A review of the new science book “White Holes” by Carlo Rovelli
This is the third book that I’ve read written by the famous Italian theoretical physicist Carlo Rovelli. He has a lively and engaging style, unusual for scientists, and this latest work contains a series of references to Dante’s “Inferno”. But the concepts about which he writes are hard to comprehend.
Black holes used to be a theoretical conjecture but now all physicists accept their existence and we have found many, many examples of them in the universe. But white holes? What are they?
According to Rovelli, a white hole is what you would find at the very ‘bottom’ of every black hole and it would manifest itself if one reverses time and the two spacetimes (that for the black and while holes respectively) are linked with a quantum tunnel. I hope you’re keeping up. Rovelli believes that he has shown this process at work theoretically through an imaginative use of Einstein’s equations for his theory of general relativity. He insists that these equations do not change if one reverses time.
If I’ve understood Rovelli correctly, this analysis derives from a mathematical structure called loop quantum gravity. This is a theory, pioneered by Rovelli, which currently rivals string theory as an attempt to reconcile the contradictions between relativity theory and quantum mechanics with a so-called ‘theory of everything’.
If Rovelli is right and a black hole can ‘bounce’ into becoming a white hole, something similar may have happened on the cosmic scale, so that what we call the Big Bang may have been a Big Bounce in which a previous universe contracted, rebound and created our current universe. Are you still with me?
So will we ever find white holes?
Rovelli admits “I do not even know if white holes actually exist” and tells his readers that “the calculations for this transition are currently in progress” (apparently they are based on a version of loop theory called ‘covariant’ or, more colourfully, ‘spinfoam’). Meanwhile,, at present, very few scientists believe in the existence of white holes and it is considered only a mathematical exercise with no real-world counterpart.