Keep an eye peeled for future developments...
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