The Future of Big Bang Theory:
Measuring the universe on scales relevant to the geometry and timeline of the structures within is not easy.  But because of advances in scientific instruments and more importantly scientific thought, difficult problems can be grappled with.  If there exists a theory that unites the electric and nuclear forces with gravity in a single field, we ought to look for it.
The source of the cosmological expansion, and acceleration, is not known, but attempts to derive the energy (now called auspiciously 'Dark Energy') are begining from quantum mechanics.  Whether string theory or better M-theory will contribute significantly remains to be seen.  The anomalous acceleration of the Pioneer spacecraft at the limit of the solar system has not been explained either.  Humankind, when confronted with seemingly unsolvable problems, will try to solve them.