Through string theory, physicists hope to answer many questions about black holes, the big bang, and beyond if possible. Physicists don't know yet whether the universe will continue to expand forever or whether the expansion will eventually halt and begin to contract in a big crunch. If the average density of the universe exceeds the critical density of a hundredth of a billionth of a billionth of a billionth (10) of a gram per cubic centimeter, then the gravitational force will be strong enough for the latter to transpire. Through the realization that distances smaller than the Planck length have no meaning, it was discovered that the big crunch cannot actually occur to the point that everything is crunched into an infinitely small point as originally believed. Instead, the universe would slowly collapse to near Planck length, then would hit Planck length and begin expanding once again in a cosmic bounce. Using astronomer's best estimates, it has been concluded that it is unlikely the universe will ever exceed the critical density. Astronomers' estimates, however, may be missing an important factor if dark matter is present in the universe. Dark matter, if it exists, does not participate in nuclear reaction and so does not give off radiation, making it undetectable to us. If there is dark matter (as strong evidence indicates), it may push the density of our universe over the critical mark and a big crunch could occur.

The second law of thermodynamics says that everything leans to greater disorder, or entropy. Jacob Bekenstein suggested that even black holes must have entropy. The problem with this is that black holes seem too simple to have entropy. Their only defining features are their mass, spin, and charge. To have entropy, black holes must have a temperature and emit radiation. As far as physicists were concerned until 1974, black holes do not emit anything. Then Stephen Hawking discovered that black holes do emit radiation. When virtual particles pairs pop into existence near a black hole's event horizon, sometimes one is pulled into the black hole by its gravitational force before the virtual particles can annihilate one another. This causes the remaining particle to be shot away from the black hole. When this happens enough, black holes glow and emit radiation. As of yet, this has not been experimentally confirmed. It was also not known how or why black holes have entropy. Bekenstein-Hawking entropy was eventually confirmed using string theory.

In 1996, Andrew Strominger and Cumrun Vafa used string theory to theoretically "build" a black hole from scratch. They focused on extremal black holes, black holes with charge. Using branes from the second superstring revolution, they were able to concoct black holes, then figure out how many rearrangements of the microscopic elements existed that maintained the same mass, force charge, and other observable properties of the original. Using this method, they could calculate the entropy of their theoretical black holes. Their calculations precisely matched the predictions of Bekenstein and Hawking.