Did a Black Hole Give Birth to Our Universe?
Did the Big Bang begin inside a four-dimensional black hole? Researchers from the Perimeter Institute have published research which asserts that this theory is consistent with all current knowledge of the properties of spacetime, and, most importantly, can be extrapolated to form testable hypotheses.
According to classical Big Bang theory, our universe began inside of a gravitational singularity, or a portion of spacetime that has an infinite density and inside which the rules of general relativity fail to apply. The singularity would have been hot and unstable, and the pressure caused by the temperature and density would have caused rapid expansion and cooling. This expansion, in turn, gave rise to the universe as we know it today.
Although our knowledge of singularities is limited ("For all physicists know, dragons could have come flying out of the singularity," said Perimeter Institute Associate Faculty member Niayesh Afshordi), the researchers argue that it may be unlikely that our neatly ordered and logically coherent universe arose out of a chaotic singularity, and as a result it's actually more likely that the universe came into being when it wrapped around the event horizon of a black hole. In our universe, black holes are three-dimensional and have two-dimensional event horizons, so if a black hole in another universe had four dimensions, then it would have a three-dimensional event horizon that could have given rise to our three-dimensional universe. This "wrapping around" the event horizon would have occurred when a four-dimensional black hole met a violent, explosive death inside the black hole.
The researchers acknowledge that this entire idea seems "absurd," and that our minds have no way of imagining what a four-dimensional universe would look like. But they argue that this is no reason to dismiss the theory out of hand, because human intuition is often flawed and short-sighted. They cite the example of Plato's allegory of the cave, in which a group of people spend their entire lives facing a blank wall that shows them shadows from objects behind them. From their perspective, these shadows entirely compose reality, because they assume that what they're seeing is all there is. We could be perpetrating the very same fallacy by disregarding the idea of a four-dimensional universe: "Their shackles have prevented them from perceiving the true world, a realm with one additional dimension. Plato's prisoners didn't understand the powers behind the sun, just as we don't understand the four-dimensional bulk universe. But at least they knew where to look for answers."