The Albert Einstein of the popular imagination can seem a bit like Scott Pilgrim, forced into battle with new theories and young physicists. Whether he’s pitted against experiments finding faster-than-light neutrinos (a result that turned out to be spurious) or fighting possible alternatives to his theory of gravity, you’d be forgiven for thinking that physics is Albert Einstein vs. the World.
The wild-haired German’s latest foe comes to us courtesy of a story in the New York Times by Dennis Overbye. The very first sentence reads: “This time, they say, Einstein might really be wrong.” Specifically, a debate over the nature of black holes could challenge “the basis of his general theory of relativity … on which our understanding of the universe is based.”
Sounds dire, no? Poor Einstein could be refuted at last, more than 50 years after his death, his legacy shredded by the very black holes his theory predicted. But this framing presents a distorted view of the process of science.
Overbye discusses an ongoing debate between researchers in an esoteric corner of theoretical physics, dealing with the quantum character of black holes. The so-called “firewall debate” is real and potentially important for our understanding of the intersection of quantum physics and gravity. It involves questions about the destruction (or not) of information inside black holes, the creation of new particles at the surface of a black hole, and possibly the nature of space-time in the limit of very strong gravity.
In brief, the general theory of relativity predicts the existence of black holes. If a mass is dense enough, it will be surrounded by an event horizon: a barrier beyond which nothing can escape, including light. Event horizons for practical purposes define what a black hole is, since no experiment can probe inside them. From general relativity alone, an observer falling into a black hole wouldn’t notice passing the event horizon. However, if you include heuristic calculations from quantum theory, the energy at the event horizon is high enough to generate pairs of particles and their antimatter partners. The effect could create a “firewall,” a violent region that would destroy anything passing through it on its way into the black hole.
Firewalls create a paradox, though. If they exist, they potentially violate the central tenet of general relativity—the equivalence principle—or they cause problems for the conservation of information, an important principle in quantum physics. It’s deep stuff, even for someone like me trained in general relativity and quantum field theory; I recommend reading these explanations by Jennifer Ouellette for Scientific American and by Zeeya Merali for Nature.
However, it’s important that we not overstate the potential implications. Even if general relativity is violated by firewalls, the theory still holds in a vast majority of other situations. Newtonian gravity is used for most applications in astronomy, from planet orbits to the structure of galaxies; general relativity explains why Newtonian gravity works in those contexts, so we’re OK with using the simpler theory. Nobody sensible believes general relativity is the last word on gravity, if for no other reason than we lack a complete quantum theory of gravity. If firewalls point to a new theory, we’ll likely still use Einstein’s theory in the domains where it works, just as we use Newton’s.
Newer theories supplant older ones conceptually, but every theory is provisional, constantly tested by experiments and observations. Einstein, important as he was in 20th-century physics, is not the ultimate authority even on his own theories, and refinements to his work should not be framed as proving him right or wrong. Rather than saying things like “Einstein survives to fight another day” or “[throwing] Einstein under the bus,” as Overbye does, we should frame scientific discovery as a process, not a clash between people. Black hole firewalls are part of the process, which ultimately won’t be settled by debate. Let’s let Einstein sit this one out.