 Second, classical general relativity does not include quantum effects, which are expected to be relevant as the singularity is approached. Crucial assumptions of the singularity theorems may not hold once quantum effects are taken into account. The standard energy conditions do not hold for quantum fields, which can have negative energy densities. This opens up the possibility that a model including quantum fields may exhibit a “bounce” rather than collapse to a singularity. More fundamentally, GR’s classical spacetime description may fail to approximate the description provided by a full theory of quantum gravity. According to recent work applying loop quantum gravity to cosmology, spacetime collapses to a minimum finite size rather than reaching a true singularity (Ashtekar &amp; Singh 2011; Bojowald 2011). On this account, GR fails to provide a good approximation in the region of the bounce, and the apparent singularity is an artifact. Classical spacetime “emerges” from a state to which familiar spacetime concepts do not apply. There are several accounts of the early universe, motivated by string theory and other approaches, that similarly avoid the initial singularity due to quantum gravity effects.